Screening of four different agro-food by-products for the recovery of antioxidants and cellulose

Carried out under the European Project SusFoFlex, this study aimed the investigation and selection of different agro-food by-products for the recovery of antioxidants and cellulose to be further exploited for application in the development of innovative and sustainable food packaging materials. Based on literature data and partners' countries availability, four by-products were considered: brewers' spent grains, wheat straw, hazelnut shells and orange peels. A common process for the production of antioxidant extracts (a two-step hydro alcoholic solvent extraction) and another for the fractionation of cellulose (an acid hydrolysis step followed by an alkali hydrolysis and, then, an oxidative bleaching step) was applied to all the materials with the objective of selecting ideally a unique by-product for the production of both antioxidants and cellulose. The extracts were characterised in terms of total phenols content (based on Folin assay and expressed as gallic acid equivalents) and antioxidant activity (evaluated with both the radical ABTS test and the Ferric Reducing/Antioxidant Power assay).The highest total phenols recovery was obtained for orange peels (9.50±0.66 mg per g of dried by-product), while the yields for the other byproducts were not statistically different and ≤ 2 mg/g. Regarding the antioxidant activity, all the extracts showed very similar results with the ABTS assay, whereas orange peels extract exhibited the highest level of FRAP activity. The obtained cellulose residues were analysed for the total cellulose content and the level of lignin and hemicellulose impurities. In this case, the best by-product resulted wheat straw, with the recovery of 45 % of the original cellulose, a cellulose content (purity) of 84 % and residual impurities of hemicelluloses and lignin of 2 % and 12 %, respectively.