Antioxidant activity of extracts produced by solvent extraction of almond shells acid hydrolysates

The ethyl acetate-soluble fraction generated during acid hydrolysis of almond shells was evaluated for radical-scavenging capacity and protection against fish oil oxidation. The influence of the operational conditions during acid hydrolysis on: (i) the total phenolics produced; (ii) the recovery yield of ethyl acetate solubles; (iii) the phenolic content in the ethyl acetate extracts; (iv) the antioxidant activity of extracts was assessed. A one-at-a-time variation study of the hydrolysis time and sulfuric acid concentration was carried out. For a given temperature and hydrolysis time, the influence of the acid concentration was noticeable; whereas the maximal phenolics production, measured in the hydrolyzate (2.2 g gallic acid equivalents/100 g shells) was achieved with 2% sulfuric acid, the maximal recovery in the organic phase required at least 5% acid. The crude extracts showed DPPH radical-scavenging activities (EC50 < 0.5 g/l) comparable to those of synthetic antioxidants, and protected labile lipid systems, such as fish oils and fish oil-in water emulsions, from oxidation as efficiently as did propyl gallate.