The changes in quality indexes (pH, acidity, protein, fat, and lactose) of fresh yak milk during storage (1, 3, 6 days) at different temperatures (-18, 4, 20 ℃) were analyzed, at the same time, gas chromatography-ion mobility spectroscopy (GC-IMS) was used to determine the volatile flavor compounds in yak milk.Combined with chemometrics analysis, the differences in volatile substances of yak milk during storage at different temperatures were compared and the volatile substances related to the spoilage of yak milk were screened.Results showed that the fat content of yak milk changed significantly (P<0.05), while the other quality indexes did not change significantly at -18 ℃.The quality indexes of fresh yak milk were similar to those of fresh yak milk at 4 ℃ stored for 1 day and significantly changed at 3-6 days (P<0.05) but had significant changes (P<0.05) from the 1-day storage at 20 ℃.There were 46 kinds of volatile compounds in yak milk during storage, including ketones, esters, aldehydes, and alcohols.The results of principal component analysis and cluster analysis showed that the flavor of frozen samples at -18 ℃ was more similar to that of fresh yak milk, followed by refrigerated samples at 4 ℃ for 1 day and 3 days, and then refrigerated samples at 4 ℃ for 6 days and stored at 20 ℃ for 1 day, a marked deterioration in flavor was unacceptable.The results of the orthogonal partial least square discriminant analysis showed that 10 sances, 2-butanone, 3-hydroxy-2-butanone, 4-methyl-2-pentanone, hydroxyacetone, isovaleraldehyde, methyl tert-butyl ether, ethyl acetate, ethyl butyrate, tert-butyl alcohol, and pyridine were related to the spoilage of yak milk (VIP>1).This study can provide a theoretical basis for the rapid evaluation of the nutritional value and freshness of yak milk during storage.
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