Effects of galactose adaptation in yeast for ethanol fermentation from red seaweed, Gracilaria verrucosa

A total monosaccharide concentration of 39.6 g/L, representing 74.0 % conversion of 53.5 g/L total carbohydrate from 80 g dw/L (8 % w/v) Gracilaria verrucosa slurry, was obtained by thermal acid hydrolysis and enzymatic saccharification. G. verrucosa hydrolysate was used as a substrate for ethanol production by 'separate hydrolysis and fermentation' (SHF). The ethanol production and yield (Y EtOH) from Saccharomyces cerevisiae KCCM 1129 with and without adaptation to high galactose concentrations were 18.3 g/L with Y EtOH of 0.46 and 13.4 g/L with Y EtOH of 0.34, respectively. Relationship between galactose adaptation effects and mRNA transcriptional levels were evaluated with GAL gene family, regulator genes of the GAL genetic switch and repressor genes in non-adapted and adapted S. cerevisiae. The development of galactose adaptation for ethanol fermentation of G. verrucosa hydrolysates allowed us to enhance the overall ethanol yields and obtain a comprehensive understanding of the gene expression levels and metabolic pathways involved.