CHARACTERIZATION OF MILK BY INFRARED SPECTROSCOPY Caracterização de leite por espectroscopia infra-vermelho

The determination of the main constituents that compose the milk is important in the dairy food industry, for establishing the milk value, for consumers’ information and for quality control. Fat and total protein content of milk, have economic importance because, in most countries, milk trade is based on these components and the somatic cell counts. It has been an attempt for replacing traditional reference methods (like Kjeldahl for protein, RöseGottlieb or Mojonnier for fat, and polarimetry for lactose) in the last decades, by application of spectroscopy techniques, in order to save time and to avoid waste. Since the development of the first commercial mid-infrared (IR) spectrophotometer by Goulden (GOLDEN,1964) and the contributions of Biggs (BIGGS, 1967;1972), the quantitative IR spectroscopy to milk analysis has turned into a standard AOAC method (BIGGS, 1972). But this method is slower and more expensive if we compare with the relative recent technique, the near-infrared spectroscopy of foodstuffs. The advantages of NIR spectroscopy include a higher rapidity and a simultaneous, non-destructive measurement of a number of milk constituents and potential for online analysis (SATO et al., 1987; RODRIGUEZOTERO et al., 1997; TSENKOVA et al., 1999). Since the milk is composed of mostly water the only difference between various types should be the concentration of fat , with the other constituents being practically the same. The purpose of this work is to study fat concentration in milk samples and indicate a way easy, fast and cheap to determine this percentage.