Valorization of Zymomonas mobilis for bioethanol production from potato peel: fermentation process optimization

Abstract

In this study, Zymomonas mobilis was used to produce bioethanol from potato peel (PP) wastes. For this purpose, enzymatic hydrolysis was first performed on potato peel to release the fermentable sugars. Then, the effect of enzyme dosages and solid loading was investigated on the hydrolysis process. Following the hydrolysis step, to evaluate the ability of Z. mobilis in bioethanol production from PP, the effects of five important factors (initial sugar concentration, bacterial dry weight, peptone and yeast extract weights, and fermentation time) were studied, after which the factors were optimized using response surface methodology (RSM) experimental design. It was observed that a maximum of 88.2 g/l reducing sugar was produced using 50 U α-amylase and 12 U amyloglucosidase with 20%PP solid loading. The optimized conditions for fermentation step were as follows: 61.3 g/l initial sugar, 0.024 g bacterial dry cell, 0.35 g meat peptone, 0.35 g yeast extract, and 31-h fermentation time. The maximum ethanol concentration of 23.3 ± 0.015 g/l was produced under the optimum conditions. Time courses of ethanol production and sugar consumption were also studied, revealing consumption of 78.9% of initial sugars under optimum conditions.