Protein aggregation and hardening of whey based nutritional bars during storage Ted Labuza, Peng Zhou**, Xiaoming Liu**Laurie Davis* & Amy Tran Department of Food Science & Nutrition University of Minnesota **Jiangnan Univ. PRC This research was supported by the USDA, DMI & the Davisco Co* LeSueur MN QuickTime™ and a decompressor are needed to see this picture.
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Protein aggregation and hardening of whey based nutritional bars during storage
òSimplified bar model system (WB): WPI and buffer systemèBioPRO whey protein isolate from Davisco
4Protein, 97.4% on dry basis4Lactose, < 1% of dry basis (minimal Maillard
reaction)4Fat, 0.3% of dry basis ( lipid oxidation minimal)
èPhosphate buffer (10 mM, pH 7)èWPI/buffer: 3/2 (WPI, 60% of the total weight)
40.67:1 water to protein ratio4aw ~ 40% moisture wet basis Upper limit of
semimoist range4 Accelerated shelf life test
èSodium Azide (0.05% of the total weight)
òSimplified bar model system (WB): WPI and buffer systemèBioPRO whey protein isolate from Davisco
4Protein, 97.4% on dry basis4Lactose, < 1% of dry basis (minimal Maillard
reaction)4Fat, 0.3% of dry basis ( lipid oxidation minimal)
èPhosphate buffer (10 mM, pH 7)èWPI/buffer: 3/2 (WPI, 60% of the total weight)
40.67:1 water to protein ratio4aw ~ 40% moisture wet basis Upper limit of
semimoist range4 Accelerated shelf life test
èSodium Azide (0.05% of the total weight)
Extent of whey protein aggregation as f(t,T) in Model WB bar system
0
10
20
30
40
50
60
70
0 20 40 60 80 100 120Storage time (days)
45 degree C
34 degree C
23 degree C
4 degree C
0
10
20
30
40
50
60
70
0 20 40 60 80 100 120Storage time (days)
45 degree C
34 degree C
23 degree C
4 degree C
Measured Q10 aggregation ~ 3.3 from 23 to 45 °C or 14 fold factor
So 1 month at 45°C = 14 months at 23°C thus ~ 2 weeks at 45 °C = ~ 6 months at RT
Rate estimated at 37°C ~0.2%/day and 0.04%/day at 23°C or ~15% loss in one year but bar would need antimicrobials
Aggregation Rate
Aggregate particle formation by SEM
Fresh control Storage at 45 °C for 3 months
(Particle diameter 50~100 nm)
Note interparticle agglomeration
Changes in the conformation of whey protein molecules by DSC
Confirmation by FTIR for WB system
Mechanisms of proteinaggregation
n Solubility of aggregates in various solutions
Solutions Aggregate solubility(%)
Buffer (10 mM, pH 7) 4.4 ± 0.6Buffer with 0.1% SDS 7.2 ± 0.5Buffer with 6 M guanidine HCl 10.9 ± 0.7Buffer with 8 M urea 11.6 ± 1.7Buffer with 10 mM dithiotreitol 92.2 ± 0.9Buffer with SDS and dithiotreitol 97.1 ±1.7
Non-covalent
Covalent(Disulfide bond)
Note: This confirms work of Langer’s group @ MIT
ò Texture measurementèTA-XT2 texture analyzerèPlunger: 3mm diameterèCompression speed: 1mm/sèDeformation strain: 50%èHardness is recorded as the
maximum force during the compression
ò Texture measurementèTA-XT2 texture analyzerèPlunger: 3mm diameterèCompression speed: 1mm/sèDeformation strain: 50%èHardness is recorded as the
maximum force during the compression
Changes in the texture of whey protein bar model system WB
Aggregation and Hardness of whey system WB as f(t)
1
10
100
1 10 100Storage time (days)
1
10
100
1 10 100Storage time (days)
1
10
100
1 10 100Storage time (days)
45 degree C34 degree C23 degree C
(b)
Hardening in textureFormation of aggregates
Fresh bar base
Formation of separate aggregates between tiny particles
Formation of aggregate network
0
10
20
30
40
50
60
70
0 20 40 60 80Protein aggregation (%)
45 C, t(hard)=3 days, 21% aggregates
34 C, t(hard)=30days, 15% aggregates
23 C, t(hard)=60 days, 12% aggregates
Separate aggregates Formation of aggregates network
Suggested primary mechanism for texture change in whey bars due to disulfide bond interactions
3. Potential influence of sugars/polyols (humectants)on hardening in whey bar systems
ò Bar systems need an aw of < 0.75 to prevent microbial growth otherwise antimicrobial agents required
ò Accomplished by replacing water with sugars or sugar alcohols (polyols) as plasticizers in whey systemè Lowers aw and will influence:
4Local viscosity of liquid phase which controls mobility & thus reaction rates (find maxima in aw 0.6 to 0.8 range)
4Tg of system which affects molecular mobility and texture
4Protein conformation4Maillard reaction (browning) if humectant has
reducing groups (HFCS)4Crystallization (graining) if use sucrose to control
Maillard4Sugars as humectants also sweeten the product
masking Maillard reaction flavors
ò Bar systems need an aw of < 0.75 to prevent microbial growth otherwise antimicrobial agents required
ò Accomplished by replacing water with sugars or sugar alcohols (polyols) as plasticizers in whey systemè Lowers aw and will influence:
4Local viscosity of liquid phase which controls mobility & thus reaction rates (find maxima in aw 0.6 to 0.8 range)
4Tg of system which affects molecular mobility and texture
4Protein conformation4Maillard reaction (browning) if humectant has
reducing groups (HFCS)4Crystallization (graining) if use sucrose to control
Maillard4Sugars as humectants also sweeten the product
Note 1. PG cannot be measured but slightly better than glycerolNote 2. Organoleptic problems (sweetness, metallic) at those levels Note 3. Physiological problems (anal leakage, Heinz body formation)
PG estimate
Effects of sugar/polyols on lowering of awSystem WB’ (6:4.5 whey:water+polyol ratio)
0
30
60
90
120
150
180
0 20 40 60 80[Polyol/(Polyol+Water)]%
Propylene glycolGlycerolSorbitolMaltitol
(B) 7 days
Effects on texture after 1 week @ 45°C System WB’ (6:4.5 Protein:Polyol+ water ratio)
(I = 1/3 of humectant in 4.5 grams plasticizer II = 50%)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
15 25 35 45 55 65 75 85 95 105
Temperture (Degree C)
WB
WG-I
WG-II
WM-I
WM-II
WS-I
WS-II
WP-I
WP-II
Peak 1 Peak 2
Peak 2'
Peak 2'
(A)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
15 25 35 45 55 65 75 85 95 105
Temperture (Degree C)
WB
WG-I
WG-II
WM-I
WM-II
WS-I
WS-II
WP-I
WP-II(B)
Freshly prepared
Prop Glycol
sorbitol
maltitol
glycerol
control
Prop Glycol
sorbitol
maltitol
glycerol
control
* Note propylene glycol 50% system stored at 23 *C was also fully denatured
stored one week @ 45 °C
FTIR of control and bar with PG Model WB
160016201640166016801700Wavenumber (cm-1)
WB of 0 dayWB of 7 days at 45 CWP-II of 0 dayWP-II of 7 days at 45 C
Beta-strandBeta-sheetAlpha-helix
Intermolecular aggregation
Control- freshControl 7 days @ 45°C
Control- freshControl 7 days @ 45°C
PG - freshPG 7 days @ 45°C
4. Maillard reaction in the whey bar
ò Driving forces èWhey proteins are rich in lysine (>10 g/100 g protein) è The presence of reducing sugars eg. fructose/glucoseè The aw of most nutritional bars is between 0.65 ~ 0.75,
in the reactive range for Maillard reaction
0 0.2 0.4 0.6 0.8 1Water activity
Early Study
òModel system :òModel system :
ò Initial water activity: 0.78ò FDNB methodò Half life at 35°C for lysine loss = 20
days
ò Initial water activity: 0.78ò FDNB methodò Half life at 35°C for lysine loss = 20
days
18.53g/100 g
solidWater
20Microcrystalline
cellulose
20Apiezon B oil
30Whey protein
20Glycerol
10Glucose
0.3K-sorbate
%Ingredient
Schnickels, Warmbier, Labuza: Effect of Protein Substitution on Nonenzymatic Browning in an Intermediate Moisture Food System, Journal of Agricultural and Food Chem33istry, 1976
Non enzymatic browning in protein bars with HFCS and different WPI/Soy ratios at aw ~ 0.65
Soy has less available lysine
But we need an all dairy protein solution
System A
35% protein
25% corn syrup
25% HFCS
Peanut butter 10%
Glycerol 5%
Choice of humectant System WB’ASLT at 45 °C for 7 Days
Imperative: Don’t use reducing plasticizers
Maillard browning problem: reducing sugars
Pre-trial – color changes
òHFCS-CS bars stored at 35 °C & aw =0.65ò Model system A’ 35% WPI 25% corn syrup 25% HFCS 5% glycerol & 10% shortening or
same but Maltitol substituted for CS-HFCS
òHFCS-CS bars stored at 35 °C & aw =0.65ò Model system A’ 35% WPI 25% corn syrup 25% HFCS 5% glycerol & 10% shortening or
same but Maltitol substituted for CS-HFCS
0 1 2 3 4 5
Weeks of storage time for CS and HFCS system L value 89 73 62.5 56.5 52.5 48
Note that the maltitol system after 18 weeks reached an L value of 80
HFCS Model system C Q10=3.6
Shelf Life Plot Q10 = 3.6
A’
Model A’ Maltitol System No HFCS Color
Model System A’ HFCS Texture Q10= 3.6
Model System A’ HFCS Texture Q10= 3.6
Model System A’ Maltitol Texture Change
NEB effects on protein quality @ aw = 0.65 & 35°Cchemical(OPA ortho-phthaldialdehyde) vs biological
method comparison
OPA
Tetrahymena assay
Lysine Loss in Model C
HOW to make and keep a bar soft and maintain high nutritional quality ?
ò Potential solutions:
è1. Add reducing reagents and thiol-blocking reagents if allowed
è2. Add whey protein hydrolysates (Lowering the Tg of bar system)
è3. Control the types and ratio of humectants
ò Potential solutions:
è1. Add reducing reagents and thiol-blocking reagents if allowed
è2. Add whey protein hydrolysates (Lowering the Tg of bar system)
è3. Control the types and ratio of humectants
ò Try to slow down protein aggregation and hardeningè Reducing reagents: Cysteine, glutathioneè Thiol blocking reagents: N-ethylmaleimide
Model ID Protein (6g) Buffers (4g) FunctionB WPI 10 mM phosphate buffer ControlC-L WPI 0.06 M L-cysteine ReducingC-H WPI 0.45 M L-cysteine ReducingG-L WPI 0.06 M L-glutathione ReducingG-H WPI 0.45 M L-glutathione ReducingE-L WPI 0.06 M N-ethylmaleimide Thiol blockingE-H WPI 0.45 M N-ethylmaleimide Thiol blocking
System B 6:4 protein:buffer ratio no humectant aw ~ 0.97
1 . Reducing or thiol blocking reagents
30 day @ 45°C equivalent to ~ 1.3 year at 23 °C
Storage of whey system B WPI bar at 45 °C
2. Addition of protein hydrolysates
0
0.1
0.2
0.3
0.4
0 0.2 0.4 0.6 0.8 1
Water activity
WPIGAB line of WPIH1GAB line of H1H2GAB line of H2H3GAB line of H3
(A) 23 degree C
0
0.1
0.2
0.3
0.4
0 0.2 0.4 0.6 0.8 1Water activity
WPIGAB line of WPIH1GAB line of H1H2GAB line of H2H3GAB line of H3
(B) 45 degree C
H1= 5.2% hydrolyzed H2= 8.8% H3= 14.9%
Hydrolysate effectiveness is not related to greater water holding capacity
Hardness development at 45 °C Day 7 vs Day 0
Whey Hydrolysate model system B aw ~ 0.97
Hydrolysate substitution lowers Tgso softer based on T-Tg
WPI: y = -47.051Ln(x) + 205.86R2 = 0.9643
H1: y = -54.61Ln(x) + 199.22R2 = 0.9948
H2: y = -65.562Ln(x) + 212.89R2 = 0.9975
H3: y = -64.534Ln(x) + 200.85R2 = 0.996
-60
-20
20
60
100
140
1 10 100Water content (g H2O / 100 g solid)
WPIH1H2H3Log. (WPI)Log. (H1)Log. (H2)Log. (H3)
Data below for pure proteinswith water only
Degree of hydrolysis 5.2% 8.8% 14.9%
ò Bar model system C (25% replacement of the WPI with whey protein hydrolysates) aw ~0.6
H=1
H=9L=47
H=1H=1 H=1
H=3L=38
H=5L=41
H=8L=46
0%
H = hardness in Newtons
All had L ~ 90 at day 0
Day 0
Day 7
@ 45°C
System C 35% WPI, 30% corn syrup, 30% HFCS, no fat, 5% glycerol
Whey protein hydrolysates(Davisco)
Lend = 76
Lend = 75 Lend = 82
L0 = 90
Texture Change Model System A’ Maltitol+25% of protein as Hydrolyzed whey protein
System A’
Solution # 3 Replace HFCSwith maltitol
Effect of denaturation Model C
Day 0
Day 7 @45°C
Native Denatured
H=5
H=1
H=30
H=1
Denaturation by mixing 60% Whey:40% water into a dough bake @ 85°C for 1 hr; freeze dry, grind to powder
Makes -SH more exposed for interaction
Solutions reviewed
ò Use ASLT of 4 weeks @ 45°C ~ 1 year @ 23 °C
ò Add reducing agents or thiol blockers to inhibit S-S formationè Work is in progress
ò Partially replace WPI with 25% whey protein hydrolysatesè Makes a softer bar initially thus significantly slowing down
the hardening
ò Control type and ratio of humectantsè No propylene glycolè Eliminate HFCS, use sucrose instead for sweetness or
artificial sweetenerè Use glycerol in combo with sorbitol, maltitol, and xylitolè no browning and good plasticizers
ò Use ASLT of 4 weeks @ 45°C ~ 1 year @ 23 °C
ò Add reducing agents or thiol blockers to inhibit S-S formationè Work is in progress
ò Partially replace WPI with 25% whey protein hydrolysatesè Makes a softer bar initially thus significantly slowing down
the hardening
ò Control type and ratio of humectantsè No propylene glycolè Eliminate HFCS, use sucrose instead for sweetness or
artificial sweetenerè Use glycerol in combo with sorbitol, maltitol, and xylitolè no browning and good plasticizers
Questions and/or comments?
Contact: Dr Ted LabuzaDepartment of Food Science and NutritionUniversity of Minnesota St Paul 55108 USA612-624-9701 fax 625-5272 [email protected]://www.ardilla.umn.edu/Ted_Labuza