Efficient enzymatic hydrolysis of sweet potato residue by fed-batch method to prepare high- concentration glucose.

Abstract

China is the largest producer and exporter of sweet potato in the world. Sweet potato residue (SPR) separated after starch extraction account for more than 10% of the total dry matter of sweet potatoes. However, large amounts of unutilized SPR can cause environmental pollution. SPR is rich in starch and cellulose, both of which can be converted into glucose, making it a good carbon source for microbial fermentation. Therefore, an efficient SPR enzymatic process needs to be developed. The technological conditions of high-solid enzymatic hydrolysis of SPR by fed-batch was investigated in detail. Cellulase, amylase, and pectinase had synergistic effects on SPR enzymatic digestion. The experiments were first conducted to optimize the total enzyme addition of 15 mg enzyme protein/g substrate. The experiments were designed using Design-Expert (10.0) to optimize the enzyme proportions to 42%, 31.8%, and 26.2% for cellulase, amylase, and pectinase, respectively. The fed-batch enzymatic hydrolysis of SPR was investigated. The feed time and amount were optimized. The results showed that the initial SPR enzymatic hydrolysis concentration was 14% (w/v), 9% (w/v) was added at 3 h, 6 h and 12 h, respectively and the final substrate concentration was 41% (w/v). After 24 h of enzymatic hydrolysis, the glucose concentration obtained was 194.57 g/L and the glucan conversion was 63.58%. The fed-batch enzymatic hydrolysis of SPR described in this study has great potential for the whole chain utilization of sweet potato and in the microbial fermentation industry as it is environmentally friendly, economical and efficient.