A comparison of the determination of the rennet coagulation properties of bovine milk

The aim of the work was compared of two different methods (the visual method and the nephelo turbidimetry method) for determination of rennet coagulation time. It was observed the effect of heat treatment of milk; types of rennet and addition of different amount of CaCl 2 into the pasteurized milk. It was used two different chymosin rennet. For the visual method was milk sample (100 mL) equilibrated at 35 °C, 1 mL of rennet was added into milk and was measured the time required for the first visible flakes (visual method). For the determination rennet coagulation time by nephelo-turbidimetry was removed part of milk with rennet and placed into nephelo-turbidimetry. Milk had a titratable acidity in the range from 6.5 to 7.0 °SH, average pH of milk was 6.68. Dry matter content was in range from 12.351 to 13.142%. The average content of protein by Kjeldahl was 3.14%, fat by Gerber 4.34%, lactose by polarimetry 4.68% and calcium content 1.1%. The pasteurized milk had the worst rennet coagulation time about 32 s compared to the raw milk. The difference coagulation time between milk with addition of 20 µL CaCl 2 and 40 µL CaCl 2 was in range 21 s to 26 s by visual method. The difference coagulation time between milk with addition of 20 µL CaCl 2 and 40 µL CaCl 2 was 15 s by nephelo-turbidimetry method. There occurred statistically non-significant differences in most of the measurements, comparing the visual and the nephelo-turbidimetric method. The heat treatment, addition of CaCl 2 and using of different rennet had an influence on the curd category. It was obtained, that using nephelo-turbidimetry shown objective results for measuring the rennet coagulation time contrary the subjective visual method. Further, the results obtained by nephelo-turbidimetry are accurate and determined with the lower variation.