Recombinant Lamb Chymosin as an Alternative Coagulating Enzyme in Cheese Production

I. Rogelj ¹, B. Perko ¹, A. Francky ², V. Penca ¹, and J. Pungerar ³

¹ Zootechnical Department, Biotechnical Faculty, 1230 Domale, Slovenia
² BIOHIT d.o.o., 1000 Ljubljana, Slovenia
³ Department of Biochemistry and Molecular Biology, Jozef Stefan Institute, 1000 Ljubljana, Slovenia

Recombinant lamb chymosin (RLC) was prepared and tested for its potential use in cheese production. The milk clotting activity and proteolytic activity of RLC were evaluated in comparison with commercial recombinant calf chymosin (RCC), cow rennet (CR), and microbial coagulant (MC). RLC, RCC, and MC showed similar responses to pH, with a sharp increase of the coagulation time at pH 6.6 to 6.8 and decrease of curd firmness at the pH 6.5 to 6.6. In the case of CR, we observed two clear increases in the coagulation time and decreases in the curd firmness, at pH 6.4 to 6.5 and 6.6 to 6.8. Optimal clotting activity was obtained for RLC at 40°C, for both CR and RCC at 45°C, and for MC at 60°C. The temperature instability of RLC at temperatures above 45°C could constitute a benefit in making hard cheese varieties. The addition of CaCl₂ to milk resulted in enhanced clotting activity of all coagulants, most prominently for CR. The proteolytic activity of RLC was significantly lower from that of CR but not significantly different from the activity of RCC. The lower proteolytic activity in the cheese made with RLC did not have negative effect on organoleptic properties. The overall quality of the cheese made with RLC was at least comparable to that of the cheese made with RCC, and both cheeses were better scored than the cheese made with CR.

Key Words: lamb chymosin • coagulant • cheese

Submitted on August 29, 2000
Accepted on November 13, 2000