Integrated process for fungal citric acid fermentation using apple processing wastes and sequential extraction of chitosan from waste stream

The present study was carried out to explore the possibility of extracting chitosan (CTS) from waste fungal mycelium as co-product during citric acid (CA) fermentation. CA biosynthesis was carried out through solid-state (SSF) and submerged fermentation (SmF) in lab scale fermenters using apple pomace (AP) and apple pomace ultrafiltration sludge (APS) by Aspergillus niger NRRL 567. CA production of 182.8 ± 8.2 and 294.2 ± 13.2 g/kg dried AP and 18.4 ± 1.24 and 40.3 ± 2.0 g/L APS was achieved through SSF and SmF after 120 h and 132 h fermentation period, respectively in control and in treatment with methanol as an inducer.The resulting waste fungal biomass during CA production was used for CTS extraction using ambient conditions. Extractable CTS was found to be higher in control (treatment with no inducer) with 6.40% and 5.13% of dried fungal mycelium resulting from the SSF and SmF, respectively as compared to treatments supplemented with inducers (ethanol and methanol). Degree of deacetylation of the CTS ranged from 78 to 86% for fungal biomass obtained from SSF and SmF. The viscosity of fungal CTS was in a range of 1.02-1.18 Pa s−1, comparable to the commercial crab shell CTS. The study indicated the possibility of sequential extraction of superior quality CTS from waste fungal biomass resulting from various fungal-based biotechnological industries including CA.