The effects of high hydrostatic pressure and protein concentration on the denaturation and gelation of whey protein were investigated. Industrial whey protein isolate (WPI) and whey protein concentrate (WPC) solutions (pH 6.8) at various concentrations were pressurized for 10 min at 30 degrees C under 200-1000 MPa. With the WPI solution, the concentration for affecting the turbidity was 1% and was 6% for the viscosity at 400 MPa, while for inducing gelation, it was 10% at 600 MPa. With the WPC solution, the viscosity changed at a concentration >12%, and gel formation began at >18% at 400 MPa. The hardness and breaking stress of pressure-induced WPI gels increased with increasing concentration of WPI (12-18%) and hydrostatic pressure, the ratings for the 20% WPC gels being one-third those of the 20% WPI gels. The solubility of proteins from the pressure-induced WPI gels decreased with increasing pressure, while that of WPC gel induced at >600 MPa remained constant at approximately 50%. The microstructure of the WPI gels had a porous network form, whereas the WPC gels were irregular particulates. beta-Lactoglobulin, alpha-lactalbumin, and serum albumin preferentially participated in pressure-induced aggregation and gelation through S-S bonding.

The effects of sugars (xylose, arabinose, fucose, fructose, galactose, glucose, sorbitol, maltose, sucrose, and lactose; 0-20% w/v) on the properties of the pressure-induced gel from a whey protein isolate (20%, 800 MPa,30 C, 10 min) were studied. All the sugars decreased the hardness, breaking stress and waterholding capacity of the gel at the same concentration of 55.5 mM. Increasing the sugar content changed the microstructure of the gel from a honeycomb-like structure to a stranded structure, while the strand thickness was progressively reduced. These results suggest that sugars decreased the degree of intermolecular S-S bonding of proteins and non-covalent interaction, and restrained the phase separation during gelation under high pressure.Key words: hydrostatic high pressure; gelation; sugar; whey protein isolate; phase separation Milk whey proteins are important ingredients in many food products, providing essential amino acids and exhibiting a broad range of functional properties such as gelation, foaming, and emulsification. [1][2][3][4] Commercial whey protein products vary in their functional properties depending on the method used to isolate them.1) This variability may be attributed to differences in the amount of protein, lactose, fat and minerals, in the ratio of the major whey proteins such as -lactoglobulin (-Lg), -lactalbumin and bovine serum albumin, and in the degree of protein denaturation and aggregation caused by processing. 5)One of the functional properties of whey proteins is their gelation, which is known to be induced by heat treatment, 2,6,7) although such other factors as salt addition, 8) acidification 9,10) and enzyme treatment can cause gelation with or without heating.11-14) Hydrostatic pressure has recently been shown to induce gelation in whey proteins under appropriate conditions. 15-21) Kanno et al. have shown that the gelation of a whey protein isolate (WPI) was induced by a high pressure of 600 MPa for 10 min.17) The rheological properties of a whey protein, i.e., the gel strength, 17,19,20) storage modulus G 0 and loss modulus G 00 , 21) increase with increasing protein concentration. In addition, the gel strength also increases with increasing pressure and holding time. 17,19,20) The contribution of intermolecular S-S bonds to the aggregation and gelation of whey proteins has been demonstrated by Kanno and Mu,16) Kanno et al. 17) and Tanaka et al. 22)There is, however, limited information concerning the effect of such cosolvents as sugars on the properties of a pressure-induced gel from whey proteins. Sugars are utilized in a wide variety of food products to alter the conformation and interaction of proteins and, as a result, their functional properties through a variety of different physicochemical mechanisms. [23][24][25] It is also known that sugars increase the denaturation temperature of globular proteins. [26][27][28] This effect involves the sugar molecules being preferentially excluded from the region surrounding the proteins in an aqueous solution 23,24,27,29) ...

No abstract

No abstract