The Application Of Torulaspora Delbrueckii In The Fermentation Of Sweet White Wines

Torulaspora delbrueckii,the anamorphic form of Candida Colliculosa,is a kind of non-Saccharomyces related to winemaking.T.delbrueckii could deplete massive amount of sugar gradually and endure high concentrations of glucose,and has a positive effect on the sensory quality of the final wine.This study aimed to observe the physiological and biochemical characteristics,as well as fermentation features of T.delbruecki.In addition,mixed fermentations of T.delbrueckii and S.cerevisiae were applied according to sweet wine fermentation techniques of small container,hoping to improve the flavor of the sweet white wine with good quality and unique characteristics.The results are as follows:1.T.delbrueckii R12 with good fermentation performance was selected.T.delbrueckii R12?R85?R150 were used for physiological characteristics analysis,such as fermentation activity,the tolerance of alcohol,SO2 and high sugar.Meanwhile,their fermentation characteristics in simulation grape juice under different sugar content(200g/L,300g/L,400 g/L)were also investigated.The results were:(1)Among the three T.delbrueckii strains,there was no significant difference for their fermentation powers,and all the strains were able to resist the 14%(v/v)alcohol,600 mg/L SO2 and 400 g/L sugar;(2)In simulation grape juice with 300 g/L sugar,fermentations of T.delbrueckii R12,R85 and R150 still left about 71.3 g/L,34.2 g/L,68.3 g/L sugar at the end of the fermentaiton.Additionally,when compared with R85 with R150,lower amount of volatile acid and higher content of glycerol were produced by R12 in three fermentations with different sugar concentrations.Further sensory evaluation also confirmed that T.delbrueckii R12 was the potential suitable fermentation strain for sweet white wine.2.Simultaneous inoculation of T.delbrueckii R12 and S.cerevisiae NX11424(with the inoculation ratio of 20:1)could improve the quality of the sweet white wine.In Chardonnay grape juice fermentation,we used simultaneous inoculation and interval inoculation with the proportion of 20:1 and 1:1.The results showed that(1)Sequential inoculation(5 days)of T.delbrueckii and S.cerevisiae could decrease the amount of volatile acid to 0.63 g/L(inoculation proportion of 20:1)and 0.75 g/L(inoculation proportion of 1:1)when compared with simultaneous inoculation.In addition,as the content of T.delbrueckii increased,the rate of fermentation and the content of volatile acid decreased during the fermentation process,but the content of glycerol increased regardless of the way of inoculation.(2)The highest scores of sensory evaluation were achieved by simultaneous inoculation of 20:1(90.33),while the lowest was simultaneous inoculation of 1:1(71.33).3.The mixed fermentation by sequential inoculation of T.delbrueckii R12 and S.cerevisiae NX11424 could significantly reduce the volatile acid content in ice grape juice.T.delbrueckii and S.cerevisiae with the proportion of 20:1,10:1 and 1:1 were inoculated in ice grape juice(Vidal)by simultaneous and at 5 d interval.The results showed that:(1)The content of volatile acid in the wine were 0.42 g/L(inoculation proportion 20:1),0.43 g/L(inoculation proportion 10:1)and 0.47 g/L(inoculation proportion 1:1),which was lower than that of by simultaneous inoculation.Whether inoculated simultaneously or at 5 d interval,the rate of fermentation and the content of volatile acid decreased with the increasing content of T.delbrueckii.The content of volatile acid in mixed fermented wine always lower than that of the wine with single fermentation by T.delbrueckii or S.cerevisiae,respectively.(2)In mixed fermentations,the production of glycerol was higher in simultaneously inoculation than in wine inoculated at 5 d interval.During the mixed fermentation,the cell number of T.delbrueckii was larger than S.cerevisiae before the middle stage of fermentation,but reduced at the late fermentation.In summary,mixed fermentation of T.delbrueckii and S.cerevisiae by sequential inoculation could be effectively reduced the content of volatile acid during the fermentation of ice grape juice.