AN ABSTRACT OF THE THESIS OF
Rong-Yue Chao
in
for the degree of
Food Science and Technology
Master of Science
presented on
May 7, 1979
Title: IMPROVEMENT OF THE PEELABILITY OF PACIFIC SHRIMP ( PANDALUS
JORDANI) WITH CITRIC ACID AND HEAT PRETREATMENT
Abstract approved:
Dr. David L. -Crawford
Parameters affecting the machine peel ability of raw and steam
precooked Pacific shrimp were investigated utilizing a laboratory scale
mechanical peeler.
Means of improving shell removal and their effect on
the cooked meat yield function of peel ability were evaluated to improve
the flexibility, rate and efficiency of processing.
The time and temperature mediated degradative changes occurring in
the body proteins of round shrimp were directly related to improve
mechanical shell removal and a reduction in cooked meat yield.
Colla-
gen-like proteins important to the structure of the sub-cuticle layers
of the shell and the epidermis between the muscle and the shell were
readily susceptible to solubilization induced by heating which was
enhanced by proteolytic attack .during ice storage.
Enzymatic action on
protein not solubilized and lost through processing increased the waterholding capacity of shrimp meat through cooking.
Steam precooking prior to mechanical peeling improved shell removal
efficiency over raw peeling.
Raw peeling of very fresh shrimp (.<_ 2 days
in ice) followed by cooking in water produced superior cooked meat
yields to peeling steam precooked; no yield advantage was apparent with
extended ice storage.
Inferior shell removal efficiency reducing the
degree of mechanical and washing action on exposed meat surfaces of raw
shrimp complicated this general observation.
Pretreatment of round shrimp in 0.01-0.05 M citrate buffer CpH 5.56.0) for <_ 3 min at 160C prior to peeling raw or steam precooked markedly improved mechanical shell removal efficiency.
The efficiency of
shell removal was nearly independent of pH at levels ^ 6.0.
Cooked meat
yield dry weight was reduced in a linear manner as pH was lowered to
2.6.
The favorable action of citrate buffer on shell removal efficiency
was markedly enhanced by increased exposure time (10 min) and at elevated temperature (450C), but cooked meat yield was unacceptably
reduced.
A short (<_ 3 min) pretreatment coupled with the rapid heating
of steam precooking produced optimum shell removal efficiency and cooked
meat yield.
The degradative mechanism by which shell removal efficiency was
improved was mediated by proteolytic enzymes during storage of round
shrimp in ice.
The very rapid effect of citrate buffer, independent of
the marked pH optima indicative of proteolytic activity, supported a
chelation mechanism for the action of citrate buffer.
Ionic bonding
between connective tissue proteins and the chitin-mineral matrix of the
shell may be the primary linkage of the shell to the soft body portion
of the shrimp.
The magnitude of solubility induced by heating produced
by the citrate pretreatment indicated that ionic bonding was probably
important not only in the direct attachment of the muscle to the shell,
but also to the stability of the entire collagen based connective tissue
content of the shrimp.
The action of citrate buffer on round shrimp under widely varying
pretreatment time, temperature, concentration and pH conditions did not
adversely affect cooked meat quality.
A citrate pretreatment did not
accentuate the deteriorative changes occurring during ice storage of
round shrimp or the frozen storage of cooked meat over a six month
period.
A short (.<_ 3 min) pretreatment of very fresh round shrimp in dilute
(0.01-0.05 M) citrate buffer (pH 5.6) could markedly improve mechanical
shell removal efficiency under commercial conditions.
Methods for
restricting the destabilizing action of citrate on shrimp muscle
proteins solubilized by heat to minimum levels required for efficient
mechanical shell removal will be needed to optimize cooked meat yield.
Improvement of the Peelability of Pacific Shrimp (Pandalus jordani)
with Citric Acid and Heat Pretreatment
by
Rong-Yue Chao
A THESIS
submitted to
Oregon State University
in partial fulfillment of
the requirements for the
degree of
Master of Science
June 1979
APPROVED:
Professor of Food Science andZTechnology in charge of major
Head of Department of Food Science and Technology
Dean of Graduate School
Date thesis is presented
Typed by Rong-Yue Chao
May 7, 1979
ACKNOWLEDGEMENTS
I want to express deeply gratitude to
Dr. David L. Crawford, my
advisor, for his invaluable guidance throughout this research.
Sincere appreciation is extented to Dr. Jerry K. Babbitt, Mr.
Duncan Law, Mr. Lewis Richardson and the staff at the Oregon State
University Seafoods Laboratory in Astoria, Oregon, for their generous
help.
A special thanks is directed to Miss. Nancy Collins, whose timely
assistance contributed greatly to this study.
This work was supported in part by National Oceanic and Atmosphere
Administration (maintained by the U.S. Department of Commerce) institutional Sea Grant 04-7-158-4408 and 04-8-M01-144 and the Trawl Commission of Oregon.
Special appreciation is extended to Marine
Constrction and Design Co. of Seattle, Washington for the loan of their
laboratory scale mechanical shrimp peeler.
Sincere thankful!ness is also extended to my parents and my wife
Lucia for their constant encouragement and support.
TABLE OF CONTENTS
Pa£e
I.
II.
INTRODUCTION
REVIEW OF LITERATURE
Pacific Shrimp (Panda 1 us jordani)
III.
2
3
Life Span
3
Shrimp Structure
3
Quality Changes in Pacific Shrimp during Storage
5
Shrimp Peeling Characteristics
6
Machine Peeling
6
Current Peeling Improvement
7
EXPERIMENTAL
9
Source of Material
9
Machine Peeling Apparatus
9
Basic Peeling Procedure
11
Determination of Shell Removal Efficiency
and Meat Yield
11
Pretreatment Procedures
12
Effect of Pretreatment Time and Water Temperature
on Peelability of Raw Shrimp
12
Effect of Pretreatment Buffer pH on the
Peelability of Raw Shrimp
Effect of Cooking Time in Water on Shrimp Meat
Yield
12
13
Comparative Evaluation of the Citrate Buffer
Pretreatment Procedure
Effect of Pretreatment Time and Temperature on
13
the Peelability of Raw and Steam Precooked
Shrimp
14
Effect of Pretreatment Buffer pH on the Peelability
of Steam Precooked Shrimp
14
Evaluation of the Citrate Buffer Pretreatment for
Improving the Peelability of Fresh Iced Shrimp 15
Relationship of the Ratio of the Soaking Medium
Volume to Round Shrimp Weight to Peelability
15
Relation of Soaking Time and Citrate Buffer
Concentration to Shrimp Peelability
Flavor Panel Evaluation of Shrimp Meat
IV.
RESULTS AND DISCUSSION
Effect of Pretreatment Time and Water Temperature
on Peelability of Raw Shrimp
16
16
17
17
Effect of Pretreatment Buffer pH on Peelability
of Raw Shrimp
Effect of Cooking Time in Water on Shrimp Meat Yield
20
20
Comparative Evaluation of the Citrate Buffer
Pretreatment Procedure
22
Effect of Pretreatment Time and Temperature on the
Peelability of Raw and Steam Precooked Shrimp
24
Effect of Pretreatment Buffer pH on the Peelability
of Steam Precooked Shrimp
29
Evaluation of the Citrate Buffer Pretreatment for
Improving the Peelability of Fresh Iced Shrimp
31
Relationship of the Ratio of the Soaking Medium
Volume to Round Shrimp Peelability
33
Relation of Soaking Time and Citrate Buffer Concentration to Shrimp Peelability
34
Mechanism for the Improvement in the Shell Removal
Function of Peelability
Sensory Characteristics of Meat from Round Shrimp
Pretreated in Citrate Buffer
V.
SUMMARY AND CONCLUSIONS
BIBLIOGRAPHY
37
43
54
58
LIST OF TABLE
Table
Page
1.
Effect of pretreatment temperature in water
on peel ability
2.
Effect of pretreatment time in water at 45 C
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
19
on peel ability
19
Effect of 450C pretreatment water pH (0.05 M citrate
buffer) on peel ability
21
Effect of water cooking time for new peeled shrimp
on meat yield, moisture content and weight loss
21
Comparison of the effect of the citrate buffer
pretreatment procedure on peelability to simulated
commercial processes
24
Effect of pretreatment time and temperature on the
peelability of raw and steam precooked shrimp
28
Effect of pretreatment buffer pH on the peelability
of steam precooked shrimp
30
Effect of a citrate buffer pretreatment on the
peelability of fresh and ice stored shrimp
32
Effect of a citrate buffer pretreatment on the
peelability of fresh and iced stored shrimp
32
Effect of the Ratio of the pretreatment citrate
buffer solution volume to round shrimp weight on
the peelability of steam precooked shrimp
34
Effect of soaking time and citrate buffer concentration
on shrimp peelability
36
Effect of variance of meat yield and shell-index values
for round shrimp treated in citrate buffer solutions
of varying concentration and for varying time periods
37
Mean flavor panel scores for fresh frozen meat from
round shrimp treated in citrate buffers at varying
temperatures prior to steam precooking and subsequent
peeling
44
Mean flavor panel scores for fresh frozen meat from
round shrimp treated for varying time periods in
citrate buffer prior to steam precooking and
subsequent peeling
46
Table
15.
16.
17.
18.
19
20.
21.
Page
Mean flavor panel scores for fresh frozen meat from
round shrimp treated in citrate buffers of varying
pH prior to steam precooking and subsequent peeling
46
Mean flavor panel scores for fresh frozen meat from
round shrimp treated for varying time periods in
citrate buffers of varying strength prior to steam
precooking and subsequent peeling. Analysis of
variance factorial design
47
Interaction of round shrimp storage in ice and meat
frozen storage (-17.80C) with mean flavor panel scores
for meat from round shrimp treated in citrate buffer
prior to steam precooking and subsequent peeling.
Flavor panel scores
48
Interaction of round shrimp storage in ice and meat
frozen storage (-17.8 C) with mean flavor panel scores
for meat from round shrimp treated in citrate buffer
prior to steam precooking and subsequent peeling.
Analysis of variance factorial design
49
Mean flavor panel scores for meat from round shrimp
treated in citrate buffers of varying pH prior to
steam precooking and subsequent peeling after six
months frozen storage (-17.8 C).
51
of frozen storage (-17.80C) on mean flavor panel
for meat from round shrimp treated in citrate
prior to steam precooking and subsequent peeling.
panel scores
52
Effect of frozen storage (-18 C) on mean flavor panel
scores for meat from round shrimp treated in citrate
buffer prior to steam precooking and subsequent peeling.
Analysis of variance factorial design
53
Effect
scores
buffer
Flavor
LIST OF FIGURE
Figure
1.
Laboratory shrimp peeling unit
10
IMPROVEMENT OF THE PEELABILITY OF PACIFIC SHRIMP (PANPALUS JORDAN I)
WITH CITRIC ACID AND HEAT PRETREATMENT
INTRODUCTION
Shrimp has been the most valuable marine resource of the United
States since 1952, replacing salmon and tuna (Idyll, 1976).
In the
coastal waters from Alaska to northern California, Pacific shrimp
represents a major seafood resource.
Oregon shrimp landings of 0.5
million pounds in 1954 reached 48.5 million pounds in 1977.
Shrimp are captured with a towed trawl net, separated from the
trash without being beheaded and washed with sea water.
As the shrimp
are sorted, they are stored in alternate layers of ice in bins within
the hold of the vessel according to catch-date.
The age of landed
shrimp usually varies from one to four days post-catch.
Landed shrimp
are washed immediately after off-loading and either processed or iced
in a varying degree depending upon the time period before processing.
Two models of Lai tram machine peelers are used in Pacific states.
The larger Model A machine peels shrimp in the raw state.
The peeled
raw shrimp are then precooked in water or steam and thermally processed.
Cooked shrimp meat, fresh or frozen, is produced with Model PCA
Laitram machines.
These machines are smaller and are equipped with a
steam cooker that precook the round shrimp prior to peeling.
peeling equipment was developed originally in the Gulf states.
Machine
The
use of this equipment for small Pacific shrimp in the Northwest reduces
the cost of processing by eliminating hand labor in the heading and
peeling process (Idyll, 1976).
Pandalidae species that included the pink shrimp (Randalus
boreal is), the con-trip (P_. hupsinotus) and the side-trip (fandalopsis
dispar) are difficult to machine peel when fresh (Collins and Kelley,
1969). . According to Cool ins and Kelley, shrimp are commonly held in
iced or refrigerated sea water for at least two days.
aid in the machine peeling operation.
This is said to
Holding shrimp, however, in-
creases cost and results in a lower yield because of physical damage and
leaching of soluble components and development of off-flavors and odors
(Collins et a]_., 1960; Collins, 1960a; Collins, 1960b; Seagran et al-,
1960; Collins, 1961).
Deterioration of shrimp quality that occurs
during storage in iced is considered to result from the combined action
of tissue enzymes and microbial contamination (Fieger et a]_., 1958;
Bethea and Ambrose, 1962; Flick and Lovell, 1972; Flores and Crawford,
1973; Argaiz, 1976; Madero, 1978).
The cost of machine separation of nonedible parts is high in comparison to product yield and the rate of production is limited to the
rate of the mechanical means (Gillies, 1975).
ThaN reduction of pro-
cessing cost through the improvement of peel ability is of economic
importance for a product of high market value such as shrimp.
Shell
removal and meat yield are the primary functions of peelability.
In-
vestigation were initiated to evaluate aqueous pretreatments that would
enhance the shell removal function of peelability for both raw (Laitram
Model A) and precooked (Laitram Model PCA) round shrimp.
The effects
of pretreatment time, temperature, citrate concentration, pH, volume :
round shrimp weight relationship and round shrimp age (post catchstorage) on shell removal, meat yield and sensory characteristics are
also evaluated.
LITERATURE REVIEW
Pacific Shrimp (Pandalus jordani)
Life Span
Pacific shrimp are generally found at depths of 240 to 750 feet
over a green mud of mixed mud and sand bottom in California (Dahlstrom,
1972).
Most are protandric hermaphrodites.
The normal pattern is for
an individual to mature and function as a male during the second or
third year of life and then change sex, mature and function as a
female.
Gonads of the shrimp begin developing during the summer and
become visible within the carapace as maturing bluish-green ovaries in
the autumn.
Females carry the eggs on posterior swimming appendices
until the larvae hatch (Dahlstrom, 1972).
Shrimp Structure
A shrimp body is divided into two distinct sections; the anterior
cephalothorax and posterior abdomn.
The cephalothorax consists of the
head and thorax, which are covered by a common shield, the carapace.
The carapace protects the most important viscera, the digest system
(Burukovski and Bulanenkov, 1969).
segments.
The abdomn) is divided into seven
The shrimp body is enclosed in a fairly thick shell whose
main constituent is chitin (polyacetyl-glucosamine) together with noncollagen proteins (Rudall, 1955; Dennell, 1960; Lockwood, 1967).
The
shell, also called the cuticle or integument, is not of uniformly equal
4
strength.
It is broken into a series of segmental rings connected by
flexible arthrodial membranes to allow movement and locomotion [Dennel,
1960; Burukovski and Bulanenkov, 1969).
The tough and rigid cuticle
provides protection for the body and an exoskeleton for muscle attachment (Lockwood, 1967).
The cuticle of Decapoda is subdivided into four main layers; the
epicuticle, pigmented, calcified, and uncalicified layers (Dennel.,
1960).
These layers, with the possible exception of the epicuticle,
are laid down successively during the development of the cuticle.
The
epicuticle is a more or less homogeneous layer of lipid and protein
tanned by quinone cross links (Dennel, 1947; Travis, 1955).
The pigm-
ented layer which lies below the epicuticle, is a heavily calcified
chitin layer that also contains tanned protein in its outer region
(Dennel, 1947).
It is characterized by the presence of a granular
deposit of a melanin-like pigment (Dennel, 1960).
The production of
crustacean epicuticle has been attributed to the tegumentai glands
(Yonge, 1936).
The calcified layer is an untanned chitinous layer more
or less heavily impregnated with calcium salts.
thickness of the whole cuticle (Lockwood, 1967).
It forms much of the
The uncalcified layer,
or membranous layer, is composed of a chitin-protein complex which does
not undergo modification either by calcification or quinone tanning and
lies adjacent to and above the epidermis (Dennel, 1960).
Mauchline et al_. (1977) described the pores present in the cuticle
as connection between the subcuticle tissue and the outside environment.
The pores are considered to be the openings of the tegumentai gland duct
(Dennel, 1960).
Richards (1951) surveyed the mode of attachment of
muscle to the cuticle and stated that the myofibrils of the muscle were
continuous with fibrils of different composition, the tonofibrils.
The latter may be attached to the basement membrane of the epidermis,
penetrate the epidermis to the inner surface of the cuticle.or pass
into the cuticle itself.
Quality Changes in Pacific Shrimp during Storage
The period between the time fish are killed and actually processed
is critical in minimizing degradation in quality caused by the action of
bacteria and autolytic enzymes (Yonge, 1956).
Sensory evaluations made
by Fieger and Friloux (1954) with ice-stored fresh headless shrimp
showed that characteristic sweet flavor was gradually lost during the
first 7 days of ice storage.
This was followed by a period of 7 days
during which they were tasteless and beyond 14 days storage spoilage
occurred with the development of off-flavor.
Flores and Crawford (1973)
observed a progressive increase in pH from 7.6 to 8.8 for intact shrimp
during 8 days of ice storage and suggested that seasonal variations and
catch procedures might greatly affect the pH of shrimp immediately after
removal from water.
Fieger and Friloux [1954) postulated that loss of
quality during the early period of storage was caused by autolysis and
with longer storage, spoilage occurred mainly through bacterial action.
Argaiz (1976) observed that dimethylamine and formaldehyde were
produced in a linear manner in whole shrimp during iced storage and in
derived raw and cocked meat.
Trimethylamine levels slowly increased
during the first 4 days of ice storage followed by rapid increasing
during the latter 4 days reflecting a rapid microbial outgrowth (Argaiz,
1976).
These results are not in agreement with the findings for shrimp
6
of Gulf of Maxico (Fieger and Friloux, 1954; Baily, et al_., 1956).
The
differences observed are due to varying handling and processing procedures (Argaiz, 1976).
The continuous washing action of melting ice
causes a leaching of the native non-protein nitrogen and that formed
through enzymatic hydrolysis of protein upon extended storage (Collins
£t aj_. , 1960).
Madero (1978) found the degradation of frozen cooked
meat quality to be related to round shrimp age.
Levels of trimethyl-
amine oxide, trimethylamine, inosine monophosphate and hypo-xanthine in
cooked meat reflected the age of round shrimp (Madero, 1978).
Differ-
ence in levels was related to chemical decomposition, drip loss and/or
bacterial outgrowth.
Shrimp Peeling Characteristics
It has been recognized that very fresh Pacific shrimp can not be
efficiently machine-peeled and an aging time is required.
Decker (1975)
claimed there was a complicated relationship between processing, quality
and autolysis of Pacific shrimp.
Thompson and Farragut (.1971) noted an
effect of the shell type and strength of the cuticle for various species
upon the peeling characteristics.
Machine Peeling
Laitram peelers are popular with Northwest shrimp processors.
The
peeling step of the process is performed in a peeling channel which is
composed of two reciprocating rubber rollers with a second curvilinear
surface between them provided by a metal plate with longitudinally
7
oscillating movement (Lapeyre, 1966; 1968).
The relative movement
between surfaces causes a nipping or pinching action on the shrimp.
The
curvilinear forms of both the rollers and the metal center plate with
progressively narrowing throates exert squeezing prepare on the shrimp,
gradually collapsing the shell and expelling the meat.
Removed shell
are thus separately collected from the recovered meat (Lapeyre, 1966).
Besides Laitram peelers, there are other peeling apparatus which
are designed specifically for shrimp (Willis and Sundberg, 1969; Jones
jr., 1970; Jones jr., 1972).
Current Peeling Improvement
Attempts have been made to increase shrimp quality and improve the
peel ability of fresh shrimp with various treatments prior to machine
peeling.
Lapeyre (1966) found that cooking whole shrimp just prior to
peeling produced a better yield and also preserved the naturally
pigmented material on the surface of the shrimp .meat.
Collins and Kelly
(1969) noted that peeling properties of fresh pink shrimp were improved
by dipping the shrimp in a water bath at 430C or 540C for 2 min.
Bynagte (1972) reported that soaking fresh shrimp with agitation in a
solution of water, sodium acid phosphate and sodium triphosphate for
about 2 min prior to cooking for 2 min at 930C improve peelability.
Aepli and Schultz (1971) enhanced the removal of the non-edible parts
of raw or cooked shrimp by treatment in an aqueous solution containing
hypochlorite ions with sodium hydrohydroxide, fatty acid and a wetting
agent or defoamer.
D'Aquin (1965) also demonstrated an acid pretreat-
ment for softening crab shell.
Although various treatments have been
8
observed to improve shell removal efficiency,
a simple and effective
method of pretreatment to improvement both the shell removal and yield
of functions of Pacific shrimp peelability has not been clearly
established.
EXPERIMENTAL
Source of Material
Samples of Pacific shrimp of less than one day post-catch in ice
were obtained through commercial plants in Astoria, Oregon.
Each
sample of fresh shrimp was brought to the Oregon State University
Seafoods Laboratory in Astoria and utilized for only one independent
experimental design.
Machine Peeling Apparatus
All experimental samples were processed using a laboratory model
shrimp peeling machine constructed by Marine Construction and Design
Co., Seattle, Washington.
The shrimp peeler was comprised of four
basic units: 1) a peeling channel of 1.22 m long, 2) a hydraulic pump,
3) a continuous steam precooking line equipped with a variable speed
wire mesh conveyor, and 4) a water and roller-speed control panel (Figure 1).
Shrimp were permitted to feed into the peeling channel from a
wire mesh conveyor at a rate of 500 gm per min.
The action of the
peeler channel rollers and moving center plate was supplemented by a
continuous water spray.
Shrimp that were precooked prior to peeling
were subjected to steam (101 C) in a single shrimp layer for a period of
90 sec followed by a 20 sec water spray.
Steam was provided by a box
150 cm long equipped with perforated steam pipes serviced by a steam
line with appropriate controls.
The steam box was positioned 6 cm above
the variable speed wire mesh conveyor.
Shrimp peeled raw were
10
Figure 1.
Laboratory shrimp peeling unit.
11
subjected to the same process except steam heating was deleted prior to
machine processing.
Basic Peeling Procedure
Shrimp samples were either immediately, stored in ice at 2 C or
individually quick frozen ClQF) (-27 C) depending upon experimental
requirements.
The IQF shrimp were stored at -27 C before using.
Frozen shrimp were thawed in a spray of tap water for a designated time
prior to pretreatment.
Shrimp samples were divided into 500 gm units
and successively dumped on the mesh conveyor in a continuous single
layer at a rate of 1 unit per min (500 gm/min), passed through the steam
box and deposited by the conveyor into the peeling channel.
For con-
venience of discussion, this peeling procedure was designated as method
B.
Peeling shrimp in the raw state was designated as method A.
Determination of Shell Removal Efficiency and Meat Yield
The efficiency of shell removal was determined by the weight of
shell attached to the meat after machine peeling.
A shell-index was
computed as the ratio of the weight of shell removed by hand peeling per
unit of clean shrimp meat.
The shell-index was reported in percent.
Clean meat yield was reported as percent based upon round shrimp weight
prior to pretreatment.
12
Pretreatment Procedures
Pretreatments were set up to modify either the temperature or pH
of a soaking-medium.
Pretreatment time and the concentration of the
buffer used to adjust the pH of soaking-medium were also variable.
Effect of Pretreatment Time and Water Temperature on Peel ability of
Raw shrimp
A 23 kg lot of round shrimp (less than 12 hr post-catch in ice) was
individually quick frozen (IQF) overnight at -27 C and divided into 5
sub-lots of approximately 5 kg each.
Each frozen sub-lot was treated
in 24 1 of preheated water and mildly stirred by hands for 10 min.
Pretreatments were carried out at 35, 45, 55, 65 and 85 C.
The treated
sub-lots were placed in a drainer and cooled with tap water for 2 min.
The sub-lots were then drained at least 5 min and peeled according to
method A (raw peeling).
A second 25 kg lot of round shrimp (frozen less than 12 hr postcatch in ice ) was obtained, frozen and subdivided into the same manner
previously described.
Sub-lots of round shrimp (5.0 kg) were held for
0, 3, 5, 10 and 15 min at 45 C and processed in similar manner.
Nine
to ten min were required for the treatment water to reach 45 C after
introducing the frozen shrimp.
Effect of Pretreatment Buffer pH on the Peel ability of Raw Shrimp
13
To evaluate the effect of pH. on the peelability, a 35 kg lot of IQF
round shrimp (.less than 12 hr post-catch in ice) was divided into 7
equal sub-lots.
The control sub-lot was soaked in 24 1 of preheated
water at 450C for 3 mim prior to being peeled using method A.
The
remaining sub-lots were pretreated under similar conditions in pretreatment water 0.;05 M to citric acid-sodium citrate (CgHgCL-ONa3C6H507-2H20) at pH 3.0, 4.0, 4.6, 5.0 and 6.0.
Effect of Cooking Time in Water on Shrimp Meat Yield
A 60 kg lot of round shrimp (.less than one day post-catch in ice)
was stored in ice for 3 days to assure ease of peeling.
The iced shrimp
lot were then divided into 2 sub-lots of 30 kg each and peeled according
to method A with and without a citrate-sodium citrate buffer pretreatment
(3 min in pH 5.6
0.05 M citrate buffer).
removed as rapidly as possible.
After peeling, the shell was
Each peeled sub-lot was further divided
into appropriate size units and cooked in boiling water from 45 to 120
sec at 15 sec intervals.
Comparative Evaluation of the Citrate Buffer Pretreatment Procedure
A 90 kg lot of round shrimp (less than one day post-catch in ice)
was obtained and allocated into 9 nearly equal weight sub-lots.
Three
of the sub-lots were immediately peeled according to method A, method A
with pretreatment (pretreated in 0.05 M citrate buffer at pH 5.6 for 3
min prior to raw peeling)(AT) and method B (steam precooked at 1010C
for 90 sec prior to peeling).
The remaining 6 sub-lots of round shrimp
14
were well iced and stored at 2 C.
At 2-day intervals, 3 sub-lots were
processed in a similar manner.
Effect of Pretreatment Time and Temperature on the Peel ability of Raw
and Steam Precooked Shrimp
Two different samples (approximately 40 kg each) of IQF round
shrimp (less than one day post-catch in ice) were mechnically peeled
using methods A and B.
Each sample of shrimp was divided into eight
lots (approximately 5 kg each).
Four lots were soaked before peeling in
24 1 0.05 M citrate buffer at 16, 25, 35 and 450C for 1.33 min.
Three
lots were soaked in 24 1 0.05 M citrate buffer at 160C for 3, 5 and 10
min.
The remaining lot from each sample was immediately thawed in water
(16 C) and peeled according to the peeling procedure assigned to that
sample.
Shrimp peeled raw were cooked 90 sec in boiling water (99-
100 C).
Shrimp meat samples were packed in styrofoam containers with
plastic lids (180 gm per unit) and frozen at -270C.
After freezing the
containers were sealed in moisture-vapor proof film and stored at -180C
prior to flavor panel evaluation.
Effect of Pretreatment Buffer pit on the Peel ability of Steam Precooked
Shrimp
A 60 kg sample of IQF shrimp (less than one day post-catch in ice)
was equally divided into 12 lots of 5.0 kg each.
The lots were indi-
vidually subjected to a 3 min soak at 160C in 24 1 0.05 H citrate
buffers at pH 2.6, 3.0, 3.5, 4.0, 4.6, 5.0, 5.2, 5.6, 6.0 and 0.4.
15
The pH 2.6 and 8.4 soaking solutions were prepared with only citric
acid and sodium citrate, repectively.
was used as a control.
A lot soaked in untreated water
The cooked meat samples were packaged, frozen
and stored as previously described.
Evaluation of the Citrate Buffer Pretreatment for Improving the Peelability of Fresh Iced Shrimp
Three different lots of very fresh (.less than one day post-catch in
ice) shrimp (5.0 kg) were pretreated in 24 1 of 0.05 M citrate-sodium
citrate buffer (pH 5.6) for 3 min.
The pretreated shrimp and appropri-
ate control samples were mechnically peeled after steam precooking (90
sec at 101 C).
One sample was stored in ice at 2 C and processed in a
similar manner after 2, 3 and 4 days in ice at 20C.
Cooked meat from
all samples was packaged, frozen and stored prior to flavor panel
evaluation in a manner previously described.
Relationship of the Ratio of the Soaking Medium Volume to Round Shrimp
Weight to Peelability
A 20 kg lot of IQF shrimp (.frozen less than one day post-catch in
ice ) was divided into 4 equal sub-lots.
thawed in a spray of tap water for 3 min.
Each sub-lot (.5.0 kg) was
Three sub-lots were soaked in
24, 10 and 5 1 of 0.05 M citrate buffer (pH 5.6) at 160C for 5 min
yielding solution/round shrimp weight ratio of 4.8, 2.0 and 1.0,
respectively.
for 5 min.
A control sub-lot of shrimp was soaked in 5.0 1 of water
All samples were processed according to method B (steam
16
precooked at 1010C for 90 sec prior to peeling).
Relation of Soaking Time and Citrate Buffer Concentration to Shrimp
Peel ability
Five different lots of IQF shrimp (frozen less than one day postcatch in ice) were divided into equal sub-lots (5.0 kg each).
Sub-lots
of each lot were soaked in 0.01, 0.025 and 0.05 M citrate buffer (pH
5.6) for 5 and 20 min in a buffer volume/round shrimp relationship of
1:1 (wt/wt).
The pretreated shrimp samples were processed according to
method B (steam precooking at 101 C for 90 sec prior to peeling).
Meat
samples were packaged and stored as previously described prior to
flavor panel evaluation.
Flavor Panel Evaluation of Shrimp Meat
Flavor panel evaluations of shrimp meat samples were carried out
using 10 staff members who usually participate in sensory evaluation of
the Department of Food Science and Technology in Corvallis, Oregon.
Samples were thawed overnight at refrigerator temperature and submitted
to judges isolated in individual booths.
Samples were evaluated for
odor, texture, juiciness, flavor and over-all desirability on a 9-point
hedonic scale, ranging from 9, "extremely desirable", to 1, "extremely
undesirable".
Some evaluations consisted of duplicate and triplicate 10
judgment evaluations of the same sample using identical judges, but at
different times.
The significance of difference among mean scores was
determined using analysis of variance procedures ( Snedector and Cochran,
1976; ASTM, 1977).
17
RESULTS AND DISCUSSION
Effect of Pretreatment Time and Water Temperature on Peel ability of Raw
Shrimp
Pacific shrimp were subjected to pretreatment in heated water prior
to mechnical peeling to evaluate potential improvements in shell removal
efficiency.
The shell indices for shrimps pretreated for 10 min in
water at temperatures ranging from 35 to 85 C showed that pretreatment
at 450C provided the best enchancement (Table 1).
The shell-index was
improved nearly 14 percentage points by a 45 C pretreatment over that
observed at 350C.
Pretreatment at temperatures greater than 450C
yielded reduced shell removal efficiencies as reflected in shell
indices based upon cooked meat weight.
The actual quantity of shell
remaining after peeling based upon round shrimp weight was reduced.
This result was in agreement with the findings of Collins and Kelly
(1969).
Raw meat yield from mechnical peeling was also optimum after a
pretreatment in 45 C water (Table 1).
Yield increased by 9 percentage
points with a pretreatment temperature increase from 35 to 450C, but
was considerably reduced at higher pretreatment temperatures.
The dry
weight yield of raw meat based upon round shrimp weight generally
reflected the changes observed for wet weight yield.
The moisture
content of meat derived from samples pretreated at 35, 45 and 550C was
nearly equal.
However, reductions in moisture content, as well as dry
weight yield, did reflect marked yield reduction at pretreatment temperatures greater than 55 C.
18
The efficiency of mechnical shell removal generally improved with
an increase in the pretreatment time at 45 C, but raw meat yield was
optimum after only a 3 to 5 min exposure (Table 2).
Wet and dry weight
raw meat yield based upon round shrimp weight decreased with pretreatment
exposure in excess of 5 min.
The moisture content of the peeled meat
remained relatively constant over the 15 min pretreatment time investigated and only partially reflected the losses observed in both wet and
dry weight meat yield.
Soluble solid components were lost from the meat
during exposure in excess of 5 min.
Meat yield and shell-index values varied considerably from one lot
of shrimp to another (Table 1 and 2).
The operational parameters of the
peeler itself, including the speed of the rollers and the bell-conveyor
delivering shrimp to the peeling channel and especially the width
between each roller and the center plate, affected both the shell-index
and meat yield.
Adjustment of the operational parameters of the peeler
was needed for each lot of shrimp to optimize meat yield and shell
removal.
Lots composed largely of small shrimp (averaging below 4.0 gm)
were "chewed up" by the peeler if the distance between the peeler rollers and the center plate was too great.
Similarly, those lots composed
of large sized shrimp (larger than 6 gm) mostly passed through the
peeling channel without being peeled.
For investigational purposes the
conveyor speed of the peeler was adjusted to 7.6 to 8.4 pounds per min
and the distance between the peeler rollers and the center plate was
fixed for optimum shell removal and meat yield based on the average
weight of Pacific shrimp (4.0 to 6.0 gm) reported by Langmor and Rudkin
(1970).
The sorting of round shrimp before peeling into lots of more
uniform size to optimize peelability was not carried out so that results
19
Table 1.
Effect of pretreatment of temperature in water on peelability.
35
Pretreatment temperature ( C)
45
55
65
85
Wet wt. (%)
27.11
36.09
21.59
12.07
16.43
Dry wt. (%)
5.06
6.61
3.98
2.44
3.69
Shell-index (%)
28.78
15.13
24.52
35.41
24.15
Wt. of shell/
wt. of shrimp wt. (%)
7.80
5.46
5.29
4.27
3.97
Moisture content (%)
81.32
81.67
81.54
79.76
77.51
Meat yield
Pretreament time: 10 min.
Table 2.
Effect of pretreatment time in water at 450C on peelability.
Pretreatment time (min)
0
3
5
Wet wt. (%)
37.35
38.50
38.32
36.32
30.36
Dry wt. (%)
6.98
7.02
7.28
6.62
5.85
Shell-index {%)
10.52
10.19
11.40
10.17
9.03
Wt. of shell/
wt. of round shrimp (%)
3.92
3.92
4.37
3.69
2.74
Moisture (%)
81.30
81.77
81.77
81.01
80.73
10
15
Meat yield
20
would more clearly reflect commercial processing operations.
Effect of Pretreatment Buffer pH on the Peel ability of Raw Shrimp
The addition of a citrate buffer system (0.05 M) to pretreatment
water heated to 45 C yielded additional enhancement of the mechanical
shell removal function of peel ability [Table 3).
A 3 min soak in
0.05 M pH 6.0 buffer system yielded a marked improvement in mechanical
shell removal.
Increasing the acidity of the pretreatment solution did
not further enhance mechanical shell removal.
The yield function of peelability was not improved by the citrate
buffer system.
Raw meat yield (wet and dry weight) was reduced by a pH
0.05 M citrate buffer over a water control (Table 3).
Raw meat yield
wet (r=.9838; p^.005) and dry 0=.9698; p^.005) weight was reduced in a
linear manner as the acidity of the buffer system was strengthened.
The reduction in yield was related to both a reduced meat moisture
content and a loss of soluble meat solids during soaking and/or through
the mechnical and washing action of the peeling operation.
The optimum
conditions for both the meat yield and shell removal functions of
peelability appeared to be between pH 5.0 and 6.0 for raw shrimp.
Effect of Cooking Time in Water on Shrimp Meat Yield
Pretreatment of round shrimp in heated (450C) citrate buffer (0.05
M, pH 5.6) prior to peeling raw (method AT) adversely affected meat
yield through cooking over non-treated samples (method A) (Table 4).
The weight loss of raw meat derived from treated shrimp through cooking
21
Table 3.
pH
Effect of 450C pretreatment water pH (0.05 M citrate buffer)
on peel ability.
Shellindex [%)
Peeled meat
moisture (%)
2.90
2.53
3.86
2.02
2.31
2.19
7.70
82.50
82.88
82.95
82.51
82.91
83.08
83.11
3.0
4.0
4.6
5.0
5.6
6.0,
6.71
Yield (%)
Wet wt.
Dry wt.
26.05
28.72
28 65
30.20
32.19
32.44
33.68
4.56
4.92
4.88
5.28
5.50
5.49
5.69
Pretreatment time: 3 min.
Control: non-acidified water.
Table 4.
Effect of water cooking time for raw peeled shrimp on meat
yield, moisture content and weight loss.
Moisture content
Cooking
time
(sec)
45
60
75
90
105
120
2
(%)
A
83.,97
82.,80
82.,90
82.,40
82.,21
82..77
/^
80.,84
80.,24
80.,73
80.,28
80.,25
79.,94
Yield (%)2
.Dry Wt.
Wet wt.
Al
A
A
AT
32..28
28,.82
28..24
27,.70
25,.69
26,.50
21. 61
5.17
4.14
20. 31 4.93
20. 31 4.83
21. 06 4.87
20. 49 4.57
19. 68 4.54
4..01
3.,91
4.,15
4.,05
3.,95
Raw meat
wt. loss I{%)
A
AT
13. 96
23.,71
25.,16
25.,98
31.,91
30.,27
30,.85
34,.72
34,.46
33,.63
34,.81
37,.23
Pretreatment conditions: pH 5.6 citrate buffer 0.05 M; 45 C; 3 min.
Based upon shrimp weight.
22
and computed meat yields (wet and dry weight) based upon round shrimp
weight was markedly reduced by only a 45 sec water cook.
Cooking time
in boiling water of from 60 to 120 sec did not greatly affect meat yield
based on round shrimp weight or weight loss from the raw nieat during
water cooking.
Samples peeled without a citrate buffer pretreatment showed a raw
meat weight and yield loss related to cooking time by well defined
power curves (Y = b X ).
The power regression of wet and dry weight
meat yield on cooking time in water following the power functions of
Y=68.8954 x"*20545 (r=-.9445; p^.005) and Y=35.0302 X"'1241(r=.9474;
p>_.005), respectively.
The weight loss of raw meat from treated round
shrimp cooked for only 45 sec was roughly equivalent to that from nontreated shrimp cooked for 120 sec.
While the moisture content of
cooked meat derived from treated round shrimp was about 2 percentage
points less than the content of non-treated samples, the moisture in
cooked meat from both processes (A and AT) was not greatly affected by
the length of cooking time in water.
Yield loss through cooking for
both processes was largely related to solubilized solids.
Meat from
shrimp treated in a citrate buffer was far more subject to solubilization at boiling water temperature.
Comparative Evaluation of the Citrate Buffer Pretreatment Procedure
Process evaluations were carried out to establish the efficiency
of the citrate buffer pretreatment procedure for improving mechanical
shell removal from raw shrimp (method AT).
The procedure was evaluated
for processing very fresh iced shrimp and shrimp stored in ice for an
23
extended period of time and compared to the efficiency of peeling raw
(method A) and after steam precooking (method B) without a prior citrate
treatment.
pH 5.6
The optimum conditions for the procedure (.3-5 min in 45 C
0.05 M citrate buffer) were established using very fresh indi-
vidually quick frozen and thawed round shrimp.
Storage in ice and the
physical process of freezing and thawing markedly affected the efficiency of mechanical shell removal from round shrimp.
Storage in ice, steam precooking prior to peeling and the citrate
buffer pretreatment markedly improved the shell removal function of
peel ability (Table 5).
The efficiency of machine shell removal pro-
gressively improved during ice storage for shrimp peeled raw or steam
precooked.
Shell removal from steam precooked shrimp was 1.4, 2.3 and
3.8 times more efficient than peeling raw after <1, 2 and 4 days
storage in ice, respectively.
Treatment in the citrate buffer system
produced a shell removal efficiency from shrimp stored in ice <1 day of
22.3 times that of non-treated shrimp.
The very high shell removal
efficiency produced by the citrate pretreatment eliminated the potential effect of the ice storage mediated degradative process reflected
in shell removal efficiencies.
The rigorus heat denaturation of steam precooking and the degradative processes occurring during storage in ice markedly influenced
meat yield in a manner that was counter to improve shell removal efficiency (Table 5).
Peeling very fresh shrimp (<1 to 2 days in ice) in
the raw state followed by water cooking produced a superior meat yield
(w(wet and dry weight) to peeling after steam precooking.
Mechanical
peeling of shrimp stored in ice for 4 days in the raw state produced an
inferior dry weight yield to that observed for steam precooked shrimp.
24
Table 5.
Comparison of the effect of the citrate buffer pretreatment
procedure on peelability to simulated commercial processes.
Peelability function
Cooked meat yield (%)1
Shell-index (%)2
Cooked meat moisture
content (%)
Raw meat weight loss
uuring cooking {%)■*
Processing
method
Storage time in ice (days)
< 1
2
4
A4
29.63
(8.37)
29.'34
(6.91)
27.09
(4.77)
B5
26.94
(5.81)
27.74
(5.13)
27.03
(5.14)
AT6
21.76
(4.97)
19.79
(4.15)
21.21
(4.28)
A
31.49
16.74
3.49
B
22.53
7.22
0.91
AT
1.41
1.05
2.24
A
79.32
80.68
82.37
B
78.44
78.99
81.00
AT
76.63
79.01
79.82
A
18.20
23.94
27.50
B
_
_
_
AT
35.56
35.00
33.58
Based upon round shrimp weight; values in ( ) equal meat dry weight
yield.
2
Weight of attachment shell after peeling/weight of clean meat x 100.
3
Weight of cooked clean meat/weight of round clean meat x 100.
4
Peeled raw; cooked 90 sec in water (99-100oC).
5
o
Steam precooked (101 C) 90 sec just prior to peeling.
fi
o
Pretreated 3 min in 45 C pH 5.6 0.05 M citrate buffer; peeled raw;
cooked 90 sec in water (99-100 C),
25
The wet weight yields v/ere nearly equal.
Meat yield reduction related
to ice storage was complicated by an increase in cooked meat moisture
content.
The dry weight yield reduction induced by ice storage was
greater for shrimp peeled raw than for shrimp peeled after steam precooking and was directly related to ice storage time dependent loss of
soluble solids through water cooking of the raw peeled meat.
Treatment of round shrimp in citrate buffer prior to raw peeling
and subsequent to water cooking, while producing exceedingly efficient
mechanical shell removal, markedly reduced meat yield over both raw and
steam precooked shrimp with no pretreatment (Table 5).
The degradative
action of the brief (3 min) citrate buffer treatment eliminated the
effects of ice storage.
Treatment of fresh shrimp (<1 day in ice) in
citrate buffer reduced dry weight yield and increased weight loss
through water cooking to a level similar to non-treated samples held in
ice for 4 days.
The weight loss of peeled meat from non-treated shrimp
through water cooking increased with ice storage reflecting degradative
processes; meat from shrimp treated in a citrate buffer yielded approximately the same weight loss regardless of the storage time in ice.
The
rather constant level of dry weight meat yield and loss of weight from
peeled raw meat through water cooking regardless of ice storage time
indicated that the citrate buffer treatment induced solubility to a
specific fraction of the shrimp meat in a relatively quantitative manner.
Effect of Pretreatment Time and Temperature on the Peel ability of Raw
and Steam Precooked Shrimp
The pretreatment of round shrimp in 450C v/ater for 3-5 min prior
26
to mechanical peeling markedly improved shell removal efficiency.
The addition of a 0.05 M citrate buffer CpH 5.0-6.0} to this pretreatment yielded further improvement.
The time and temperature dependency
of the citrate buffer pretreatment was determined for shrimp peeled raw
(Method A) and after steam precooking (method B).
Pretreatment of round shrimp for 1.33 min in pH 5.6
0.05 M citrate
buffer at ambient water temperature (160C) reduced the attached shell
on raw shrimp meat to 73.5% of its control (Table 6).
Further
reductions to 40.3, 31.1 and 30.3% of the control were observed at 25,
35 and 45 C, respectively.
Nearly similar improvements in efficiency
were achieved by extended pretreatment times at 16 C.
The quantity of
attached shell was reduced to 40.3, 36.6 and 34.5% of its control after
treatment for 3.0, 5.0, 10.0 min, respectively.
Treatment for periods
greater than 5 min or at temperatures greater than 35 C did not appear
to improve shell removal efficiency.
The time and temperature dependency of the citrate buffer pretreatment on the efficiency of shell removal from steam precooked shrimp
was similar in pattern to shrimp peeled raw, but greater in relative
magnitude.
Pretreatment for 1.33 min in pH 5.6 0.05 M citrate buffer at
160C reduced the attached shell on precooked meat to 27.9% of its
control (Table 6).
Additional reductions to 19.3, 8.2 and 4.0% of the
control were observed after pretreatment for 80 sec at 25, 35 and 450C,
respectively.
Pretreatment for longer than 3 min at 16 C did not
improve efficiency.
The attached shell was reduced from 27.9% of its
control for samples pretreated for 80 sec to 7.1, 19.9 and 6.6% of the
control after 3.0, 5.0 and 10 min, respectively.
The temperature of the citrate buffer pretreatment was directly
27
related to cooked meat yield.
The cooked meat yield (wet weight), from
shrimp peeled raw (r=-.9711; p_>.Q5) and steam precooked (r=-.9827;
p_>.025) decreased in a linear manner as the temperature of the pretreatment was increased.
Cooked meat moisture contents did not show an
appreciable degree of dependence on pretreatment temperature which
resulted in dry weight yield relationships very closely approximating
those based upon wet weight yield.
The loss of solids through pre-
treatment, peeling and subsequent water precooking of raw meat was more
markedly affected by elevated pretreatment temperatures.
The rate of
yield reduction as the pretreatment temperature was increased for
shrimp peeled after steam precooking was 1.3 times that observed for raw
shrimp. Solids lost through a steam precook (90 sec at 101 C) in the
shell exceeded loss through 90 sec water cook at 99-100clC.
Pretreatment of shrimp in citrate buffer at ambient temperature
(16 C) for 80 sec yielded superior cooked meat yields over control
samples thawed in water and immediately peeled raw or steam precooked.
Extended pretreatment for up to 10 min further enhanced wet weight yield
for shrimp peeled after steam precooking, but dry weight yields were not
improved for pretreatment times greater than 3.0 min.
Extended pre-
treatment at 16 C yielded steam precooked meat with higher moisture
contents.
Pretreatment of shrimp peeled raw resulted in a linear re-
duction of wet weight yield (r=-.9815; p>_.025) as pretreatment at 160C
was extended from 80 sec to 10 min.
Dry weight yield was only reduced
at pretreament times greater than 3.0 min.
This reduction in yield was
directly related to time dependent degradative processes that occurred
prior to water cooking.
The relatively greater magnitide of yield loss
observed during extended pretreatment time at 160C of shrimp peeled
28
Table 6.
Effect of pretreatment time and temperature on the peel ability
of rae and steam precooked shrimp.
Citrate buffer1
pretrea tment
condit ion
Yie Id (%)
BT3
AT4
0
Min
45
1.33
16.69
(3.86)
19.68
(4.50)
35
1.33
20.55
(4.35)
25
1.33
16
Cook ed meat
moist ure (%)
Shell- index (%)
AT
BT
AT
1.28
6.22
77.16
77.15
21.60
(4.57)
2.61
6.40
77.12
78.84
25.63
(5.73)
26.30
(5.88)
6.13
8.28
76.92
77.65
1.33
26.90
(6.87)
27.11
(5.91)
8.89
15.11
76.97
78.18
16
3.0
27.89
(6.30)
26.86
(6.10)
2.25
8.29
77.39
77.29
16
5.0
27.35
(6.22)
26.16
(5.57)
6.34
7.53
77.27
78.77
16
10.0
28.34
(6.14)
25.47
(5.42)
2.10
7.09
78.32
78.70
26.45
(5.63)
26.11
(5.56)
31.80
20.55
78.72
78.69
C
Control
-
BT
^.OBM . pH 5.6.
Based upon round shrimp weight; values in ( ) equal meat yield dry
weight.
Pretrreated, precooked 90 sec in steam (1010C) and peeled.
Pretreated, peeled and cooked 90 sec in water (99-100 C).
29
raw over those peeled after steam precooking was probably related to
the difference in time elapsed before cooking and subsequent inactivation
of degradative enzymes.
Effect of Pretreatment Buffer pH on the Peel ability of Steam Precooked
Shrimp
A 3.0 min citrate buffer (0.05 M) pretreatment of from pH 6.0 to
2.6 at 16 C produced shell removal efficiencies from steam precooked
shrimp that were improved over an equal time soaked in water or sodium
citrate (pH 8.4) (Table 7).
The inferior efficiency produced by the
sodium citrate pretreatment to that of water or citrate buffer at pH 6.0
indicated that the action of citrate required acidic conditions.
Although the use of a frozen and thawed sample did not produce large
differences in shell removal efficiency, the occurrence of three optimum efficiencies observed near pH 6.0, 5.0 and 3.6 was striking.
These
three optima roughly occurred at the 3.06, 4.76 and 5.4 pKa values for
citric acid.
The maximum ionization occurring at these pKa values
would provide the highest chelation capacity for divalent cations that
could provide ionic bonding improvement to the stability of tissue
attaching the muscle to the calcified layers of the shell.
This ob-
servation is supported by similar optimum shell removal efficiencies
from raw shrimp observed at pH 6.0, 5.0 and 4.0 at 450C (Table 3).
Reduction of the pH of the citrate buffer pretreatment resulted in
diminished cooked meat yields similar to those observed for shrimp
peeled raw (Jable 3).
Cooked meat yield wet Cr=-9500; p^.OOS] and dry
(r=.9357; p>_.005) weight was reduced in a linear manner as the pH of the
30
Table 7.
Buffer
PH
Effect of pretreatment buffer pH on the peelability of
steam precooked^ shrimp.
Meat yi eld (%)
wet
Dry
Shellindex (%)
Cooked meat moisture {%)
2.6
22.01
4.84
4.34
77.99
3.0
21.84
4.89
3.37
77.62
3.6
23.68
5.14
3.06
78.31
4.0
24.33
5.31
5.84
78.19
4.6
25.60
5.85
4.64
77.15
4.8
26.08
5.53
4.01
78.31
5.0
26.83
5.78
3.89
78.46
5.2
25.42
5.62
5.57
77.89
5.6
26.02
5.70
5.05
78.08
6.0
27.48
5.94
4.13
78.37
8.4
27.51
5.85
10.58
78.73
25.21
5.50
7.99
78.81
Control
^.O min in 160C 0.05 M citrate buffer.
2
90 sec in steam (101°).
Treated 3.0 min in 16 C water prior to peeling,
31
citrate buffer was lowered from pH 6.0. to 2.6.
Cooked meat moisture
contents were only slightly reduced in an irregular manner.
The loss of soluble proteins through steam precooking and subsequent peeling was favored by acidic pretreatroent conditions.
The opti-
mum conditions for shell removal efficiency from steam precooked shrimp
that would provide maximum cooked meat yield appeared to be between
pH 5.0 and 6.0.
Evaluation of the Citrate Buffer Pretreatment for Improving the Peelability of Fresh Iced Shrimp
Three different very fresh samples of iced shrimp subjected to 3.0
min pretreatments in 160C 0.05 M citrate buffer (pH 5.6) prior to steam
precooking and subsequent peeling showed marked improvement in shell
removal efficiency (Table 8).
The brief citrate buffer pretreatment
reduced the attached shell on the cooked meat after peeling by 69.+7.8%.
The improved shell removal efficiency was accompanied by a reduction in
cooked meat yield averaging 6.2+4.7% (1.74+1.32 percentage points).
Fresh shrimp (sample lot III) stored in ice at 20C was pretreated
prior to steam precooking and subsequent peeling to further characterize
the action of the citrate buffer on peelability.
The enhanced effi-
ciency of shell removal induced by ice storage was improved upon by the
citrate buffer pretreatment even after 3 and 4 days of ice storage
(Table 9).
The pretreatment produced a 61.6, 55.9, 24.9 and 31.8%
reduction in the shell attached to the cooked meat derived from shrimp
stored for
1, 2, 3 and 4 days in ice, respectively.
The action of the
citrate buffer pretreatment improved the shell removal efficiency
32
Table 8.
Effect of a citrate buffer pretreatment on the peelability
of fresh shrimp.
Meat yi eld (%)
Sample
lot
B1
I
II
III
Mean
S.D.
Shell--index (%)
BT2
B
BT
28.48
26.12
27.47
25.79
25.89
25.17
24.40
12.39
14.98
5.56
3.74
5.75
27.36
1.18
25.62
0.39
17.26
6.32
5.02
1.10
Precooked 90 sec in steam (101 C) and peeled.
p
"Pretreated
Pretreated 3.0 min in 0.05 M citrate
ci1
buffer (pH 5.6), precooked 90
sec in steam (101oC) and peeled.
Table 9.
Effect of a citrate buffer pretreatment on the peelability
of fresh and ice stored shrimp.
Storage
time in
ice
Meat yield (%)
< 1 day
B1
BT2
Moisture content (%)
Shell- index (%)
B
BT
B
BT
27.47 . 25.17
(6.OS)13 (5.56)
77.97
77.90
14.98
5.75
2 day
28.16
(6.13)
27.21
(5.63)
78.22
79.11
9.20
4.06
3 day
28.47
(5.70)
27.79
(5.70)
79.98
79.34
3.33
2.50
4 day
27.67
(5.51)
28.27
(5.83)
80.01
79.37
4.49
3.06
Precooked 90 sec in steam (101 C) and peeled.
2
3
Pretreated 3.0 min in 0.05 M citrate buffer pH 5.6, precooked 90 sec
in steam (1010C) and peeled.
Yield dry weight in ( ).
33
produced by the degradative changes occurring during ice storage.
Pretreatment in the citrate buffer reduced meat yield loss produced
by the degradative processes occurring during ice storage.
Shrimp peeled without the pretreatment showed a reduction in dry weight
yield after 3 and 4 days of ice storage (Table 9).
A nearly linear
increase in cooked meat moisture content with respect to ice storage
time precluded reductions in wet weight yield.
Conversely, the cooked
dry weight yield for shrimp that were pretreated prior to peeling
increased with respect to ice storage.
The dry weight yield for pre-
treated shrimp stored 4 days in ice approximated that for untreated
shrimp stored <1 day and was superior to that for shrimp stored in ice
for an equal period of time.
This improved cooked meat yield for pretreated shrimp stored for an
extended period of time in ice could be related to the reduced mechanical action required for shell removal.
The lower moisture contents
for meat from pretreated shrimp indicates that the citrate buffer may
have altered the water-holding capacity of certain muscle.
The former
mechanism was not supported by a large difference in shell-index values.
Relationship of the Ratio of the Soaking Medium
VOIIMP
tn RmmH Shr-imp
Weight to Peel ability
The shell removal function of peelability was improved by increasing the volume of citrate buffer [0.05 M, pH 5.6) in relation to shrimp
weight; meat yield, both wet and dry weight, was not effected by the
34
Presence of citrate or the volume of citrate buffer to round shrimp
relationship (Table 10).
The shell-index for shrimp, while improved
over a control lot by a 5 min treatment in a 1:1 solution:round shrimp
relationship (wt/wt), was further improved at 2:1 and 4.8:1 relationship.
The efficiency of mechanical shell removal appeared to have a
degree of relationship to the quantity of citrate per unit of round
shrimp and/or the superior exposure of the round shrimp at higher
solution:round shrimp relationships brought about by a higher degree of
physical movement during the pretreatment.
A relationship of 1:1
provided just enough solution to cover round shrimp within a container.
Table 10.
Effect of the ratio of the pretreatment citrate buffer
solution volume to round shrimp weight on the peelability
of steam precooked^ shrimp.
Citrate buffer/roumd shrimp (wt/wt)
4.8
2.0
1.0
control
Yield {% wet wt.)
27.45
28.48
27.94
27.89
Yield (% dry wt.)
6.20
6.03
6.05
6.07
77.50
78.81
78.35
78.24
5.66
6.21
8.57
15.94
Moisture content (%)
Shell-index (%)
1
0.05 M citrate buffer (pH 5.6) at 160C for 15 min,
2
90 sec in steam (101oC).
Relation of Soaking Time and Citrate Buffer Concentration to Shrimp
Peelability
The concentration of the citrate buffer pretreatment solution
35
CO.01, 0.025 and 0.05 M) and pretreatment time C5 and 20 rain) did not
significantly Cp_.05) affect meat yield expressed as a percent of control lots (Table 11 and 12).
Wet weight yield for treated lots was
improved over control lots by the enhanced ease of mechanical shell removal afforded shrimp by the citrate buffer pretreatment.
The average
meat yield for control lots of 24.88+1.48% (n=5) was improved to an
average of 26.01+1.29 and 25.91+1.36% for lots treated for 5 and 20 min,
respectively (all citrate buffer concentrations; n=15).
This meat yield
increase clearly demonstrated the relationship of the shell removal and
yield functions of peelability.
Varying the concentration of the citrate buffer pretreatment did
not significantly (p<_.05) improve the shell removal efficiency expressed
as a percent of the control (Table 12).
Mean shell-index values (Table
11), however, did show a small degree of buffer concentration dependency
after a 5 min soaking time which was less pronounced after a 20 min
pretreatment.
These small differences, while not significant, could be
important for fresh shrimp that has not been subjected to a freezing
and thawing process.
Fresh frozen round shrimp while providing a more
standard sample for experimental purposes did mask potential small
differences between treatment and control samples.
Shell removal efficiency was significantly improved by increasing
the soaking time from 5 to 20 min as judged by the shell-index value
expressed as a percent of appropriate control lots (Table 12).
Most of
the improvement in shell removal efficiency over control samples was
achieved by a 5 min soak (Table 11).
The improvement observed by
lengthening the soak from 5 to 20 min while significant (p>_.05) was much
less than that observed for a 5 min soak over control lots.
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37
The progressive improvement in shell removal efficiency with the time of
exposure in the citrate buffer followed a power curve; 0.05 M: y = 9.336
x"'285(r= -.9114); 0.025 M: y = 9.175 x"-224(.r= -.8279); 0.01 M: y =
9.357 x
(r= -.7709)(.p>_.005, n = 15).
The highest concentration of
citrate buffer evaluated (0.05 M) was clearly most effective with
respect to the relationship of soaking time to shell removal efficiency
improvement.
Table 12.
Effect of variance of meat yield and shell-index values for
round shrimp treated in citrate buffer solutions of varying
concentration and for varying time periods.
F-value
Meat yield ?
{% wet wt.)
Shell-index (%)2
.3
5.28
Pretreatment time
0.07a
0.07"
Citrate buffer concentration
1.25
1.25"a
0.57a
Time X concentration
2.18a
2.18"
0.15a
aN.S. p4.05
3
bc.
Sig. p>. 05
3 (buffer concentration) X 2 (pretreatment time) factorial design;
n = 5.
Computed as a percent of the control lot.
Ranking of level mean: 5 min, 20 min.
Mechanism for the Improvement in the Shell Removal Function of Peelability.
The efficiency of mechanical shell removal was enhanced by degradative processes.
The actions of native enzymes and microbial growth
38
produce soluble nitrogenous constitutents that are washed from round
shrimp by melting ice during storage (Flick et al_., 1972; Flores et al.,
1973). Decker [1975) suggested that the action of native proteases
enhanced the segregation of the muscle from the outer shell of the
shrimp body.
This process was histologically described by Lightner
(1974) for brown shrimp (Penaeus aztecus) as a rapid degradation of
the subcuticle layers in the area of the cephalothorax.
Joly (.1965) observed that such natural processes could be augumented by heat and other methods.
Lapeyre (1968) reported that a heat
pretreatment of shrimp enhanced shell removal efficiency.
He observed
that heating induced the formation and accumulation of a fluid and
moisture zone between the muscle and shell of the shrimp body.
The
superior shell removal efficiency observed in this investigation for
steam precooked over raw shrimp (Table 5) supports the augumenting
-action of heat.
The simple mechanism postulated by Lapeyre (1968) by
which heating improves shell removal efficiency, however, must be modified to account for the associated reductions in meat yield through the
loss of protein during heating.
The results of this investigation show that processes which improve
the efficiency of mechanical shell removal reduced meat yield.
Storage
of round shrimp in ice enhanced shell removal but mediated a proteolytic
degradation of shrimp body proteins increasing their susceptibility
toward heat induced solubilization [Table 5 and 9).
This proteolytic
action was further documented by the storage time dependent increase in
the water-holding capacity of meat through cooking.
Pretreatment of
round shrimp at elevated temperatures showed the optimum temperature for
enhancing shell removal to be near the 45 C optimum for enzymatic
39
autolysis reported by Decker (1975) (Table 1).
The degradative process
that renders protein more susceptible to heat solubilization was associated with efficient mechanical shell removal, but the quantitative loss
of protein required for efficient shell removal was not well defined.
Thompson and Thompson (1968, 1970a and 1970b) found the composition of the connective tissue of white shrimp (Penaeus setiferous)
to be largely composed of "collagen-like" proteins.
This protein diff-
ered from collagen of vertebrates and other invetebrates by the replacement of hydroxyproline (the binding amino acid of collagens) with
tryptophan in its amino acid composition.
The ratio of unformed
collagen to collagen laid down as a tissue is much greater than other
animals.
Sub-cuticle layers and the epidermis between shrimp muscle and
shell composed of this collagen connective tissue would be readily
susceptible to heat solubilization which would be enhanced by proteolytic attack.
The marked relationship of heat induced protein loss
through cooking with shell removal efficiency observed in this investigation supports the importance of a collagen protein to the integrity of
the tissue associating shell with muscle in Pacific shrimp.
The action of a citrate buffer pretreatment of round shrimp prior
to mechanical peeling produced an improved shell removal efficiency and
reduced meat yield similar to that observed for degradative processes
occurring during ice storage.
Pretreatment enhanced the efficiency of
shell removal, but increased the degree of heat induced solubilization
of proteins through cooking resulting in reduced cooked meat yields
(Table 4, 5, 8 and 9).
The magnitude of the action of citrate pre-
treatments was time and temperature dependent (Table 6).
Elevated
citrate pretreatment temperatures prior to either peeling raw or steam
40
precooked greatly improved shell removal efficiency, but produced
marked reductions in meat yield.
The reduction in meat yield was
directly dependent upon the acid strength of the buffer at pH levels
<6.0 (Table 3 and 7).
Independence of the improvement in shell removal
efficiency from pH at levels <6.0 suggested that the action of citrate
in improving this function was not necessarily associated with observed
reductions in meat yield.
The action of citrate buffer on very fresh round shrimp was observed to bring about rather marked physical changes in the separated
shell after mechanical peeling.
Shell from very fresh shrimp appeared
uniformly transparent and smooth to the touch on the sub-cuiticle
surface.
The shell from shrimp treated with citrate possessed a sandy
or rough sub-cuticle surface detectable to the touch.
Numerous "white
spots" could be observed with the naked eye on the epicuticle surface.
The sub-cuticle surface possessed rather large areas that were white and
granular in appearance lacking transparency.
The action of citrate and
heat apparently induced a high degree of connective tissue solubility
through precooking and peeling yielding areas nearly devoid of protein
leaving only the white appearing chitin-mineral matrix of the subcuticle.
The more defined white spots on the epi-cuticle represented
the denatured tegumental gland duct openings.
The difference between
observed alternations in shell from citrate treated and non-treated very
fresh shrimp were similar to those changes that occurred in the shell of
the shrimp stored in ice which accompanied improved mechanical shell
removal efficiency.
The mechanism for the action of citrate buffer in improving shell
removal efficiency could have as a basis the following physio-chemical
41
functions alone or in combination: (1\ The pretreatment of round shrimp
with citrate buffer could produce pB. conditions that would accelerate
the activity of proteolytic enzyme systems during the pretreatment and
initial stages of precooking.
(2) Citrate could chemically render
instability to the tissue associating muscle with shell.
Acid con-
ditions could increase the heat induced solubility of collagen proteins
forming the sub-cuticle layers and epidermis of tissue attaching muscle
to shell.
Chelation of divalent cations important to the heat stability
of the collagen protein based tissue by citrate could also represent a
potential function.
This chelating function of citrate could also break
ionic bonding associating connective tissue with the chitin-mineral
matrix of the shell.
Proteolytic enzymes clearly play a major role in improving the
shell removal function of peelability during storage of round shrimp in
ice.
Evidence did not support the acceleration of this process by more
favorable pH conditions induced by brief citrate pretreatments.
Shell
removal efficiency was nearly independent of pH at levels <6.0 (Table 3
and 7).
The proteases of Pacific shrimp have rather specific pH opti-
ma, particularly under more acid conditions where their activity is
greatly accelerated (Decker, 1975).
If protease activity was acceler-
ated by the citrate buffer pretreatment, shell removal efficiency would
have to some degree reflected these optima.
In addition, accelerated
protease activity at reduced pH levels would have resulted in increased
water-holding capacity through cooking (Hamm et al_., 1960; Hamm, 1966;
1971).
Conversely, cooked meat moisture contents were reduced by more
acid pretreatments.
The direct chemical action of citrate on the tissue associating the
42
muscle with the shell of the shrimp body appears to be the primary
mechanism by which mechanical shell removal efficiency was improved.
Citrate ions in the pretreatment solution penetrated through the pores
of the shrimp cuticle and/or the arthrodial membranes between the seven
segments of the shell and interacted with the protein matrix of the subcuticle layers and the epidermis.
This interaction introduced a high
level of instability to the collagen/pro-collagen content of the connective tissue toward heat solubilization.
The magnitude of this in-
teraction was dependent upon the time and temperature (Table 6) and pH
of the citrate pretreatment (Table 3 and 7).
Improved shell removal
efficiency only required the development of connective tissue instability toward heat solubilization, not a relatively high level of actual
This is supported by the observed dependence of meat yield and largely
independence of shell removal efficiency on pretreatment buffer pH
(£6.0) (Table 3 and 7) and the marked shell removal efficiency observed
for citrate treated raw shrimp where reductions in meat yield were
largely associated with cooking in water (Table 5).
The chelation capability of citrate appears to form the most
feasible basis for interaction with tissue associating muscle with
shell.
A simple acidulation effect increasing the solubility of
collagen of connective tissue during heating, while shown to be pH
dependent, did not greatly affect shell removal efficiency (Table 3 and
7).
The chelation of divalent cations Cpresumably calcium and mag-
nesium) forming ionic bonding between connective tissue proteins and the
chitin-mineral matrix of the shell would clearly breakdown the association of muscle with shell. This action is supported to a degree by
43
the three optima shell removal efficiencies observed at pH 6.0, 5.0 and
3.6 for shrimp peeled after steam precooking (Jable 7) and at pH 6.0,
5.0 and 4.0 for shrimp peeled raw after a pretreatment at 45 C (Table
3).
These three optima roughly occurred at the 3.06, 4.76 and 5.4 pKa
values for citric acid.
The maximum ionization occurring at these pKa
values would provide the highest capacity for chelation of divalent
cations.
The magnitude of heat induced protein solubility produced by brief
citrate buffer pretreatments indicated that the integrity of the entire
protein matrix may be stabilized by ionic bonding.
At the molecular
level, ionic bonding may not only link connective tissue proteins to the
chitin-mineral matrix of the shell, but provide stability to the entire
collagen/pro-collagen matrix of connective tissue between muscle and
shell and between muscle segments.
Sensory Characteristics of Meat from Round Shrimp Pretreated in Citrate
Buffer
The action of citrate buffer under widely varying conditions on
round shrimp prior to steam precooking and subsequent peeling did not
affect the quality of fresh frozen cooked meat.
Favorable alternations
in the mechanical peelability of shrimp induced by varying the temperature Cl6-45dC) and time (.1.33-20 min) of the citrate buffer (0.05 M;
pH 5.6) pretreatment (Table 6) did not affect panel scores for odor,
texture, flavor and overall desirability [Table 13 and 14).
Flavor
panel scores for fresh frozen cooked meat from round shrimp treated in
buffer within a pH range from 3.0 to 6.0 C3 min; 160C; 0.05 M) (Table
44
Table 13.
Mean flavor panel scores for fresh frozen meat from round
shrimp treated2 in citrate buffers at varying temperatures
prior to steam precooking^ and subsequent peeling.
Sensory factor
Pretreatment
temperature ( C)
45
35
25
16
F-value:
Odor
Texture
Juiciness
Flavor
Over-all
desirability
6.65
6.90
6.75
6.85
6.80
6.20
7.70
6.80
7.05
6.65
6.80
7.25
6.55
6.55
6.90
6.90
6.60
6.40
6.90
6.80
0.315
1.945
2.065
0.815
0.885
2
n =20 judgments.
30 sec.
3
0.05 M; pH 5.6.
lore.
4
90 sec at
5
N.S. p^.05.
Table 14.
Mean flavor panel scores for meat from round shrimp treated2 for varyi ng time per iods in citrate buffeir prior to
steam [Drecook ing^ and su bsequent pee'ling.
Sensory factor
Pretreatment
time (rrtin)
1.33
3.0
5.0
10.0
20.0
F-value:
n = 20 judgments.
4
o
90 sec at 101 C.
5
N.S. p<.05.
Over-all
desirability
Odor
Texture
Juiciness
Flavor
6.20
6.45
6.55
6.20
6.70
6.75
6.95
6.60
6.65
7.00
7.00
6.50
7.00
6.65
7.20
7.05
6.50
7.00
6.70
7.05
6.90
6.70
6.80
6.65
6.95
1.175
0.725
2.425
0.555
0.415
2
160C.
3
0.05 M; pH 5.6.
45
7) and in 0.05, 0.025 and 0.01 M citrate buffer (pH 5.6; 16QC) for 5
and 20 min (Table 11) did not vary significantly Cable 15 and 16).
The texture, flavor and overall desirability of cooked meat derived
from shrimp stored in ice for 0, 1, 2 and 3 days (Table 9) deteriorated
in a significant and progressive manner (Table 17 and 18).
Flores and
Crawford (1973), Argaiz (1976) and Madero (1978) showed a similar
quality deterioration in cooked meat during the ice storage of round
Pacific shrimp.
A citrate pretreatment prior to processing did not
appear to greatly accelerate this deteriorative process.
Mean flavor
panel scores for both fresh frozen and stored (6 mos) cooked meat did
not vary significantly with regard to processing method and no significant interaction between processing method and ice storage was
observed (Table 18).
Inspection of individual treatment means for
citrate treated shrimp did show some reduction for scores for texture,
juiciness, flavor and overall desirability of fresh frozen and stored
control meat samples derived from round shrimp stored in ice for 2 and
3 days (Table 20).
These reduced scores were not significant.
The frozen shelf-life of cooked meat derived from citrate buffer
pretreated round shrimp was not altered.
A significant variation in
texture and juiciness scores was observed for meat derived from round
shrimp treated in citrate buffer (3 min; 0.05 M; 16 C) at various pH
levels (Table 7), but the differences were not related to the degree of
acidity (Table 9).
Although no similar significant variation was
observed for fresh frozen cooked meat from the same lot of round shrimp
(Table 15), the detection of differences by panelists after six months
frozen storage probably represented a composition and/or time dependent
panel response.
The sensory evaluation of cooked meat derived from
Table 15.
1
2
Mean flavor panel scores for fresh frozen meat from round
3
4
shrimp treated in citrate buffers of varying pH prior to
steam precooking^ and subsequent peeling.
Sensory factor
PH
Odor
Texture
Juiciness
Flavor
Over-all
desirability
3.0
7.00
7.23
7.13
7.50
7.27
3.6
7.20
7.10
7.07
7.17
7.13
4.0
6.87
7.27
6.97
7.17
7.07
4.6
7.13
7.03
7.07
7.20
7.13
4.8
6.93
6.70
6.87
6.64
6.60
5.0
7.10
7.17
7.10
7.23
7.13
5.6
7.10
7.00
7.17
7.20
7.03
6.0
7.17
6.90
7.07
7.03
6.87
0.606
0.946
0.366
2.016
1.446
Pretreatment
F-value:
n = 30 judgments.
2
Less than 2 wweks.
3
3 min at 160C.
4
0.05 M.
5
90 sec at 1010C.
6
N.S. p_<.05.
46
47
Table 16.
Mean flavor panel scores for meat from round shrimp treated^ for varying time periods in citrate buffers-^ of varying
strength prior to steam precooking^ and subsequent peeling.
Analysis of variance fatorial design.
Pretreatment time (min)/concentration (M)
5
Sensory factor
20
0.05
0.025
0.01
0.05
0.025
0.01
Odor
7.07
6.98
6.88
6.95
6.92
6.92
Texture
7.37
7.37
7.12
7.32
7.15
7.23
Juiciness
7.27
7.38
7.15
7.25
7.15
7.22
Flavor
7.18
7.25
7.12
7.05
7.02
7.10
Over-all
desirability
7.20
7.23
7.17
7.12
6.95
7.07
F--value
Treatment 5
time (min)
Buffer
strength (M)
Time x r
strength'
Odor
0.27
0.54
0. 14
Texture
0.34
1.61
0. 14
Juiciness
0.27
0.21
0.,57
Flavor
0.74
0.01
0. 18
Over-all desirabi;lity
1.86
0.11
0. 32
Sensory factor
1 n = 20 judgments.
2
160C.
3
pH 5.6.
4
90 sec at 101oC.
5
N.S. p^.05
48
Table 17.
Interaction of round shrimp storage in ice and meat frozen
storage (-17.8 C) with mean-1- flavor panel scores for meat
from round shrimp treated in citrate buffer prior to steam
precooking and subsequent peeling. Flavor panel scores.
Frozen meat storage (mos)
0
6
Processing method
Sensory
factor
Ice storage
(days)
0
Odor
Texture
Juiciness
Flavor
BT3
B
BT
1
2
3
7.20
6.65
6.85
6.65
7.00
6.75
6.20
6.55
6.75
6.85
6.75
6.55
6.85
6.90
6.80
6.90
0
7 05
7- 40K
6.90b
6.40^
6.30C
7.45?
7.35?
6.60^
6.00c
3
6.45b
6.85^
6.75b
5.85°
5.85b
0
1
2
3
6.90
6.55
7.05
6.70
6.70
7.00
6.30
6.45
7.20
7.15
7.20
7.00
7.25
7.15
6.95
6.35
0
6.75^
6.55^
6.35°
6.00b
6.45^
6.60^
5.80b
5.85b
6.55b
7.15f
6.95^
6.40b
6.90?
7.00?
6.40b
6.20b
6.85^
6.35
6.20°
6.05°
6.65!*
6.50?
5.70P
5.80b
6.80^
6.85^
6.85?
6.95?
1
2
1
2
3
0
Over-all
desirabil'ity
B2
1
2
3
- h
6.55°
6.3J
6.85K
6.40b
6.20b
1n = 20 jijdgments.
Steam precooked 90 sec at 101 C prior to peeling.
Treated 3 min at 16 C in 0.05 M citrate buffer, pH 5.6 prior to steam
precooking 90 sec at 101 C and subsequent peeling.
Mean values in a column for each sensory factor with same exponent
letter did not vary significantly (p=.05).
49
Table 18.
Interaction of round shrimp storage in ice and meat frozen
storage (.-180C) with mean flavor panel scores for meat from
round shrimp treated in citrate buffer prior to steam precooking and subsequent peeling. Analysis of variance
factorial design.
F-value
Juiciness
Flavor
Over-all
desirability
14.233
0.961
4.722
6.152
0.04
0.531
1.371
1.671
1.711
0.40
6.613
10.913
7.613-
9.533
Ice storage x method 0.41
1.551
1.641
O^S1
0.671
Ice storage x
frozon storage
1.12
0.771
0.QZ1
0.501
0.761
Method x frozen
storage
1.85
2.261'
0.131
0.121
0.041
Ice storage x method
0.41
x frozen storage
0.221
0.731
0.421
0.251
Source of variation
Sensory factor
Ranking of level mean
Texture
Ice storage
0 > 1 > 2 > 3 (days)
Texture
Frozen storage
0
<
6^
(mos)
Juiciness
Frozen storage
0
<
6
(mos)
Flavor
Ice storage
Flavor
Frozen storage
Over-all desirability
Ice storage
Over-all desirability
Frozen storage
i
1
Source of variation
Odor
Texture
Ice storage
1.50
Processing method
Frozen storage
l
K
n.S. p<.05
-,
Level means with same
(p=.05).
Level means with same
1 > 0 > 2 > 3 (days)
0
<
j5
(mos)
0 > 1 > 2 > 3 (days)
0
<
6^
(mos)
2CSig.
.
3CSig.
. p>_. ni
p>_. nc
05.
01
exponent letter did not vary significantly
underline did not vary significantly (p=.05).
50
three separate replicate lots of citrate buffer pretreated C3 min; 16 C;
0.05 M; pH 5.6) (Table 8) round shrimp showed no deteriorative effect of
citrate buffer pretreatment, frozen meat storage or an interaction
between processing method and storage (Table 20 and 21).
Although
scores for juiciness and texture varied significantly (p^.01), scores
after six months were superior to those for fresh frozen meat.
A
similar relationahip was observed for another sample of round shrimp
(Table 9) stored for 0, 1, 2 and 3 days in ice (Table 18 and 19).
Scores for texture, juiciness, flavor and overall desirability were
significantly superior after six months of frozen storage regardless of
processing procedure (Table 19).
The results of these flavor panel evaluations do not support a
deteriorative action for citrate on the quality of the fresh frozen
meat or an increase in degree of quality deterioration during frozen
storage.
Meat quality did not vary under a wide range of citrate buffer
pretreatment times, temperature, pH or concentration.
The effect of a
citrate buffer on meat quality does not appear to be a prime consideration in its application under widely varying commercial conditions.
51
Table 19.
1
2
Mean flavor panel scores for meat from round shrimp treated
in citrate buffers^ of varying pH prior to steam precooking^
and subsequent peeling after six months frozen storage
(-17.80C).
Sensory factor
Pretreatment
PH
Odor
Texture
Juiciness
Flavor
Over-all
desirability
2.6
6.75
7.20ab
7.00a
6.80
7.00
3.6
6.60
6.60d
7.25cd
6.80
7.00
4.0
6.85
7.10abc
7.50C
7.30
7.20
4.6
6.80
6.85e
6.95b
6.60
6.80
5.2
6.95
7.25a
7.20cd
7.45
7.45
6.0
6.80
7.00abc
7.35cd
7.15
7.25
0.945
2.806
3.367
2.045
1.445
F-value:
1n = 20 judgments
2
4
5
90 sec at 101oC
7
3 min at 160C
N.S. p<_.05
3
0.05 M
5
Sig. p^.05
Sig. p>_.01
Mean values in a column with same exponent letter did not vary
significantly (p=.05).
52
Table 20.
Effect of frozen storage (-17.8 C) on mean flavor panel
scores for meat from round shrimp treated in citrate buffer
prior to steam precooking and subsequent peeling. Flavor
panel scores.
Frozen meat storage (mos)
Processing method
Sensory factor
Sample
lot
Odor
III
Texture
III
Juiciness
III
Flavor
III
Over-all
desirability
III
B2
BT3
6.75
6.95
6.65
6.80
6.60
6.80
6.50
6.70
6.70
6.70
6.80
6.90
7.10
7.00
7.45
7.45
6.95
6.70
7.25
7.30
7.20
6.95
7.50
7.35
7.05
6.95
7.35
7.45
7.30
7.15
7.55
7.25
7.00
7.10
7.30
7.45
6.90
6.65
6.60
6.80
6.60
6.55
6.65
6.85
6.80
7.05
6.70
7.05
6.90
6.55
6.70
7.00
6.55
6.50
6.70
7.00
6.80
7.05
6.80
7.15
B
n = 20 judgments.
Steam precooked 90 sec at 101 C prior to peeling.
Treated 3 min at 16 C in 0.05 M citrate buffer (pH 5.6) prior to
steam precooking 90 sec at 101 C and subsequent peeling.
BT
53
Table 21.
Effect of frozen storage (-13 c) on mean flavor panel scores
for meat from round shrimp treated in citrate buffer prior
to steam precooking and subsequent peeling. Analysis of
variance factorial design.
F-valije
Flavor
,
Over-all ,
desirability
0.361
0.55
0.55
1.171
0AZ1
0.34
0.98
0.01
13.772
9.492
0.08
0.78
Sample x method
0.07
0.111
0.741
0.27
0.19
Sample x storage
0.53
0.051
0.311
0.17
0.15
Method x storage
0.62
0.601
0.031
0.76
1.21
Sample x method
x storage
6.53
0.061
0.551
0.10
0.12
Source of variation
Odor1 Texture
Sample lot
1.35
1.021
Processing method
3.71
Frozen storage
Source of variation
Juiciness
Sensory factor
Ranking of level mean
Frozen storage
Texture
0 mos < 6 mos
Frozen storage
Juiciness
0 mos < 6 mos
1
2
M.S. p_<.05
Sig. P2..01
Level means with same underline did not vary significantly (p=.05).
54
SUMMARY AND CONCLUSIONS
The mechanical separation of shell from the edible parts of very
fresh Pacific shrimp is difficult.
Parameters effecting the machine
peelability of raw and steam precooked Pacific shrimp were investigated
utilizing a laboratory scale mechanical peeler.
Means of improving the
shell removal and their effect on the meat yield function of peelability
were evaluated to improve the flexibility, rate, and efficiency of
processing.
Round shrimp begin to undergo a degradative change in muscle
proteins immediately post-catch.
This degradative process which oc-
curred during storage in ice was directly related to improve mechanical
shell removal and a reduction in the cooked meat yield function of
peelability.
The yield reductions were associated with an increased
water-holding capacity of the meat through cooking.
Moisture partially
replaced dry matter in wet meat yield after extended storage in ice.
The connective tissue of shrimp appeared to be composed of "collagen—like" proteins labile to heat induced solubilization.
Sub-cuticle
layers of the shell and the epidermis between the muscle and shell
composed of this collagen protein were readily susceptible to heat
induced solubilization which was enhanced by proteolytic attack during
ice storage.
Enzymatic action on protein not solubilized and lost
through processing increased the water-holding capacity of shrimp meat
through cooking.
Steam precooking prior to mechanical peeling improved shell removal
efficiency over peeling raw.
Heat induced-solubilization of the protein
matrix within the sub-cuticle layers and composing the epidermis reduced
55
meat yield but improved shell removal efficiency.
Raw peeling of fresh
shrimp followed by cooking in water produced superior meat yields over
steam precooking prior to mechanical peeling.
Storage in ice for more
than two days reduced the yield advantage of raw peeling.
This general
observation was complicated by the inferior shell removal efficiency of
shrimp peeled raw reducing the degree of mechanical and washing action
on exposed meat surfaces during processing.
Pretreatment of round shrimp in citrate buffer prior to peeling raw
or steam precooked improved shell removal efficiency.
Concentrations
ranging between 0.01 and 0.05 M (pH 5.6) provided equal shell removal
efficiency and meat yield.
This result was clearly defined but com-
plicated by the effects of freezing and thawing round shrimp samples.
A favorable improvement in shell removal efficiency as the ratio of
pretreatment solution: round shrimp was increased indicating that the
quantity of citrate available per unit of round shrimp may play a role
in determining shell removal efficiency within a 0.01 to 0.05 M concentration range.
A citrate buffer between pH 5.5 - 6.0 produced optimum shell
removal efficiency and cooked meat yield.
The efficiency of shell
removal was nearly independent of pH at levels <^ 6.0.
Meat yield dry
weight was reduced in a linear manner as pH was lowered to pH 2.6.
The favorable action of citrate buffer on shell removal efficiency
that was markedly enhanced by increased exposure time and/or elevated
temperature reduced cooked meat yield.
Optimum shell removal efficiency
and meat yield from raw and steam precooked shrimp was achieved at a low
pretreatment temperature (16 C).
Exposure times of 3 to 10 min provided
marked improvement in shell removal efficiency and only limited
56
reductions in meat yield.
Extended exposure time at low temperature
(16 C) produced a more unfavorable meat yield reduction for shrimp
peeled raw than precooked.
Degradation of raw meat during extended
exposure and subsequent processing increased soluble protein loss
during water cooking.
A short [<_ 3 min) pretreatment coupled with the
rapid heating of steam precooking produced optimum shell removal
efficiency and cooked meat yield.
The chelation of divalent cations by citrate that could form ionic
bonding between connective tissue proteins and the chitin-mineral
matrix of the shell appeared to be the most feasible mechanism by which
mechanical shell removal efficiency was improved.
The penetration of
citrate through the pores of the shrimp cuticle and/or the arthrodial
membranes between the seven segments during pretreatment induced a high
level of instability to the collagen/pro-collagen content of the
-connective tissue toward heat solubil ization.
The magnitude of
solubility induced by heat produced by the citrate pretreatment
indicated that ionic bonding may be important not only in the direct
attachment of muscle to shell but also to the entire collagen based
connective tissue content of the shrimp.
The action of citrate buffer on round shrimp under widely varying
pretreatment time, temperature, concentration and pH conditions did not
adversely affect cooked meat quality.
Flavor panel scores for texture,
juiciness, flavor and over-all desirability of fresh frozen cooked meat
were not significantly altered in an adverse manner by the pretreatment.
The pretreatment did not accentuate the deteriorative changes occurring
during ice storage of round shrimp or the frozen storage of cooked meat
over six month period.
57
A short C<3 min) pretreatment of very fresh round shrimp in dilute
(0.01-0.05 M) citrate buffer (pH 5.6) could markedly improve mechanical
shell removal efficiency under commercial conditions.
The application
of this process would allow for the elimination of time-related
processing constraints and the production of high quality cooked meat
from very fresh round shrimp.
Strict control of time and temperature
relationships would be important in maintaining acceptable cooked meat
yields.
Additional research is required to develop means of restricting
the destabilizing action of citrate on shrimp muscle proteins solubilized by heat to minimum levels required for efficient mechanical
shell removal.
58
BIBLIOGRAPHY
Aepli, 0. T. and Schultz, R. W. 1971.
Parts. U.S. Patent 3,622,347.
Removal of nonedible shrimp
Argaiz, A. 1976. Relation of the decomposition of trimethylamine oxide
and the quality of Pacific shrimp (Pandalus jordani). Master's
thesis. Oregon State University, Corvallis, Oregon. 67 numb,
leaves.
ASTM.
1968. "Manual on Sensory Testing Methods." American Society for
Testing and Materials, Philadelphia, Pa. 77 p.
Bailey, M. E., Fieger, E. A. and Novak, A.F. 1956. Objective tests
applicable to quality studies of iced stored shrimp. Food Res.
21:611-620.
Bethea, S. and Ambrose, M.E. 1962. Comparison of pH, trimethylamine
content, and picric acid turbidity as indices of iced shrimp
quality. Comm. Fish. Rev. 24(3):7-10.
Burukovskii, R.N. and Bulanenkov, S. K. 1969. Pink shrimp, biology and
fish (translated from Russian), pp.2-7. Israel Program for Scientific Translation, Jerusalem, Israel.
Bynagte, P. W. 1972. Soaking shrimp in a phosphate solution before
peeling. U.S. Patent 3,705,040.
Collins, 0. 1960a. Processing and quality studies of shrimp held in
refrigerated sea water and ice, part I-priliminary observations on
machine-peeling characteristics and product quality. Comm. Fish.
Rev. 22(3):l-5.
Collins, J. 1960b. Processing and quality studies of shrimp held in
refrigerated sea water and ice, part 4-interchange of the components in the shrimp-refrigerated-sea-water system. Commer.
Fish. Rev.22(7):9-14.
Collins, J. 1961. Processing and quality studies of shrimp held in
refrigerated sea water and ice, part 5-interchange of components
in a shrimp-ice system. Comm. Fish. Rev. 23(7):l-3.
Collins, J. and Kelley, C. 1969. Alaska pink shrimp, Pandalus
boreal is : Effects of heat treatment on color and machine
peelability. U.S. Fish Wild!. Serv., Fish. Ind. Res. 5:181-189.
Collins, J. , Seagran. H. and Iverson, J. 1960. Processing and quality
stidies of shrimp held in refrigerated sea water and ice, part
2-comparison of objective methods for quality evaluation of raw
shrimp. Comm. Fish. Rev. 22(4):l-5.
59
Dahlstrom, W. A. 1972. Status of the California ocean resource and
its management. Marine Fish. Rev. 35C3-4);;55-59.
D'Aquin, E. L. 1965. Chemical treatment for producing soft-shell
crabs. U.S. Patent 3,222,186.
Decker, C. D. 1975. Proteolytic activity in Pacific shrimp (Panda!us
jordani) processing waste: distribution, effects on muscle proteins, and partial characterization. Ph.D. thesis. Oregon State
University, Corvallis, Oregon, 95 numb, leaves.
Dennel, R. 1947. The occurrance and significance of phenolic hardening
in newly formed cuiticle of crustacean decapoda. Pro. R. Soc.
Lond., B, 134:485-503.
Dennel, R. 1960. Integument and exoskeleton. In: The Physiology of
Crustacea, Vol. 1, ed. Waterman, T. H., pp.449-472. Academic
Press, New york.
Fieger, E. A. and Friloux, J. J. 1954. A comparison of objective
test for quality of Gulf shrimp. Food Tech. 8(l):35-38.
Fieger, E. A., Bailey, M. E. and Novak, A. F. 1958. Effect of delayed
handling upon shrimp quality during subsequent refrigerated
storage. Food Tech. 12:297-300.
Flick, G. J. and Lovell, R. T. 1972. Post-mortem biochemical changes
in the muscle of Gulf shrimp, Penaeus atzecus. J. Food Sci.
37(4):609-611.
Flores, S. C. and Crawford, D. L. 1973. Post-mortem quality changes
in iced Pacific shrimp (Randalus jordani). J. Food Sci. 38:
575-579.
Gillies, M. T. 1975. "Fish and Shellfish Processing," pp.194-212.
Noyes Data Corp., New York.
Hamm, R. and Deatherage, F. E. 1960. Changes in hydration, solubility
and charges of muscle proteins during heating. Nature, 207:1269.
Hamm, R. 1966. Heating of muscle systems. In: The Physiology and
Biochemistry of Muscle as a Food, ed. Briskey, E. J., Cassens,
R. G. and Trautman, J. C., pp. 363-385. The University of
Wisconsin Press, Madison, Milwaukee and London.
Hamm, R. 1971. Interactions between phosphates and meat proteins.
In: Symposium : Phosphates in Food Processing, ed. DeMan, J. M.
and Melnychyn, P. The AVI Publishing Co., Westport, Conn.
Idyll, C. P. 1976. The shrimp fishery. In: Industrial Fishery
Technology, ed. Stansby, M. E. and Dassow, J. A., 2nd ed., pp.
150-162. Reinhold Publishing Co., New York.
60
Joly, M. 1965. "A Physical-Chemical Approach to the Denaturation
of Proteins," pp. 9-306. Academic Press, New York.
Jones jr., J. M. 1970. Methods of processing shrimp and related
shellfish. U.S. Patent 3,528,125.
Jones jr., J. M.
3,698,038.
1972.
Shellfish processing machine.
U.S. Patent
Langmo, R. D. and Rudkin, T. M. 1970. Relationship of shrimp width
and weight to mechnical sizing. 1970. Special report No. 308,
Agricultural Experiment Station, Oregon State University,
Corvallis, Oregon.
Lapeyre, J. M. 1966. Process for peeling pre-cooked shrimp.
Patent 3,276,878.
Lapeyre, J. M. 1968.
3,383,734.
Apparatus for peeling shrimp.
U.S.
U.S. Patent
Lightner, D. V. 1974. Normal postmortem changes in the brown shrimp,
Penaeus aztecus. Fish. bull. 72(l):223-236.
Lockwood, A. P. M. 1967. "Aspects of the Physiology of Crustacea."
W. H. Freeman and Company, San Francisco, 328 p.
Machline, J., Aizawa, Y., Ishimaru, T., Nishida, S. and Marumo, R.
1977. Integumental sensilla of pelagic decapod crustaceans.
Marine Biol., 43:149-155.
Madero, C. F. 1978. Effects of initial quality on the frozen shelllife of Pacific shrimp (Pandalus jordani). Master's thesis.
Oregon State University, Corvallis, Oregon. 71 numb, leaves.
Richards, A. G. 1951. "The Integument of Arthropods".
of Minnesota Press, Minneapolis, Minnesota.
University
Rudall, K. M. 1955. The distribution of collegen and chitin.
Soc. exp. Biol. 9:49-71.
Symp.
Seagran, H. Collins, J. and Iverson, J. 1960. Processing and quality
studies of shrimp held in refrigerated sea water and ice, part 3holding variables and keep quality of the raw whole shrimp. Comm.
fish. rev. 22C5):l-5.
Snedecor, G. W. and Cochran, W. G. 1967. "Statistical Methods,"
6th. ed. The Iowa State University Press, Ames, Iowa. 593 p.
Thompson, H. C. and Thompson, M. H. 1968. Isolation and amino acid
composition of the collagen of white shrimp (Penaeus setiferous)
Comp. Biochem. Physio!. 27:127-132.
Thompson, H. C. and Thompson, M. H.
1970.
Amino acid compositional
61
relatedness between the procollagen and insoluble collagen of
white shrimp (Penaeus setiferous) and the collagens of certain
other invertebrates. Comp. Biochem. Physio!. 36:189-193.
Thompson, H. C. and Thompson, M. H. 1970. Isolation and amino acid
composition of the collagen of white shrimp (Penaeus setiferous)II. Comp. Biochem. Physio!. 35:471-477.
Thompson, M. H. and Farragut, R. N. 1971. Shrimp freezing and refrigeration in the U.S.A. Procedings, conference on the Canadian
shrimp fishery. Saint John, New Brunswick, October 27-29, 1970.
pp.187-191. Canadian Fisheries Reports, No. 17.
Travis, D. F. 1955. The moulting cycle of the spiny lobster,
Panulirus argus, Latreille II, pre-ecdysial histological and
histochemical changes in the hepatopancreas and integumental
tissues. Biol. Bull. Woods Hole, 108:88-112.
Willis, J. C. and Sundberg, 0. B. 1969. Process and apparatus of
deshelling cooked shrimp. U.S. Patent 3,466,699.
Yonge, C. M. 1936. On the nature and permeability of chitin, II,
permeability of the uncalcified chitin lining of the foregut
of Kormarus. Proc. R. Soc. B. 120:15-41.
Yonge, 0. C. 1956. Some factors affecting the shelf life of frozen
fish. Trade News, 9(1):9-14.