Valorization of locally available waste plant leaves for production of tannase and gallic acid by solid-state fermentation

To evaluate the potential of various indigenous plant leaves for the biosynthesis of value-added products including tannase and gallic acid by Aspergillus oryzae FCBP-PTF-1202 in solid-state fermentation. Tannic acid-rich indigenous plant leaves Psidium guajava (guava), Syzygium cumini (black plum), Eucalyptus globulus (Eucalyptus), Ficus benghalensis (Banyan), Citrus limon (lemon), Ficus religiosa (Sacred fig), Citrus sinensis (Orange), and Mangifera indica (Mango) were analyzed to explore their potential as substrates for the production of tannase and gallic acid. From different substrates tested, black plum leaves produced a significantly (p < 0.05) higher yield of tannase (138.34 U/g) and gallic acid (0.565 mg/g). Various influential physicochemical parameters were optimized to improve the yield of gallic acid. Results revealed that black plum leaves at a substrate water ratio of 1:2, pH 5.5, and temperature 30 °C yielded the best production after 72 h of the incubation period. Supplementation of glucose and nitrogen source to basal media increased the yield of tannase (179.95 U/g) and gallic acid (0.986 mg/g). Furthermore, the gallic acid produced was extracted by Soxhlet apparatus and identified by Fourier-transform infrared spectroscopy (FTIR). The purity of gallic acid produced was 98.5% as quantitatively analyzed by high-performance liquid chromatography (HPLC). In the end, the production of tannase and gallic acid from plant leaves through the optimized environment via solid-state fermentation can be exploited commercially to enhance our economy.