Gluconic Acid Production from Potato Waste by Gluconobacter oxidans Using Sequential Hydrolysis and Fermentation

Potato pulp, which is the industrial residue of potato processing for starch production, can be used for biochemicals production. In this study, a green, sustainable, highly productive technology for producing gluconic acid from potato pulp was developed. The cocktails of cellulases from Trichoderma reesei TX and Penicillum oxalicum JUA10–1 with commercial pectinase were prepared and used to hydrolyze hydrothermally treated potato pulp into fermentable sugars at a solids content of 25% (w/v). Eighty percent of the glucan in the potato pulp was able to be converted into glucose when 8 FPU/g of dry material (DM) of cellulase and 1000 PGU/g DM of pectinase were added. The enzymatic hydrolysates of the potato pulp were fermented into 81.4 g/L gluconic acid by Gluconobacter oxidans DSM 2003 for 20 h at 30 °C. The overall conversion yield from glucose to gluconic acid was 94.9%, and the productivity was 4.07 g/L/h, which was significantly better than that of previous studies. Finally, 546.48 g of gluconic acid was produced from per kilogram of dried potato pulp with this process.