Study On Protein Quality Evaluation Of Raw Milk And Milk Products

In order to get a convenient and sample method to evaluate protein quality, we have determined the protein content and non-protein nitrogen content of raw milk, milk powder, yoghurt, milk beverage, sterilized pure milk by Micro-Kjeldahl Method and trichloroacetic -acid precipitation method, and calculated the protein nitrogen index and non-protein nitrogen index of raw milk and milk products above, and set up the protein nitrogen index and non-protein nitrogen index model.The results indicated that it was available to evaluate the protein quality of raw milk and milk products with the protein nitrogen index and non-protein nitrogen index model . The protein nitrogen index range of raw milk of Heilongjiang Province is 0.9981～0.9989, the non-protein nitrogen index range of it is 0.0011～0.0019(to set temporarily). Respectively the protein nitrogen index range of certified milk powder, yoghurt, milk beverage, sterilized pure milk are 0.990～0.996, 0.870～0.956, 0.402～0.633 and 0.929～0.943, and the non-protein nitrogen index range of which are 0.004～0.010, 0.084～0.130, 0.367～0.598 and 0.069～0.071(to set temporarily). There had great differences between the protein nitrogen index and the non-protein nitrogen index of Heilongjiang commercially available milk products .On the whole, the protein quality of Heilongjiang commercially available milk products measures up to the national standard.