Volatile compounds and chemical changes in ultrapasteurized milk packaged in polyethylene terephthalate containers

摘要

The volatile compounds profile and chemical stability of ultrapasteurized 2% milk bottled in amber polyethylene terephthalate (PET) were studied along with its shelf life of 60 d at 5 degrees C. Identification of volatile compounds using a solid-phase microextraction (SPME) technique with gas chromatography-mass spectrometry was performed in situ in the commercial product. Chemical stability was determined by measuring dissolved oxygen, free sulfhydryl groups, ascorbic acid, and headspace oxygen. The classes of volatile compounds identified were ketones, aldehydes, hydrocarbons, fatty acids, alcohol, and miscellaneous compounds. Volatile compounds found consistently during the storage period were 2-heptanone, methoxy-phenyl-oxime, decane, 1-ethyl-2,4-dimethylbenzene, D-limonene, 2-nonanone, octanoic acid, dodecane, and 4-(1,1,3,3,-tetramethylbutyl) phenol. Possible products of lipid oxidation, such as hexanal, octanal, and nonanal, were also positively identified. Chemical stability of PET-bottled milk was demonstrated by the insignificant changes in pH or TA, with the exception of ascorbic acid concentration, which degraded in the product at 60 d of refrigerated storage. Sensory evaluation of the milk samples revealed that there is no noticeable oxidized or rancid off-flavor at 60 d of storage.