EXTRACTION, PARTIAL PURIFICATION AND UTILIZATION OF PROTEOLYTIC ENZYME FROM KIWI FRUIT (Actinidia deliciosa) FOR MAKING SOFT CHEESE

Abstract

The aim of the present study was to extract, partially purify and utilize the proteolytic enzyme from kiwi fruit (Actinidia deliciosa) for making soft cheese. The pulp of kiwi fruits was blended with sodium phosphate buffer (pH 7.0) in the ratio of 1:1 and the juice obtained was centrifuged at 4000 rpm for 10 min under cool condition (4°C). The partial purification of the suspended (crude extract) was obtained by ammonium sulphate precipitation at the saturation of 30, 40, 50, 60, 70 and 80%. The optimum saturation was selected on the basis of milk clotting activity (MCA). Optimum conditions of temperature and pH of milk for maximum MCA and minimum time of coagulation (TOC) were determined by response surface methodology. Milk clotting activity (MCA), proteolytic activity (PA) and protein content of the extracted protease were measured. The partially purified protease was used as milk coagulant in soft cheese preparation at optimized conditions. The physicochemical and microbiological properties of prepared cheeses were compared with rennet cheese. Out of the fractions obtained by precipitation, the highest milk clotting activity was observed in the 50% fraction. Numerical optimization study revealed that the optimum condition for milk clotting was found to be at 55°C at pH 6.5. The optimized TOC and MCA for partially purified kiwi protease was found to be 30 s and 841.65 unit. The cheese manufactured by kiwi protease showed similar textural properties and physico-chemical compositions to rennet cheese. The physico-chemical analysis showed non-significant (P>0.05) difference in protein content between soft cheeses prepared by kiwi protease and rennet. However, significantly (P<0.05) higher level of moisture, ash content, acidity and calcium content, and lower level of fat were observed in kiwi protease cheese as compared to rennet cheese. Microbiological analysis revealed significantly (P<0.05) higher level of total plate count in kiwi cheese. There was no significant difference (P>0.05) in yeast and mold count between kiwi protease and rennet cheeses