Effect of salmon plasma protein on Pacific whiting surimi gelation
under various ohmic heating conditions
Fowler, M. R., & Park, J. W. (2015). Effect of salmon plasma protein on Pacific
whiting surimi gelation under various ohmic heating conditions. LWT-Food
Science and Technology, 61(2), 309-315. doi:10.1016/j.lwt.2014.12.049
10.1016/j.lwt.2014.12.049
Elsevier
Accepted Manuscript
http://cdss.library.oregonstate.edu/sa-termsofuse
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Effect of Salmon Plasma Protein on Pacific Whiting Surimi Gelation under Various
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Ohmic Heating Conditions
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Matthew R Fowler, Jae W Park
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Oregon State University Seafood Research and Education Center
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2001 Marine Dr Rm 253, Astoria, OR 97103, USA
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Corresponding Author:
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Jae W Park
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(503) 325-4531 Ext #3
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Jae.park@oregonstate.edu
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To be submitted to LWT- Food Sci and Tech
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ABSTRACT:
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The effect of salmon blood plasma (SPP) on the gelation of Pacific whiting surimi under
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different ohmic heating conditions was investigated. SPP was found to significantly increase gel
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strength in gels heated ohmically to and held at 60° for 30 min followed by heating ohmically to
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90°C. SPP at a level of 1 g/100g was also found to increase gel strength in gels held at 25°C for 2
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h prior to ohmic heating. This increase was not seen in gels where EDTA was added to inhibit
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the activity of endogenous transglutaminase (ETG). SPP also created a more pronounced setting
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effect as measured by dynamic rheology and SDS-PAGE. SPP was found to effectively inhibit
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protease activity through TCA-soluble peptide analysis. Scanning electron microcopy revealed a
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loosely arranged gel network caused by protease enzymes. It was reversed by the addition of
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SPP as well as setting at 25oC due to ETG.
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Keywords: salmon plasma, surimi gelation, ohmic heating, transglutaminase, protease
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Highlights:
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Various ohmic heating rates effectively isolated enzyme activity in surimi
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Salmon plasma protein effectively inhibited protease in Pacific whiting surimi
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Salmon plasma protein increased gel strength during setting
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Salmon plasma protein is an effective inhibitor at low levels (0.5 g/100g or less)
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Introduction
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In the United States, surimi is made from two types of fish: Alaska pollock (AP) and Pacific
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whiting (PW). Unlike AP, PW contains a high amount of protease enzymes that degrade the
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quality of the surimi gel when heated slowly (Klesk, Yongsawatdigul, Park, Viratchakul, &
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Virulhakul, 2000). The major protease enzymes found in PW are cathepsins B, H, and L. After
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PW has gone through the rinsing step of surimi manufacturing, most of cathepsin B and almost
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all of cathepsin H proteases are removed. However, cathepsin L, a protease associated with
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myofibrillar proteins, is not removed during the washing process and was found to be the main
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protease responsible for degradation of the surimi gel (An, Weerasinghe, Seymour, &
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Morrissey, 1994). Cathepsin L is a heat activated cysteine protease, having an optimum
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temperature of around 55-60°C (Seymour, Morrissey, Peters, & An, 1994; Visessanguan,
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Benjakul, & An, 2003). Incubating PW surimi around this temperature range for 30 min before
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heating to 90oC will result in a complete disappearance of the myosin heavy chain as well as an
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inability to form a gel network (Morrissey, Wu, Lin, & An, 1993; Rawdkuen, Benjakul,
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Visessanguan, & Lanier, 2007a). Surimi that is heated at a slow rate (such as in a water bath)
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also suffers protoeolytic degradation (Yongsawatdigul, Park, Kolbe, Dagga, & Morrissey, 1995).
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In the past, bovine blood plasma (BPP) was added to PW surimi as a protease inhibitor. This
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practice was discontinued however due to public fear of Bovine Spongiform Encephalopathy
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(BSE). Since then, BPP has been replaced by dried egg white (DEW), which contains mainly
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serine protease inhibitors (Yongswatdigul, Hemung, & Choi, 2014). Since DEW is not as effective
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as BPP at inhibiting cysteine proteases, such as cathepsin L (Yongswatdigul et al., 2014), finding
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an alternative inhibitor that can be used at small concentrations would be beneficial. Blood
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plasma from other sources, such as pork (Benjakul, Srivilai, & Visessanguan, 2001;
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Visessanguan, Benjakul, & An, 2000) and chicken (Rawdkuen et al., 2007a; Rawdkuen, Lanier,
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Visessanguan, & Benjakul, 2004, 2007b), have been found to be effective inhibitors of protease
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enzymes found in surimi.
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In addition to protease inhibitors, blood plasma also contains other proteins that may enhance
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the gelation of surimi. Blood plasma proteins such as fibrinogen exhibit their own gelling ability
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upon heating (Davila, Pares, Cuvelier, & Relkin, 2007). Also, blood plasma has been shown to
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contain endogenous transglutaminase (ETG) enzymes (Lorand, 2007). ETG is a naturally
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occurring enzyme in PW and other species of fish. ETG is a calcium dependent enzyme that
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mediates covalent cross linking of myofibrillar proteins, resulting in a higher gel strength (An,
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Peters, & Seymour, 1996). Since endogenous PW and AP ETG has an optimum temperature of
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around 25°C, leaving surimi paste at room temperature for 1 or 2 hr before heating results in
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stronger gels. This ETG mediated formation of non-disulfide covalent cross links before heating
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is known as “setting”. Addition of calcium and calcium containing compounds to surimi has
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been shown to increase the effect of setting (Lee & Park, 1998) and the addition of calcium
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chelating compounds, such as EDTA, has been shown to completely inhibit setting (Kumazawa,
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Numazawa, Seguro, & Motoki, 1995). Since blood plasma contains ETG, it may also contribute
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to the setting phenomenon when added to surimi in sufficient amounts.
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The activity of these two different types of enzymes (proteases and ETG), pose a problem when
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evaluating the quality of PW surimi gel. Traditionally, surimi is heated in a water bath to 90°C
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before conducting gel texture measurement. This slow heating allows for the activity of both
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ETG (enhances gel strength) and proteases (lowers gel strength). Surimi crabstick, however, is
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manufactured in a thin sheet under gas and/or steam heating, which quickly deactivates both
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types of enzymes and does not allow for any activity beyond 75oC. Therefore, these testing
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methods do not accurately assess the quality of the surimi seafood being produced in a thin
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sheet under fast heating. Rapid heating methods, such as ohmic heating, allow for a better
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assessment of surimi containing protease enzymes (Yongsawatdigul et al., 1995). The objective
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of this study was to isolate the activities of both proteases and ETG at various heating rates
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under ohmic heating, and evaluate the effect of salmon plasma protein (SPP) on the gelation of
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PW surimi in combination with these enzymes.
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2. Materials and Methods
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2.1.
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Pacific whiting surimi (FA grade) without the addition of egg white, 2 months old, was obtained
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from American Seafoods (Seattle, WA, USA) and kept at -30°C until used. Protein markers and
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other electrophoresis chemicals were purchased from Bio-Rad Laboratories (Hercules, CA,
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USA). All other chemicals used were of reagent grade.
Materials
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2.2.
Collection of salmon blood and preparation of plasma
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Whole blood was collected at the Klaskanine Fish Hatchery (Astoria, OR, USA) from female
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Chinook salmon immediately before roe collection. Blood was collected from bleeding fish
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into bottles containing 3.8g/100mL sodium citrate (as an anti-coagulant), and gently mixed at a
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ratio of 9:1 (mL:mL) blood to sodium citrate (Li, Lin, & Kim, 2008; Rawdkuen et al., 2007b).
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Blood was kept on ice and transported back to the Oregon State Seafood Laboratory (Astoria,
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OR, USA) where it was centrifuged for 15 min at 1,500 × g at 4°C using a Beckman J6-MI
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centrifuge (Beckman Coulter, Fullerton, CA, USA). The supernatant was then lyophilized in a
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Labconco freeze drier (Kansas City, MO, USA) and regarded as salmon plasma protein (SPP). SPP
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was stored at -80°C until used. Samples were not stored longer than 3 months.
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2.3.
Surimi gel preparation
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Paste and gels were prepared according the method of Poowakanjana, Mayer, and Park (2012)
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with various heating methods. Partially thawed surimi was chopped at 1,800 rpm for 1 min
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using a silent cutter (UM 5 universal, Stephan Machinery Corp, Columbus, OH, USA). After a
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2g/100g addition of salt, surimi was chopped for an additional 1 min at 1,800 rpm. Moisture
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content was then adjusted to 78g/100g using ice. At this time SPP (0, 0.5 or 1 g/100g) as well as
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EDTA (0 or 0.1 g/100g) was added. A preliminary study conducted in our laboratory indicated
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that 0.1 g/100g EDTA was sufficient to completely inhibit ETG activity in PW surimi (data not
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shown). Following the addition of ice and other dry ingredients, surimi was chopped again for 1
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min at 1,800 rpm. Chopping was then continued at 3,600 rpm under vacuum (40-60 kPa) for an
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additional 3 min and a total chopping time of 6 min. Care was taken so that the final
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temperature of the surimi paste was less than 15°C. Paste was packed in a polyethylene bag
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and subjected to vacuum to remove any air pockets developed during packing. The paste was
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then stuffed into a 15 cm x 3 cm nylon tube. 3 different heating methods were used: 1. Ohmic
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(rapid) heating to 90°C at a voltage gradient of 12.62 V/cm with settings of 250 V and 10 kHz to
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prevent the activity of both ETG and proteases (OH); 2. Ohmic heating to 60°C followed by
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ohmically holding at 60°C for 30 min before ohmically heating to 90°C to prevent the activity of
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ETG and maximize the activity of proteases (60/OH); and 3. Holding in a 25°C water bath for 2 h
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(to maximize the activity of ETG) followed by ohmic heating to 90°C to prevent the activity of
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proteases (25/OH). Two sausages were made per heating method. Following heating, gels were
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placed in a plastic bag, submerged in ice water for 15 min, and stored overnight at 4°C.
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2.4.
Oscillatory dynamic measurement
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Surimi paste was subjected to a temperature sweep using a CVO rheometer (Malvern
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Instruments Ltd., Worcestershire, UK) using a cone (4° and 40 mm diameter) and plate
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geometry with a gap of 150 μm. Surimi gels prepared as described above were thinly cut to a
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thickness of 2 mm and subjected to a frequency sweep using parallel plate geometry (20 mm
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diameter) and a gap of 1 mm. Surimi gel (3 cm diameter) was trimmed to 2 cm using a small
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knife and moisture trap containing a moistened sponge was used to minimize drying of sample.
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Temperature sweeps were conducted from 10 °C-90 °C at a heating rate of 2 °C/min at a fixed
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frequency of 0.1 Hz. Frequency sweeps were conducted from 0.1 to 10 Hz at a fixed
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temperature of 25 °C. A shear stress of 50 Pa, determined by stress sweep to be in the linear
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viscoelastic region, was used.
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2.5.
Fracture gel evaluation
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The day after heating, gels were removed from refrigerated storage and held at room
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temperature for 2 h prior to testing. Gel samples were cut into 30 mm lengths and the breaking
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force (g) and penetration distance (mm) were determined using a texture analyzer (TA-XT plus,
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Texture Technologies Corp, NY, USA). Gels were punctured with a spherical probe (5 mm
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diameter) at 1 mm/sec.
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2.6.
Color analysis
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L*, a*, and b* values of surimi gels were determined from 30 mm samples using a Minolta
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colorimeter (CR-310; Minolta Camera Co. Ltd., Osaka, Japan). The instrument was standardized
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using a Minolta calibration plate and a Hunter Lab standard hitching file according to the
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method of Park (1994). Whiteness was calculated using the equation L*-3b*.
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2.7.
Determination of TCA soluble peptides
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Eighteen mL of 5 g/100mL trichloroacetic acid (TCA) was added to 2 g of sample followed by
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homogenization for 2 min at 15,000 rpm using a Tissue Tearor homogenizer (Biospec Products
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Inc., Bartlesville, OK, USA). Homogenate was then held at 4 °C for 1 h before centrifugation at
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8,000 × g for 5 min using a Sorvall RC-5B centrifuge (DuPont Instruments, Newton, CT, USA).
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The TCA-soluble peptide content of the supernatant was measured by the method of Lowry et
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al. (1951) using tyrosine as a standard and expressed as μmol tyrosine/ g sample. Samples were
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measured in triplicate.
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2.8.
SDS PAGE
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Surimi gels were examined for protein patterns based on their molecular weight according to
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the method of Laemmli (1970). Gels were solubilized in 5g/100mL sodium dodecyl sulfate at 90
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°C according to the method of Morrissey et al. (1993). A 4g/100mL acrylamide stacking gel and
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10g/100mL acrylamide separating gel were used. Gels were fixed and stained in 0.125g/100mL
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Coomassie R-250 (Bio-Rad, Richmond, CA, USA), and de-stained in a 50mL/100mL methanol,
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10mL/100mL acetic acid solution. Molecular weights of bands were determined by comparison
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to a molecular weight standard (Protein Plus All Blue, Bio-Rad Laboratories, Hercules, CA, USA).
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2.9.
Scanning electron microscopy
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Gels were cut into 2 mm x 2 mm sections and rinsed two times in distilled water for 30 min
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prior to fixing for 2 hr in a 0.1 mol/L cacodylate buffer containing 2.5g/100mL glutaraldehyde
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and 1g/100mL paraformaldehyde. Samples were then dried through serial acetone dilutions
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(10, 30, 50, 70, 90 and twice in 100%) followed by critical point drying. Samples were then
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coated with gold and palladium (40:60 ratio) and examined in a Quanta 600 FEG field emission
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scanning electron microscope (FEI Inc., Hillsboro, OR). This microscopy work was done at the
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Oregon State University Electron Microscope Facility (Corvallis, OR, USA).
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2.10. Statistical analysis
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Data were subjected to analysis of variance (ANOVA). Comparison of means was carried out by
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Tukey test (Ramsey & Schafer, 2012). Statistical analysis was done by Sigma Plot software
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package (Sigma Plot 12.5, Systat Software Inc, San Jose, CA, USA). Two batches were made for
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each treatment and all experiments were repeated.
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3.
Results and Discussion
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3.1.
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The maximum elastic modulus (G’) of surimi heated at 2°C/min decreased as more SPP was
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added (Fig 1A-1C). Visessanguan et al. (2000) found that the addition of pork plasma protein to
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Pacific whiting actomyosin also decreased G’. It was postulated that this was due to plasma
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proteins having different thermal stabilities and gelation properties than fish muscle proteins.
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The formation of two different gel networks (plasma protein and fish protein) with different
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properties may lead to the observed decrease in G’. However, for pastes with 0.5g/100g SPP
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(Fig 1B) and 1g/100g SPP (Fig 1C), the maximum G’ was higher for samples containing no EDTA
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than samples containing EDTA. This difference was not observed in the control containing no
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SPP. The difference between samples with and without EDTA is attributed to the setting effect
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due to the action of ETG. This activity, however, may be offset by proteases active in the control
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paste that are inhibited in the samples containing SPP. Therefore, the influence of setting
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during heating at 2°C/min is more pronounced when SPP is added. In addition, ETG and calcium
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present in SPP may serve to enhance the setting effect. Yin & Park (2014) found that adding
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calcium containing nano scale fish bone to surimi also increased gel strength.
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Rheological properties of the final gel were also evaluated by frequency sweep (Fig 1D). The G’
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of the control sample held at 60°C before ohmic heating showed a significantly higher
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frequency dependence than the control sample ohmically heated directly to 90°C. Samples
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containing both 0.5g/100g SPP and 1g/100g SPP and held at 60°C before ohmic heating showed
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similar frequency dependence as the control heated to 90°C. G’ values of less cohesive gels
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exhibit higher frequency dependency. Therefore, G’ increases at a higher rate as frequency
Oscillatory rheology
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increases than is observed in a more cohesive gel (Picout & Ross-Murphy, 2003). These results
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indicate that adding SPP to surimi to inhibit proteases lead to a less frequency dependent, more
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cohesive gel network in the finished product.
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3.2.
Fracture gel evaluation
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Both breaking force (Fig 2A) and penetration distance (Fig 2B) of 60/OH gels were greatly
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increased by the addition of 0.5g/100g and 1g/100g SPP with or without the addition of EDTA
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(P<0.05). There was no difference for this heating method between 0.5g/100g and 1g/100g
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SPP. This heating condition maximized the action of endogenous proteases while minimizing
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the activity of ETG to less than 10% (Park, Ooizumi, & Hunt, 2014). This indicates SPP at a level
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of 0.5g/100g is sufficient for inhibiting protease activity and no added benefit in this regard is
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seen from increasing concentration.
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Compared to OH gels, 25/OH gels without EDTA showed a greater breaking force and
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penetration distance (P<0.05). This heating method was favored by ETG and the activity of
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protease enzymes was not significantly noted. Therefore, this increase of gel strength is due to
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the setting phenomenon. In addition 25/OH gels without EDTA and containing 1g/100g SPP
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showed the highest breaking force and penetration distance of all samples (P<0.05). It may be
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postulated that transglutaminase present in SPP contributed additionally to enzyme-mediated
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covalent cross linking during settings. Both OH and 25/OH gels containing no SPP decreased
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moderately and significantly, respectively, in breaking force and penetration distance when
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EDTA was added (P<0.05). EDTA chelates calcium, which in addition to being a cofactor for ETG
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may also play other roles in gelation (Lee & Park, 1998). However, both OH and 25/OH gels
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containing EDTA showed a higher breaking force and penetration distance with the addition of
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SPP as compared to the control (P<0.05), indicating a significant role of SPP as a gel enhancer.
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In addition to transglutaminase being present in SPP, it may also be a source of additional
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calcium (Heaton & Pomare, 1974; Maye, Keaton, Hurst, & Habener, 1979), leading to greater
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gel strength.
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3.3
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Whiteness decreased markedly as SPP concentration increased (P<0.05) (Fig 3D). Increase in
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SPP was also associated with a lower L* value (less lightness) (Fig 3A), more negative a* value
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(more redness) (Fig 3B) and a higher b* value (more yellowness) (Fig 3C). The decrease in color
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quality is due to hemolysis in the blood plasma. When blood is collected and plasma is
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processed, damage to the red blood cells can result in plasma containing a pinkish hue as
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opposed to a straw yellow color (Field, Elvehjem, & Juday, 1943; Li et al., 2008). In addition, as
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salmon is a cold water species, blood plasma may exhibit lower thermal stability and therefore
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be more susceptible to hemolysis than blood plasma from mammals. This issue may be partly
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intervened by the fact that SPP is needed only at very low levels (maximum of 0.5g/100g as
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shown by the results in Fig 2) in order to prevent proteolysis in PW surimi. It is suggested
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however that further studies be conducted to determine collection and processing methods
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that will reduce hemolysis. In addition, 60/OH gels showed greater L* values, less negative a*
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values, and higher b* values than other gels (P<0.05). However, overall whiteness was not
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affected by heating conditions.
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Color gel analysis
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3.4
TCA soluble peptide content
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At a TCA concentration of 5g/100mL, all proteins except for small oligopeptides are insoluble
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(Yvon, Chabanet, & Pelissier, 1989). Since small peptides are the result of the action of
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endogenous proteases on PW muscle, the protein content in the 5g/100mL TCA supernatant
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after centrifugation is related to total protease activity in the surimi. Control 60/OH gels with or
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without EDTA had significantly higher TCA soluble peptide content compared to other gels
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(P<0.05) (Fig 4). The addition of SPP to these gels showed a significant decrease in TCA soluble
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peptide content (P<0.05). There was no difference between 0.5g/100g and 1g/100g SPP.
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Besides 60/OH gels, no difference was seen in TCA soluble peptide content between other
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treatments and 60/OH gels containing SPP. This confirms the fact that an SPP concentration of
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0.5g/100g is sufficient to inhibit protease activity and no additional inhibition is seen from
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increasing concentrations. In addition, this confirms that the fast heating treatments (OH and
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25/OH) effectively eliminate protease activity.
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3.5
SDS PAGE
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For OH gels, there was no discernible difference in protein pattern between gels prepared
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without EDTA (Fig 5A) and gels with EDTA (Fig 5B). Among this group, SPP also had no
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noticeable effect on protein pattern. This is because the OH treatment eliminated the activity of
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both protease enzymes and ETG, therefore there was no setting effect or degradation of the
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myosin heavy chain. For the 25/OH samples, however, a protein band is visible in the high
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molecular weight range (>250 kDa) for gels treated without EDTA that is not present for gels
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treated with EDTA (dotted line in Fig 5A). Yin and Park (2014) found that ETG-mediated cross
280
linking in surimi led to the appearance of high molecular weight bands. This band is due to the
281
crosslinking of myosin heavy chain proteins, leading to higher molecular weight proteins
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(Kamath, Lanier, Foegeding, & Hamann, 1992). The disappearance of this band in the EDTA
283
samples confirms the inhibition of ETG by EDTA. The high molecular weight band is also darker
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for 1g/100g SPP than the control, indicating that SPP might have played a role in the setting
285
phenomenon as transglutaminase is one of various proteins present in blood plasma (Folk,
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1980).
287
The 60/OH group showed no difference between samples with and without EDTA. In this
288
treatment, only protease enzymes are active and the action of ETG was eliminated. This heating
289
treatment completely destroyed the myosin heavy chain band in the control samples due to the
290
activity of proteases. When SPP was added at 0.5g/100g however, the myosin heavy chain band
291
remained intact. Increasing SPP concentration did not affect the intensity of the myosin heavy
292
chain band. This confirms that 0.5g/100g SPP is sufficient to inhibit proteases and prevent
293
myosin heavy chain degradation.
294
295
3.6
Scanning electron microscopy
296
The 60/OH gel with no SPP added showed the greatest number of voids and the least compact
297
structure among the samples tested (Fig 6B). This is consistent with the results from the
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puncture test as well as the TCA-soluble peptides. This confirms that protease enzymes active
299
at this temperature serve to break up and weaken the gel structure. 60/OH gel with 1g/100g
300
SPP (Fig 6E) showed a significantly more orderly and continuous gel structure with less voids
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than the 60/OH gel with no SPP present, indicating effective inhibition of protease enzymes.
302
However, there were a greater number of voids present in this gel than in the OH gels (Fig 6A
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and 6D), indicating residual protease activity. 25/OH gels without and with 1g/100g SPP (Fig 6C
304
and 6F, respectively) had a more compact and continuous structure compared to OH gels
305
without and with 1g/100g SPP (Fig 6A and 6D, respectively). This is due to the addition of extra
306
covalent cross linking in the gel structure due to the action of ETG. In addition, 25/OH gel with
307
1g/100g SPP had a more compact structure with less voids than the 25/OH gel without SPP.
308
This may be due to transglutaminase present in SPP in addition to ETG of surimi, leading to
309
additional cross linking during setting. 25/OH sample containing no SPP and 0.1g/100g EDTA
310
(Fig 6G), had a greater number of voids than the OH samples. The purpose of EDTA addition
311
was to chelate calcium in order to prevent the activity of ETG. However, these results indicate
312
that calcium may play other roles in gelation in addition to being a cofactor for ETG.
313
314
4. Conclusion
315
SPP was found to effectively inhibit endogenous proteases in PW surimi at levels as low as
316
0.5g/100g. Higher concentrations of SPP may also aid in transglutaminase-mediated gel setting,
317
leading to an increase in gel strength. However, increasing SPP concentrations also led to a
318
decrease in the elastic modulus as well as a decrease in whiteness. This balance must be kept in
319
mind when formulating surimi with SPP. Holding at 25°C before ohmic heating was found to
320
optimize ETG activity while controlling protease activity. Rapidly heating to and holding at 60°C
321
before ohmic heating to 90°C was found to optimize protease activity while minimizing ETG
322
activity.
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5. Acknowledgment
325
This research was supported by a scholarship (2013 NPRD Graduate Research Award) from the
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North Pacific Research Board (Anchorage, AK). We are thankful for Teresa Sawyer of the
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Oregon State University Electron Microscope Facility (Corvallis, OR) for her assistance with the
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scanning electron microscopy.
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20
FIGURES
80000
80000
Elastic modulus (Pa)
100000
Elastic modulus (Pa)
100000
60000
40000
20000
A
60000
40000
20000
0
B
0
10
20
30
40
50
60
70
80
90
10
Temperature (°C)
20
30
40
50
60
70
80
90
Temperature (°C)
100000
10000
80000
Elastic modulus (Pa)
Elastic modulus (Pa)
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
60000
40000
20000
C
0
10
20
30
40
50
60
Temperature (°C)
70
80
D
1000
90
0.1
1
Frequency (Hz)
Figure 1 – Elastic (Storage) modulus of Pacific whiting surimi paste as affected by temperature
sweep and 0, 0.5 and 1g/100g SPP additions (A, B, and C, respectively) and gel as affected by
frequency sweep (D) after various treatments.
without EDTA
with EDTA
Control OH Control 60/OH 0.5g/100g SPP 60/OH 1g/100g SPP 60/OH
10
21
449
600
452
453
454
Breaking Force (G)
451
500
400
300
200
100
0
A
Penetration Distance (mm)
450
20
18
16
14
12
10
8
6
4
2
0
B
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
Figure 2 - Breaking force (A) and penetration distance (B) of Pacific whiting surimi gel as
affected by SPP concentration, EDTA, and heating method. Error bars represent the standard
deviation of 6 determinations.
control
0.5g/100g SPP
1g/100g SPP
22
474
475
85
476
80
A
B
-3
a*
75
L*
477
-4
-2
70
478
-1
65
60
0
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
8
80
b*
6
4
2
0
C
Whiteness (L*-3b*)
479
480
481
482
60
D
40
20
0
Figure 3 - L* (A), a* (B), b* (C), and whiteness (D) values of Pacific whiting surimi gels as
affected by SPP concentration, EDTA, and heating methods. Error bars represent the standard
deviation of 6 determinations.
23
μmol tyrosine/g sample
2
1.5
1
0.5
0
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
Figure 4 - TCA soluble peptide contents in Pacific whiting surimi gel as affected by SPP
concentration, EDTA, and heating method. Error bars represent the standard deviation of 3
determinations.
24
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
Figure 5 - SDS PAGE pattern of surimi gels without (A) and with (B) 0.1g EDTA/100g as affected
by SPP concentration and heating methods. MW=molecular weight marker, C=control,
0.5=0.5g/100g SPP, 1=1g/100g SPP, MHC=myosin heavy chain, Ac=Actin, 20-250=molecular
weight in kDa.
25
575
576
577
578
579
580
581
582
583
584
585
586
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592
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600
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603
604
605
606
607
608
609
610
611
612
613
614
615
616
OH
60/OH
25/OH
A
B
C
D
E
F
Control
1g/100g
SPP
G
Control
EDTA
Figure 6 – Scanning electron microscope image of surimi gels. A = Ohmic heating with no SPP
added; B = 60°C holding for 30 min followed by ohmic heating with no SPP added; C = 25°C
holding for 2 hr followed by ohmic heating with no SPP added; D = Ohmic heating with 1g/100g
SPP added; E = 60°C holding for 30 min followed by ohmic heating with 1g/100g SPP added; F =
25°C holding for 2 hr followed by ohmic heating with 1g/100g SPP added; G = 25°C holding for 2
hr followed by ohmic heating with no SPP added and 0.1g EDTA/100g. Magnification = 10,000x.