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A comparison of various methods for the estimation of solids-not-fat in milk and whey

Summary The total solids (TS) content of milk was estimated using freeze-drying followed by a Karl Fischer (KF) titration. The average solids-not-fat (SNF) value for 12 milks calculated from the TS results by this method was 0·003±0·039 % lower than that calculated from the TS results by the British Standard (1963) gravimetric method (BS). The average SNF value calculated from the sum of the contents of lactose anhydride, ‘total’ protein and ash was slightly higher (+0·017±0·068 %) than that obtained from the BS method. Certain modifications of the BS method for TS gave erroneous results. Heating 1 or 2 g milk at an oven temperature of 100 °C for 5 h, however, gave results agreeing fairly closely with the BS values. For lactic (starter) casein whey the average SNF content from freeze-drying and KF titration was 0·075 % higher than that obtained by following the BS procedure (for TS in milk). Average values for the sum of the SNF constituents (including lactic acid) were 0·08–0·11 % lower than those obtained from BS method. In many of the values recorded in the literature there is an unexplained discrepancy between the SNF content calculated from the sum of the constituents and that calculated from the TS content estimated gravimetrically by an alternative British Standard (1951) method. The need for a uniform method for estimating TS is stressed.