Studies On The Application Potential Of Optimized Pichia Fermentans In Reducing Acid During The Fermentation Of Citrus Wine

Citric acid is the main organic acid in citrus wine,and its high content will cause a sour taste.It is of great significance to select yeast which can degrade citric acid to solve the problem of high acidity of citrus wine.In this study,eight strains of Pichia fermentans were evaluated for their fermentation characteristics and citric acid metabolic ability,and potential strains with strong citric acid metabolism were screened out.The selected strains mixed with Saccharomyces cerevisiae were fermented to simulate juice through different mixed inoculation methods to explore the application potential of optimized mixed fermentation combination in citrus wine,in order to provide theoretical guidance for biodeacidification of citrus wine.The main research results are as follows:(1)Selection of yeasts that can reduce citric acid and study on fermentation characteristicsUsing S.cerevisiae RV002 as a control,eight strains of P.fermentans(JT6-2,JT1-3,JT20-4,JP17-2,JT1-5,JP17-1,JT20-3,JST8-2)previously selected in the laboratory were individually inoculated in simulated juice to assess the fermentation characteristics and the ability to metabolize citric acid.The results showed that the citric acid metabolic rates of JT6-2,JT1-3 and JP17-1 were 33.61%,31.21% and 14.66%,respectively,which were higher than those of other yeasts.In addition,the maximum carbon dioxide cumulative weight loss of these three strains were 9.86±0.03 g,13.76±0.59 g and 10.52±0.39 g,respectively,with faster fermentation rates.The fermentation process of JT1-3 and JP17-1were more completed,completing at 312 h.Therefore,JT6-2,JT1-3 and JP17-1,which have the potential in wine fermentation,were selected for the next experiment.(2)Effects of different inoculation methods on the reduction of citric acid by yeastP.fermentans JT6-2,JT1-3 and JP17-1 were mixed with RV002 in simulated juice,respectively.Four experimental treatments were set as simultaneous inoculation(inoculation ratio are 1:1 and 10:1)and sequential inoculation(inoculated with P.fermentans first and followed by S.cerevisiae after 48 h,inoculation ratio are 1:1 and 10:1).The dynamic changes of the number of yeast,cumulative carbon dioxide weight loss,p H,total sugar content,citric acid content and malic acid content were analyzed during fermentation process,and the main physicochemical indexes after fermentation were determined.The results showed that compared with single inoculation,the mixed inoculation group significantly reduced the residual sugar content,shortened the fermentation time,and improved the alcohol content of the simulated wine.At the end of fermentation,the p H value of each treatment group was between 3.15 and 3.46,the total acid content was between 12.57 g/L and 14.86 g/L,and the alcohol content was between6.90% vol and 10.60% vol.The metabolism rate of citric acid in sequential inoculation of JT6-2 and RV002 with a ratio of 1:1,sequential inoculation of JT1-3 and RV002 with a ratio of 1:1,simultaneous inoculation of JP17-1 and RV002 with a ratio of 10:1 was higher than that of other fermentation groups,which were 16.05%,15.10% and 11.15%,respectively.These three inoculation methods were chosen for citrus wine according to their ability to metabolize citric acid.(3)Effects of mixed inoculation fermentation on the quality of citrus wineJT1-3,JT6-2 and JP17-1 were mixed with RV002 to ferment with citrus wine according to the preferred mixed inoculation methods in the previous chapter,and individually inoculated RV002 was used as the control to determine the cumulative carbon dioxide weight loss,the number of yeast and total sugar content during the fermentation process,and to analyze the main physicochemical indexes,organic acids,volatile aroma components and sensory quality of the citrus wines with different treatments.The results showed that JT6-2 fermentation group has the highest citric acid metabolism rate(21.39%).JT1-3 fermentation group has the highest malic acid metabolism rate(41.04%).The total content of volatile aroma compounds in the JP17-1 fermentation group(580.50±0.61 mg/L),the content of esters(110.37±0.07 mg/L),alcohols(444.39±0.07 mg/L)and ketones and ethers(4.95±0.07 mg/L),were significantly higher than the rest of the fermentation groups(P<0.05),with the main aroma components,such as ethyl 3-phenylpropionate,linalool,ethyl caprate,1-amyl alcohol and phenethyl acetate and so on,imparted a unique floral and fruity aroma to the citrus wine.In addition,compared to the CK fermentation group,the mixed fermentation group showed a reduction of 82.11% to 92.53% in acidic compounds,reducing the sourness and rancidity in the wine.Principal component analysis of the volatile aroma components revealed that the CK fermentation group was relatively distant from the three mixed fermentation groups,indicating that there was a large difference between them.The sensory evaluation of different citrus wines showed that JT1-3 fermentation group had the highest score in sweetness,imparting a moderate sweetness to the citrus wine.JT6-2fermentation group had the highest scores in fruitiness,sourness and bitterness,adding a strong citrus flavor and suitable acidity to the fruit wine while reducing bitterness.JP17-1fermentation group had higher scores in typicality,color,state and overall than the other fermentation groups.Thus,JP17-1 fermentation group has a distinctive citrus wine flavor,with a pleasant color and best acceptance.