InfluenceofMilkTreatmentandAdjunctCulture on Quality of Ras Cheese

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. Microfiltrationconstitutesanalternativetoheattreatmenttoreducethepresenceofbacteriaandimprovethemicrobiological safety of dairy products without modifying the physic-chemical properties of milk. In this study, the effect of microfiltration(MF)andpasteurizationonproteolysis,lipolysisandflavordevelopmentinRascheeseduring 4 months of ripening were studied. Mixtures of adjunct cultures, isolated from artisanal dairy products, have been also evaluated in experimental Ras cheese for flavordevelopment.Inthefirsttrial,rawskimmilkwasmicrofilteredand 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 “microfiltrationorpasteurization”affectinthecheesemakingprocedure for amount of added chymosin and cooking time. The chemical composition of cheeses seems to be affected by milk treatment “microfiltrationorpasteurization”ratherthantheculturetypes.Themoisturecontentwashigherand the pH was lower in pasteurized milk cheeses than in microfiltratedmilkcheesesatdayoneofmanufacture.Proteolysis and lipolysis during cheese ripening were lower in microfiltratedmilkcheesescomparingtopasteurizedmilk cheeses. Very significantvariationsinfreeaminoacids,freefattyacidsandsensoryevaluationhavebeenfoundamong the cultures used in Ras cheesemaking. In general, microfiltratedmilkcheesesreceivedhigherscoreinbody& texture and lower score in flavorcomparingwithpasteurizedmilkcheeses.