Milk is one of the most important dietary products which contains nearly all the nutrients necessary to sustain life [1]. Being a complex natural fluid in which water is a major constituent, milk contains varying quantities of lipids, proteins and carbohydrates as well as smaller amounts of minerals and other fat-soluble or water-soluble components [2].
Another vibrational spectroscopy technique, Raman spectroscopy, is suitable for the analysis of solid and liquid samples, providing qualitative and quantitative data [10], [11] and [12]. It is a non-destructive analytical method, where studied objects require no special preparation and the spectra are recorded for samples in their native state, significantly simplifying analyses. An important advantage to this method is that Raman data can be collected for substances placed in glass and polymer packaging [13], and may have potential applications in the milk industry.
Raman spectroscopy has been used for quality control and quantitative analysis of powdered milk constituents [14] and [15], and to screen samples adulterated with whey [16] and [17] and melamine [18] and [19]. In the case of liquid milk samples, Raman spectroscopy in combination with gel filtration was utilised to detect whey proteins in milk [20]. However, the widespread application of Raman analysis to liquid milk samples is hampered by the low intensity of its spectra, which are dominated by water bands. The spectral contributions of the remaining constituents in milk, accounting for little more than a few percent of the liquid mass, are weak.
Raman spectra of liquid milk samples are usually characterised by a poor signal to noise (S/N) ratio which makes traditional univariate analyses difficult to perform. To overcome these limitations and extract relevant information from spectral data, chemometric methods can be utilised [21]. The use of multivariate data analysis techniques often yield robust calibration models, even for noisy systems poorly modelled by univariate techniques [22] and [23]. Raman spectroscopy in conjunction with PLS modelling was applied to quantify fat in liquid milk samples [24].
This study used FT-Raman spectroscopy to simultaneously quantify fat, protein, carbohydrates and dry matter, the main components of milk. These results were compared to data obtained using a single reflection ATR accessory.