Impact of cooling rates on the flavor of cooked rice during storage

This study aimed to evaluate the impact of cooling rates (0.19, 1.27, 1.74 and 2.88°C/min) on the flavor of cooked rice during storage. The results obtained from flash gas chromatography electronic nose and sensory analysis showed that higher cooling rates prolonged rice fragrance retention, whereas faster deterioration of flavor acceptability of cooked rice was observed at lower cooling rates during storage. The contribution of 43 flavor compounds in cooked rice was validated in three parallel tests by gas chromatography-mass spectrometry combined with principal component analysis, which indicated that 2-acetyl-1-pyrroline and alcohols contributed to the fragrance, while aliphatic aldehydes (at high concentration), benzene derivatives, and acids were responsible for flavor deterioration. Partial least squares regression further identified that eight flavor compounds [(E,E)-2,4-decadienal, 2-butyl-2-octenal, 1-hexanol, 2-propyl-1-pentanol, 2-butyl-furan, geranylacetone, 2-acetylthiazole, and 2-acetyl-1-pyrroline] had significantly positive contributions to sensory evaluations, while nine flavor compounds [hexanal, octanal, (E)-2-octenal, decanal, (E)-5-methyl-4-hepten-3-one, n-hexadecanoic acid, ethylbenzene, o-xylene and p-xylene] had significantly negative contributions to sensory evaluations during storage (p < 0.05). The water migration and/or starch crystallization of cooked rice during storage affected by cooling rates were supposed to affect the release of the flavor compounds. These findings could provide a reference for the flavor preservation of instant rice.