Effects of Zygosacharomyces mellis and post-fermentation on the flavor of black glutinous rice wine

Abstract: Flavor of black glutinous rice wine depends significantly on starter cultures and the post-fermentation conditions. In this study, a systematic investigation was made to explore the effects of brewing koji (wheat koji, wheat koji+angie yeast and wheat koji+Zygosacharomyces mellis) and post-fermentation(time and temperature) on the flavor of black glutinous rice wine, where the amino acids, organic acids, and volatile aroma components were determined using gas chromatography-mass spectrometry (GC-MS) and high performance liquid chromatography (HPLC). Angie yeast and Zygosacharomyces mellis were added to the wheat koji for co-fermentation. The lactic acid of black glutinous rice wine that prepared by Z. mellis and wheat koji accounted for 20% of the total organic acid, lower than that prepared by wheat koji and its combination with angie yeast（P<0.05）. Z. mellis was found to inhibit the excessive accumulation of lactic acid, while to increase content of malic acid (2.5 mg/mL) and succinic acid (1.1 mg/mL) （P<0.05）, bringing the overall compatible flavors to the black glutinous wine. Meanwhile, the content of amino acids was 113 mg/L in the black glutinous rice wine prepared by Z. mellis with wheat koji, which was significantly higher than that prepared by wheat koji. In addition, it was found that aldehydes were the main volatile flavor substances in black glutinous rice wines that prepared by three different starter cultures. The relative contents of furfuraldehyde were 9.11 % and 10.00 % in black glutinous rice wine that prepared by angie yeast and Z. mellis starters, respectively, twice as much as that prepared by wheat koji（P<0.05）. Therefore, the flavors of black glutinous rice wine that prepared by Z. mellis starter group was better than that prepared by other two groups. Z. mellis combined with wheat koji was used to produce black glutinous rice wine, in order to further investigate the effects of post-fermentation time and temperature on the flavor of black glutinous rice wine. After 30 days of post-fermentation, the content of amino acids was highest with 1073 mg/mL in the wine, and the content decreased and kept stable at 40 days of fermentation. Meanwhile, it was found that the bitter amino acids in the wine rapidly decreased at 40 days of fermentation. Besides, the varieties and contents of organic acids in the wine were more coordinated, and the relative contents of alcohols, esters and aldehydes in the volatile aroma components were the highest (85.7%). Therefore, the flavor of black glutinous rice wine was best at 40 days of fermentation. When the post-fermentation temperature was 20 ℃, the content of amino acids was 229 mg/L with only 8 kinds of amino acids. At 24 ℃, the total content of amino acids reached 383 mg/L and the varieties of amino acids increased to 13. The relative content of esters and aldehydes reached the highest in the black glutinous rice wine at this temperature. The post-fermentation temperature of 24 ℃ was favorable for the accumulation of amino acids and main volatile flavor substances. Therefore, this finding can provide a sound reference to improve the flavor of black glutinous rice wine using Zygosacharomyces mellis.