Chicken Pepsin as a Rennet Substitute

Abstract

Semi-purified chicken pepsin was prepared from proventriculae at a yield of 33% of the original pepsin activity using a procedure based on the method described by Bohak (1970). Cheddar cheese was produced using the chicken pepsin preparation, and with calf rennet as a control, in two trials. The enzymes were standardized to the same milk-clotting strength on Berridge's substrate at ca pH 6.3; the setting times were a little more than twice as long as calf rennet. While the composition and yield of cheese from the two enzymes were not significantly different (P<0.05), observed moisture was higher (1.9%) and moisture-adjusted yields lower (2%) with chicken pepsin. Cheeses were stored under refrigeration and analysed 3, 6, and 9 months after production. Sensory analysis of pepsin cheese demonstrated the development of bitterness between 3 and 6 months as compared to immediate bitterness found in a previous study. This change was paralleled by increases in acid soluble nitrogen and in stress relaxation, a textural parameter measured by the Instron apparatus. Scanning electron micrographs of the 9 month cheese revealed a breakdown in the matrix of the chicken pepsin cheese compared to the control. It would appear that this level of purity of chicken pepsin might be capable of producing acceptable Cheddar cheese for applications that do not require aging of more than 3 months and use heat to inactivate the enzyme, such as processed cheese spread. Further purification may improve the specificity of the enzyme and reduce delayed proteolysis but would increase its cost concomitantly.