Valorization of Corncob as a Sustainable Feedstock for Lactic Acid Production via Improved Biomass-to-Glucose Conversion Based on KOH Pretreatment

Abstract

Biorefining of food waste has gained increasing attention as a sustainable approach for producing platform chemicals such as lactic acid. In this study, corncob (CC), a byproduct of corn processing, was utilized as a feedstock for biorefining through biomass hydrolysis and lactic acid fermentation. Due to the low enzymatic digestibility of raw CC caused by its lignin content, KOH pretreatment was conducted prior to enzymatic hydrolysis to enhance glucose recovery. Among the tested KOH concentrations (1–5%), 3% KOH pretreatment yielded the highest biomass-to-glucose conversion (25.38%), with a solid recovery (SR) of 47.60%, glucan content (GC) of 57.23%, and enzymatic digestibility (ED) of 84.70%. These values represent a significant improvement compared to raw CC (biomass-to-glucose conversion: 7.97%; SR: 100%; GC: 35.22%; ED: 20.57%). Compositional and physicochemical analyses confirmed that 3% KOH-pretreated CC (3%KpCC) had a reduced lignin content (11.69%) compared to raw CC (20.48%), along with irregular cracks and crevices that improved enzymatic digestibility via easier enzyme access. Fermentation of Lacticaseibacillus rhamnosus with the hydrolysate as an alternative carbon source for 24 h was found to produce about 9.89 g/L lactic acid and 98.9% conversion, similar to the control medium (about 9.81 g/L production and 98.1% conversion). Overall, the mass balance analysis revealed a 3.2-fold increase in lactic acid production (251 g/kg biomass) with the 3% KOH pretreatment process compared to the control. This study demonstrates a significantly improved biorefinery strategy that effectively contributes to both CC waste management and value-added chemical production.