Abstract:
This study was aimed to extract milk-clotting enzyme from sunflower (Helianthus annuus) seeds and to determine its potentiality for manufacturing white soft cheese from cows and goats milk during storage. The parameters evaluated included: coagulation time, yield, physicochemical composition, microbiological analyses and sensory characteristics of the manufactured cheese. The sunflower seeds' were blended and extracted using two types of buffers, Na acetate buffer and 5% NaCl acetate buffer. Milk-clotting and proteolytic activities were evaluated. The enzyme was partially purified using ammonium sulfate fractionation techniques. Twenty five (25) liters of fresh cow's full cream milk were purchase from the farm of College of Animal Production Science and Technology, Sudan University of Science and Technology, and (25) liters goats' milk was purchased from a private farm at Khartoum North. Four treatments were carried out in this study as follows: In the first and second treatments cow's milk cheese was made from rennet and sunflower enzymes respectively. In the third and fourth treatments goat's milk cheese was made from rennet sunflower enzymes respectively. And milk pasteurization, 0.02% CaCl2 and 2% starter culture were added then white cheese was made and stored at 4°c for 63 days. Physicochemical composition, microbiological analyses and sensory evaluations was done for the cheese samples at 0, 7, 14, 21, 28, 35, 42, 49, 56 and 63 days intervals. Results indicated that sunflower seeds extracted with 5% NaCl in 50 mmol/L acetate buffer, pH 5.0, had the highest milk-clotting activity (MCA) and lowest coagulation time compared to that extracted with only acetate buffer (pH 5.0). Ammonium sulfate at 30–50% saturation purified the enzyme to 4.3 folds with MCA of 241.0 U/mL and final enzyme yield of 10.9%. The partially purified enzyme was characterized by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) that showed two bands with molecular weight of 120 and 62 kDa. When compared with other plant enzymes, the partially purified sunflower enzyme was found to have higher milk-clotting activity and lower proteolytic activity. The results showed that milk source significantly (p<0.01) affected the cheese yield, while did not showed significant effect on coagulation time. Coagulant type was significantly (P<0.05) and (p<0.01) affected the cheese yield and coagulation time, respectively. Cheese made from cow milk using sunflower enzyme had higher yield compared to that obtained using commercial rennet, whereas the opposite was observed when using goat milk. Milk source, coagulant type and storage period significantly (p<0.01) affected all the studied physicochemical parameters: total solids contents, ash, fat, protein, acidity, tryptophan and tyrosine. Microbiological analyses showed significant (P<0.01) effect of milk source on total viable bacterial count,
