| Brandy is one of the world’s famous distilled spirits,which is made by fruit fermented,distilled,aged and blended,and the ethanol content is usually around 40%v/v.The quality of brandy is determined by the variety and content of its aroma components.At present,the use of non-Saccharomyces cerevisiae to improve the flavor of wine is a hot topic.Therefore,in this paper,Torulaspora delbrueckii NCUF305.2and Saccharomyces cerevisiae NCUF309.2 were used as experimental strains.The pure fermentation of S.cerevisiae NCUF309.2 was the control group(PF),and mixed fermentation by S.cerevisiae NCUF309.2 and T.delbrueckii NCUF305.2 were the experimental group(MF).The effect of T.delbrueckii NCUF305.2 on the flavor of navel orange original brandy by alcoholic fermentation and secondary distillation of navel orange juice was explored.The main findings are as follows:(1)T.delbrueckii NCUF305.2 with different inoculation ratios and S.cerevisiae NCUF309.2 were used to mix fermented navel orange wine to determine the optimal inoculation ratio of the two yeasts by evaluating their physicochemical properties,volatile compounds,and sensory properties.The results of yeast growth changes showed that when S.cerevisiae NCUF309.2 and T.delbrueckii NCUF305.2 were co-inoculated for fermentation in a ratio of 1:10(MF2),the growth of S.cerevisiae NCUF309.2 was almost unaffected,and T.delbrueckii NCUF305.2 grew well,and the number of viable cells could reach 4.37×10~7 CFU/m L.The results of the physicochemical properties showed that the ethanol contents of navel orange wines were increased by mixed fermentation.Moreover,after mixed fermentation,the methanol contents of navel orange wines were significantly reduced by 15%-20%(P<0.05),and its organic acid content increased by 2%-4.5%.The result of HS-SPME-GC-MS showed that the total volatile compound content of navel orange wine in MF2exceeded that of the other three samples by 10%-23%.In particular,volatile compounds of OAV>1,such as isoamyl acetate,ethyl octanoate,2-methylbutyl acetate,phenethyl acetate,ethyl hexanoate,phenethyl alcohol,and citronellol.The results of sensory analysis showed that the four navel orange wines had statistically significant differences in taste and aroma(P<0.05),and they performed well in MF2.Therefore,when T.delbrueckii NCUF305.2 and S.cerevisiae NCUF309.2 were mixed,inoculated,and fermented at a ratio of 10:1,the two yeasts could cooperate to produce alcohol and aroma,which was of great significance for improving the flavor of navel orange wine.(2)The PF was the control group,and T.delbrueckii NCUF305.2 and S.cerevisiae NCUF309.2 were mixed fermentation with a 10:1 inoculation ratio as the experimental group(MF).The first distillation of two navel orange original wine was carried out respectively.Compared with navel orange original wine,the first distillation had enriched volatile compounds.The total volatile compound contents of the two kinds of navel orange original brandies showed a downward trend with the first distillation.Among them,ethyl acetate,ethyl butyrate,isoamyl acetate,ethyl hexanoate,ethyl benzoate,ethyl octanoate,ethyl caprate,ethyl laurate,ethyl myristate,and ethyl palmitate were the key esters in the early and middle stages of distillation,and phenethyl acetate played a key aromatic role throughout the first distillation process.Isoamyl alcohol and phenethyl alcohol exerted their respective aromatic roles before,during,and after distillation,respectively.α-Terpineol was the key terpene for two navel orange original brandies.Caprylic acid was the key fatty acid in the later stages of distillation.(3)Secondary distillation of the crude navel orange original brandy obtained from the first distillation was carried out.Compared with the first distillation,the variety of volatile compounds of the two kinds of navel orange original brandies decreased during the second distillation process,but they were accompanied by the formation of different new compounds and the accumulation of volatile compounds.At fractions 2-1,the total volatile compound content in MF was higher than in PF.Moreover,esters were the most important volatile components in this fraction,followed by alcohols.However,from fractions 2-2,alcohols became the largest volatile component until the end of second distillation.The key esters of fraction 2-1 in the two kinds of navel orange original brandies were ethyl acetate,ethyl butyrate,isoamyl acetate,ethyl hexanoate,ethyl benzoate,ethyl caprylate,phenethyl acetate,ethyl caprate,ethyl laurate,ethyl myristate,and ethyl palmitate.Moreover,the content of these 11 esters in different fractions of navel orange original brandy in MF was greater than that in PF.Ethyl hexanoate was a key ester in the second distillation of sample MF.Isoamyl alcohol and phenethyl alcohol were the key alcohols in the second distillation process.α-Terpineol was a key terpene after fractions 2-2 in both samples.(4)The head and tail of the crude navel orange original brandy were cut in the second distillation process and the basic physicochemical indexes of the navel orange original brandy obtained were analyzed.The results showed that the total acidity content was reduced by 56.52%,and the methanol content was reduced by 0.43%.The result of HS-SPME-GC-MS showed that the volatile compound content of navel orange original brandy in MF was significantly(P<0.01)higher than that of PF by17.57%,esters by 4.13%,alcohols by 21.93%(P<0.001),terpenes and other groups by52.07%and 40.99%(P<0.01),respectively.This showed that T.delbrueckii NCUF305.2 was beneficial to improving the volatile flavor of navel orange original brandy.Among them,the contents of key volatile compounds such as ethyl benzoate,ethyl octanoate,ethyl caprate,ethyl laurate,ethyl myristate,ethyl palmitate,and isoamyl alcohol were higher in MF.α-Terpineol was the key terpene in MF.Combined with an electronic nose and multivariate statistical analysis,the sensitivity of navel orange original brandy to nitrogen oxides,methyls,ammonia,aromatic compounds,and alkanes increased after mixed fermentation,and the correlations between the W1S(sensitive to methane)and W5S(mainly nitrogen and oxygen compounds)sensors and the sample MF were stronger.Sensory analysis showed that sample MF showed better citrus-like flavor and higher scores in overall perception. |
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