Characterization, identification and comparative evaluation of bioethanol tolerance and production capacity of isolated yeast strains from fermented date palm sap (Toddy)

Abstract

Aims: Toddy, an alcoholic beverage produced from naturally fermented date palm sap and commonly used as traditional drink in Southern India including Odisha, is a source of natural yeasts, capable of fermenting sugar to alcohol. The present study was carried out to isolate and identify predominant yeast strains from toddy, fermented date palm sap and to evaluate their ethanol tolerance and comparative bioethanol production capacity to select potential yeast strains for efficient bioethanol production for their application in fermentation industry. Methodology and results: Eight morphologically distinct yeast isolates (BS1-BS8) were identified on the basis of morphological and biochemical characterization. The yeasts identified include four strains of Saccharomyces cerevisiae, one strain each of Pichia besseyi and Trycosporon capitatum and two strains of Candida albicans. The strains were evaluated for their ethanol tolerance capacity in in vitro condition. The strains P. besseyi (BS2) and S. cerevisiae (BS7) tolerated ethanol concentration up to 10% (v/v), while two isolated S. cerevisiae strains (BS1 and BS5) showed tolerance up to 9% of ethanol concentration. The remaining two strains showed tolerance of 7% (v/v). The identified strains along with commercial yeast strain (S. cerevisiae, CTCRI) were evaluated for comparative bioethanol production capacity in different carbohydrate substrates (grape juice, mahua flower extract, molasses, sugarcane juice and saccharified sweet potato root flour broth). Taking different strains and substrate conditions into account, strain P. besseyi (BS2) showed in overall the highest ethanol production capacity followed by the strains of S. cerevisiae (BS5, CTCRI, BS2 and BS7 in an order of their performance). On the other hand strains of C. albicans (BS4 and BS6) and T. capitatum (BS3) exhibited least ethanol production capacity. Conclusion, significance and impact study: In conclusion, the present research work characterizes eight yeast strains isolated from fermented date palm sap (toddy) by conventional morphological and biochemical methods and identified them as four species of Saccharomyces cerevisiae, two strains of C. albicans and one strain each of P. besseyi and T. capitatum. The isolate P. besseyi showed very high ethanol tolerance and production capacity with some promising fermentation capacity towards different substrates compared to commercial yeast strain S. cerevisiae.

Isolation and Evaluation of Comparative Ethanol Production Capacity of Yeasts in Presence of Different Carbohydrate Sources from Soil

“…In a study carried out by Dash et al . 6 , it has been reported that the isolated yeast strains can ferment all types of sugars expect lactose. This supports to the studies by Walker et al 21 who reported that all the yeast isolates ferment at least one type of sugar.…”

“…However, a majority of these isolates which ferment glucose, galactose, maltose, sucrose and raffinose, belonged to the genus S. cerevisiae. The isolated strains were inoculated in TGY broth medium and incubated at different pH (3)(4)(5)(6)(7)(8) and temperature (20-40°C) conditions. All the strains isolated from soils samples were well grown at temperature 35°C.…”

“…On the basis of morpho-physiological characteristics and biochemical characterization, the yeast strains isolated from soil samples were identified as six strains of S. cerevisiae (YS1, YS2, YS4, YS5, YS7 and Y10), three strains of Candida albicans (YS3, YS8 and YS9) and three strains each of Trycosporon capitatum (YS6, YS11 and YS12).In another study Dash et al 6 has reported isolation of eight distinct yeast strains from fermented beverage samples and identified as four strains of Saccharomyces cerevisiae, one strain each of Pichia besseyi and Trycosporon capitatum and two strains of Candida albicans on the basis of microscopic and macroscopic observation. Bullock.…”

“…8 isolated two yeast isolates from soil samples and concluded that two strains were able Naturally growing yeast strains showed higher ethanol tolerance up to 13 % has been reported by Kumar et al 10 . Dash et al 6 studied on ethanol tolerance capacity of isolated yeast strains from toddy and found that the yeast strains could tolerate upto 10 % of ethanol. Use of efficient yeast strains with higher ethanol tolerance to improve ethanol yields in the fermentation product (cane molasses) would reduce distillation costs and hence the profitability of the overall process 4 .…”

“…Choi et al 5 isolated two ethanol producing yeast strains from soil sampls and studied their ethanol production capacity on cassava starch. Dash et al 6 also isolated and screened fermentation ability of eight yeast strains on different sugary and starchy substrates for further use in industrial scale. It may be noted that the strain YS2 and YS7 has shown high ethanol production and tolerance capacity among the others.…”