Evaluation of aroma of pasteurized and UHT processed milk by aroma extract dilution analysis

For the purpose of examining the influence of pasteurization and UHT processing on the aroma of milk, aroma substances from extracts of raw milk, LTLT milk, HTST milk and UHT processed milks which were distilled under reduced pressure were analyzed by gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS) and aroma extract dilution analysis (AEDA). As a result, 101 compounds were identified or presumed. As the level of heating was increased, there was a significant increase in the concentrations of 2-pentanone, 2-heptanone, 2-nonanone and 2-undecanone. In addition, a large number of pyrazines were newly detected. In all of the milks, hexanoic acid, octanoic acid and decanoic acid were detected in large quantities. Those acids were from 8% to 24% of the total aroma concentration in each of the milks. Compounds contributing to milk odor according to the AEDA were shown in 70 locations on the gas chromatogram. Of those 70 locations, the flavor dilution (FD) factors of 44 were changed due to heating, while 26 were unchanged. Odors of 2, 6-dimethylpyrazine, 2-ethylpyrazine, 2-nonanone, 2-ethyl-3-methylpyrazine, methional, pentanoic acid, an unknown compound (Kovats index 1747), an unknown compound (Kovats index 1757), benzothiazole and vanillin were potent due to heating. Vanillin was potent in HTST milk, the unknown compound (Kovats index 1747) and the unknown compound (Kovats index 1757) in UHT milk. These were thought to characterize HTST milk and UHT processed milks respectively. The aromas which contribute to the odor of milk were not necessarily large in quantity.