Whey gels formation

Procedures and conditions for whey protein concentrate (WPC) gel formation have been described (14,15,16,25). Several commer-... 

Structure-fracture measurements have been made on the same whey protein/ amylopectin mixtures previously discussed with regard to gel formation. In Figure... 

Bulca, S., Leder, J., and Kulozik, U. (2004). Impact of UHT or high heat treatment on the rennet gel formation of skim milk with various whey protein contents. Milchwissenschaft 59, 590-593. 

Mleko, S. and Foegeding, E. A. 2000. pH induced aggregation and weak gel formation of whey protein polymers../. Food Sci. 65 139-143. 

An alternative approach to the formation of whey gels is to predenature whey proteins under carefully controlled conditions to form aggregates, followed by cold gelation in the presence of salts (Bryant and McClements,... 

Polyacrylamide gel electrophoresis results suggest that p-LG undergoes a greater conformational loss as a fimction of extrusion temperature than a-LA, presumably due to intermolecular disulfide bond formation. Atomic force microscopy indicates that texturization results in a loss of secondary structure of aroimd 15%, total loss of globular structure at 78 °C, and conversion to a random coil at 100 °C (Qi and Onwulata, 2011). Moisture has a small effect on whey protein texturization, whereas temperature has the largest effect. Extrusion at or above 75 °C leads to a uniform densely packed polymeric product with no secondary structural elements (mostly a-helix) remaining (Qi and Onwulata, 2011). 

Although the gelation properties of whey proteins are of great importance in many foods (Mulvihill, 1992) and it is possible to form a weak gel in creams by the formation of a continuous network of fat globules, most important milk gels are those involving casein micelles which can be made to form a gel matrix either by isoelectric precipitation (acid-induced gel) or by the action of a proteolytic enzyme (rennet-induced gel). Both gel types... 

Part of the process to make cheese involves the flocculation of an electrostatically stabilized colloidal O/W emulsion of oil droplets coated with milk casein. The flocculation is caused by the addition of a salt, leading to the formation of networks which eventually gel. The other part of the process involves reaction with an enzyme (such as rennet), an acid (such as lactic acid), and possibly heat, pressure and microorganisms, to help with the ripening [811]. The final aggregates (curd) trap much of the fat and some of the water and lactose. The remaining liquid is the whey, much of which readily separates out from the curd. Adding heat to the curd (-38 °C) helps to further separate out the whey and convert the curd from a suspension to an elastic solid. There are about 20 different basic kinds of cheese, with nearly 1000 types and regional names. Potter provides some classification [811]. 

The primary (enzymatic) phase of renneting overlaps somewhat with the secondary phase of aggregation. The gel subsequently undergoes syneresis to produce curds and whey while a slow but more general proteolysis of the caseins begins, which eventually contributes substantially to the distinctive flavor and texture of cheese. The enzymatic coagulation of milk and formation of the curd has been reviewed by Dalgleish (1987). Here, attention will be confined to parts of the subject that most clearly relate to the structure and stability of bovine casein micelles. 

Cold-set whey protein gels obtained by addition of calcium ions to preheated whey proteins have been used to deliver iron (Remondetto et al. 2002). By modulating the conditions of formation, gels with different microstructures (particulate or filamentous) were formed with different encapsulating properties. Filamentous whey protein gels were more efficient than particulate gels in delivering bioavailable iron to the intestine, as less iron was released at acidic but more at alkaline pH (Remondetto et al. 2004). 

Blends of whey protein isolate and denatured whey protein isolates were microparticulated using a microfluidizer prior to the formation of heat-set gels. Increasing the number of passes in the microfluidizer increased the hardness of the gels, an effect attributed in part to the more homogenous gelation of smaller aggregates (Sanchez et al., 1999). 

Lucey, J.A., Tamehana, M., Singh, H., and Munro, P.A. (1998). Effect of interactions between denatured whey proteins and casein micelles on the formation and rheological properties of acid skim milk gels. f. Dain/ Res. 65, 555-567. 

---