Phenolic composition and antioxidant activity of agroindustrial residues

Nowadays, the agro-industrial processing produces millions of tons of wastes. Many of them are rich in bioactive compounds, being a potential natural source of these substances. This study aimed to evaluate the content of total phenolics, antioxidant activity and phenolic composition of residues generated by three Brazilian agribusiness: Isabel grape pomace (PI) (Vitis labrusca), Verdejo grape pomace (PV) (Vitis vinifera) and guava pomace (PG) (Psidium guajava). The results of total phenolics content (mg GAE g(-1)) found in the ethanol and aqueous extracts of residues were: PV (20.94 +/- 0.46; 8.03 +/- 0.43) > PI (16.57 +/- 0.19; 4.41 +/- 0.01)> PG (3.41 +/- 0.09; 1.88 +/- 0.06). High antioxidant activity of these extracts, particularly PV and PI, was found by the methods DPPH, ABTS and beta-carotene bleaching method. A strong positive correlation between antioxidant activity and content of total phenolic compounds was found. The following phenolic compounds were found by gas chromatography with mass spectrometry (GC-MS): gallic acid, epicatechin, quercetin (PV, PI and PG); isovanilic acid (PI, PG), p-coumaric acid (PI), caffeic acid and resveratrol (PV, PI). The results show that these residues, particularly the wineries, are rich in bioactive substances and should be exploited by the food industry and pharmaceuticals.