Optimization of the extraction of natural antioxidants from inajá processing residue

Brazilian native fruits have been used for oil extraction thus generating large amounts of processing by-products. As sources of phenolic antioxidants, oil processing by-products may still find better applications as nutraceuticals and/or functional food ingredients. However, to date several oil processing by-products are still undervalued and sometimes discarded. Inajá (Maximiliana maripa Aubl. Drude), a Brazilian native species from Pará state, is among the feedstocks used for oil extraction. Bioactive molecules, including phenolic antioxidants, are plant secondary metabolites and are present as minor compounds. Therefore, increasing their recovery is deemed necessary. Furthermore, the extraction and recovery of phenolic compounds is influenced by several factors (e.g. solvent concentration and temperature). The aim of the present study was to optimize the extraction of phenolic antioxidants from inajá by-products in order to fill the existing gap in the available literature. A multivariate experimental design with a central composite rotatable design (CCRD) was applied and the results were evaluated by response surface methodology and statistical analysis. Independent variables [temperature of extraction (°C) and ethanol concentration (%, v/v)] were investigated with respect to their effects on the antioxidant potential (ABTS radical cation scavenging assay) and reducing power (FRAP assay). The antioxidant potential of the extracts towards ABTS radical cation ranged from 79.40 to 175.3 µmol trolox equivalents g-1 while the reducing power ranged from 35.71 to 156.5 µmol equivalents Fe2+ g-1. Statistical analysis demonstrated that 70°C and 50% (v/v) ethanol were the ideal combination to obtain an extract with improved antioxidant potential and reducing power. Optimization allowed the recovery of phenolic extracts with, approximately, 6.5 and 11.6 times higher antiradical and reducing power activity, respectively. Furthermore, the total phenolic content of the extract obtained under optimized conditions was 640.4 ± 61.0 mg gallic acid equivalents g-1 while the scavenging activity towards DPPH radical was 5.0 ± 0.3 µmol trolox equivalent g-1. Monomeric flavonoids and procyanidins were identified by LC-ESI-QTOF-MS. Therefore, it was possible to set a standard condition to recover phenolic antioxidants from inajá by-products and identify several compounds, which may increase its potential application as a new source of natural phenolic antioxidants.