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Protective influence of several packaging materials on light oxidation of milk.

Light-induced degradation reactions in milk create a serious problem for the dairy industry because of the development of off-flavors, the decrease in nutritional quality, and the severity and speed by which these phenomena develop. Packaging materials are essential to avoid this particular deterioration of milk. Therefore, efforts are being made to design protective polyethylene terephthalate (PET) packages. In the present study, a number of PET bottles were compared for their ability to avoid photo-oxidation in UHT semi-skimmed milk. The milk was packed in 3 types of PET bottles: one transparent bottle provided with an active oxygen-binding inner layer, one bottle with perfect light barrier, and one transparent bottle provided with a UV-absorbing additive. During 2 storage experiments, running parallel to each other for 2 mo, chemical milk quality parameters such as fat oxidation, vitamin and protein degradation, oxygen consumption, and color change were monitored. A trained taste panel compared the sensory quality of the illuminated milk stored in these bottles, with milk perfectly protected against light and oxygen. In the first study, milk was continuously illuminated at room temperature. A comparison was made for milk under storage conditions that simulated those expected during display in retail and supermarkets. The results of the 2 shelf-life studies showed that an adequate light barrier was apparently sufficient to avoid the light-induced oxidation of milk during extended storage. Oxygen barriers, on the other hand, did not provide a significant protection, nor did bottles with UV filter. If wavelengths detrimental to riboflavin were not completely excluded by the packaging material, incoming light could still give rise to photo degradation of milk. Accordingly, riboflavin and vitamin A were gradually degraded, milk fat was photo-oxidized, oxygen dissolved in the milk was consumed, and the sensorial quality decreased significantly.