Evaluation of polyethylene terephthalate as a packaging material for premium quality whole pasteurized milk in Greece

Chemical, microbiological, and sensorial changes in premium quality whole pasteurized milk stored at 4 °C under fluorescent light for one day followed by storage in the dark for an additional 12 days was studied. Milk containers tested included 1 l bottles made of (a) clear PET + UV blocker, 350-400μm in thickness bearing a transparent label, (b) clear PET + UV blocker, 350-400 μm in thickness bearing a white colored label, (c) clear PET 350-400 μm in thickness. Milk packaged in 1 l coated paperboard cartons and stored under the same experimental conditions served as the “commercial control” sample. Data were obtained for lipid oxidation, lipolysis, proteolysis, vitamin A, E, and riboflavin content, microbial growth including mesophilic and psychrotrophic counts and sensorial attributes (odor and taste) of whole pasteurized milk. Results showed satisfactory protection of milk packaged in all containers with regard to microbiological and chemical parameters assessed over the 13 day period. Based on sensory analysis, the shelf life of premium quality whole pasteurized milk tested in the present study was 10-11 days for samples packaged in clear PET+UV bottles and 9-10 days for clear PET bottles and paperboard cartons. Vitamin A losses recorded after 10 days of storage were respectively 15.9, 20.6, and 14.3% for samples packaged in clear PET+UV protected bottles, clear PET, and control samples. Respective losses for Vitamin E were 26.4, 36.6, and 35.0% and for riboflavin 32.9, 38.3, and 32.5%. Clear PET + UV provided equal or better protection to milk as compared to the paperboard carton. Clear PET was the least effective in retaining light-sensitive vitamins. Based on spectral transmission curves of packaging materials tested, it is suggested that the use of a UV blocking agent in combination with a dark color pigmentation (blue, green etc.) in fresh milk packaging will provide a better protection to light-sensitive vitamins in cases where the expected shelf life of milk exceeds 5-6 days.