Laccase Production by Trametes pubescens from Citrus Industry By-Products

PurposeLaccases have become one of the most interesting green biocatalysts with possible technological impact on several biotechnological sectors, including pollutants bioremediation, bio-bleaching of pulp and fabrics, cosmetics, etc. To overcome the consistent production costs, agro-industrial wastes can offer a renewable, cheap, and nutritionally rich alternative to synthetic fermentation media. Despite their potential, many wastes have not been extensively valorized and their actual exploitation in microbial fermentation is still unexplored, including the here studied orange peel waste (OPW). This study investigated the possibility to use a sustainable medium to produce laccases by the fungus Trametes pubescens MUT 2400. Most of the research run microbial fermentation in solid state mode, even though this technology has many technical drawbacks, including the unsustainable scale up. Submerged fermentation may help to overcome these issues and was hence considered in the present study.MethodsWe used a factorial approach to study laccase production and biomass growth in submerged fermentation on media based on OPW. A replicated full factorial design with center point allowed to study the main effects and interactions of OPW and nitrogen concentration varying in the range of 30-50 g/L and 8.7-28.7 g/L, respectively, as well as their contribution to the curvature of the responses.ResultsThe key role of carbon and nitrogen source concentration on laccase productivity has been highlighted. The nitrogen concentrations used did not limit growth but affected laccase overproduction interacting with the concentration of OPW. The maximum laccase activity of 46.0 U/mL, more than 50% higher than the lowest detected activity in the experiment, was obtained at high concentration of OPW and nitrogen source.ConclusionsThese results demonstrate that OPW can effectively sustain submerged fermentation of T. pubescens, causing an extensive growth and laccase production. The production yield was approx. 900 U/g of OPW, raising the interest of the potential effect on the receiving market. Indeed, considering that citrus sector has approx. 50-60% of losses, generating millions of tonnes of wastes that could become a valuable by-product. In contrast to traditional culture techniques, factorial design highlighted the interaction between the operative parameters under study and their combined role on laccase production, confirming to be a valuable tool for media development in microbial fermentation.