Study On Control Of Fusel Oil Content In Pitaya Wine

With the development of modern society,the fruit wine industry is developing rapidly,and there are many types of fruit wines,which are more and more popular to the public.Pitaya wine is welcomed because of its nutritional value and pleasing colors.However,such problems as high fusel oil content,insufficient aroma and poor flavor in pitaya wine have seriously affected the quality of pitaya wine.In order to reduce the content of fusel oil and increase the aroma in pitaya wine,we first explored the best commercial Saccharomyces cerevisiae strain and the best non-Saccharomyces yeast strain for pitaya wine fermentation.Secondly,the effects of inoculation methods of Saccharomyces cerevisiae and nonSaccharomyces yeast at different ratios or sequences on the fusel oil and flavor were studied.Finally,the effects of fermentation process and parameters on the fusel oil content of pitaya wine were studied.The main results are as follows.(1)7 yeasts,including 5 commercial Saccharomyces cerevisiae(D254,BV818,DV10,RC212,EC1118)and 2 non-Saccharomyces yeasts(Metschnikowia agaves P3-3?Candida tropicalis P3-4),were inoculated in pitaya juice,respectively.The results showed that the fusel oil content of 231.58 mg/L,fermented by D254,was the lowest among the 5commercial yeasts,which was significantly lower than those by other commercial yeasts,and had the highest sensory score.The fusel oil content of 238.29 mg/L,fermented by P3-3,was significantly lower than that by P3-4,and showed the higher sensory score.(2)The mixed fermentation was investigated,considering the ratios of inoculum of S.cerevisiae D254 and M.agaves P3-3 at the same time or in different sequences,it was found that by inoculating S.cerevisiae D254 and M.agaves P3-3 simultaneously at the ratio of 1:1,the fusel oil content of pitaya wine was 183.10 mg/L,11.9% and 11.2% lower than that of S.cerevisiae D254 and M.cerevisiae P3-3 alone,respectively.And the wine showed the highest sensory score with a pleasant and unique flavor.(3)The solid phase microextraction-gas chromatography-mass spectrometry(SPMEGC-MS)technology was used to detect the volatile components of each wine sample,and the main component analysis(PCA),partial least squares-discriminant analysis(PLS-DA),and orthogonal partial least squares discriminant analysis(OPLS-DA)was used for multivariate statistical analysis.The results showed that the main differentially expressed metabolites were as follows: nonanoic acid,hexanoic acid,2,4-dihydroxybenzoic acid,ethyl phenylpropionate,isoamyl octoate,ethyl undecanoate,ethyl benzoate,Hexyl hexanoate,2-decanol,2-heptanol,and nonanal.(4)The effects of initial sugar content,initial p H,pectinase addition and nitrogen sources on fusel oil production were investigated.The results showed that the fusel oil content increased as the initial sugar content and p H increased with no change of the composition of the fusel oil,indicating that the initial sugar content and p H only affected the fusel oil production rate but not compositions of fusel oil.The fusel oil content reduced significantly by 8.1% by adding 50 mg/L pectinase.The fusel oil content was significantly higher by adding 100 mg N/L of alanine,arginine,respectively.When ammonium bicarbonate was added,the fusel oil content reduced significantly by 5.84%.No significant effect was found by addition of glycine or diammonium phosphate.The composition of fusel oil did not change significantly by adding different types of assimilable nitrogen except for valine.However,the proportion of isoamyl alcohol decreased significantly,while the proportion of isobutanol increased significantly while valine was added.