On Whey Protein Isolates
The hardness and brittleness are key characteristics of protein molecules that can be used in determining the nature of the proteins. The hardness of the protein molecules refers to how well the molecules are bonded together making it more difficult for the denaturation of the protein molecule (Vardhanabhuti, & Foegeding, 1999).On the other hand, the brittleness of the protein molecule refers to the character of the protein molecule that prevents breakage in the bond linkage when subjected to different conditions.
A major function of proteins among the food systems is the process of gelation. The process constitutes a three-dimensional matrix that is formed through the linking of protein and hydrogen atoms which allows for the immobilization of water molecules within the structure of the gel (Morr & Ha,1993).
WPI gels that were acquired at pH 3 were found to be weak and brittle, while gels acquired at pH of between 4 and 6 were found to be opaque and prone to whey syneresis. They failed to fracture at 80% deformation. At a pH of between 7 and 8, gels that were quite strong and highly elastic were obtained. The high elastic quality prevented their deformation. They failed to exhibit whey syneresis while under compression during the experiment. Previous research noted a similar behaviour of whey protein heat-induced gels. When compressed, the volume of the pores in the gel decreased which resulted in whey syneresis. At pH levels greater than 8, the surface charge of the whey proteins was observed to be high and exhibited repulsive forces which enhanced the ordered aggregation of proteins and ultimate formation of flexible and long strands. It has been noted that formation of disulfide bonds as well as exposing of residues of hydrophobic amino acids is the initial coagulation step. Further heating as observed in the charts causes the polymerization of intermolecular sulfyhydryl-disulfide. This enables the formation of a network that gives it the ability to coagulate.
REFERENCES
Tang, Q.; McCarthy, O.; Munro, P. Oscillatory study of the effects of pH and salts on gel development in heated whey protein concentrate solutions. J. Dairy Res. 1995, 62, 469
Morr, C. V., & Ha, E. Y. (1993). Whey protein concentrates and isolates: processing and functional properties. [Review]. Crit Rev Food Sci Nutr, 33(6), 431-476. doi: 10.1080/10408399309527643
