Lamb rennet paste in ovine cheese (Idiazabal) manufacture. Proteolysis and relationship between analytical and sensory parameters

Cheeses were manufactured with 2 levels of lamb rennet paste or bovine rennet, at two times of the year, to study the effect of artisanally prepared lamb rennet paste (at high and low levels) on the concentrations of proteolysis products (nitrogen fractions, casein degradation and free amino acids). Cheeses made with the lamb rennet paste presented a significantly different evolution of the α s1-I-casein fraction during ripening, as measured by urea polyacrylamide gel electrophoresis. The time of the year affected the concentrations of 39% of the individual free amino acids, as determined by reversed-phase high-pressure liquid chromatography. The relationship between some biochemical parameters (gross composition, degrees of lipolysis (Lamb rennet paste in ovine cheese manufacture. Lipolysis and flavour. International Dairy Journal (2003) in press) and proteolysis) and the sensory characteristics of the cheese (Virto et al., 2003) were studied by a principal component analysis. The effect of the technological parameters “type of rennet” and “time of the year” on these analytical variables and sensory characteristics of the cheese was described by three principal components which explained 80.8% of the total variance. The factor “rennet paste” included concentrations of short chain free fatty acids, sensory descriptors related to strong odours and flavours, an unidentified peptide A1, and α s1-I-caseins. The effect of the ‘time of the year’ was described by two other factors: the “secondary proteolysis” factor, which included the concentrations of free amino acids and could be related to the different endogenous microflora of the raw milk, and the “seasonal milk composition” factor, which included the fat content and the plasmin activity of the milk.