Influence of milk treatment and adjunct culture on quality of Ras cheese [electronic resource].

Includes references.

Classical techniques used to improve milk's shelf life and safety are based on heat treatments, like pasteurization and sterilization. Those techniques modify some physic-chemical properties of milk, for example its coagulation by rennet. Microfiltration constitutes an alternative to heat treatment to reduce the presence of bacteria and improve the microbiological safety of dairy products without modifying the physic-chemical properties of milk. In this study, the effect of micro filtration (MF) and pasteurization on proteolysis, lipolysis and flavor development in Ras cheese dur¬ing 4 months of ripening were studied. Mixtures of adjunct cultures, isolated from artisanal dairy products, have been also evaluated in experimental Ras cheese for flavor development. In the first trial, raw skim milk was microfiltered and then the protein! fat ratio was standardized using pasteurized cream. The pasteurized milk with same protein/ fat ratio was also used in the second trial. Milk treatment "microfiltration or pasteurization" affect in the cheese making procedure for amount of added chymosin and cooking time. The chemical composition of cheeses seems to be affected by milk treatment "microfiltration or pasteurization" rather than the culture types. The moisture content was higher and the pH was lower in pasteurized milk cheeses than in microfiltrated milk cheeses at day one of manufacture. Proteolysis and lipolysis during cheese ripening were lower in microfiltrated milk cheeses comparing to pasteurized milk cheeses. Very significant variations in free amino acids, free fatty acids and sensory evaluation have been found among the cultures used in Ras cheesemaking. In general, microfiltrated milk cheeses received higher score in body & texture and lower score in flavor comparing with pasteurized milk cheeses.

Summary in Arabic.