| Selenium is an essential trace element for human beings,and selenium deficiency is closely related to the occurrence of more than 40 diseases which seriously threaten human health.About 70% China soil has insufficient selenium content and uneven distribution,resulting in about 1/3 of Chinese daily selenium intake is much lower than the recommended value.Huangjiu is a kind of alcoholic beverage made from glutinous rice,wheat starter and other grains through the steps of soaking,steaming,fermentation,raking and decocting.Saccharomyces has a good ability to enrich and transform selenium.Organic selenium can be released into wine by Saccharomyces through autolysis at the late brewing stage,and the selenium content of Huangjiu can be significantly increased,which is a promising method for developing selenium-rich food.Because of the toxicity of inorganic selenium,it is not allowed to be directly used in the fermentation of Huangjiu.Meanwhile,the application of organic selenium in the production of selenium-rich food is limited because its long production cycle and high cost.Nano-selenium is a non-toxic source of selenium with zero valence,high bioavailability and relatively low cost.In this paper,the effects of nano-selenium on the quality of Huangjiu and the fermentation performance of Saccharomyces cerevisiae as well as the relevant mechanisms were investigated,in order to provide data support and theoretical basis for the production of selenium-rich Huangjiu with nano-selenium.(1)The effects of nano-selenium on fermentation process and quality of Huangjiu were evaluated by means of fermentation parameters analysis,atomic fluorescence spectrometer(AFS),atomic absorption spectrometer(AAS),high performance liquid chromatography(HPLC)and antioxidant analysis.The results showed that the total selenium and organic selenium in the Huangjiu prepared by nano-selenium were7.73～44.44 times and 7.53～41.18 times higher than that in the control group.When the addition of nano-selenium in Huangjiu was 1 mg/L and 2 mg/L,the conversion rate of organic selenium was higher than 95%.The addition of 1～3 mg/L nano-selenium could promote the growth of microorganisms during fermentation,accelerate the consumption of reducing sugar and increase the alcoholic strength and amino acid nitrogen content.However,high concentration of nano-selenium caused the total acid in Huangjiu to be excessive.In conclusion,the Huangjiu supplemented with 2 mg/L nano-selenium had the best antioxidant activity and food safety,the total phenol and total flavone increased by 11.22% and 17.42%,and the total biogenic amine content decreased by 34.73% compared with the control group.(2)The effects of nano-selenium on the flavor of Huangjiu were evaluated by HPLC,colorimeter,quantitative description analysis(QDA)and gas chromatographymass spectrometer(GC-MS).The results showed that adding 2 mg/L nano-selenium could improve the taste intensity of bitter(7.76%),sour(5.53%)and umami(6.96%)amino acids in Huangjiu,while the taste intensity of sweet(2.38%)amino acids was slightly decreased.The addition of nano-selenium increased the color index a* and b*,but decreased the brightness value L*.The addition of 1～3 mg/L nano-selenium could increase the total volatile compounds in Huangjiu by 10.37% ～ 40.58%,and the OAVs of 28 main aroma-active compounds in 2 mg/L nano-selenium addition group were significantly increased,which improved the aroma characteristics of fruity,caramellike,cellar fragrance and medicinal aroma.However,high concentration of nanoselenium(4 mg/L)had a negative effect on the flavor of Huangjiu.(3)The mechanism of nano-selenium enhancing ethanol tolerance of S.cerevisiae was preliminarily elucidated by the indexes of viable bacteria count,malondialdehyde(MDA),antioxidant enzyme activity,trehalose,cell membrane permeability and cell morphology under ethanol stress.The results showed that the supplementation of 1～3mg/L nano-selenium increased the number of viable bacteria and reproductive rate of S.cerevisiae under ethanol stress.Nano-selenium could reduce the content of MDA in cells and relieve the degree of lipid peroxidation.The improvement of antioxidant enzyme activity of S.cerevisiae by nano-selenium followed the rules: glutathione peroxidase(GSH-Px)> superoxide dismutase(SOD)> catalase(CAT).But,nanoselenium had no significant effect on trehalose content in S.cerevisiae under ethanol stress.The addition of 2 mg/L nano-selenium could reduce the permeability of S.cerevisiae cell membrane under ethanol stress,relieve the phenomenon of holes and folds in cells,and make the cell morphology plump.(4)The effects of 2 mg/L nano-selenium on the growth and metabolism of S.cerevisiae under ethanol stress were further analyzed by transcriptomics.The results showed that 186 genes of S.cerevisiae with nano-selenium added were down-regulated and 222 genes were up-regulated under ethanol stress.Nano-selenium could regulate the differential expression of related genes in carbon metabolic pathway,pentose phosphate pathway,glycolysis/gluconeogenesis pathway to enhance S.cerevisiae fermentation ability and carbon source utilization in ethanol stressed environment.Nano-selenium could enhance the ability of anti-oxidative stress and self-repair and improve the ethanol tolerance of S.cerevisiae through the differential expression of related genes in starch and peroxisome pathway,arginine biosynthesis pathway,yeast autophagy pathway and MAPK signaling pathway.In summary,nano-selenium not only significantly improved the selenium content and quality of Huangjiu,but also improved the fermentation performance of S.cerevisiae,which provided a theoretical basis for the application of nano-selenium in fermented alcoholic beverages. |
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