NUSANTARA BIOSCIENCE ISSN: 2087-3948 Vol. 13, No. 1, pp. 1-10 E-ISSN: 2087-3956 May 2021 DOI: 10.13057/nusbiosci/n130101 Potential of Candida glabrata from ragi as a bioethanol producer using selected carbohydrate substrates MICKY VINCENT ♥ , QUEENTETY JOHNNY, DAYANG SALWANI AWANG ADENI, NURASHIKIN SUHAILI Faculty of Resource Science and Technology, Universiti Malaysia Sarawak. 94300 Kota Samarahan, Sarawak, Malaysia. Tel.: +60-825-82985, Fax.: +60-825-83160,  email: vmicky@unimas.my Manuscript received: 16 September 2020. Revision accepted: 1 December 2020. Abstract. Vincent M, Johnny Q, Adeni DSA, Suhaili N. 2021. Potential of Candida glabrata from ragi as a bioethanol producer using selected carbohydrate substrates. Nusantara Bioscience 13: 1-10. The flexibility and efficiency of fermenting microorganisms to convert substrates to ethanol are important factors in achieving high bioethanol yields during ethanolic fermentation. In this study, Candida glabrata, a common yeast found in fermented food, was evaluated in terms of its capability to produce ethanol using different types of carbohydrates, which included simple saccharides (glucose, maltose, sucrose), polysaccharides (starch and cellulose) and complex carbohydrates (total sago effluent, TSE). Our results indicated that C. glabrata was able to efficiently produce ethanol from glucose at 79.84% TEY (Theoretical Ethanol Yield). The ethanol production from sucrose was low, which was only 6.44% TEY, while no ethanol was produced from maltose. Meanwhile, for complex carbohydrate substrates such as starch and cellulose, ethanol was produced only when supplementary enzymes were introduced. Simultaneous Saccharification and Fermentation (SSF) of starch dosed with amylases resulted in an ethanol yield of 55.08% TEY, whilst SSF of cellulose dosed with cellulases yielded a TEY of 31.41%. When SSF was performed on TSE dosed with amylases and cellulases, the highest ethanol production was recorded within 24 h, with a yield of 23.36% TEY. Lactic acid and acetic acid were found to be at minimal levels throughout the fermentation period, indicating an efficient ethanol conversion. A notable increase in C. glabrata biomass was observed in cultures fed with glucose, starch (with supplementary amylases), and TSE (with supplementary amylases and cellulases). The current study indicates that C. glabrata can be used for bioethanol production from glucose, polysaccharides, and complex starchy lignocellulosic substrates such as TSE via SSF. Keywords: Bioethanol, Candida glabrata, Metroxylon sagu, simultaneous saccharification and fermentation, total sago effluent INTRODUCTION The interest in producing renewable fuels has increased tremendously over recent years due to the instabilities of fossil fuel supplies and increasing global demands (Wei et al. 2015; Wong and Vincent 2019; Mohammad et al. 2020). Alternative liquid biofuel, such as bioethanol, is seen as the current choice of such renewable fuel to supplement and substitute petroleum-based fuel, due to its sustainability and carbon dioxide neutrality (Vincent et al. 2015; Hung et al. 2018). Compared to conventional gasoline, bioethanol is highly attractive as it offers cleaner combustion that is friendlier towards the environment. Economically, the bioethanol production and supply chain are also desirable as it creates many jobs and financial opportunities for both urban and rural areas (Ştefănescu-Mihăilă 2016). In mass bioethanol production, substrate selection plays a major role. It is one of the main cost factors for the ethanol industry (Vincent et al. 2015). There are currently many feedstock sources that are used as substrates for bioethanol production (Techaparin et al. 2017; Ahorsu et al. 2018; Mohammad et al. 2020). When substrates such as lignocellulosic biomass are used to produce bioethanol, this type of bioethanol is termed as second-generation bioethanol (Zhang et al. 2016). It is projected that in the future, second-generation bioethanol will replace first- generation bioethanol, which is mostly produced from food-based materials, because of its low cost and feedstock abundance (Vincent et al. 2015; Ştefănescu-Mihăilă 2016). In bioethanol production, the typical bioprocess engaged is Simultaneous Saccharification and Fermentation (SSF) as this procedure offers higher reaction rates, higher yields, and greater ethanol concentrations compared to its closest counterparts such as Separate Hydrolysis and Fermentation. The efficiency of ethanol production is also influenced by the species of microorganisms used. The desired microorganism should be robust and capable of converting substrates to ethanol effectively. The most common examples of ethanol producers are Saccharomyces cerevisiae, Zymomonas mobilis and Fusarium oxysporum (Ali et al. 2016; Vincent et al. 2018; Mohammad et al. 2020). Among these, S. cerevisiae has been mostly used in alcoholic fermentation due to its ethanol productivity. However, this particular species has several limitations. For example, poor stress tolerance and incapability to ferment xylose and arabinose, the main sugars released from hemicelluloses. Therefore, several genetic engineering studies to improve sugar utilization, ethanol production, and other applications have been explored (Carrasco et al. 2013; Pagliardini et al. 2013; Wong and Vincent 2019). Another approach is to search for new fermenting yeasts that may perform better or are more flexible than S. cerevisiae (Vincent et al. 2018). Another yeast species that has similar characteristics to S. cerevisiae is Candida glabrata, which can be commonly