Investigation of the effects of season, milking region, sterilisation process and storage conditions on milk and UHT milk physico-chemical characteristics: a multidimensional statistical approach.

摘要

Milk samples were collected in five dairy plants located in different regions of France (North, North-West, South-West and centre of France), during spring and autumn, at receipt (bulk-raw milk), and following pasteurization and UHT sterilisation. Corresponding UHT milks were then stored at three temperatures (4, 20 and 40.C) and analysed after different times (21, 42, 62, 90, 110 and 180 d). The physico-chemical characteristics of these different milks, including composition, micellar properties and stability as assessed by heat, ethanol and phosphate tests, were determined. The database was processed by principal component analysis and common components and specific weights analysis. The effects of season, milking zone, process and storage conditions were highlighted, and the involved physico-chemical characteristics were determined. For the region effect, numerous parameters related to the global composition and the casein micelles intervened. Some differences in milk stability as evaluated by the ethanol and phosphate tests were also observed. Considering the season, spring milks had higher values of pH, lactose, soluble phosphate and micellar hydration than milks collected in autumn. These spring milks also had lower values of fat and heat stability than autumn milks. The UHT process effect was observed through decreases in non-casein nitrogen content and in micellar hydration and by an increase in casein micelle size for UHT milks. The stability values derived from phosphate and ethanol tests were increased following the UHT process. Concerning storage conditions, the temperature of 40.C led to a decrease in pH and increases in non-casein and non-protein nitrogen contents of milks. At 40.C, low values of stability for the heat test and high values for the phosphate test were observed.