High citric acid production in solid-state fermentation by Aspergillus brasiliensis on polyurethane foam

A statistical approach based on fractional and complete factorial designs to increase the citric acid yield was used. Polyurethane foam (PUF) was used as inert support for solid-state fermentation (SSF) due to its high-water retention capacity (up to 60-fold of its weight), resulting in the recovery of concentrated citric acid by squeezing it. The maximum yields for citric acid (0.62 Cmol/Cmol glucose) and polyols (0.11 Cmol/Cmol glucose) are obtained by growing Aspergillus brasiliensis in a well-defined culture medium (at 30°C for 120 h). Citric acid, polyols, and glucose consumption are negatively affected by a high glucose concentration (250 g/L). In contrast, enrichment of the culture medium with yeast extract only enhances citric acid production yield (0.54 Cmol/Cmol glucose). This study demonstrates that the citric acid production yield is negatively affected by phosphate (> 4.54 g/L) and magnesium (> 0.26 g/L). The PUF for SSF is an inexpensive and useful support for the commercial production of citric acid. The utilization of low-cost inert supports through SSF can contribute to achieving industrially viable and sustainable citric acid production. As far as we know, this work reports the highest citric acid production yield using SSF on an inert support such as PUF soaked with a defined medium.