Biotechnological potential of industrial wastes for economical citric acid bioproduction byAspergillus nigerthrough submerged fermentation

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Submerged citric acid (CA) bioproduction was carried out by Aspergillus niger NRRL-567 using various industrial wastes, such as brewery spent liquid (BSL), lactoserum and starch industry water sludge. CA bioproduction was carried out by varying the temperature (25–35 °C), pH (3–5), addition of inducers, incubation time and supplementation with different proportions of apple pomace ultrafiltration sludge (APS). The results indicated that under the best conditions with 3% (v/v) methanol, the optimal concentration of 11.34 g L−1 CA was recorded using BSL at pH 3.5 and temperature 30 °C after 120-h incubation period. Supplementation of methanol resulted in an increase of 56% CA production. Meanwhile, under similar conditions, higher concentration of 18.34 g L−1 CA was reported with the supplementation of BSL with 40% (v/v) APS having suspended solids concentration of 30 g L−1. The present study demonstrated the potential of BSL supplemented with APS as an alternative cheap substrate for CA fermentation.

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