The effect of micro- and macro-molecules on the microstructure and gel characteristics of whey protein concentrate and albumen

Avian egg albumen and whey protein concentrates from milk are widely used in the food industry as binder systems, emulsifiers, and foaming agents and for general consumption. In meat-like analogues such as Quom, the whey protein concentnite and egg albumen are relied upon to produce tough gels with the application of heat. Like many food products, the heat-inauced gelation of the protein molecules depend on the environmental conditions and other materials present in the system as well as any interactions between them. A study of a range of ingredients as well as environmental the factors of pH, material concentration and various blends of whey protein concentrate and albumen was initiated in the hqpe, of quantifying the effect of the materials on gel structure. Texture Profile Analysis (TPA) , stress relaxation, protein gel dissolution, ' colour measurement and confocal laser scanning microscopy (CLSM) were employed to assess, measure and quantify the relationships between the environmental factors and the added materials. The results obtained indicated that whey protein 'and albumen form an interpenetrating gel under normal conditions. The optimum ratio at which the combined binder exhibited it maximum values was of the order of 2:1 (whey/albumen). The pH'of the, media had the biggest effect on the gel properties. Alteration' in pH close to 'the isoelectric point changes the gel from a fine-stranded network to one with a particulate or filamentous network. Significant interactions were observed between all the main variables on at least one of the responses. Addition of hydrocolloids with large molecules in relation to the protein such as methylcellulose and pectin led to phase separation. Methylcellulose induced' a change in the gel from one that imbibed water to one that exuded water as the concentration of the material was increased up to 2%. With high methoxyl pectin, there was phase separation at pectin concentration of as little as 0.5% and phase inversion at pectin concentration in excess of 0.5%. The starch products generally delivered the largest incret;Jse in the gel hardness, but there were changes to other gel properties depending on what type of starch was used. Milk-derived ingredients such as lactose, casein and glycomacropeptide (GMP) were not necessarily compatible with a whey protein/albumen gel. Dissolutions tests with protein perturbing agents such as DTE, SDS and urea showed that some of the added materials interfered with protein'-protein gel formation by one of two ways (1) by blocking· the formation of the bonds necessary to stabilize the protein structure and/or (2) interacting with the water molecules in ' preference to the protein molecules. In addition the CLSM micrographs proved that there was indeed phase separation of the molecules when the conditions were not favourable.