Alkaline washing effect on the physical and physicochemical properties of olive mill waste powder

Abstract

Olive mill waste, a by-product of olive oil extraction has recently gained attention due to its environmental impact and potential valorisation in many industries. Despite its importance, limited data are available on how different processing methods can affect its properties. To address this gap, this study analysed the effects of freeze-drying and NaOH washing treatment on the physical and physicochemical properties of olive mill waste. Specifically, handling properties (bulk, tapped, particle densities, porosity, Carr’s Index, Hausner Ratio, angle of repose) were assessed, the colour and water activity, and powder properties (wettability, water, and oil holding capacities). Results showed that the NaOH-treated powder exhibited lower bulk and tapped densities, Carr’s Index, and Hausner Ratio than the FD powder. Parameters including colour, water activity, and water-holding capacity were also lower. The FD sample had lower particle density, porosity, angle of repose, worse wettability, and a lower oil-holding capacity. Overall, this study highlighted how different processing methods can affect the functional properties of olive mill waste, offering a deep understanding of its behaviour, while supporting its application in different industries.