Study On The Changes Of Physicochemical Index And Antioxidant Activity During The Pitaya Wine Fermentation Process

With red pitaya as raw material,four commercial saccharomyces cerevisiae(R2,D254,DV10,RC212)were selected for the selection of the optimal yeast during the pitaya wine fermentation with clarified juice or with slag process.On the basis of selecting the fermentation with clarified juice,studying on pigment stability and changes in antioxidant activity under different citric acid concentration,different sugar levels and different clarifying agent.The main experimental results are as follows:(1)For pitaya wine fermented with clarified juice.the results showed that the fermentation rate of R2 yeast was faster than the others,the alcohol content was 11.57%,betanin content was 100.143 mg/L,polyphenol content was 272.521 ?g/mL,among the antioxidant activities,the IC50 of DPPH scavenging rate was 24.92%,the IC50 of hydroxyl radical scavenging rate was 8.84%and the IC50 of reducing power was 28.52%,significantly higher than other three yeasts.At the end of fermentation,the change of L*was not significant,a*rised and the b*decreased.(2)For pitaya wine fermented with slag,the results showed the alcohol content was 11.27%,betanin content was 89.509 mg/L,polyphenol content was 265.656 ?gg/mL,among the antioxidant activities,the IC50 of DPPH scavenging rate was 23.77%,the IC50 of hydroxyl radical scavenging rate was 14.24%and the IC50 of reducing power was 31.06%,higher than other three yeasts,but significantly lower than the pitaya wine fermented with clarified juice.At the end of fermentation,the L*change was not significant,the a*of the pitaya wine fermented with slag was lower than the pitaya wine fermented with clarified juice,theb*was significantly higher than the pitaya wine fermented with clarified juice.(3)Study on the change of the organic acids and volatile substances of pitaya wine fermented with clarified juice.After the fermentation,the content of organic acids increased in different degrees,the content of oxalic acid,tartaric acid,citric acid and succinic acid were higher in the pitaya wine fermented by RC212 yeast,the content of malic acid was higher in the pitaya wine fermented by R2 yeast,the content of oxalic acid,tartaric acid content were higher in the pitaya wine fermented with clarifying juice.For the volatile substances,ethyl acetate,ethyl caproate and ethyl octylic acid and decanoic acid ethyl ester were the main esters in the pitaya wine,the content of ester in the pitaya wine fermented by D254 yeast was high.Besides ethanol,the main alcohols in the pitaya wine were phenyl alcohol,isobutanol,isoamyl alcohol,dimethyl butanol,dimethyl butanol and dimethyl sidiol,the content of alcohol in the pitaya wine fermented by R2 yeast was high.There were three main kinds of volatile acids in the pitaya wine:acetic acid,caproic acid and caprylic acid,the content of caprylic acid was high in the pitaya wine fermented with clarifying juice.The main carbonyl compound was acetaldehyde.(4)Study on the change of the organic acids and volatile substances of pitaya wine fermented with slag.After the fermentation,the content of a-ketoglutaric acid and acetic acid were higher in the pitaya wine fermented by R2 yeast,the content of malic acid was higher in the pitaya wine fermented by D254 yeast,the content of tartaric acid was higher in the pitaya wine fermented by DV10 yeast,the content of acetic acid,citric acid and succinic acid in the pitaya wine fermented with slag were high.For the volatile substances,the content of esters and alcohol were lower than the pitaya wine fermented with clarified juice,and the content of acetic acid and acetaldehyde were higher than the pitaya wine fermented with clarified juice.The results showed that the fermentation with clarified juice method was suitable for pitaya wine fermentation.(5)On the basis of the fermentation with clarified juice,under the condition of different citric acid concentration,the pH of no citric acid addition pitaya wine was 4.53,under this condition,the betanin content,polyphenol content and antioxidation activity of the pitaya wine were better than other additives,pigment retention rate was about 89.88%;Under the condition of different sugar content,the difference of betanin content was not significant,but with the increasing of sugar,the concentration of betanin content in the pitaya wine decreased.when the sugar is 17%,the betanin content,polyphenol content and antioxidant activity of pitaya wine were better than other concentration,pigment retention rate was about 89.19%;Under the condition of different color fixative type(Sodium hexametaphosphate,D-isoascorbic acid sodium,L-cysteine,disodium hydrogen phosphate,tea polyphenols and ascorbic acid),the betanin content,polyphenol content and antioxidant activity of pitaya wine which adding ascorbic acid were higher than other color fixatives,and when the concentration of ascorbic acid is 0.1%,the betanin content was the highest,pigment retention rate was about 95.62%.(6)On the basis of the fermentation with clarified juice,under the treatment of different clarifying agents(agar,gelatin,chitosan,pvpp,bentonite and diatomite),the content of betanin content and polyphenol content in the pitaya wine were significantly reduced.The clarity of the pitaya wine under treatment of gelatin was the highest,the light transmittance was 88.14%,but the loss of the betanin content was also the most serious.The betanin content,polyphenol content and antioxidant activity of the pitaya wine under treatment of pvpp were better than other five clarifying agents,under the concentration of 1.0 g/L,the betanin content was the highest,pigment retention rate was about 95.3%.