Analysis of milk by infra-red absorption

Abstract

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/tm. Solids-not-fat (SNF) content can be obtained from a single intensity measurement at 7-9 /im. 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. This paper presents the basic principles and preliminary results of a rapid method for the quantitative analysis of milk by means of infra-red absorption. The method has already been reported briefly (Goulden, 1961a) and is covered by a patent vested in the National Research Development Corporation (Goulden, 19616). A commercial instrument employing this principle is now being developed and its constructional features have been described by Goulden, Shields & Haswell (1964). THEORETICAL Infra-red absorption spectroscopy is commonly used for the quantitative analysis of multicomponent systems, but the high water content and radiation scattering properties of milk make it a particularly difficult system for analysis by this method. As can be seen from the spectra shown in Fig. 1, even thin films of water absorb strongly throughout the 2-10 /iva wavelength region. The water absorption bands are so intense that it is almost impossible to discern bands due to other milk constituents. When a double-beam spectrometer is used to cancel out automatically the water absorption, the characteristic bands of the other components become clearly visible as in the spectra shown in Fig. 2. These bands arise from particular components of milk and when recorded as optical densities (absorbancies), the band intensities are proportional to the concentration of each of the major constituents.

Drying of Liquid Food Droplets Enzyme Inactivation and Multicomponent Diffusion

“…First the dry weight content was determined by means of a vacuum dryer, in which the slices were dried at 70 °C for two days. After that the sucrose and sodium caseinate concentrations were determined by an automatic infrared analyser, type Milkoscan 104 A/B (Foss Electric, Denmark) (Goulden, 1964)), after dissolution and dilution of the dried slices. The accuracy of the analysis depended on the initial solids content of the model system.…”

Milk protein analysis

“…The main indigenous source of such groups is citrate. Gaudillere and Grappin (1982) and Sjaunja and Anderson (1985) have The formation of carboxylic acids by fermentation of lactose may also cause interference absorption at the protein wavelength (Goulden, 1964). Similarly, it has been demonstrated that lipolysis induces an increase of the protein signal by 0.01 percent unit per millimole of free fatty acid (Sjaunja, 1982).…”

Comparison of methods for the analysis of New Zealand sea lion,Phocarctos hookeri, milk

“…Failure to homogenise milk adequately so that fat droplets are of uniform size may increase the variation in the results for fat determined by MilkoScan T M FT 120 because light scattering increases with the particle Mean milk component concentration (%) size/wavelength ratio (Goulden 1964;Sjaunja 1984a (Walstra 1995) or release free fatty acids (lipolysis) resulting in variation between methods in the analysis of cow's milk (Ng-Kwai-Hang et al 1988). any deterioration of the milk samples in the present study, would be associated with the freezing and thawing of the samples and the length of time they were stored.…”

“…Since the late 1940s, the dairy industry has developed automated infrared instruments (Conn 1960;Gunzler & Gremlich 2002), which allow the simultaneous determination of fat, protein and lactose in milk based on their absorption at specific wavelengths (Goulden 1964). Quantitative analysis was improved markedly with the development of Fourier transform infrared (FT-iR) spectroscopy in the 1960s (Griffiths & Haseth 1986), and with the improved data handling capacity of modern computers, FT-iR spectroscopy has become the dominant method for determining milk composition in the dairy industry (Gunzler & Gremlich 2002).…”