Studies on Acceleration of Ras Cheese Ripening by Aminopeptidase Enzyme from Buffaloes' Pancreas. II-Utilization of Buffaloes' pancreas aminopeptidase in acceleration of Ras cheese ripening

Abstract: Aminopeptidases are an exopeptidase that catalyzes the hydrolysis of amino acid residues from the Nterminus of peptide or protein substrates, these are believed to act in concert to completely degrade the products of proteolysis into amino acids. The presence of free amino acids in Cheddar cheese and their contribution to aged flavor clearly and debittering effect in cheese indicates the importance of aminopeptidases in the ripening process. Fresh mixture of buffaloes' and cows' milk (1:1) was divided into five portions. The first portion was left without treatment and served as a control (C). The aminopeptidase was added at levels of 0.03 (T1), 0.06 (T2), 0.09 (T3) and 0.15 (T4) units / kg milk. All five milk samples were manufactured into ras cheese. Ras cheese samples were taken periodically when fresh and after 15, 30, 45, 60, 75, 90, 105 and 120 days of storage at 14 ± 1°C for analysis. After 60 days of ripening, sample T2 was more superior as it had an acceptable acidity and pH value and the difference between it and control was significant. The moisture and total nitrogen contents of sample T2 were 36.65 and 4.643% and there is no significant difference between T2 and control. The level of soluble nitrogen in the control cheese was lower than those of treated cheeses and the difference between sample T2 and control was significant. The use of buffaloes' pancreas aminopeptidase increased soluble tyrosine and tryptophan contents in the resultant cheeses as compared with the control. Specific assessment of proteolysis by measuring decrease in the intensity of protein bands by urea-PAGE showed considerable decreases in intact α s1 and β-casein in sample T2 compared to the control. Organolyptically treatment 2 had the highest total score among treatments followed by sample T1 then T3, T4 and finally control cheese. Therefore addition of 0.06 units of buffaloes' pancreas aminopeptidase / kg milk would accelerate the ripening process of Ras cheese through 60 days without any defects in its properties