Effects of Sugars on the Cross-Linking Formation and Phase Separation of High-Pressure Induced Gel of Whey Protein from Bovine Milk

Abstract

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) ...

Effects of pH and ionic strength on the rheology and microstructure of a pressure-induced whey protein gel

“…Gel strength also increases with increasing pressure and holding time (Van Camp & Huyghebaert, 1995a;Van Camp et al, 1996). The presence of sugars decreases the extent of intermolecular crosslinking of proteins and restrains phase separation during gelation of whey protein isolate (WPI) under high pressure (He, Azuma, Hagiwara, & Kanno, 2006;Kanno, He, Ametani, & Azuma, 2002). However, there is limited information on the effects of pH and ionic strength (I) on the properties of whey protein gels formed under high pressure.…”

Application of an Artificial Neural Network for Predicting the Texture of Whey Protein Gel Induced by High Hydrostatic Pressure

“…Unfolded β-Lg can interact, through SH/SS interchange reactions, with proteins containing disulfide bonds, e.g. α-La, BSA, and β-Lg [19,25]. Regarding pressure-induced gelation of a WPI solution, the formation of intermolecular S-S bonds between proteins has been confirmed [18,25], and it is likely that the gel is mainly formed by the cross-linking of intermolecular S-S bonds [25].…”

“…The gelation of protein is influenced in a complex manner by the processes of protein denaturation and aggregation [22,29]. Sugars decrease the degree of intermolecular S-S bonding of proteins [25], and restrain phase separation during the gelation of WPI under high pressure. Fig.…”

Protein–Saccharide Interaction

“…He et al (2006) reported that monosaccharides and disaccharides, such as xylose, glucose, sucrose, and lactose, decreased the rigidity of the pressure-induced whey protein gel at 800 MPa. They concluded that sugars influenced the characteristics of the pressure-induced gels by inhibiting the intermolecular cross-linking of the proteins and restricting the phase separation of change in the microstructure of the gel from a honeycomb to a thin-stranded structure.…”