Comparison of simultaneous and separate processes: saccharification and thermophilic L-lactate fermentation of catch crop and aquatic plant biomass

Abstract

Catch crop candidates (corn, guinea grass) for recovering nutrients from farm soil and aquatic plants (water caltrop, water hyacinth) were utilized to produce l-lactic acid. The efficiencies of pre-treatment methods for enzymatic saccharification and l-lactate production of two fermentation processes, thermophilic simultaneous saccharification and fermentation (SSF), as well as separate saccharification and fermentation, were compared. Conditions were set at 55°C and pH 5.5 for non-sterile fermentation. Alkaline/peroxide pre-treatment proved the most effective for saccharification in pre-treated corn, guinea grass, water caltrop and water hyacinth with glucose yields of 0.23, 0.20, 0.11 and 0.14 g/g-dry native biomass (24-hour incubation period), respectively. Examination of the two types of thermophilic l-lactate fermentation employed following alkaline/peroxide pre-treatment and saccharification demonstrated that the l-lactate yield obtained using SSF (0.15 g/g in the case of corn) was lower than that obtained using separate saccharification and fermentation (0.28 g/g in the case of corn). The lower yield obtained from SSF is likely to have resulted from the saccharification conditions used in the present study, as the possibility of cellulase deactivation during SSF by thermophilic l-lactate producing bacteria existed. A cellulase that retains high activity levels under non-sterile conditions and a l-lactate producer without cellulose hydrolysis activity would be required in order for SSF to serve as an effective method of l-lactate production.

Keywords:

• alkaline/peroxide
• cellulase deactivation
• pre-treatment
• Bacillus coagulans
• SSF

Acknowledgements

This work was supported by the Japan Science and Technology Agency, CREST and the Ministry of Education, Culture, Sports, Science and Technology in Japan, KAKENHI (21310054). We would like to thank Mr Masukawa for his assistance with ICP-AES analysis and Meiji Seika Kaisha Ltd for supplying the Meiselase used in this study.