Drying temperature effect on the physical characteristics of olive oil mill waste powder

Abstract

This research reports the effect of oven drying on the physicochemical and handling properties of olive mill waste (OMW) powder, an economically valuable functional byproduct of olive oil production. OMW samples were oven-dried at 60 and 80 °C and bulk and tapped density, porosity, flowability (Hausner ratio, Carr index, angle of repose), wettability, water/oil holding capacities (WHC/OHC), water activity (aw), and color were determined. Higher drying temperatures decreased moisture content and water activity, thereby improving the stability and flowability of powder while increasing structural collapse and darkening as a result of thermal browning. OD80 was shown to present optimal flow (lower angle of repose and Carr index) and quicker imbibition, while OD60 was found to contain higher WHC and hydration potential which did not vary. The particle densities were also high and indicated the heavy inorganic materials present in both the samples. The research provides evidence in the tradeoff between the dehydration efficiency and quality preservation during the heat processing. Further research should concentrate on optimization of the drying conditions and/or the use of alternative drying technologies, including vacuum or microwave-assisted drying to maintain bioactives while obtaining microbiological stability. These findings favor the valorization of OMW as sustainable functional food ingredient, which would be useful to realise circular economy in agro-industrial waste management.