Influence of Protein and Fat Contents of Ultrafiltered Milk on Rheological Properties of Gels Formed by Chymosin

Enzymatically induced gelation of milk and milk concentrated by ultrafiltration was studied with a curd firmness tester which measured transmission of oscillatory deformations through the product. Scott Blair's relationship between pseudo modulus of rigidity (G) and time after clotting (t), G = G= e--h/t, described the gelation of ultrafiltered retentates satisfactorily. Maximum gel firmness G, and X, which is the time to reach a firmness of GJe, were affected substantially by protein content. The effect of protein content on rates of firming of gels were evaluated at different stages of gel formation. At the onset of gelation, rates increased up to protein content 90 g.kg -1 but decreased at higher protein concentrations. At a later stage, this decrease disappeared and rates correlated with protein content.-Those observations are discussed relative to effects of protein content on proteolytic and aggregation phases of milk clotting.