Acid hydrolysis of almond shells was carried out with 2.5 and 5% sulfuric acid, and the ethyl acetate soluble fraction of hydrolysates (EASH) was fractionated on a Sephadex Uppsala, Sweden) column. Three fractions were recovered from the crude extract produced by hydrolysis with 2.5% sulfuric acid (EASH-2.5), and five from the one produced with 5% sulfuric acid . The recovered fractions were assayed for phenolic content, radical-scavenging activity (measured by the a,a-diphenylb-picrylhydrazyl and Trolox equivalent antioxidant capacity [TEAC] methods) and reducing capacity (measured by the ferric-reducing antioxidant power [FRAP] and the reducing power methods). The highest contents of phenolics corresponded to the third fraction (F3) from EASH-2.5 and to the fourth fraction (FЈ4) from EASH-5, whereas fraction 1 (F1) from EASH-2.5 and fraction 4 from EASH-5 showed the highest TEAC and FRAP values, and reducing power.
PRACTICAL APPLICATIONSAcid-catalyzed hydrolysis for producing xylose is the most common technology for processing almond shells into chemicals, and allows fractionation of this residue into a solid fraction (cellulose and lignin) and a liquid stream containing monomeric sugars, sugar degradation products, extractives and lignin depolymerization compounds. To destine the monomeric sugars as a carbon source for bioconversion purposes, a detoxification step is required. Solvent extraction with ethyl acetate yields a by-product fraction consisting of compounds with phenolic nature and antioxidant activity, and its utilization 1 Corresponding