The effect of rennet and container types was evaluated on proteolysis of traditional Kurdish cheeseduring 60 days ripening. The enzymes involved were commercial chymosin and traditional rennetfrom lamb abomasum. Goat skin (traditional container) and plastic containers were used as storagecontainers. The trend of proteolysis was determined by measuring the content of nitrogen (N) incompounds soluble in water, 12% trichloroacetic acid and 5% phosphotungstic acid along with theurea–polyacrylamide gel electrophoresis method. The results showed that the nitrogen in com-pounds soluble in water, 12% trichloroacetic acid and 5% phosphotungstic acid was higher inripened cheeses into plastic containers; however, the containers had no significant effect on thebreakdown of a- and b-caseins (P < 0.05). Using commercial rennet caused the breakdown ofa- and b-caseins and the level of nitrogen in compounds soluble in water to increase. Finally,however, the amount of a- and b-caseins breakdown was trivial, and a-casein was decreased morethan b-casein in all samples.Keywords Container, Proteolysis, Rennet, Traditional Kurdish cheese.INTRODUCTIONNumerous biochemical and microbiologicalchanges take place during cheese ripening ofwhich one of the most important is known asproteolysis (Fox et al. 1993). Proteolysis origi-nates from enzymes contained in milk (plasmin)and rennet (pepsin and chymosin) or released bymicro-organisms. The enzymes activities reducethe concentration of casein (CN) (a-s1, a-s2, b-and j-CN) and as a consequence lead to the for-mation of large- and intermediate-size peptides.Also, these peptides may be further degraded byproteolytic enzymes, originating from the micro-flora [starter bacteria, nonstarter lactic acid bac-teria (LAB) and probiotic adjuncts] of thecheese, into small peptides and free amino acids(FAA). Cheese quality is greatly influenced bythe peptides and amino acids caused by proteol-ysis (Igoshi et al. 1986).Several studies (Fernandez-Salguero and Sanj-uan 1999; Irigoyen et al. 2000, 2001, 2002;Sanjuan et al. 2002; Bustamante et al. 2003;Moatsou et al. 2004; Prieto et al. 2004; Pradoset al. 2006; Pirisi et al. 2007; Pereira et al.2008; Tejada et al. 2008; Pino et al. 2009) haveshown differences in the proteolysis trend ofcheeses regarding various rennet types vs time.These studies mostly have demonstrated thata-s1-casein is degraded more extensively thanb-casein.Kurdish cheese is one of the most favouredtraditional raw milk cheeses in Iran where itsripening period occurs in goat skin. It is verydifficult to produce a permanent high-qualityproduct due to using traditional methods andlack of standardisation in most manufacturingsteps, especially the ripening conditions. Asthere is no study about the effect of packagingmaterials and the type of coagulant on Kurdishcheese properties, the objective of this study,which forms part of a wider investigation of thebiochemical and microbiological characterisationof raw milk Kurdish cheese, was to study theproteolysis during the maturation of this cheese.Also, the effect of different types of coagulant