Extraction and Characterization of Biomolecules from Agricultural Wastes

Chestnut (Castanea sativa Mill.) and hazelnut (Corylus avellana L.) shells product from farming and food industry processes, because of their valuable biomolecules content, were analysed as promising source of antioxidant compounds. The aim of this study was to evaluate several extraction procedures of such agricultural by-products and to characterize specific phenolic molecules contained in the shells of chestnuts and hazelnuts. For these purpose we used different extraction solvents, such as water, methanol/H2O 70/30(v/v), and absolute methanol. Specifically, the extraction yield, the content of total polyphenols by Folin-Ciocalteu colorimetric assay, and the antioxidant activity by FRAP (Ferric Reducing Antioxidant Power) were measured. In particular the following specific phenolic compounds were detected and determined by HPLC analysis: gallic, chlorogenic, ferulic, p-coumaric, and ellagic acids, (+)-catechin, (-)-epicatechin, and rutin. The values of extraction yield and total polyphenol content decreased according to the extraction solvent in the following order: absolute methanol > 70% methanol > water. The antioxidant activity showed the opposite trend among the three types of extraction. The values obtained from the analysis were higher in chestnut rather than in hazelnut shell. The specific amount of phenolic compounds varied depending on the solvent used for the extraction. Gallic acid was found in all samples extracted, though with lower values in hazelnut shells treated in water. High values of (-)-epicatechin, chlorogenic acid and ellagic acid were found in hazelnut samples extracted with hydro-alcoholic solution and water. A fair amount of catechin was detected in all samples, whilst rutin, p-coumaric acid and ferulic acid were present in small amounts, although the best results were obtained in absolute methanol. The results of this study demonstrated that with a simple extraction process considerable amount of phenolic compounds with high antioxidant activity were obtained from chestnut and hazelnut shells.