Enhanced melanin production in Inonotus hispidus by the use of agricultural straw

As a novel polymer with various functions, melanin has broad application prospects in medicine, bioremediation, biological stress and biological oxidative stress. However, the mechanism of melanin production by Inonotus hispidus remains unclear. In this study, we obtained I. hispidus from the wild, isolated and purified a strain with the ability to produce melanin, and added the agricultural wastes of corn straw (CS), soybean straw (SS) and rice straw (RS) for the production of melanin. The effects of different agricultural wastes on melanin production were evaluated via FTIR, organic element analysis, scanning electron microscopy (SEM) and UV spectrophotometry. The results showed that I. hispidus could produce melanin from corn straw, soybean straw and rice straw. However, soybean straw produced the highest amount of melanin, at 1.85 ± 0.06 g·L^-1. In addition, the purified melanin was identified as I. hispidus melanin. The stability results revealed that the weight loss rate of CS melanin was 19 % at 77 °C for the first thermal decomposition, 50 % for the second decomposition at 508 °C, and 59 % for the third decomposition at 900 °C. I. hispidus melanin also has good antioxidant ability. The hydroxyl free radical scavenging rate of CS melanin was 99.3 ± 0.36 % at 3.0 mg·mL^-1. This study can be used to develop high-yield melanin strains and provide a basis for the reuse of agricultural wastes.