The effect of casein/whey protein ratio and minerals on the rheology of fresh cheese gels using a model system

An objective of the present study was to determine the effects of protein interactions on acid gelation behaviour at the higher concentrations encountered in fresh cheeses. A fresh cheese model was created by means of chemical acidification (glucono-delta-lactone) of 120 g L(-1) protein solutions prepared from native phosphocasein, sodium caseinate and whey protein isolate (WPI) in lactose-free simulated milk ultrafiltrate. The effects of varying the ratios of (i) casein/whey protein, and (ii) phosphocasein/sodium caseinate (on a protein basis) on the rheology of the resulting acid gels were studied. The results showed that storage moduli of acid gels after 4 h (G'240) at 30 degrees C increased as the amount of pre-denatured whey protein (78 degrees C, 30 min) was increased to a maximum of 15 g L(-1). At a constant protein content of 120 g L(-1), the storage modulus increased from 250 Pa (no whey protein present) to 3.15 kPa following substitution with 15 g L(-1) pre-denatured whey protein. At higher pre-denatured whey protein concentrations, the storage modulus decreased. Gelation also occurred more quickly and at a higher pH by increasing the amount of added pre-denatured whey protein up to the optimum level of inclusion. In the absence of whey protein, partial substitution of phosphocasein (40 g L(-1)) with sodium caseinate (80 g L(-1)) reduced Ca and P concentration to levels that typify fresh acid curd, and increased gel strength (G'240 > 1000 Pa). The inconsistent acid gelation behaviour arising from substitution (20-60 g L(-1)) with solubilised rennet casein in the form of sodium para-caseinate suggests that rennet addition may be unnecessary when protein concentration is high. The study demonstrates that the strong acid gels formed by recombination of novel and existing milk protein ingredients with defined functional characteristics have potential application in fresh cheese product developments.