Valorization of onion skin wastes using subcritical water: flavonoids and pectin recovery

Abstract

Onion skin wastes (OSW) represent around 10% of the total onion production and end up in landfills because they are not suitable for human consumption or animal feeding. Nevertheless this non-edible brown skin and external layers of onions are rich and phenolic compounds, mainly flavonoids such as quercetin and derivatives, which are high-added valye natural antioxidants. Additionally, onion skin has gained attention as a good source of pectin. Pectin, a complex polysaccharide composed by uronic acids (66.4%) and neutral sugars (galactose, arabinose, xylose, mannose, glucose or rhamnose) in variable composition, is the major structural component onion cell walls (42,4%). Considering that according to FAO, 2020 onion worldwide production was 104 Mt, there is a great potential for the calorization of the OSW through the recovery of flavonoids and pectin.