Αpplication of Aspergillus niger for Extracellular Tannase and Gallic Acid Production in Non-sterile Table Olive Processing Wastewaters

Abstract

Aspergillus niger B60 was screened for the first time toward extracellular tannase and gallic acid production by submerged fermentation using synthetic media supplemented with tannic acid as the sole carbon source at a wide concentration range (5–150 g/L). Maximum tannase (47 IU/mL) and gallic acid production (36 g/L) was obtained at initial tannic acid concentration 100 g/L. For this study, it was of interest to valorize non-sterile table olive processing wastewaters for fungal tannase production. In particular, lye and washing water effluents from Spanish-style green olive processing enriched with 100 g/L tannic acid provided effective alternative substrates for the production of tannase (21 IU/mL and 17 IU/mL, respectively) and gallic acid (22 g/L and 14 g/L, respectively). The fungal growth and tannase production kinetics were described by the Logistic and Luedeking–Piret models, respectively. The maximum dry biomass content and the maximum specific growth rate were more pronounced in the tannic acid-rich effluents (16–18 g/L and 0.5–0.6 1/h, respectively) than in the synthetic medium (11 g/L and 0.4 1/h, respectively) although in all cases tannase production was growth-associated. These novel findings cast a new light on successful biorefinery strategies of the effluents and warrant further investigation via process scaling-up and optimization. Graphical Abstract: (Figure presented.)