Determination of whey protein to total protein ratio in UHT milk using fourth derivative spectroscopy

Abstract

A fourth derivative spectroscopy method was applied for the quantification of whey protein to total protein ratio in UHT milks. Some analytical features such as model compounds, selection of wavelength, linearity, repeatability and interference of milk fat were studied. The effect of refrigerated storage of raw milk, UHT treatment, and storage of UHT milk at room temperature on whey protein to total protein ratio was evaluated. No significant (p<0.05) differences among samples were found in any case. The ratio of whey protein to total protein was also determined in batches of whole (n=28) and skimmed (n=27) commercial UHT milks from different Spanish geographic areas processed by direct or indirect UHT systems in different periods of the year. The mean value was 18.1% for both whole and UHT skimmed milks. The analysis of laboratory-made mixtures of UHT milk with acid and rennet whey (2.5–15% of whey in milk expressed in protein) indicated that adulterations of UHT milk with whey up from 5% could be detected by the proposed method.