Rapid Visco Analyser
for
Grain, Flour, Food & Feed
Outline
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What is an RVA?
Hardware & advantages
Software & advantages
What it measures
Sample presentation
Running a test
Applications
Conclusions
What is an RVA?
• Rotational viscometer that is
able to continuously record the
viscosity of a sample under
conditions of controlled
temperature and shear rate
• Especially configured for testing
the pasting properties of starch
and starchy products
• Programmable, multi-step test
profiles
Variable
temperature
Variable mixing
speed (shear)
Hardware - RVA
• Sample can & paddle
• Drive motor & coupling
• Copper block
– Hydraulics
– Heating
– Cooling
• PCB
Hardware Advantages 1
• Can and paddle
– Paddle blade “propeller” shape
• Keeps starch granule suspension
homogenous prior to gelatinization
• Resists cavitation
• Average shear rate known
(20.1/rev, 53/s at 160 rpm)
– Canister
• Crushes in block giving good
thermal transfer
• Disposable or re-usable (x10)
Hardware Advantages 2
• Searle vs Couette rotational viscometers
– RVA is a Searle system, ie. inner paddle rotates
– Fixed outer cup can be clamped to heating system
• Allows rapid heating & cooling so fast tests
• Allows precise temperature control so repeatable results
Searle
Couette
Hardware Advantages 3
• Temperature control and measurement
– PT-100 temperature sensors with
4 wire sensing
• Accurate to 0.1°C, fast response
(+/- 14°C/min), reliable
• Placed close to major shear point
where sample viscosity is measured,
ie. between outer paddle blade and cup
– Profile temperature control
• Precisely ramped temperature changes in test
– Measuring block temperature vs sample temperature
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Sample temperature ‘lags’ block temperature
Temperature gradient in sample when heating or cooling
Sensors in the sample only measure temperature at one point
Sensors in the sample disturb the flow (ie viscosity)
Hardware Advantages 4
• Viscosity measurement:
– Speed control
• Rapid proportional loop
• Crystal locked, never needs calibrating
– High precision gearless Maxon motors
– Precious metal (RVA-TecMaster)
• Linear torque to current
• Low friction
– Brushless (RVA 4500)
• Linear torque to current
• Very low friction
• Low electrical noise
– High precision 16 bit digitization
Software - TCW
• Real time graphing with
overlay and QC limits
option
• Tabbed interface
• Interactive display
• Customizable, multistep
methods and analyses
with advanced options
• Automation “short cuts”
• Single page report with
traceability data, results
and graph
• ER/ES compliant
Software - Advantages
• Real time graphing, overlay and QC options for instant results
during a test plus clarity.
• Tabbed interface is familiar, easy to learn, intuitive to use.
• Interactive display for clarity and ease of use.
• Customizability and advanced options give flexibility for research
and unique products and applications.
• Automation “short cuts” are easy for routine operators, less
experienced and infrequent users and students.
• Single page report is convenient, complete, secure and includes
traceability data.
• ER/ES compliance ensures data security for food and drug safety
audits. Log-on protects data and method profiles from accidental
corruption or deletion. Auto generated backup file for safe storage.
What it measures
• Pastes of plant polymers and associated enzymes
• Starch and starchy products eg. grains, flour
– Food (thickener, binder, stabilizer)
– Industrial (paper, adhesives, textiles)
– Alpha-amylase (sprouting, malting, fungal)
• Protein
– Dairy, soy, gluten, gelatine
– Protease, TG
• Gum
– Carrageenans, Xanthan, Pectin, Arabinoxylan
– Xylanase
Starch Cooking in Excess Water
5000
(x 400)
4000
Viscosity (cP)
• Gelatinization
– Loss of crystalline
order in
starch lamellae
• Pasting
– Swelling, leaching of
AM, polymer
alignment
• Retrogradation
– Network formation
– Amylose, amylopectin
1 min
3000
4 min
2000
12 min
7.6 min
1000
0
0
4
8
Time (min)
12
Sample Presentation
• Sample & water in can
– 2 - 4 g sample
– 25 mL water
• Paddle inserted into
paddle coupling
• Tower lowers assembly
into split copper block
• Copper block closes &
paddle rotates
• Sample viscosity
measured & recorded
continuously
Running a Test
• Prepare sample
• Insert can & paddle
• Press down tower
– Copper block closes
– Motor rotates paddle
– Speed controlled
– Temperature controlled
– Sample viscosity measured
– Data sent to PC
• Test ends
– Tower raises
– Discard sample
Applications
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Food research groups, public and private
Plant breeders
Starch manufacturers
Flour millers
Food ingredient manufacturers
Processed food manufacturers
Pet food and fish feed manufacturers
Grain traders
Applications – Whole Grain
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Wheat
Durum
Rice
Corn
Barley
Oats
Wheat – Whole Grain 1
Wheat Stirring Number
80
200
60
SN = 127
100
SN = 88
40
20
SN = 22
0
0
1
2
3
Temperature (C)
100
300
Viscosity (RVU)
• Stirring Number (SN) test
– Viscosity after 3 minutes,
95oC test
– Starch is rapidly cooked then
digested by alpha-amylase enzyme
produced during sprouting, if any
– Small time window between
gelatinization and denaturation
• Wheat, barley, rye
• High levels of damage give low
viscosity, similar to FN method
• ICC 161, AACC 22-08, Other
0
4
Time (min)
Stirring Number profile for testing
sprout damage in cereals
95oC @ 0’0”
960 rpm @ 0’0”
160 rpm @ 0’10”
95oC @ 3’0”
end @ 3’0”
4.00g wholemeal, 25.0 mL water
Measure “Stirring Number” in RVU
Wheat – Whole Grain 2
• Late maturity amylase, or
“green amylase” associated
with grain maturation
• Does not require sprouting
• Found in specific cultivars
• SN & FN tests can fail to
detect it
• 20 minute RVA pasting test
detects it
Wheat – Durum
• Wheat, semolina, flour and pasta
• Pasta quality
– Mainly depends on protein
– Drying effects → RVA
• High temperature drying
– “Parboils” the pasta
– Reduces cracking & cooking loss
– Improves quality
• RVA method
– “Critical Paste”
– Higher, earlier peak
Profiles for testing pasta
quality (Whalen 2001)
25oC @ 0’0”
960 rpm @ 0’0”
160 rpm @ 0’10”
63oC @ 5’0”
end @ 15’0”
4.0g wheat & semolina,
5.75g pasta
Rice 1
Viscosity (cP)
• Eating quality
– “Setback” (Final – Peak)
3000
correlates to cooked rice texture
Mochi
– Detect effects of variety, aging,
2000
particle size, lipid binding
Basmati
• Breeders
1000
– Small samples, rapid tests
– 3.5g, 12.5 minute RVA
0
0
3
pasting profile
– AACC 61-02
• Many ideotypes
– Japonica, Indica, arboreo, fragrant, waxy
– Short, medium, long; variable AM:AP24
Century Patna
Pelde
Nippon Bare
Doongara
Dular
6
9
Time (min)
12
Rice 2
• Japanese method
– Prefer soft, cohesive rice
– Discerning market
– Larger sample (3.5 g)
– 19 minute method for greater discrimination
500
400
300
Kinuhikari
Sasanishiki
200
100
Japanese
AACC
Final
Brkdn
Peak
Final
Brkdn
0
Peak
Viscosity (RVU)
Japanese rice pasting method
50oC @ 0’0”
960 rpm @ 0’0”
160 rpm @ 0’10”
50oC @ 1’0”
93oC @ 5’0”
93oC @ 12’0”
50oC @ 16’0”
end @ 19’0”
Rice 3
100
4000
Raw
80
3000
(Temp)
2000
40
Parboiled
1000
Precooked
0
0
60
4
8
Time (min)
12
20
0
Temperature (oC)
Viscosity (cP)
• Pre-cooked rice
– Parboiled, “instant”
– Shorter cook time
– Reduced cracking, higher
proportion of whole grains
• Rice grading
– Visual assessment cannot detect
low levels of pre-cooking
– Cheating on head yield
– RVA method readily detects precooking by lowered peak & final
viscosities
– AACC method 61-02
Rice 4
• Pasting temperature method
– Rapid heating in RVA gives higher
pasting temperature results than
Amylograph or DSC
• Method
– Higher sample size (6 g)
– Slower temperature ramp
• AACC method (first approval)
 
Pasting temperature method
50oC @ 0’0”
960 rpm @ 0’0”
160 rpm @ 0’10”
50oC @ 5’0”
95oC @ 20’0”
end @ 20’0”
6.00g ground white rice,
24.0g water
Measure PT
Corn
• Hard & Soft types
– Hydration rate &
processing quality
– RVA test more
sensitive than
density / flotation
tests
– High solids, slow
temperature ramp
• Masa, tortilla, corn chips
Profiles for corn hardness
a) Hard corn
50oC @ 0’0”
960 rpm @ 0’0”
160 rpm @ 0’10”
50oC @ 1’00”
95oC @ 20’0”
end @ 25’0”
28.0g aqueous slurry with
18% wholemeal dwb
b) Soft corn
50oC @ 0’0”
960 rpm @ 0’0”
160 rpm @ 0’10”
50oC @ 2’0”
95oC @ 6’30”
95oC @ 11’00”
50oC @ 15’0”
end @ 17’30”
28.0g aqueous slurry with
18% wholemeal dwb
Barley 1
14
Moisture Content (% as is)
• Storage of malting barley
– For making beer & spirits
– >95% viability to malt
– Storage life depends on sprout
damage and storage conditions
• Sprout damage measured by RVA SN
method
• Storage temp & grain moisture content
• Model to estimate safe storage life used
to manage grain storages
13
12
175
150
125
100
11
75
50
10
SN
9
20
30
40
o
T e m p e ra tu re ( C )
50
Barley 2
• Malting
– Predict malting quality from barley
– Monitor green malt conversion
– AgNO3 inhibition to track starch
degradation during germination
Profile for assessing barley
and malt
50oC @ 0’0”
960 rpm @ 0’0”
160 rpm @ 0’10”
50oC @ 1’0”
90oC @ 4’12”
90oC @ 9’12”
50oC @ 14’12”
end @ 15’0”
Barley: 4.00g, Malt: 7.00g
autolytic, 4.00g inhibited
Modify profile to max.
temperature 69 oC for
autolytic tests on malt.
Amylase activity can be
inhibited using 0.1 mMol
AgNO3/g malt or barley.
Barley 3
• Brewing
– Measure adjunct pasting
temperature
• Ensure it gelatinizes before
heat deactivates amylase in
the mash
– Effect of added enzymes
• Filtration issues due to
residual starch, beta-glucan
and protein
– Process emulation
• Process behavior
of a malt
• Standard method
– Mebak II 2.7 (STD1)
Oats
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Food applications
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Rolled oats & groats
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Health claims
Differs from other cereals
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Starch is shear sensitive
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High lipids, high beta-glucans
RVA method
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20 min reduced shear test
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Also AACC 76-22
Applications
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Breeding
–
Process control (steaming,
kilning, rolling)
Profile for assessing oats
40oC @ 0’0”
960 rpm @ 0’0”
115 rpm @ 0’10”
40oC @ 1’00”
90oC @ 4’0”
90oC @ 10’30”
40oC @ 15’0”
end @ 20’0”
3.63g ground oats (dwb)
Applications – Wheat Flour
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Baking flour
Noodle flour
Malt amylase
Fungal amylase
Solvent Retention Capacity of soft wheat flour for
cakes, cookies, biscuits, pastries
Wheat – Flour 1
• Higher peak associated with lower AM (null 4A)
→ good quality
– Yellow alkaline
100
80
200
60
40
100
20
0
0
5
10
Temperature (C)
Viscosity (RVU)
• Baking flours → pan breads
– Standard 1 test
– More sensitive measure of amylase:
peak & final viscosity
– Detects heat treatment - peak
– 8x faster than Visco/Amylo/Graph
– ICC 162, AACC 76-21 etc.
• Noodle flours
– Silver nitrate to deactivate amylase
– White salted
Wheat Flours
300
0
15
Time (min)
Profile for testing pan bread
flour quality – STD1 profile
50oC @ 0’0”
960 rpm @ 0’0”
160 rpm @ 0’10”
50oC @ 1’0”
95oC @ 4’42”
95oC @ 7’12”
50oC @ 11’0”
end @ 13’0”
3.50g flour, 25.0 mL water
• Correlates with Visco/Amylo/Graph
• Pin and paddle types
• Care
– Amylograph or Viscograph
– Torque cartridge (ie. need to
define “BU” as cmg)
• Correlations are product-dependent
(different for eg. rice, corn etc.)
RVA Viscosity (RVU)
Wheat – Flour 2
RVA vs Viscograph Peak
Japanese Method
300
Visc PV = 2.64 x RVA PV - 28
r = 0.93
200
100
200
400
600
Viscograph Viscosity (cmg)
Wheat – Flour 3
100
80
o
4000
Temperature ( C)
(Temperature)
Viscosity (cP)
• Malt amylase
– Small amount of amylase improves
bread quality
– 3 minute SN test to optimise dosage
• Fungal amylase
– Anti-staling additive
– Doesn’t persist through baking
– 20 min 50°C RVA test using a
pregelled substrate
– Dosage control
60
Malt
addition
2000
0
0
1
0.0%
0.1%
40
0.2%
0.5%
1.0%
1.5%
20
2
3
Time (min)
4
0
Graphical Analysis Results - 20000302
Clarase Premix Dosage Rate 0 to 1x
V
I 4500
S
C
O
S 3000
I
T
y
cP 1500
Substrate:Bakels Bakers flour 2g:2g
Distilled water 25mL
Dosa ge 0x
Dosa ge 0.1x
Dosa ge 0.2x
Dosa ge 0.5x
Dosa ge 1x
Newport Scientific Pty Ltd
0
0
4
8
Time mins
12
16
20
Wheat – Flour 4
• Solvent retention capacity (SRC)
for soft wheat flours
• Four solvents:
– Water
– 50% sucrose: pentosans, gliadin
– 5% sodium carbonate:
damaged starch (high pH to
solubilize it)
– 5% lactic acid: partially
solubilises the gluten proteins
• Biscuits, cakes, cookies, pastries
• 10 minute, 25 to 50°C test
• Correlates to Extensograph
Applications – Food
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Native starch ingredients
Modified starch ingredients
Hydrocolloid ingredients
Soup
Salad dressings
Corn flakes
Yoghurt
Processed cheese
Native Starches
100
80
o
Wheat (3.0g)
Maize (3.0g)
3000
Temperature ( C)
4000
60
(Temperature)
Potato (2.0g)
2000
40
Tapioca (2.5g)
1000
0
20
0
5
0
20
10
15
Time (min)
5000
100
4000
80
o
Temperature ( C)
Viscosity (cP)
5000
Viscosity (cP)
• STD1 most commonly used
• Cereal
– Higher pasting temp re lipids
– Strong setback due to amylose
• Root & tuber
– Higher peaks, lower PT
– Inhibited setback – phosphorylation in
potatoes
• Waxy
– Lower PT, no lipid binding
– Low setback, no amylose network
• High Amylose
– Require temp > 100°C to paste
Waxy (2.5g)
3000
60
2000
40
Regular (3.0g)
1000
20
Corn Starch
0
0
5
10
Time (min)
0
15
Modified Starch
100
80
o
Modified
Waxy
1500
60
1000
40
500
Unmodified
Waxy
0
0
10
20
30
Time (min)
Temperature ( C)
2000
Viscosity (cP)
• Example: crosslinking &
substitution
• Uses: thickeners, stabilizers
and clarifiers in soups,
puddings, pie filings and
retorted foods
• Extended time at high heat
and moderate shear
• Reveal stability related to
batch cooking processes
20
0
40
Dextrins and Instant Starches
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•
Dextrins
– Highly depolymerized
– Low viscosity, soluble, DE
sweetness, yellow – white
– Adhesive pastes, sweeteners,
binders, batters
Instant Starches
– Low temp or cold-swelling
– Pregelatinized or highly substituted
– Sauces, soups, microwaved products,
bakery, beverages
– RVA method shows cold solubility, residual
hot-swelling starch, and cooking stability
Carrageenan 1
• Structure
– Alt. -1,3 & -1,4 galactopyranose
– Three types: kappa, iota, lambda (see below)
• Properties
– Ionic – gelling promoted by cations eg. in milk
– -carrageenan forms strong, thermoreversible, brittle gels;
syneresis prone. -carrageenan forms weaker gels. -carrageenen
does not form a gel. Also hybrid  & .
• Applications
– Thickened and gelled dairy products
OSO3- OH
O
O
O
Kappa
OH
O
OSO3-
OH
O
O
O
O
OH
OH
X
Lambda
OH
O
X=OH (30%) OSO 3
X=OSO3- (70%)
OSO3- OH
O
O
O
O
O
OH
Iota
OSO3-
Carrageenan 2
• Rheology
– Fundamental rheometers often used
– RVA: simpler, faster method
• RVA method
– “diagnostic” for determining type of gum(s) in product
– Cooling ramp (80 – 20°C) to reveal gelling behaviour
– Gum at 0.2%, starch 1.5%, milk; gum pre-hydrated
90
Kappa
1500
75
Hybrid
1000
500
Iota
45
30
0
15
0
15
30
Time mins
45
60
75
Temp 'C
Viscosity cP
60
Xanthan, locust bean and guar 1
• Structure
– Xanthan: -1,4 glucopyranose,
C3 trisaccharide residues
– LBG, guar: -1,4 mannose spine,
-1,4 galactose residues
• Properties
– Xanthan: High pH stability, heat/salt/acid induce ordering,
shear-thinning, thixotropic, syneresis-resistant
– LBG: Hot soluble (>85°C), very weak gels G:M 1:4
– Guar: Cold soluble, pH stable, does not gel, G:M 1:2
• Applications
– General food thickeners, texturizers and gelling agents
– Synergistic gelling between Xanthan & LBG and guar
Xanthan, locust bean and guar 2
• RVA method 1
– Cooling ramp (80 – 20°C) to reveal gelling behavior
– Gum at 1%
• Weak gel forming of individual gums on cooling
• Synergistic gelling of xanthan and LBG
1600
Xanthan / LBG
Guar
80
80
60
Xanthan
800
40
60
3000
Xanthan / Guar
40
1500
400
20
20
0
0
15
30
Time mins
45
60
75
0
0
15
30
Time mins
45
60
75
Temp 'C
LBG
Viscosity cP
1200
Temp 'C
Viscosity cP
4500
Xanthan, locust bean and guar 3
1200
1000
1.00%
Guar
0.75%
0.50%
0.25%
800
Viscosity (cP)
• RVA method 2
– High and low shear during
temperature ramp
– Designed to detect point of gum
solubilization
– Can be performed at different
ionic and pH conditions
Water
600
400
200
0
-200
20 25 30 35 40 45 50 55 60 65 70 75 80 85 90
Temperature (°C)
1200
1000
1.00%
Xanthan
0.75%
0.50%
0.25%
90
80
70
60
50
40
30
20
60 120 180 240 300 360 420 480 540 600 660 720 780 840
Time (sec)
Speed
Temperature
Viscosity (cP)
1000
900
800
700
600
500
400
300
200
100
0
0
Temperature (°C)
Speed (rpm)
800
Water
600
400
200
0
-200
20 25 30 35 40 45 50 55 60 65 70 75 80 85 90
Temperature (°C)
Pectin 1
• Structure
– -1,4 D-galacturonic acid (“smooth” regions) with acid &
methyl ester groups (high or low sub), and 1,2-  rhamnopyranose units with galactose & arabinose side chains
(“hairy” regions). Can be modified with amides.
• Properties
– HE sub: Gelling requires
low pH and >55% sugar
– LE sub: Ionic, gels
with Ca2+
• Applications
– Confectionary, jams
Pectin 2
• RVA method
– Cooling ramp (80 – 20°C) to reveal gelling behavior
– Curves similar but high ester >10x higher viscosity
750
100
70
Viscosity cP
Temp °C
Viscosity cP
9000
6000
75
600
90
80
90
60
450
45
300
30
60
3000
150
15
0
8
16
24
32
40
0
20
40
Time mins
Time mins
High ester
Low ester
60
80
Temp °C
12000
Konjac
• Structure
– Copolymer -1,4 D-mannose with D-glucose residues
• Properties
– Viscous, shear thinning solutions, strong gelling at high pH
– Forms thermoreversible gels with xanthan
• Applications
– Beverages
• RVA method
– Cooling ramp (80 – 20°C)
to reveal gelling behavior
– Sudden gelling on cooling
– Breakdown on shear
400
75
60
200
45
100
30
0
0
15
30
Time mins
45
60
15
Temp °C
Viscosity cP
300
Hydration of Hydrocolloids
LBG
Guar
Viscosity (cP)
20000
16000
12000
8000
4000
0
20 25 30 35 40 45 50 55 60 65 70 75 80 85 90
Temperature (°C)
Sandra Hill and Nuno Sereno, Division of Food Sciences, University of
Nottingham, UK
Powdered Soup Mix
Cream of Chicken,
Chicken Noodle,
Hearty Beef,
French Onion,
Tomato,
Vegetable
Salad Dressings
Cornflakes
400
Viscosity (cP)
• Reverse engineering
• Original cornflakes
– Batch cook and flake process, slow
and costly
– Low cold viscosity – good bowl life
• “Copy” product
– High shear process, ie. extrusion
– Cold swelling – poor bowl life
– Could be fixed eg. add surfactant!
Cornflakes
Generic
200
Original
0
0
10
Time (min)
20
Yoghurt
• Description
– Semi-gelled milk fermentation product
– Integrate incubation and test in RVA – “mini pilot plant”
• RVA
– Multiple temperature and shear profile to sterilize etc.
– Effects of season, processing, aging, formulation
SMP heat treatment
low
medium
high
Processed Cheese
• Description
– Emulsifying salts used to hydrate protein complex,
sequestering calcium that previously stabilized the casein
– Rate of hydration important for processing
– Mini pilot plant
• RVA
– 7 minute, 80°C
– High shear to
– emulsify
– Modified paddle
Applications – Feed
• Dog food
• Cat food
• Aquatic feed
Application Example 2
Dog Food
1600
Brand C
Brand A
1200
Viscosity cP
• Dry dog food
– Starch binds pellets,
– Controls texture
• Omnivores
– Some starch in diet
• Brand and batch effects
• Similar general curve shape, one
obviously low viscosity sample
Brand D
800
Brand B
400
0
Newport Scientific Pty Ltd
0
4
8
12
Time mins
16
20
Application Example 3
• Dry cat food
• Obligate carnivores
– Raw or retrograded starch can
make cats sick
– Starch must be fully cooked
• Aged food
– Loss of cold viscosity
– Retrogradation of starch
Application Example 4
• Fish food
– Salmon, high fat
– Starch <10%
• RVA test
– 12 g sample
– Ethanol dispersal
• Feeds
– Large range in viscosities!
– Green curve undercooked
• Poor cohesion
• Dead fish
900
Viscosity cP
• Controls binding, durability
• Controls density – float/sink rate
Fish Feed
600
300
0
New port Scientific Central Laboratory
0
4
8
12
Time mins
16
20
Conclusions
• Innovative and state-of-the-art
hardware and software
• Providing many advantages
– Easy to use
– Fast tests
– Small sample size
– Precise and repeatable results
– Flexible test routines
– Traceable
– Robust
– Applications in software,
RVA Handbook and library
of publications