Commodity and innovative analysis to monitor the quality of UHT milk during storage

The storage of the UHT milk results in physicochemical changes, which can sometimes lead to milk aggregation or sedimentation. The consumers can easily perceive the alteration of the sensory properties, by the formation of volatile compounds, resulting from degradation and lipid oxidation reactions. GC-MS (Gas Chromatography-Mass Spectrometry) technique, applied to volatile organic compounds (VOCs), allows their characterization and quantification, as relative abundance, in food samples. Moreover, the smaller size of fat globules and the high Z potential are both related to a lower susceptibility to agglutination and can then provide useful information on the product stability. The aim of the present research was: i) the collection of a series of commodity data and technical information about the milk storage, and ii) the identification of suitable parameters, useful to monitor and to increase the shelf-life of the UHT milk, from the actual values of 3-4 months until to 10 months. An accelerated ageing protocol was applied, to evaluate the product stability as a function of direct and indirect UHT treatment. Solid Phase Micro Extraction (SPME) was used as the sampling technique since it is reported to be a sensitive and reproducible tool for the collection of a broad range of metabolites, correlated to the organoleptic properties and oxidative phenomena, such as methyl ketones and fatty acids. Z potential values decreased from -39, -43 mV to about -30 mV in non-compliant samples. Other parameters, such as pH, NH3, lactic acid concentration, gel precipitation, surfacing of fats, viscosity and organoleptic were suitable till 11 months of shelf-life and the UHT milk obtained with the indirect method (143°C and 150 bar) showed the best results. Finally, the accelerated ageing protocol can be actually used as a predictive method for milk stress and stability over time, depending upon the production technology. An increased shelf life of UHT milk can be hopefully exploited by dairy product companies, which could increase the export of their products in Eastern Countries, where the demand for Italian milk is rapidly growing.