Chilean wine industry generates large amounts of grape pomace, a by-product which can be considered an excellent source of polyphenols. Green technologies have been successfully developed to obtain polyphenol extracts from this agroindustrial waste, however care must be taken with the thermal degradation and possible generation of objectionable compounds such as 5-hydroxymethilfurfural (HMF) during extraction since it is commonly carried out at high temperatures (≥100 °C).
A sustainable valorisation process of Carménère pomace is developed considering the application of hot presurizzed liquid extraction with the addition of glicerol as alternative co-solvent, to obtain safe polyphenol extracts with high antioxidant capacity and lower contents of both 5-hydroxymethilfurfural (HMF) and reducing sugars.
In this work the effect of (i) increasing the glicerol content as co-solvent (15%-50%) and (ii) decreasing the extraction temperature (150-90°C) over the global performance of the process were explored.
The addition of glicerol (50%), allows working at lower temperatures (130°C) during liquid extraction without significantly (p ≥ 0.05) affect the antioxidant propierties of the extracts (IC50: 300 mg/ml; TPC: 45 mg GAE/g dried pomace).
Additionally, the use of glicerol significantly (p ≤ 0.05) decreases the reducing sugar extraction yields (~25%). Under these processing conditions, the formation of HMF is decreased, not only because of the lower temperature applied during extraction but also because of the reduction of reducing sugars which are the main precursors of HMF. The proposed methodology allows producing safe polyphenols extracts, i.e., free of HMF and reducing sugars