Studies on Milk-Clotting Enzyme from the "Litsusu" Tree (Wrightiana calysina): Evidence for Milk Coagulation

Abstract

The bark of the "litsusu" tree (Wrightiana calysina) is commonly used as a coagulant for the manufacture of "litsusu", a traditional cheese-like product in Indonesia. In the present study, the authors prepared an extract (pH6.3, N content; 473μg/ml) from a twig of "litsusu" and examined its milk-clotting and proteolytic properties. The "litsusu" extract exhibited maximum milk-clotting activity at pH6.0, whereas the optimum pH curve of the proteolytic activity fluctuated with two maxima at pH7.5 and 8.5. The optimum temperatures for milk-clotting and proteolytic activities were both 70°C. Milk-clotting of the"litsusu"extract was very stable at temperatures even higher than 70°C, and 70% of original milk-clotting activity remalned after heating the "litsusu" extract at 90°C for 30min and at pH6.3. A scanning electron microscopic comparison among the curds prepared by coagulating milk with rennet, the "litsusu " extract and HCl indicated that the surfaces of rennet-and "litsusu" -curds had several common features.