Browsing by Author "Jayasekara, S. K."

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Efficient ethanologenic yeast isolates for potential application in bioethanol production
(Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, Sri Lanka, 2018) Jayasekara, S. K.; Abayasekara, C. L.; Ratnayake, R. R.
Yeast plays an essential role in bioethanol production as sugar fermenters. As all yeasts are not efficient ethanol producers, evaluation of yeast for ethanol production ability is essential if novel yeast varieties are to be used in the production of ethanol. The aim of the current study was to choose efficient ethanologenic yeast isolates by assessment of their ethanol production, utilizing different glucose and xylose combinations. Yeasts were isolated from fruits including orange, mango and grapes. The microscopic observation of oval shape budding cells in stained smears was a preliminery confirmation of the isolates to be yeast. In order to facilitate the ethanol production, the isolates were aerobically incubated in a standard ethanol production medium for 24 hr followed by 24 hr of anaerobic incubation. The ethanol detection was done by High-Performance Liquid Chromatographic (HPLC) analysis using an ethanol standard series of 1-30%. The concentrations of ethanol produced were compared among the tested yeast varieties. The retention time for ethanol was approximately 21 min. Most of the yeast isolates were found to be ethanologenic yeast producing an ethanol concentration of more than 1%, while the highest amounts of ethanol were exhibited by isolates Y1, Y3 and Y20. The highest ethanol concentration, which was 9.65%, was yielded by Y3 fermenting glucose: xylose at a 2:1 ratio. The other ratios of glucose: xylose were 1:1,1:2,1:0 and 0:1. The ethanol concentrations given at those ratios were below 3%. Y1 showed an ethanol yield above 4.5% at each sugar combination tested, while the highest yield of 5.8% was obtained when glucose was the sole source of sugar, indicating differrent sugar utilizing patterns of yeast. When xylose was the sole source of sugar, the yield of ethanol given by each isolate was negligible, indicating that all the yeast isolates investigated maybe non-xylose fermenting yeast. Furthermore, an overall reduction in the yield of ethanol was observed when xylose was added into the medium. The current study concludes the identification of three efficient ethanologenic yeasts (Y1, Y3 and Y20) under the conditions of investigation, which could be further developed for future industrial application.
Screening local fungal isolates for their cellulases production: the applicability in producing bioethanol from cellulose.
(International Research Symposium on Pure and Applied Sciences, 2017 Faculty of Science, University of Kelaniya, Sri Lanka., 2017) Jayasekara, S. K.; Abayasekara, C. L.; Ratnayake, R. R.
Being a highly abundant, inexpensive polysaccharide present in the environment, cellulose could be used as a substrate for good bioethanol production. However, the conventional physical and chemical methods of breaking down cellulose into its monomer sugars have been costly, making it barely feasible in an industrial scale. At the same time, enzymatic hydrolysis of cellulosic material has been found to be cheaper, as well as an effective mode of cellulose degradation. Therefore, different microorganisms have been studied extensively because of their great potential to produce cellulose, which is the enzyme complex that breaks down cellulose into its simple fermentable sugar forms. The current study mainly focuses on exploring efficient, local fungal isolates for cellulase enzyme production with special reference to their ability of releasing glucose and xylose from cellulose. Sixty five fungal strains isolated from different environments, were evaluated for their ability to produce cellulases. Enzyme production was carried out by submerged fermentation in a medium modified with Mendel’s mineral salt solution with an initial pH of 5.5. The enzyme production was conducted at 30˚C with continuous shaking at 120 rpm for a period of one week. Total cellulases assay was conducted using Whatman No.1 filter paper as the substrate. The reducing sugars formed were measured colorimetrically using UV-Visible spectrophotomer at 540 nm against glucose standards. Xylanase activities were measured by modifying the Gottschalk et al. method. Reducing sugars formed, were measured by the same colorimetric method, using xylose standards. The highest total cellulases activity was observed in fungal isolate F1 as 0.6163 filter paper units /ml (FPU/ml), while highest xylanase activity was given by fungal isolate F3 as 14.762 (IU/ml). When the enzyme activity increased, the amount of sugar released gradually increased. According to the results, all the fungal isolates investigated showed cellulases activities above 0.01 FPU/ml. Ten isolates were categorized as best, having cellulases activity above 0.1 FPU/ml. Some isolates were very efficient in releasing xylose. Almost all the strains had xylanase activity above 0.1 IU/ml. Sixteen isolates showed xylanase activity above 9 IU/ml. According to morphological studies, fungal isolates F1 and F3 were tentatively identified to be Trichoderma sp. Thirteen yeast isolates were also tested for their ability to utilize glucose and xylose in order to use them in fermentation studies. All the tested isolates were capable of growing on glucose. However, only four isolates were capable of growing on xylose. These yeast isolates could be studied for co-culturing possibilities with the above glucose and xylose releasing fungal strains for bioethanol production.