CHARACTERISATION AND FUNCTIONAL PROPERTIES OF YEAST ISOLATED FROM TRADITIONAL FERMENTED ALCOHOLIC BEVERAGES AND CEREAL GRUEL FOR APPLE CIDER PRODUCTION

Abstract

Various groups of microorganisms are associated with traditional apple cider production. These include molds, yeasts and bacteria whose incidental occurrence often leads to inconsistency in the products’ quality. The unpredictability of the complex microflora in the fermentation and inadequate taxonomic knowledge often hinder optimisation of the apple cider fermentation process. Therefore, this study was designed to characterise yeasts from selected fermented foods and determine their functional properties for apple cider fermentation.

Yeast species were isolated from palmwine, burukutu and ogi-baba samples collected within Ibadan metropolis and laboratory-prepared agadagidi. Isolates were identified phenotypically and by 26S rDNA gene sequencing. Functional properties including acid and bile tolerance, gastric transit test, hydrophobicity, auto-aggregation, bile salts deconjugation and wine traits tests were screened using standard methods. The best yeast strains were selected and used to produce wine from apple (Malusdomestica) juiceusing conventional fermentation technique. The wine produced was analysed for physico-chemical properties and the sensory evaluation was done by 20-man panellists using 9-point Hedonic scale. Data were analysed using descriptive statistic and ANOVA at α0.05.

One hundred and twenty-six yeast strains were obtained. Forty-two were identified as Saccharomyces cerevisiae (14), Pichiafabianii (7), Pichia guilliermondii (1), Pichia kudriavzevii (1), Galactomycesgeotrichum (1), Trichosporonspecies (1) Candida tropicalis (5), C. parapsilosis (2) and C. glabrata (10). All the strains grew in 0.1-1.0% ox-bile. In 3.0% bile salt, the viable count ranged from 4.81to 5.35 log10cfu/mL. For the gastric transit test, the viable count ranged from 6.80 to 9.50log10cfu/mL and 7.40 to 8.40log10cfu/mL for pH 2 and pH 3, respectively. Selected Saccharomyces cerevisiae strains showed viable count which ranged from 5.4 to 7.5 log10cfu/mL and 6.2 to 7.7 log10cfu/mL at pH 2 and pH 3, respectively. Hydrophobicity of the selected strains ranged from 35.7 to 83.5% while auto-aggregation ranged from 89.8 to 99.9% indicating the ability of yeast strains to survive gastrointestinal tract stress.All the selected strains deconjugated the sodium bile salts.Saccharomyces cerevisiae PW02 and S. cerevisiae AG08 produced alcohol of 9.4.0% and 9.2% respectively at initial oBrixof 28.0% and had the highest attenuation activity (percentage of sugar converted to alcohol) of 52.5% and 41.6% respectively. The highest fermentation efficiency of 45% and 27% were observed in S. cerevisiae PW02 and S. cerevisiaeAG08. The pH of the apple cider produced ranged from 3.57 to 3.63 in samples fermented with S. cerevisiae PW02 and S. cerevisiae AG08 with corresponding total titratable acidity of 38.40 mg/mL and 40.80 mg/mL.Saccharomyces cerevisiae PW02 produced 10.2% alcohol and had the highest overall acceptability value of 7.82 which was significantly different from others. Saccharomycescerevisiae PW02was identified and exhibited optimal functional properties for apple cider production.