METABOLITE CONTENT AND ANTIOXIDANT ACTIVITY OF SPENT COFFEE GRAIN FERMENTED WITH Pleurotus pulmonarius MYCELIUM

Abstract

Spent coffee beans are agro-industrial waste that contain nutrients and bioactive compounds that can be recovered by fungal fermentation-assisted extraction using edible fungal strains. In this study, the metabolite content and antioxidant activity of the aqueous extract of spent coffee beans fermented in a submerged culture using the mycelium of Pleurotus pulmonarius were evaluated. The total carbohydrate, phenol, flavonoid, and caffeoylquinic acid contents of the extract were determined, as well as the antioxidant activity by free radical and cation inhibition, reducing power, and lipid oxidation inhibition. The experimental design was completely randomized using a factorial arrangement, with three independent experimental replicates. The data were examined using analysis of variance (ANOVA) and the Tukey-Kramer mean comparison test (p ≤ 0.05). To determine the association between variables and parameters evaluated, a principal component analysis was used. The results showed that the aqueous extract obtained by submerged culture fermentation using P. pulmonarius and different levels of spent coffee beans presented a high content of metabolites such as carbohydrates (70.2 %), phenols (64.5 %), flavonoids (61.9 %), and caffeoylquinic acid (90.8 %), as well as a higher antioxidant activity by inhibiting the formation of 2,2-diphenyl-1-picrylhydrazyl (DPPH•) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS•+) radicals (31.6 and 31.9 %, respectively), lipid oxidation (70 %), reducing power (14.9 %), and Ferric Reducing Antioxidant Power (FRAP) (89.4 %), compared to the control. Furthermore, the first two main components explained 91.3 % of the variation, revealing that fermented samples with and without mycelium differed in terms of metabolite content and antioxidant activity, which were dependent on the proportion of wasted coffee beans. In conclusion, the fungal fermentation of spent coffee beans is a potential strategy for the recovery of antioxidant ingredients.