Abstract
For practical applications of bioethanol, the uses of both highly concentrated biomass materials and their effective fermentation by yeasts are indispensable in order to produce ethanol at low costs. However, as the saccharified products of those biomass generally contain abundant sugars, the yeasts are affected by the compounds and are inclined to decrease their physiological activities. In the process of fermentation, ethanol is gradually produced by the yeasts in the culture; the concentrated metabolic product also damages itself, and inhibition of the fermentation frequently occurs. The application of yeasts with high fermentative activities under stress pressures such as sugars and ethanol is thus desired for bioethanol production. In this study, various types of high-fermentative yeasts under stress pressures were isolated mainly from coastal waters in Japan and characterized. All yeast strains with high fermentative activities under 20% v/v ethanol were found to be Saccharomyces cerevisiae. The HK21 strain isolated from Tokyo Bay and identified as S. cerevisiae had the highest fermentation activity under 30% w/v sorbitol and under 20% v/v ethanol, and it produced approx. 70 g/l (9% v/v) ethanol from the 15% w/v glucose solution at 25 oC within 5 days.
Highlights
Today, the United States is the largest bioethanol producer in the world, with corn and wheat as the main materials used to make bioethanol
The HK21 strain isolated from Tokyo Bay and identified as S. cerevisiae had the highest fermentation activity under 30% w/v sorbitol and under 20% v/v ethanol, and it produced approx. 70 g/l (9% v/v) ethanol from the 15% w/v glucose solution at 25 ̊C within 5 days
All seven of the following strains had fermentative activity under both 20% v/v ethanol and 30% w/v sorbitol: HK6, HK21, HK27, K6-38, and C-19 identified as S. cerevisiae, M39 identified as M. bicuspidata, and RB59 identified as C. tropicalis
Summary
The United States is the largest bioethanol producer in the world, with corn and wheat as the main materials used to make bioethanol. N. Urano et al 350 corn and wheat is saccharified with both α-amylase and glucoamylase, followed by yeast fermentation; the final ethanol concentration reaches 8% - 10% v/v [1] [2] [3]. The second biggest bioethanol producer in the world is Brazil. Sugarcane juice and molasses are used as substrates in Brazil, and a few days’ fermentation of these materials provides a 6% - 8% ethanol concentration [4] [5]. The constancy of the crops’ supply seems to be lacking due to the inadequate utilization of these agricultural products all year round
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