Isolation,Screening And Brewing Technology Of Peach Yeast

Background and Aim:The development of peach winemaking in China,could create a new industry,add value to the fruit and reduce waste in an over-supplied market.Presently,those developments rely on wine fermented with Saccharomyces yeasts widely used for grape winemaking and originally selected from natural ferments and now commercially propagated.The aim of this study was to collect,characterize and evaluate a wild yeast from peaches to improve the qualities and value of peach wines.Methods:The peaches used in this study were grown at Yangshan Town,Wuxi.The research methods were as follows:(1)Selection of ideal peach cultivar for fermentationBased on determination of the juice yield and physicochemical properties of a number of peach cultivars at a range of and maturities,the white-fleshed cultivar Hujing with high sugar content and juice yield,bright color and rich aroma was selected for fermentation trials.(2)Isolation and screening of wild yeastsA large number of wild yeasts were isolated from peach skin,and then screened for morphological characteristics,aroma,and growth rate.Then,a small-scale experiment was carried out to investigate the fermentation performance of the yeasts and whether they could consume the sugar in the juice to produce ethanol.After selection of several yeasts with suitable fermentation ability,the yeast species were identified by reference to a yeast strain DNA library and the fermentation ability was confirmed by reference to similar yeasts found in the strain library.(3)Compositional and sensory analysis of peach wineThe selected yeast was then used in small scale fermentation of Hujing peach juice supplemented with honey and the parameters affecting the quality of the wine were measured.The main quality parameters were ethanol content,residual sugar content,total acid content and taste score.In addition,the determination of aroma composition was an important parameter for the quality of the wine.(4)Determination of optimal fermentation conditions of the selected yeastFinally,on the premise that the yeast could produce high quality wine,it was used as a single yeast factor in medium scale fermentation experiment with Hujing peach to determine the optimal fermentation conditions of peach wine.Results:A total of 86 strains of natural yeast were isolated from the ripe peaches.The yeast selected for further investigation was smooth,round, milky white,with light aroma.It grew rapidly,consumed sugar,and produced ethanol.It was identified as a Pichia strain and designated as hsmt-1.In the small-scale experiment of peach wine fermented with the Pichia hsmt-1 strain,the ethanol content was almost 7%,leaving about 3.1 g/L of total sugar,the titratable acid content was 3.2 g/L.Analysis of key compounds revealed that wine was rich in about 10 esters,7 alcohols,1 ketone and 2 olefins.The wine retained the flavor and aroma of peach but also had a rich floral flavor.Its taste was sweet and sour,and its mouthfeel was mellow.In the single factor experiment,the initial juice sugar content was 15%and the initial pH value was 4.The concentration of added SO₂was 50 mg/L.After inoculation of 0.5%Pichia hsmt-1,the must was fermented at 20?.Under these conditions,the wine quality was the best according to the standard wine parameters and sensory evaluation.The yeast found in this study comes from the natural environment.Its use to ferment peach wine provided an innovative product with unique and delicious taste.It also represents the rational and environmentally-safe use of a local ecological resource.