Volatile Organic Compounds in Japonica Rice and Their Influence on Flavor Substances and Sensory Characteristics of Beer

Nine widely cultivated japonica rice varieties in China was chosen as materials. The volatile organic compounds (VOCs) were analyzed by HS-SPME-GC-MS, and the clustering of varieties and key VOCs was carried out by heat map analysis. By using the beer with whole wheat additive as control, the VOCs and sensory characteristics of the beer with fragrant japonica rice additive were analyzed. The results showed that the total amount of VOCs in DHX and NG9108 were relatively higher than other varieties ( P < 0.05). The popcorn-flavored substance 2-acetyl-1-pyrroline was detected in SG27 (26.80 ng/g), DHX (25.25 ng/g), NG9108 (21.18 ng/g), and SG18 (11.62 ng/g) with the former three varieties significantly higher that the latter one. In addition, DHX had higher amount of nonanal (96.02 ng/g), benzaldehyde (26.57 ng/g), 2-pentyfuran (20.41 ng/g), and geranylacetone (12.58 ng/g), and NG9108 had higher amount of 4,7-dimethyl undecane (59.97 ng/g) and 1-octen-3-ol (12.78 ng/g). The total content of VOCs in LK2021, JG818, and LG31 was relatively low. Through the circular heat map analysis, 9 japonica rice varieties could be classified into three major categories: fragrant japonica rice form north China (DHX), fragrant japonica rice from south China (NG9108), and others. 10 characteristic VOCs of different japonica rice varieties were explored. They were nonanal, hexanal, 2-acetyl-1-pyrroline, 1-octen-3-ol, 2-pentylfuran, 1-(2-methoxy-1-methylethoxy)propan-2-ol, 2,3-butanediol dinitrate, geranylacetone, benzaldehyde, and 4,7-dimethyl undecane. It found that rice VOCs were not detected in the beer brewed with fragrant japonica rice as an additive. The additive of rice could promote the formation of banana flavor and reduce the rich and mellow taste of beer. It could help understand the differences in VOCs among widely cultivated japonica rice varieties in China, and also provide new insights into the flavor formation in rice-based beer brewing, promoting the development of deep processing applications of rice.