Effect Of Lachancea Thermotolerans Mixed Fermentation On Improving Sensory Quality Of Ice Wine

Due to ice wine high sugar content,it requires a certain acidity to balance the sweetness,and high-quality ice wine also needs a complex,typical aroma to support its sensory needs.Yeast is a key strain of wine brewing,and some excellent non-saccharomyces cerevisiae have a positive effect on the quality and style of wine.Lachancea thermotolerans metabolizes to produce lactic acid,which increases the acidity and flavor of the wine.It has strong tolerance and medium alcohol fermentation capacity.Torulaspora delbrueckii can tolerate high osmotic pressure,and produce higher levels of glycerin,higher concentrations of terpenes,and lower concentrations of higher alcohols,with medium alcohol fermentation capacity.In order to improve the acidity and aroma quality of ice wine,this study took 3 strains of L.thermomotolerans（LT1,LT2,LT3）and 3 strains of T.delbrueckii（TD1,TD2,TD3）as test strains to analyze their growth dynamics,tolerance and the fermentation characteristics under ice grape juice habitat,from which L.thermotolerans strain LT2 and T.delbrueckii strain TD2with excellent traits were selected.Using Italian Riesling Ice Grape Juice as the raw material in the production area of Hexi Corridor in Gansu.To explore the mixed fermentation mode in which LT2 strain is inoculated sequentially with commercial Saccharomyces cerevisiae and TD2 strain and simultaneously inoculated in different proportions on lactic acid content,main fermentation parameters and main volatile compounds,combined with sensory evaluation,the influence of mixed inoculation fermentation with L.thermomotolerans on the quality style of Italian Riesling Ice wine was discussed.The main results were as follows:1.Both the LT2 strain and the TD2 strain entered the logarithmic growth phase after a lag period of 4⁶ h in YPD liquid medium,the stable period was long,the bacterial volume level was high,and the growth ability was good.In terms of tolerance,both LT2 and TD2strains can tolerate 500 g/L of glucose,15%（v/v）of ethanol,400 mg/L of SO₂ and lower temperatures（10²0°C）;The LT2 strain produced the highest lactic acid content on the 6 th day,which was 2.195 g/L;The volume fraction of ethanol fermented by LT2 and TD2 strains alone can reach 12%（v/v）.The alcohol fermentation capacity of TD2 strain is slightly higher than that of LT2 strain.2.LT2 strain and S.cerevisiae mixed fermentation wine sample than S.cerevisiae single fermentation wine sample reached an alcohol level of 10¹1%（v/v）longer than the time of 2to 4 days,its total acid and glycerin content were significantly higher than the control41.4%⁶8.3%,0.93¹.26 times,volatile acid content was significantly lower than the control wine sample 50.0%⁶6.0%;The lactic acid content of 10⁴:1 wine samples in the three treatment groups inoculated at different ratios was significantly increased by 8.4 times compared with the control;The content of some esters and terpenes in the aroma components is high;the comprehensive evaluation score is higher than other proportions and inoculation treatment.The lactic acid content of wine samples inoculated sequentially at 6 days intervals was significantly increased by 23.52 times compared with the control,which was significantly higher than that of 10⁴:1 wine samples;The content of aromatic alcohols,terpenes and aldehydes and ketones in the wine components of the aroma components was significantly higher than that of the 10⁴:1 wine sample,and the overall score of sensory evaluation was slightly higher than that of the 10⁴:1 wine sample.3.LT2 and TD2 strain mixed fermentation wine sample than TD2 strain single fermentation wine sample reached an alcohol level of 10¹1%（v/v）longer than the time of 4days,its total acid and glycerin content were significantly higher than the control13.1%⁴4.8%,5.97%⁶2.1%,volatile acid content was significantly lower than the control wine sample 20.2%⁴1.6%;The lactic acid content of 10²:1 wine samples in the three treatment groups inoculated at different ratios was significantly increased by 1.36 times compared with the control;The types and contents of acetate,terpenes and aldehydes and ketones in the aroma components are high;the comprehensive evaluation score is higher than other proportions and inoculation treatment.The lactic acid content of wine samples inoculated sequentially at 6 days intervals was significantly increased by 2.03 times compared with the control,which was significantly higher than that of 10²:1 wine samples;The aroma components have higher content of higher alcohols,terpenes and aldehydes and ketones,and the overall score of sensory evaluation is slightly higher than that of 10²:1 wine sample.4.Compared with LT2 strain and S.cerevisiae mixed fermentation and LT2 and TD2strain mixed fermentation,their wine samples can reach the required alcohol level of 10¹1%（v/v）,The acid-increasing effect is obvious,and the overall score of sensory evaluation is also high.The acid-increasing effect is obvious,and the overall score of sensory evaluation is also high.However,the content of total acid and lactic acid,higher alcohols,terpenes and aldehydes and ketones in the wine samples inoculated with LT2 and TD2 strains were significantly increased compared with the LT2 strain and S.cerevisiae sequential wine samples.The scores are also high,and the overall evaluation score is high.The flowers and fruits have a strong aroma,a soft taste,and a sweet and sour balance.5.The mixed fermentation of non-Saccharomyces cerevisiae（LT2 and TD2）can carry out alcohol fermentation normally,without the help of Saccharomyces cerevisiae,which shows that there is a certain potential for the use of non-Saccharomyces cerevisiae to inoculate wine with lower alcohol content.