Evaluation of selected agri-industrial residues as potential substrates for enhanced tannase production via solid-state fermentation

Abstract

Tannase is an important enzyme widely used in the production of food, feed, pharmaceuticals, beverages, leather and cosmetics, but its industrial application is still limited because of its high production cost. Agri-industrial residues are generally rich in tannins and can be used as low-cost substrates for tannase production. In this study, selected agri-industrial residues were evaluated as potential substrates for enhanced tannase production by a locally isolated fungal strain via solid-state fermentation. Among all four agri-industrial residues tested, rice bran, a nutrient-rich substrate with a low tannin level, showed the highest tannase activity during solid-state fermentation, followed by brewer's rice, spent coffee ground and desiccated coconut residue. Spent coffee ground contained the highest tannin content (155 mg tannin/g substrate), but exhibited poor fungal growth, possibly because of the high tannin content in spent coffee, which might have inhibited fungal growth. However, the incorporation of small amounts of spent coffee ground (0.5% tannic acid equivalent, TAE) into rice bran enhanced tannase activity by 1.8-fold and 3-fold in comparison to rice bran used as single substrate or with the addition of tannic acid, respectively, with 260.39 U/g tannase being produced. The use of nutrient- and tannin-rich agri-industrial residues, such as rice bran and spent coffee ground, enhances tannase activity, suggesting that such low-cost substrates can be used in industrial tannase production.