ISOLATION AND IDENTIFICATION OF YEAST STRAINS FROM SUGARCANE MOLASSES, DATES AND FIGS FOR ETHANOL PRODUCTION UNDER CONDITIONS SIMULATING ALGAL HYDROLYSATE

ABSTRACT Yeast strains were isolated from sugar cane molasses (S1), dates (S2) and figs (S3) and the ethanol production was evaluated in batch condition. A comparison was made with the yeast Saccharomyces cerevisiae. The strains showed tolerant characteristics to stressful conditions like salinity and ethanol. The isolated strains produced ethanol; at 20 h of fermentation ethanol yields were 0.38-0.39 g.g-1, and the productivities were almost 0.58 g.L-1. S. cerevisiae and S1 tolerated up to 14% (v/v) of ethanol; while interestingly the isolates S2 and S3 were highly tolerant, up to 20% (v/v) ethanol. Thus, S2 and S3 could serve as potential strains for ethanol fermentation, with 0.27 and 0.29 g.g-1 yield of ethanol in the presence of 1.37 mol.L-1NaCl. These values were higher than the value obtained using the yeast of reference and S1 (0.16 g.g-1). Co-cultures of S2 and S3 enhanced the ethanol production, increasing the yield of ethanol by 12.5% compared with the single culture. The strains were identified as species S.cerevisiae, and S2 and S3 were very similar. For an application in the valorization of biomass such as green macro-algae, some assays were done on a synthetic model medium of hydrolysate of macro-algae and the strains S2 and S3 demonstrated excellent fermentative performances.摘要 本研究从甘蔗糖蜜（S1）、椰枣（S2）及无花果（S3）中分离得到酵母菌株，于分批培养条件下评估其乙醇合成能力，并与酿酒酵母（Saccharomyces cerevisiae）进行对照比较。结果显示，受试菌株对盐度、乙醇等胁迫环境均具备耐受特性。分离菌株可合成乙醇：发酵至20 h时，乙醇得率可达0.38~0.39 g·g⁻¹，生产强度约为0.58 g·L⁻¹。酿酒酵母与S1菌株可耐受最高14%（v/v）乙醇浓度；而值得注意的是，分离株S2与S3的耐受性更为优异，可耐受最高20%（v/v）乙醇浓度。综上，S2与S3可作为乙醇发酵的潜在优势菌株：在1.37 mol·L⁻¹氯化钠胁迫环境下，二者的乙醇得率分别为0.27 g·g⁻¹与0.29 g·g⁻¹，高于对照酿酒酵母与S1菌株的0.16 g·g⁻¹。将S2与S3进行共培养可提升乙醇生产性能，较单培养模式使乙醇得率提升12.5%。经鉴定，所有受试菌株均为酿酒酵母，且S2与S3的亲缘关系极为相近。为实现菌株在大型绿藻等生物质增值利用中的应用，本研究采用大型藻水解液合成模拟培养基开展发酵试验，结果表明S2与S3展现出优异的发酵性能。