Browsing by Author "Negera, Taye"

Now showing 1 - 1 of 1
  • No Thumbnail Available
    Item
    Isolation and Characterization of Ethanol, Sugar and Thermo Tolerant Yeast Isolates for Biomass and Bio-Ethanol Production
    (Addis Ababa University, 2014-12) Negera, Taye; Alemu, Tesfaye(PhD); Beyene, Dereje(PhD); Asfaw, Araya(PhD)
    The aim of the study was to isolate and characterize ethanol, sugar and thermo tolerant yeast to optimize maximal ethanol production from coffee husk. The yeasts were isolated from (Psidium guajava), grapefruit (Citrus paradise), avocado (Persea americana), papaya (Carica papaya) and gishita (Annona senegalensis pers.). All the yeast isolates were first tested for carbohydrate fermentation using Durham tube fermentation method in yeast extract peptone dextrose broth. Four isolates which were relatively high fermentative in Durham tube fermentation method were selected for testing of the isolates for ethanol, sugar and thermo tolerance. Further, the optimum conditions for isolation and characterization of yeast isolates were determined. The investigation revealed that the optimum conditions are 37°C temperature, 30% sugar concentration, 15% ethanol concentration, pH 5 and 15% diammonium hydrogen phosphate ((NH4)2HPO4) were used as nitrogen source in M9 minimal medium. According to the morphological and biochemical characterization, the selected yeast isolates were belonged to the genus saccharomyces. The results showed that the content of sugars increased as the acid (H2SO4) was increased from 0.25M - 3 M and decreased as the acid concentrations increased beyond 3 M. At the optimal acid concentration (3M; H2SO4), the sugar yield obtained was 85% from the coffee husk. The optimum condition for acid hydrolysis was 3M H2SO4, 10 min hydrolysis time, pH 5 and 30°C temperature at 48 hrs fermentation time. Under the optimum conditions the maximum yield of ethanol (5.56% v/v) was obtained using AAUP1 yeast isolate. The results indicated that locally available cheap substrate which occurs in excess and non-edible material, coffee husk will be a potential feedstock for bio-ethanol production. Keywords: Fermentation parameters, fruits, optical density and S. cerevisiae