_ Food Science and Technology Research, 26 (3), 411 422, 2020 Copyright © 2020, Japanese Society for Food Science and Technology http://www.jsfst.or.jp doi: 10.3136/fstr.26.411 Original paper Characterization of Flavor Compounds in Rice-flavor baijiu, a Traditional Chinese Distilled Liquor, Compared with Japanese Distilled Liquors, awamori and kome-shochu 1 1,2* 2 3 2 4 Xuan YIN , Yumiko YOSHIZAKI , Shugo KURAZONO , Mina SUGIMACHI , Haruka TAKEUCHI , Xing-Lin HAN , 2 1,2 1,2 1,2 Kayu OKUTSU , Taiki FUTAGAMI , Hisanori TAMAKI and Kazunori TAKAMINE 1The United Graduate School of Agricultural Sciences, Kagoshima University, 1-21-24 Korimoto, Kagoshima City, 890-0065, Japan 2Education and Research Center of Fermentation Studies, Faculty of Agriculture, Kagoshima University, 1-21-24 Korimoto, Kagoshima City, 890-0065, Japan 3Graduate school of Agriculture, Kagoshima University, 1-21-24, Korimoto, Kagoshima City, 890-0065, Japan 4China National Research Institute of Food and Fermentation Industries, 24-6 Jiuxianqiao Road, Chaoyang District, Beijing 100096, China Received November 14, 2019 ; Accepted January 16, 2020 This study aimed to reveal the chemical and flavor profiles of rice-flavor baijiu by comparison with awamori and kome-shochu, traditional Japanese liquors. Rice-flavor baijiu is similar to awamori and kome- shochu with regard to ingredients and the fermentation starter. Of the 15 rice-flavor baijiu samples in this study, 3 had a light yellow to dark-brown color. Dark-brown samples had high glucose and low amino acid contents. Lactic acid was detected in all rice-flavor baijiu samples. Compared to awamori and kome-shochu, rice-flavor baijiu contained more acetic acid. Thirty-four volatile compounds in rice-flavor baijiu were identified and quantified. In all, 18 compounds in rice-flavor baijiu, 15 in awamori and 13 in kome-shochu had an odor activity value (OAV) of >1. Of these, 11 compounds showed a three-fold higher OAV in rice-flavor baijiu than in awamori and kome-shochu. Principal component analysis revealed that ethyl lactate is a key volatile compound that is distinct to rice-flavor baijiu. Keywords: Chinese distilled liquor, flavor, rice-flavorbaijiu , shochu, volatile compounds, ethyl lactate Introduction xiaoqu is added and mixed well (Fig. 1), and then the solid Baijiu is a traditional Chinese distilled liquor, and rice- mixture is incubated for 20–30 h at room temperature. After flavor baijiu is mainly produced in southern China. Rice-flavor incubation, water is added and the mixture is fermented in a baijiu is made from rice as the sole ingredient and xiaoqu as liquid state for 6–8 days. Finally, the fermented mash is the fermentation starter, which is comprised of rice powder and distilled in the liquid state. rice bran (Zheng and Han, 2016). A few types of microorganisms The manufacturing process of rice-flavor baijiu is very are present in xiaoqu, including Rhizopus sp., Mucor sp., and different from that of other types of Chinese baijiu (Fig. 1). yeasts (Zheng and Han, 2016). Those types of Chinese baijiu, such as strong-flavor baijiu, The rice-flavor baijiu manufacturing process involves sauce-flavor baijiu and light-flavor baijiu, are typically made of semi-solid-state fermentation (semi-SSF) (Zheng and Han, several cereals, such as sorghum, wheat and rice, and complex 2016). SSF is performed using a solid matrix in the absence of microorganisms from the natural mixed starter daqu. SSF is free water. Briefly, after steaming the rice, a small amount of performed for several months in a mud pit or earthen jars *To whom correspondence should be addressed. E-mail: [email protected] 412 X. YIN et al. Fig. 1. Schematic diagram of manufacturing of rice-flavorbaijiu , awamori and kome-shochu. (Zheng and Han, 2016). Many microorganisms, such as caproic 1996; Koseki and Iwano, 1998). Firstly, ferulic acid present in acid–producing bacteria, live in mud pits and earthen jars the rice cell wall is liberated by a ferulic acid esterase produced (Xiong et al., 2010), and this complex microbial flora by A. luchuensis during fermentation. Then, the ferulic acid is contributes to the flavor of the liquor (Wanget al., 2014a). transferred to 4-vinylguaiacol (4-VG) by heating during On the other hand, the manufacturing process of rice-flavor distillation. Finally, 4-VG is converted to vanillin by chemical baijiu is similar to that of awamori and kome-shochu, two transformation via oxidation during aging. pH and alcohol traditional Japanese distilled liquors. Awamori uses tane-koji as concentration during aging influence the chemical a fermentation starter, which is prepared from koji mold transformation of ferulic acid to vanillin. (Aspergillus luchuensis). Rice koji is a solid culture of koji Rice-flavor baijiu has a characteristically sweet aroma and mold grown on steamed rice for approximately 42 h. Rice koji, a clear aftertaste (Zheng and Han, 2016). Ethyl lactate and water and yeast seed culture are mixed and fermented in a β-phenylethyl alcohol are key volatile compounds liquid state for 10–12 days. After fermentation, the mash is characteristic of rice-flavor baijiu compared to other types of distilled in the liquid state. Kome-shochu is made from rice and baijiu (Jin et al., 2017). However, to date, no studies have rice koji prepared from A. luchuensis (Fig. 1). It is produced investigated the flavors specific to rice-flavor baijiu in according to the same method as for awamori, except that the comparison with awamori and kome-shochu. Okinawa main ingredients are added separately after the first Prefecture in Japan, the main production center of awamori, fermentation. and Guangdong and Guangxi provinces in China, the main Awamori flavor is typically expressed as koji-like, production centers of rice-flavor baijiu, are geographically mushroom-like, fruity, and sweet flavors. These descriptions close. Therefore, rice-flavor baijiu is important for are also contained in the flavor wheel of awamori (Miyamoto, understanding the historical and technical relationships 2018). Kome-shochu has a characteristic fruity flavor between Chinese and Japanese distilled liquors. Knowledge of (Hayashida, 1998). Isobutyl alcohol, 1-octen-3-ol, nerolidol the chemical and flavor profiles of rice-flavor baijiu will assist and S-methyl thioacetate are the key volatile compounds in in understanding the similarities and/or differences between awamori compared to other Japanese shochu types (Fukuda et Chinese and Japanese distilled liquors. al., 2016). In particular, 1-octen-3-ol, which is derived from This study aimed to determine the characteristic flavor rice koji, imparts the mushroom-like flavor to awamori compounds of commercially available rice-flavor baijiu in (Yoshizaki et al., 2010). Vanillin, the most studied volatile comparison with awamori and kome-shochu. First, the compound in awamori, contributes to the sweet aroma and is concentrations of alcohol, sugar, amino acids, and organic produced by biochemical and chemical reactions (Koseki et al., acids in rice-flavor baijiu were measured by high-performance Flavor Compounds of Rice-flavor baijiu 413 Table 1. Sample informations used in this study. Sample Aging periods Alcohol† Types of liquor Region, Country Company Distillation type Name (years) (%, v/v) S1 Rice-flavor baijiu Guangxi, China A 5 Atmospheric* 35 S2 Rice-flavor baijiu Guangxi, China A Non aging* Atmospheric* 30 S3 Rice-flavor baijiu Guangxi, China B 18 - 49 S4 Rice-flavor baijiu Guangxi, China C 18 - 53 S5 Rice-flavor baijiu Guangxi, China D 5 - 49 S6 Rice-flavor baijiu Guangxi, China D - - 46 S7 Rice-flavor baijiu Guangxi, China D - - 48 S8 Rice-flavor baijiu Guandong, China E 5 Atmospheric* 48 S9 Rice-flavor baijiu Guandong, China E Non aging* Atmospheric* 52 S10 Rice-flavor baijiu Guandong, China F Non aging* - 49 S11 Rice-flavor baijiu Guandong, China F 10 - 54 S12 Rice-flavor baijiu Guandong, China F 5 - 48 S13 Rice-flavor baijiu Guandong, China G - - 47 S14 Rice-flavor baijiu Liaoning, China H - - 50 S15 Rice-flavor baijiu Liaoning, China H - - 54 A1 Awamori Okinawa, Japan <3* Atmospheric 30 A2 Awamori Okinawa, Japan <3* Mixture of vacuum and atmospheric 30 A3 Awamori Okinawa, Japan <3* Vacuum 20 A4 Awamori Okinawa, Japan <3* Atmospheric 30 A5 Awamori Okinawa, Japan <3* Mixture of vacuum and atmospheric 30 A6 Awamori Okinawa, Japan <3* Atmospheric 30 K1 Kome-shochu Kumamoto, Japan 3~5 months* Vacuum 25 K2 Kome-shochu Kumamoto, Japan <3* Mixture of vacuum and atmospheric 25 K3 Kome-shochu Kumamoto, Japan 3~5* Atmospheric 25 K4 Kome-shochu Kumamoto, Japan <3* Vacuum 25 K5 Kome-shochu Kumamoto, Japan 3* Vacuum 25 †Alcohol content of each sample was measured in our labolatory. Awamori and Kome-shochu samples are made by all different companies. Aging periods were described what was entered in to the package. “-” means we don’t have any information about aging time. *These informations were confirmed with each company directly. liquid chromatography (HPLC). Next, the concentrations of Japan). Bromothymol blue, neutral red, phenolphthalein, lactic volatile compounds in rice-flavor baijiu were measured by gas- acid, acetic acid, p-toluenesulfonic acid monohydrate, and bis- chromatography mass spectrometry (GC-MS) analysis in Tris were acquired from FUJIFILM Wako Pure Chemical comparison with awamori and kome-shochu. Finally, the Corp. (Osaka, Japan). Ethylenediaminetetraacetic acid (EDTA) characteristic flavor compounds in rice-flavor baijiu were was acquired from Dojindo Laboratories (Kumamoto, Japan). determined by principal component analysis of the quantitative Authentic standards for GC-MS were purchased from several results of volatile compounds of rice-flavor baijiu, awamori, companies as follows. Isobutyl alcohol, isoamyl alcohol, and kome-shochu. 1-hexanol, decanoic acid, dodecanoic acid, ethyl isovalerate, ethyl stearate, isoamyl caproate, isoamyl caprylate, isobutyl Materials and Methods caprylate, phenylethyl acetate, phenylethyl butyrate, and Liquor samples and chemicals Fifteen different 2-pentyl furan were purchased from FUJIFILM Wako Pure commercial rice-flavor baijiu were purchased from a local Chemical Corp.