Effects of biopolymer addition on the dynamic rheology and microstructure of renneted skim milk systems

Abstract

The influence of k-carrageenan, xanthan gum, guar gum, high-methoxyl (HM) pectin and gelatin addition on the rheological and microstructural properties of rennet-induced skim milk gels was investigated using a stress-controlled rheometer, syneresis measurement and confocal laser scanning microscopy. The elasticity, aggregation and gelation times of renneted skim milk decreased with increasing amounts of added k-carrageenan, xanthan gum and guar gum, whereas they increased with increasing amounts of added HM pectin and gelatin. Syneresis of the rennet-induced skim milk gels decreased when HM pectin and gelatin were added, but increased when k-carrageenan, xanthan gum and guar gum were added. The changes in the viscoelastic properties and syneresis of renneted skim milk were attributed to the change in the microstructure of the rennet-induced skim milk gel after the addition of the biopolymers. The branched protein network structure of the rennet-induced skim milk gel could not be formed in the presence of high concentrations of xanthan gum, k-carrageenan and guar gum because of the formation of large protein aggregates or an open network structure with large voids. PRACTICAL APPLICATIONS There has been a steady growth in cheese sales over the last decade, mainly because of the increased use of cheese as an ingredient in a number of prepared foods, in which the cheese is used to add taste, texture and nutritional quality. However, because of the high cost associated with natural cheese production and storage, as well as its functional variability, the dairy industry has been aggressively seeking alternatives. Polysaccharides are used extensively in a variety of commercial dairy products as stabilizers and thickening or gelling agents. Furthermore, the use of polysaccharides is an attractive route to cost reduction in dairy products. However, as demonstrated in the present study, under certain conditions of biopolymer concentration, e.g., the use of some polysaccharides in cheese making can result in a decrease in the gel strength and whey holding ability of the cheese. Thus, avoiding the use of polysaccharides, which are known to phase separate when mixed with milk proteins, is highly recommended. © 2007, Blackwell Publishing.