Yeast Selected To Ferment Raspberry Using Culture-dependent And Culture-independent Methods

Raspberry,alternative name was Rubus idaeus L,belongs to Rasaceae Rubus,perennial shrubs small berries.Due to high nutrition value,raspberry wins the reputation of"golden fruit".Raspberry plants is widespread in China,especially in the northeast.Raspberries were introduced into Shijiazhuang zanhuang,not only forboosting the industrialization of raspberry in north China,but also for facilitating mountain planting engineering,and improving the haze weather.In this research,the raspberry?varieties:Autumn Bliss?which was taken from zanhuang,shijiazhuang city,and used as the experimental material.During the natural fermentation,raspberry wine yeasts were screened with culture-dependent and culture-independent methods respectively,then the preliminary physical and chemical performance testing on the selected yeasts were carried out,the last,the selective strain was applied in raspberry wine fermentation.The purpose is to obtain the yeast which could improve the raspberries?acidity,make raspberry wine more popular.Firstly,raspberry wine yeast strain was separated by traditional cultivating method.Samplings were taken during the raspberry natural fermentation.Then,gradient dilution,steaking,colony morphology and cell morphology observation and 26S rDNA sequence analysis were carried out.Three kinds of yeast strains were isolated,Issatchenkia terricola,Hanseniaspora uvarum and Saccharomyces cerevisiae,respectively.Secondly,raspberry wine yeast was separated by culture-independent mothed.The raspberry samples of different fermentation stages were analyzed through extracting total genomic DNA,26S rDNA amplification and DGGE.Through analysis of DGGE,5 bands were detected,Saccharomyces cerevisiae,Saccharomycopsis fibuligera,Wickerhamomyces anomalus and two Uncultured fungus,respectively.Thirdly,physical and chemical properties of selected yeasts were studied.Yeasts growth and tolerance characteristics were studied by spectrophotometer,citric acid degradation rate was studied by high performance liquid chromatography?HPLC?in carbon-free experiment and citric acid gradient experiment.Results showed that the growth curve of four kinds yeasts were similar,that 4 h¹4 h as the logarithmic phase.The tolerance of Issatchenkia terricola was the best,acid-resistance limitation of pH 2,sugar content 0 g/L,alcohol 10%,SO₂ 600 mg/L.In carbon-free experiment and citric acid gradient experiment,growth of Issatchenkia terricola is obviously better than the other strains,the degradation rate was up to 90.46%when citric acid content was 12 g/L.In raspberry juice fermentation experiments,Angel yeast and mixed strains?Issatchenkia terricola:saccharomyces cerevisiae 5:5?had the better fermentation ability,reducing saccharides fast,high alcohol formation rate.Finally,the fourth part,raspberry wine was fermented by using the selected yeasts.Raspberry wine was brewed by using Issatchenkia terricola:saccharomyces cerevisiae5:5?short for 5:5?,Issatchenkia terricola:saccharomyces cerevisiae 2:8?short for 2:8?,Issatchenkia terricola:saccharomyces cerevisiae 8:2?short for 8:2?as experimental strains,Angel yeast as reference strains.Organic acid of raspberries wine were detected by using HPLC,the aroma substances were detected by GC-MS,chroma and hue were measured by spectrophotometer.Sensory evaluation of four raspberry wines were carried out according to wine sensory evaluation standard.According to the results of organic acid degradation rate,aroma substance content,chroma and hue,and sensory evaluation,the5:5 strains brewing wine was the best.In this research,raspberry wine yeasts were selected with culture-dependent and culture-independent methods during the natural fermentation.After preliminary physical and chemical performance study,the selected yeasts were applied to brew raspberry,at the same time,the optimal proportion of strains was studied,too.Because the commercial Angel yeasts were used to raspberry fermentation usually,this study made up for the blank of the special yeasts.This research provided the theory basis for further improving the fermentation technology and taste,it also help to lay a foundation to expand market share.