Bioproduction and extraction optimization of citric acid from Aspergillus niger by rotating drum type solid-state bioreactor

Solid-state citric acid fermentation was conducted in a 12-L rotating drum type bioreactor. The effect of inducers, ethanol and methanol were studied on citric acid bioproduction by Aspergillus niger NRRL 567 cultivated on apple pomace as a solid-substrate. Optimum conditions achieved for higher citric acid bioproduction (220.6 ± 13.9 g/kg dry solids, DS) were 3% (v/v) methanol, intermittent agitation of 1 h after every 12 h at 2 rpm and 1 vvm of aeration rate and 120 h incubation time. The response surface optimization proved effective for higher citric acid extraction from fermented solid-substrate. Higher citric acid extraction of 294.19 g/kg DS was achieved at optimum conditions: extraction time of 20 min, agitation rate of 200 rpm and extractant volume of 15 ml by response surface methodology.

► Economical and sustainable citric acid (CA) production using apple pomace waste.
► To met the rising demand of CA in many advanced applications in food and biomedicines.
► To lessen the environmental hazards caused by the disposal of agro-industrial wastes.
► Environmental capture of waste carbon leading to mitigation of climate change.