Isolation and characterization of some dominant yeast isolates for production of ethanol from Wet Arabica Coffee (Coffea Arabica l.) Processing effluent and pulp

Abstract

Biofuels are alternatives to fossil fuels to ensure energy security and mitigate climate change. Currently, most biofuels are in the form of bioethanol that is generated from starch or sugar. Hence, the current study was initiated to isolate and characterize yeasts from wet Arabica coffee processing for ethanol production. Fifteen (15) yeast were isolated from wet Arabica Coffee processing effluent1, effluent 2, effluent 3, pulp 1 and pulp2. The yeast isolates were screened and characterized for ethanol production using yeast extract peptone dextrose agar medium (YEPDA) and characterized for ethanol production. All the isolates were first tested for carbohydrate fermentation using Durham tube fermentation method in yeast extract peptone dextrose broth using common fermentative carbohydrates. Two isolates (ACP12and ACE12) which showed relatively high fermentative ability in Durham tube fermentation method were selected for ethanol production from wet Arabica Coffee processing effluent and pulp. Ethanol producing isolates were tested for ethanol, sugar, and temperature and pH tolerance using yeast extract peptone dextrose broth. The yeasts isolated from pulps (ACP12) and effluents (ACE12) recorded maximum population at 20% glucose concentration with a maximum population of (216.0±1.00, 121±1.00 x106CFU/ml), respectively and the reference culture showed maximum growth at the same concentration (153.0±1.00 x106 CFU/ml) compared to the other two isolates. Yeast isolate (ACP12) showed higher population (97.0±1.00 x106CFU/ml) at 30ºC, followed by the yeast isolate from Arabica Coffee effluent (ACE12) that showed (67.7±1.54 x106 CFU/ml). However, the standard culture (Saccharomyces cerevisiae) showed the maximum population of (87.0±1.00 x106 CFU/ml) at 30ºC. The isolates (ACP12) and (ACE12) were recorded maximum population (98.0±1.00 x106 CFU/ml) and (78.0±1.00 x106 CFU/ml) compared to the standard strain (87.0±1.00 x106 CFU/ml) at pH 5.0. Based on morphological, physiological and biochemical characteristics the two isolates (ACE12 and ACP12) were grouped to genus Saccharomyces. The amount of total sugar concentration obtained from pulp1, pulp2, effluent1, effluent2 and effluent 3 were 90%, 85%, 51%, 43.71%, 40.26%, respectively. Isolate ACP12 showed the maximum ethanol production (6.2g/l) from pulp1 compared to the standard isolate (5.49 g/l). The ethanol produced from pulps 1 was satisfactory result compared to pulp 2, effulent1, effulent2 and effulent3. From this study, it can be concluded that isolate ACP12 has a potential of ethanol production from coffee pulps compared to the rest yeast isolates and needs further supplementary activities to qualify it for industrial application. Keywords: Coffee wastewater, Arabica Coffee, fermentation, isolates, yeast, ethanol production