Low Temperature Alkali Pretreatment of Sweet Sorghum Bagasse

A team of Japanese and Korean researchers investigated the low temperature alkali (LTA) pretreatment of sweet sorghum bagasse. Pretreatment is the first step in the production of cellulose from lignocellulosic biomass, where the lignin fraction of the biomass is removed to expose the carbohydrate (cellulose, hemicellulose) fraction. The carbohydrate fraction is then converted to simple sugars for ethanol fermentation.

Bagasse from "brown midrib (BMR) mutants" of sweet sorghum was used; this variety is reported to have reduced lignin and high fiber digestibility as silage. Compared to high temperature pretreatment processes, low temperature alkali pretreatment reportedly consumes less energy and improves cellulose-to-ethanol conversion ratio.

The LTA conditions tested were: (1) sodium hydroxide concentrations from 0.5 M to 5M, (2) solid to liquid ratios of 5%, 10% and 15%, (3) temperatures of 25^oC and 50^oC, and (4) pretreatment times of 0.5 hours to 24 hours. Results showed that "the pretreated bagasse exhibited greatly improved enzymatic digestibility, with 24-hour glucan saccharification yields of about 98% (using commercially available cellulose and b-glucosidase). The disruption of the lignin-carbohydrate matrix of the sweet sorghum bagasse was thought to be a factor in digestibility improvement. The BMR (i.e. low-lignin) mutants were also shown to be more susceptible to pretreatment compared to the non-BMR mutants. The full results are published in the journal, Bioresource Technology (URL above).