A colaborative study was conducted to develop a rapid, simple and reliable procedure for determining the solubility of food protein products, e.g., spray-dried whey protein concentrate, sodium caseinate, egg white protein and soy protein isolate. The procedure was developed by modifying the nitrogen solubility index (NSI) procedure. Protein content and soluble protein were determined by micro-Kjeldahl or biuret procedures with standard deviations of ? 0.83-4.12 for all proteins except caseinate which had a value of Y? 13.95. Although the biuret and micro-Kjeldahl procedures generally provided comparable accuracy and precision for protein content and solubility of certain proteins, the biuret procedure exhibited considerable error and variability for other proteins.
This study tested the hypothesis that the amount (weight or volume) of food consumed affects the satiating potency of a food, independent of its energy content. Normal-weight young men (n = 20) were tested in a within-subjects design. Subjects were served a milk-based drink or no drink (control), followed 30 min later by a self-selected lunch and > 4 h later by a self-selected dinner. Milk drinks were equal in energy content (2088 kJ, or 499 kcal) and had similar proportions of fat (30.3%), carbohydrate (54.7%), and protein (15%) across three volumes: 300, 450, and 600 mL. Ratings of palatability, sensory properties, and energy content of the drinks and of hunger completed before consumption of the preloads were not significantly different among conditions. The results showed that preload volume affected energy intake at lunch (P < or = 0.009) such that energy intake was less after the 600-mL preload than after the 300-mL preload. This effect was still present when energy intake at dinner was included (P < or = 0.022). At lunch, including energy from the preload, subjects overate relative to the control condition (4323 +/- 322 kJ) after the 300- (5263 +/- 321 kJ) and 450-mL (5011 +/- 300 kJ) preloads but not after the 600-mL (4703 +/- 353 kJ) preload. Thus, the best adjustment for the energy in the preloads was with the largest, least energy-dense drink. Consistent with the effects on intake, the volume of the drinks affected ratings of hunger and fullness. These results indicate that the volume consumed is an important determinant of satiety after milk drinks under these conditions.
Heat-denatured whey protein isolate was hydrolyzed with trypsin, ␣-chymotrypsin, Alcalase or Neutrase to 2.8, 4.3, 6.0 or 8.0% degree of hydrolysis. Hydrolysates were fractionated by ultrafiltration and freezedried. Protein content of retentates showed little variation but permeates differed with enzyme. Surface hydrophobicity increased with hydrolysis but was not linear except for ␣-chymotrypsin. Ultrafiltration increased solubility and the permeates and retentates had better solubility than hydrolysates. Retentates had higher emulsifying activity index than hydrolysates while permeates did not form stable emulsions. Permeates formed stable foams but hydrolysates and retentates showed poor foaming characteristics. Specificity of the enzyme, and degree of hydrolysis influenced the functional properties of the peptides. Fractions generated by trypsin, at all levels of hydrolysis generally had higher solubility, emulsifying properties and foaming properties. Permeates from Alcalase hydrolysis had the best foam capacity but low foam stability.
Vanilla ice cream with 8, 13 or 18% sucrose and 10, 14 or 18% butterfat was evaluated by descriptive analysis (DA) with 15 judges, instrumental texture measurements (ITM), and hedonic rating with 146 consumers. Increased sugar caused higher vanilla, almond, buttery, custard/eggy, sweetness, fatty, creamy, doughy and mouthcoating characteristics, and lower coolness, ice crystals, melt rate (ITM) and hardness (ITM). Increased fat caused higher buttery, custard/eggy and sweet flavor, fatty, creamy, doughy and mouthcoating texture, and lower color, ice crystals and melting rate (DA). Acceptability was positively related to the vanilla, creamy, fatty and milky characters, and negatively related to color, ice crystals and ITM hardness.
Effects of pH (3.0−7.0) on aggregation of whey protein solution (WPS,
18%) were investigated by
examination of turbidity, aggregate size, and microstructure. As
expected, maximum turbidity and
aggregate sizes occurred at the isoelectric point (pI 5.2)
of whey proteins. Lower or higher pH than
the pI resulted in a steady decrease of the turbidity and
aggregate size. Microstructure analysis
revealed that the WPS at pH 5.7 contained loose and irregular
aggregates with 200−400 nm sizes.
From the pH (5.7)-aggregated WPS, gelation was induced by heating,
hydrolyzing with a protease
from Bacillus licheniformis (BLP), increasing ionic strength
with CaCl2, and quiescently acidifying
with glucono-δ-lactone (GDL), respectively. The hardness, color,
and microstructure of the gels so
formed were determined. Micrographs of BLP- and
CaCl2-induced gels showed aggregates similar
in size and shape to the parent aggregates in the WPS. Heat- and
GDL-induced gels were structured
with enlarged aggregates (500 nm and 1−2 μm). Separating the
processes of formation of aggregates
and gels may provide a means to manipulate the protein gel
properties.
Keywords: Whey proteins; aggregation; gelation; microstructure;
pH
A collaborative study involving nine laboratories was conducted over four years to evaluate a rapid, simple and reliable whipping method for measuring overrun and foam stability. Effectiveness of the method was assessed by measuring the characteristics of foams formed by three protein solutions (5%): sodium cascinate, milk protein isolate, and egg white protein; identifying and systematically eliminating sources of variability. Major sources of variability were protein dispersing technique, the mixer, and the cart exercised by the operator during sampling and weighing. The method detected differences in foam stability between egg white, casein and milk protein isolate (pooled SD = 4.5) using different mixers.
Various concentrations (1-9%) of whey protein (WP) isolate solutions were heat-denatured at 80°C for 30 min. Size exclusion HPLC and dynamic light scattering revealed formation of soluble aggregates in 3-9% denatured WP solution. Size and content of the aggregates increased with increases in preheated WP concentration. The 4-9% denatured WP solutions were diluted to 3% WP with distilled water. Upon addition of CaCl 2 (20 mM) or glucono-δ-lactone (0.6%, w/v), all 3% denatured WP solutions formed gels at 37°C. Hardness of the gels (3% WP) remarkably increased with WP concentration during preheating or with the aggregate size and content. The HPLC elution profiles showed that prolonging the heating (80°C) time (2-30 min) for 8% WP solution also gradually increases aggregate size and concentration, which then led to increases in hardness of cold-set gels. The results may guide companies in how to manipulate aggregate size and content during developing WP products with capacity for cold gelation.
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