Comparison of functional properties of 34% and 80% whey protein and milk serum protein concentrates

This study compared the functional properties of serum protein concentrate (SPC) with whey protein concentrate (WPC) made from the same milk and with commercial WPC. The experimental SPC and WPC were produced at 34% or 80% protein from the same lot of milk. Protein contents of WPC and SPC were comparable; however, fat content was much lower in SPC compared with WPC and commercial WPC. The effect of drying methods (freeze vs. spray drying) was studied for 34% WPC and SPC. Few differences due to drying method were found in turbidity and gelation; however, drying method made a large difference in foam formation for WPC but not SPC. Between pH 3 and 7, SPC was found to have lower turbidity than WPC; however, protein solubility was similar between SPC and WPC. Foaming and gelation properties of SPC were better than those of WPC. Differences in functional properties may be explained by differences in composition and extent of denaturation or aggregation.     

Lubricating properties of human whole saliva as affected by β-lactoglobulin

The effect of β-lactoglobulin (β-LG) at pH 3.5 and 7.0 on lubricating property of saliva as related to astringency perception was investigated using tribology. Saliva was adsorbed onto surfaces of a rotating poly dimethylsiloxane (PDMS) ball and disc to form a film under conditions that mimic the rubbing contacts in the oral cavity (Bongaerts, Rossetti, & Stokes, 2007) and the lubricity of saliva films upon exposure to astringent compounds was measured. While addition of non-astringent β-LG at pH 7.0 slowly increased friction of saliva film between tribopair surfaces, β-LG at pH 3.5 rapidly increased the friction coefficients of saliva, similar to other astringent compounds (epigallocatechin gallate and alum). This supports the hypothesis that astringency of β-LG arises from the loss of lubrication of saliva which is in agreement with the well-accepted astringency model of polyphenols. Increasing β-LG concentration at pH 3.5 (0.5–10% w/w) caused a rapid increase in friction coefficient; however, at the highest protein concentration, the friction coefficient, although higher than observed for water, was below the values observed for the lower protein concentrations. This suggests that static tribology testing is different from the dynamic in-mouth system such that a simple relationship between friction and sensory astringency cannot be found for all conditions.     

Functional properties of protein hydrolysates from Riceberry rice bran

Protein hydrolysate from pigmented Riceberry rice bran has great potential to be used in food products due to its protein content and antioxidative activities. In this study, characteristics, solubility, heat stability and emulsification properties of protein hydrolysates from the bran fraction of two rice cultivars, commercial rice bran (CBH) and Riceberry bran (RBH), were investigated. Both CBH and RBH showed the lowest solubility near their isoelectric point between pH 2 and 3. Solubility of RBH increased with increasing pH as the hydrolysates became more negatively charged; however, solubility of CBH was less dependent on pH. Heating did not significantly affect solubility of both hydrolysates which could be due to reduced aggregation of low‐molecular weight peptides and/or the exposure of charged and polar groups after hydrolysis. Oil‐in‐water emulsions stabilised by RBH were more stable compared to those stabilised by CBH. Maximum stability was achieved with RBH at pH 6 where no creaming was observed after 14 day storage. Higher stability could be due to increased surface protein coverage, more negative charge and higher viscosity of RBH‐stabilised emulsions. In addition, higher carbohydrate content and the presence of flavonoid could also contribute to an increase in stability. These results can be applied in food products using rice bran protein hydrolysate as nutritional ingredients.     

Foaming Properties of Whey Protein Isolate and λ‐Carrageenan Mixed Systems

Heating protein with polysaccharide under neutral or near neutral pH can induce the formation of soluble complex with improved functional properties. The objective of our research was to investigate the effects of λ‐carrageenan (λC) concentrations and pH on foaming properties of heated whey protein isolate (WPI) and λC soluble complex (h‐cpx) in comparison to heated WPI with added λC (pWPI‐λC), and unheated WPI with λC (WPI‐λC). In all 3 WPI‐λC systems at pH 7, increasing λC concentration led to improved foamability until a certain concentration before it decreased. Despite their higher viscosity, both heated systems (pWPI‐λC and h‐cpx) showed significantly better foamability and foam stability compared to WPI‐λC. Rheological results of foams with 0.25% λC suggested that higher elasticity and viscous films were produced in h‐cpx and pWPI‐λC systems corresponding to better foam stability. Foam microstructure images indicated that foams produced from h‐cpx had thicker film and consisted of smaller initial bubble area and more uniform bubble size. Results from the effect of pH (6.2, 6.5, and 7.0) further confirmed that stronger interactions between WPI and λC during heating contributed to the improved foaming properties. Foam stability was higher in h‐cpx system at all 3 pH levels, especially under pH 6.2 where there were strongest interactions between the biopolymers.     

Formation of Elastic Whey Protein Gels at Low pH by Acid Equilibration

Abstract: Whey protein gels have a weak/brittle texture when formed at pH ≤ 4.5, yet this pH is required to produce a high-protein, shelf-stable product. We investigated if gels could be made under conditions that produced strong/elastic textural properties then adjusted to pH ≤ 4.5 and maintain textural properties. Gels were initially formed at 15% w/w protein (pH 7.5). Equilibration in acid solutions caused gel swelling and lowered pH because of the diffusion of water and H⁺ into the gels. The type and concentration of acid, and presence of other ions, in the equilibrating solutions influenced pH, swelling ratio, and fracture properties of the gels. Swelling of gels decreased fracture stress (because of decreased protein network density) but caused little change to fracture strain, thus maintaining a desirable strong/elastic fracture pattern. We have shown that whey protein isolate gels can be made at pH ≤ 4.5 with a strong/elastic fracture pattern and the magnitude of this pattern can be altered by varying the acid type, acid concentration, pH of equilibrating solution, and equilibrating time. Practical Application: Low-pH shelf-stable whey protein gels having the strong/elastic texture can be made by forming gels at high pH and equilibrating in acid solutions. Acid equilibration causes the gel to swell and lower the gel pH. Moreover, gel properties can be altered by varying the acid type, acid concentration, pH of equilibrating solution, and equilibrating time.     

Extraction and characterisation of Riceberry bran protein hydrolysate using enzymatic hydrolysis

Riceberry bran protein hydrolysate (RBPH) was prepared from bran of purple‐pigmented Riceberry rice using enzymatic hydrolysis. The effect of enzyme type (Alcalase, Flavourzyme and Neutrase) and hydrolysis time (2, 4 and 6 h) on protein content, protein yield, total phenolic content (TPC), antioxidant activities (ABTS and FRAP) and molecular weight patterns of RBPH was investigated. The enzyme type significantly (P < 0.05) affected the properties of RBPH whereas the hydrolysis time had no significant effect (P ≥ 0.05) on those properties. Flavourzyme was the most effective to increase protein yield, TPC and antioxidant activities compared to Alcalase and Neutrase. The optimal hydrolysis condition was 4 h using Flavourzyme which yielded 74.9% extracted protein. This hydrolysate contained peptides ranging from 16 to 64 kDa. The high antioxidant activity was related to negative charge peptides as shown by anion exchange chromatography. With high protein content and antioxidant properties, RBPH using Flavourzyme could be practically utilised in functional foods.     

Effect of CMC Molecular Weight on Acid‐Induced Gelation of Heated WPI‐CMC Soluble Complex

Acid‐induced gelation properties of heated whey protein isolate (WPI) and carboxymethylcellulose (CMC) soluble complex were investigated as a function of CMC molecular weight (270, 680, and 750 kDa) and concentrations (0% to 0.125%). Heated WPI‐CMC soluble complex with 6% protein was made by heating biopolymers together at pH 7.0 and 85 °C for 30 min and diluted to 5% protein before acid‐induced gelation. Acid‐induced gel formed from heated WPI‐CMC complexes exhibited increased hardness and decreased water holding capacity with increasing CMC concentrations but gel strength decreased at higher CMC content. The highest gel strength was observed with CMC 750 k at 0.05%. Gels with low CMC concentration showed homogenous microstructure which was independent of CMC molecular weight, while increasing CMC concentration led to microphase separation with higher CMC molecular weight showing more extensive phase separation. When heated WPI‐CMC complexes were prepared at 9% protein the acid gels showed improved gel hardness and water holding capacity, which was supported by the more interconnected protein network with less porosity when compared to complexes heated at 6% protein. It is concluded that protein concentration and biopolymer ratio during complex formation are the major factors affecting gel properties while the effect of CMC molecular weight was less significant.     

Utilizing whey protein isolate and polysaccharide complexes to stabilize aerated dairy gels

Heated soluble complexes of whey protein isolate (WPI) with polysaccharides may be used to modify the properties of aerated dairy gels, which could be formulated into novel-textured high-protein desserts. The objective of this study was to determine the effect of polysaccharide charge density and concentration within a WPI-polysaccharide complex on the physical properties of aerated gels. Three polysaccharides having different degrees of charge density were chosen: low-methoxyl pectin, high-methoxyl type D pectin, and guar gum. Heated complexes were prepared by heating the mixed dispersions (8% protein, 0 to 1% polysaccharide) at pH 7. To form aerated gels, 2% glucono-δ-lactone was added to the dispersions of skim milk powder and heated complex and foam was generated by whipping with a handheld frother. The foam set into a gel as the glucono-δ-lactone acidified to a final pH of 4.5. The aerated gels were evaluated for overrun, drainage, gel strength, and viscoelastic properties. Without heated complexes, stable aerated gels could not be formed. Overrun of aerated gel decreased (up to 73%) as polysaccharide concentration increased from 0.105 to 0.315% due to increased viscosity, which limited air incorporation. A negative relationship was found between percent drainage and dispersion viscosity. However, plotting of drainage against dispersion viscosity separated by polysaccharide type revealed that drainage decreased most in samples with high-charge-density, low-methoxyl pectin followed by those with low-charge-density, high-methoxyl type D pectin. Aerated gels with guar gum (no charge) did not show improvement to stability. Rheological results showed no significant difference in gelation time among samples; therefore, stronger interactions between WPI and high-charge-density polysaccharide were likely responsible for increased stability. Stable dairy aerated gels can be created from WPI-polysaccharide complexes. High-charge-density polysaccharides, at concentrations that provide adequate viscosity, are needed to achieve stability while also maintaining dispersion overrun capabilities.