Effect of salts on the alkaline degradation of β-lactoglobulin gels and aggregates: Existence of a dissolution threshold

Effect of sodium triphosphate on particle size of heat-induced whey protein concentrate aggregates

Thermal treatment has been utilized to improve the functional properties of proteins for many years. In this study, we aimed to investigate the effect of sodium triphosphate (Na5P3O10) on particle size and size distribution of heat-induced whey protein concentrate (WPC) aggregates under different processing conditions. The results showed that high Na5P3O10 level (>0.5%, w/w), long heating time (>15 min), and alkaline condition (pH 8-8.5) facilitated formation of large particles (>10 μm). The WPC aggregates with small-to-medium particle size (1-3 μm) that are suitable to be applied as a fat replacer were obtained by heating the WPC solution (8%, w/v) containing 0.4% (w/w) Na5P3O10 at 85°C for 5 min. We conclude that thermal treatment of whey protein concentrate added with Na5P3O10 can obtain whey protein products with different particle sizes for certain applications.

Micromechanical Characterization of Hydrogels Undergoing Swelling and Dissolution at Alkaline pH

The swelling of polyelectrolyte hydrogels usually depends on the pH, and if the pH is high enough degradation can occur. A microindentation device was developed to dynamically test these processes in whey protein isolate hydrogels at alkaline pH 7–14. At low alkaline pH the shear modulus decreases during swelling, consistent with rubber elasticity theory, yet when chemical degradation occurs at pH ≥ 11.5 the modulus decreases quickly and extensively. The apparent modulus was constant with the indentation depth when swelling predominates, but gradients were observed when fast chemical degradation occurs at 0.05–0.1 M NaOH. In addition, these profiles were constant with time when dissolution rates are also constant, the first evidence that a swollen layer with steady state mechanical properties is achieved despite extensive dissolution. At >0.5 M NaOH, we provide mechanical evidence showing that most interactions inside the gels are destroyed, gels were very weak and hardly swell, yet they still dissolve very slowly. Microindentation can provide complementary valuable information to study the degradation of hydrogels.

Effect of N-Ethylmaleimide as a Blocker of Disulfide Crosslinks Formation on the Alkali-Cold Gelation of Whey Proteins

N-ethylmaleimide (NEM) was used to verify that no new disulfide crosslinks were formed during the fascinating rheology of the alkali cold-gelation of whey proteins, which show Sol-Gel-Sol transitions with time at pH > 11.5. These dynamic transitions involve the formation and subsequent destruction of non-covalent interactions between soluble whey aggregates. Therefore, incubation of aggregates with NEM was expected not to affect much the rheology. Experiments show that very little additions of NEM, such as 0.5 mol per mol of protein, delayed and significantly strengthened the metastable gels formed. Interactions between whey protein aggregates were surprisingly enhanced during incubation with NEM as inferred from oscillatory rheometry at different protein concentrations, dynamic swelling, Trp fluorescence and SDS-PAGE measurements.