Abstract

Due to the scarcity of natural rennet, in this study we have considered an option of using in cheesemaking a milk-clotting enzyme produced by the Irpex lacteus fungus. We describe main properties of I. lacteus coagulant: milk-clotting activity (MA), overall proteolytic activity (PA), thermal stability, MA dependence on pH level and calcium ions content. Partially purified preparations of I. lacteus milk-clotting enzyme was obtained by salting out and gel-filtration. Technological properties of the I. lacteus coagulant were compared to natural calf rennet and cow pepsin (CP). MA of I. lacteus enzyme amounted to 29.1 ± 0.7 RU/ml, with protein content of 23 mg/ml. The coagulant was completely inactivated at 60○C. Thermal stability of I. lacteus milk-clotting enzyme, MA sensitivity to pH variations and Ca2+ content were comparable to respective parameters of calf rennet and CP. Overall PA of the I. lacteus coagulant exceeded CP and calf rennet activity by 33 and 220 times, respectively. As for enzymatic specificity, the following order was observed: calf rennet (100%) > CP (14.9%) > I. lacteus coagulant (0.5%). These findings suggest that there is a need to increase the MA of I. lacteus coagulant in order to be able to use it in cheesemaking. We have considered chemical, biochemical, and genetic corrective actions applicable to technological properties of microfungal milk coagulants.

Keywords

milk-clotting enzymes, rennet, rennet substitutes, microfungal coagulants, milk-clotting activity, proteolytic activity, thermal stability, cheesemaking, mucorpepsins

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