Routine testing of farm tank milk by ir analysis iv. prediction of the freezing point depression from ir measurements and conductivity
Koops, J.; Kerkhof-Mogot, M.F.; Van-Hemert, H.
Netherlands Milk and Dairy Journal 43(1): 3-16
In the present paper details are given of a rapid method of predicting the freezing-point depression (FPD) of milk. The FPD is mainly produced by lactose and the dissolved salts. Basically, estimation of the lactose contents of herd milk, combined with determination of the conductivities therefore could be used to predict the FPDs, the latter giving information on Good Manufacturing Practice on the farms. Multiple linear regression between the FPDs and the contents of fat (F), protein (P) and lactose (L) together with the conductivity (C) values of 126 farm tank milk samples was calculated, based on cryoscopic determination of the FPD, infra-red analysis of F, P and L and estimation of C using a four-point measuring cell. Two series of farm tank milks, one consisting of winter milk (n = 225) and the other of summer milk (n = 179), were analyzed to evaluate the merits of the proposed method. With an FPD of 520 mK as the official Dutch limit, 98.6% of the samples were correctly classified by prediction of the FPDs from linear regression. Ways to improve these results are given.