Effect of chymosin/pepsin ratio on milk coagulation and physical properties of model cheese

Chymosin and pepsin are the two major enzymes in coagulants for the cheese industry. They affect milk coagulation properties, curd composition, casein hydrolysis and the consequent development of cheese texture. Limited knowledge is available on the effect of the chymosin/pepsin ratio on the mentioned factors. This study aimed (1) to better understand the effect of chymosin/pepsin ratio on milk coagulation properties, casein hydrolysis, rheological and textural properties of model cheese during storage, and (2) to link casein hydrolysis to the rheological and textural properties. For this purpose, coagulants were prepared in which the ratio between the two enzymes was systematically varied. Our results showed that even when milk clotting activity was standardized, coagulants with different chymosin/pepsin ratios had a significant effect on curd firming rate and final firmness, which could be attributed to the different specificity of chymosin and pepsin for hydrolyzing κ-CN. During 4 weeks of storage, the chymosin/pepsin ratio influenced the hydrolysis of αs1-CN, and the subsequent properties of the protein network and the cheese texture. For coagulants with a higher proportion of pepsin, less intact αs1-CN and a higher degree of casein hydrolysis (expressed as protein fraction soluble at pH 4.6) were found. Correspondingly, the cheese had a weaker and less brittle network, and was softer, less elastic and more sticky. Commercial calf rennet showed more extensive hydrolysis of αs1-CN than other coagulants, which led to the weakest protein network and the softest cheese. The present study's findings can be used to control and design cheese with desired textures. For example, coagulants with varying chymosin/pepsin ratio or from a specific source can be used to modulate the casein hydrolysis.