Valorization of unripe banana peel (Robusta) powder for the production of tannase using Bacillus xiamenensis in submerged fermentation

Abstract

Tannases are industrial enzymes used in cosmetic, pharmaceutical, food, and environmental management. In the present study, 11 tannase-producing Bacillus spp. were isolated from agricultural soil, banana root soil, vegetable garbage, and fruit garbage. These isolated bacteria were screened using tannic acid agar plates. The zone of hydrolysis varied from 9 mm to 21 mm, and the strain Bacillus xiamenensis BR1 exhibited the highest activity. The dried unripe banana peel (Robusta) was powdered, and particles between 1 and 1.5 mm were used as substrate. The banana peel consists of 7.84 ± 0.15% hydrolysable tannin, which induces the production of tannase. The production medium was prepared at 10% (w/v) unripe banana peel powder. The screening experiments revealed that fermentation period, pH, inoculums, and tannic acid improved tannase production. A two-level full factorial design revealed the influence of pH, inoculums, and incubation time on tannase production (F-value=8.99; p-value=<0.0001). The optimum concentration was analyzed using a central composite design, and the model was significant (F-value = 17.03; p-value = 0.0001). Under optimal bioprocess conditions, tannase yield was 2.4-fold higher than in an unoptimized medium. The unripe banana peel can be used as a substrate for the production of tannase by Bacillus sp.