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

The influence of kappa-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 kappa-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 kappa-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, kappa-carrageenan and guar gum because of the formation of large protein aggregates or an open network structure with large voids.