Fungal laccases production using agro-food wastes: a factorial design approach

Fungal laccases are excellent green biocatalysts but their actual exploitation at industrial scale is still limited by the commercial availability of large amount of cheap enzymes of interest. Basidiomycetes are considered great enzymes sources and, during this study, the attention was focused on a Trametes pubescens strain: its laccases were stable, versatile and, when a direct comparison was possible, more active than commercial formulates. The objective was then to stimulate laccases production by controlling medium composition and operative conditions. Traditional C/N sources (glucose, peptone) and model inducers resulted functional for this purpose, but they are not cost effective. For industrial applications, the economic balance should be indeed taken into consideration. Wastes of agrochemical and food processes may be used as alternative nourishment sources for fungi; their lignino-cellulosic matrix mimics the natural growth substrate of ligninolytic fungi, being able to sustain and trigger specific metabolisms. Tomato sauce and orange peel waste were here considered because of the large production within Italian and, more in general, Mediterrean boundary. At first, the concentration of both sources (C) and peptone (N) was evaluated in presence of Cu as inorganic inducer. A 22 plus centre point replicated factorial design was used to investigate the role of these factors and their synergic effect on laccase production. Both C and N concentration gave significant effects, even though N was more important for tomato sauce. An interaction between the two factors was always observed. The highest laccase productivity was achieved in presence of orange peel waste (46 U/ml). These data should be verified, and whether possible, acquiring chemical analysis of the wastes acquired. Further experiments are then necessary to define the optimal medium composition for laccase production. Moreover, the effect of other factors (Cu, pH, inoculum, etc.) has to be evaluated.