Atlantic Cod Pepsin — Characterization and Use as a Rennet Substitute

Abstract

Pepsin (E.C. 3.4.4.1) was isolated from the stomach lining of Atlantic cod (A.C. Gadus Morhua). A.C. Pepsin was assayed with hemoglobin as substrate and had a temperature dependent pH optimum (2.5-3.0) and Km’(0.25-0.65mM). A.C. pepsin exhibited low temperature adaption, as judged by a temperature coefficient of 1.4, an Arrhenius activation energy of 7.3kcal/mole with hemoglobin as substrate and thermal instability under both acidic and alkaline conditions. The milk clotting activity of A.C. pepsin was also investigated. A.C. Pepsin exhibited a relatively low ratio of milk clotting to peptic activity, did not clot milk efficiently above pH 6.4, showed a greater decrease in clotting activity on dilution than did calf chymosin. However, A.C. pepsin clotted milk at 15°C more efficiently than calf chymosin. Laboratory scale batches of Cheddar cheese were prepared using A.C. pepsin, porcine pepsin or calf rennet as milk clotting enzymes. All cheeses were judged to be acceptable by a sensory panel and the intensity of Cheddar flavor was calf rennet > A.C. pepsin > porcine pepsin. A.C. pepsin resulted in greater loss of N and fat to the whey than did the other clotting enzymes and this appears to be related to rapid degradation of curd proteins prior to cheddaring. It is suggested that the A.C. pepsin would be advantageous for cold renneting of milk because of its relatively low temperature coefficient.