Application of different drying techniques to fresh-cut salad waste to obtain food ingredients rich in antioxidants and with high solvent loading capacity

Wastes from iceberg salad fresh-cut processing were submitted to air-drying, freeze-drying, and supercritical-CO2-drying with or without ethanol as co-solvent. Drying was combined with grinding to obtain flours. Samples were analysed for macro- and micro-appearance, particle size, dietary fibre, polyphenol content, antioxidant activity, water vapour sorption, water and oil holding capacity. Air-drying produced a collapsed brown material allowing a flour rich in fibre (>260 g/kg) and polyphenols (3.05 mg GAE/gdw) with antioxidant activity (6.04 OD−3/min/gdw) to be obtained. Freeze-drying maintained vegetable structure and colour while partly retaining polyphenols (1.23 mg GAE/gdw). Supercritical-CO2-drying with ethanol as co-solvent, produced an expanded material able to entrap huge amounts of water and oil (43.2 and 35.2 g of water and oil for g of dry sample). Air-dried salad waste derivatives could be used as functional food ingredients, while supercritical-CO2-dried ones can be exploited as bulking agents and absorbers of oil spills or edible oils.