Extraction of polyphenols from vine pruning residues optimization

Abstract

Vine pruning residue (VPR) is a by-product obtained after annual pruning of vines, abundant in Portugal, and a natural source of compounds with antioxidant activity. In a previous work, an integral valorization of this residue was proposed in which 13.7 kg of xylooligosaccharides, 3.1 kg of phenolic compounds, 13.1 kg of ethanol and 27 kg of lignin per 100 kg of vine pruning residue were extracted[1]. Here, we aim at optimizing antioxidants extraction using different fractions of organic solvent (ethanol / water). Therefore, the objective of this work was to attain an optimum extraction condition for polyphenolic compounds from grapevine pruning using a response surface methodology. For each assay the temperature (46-114°C), the extraction time (19-221 min) and ethanol concentration (30-70%) were determined by factorial design. The solids/solvent ratio was 40:1 (mL/g). Total phenolic contents, Fe reducing power and antioxidant activity were quantified by spectrophotometry. The optimum extraction conditions were as follows: ethanol concentration, 45%; extraction time, 120 min; and temperature, 80°C. In these conditions the obtained extracts had higher concentration of phenolic compounds and thus higher antioxidant activity were obtained (FRAP = 3.81 kg Fe(II)/100 kg VPR, DPPH = 4.70 kg TE/100 kg VPR and ABTS = 16,48 kg TE/100kg VPR). In this context the vine pruning residue is a promising waste material for the production of compounds with added value.