Evaluation of antioxidant activity of the fermented product from the biotransformation of R-(+)-limonene in solid-state fermentation of orange waste by Diaporthe sp.

Through solid-state fermentation, the endophytic fungus Diaporthe sp. biotransformed the compound R-(+)-limonene, a great quantity of which is present in orange waste. The fermented orange waste was evaluated to determine its antioxidant potential. Mass spectrometry identified several biotransformation products, which were quantified by gas chromatography. The fermentation process yielded compounds such as limonene-1,2-diol, α-terpineol, (−)-carvone, α-tocopherol, dihydrocarveol and valencene, most of which have already been associated with antioxidant activity. The highest concentration of limonene-1,2-diol produced was 3.02 g/kg of dry substrate and 0.72 g/kg of α-terpineol. The DPPH, ORAC and CUPRAC methods were employed to analyze the antioxidant activity comparing the orange waste and the fermented orange waste. According to the results obtained using the DPPH method, the fermented media extract represented 20.17% of antioxidant activity, compared to 12.1% of the orange waste extract, while from the ORAC method analysis the results were 24,011.39 μmolTE/g, obtained from the fermented extract in comparison to 5226.45 μmolTE/g from the orange waste. The results from the CUPRAC method analysis were 538.05 mg TE/g of dry extract, from the fermented extract in comparison to 168.27 TE/g of dry extract, from the orange waste. These results prove that the fermentation process increased the antioxidant potential of the orange waste.