Aspergillus flavus biomass catalytic lipid modification: optimization of cultivation conditions

Abstract

AbstractStandardization of the cultivation conditions is crucial for producing fungal biomass with effective whole-cell catalytic activity. Aspergillus flavus mutant was optimized for biomass transesterification and hydrolysis of waste frying oil (WFO) as a substrate. The glucose-polypeptone medium was selected among other culture media as the primary medium for the optimization of submerged cultivation. Biomass lipolytic activities and growth of A. flavus were higher under shaking conditions compared to static conditions, and 200 rpm was optimum. Olive oil was superior to soybean, rapeseed, and waste frying oils as biomass lipase and transesterification activities inducer. Replacing glucose with sugar cane molasses enhanced the growth but inhibited the biomass lipolytic capabilities. Urea improved the biomass lipolytic capabilities as an N-source feedstock compared to corn-steep liquor and whey. Plackett Burman screening of 9 factors showed that KH2PO4 (0.1–0.9 %, w/v), urea (0.1–1.3 %, w/v), and glucose (0.5–3.5 %, w/v) concentrations were significant factors with the highest main effect estimates 38.45, −19.04, and 11.82, respectively. These factors were selected for response surface methodology (RSM) optimization using central composite design (CCD). CCD models for growth, biomass lipase activity, and transesterification capability were significant, with R2 values of 0.93, 0.91, and 0.95, respectively. The optimum concentrations for growth and biomass transesterification capability were glucose (4.5 %, w/v), urea (0.7 %, w/v), and KH2PO4 (0.9 %, w/v), and those for lipase activity of the biomass were glucose (4.4 %, w/v), urea (0.7 %, w/v), and KH2PO4 (2.1 %, w/v).