Analysis of milk by infra-red absorption

Abstract

Summary: The infra-red, absorption of milk and its main constituents has been recorded and it has been found possible to determine quantitatively the fat, protein and lactose contents from measurements of the intensities of the respective absorption peaks at 5·73, 6·46 and 9·6 μm. Solids-not-fat (SNF) content can be obtained from a single intensity measurement at 7·9 μm where the fat shows no attenuation and where the protein and lactose extinction coefficients are approximately equal. Photometric errors due to natural variations in fat globule size distribution can be eliminated by prior homogenization. Based on these observations, an automatic infra-red milk analyser (IRMA) has been constructed, which can determine the fat, protein, lactose and SNF in a pre-warmed milk sample in under 1 min. Preliminary tests carried out on 50 milk samples from individual cows, representing 3 different breeds, gave standard deviations from the chemical analyses for the percentages of fat, protein, lactose and SNF of 0·10, 0·07, 0·07 and 0·19, respectively. The standard deviations for the percentages of fat and SNF on 60 farm bulk milk samples were found to be 0·08 and 0·12.