Industrial drying for agrifood by-products re-use: Cases studies on pomegranate peel (Punica granatum L.) and stoned olive pomace (pâtè, Olea europaea L.)

Abstract

The effect of industrial drying processes on phenols and polysaccharides of olive pomace (pâté) and pomegranate peel was studied, with the aim to re-use pomegranate and olive oil by-products. Pomegranate peel (Wonderful and G1 varieties) was oven-dried at different temperatures, taking into account peel thickness and size. Pâté was freeze-dried and oven dried at 50-110 °C, at lab scale; then, an industrial drying system (150 °C) was compared to freeze-drying. All dried samples were analyzed in terms of phenolic and polysaccharides compounds. Drying at room temperature of small pieces of pomegranate peel guaranteed the highest humidity removal and recovery of phenols. Sugar analysis, DLS and ¹H NMR confirmed that polysaccharide fractions were not significantly affected by the highest drying temperatures (42 °C for pomegranate, 150 °C for pâté). The two drying procedures at large scale were suitable for avoiding degradation of phenols, maintaining the same profiles of the corresponding freeze-dried samples.

Keywords: (1)H NMR; DLS; Ellagitannins; Hydroxytyrosol; Lyophilization; Oven-drying; Pectic polysaccharides; Polyphenols.