Bioconversion of Agro-waste to Value-Added Product Through Solid-State Fermentation by a Potent Fungal Strain Aspergillus flavus PUF5

Abstract

Laccases are multicopper-containing oxidoreductase enzymes, which are commonly produced by plants and microbes, are involved in various biotechnological applications like bleaching of textile dyes, biofuels, biosensors, detoxification of effluent, bioremediation, etc. To compete efficiently with the chemical oxidizing agents, laccase must be produced in significant amounts up to industrial scale, and its production cost should also be minimized. In this concern, cheap waste products of agriculture and food industry can be used as inexpensive carbon source which can improve the economic feasibility of the enzyme production. Moreover, agro-wastes do not compete with the general food crops and cause environment pollution. So utilizing these renewable sources in solid-state fermentation (SSF) process can be considered very promising for the biotechnological production of laccase. Hence, the current study was focused on the optimization of process parameters for the higher production of laccase using a novel isolated fungi Aspergillus flavus PUF5 under SSF-utilizing waste ridge gourd peel as substrate. Fermentation parameters such as the amount of substrate, inoculum size, fermentation time, temperature, pH, and initial moisture content were optimized through one-variable-at-a-time (OVAT) method. Laccase production was further enhanced with additional carbon and nitrogen source supplementation. After 7 days of fermentation, maximum laccase yield (38.4 U/mg) was obtained using dried ridge gourd peel (5%) with 50% initial moisture content at 30 °C and pH 5.0 when 0.5% starch and peptone each were supplemented as carbon and nitrogen sources, respectively. Thus, the isolated fungal strain seems to be a potential candidate for laccase production through SSF. The process also supports economic valorization of agro-waste residues.