Pomegranate peel waste: a new substrate for citric acid production by Aspergillus niger in solid-state fermentation under non-aseptic conditions.

Citric acid production from dried and non-dried pomegranate peel wastes by the fungus Aspergillus niger B60 in solid-state fermentation (SSF) under non-aseptic conditions was investigated. The maximum amount of citric acid (278.5 g/kg dry peel) was achieved using dried (at 45 °C for 48 h) pulverized pomegranate peels with moisture content 75% and initial pH 8.0, after 8 days of fermentation at 25 °C. Under the same fermentation conditions, a higher amount of citric acid (306.8 g/kg dry peel) was observed during SSF of non-dried peels as a substrate. The addition of methanol as an inducer at a concentration of 3% (w/w) into the dried and non-dried pomegranate peel wastes increased the amount of citric acid to 300.7 and 351.5 g/kg dry peel, respectively. The non-dried pomegranate peel waste in SSF under non-aseptic conditions is a cheap and useful substrate for the commercial production of citric acid with low energy cost. The utilization of inexpensive agro-industrial wastes through SSF can contribute to achieve industrially feasible and environmentally sustainable bio-production of citric acid.