Napa Cabbage ( Brassica rapa subsp. pekinensis) Wastes as Sources of Potential Ethanol-Fermenting Indigenous Yeasts with Stress Tolerance Ability

Abstract

The research objective was to determine the occurrence of indigenous yeasts from napa cabbage (Brassica rapa subsp. pekinensis) wastes that potential in ethanol fermenting activity at stress condition such high concentration of glucose and ethanoL Indigenous yeasts were isolated from 1 g napa cabbage wastes and identified with RapID Yeasts Plus System. Glucose and ethanol tolerance was assessed by growing yeasts in modified Nutrient Broth/NB (Oxoid Ltd.) added with 10%, 20%, and 30% of glucose monohydrates or 10%. 15%, and 20% of ethanol concentration and measuring the optical density (OD) every 24 h until 72 h. The best isolates tested to ferment napa cabbage wastes were mixed with water (1:1.5) then the ethanol contents analyzed by dichromate oxidation method. Results showed that there are two potential ethanol-fermenting indigenous yeasts isolated from napa cabbage wastes which identified as Hanseniaspora guilliermondii and Candida krusei. Both yeasts have the ability to survive at 30% of glucose concentration until 72 h incubation, though the highest growth was reached at 10% of glucose concentrations for 24 h incubation. The yeasts growth in high ethanol concentration tends to decrease after 48 h for C. krusei and 24 h for H. guilliermondii. The highest ethanol production from napa cabbage fermentation showed that mixed culture (1:1) of C. krusei and H. guilliermondii with 1.43% ethanol contents for 24 h incubation.