Statistical optimisation of laccase production by isolated strain Aspergillus flavus PUF5 utilising ribbed gourd peels as the substrate and enzyme application on apple juice clarification

In the current study laccase was produced by the isolated strain Aspergillus flavus PUF5 through solid-state fermentation (SSF) using waste ribbed gourd peels as substrate. During the statistical optimisation process, influencing fermentation factors among eleven selected variables were identified using Plackett-Burman design. Among them, fermentation time (144-192 h), medium pH (3.0-7.0), concentration of starch (0.5-1%) and concentration of peptone (0.2-0.8%) were vital influencing parameters. Furthermore, the shared effects of those variables were studied following Box-Behnken design. Optimised states of selected variables were fermentation time (168 h), medium pH (4.9), concentration of starch (0.61%) and peptone (0.51%) with predicted and observed activity of laccase 174.3 and 168.9 U/g, respectively. This laccase production under optimised condition was about 3.5-fold more that the unoptimised medium. The laccase obtained through SSF was tested for its suitability in the clarification of apple juice. During enzymatic oxidation, the changes in colour, turbidity, phenolics and flavonoids in apple juice were estimated and compared with untreated sample. Results showed a significant reduction in phenolic and flavonoid content in the fruit juice during the oxidation process. The turbidity in the juice was also decreased, which indicated the suitability of the laccase form A. flavus PUF5 in fruit juice clarification.