Production of Sodium Gluconate from De-Lignified Corn Cob Residue by On-Site Produced Cellulase and Co-Immobilized Glucose Oxidase and Catalase

A wide range of products can be obtained from lignocellulosic materials, such as butanol, ethanol and other organic acids, via enzymatic hydrolysis or microbial fermentation. Despite being a suitable substitute for starch or glucose used as raw materials in fermentation industry, lignocellulose hydrolysate often contains substances that inhibit microbial growth which contributes to longer fermentation periods. Consequently, many fermentation industries keep off application of lignocellulose. Sodium gluconate can be used as a chelating agent, surface cleaning of steel or glass and as a high-efficiency retarder and superplasticizer in the concrete industry. The presence of a carboxyl group instead of an aldehyde group in the structure of gluconic acid differentiates it from that of glucose. Gluconic acid is mainly produced through microbial fermentation. The enzymes, glucose oxidase and catalase have also been seen sufficient to effectively catalyze the production of gluconic acid from glucose in vitro. In this work, enzymatic conversion of de-lignified corn cob residue has been explored.

Researchers led by Professor Yinbo Qu from the State Key Laboratory of Microbial Technology, at Shandong University in China studied the feasibility of production of sodium gluconate from de-lignified corn cob residue using in situ generated cellulace and co-immobilized glucose oxidase and catalase. Their research work is now published in the peer-reviewed journal, Bioresource Technology.

The research team commenced their empirical procedure by on-site production of cellulace that would later be used for lignocellulose saccharification. Penicillium oxalicum I1-13 was used for the production of cellulace with high β-glucosidase activity. A fed-batch saccharification process was developed to obtain high yields of glucose. Eventually, glucose oxidase and catalase were co-immobilized to catalyze de-lignified corn cob residue hydrolysate to produce sodium gluconate.

The authors observed that a certain concentration of glucose was obtained by fed-batch saccharification of de-lignified corn cob residue. The team was also able to produce certain concentrations of sodium gluconate by co-immobilizing glucose oxidase-catalase under optimal conditions. As the reusability of the immobilized enzyme was under way, the team realized that as the reusing increased, the residual enzyme activities decreased gradually. This was attributed to the breakage of immobilized enzyme particles and inactivation of immobilized enzymes during the conversions. In total the team was able to produce 20.53g of sodium gluconate using one milligram of enzymes after six times of conversion.

The study provides a potential route for the production of valuable chemicals by enzymatic conversion of lignocellulosic materials. Under the optimized conditions, de-lignified corn cob residue hydrolysate containing glucose has been obtained and sodium gluconate has been produced by co-immobilized glucose oxidase-catalase. This co-immobilized glucose oxidase-catalase has been seen to maintain over 60% activity after being reused for 6 times. Taken together, enzymatic production of sodium gluconate from lignocellulose hydrolysate proposed here has a great potential for industrial production of sodium gluconate.