Convective Drying of Papaya Seeds: Impact of Ethanol Pretreatment

Papaya seeds are agroindustrial residues rich in bioactive compounds, lipids, and proteins. Their high moisture content makes them vulnerable to chemical and microbiological deterioration. Drying is a practical process to extend shelf life. The immersion in ethanol can be used as a drying pretreatment for improving the final quality and reducing drying time. This study examined the effect of ethanol on drying kinetics, specific energy consumption, cell-wall thickness, quality parameters (water activity, color, phenolics, flavonoids, and antioxidant activity), oil yield, and mass-transfer mechanisms via mathematical modeling. Seeds were immersed in ethanol for 2 min and convectively dried at 50°C or 70°C (air velocity 1 m s^-1). The pretreatment shortened drying time by up to 55% and reduced energy demand by 54.07% at 50°C and 31.13% at 70°C, while inducing structural thinning of the cell wall that enhanced mass transfer. Drying preserved total phenolics and ABTS antioxidant activity, although flavonoids were more susceptible to ethanol-related degradation. Lowering water activity proved effective for product stability, and drying at 50°C with ethanol offered better color retention. Mathematical modeling confirmed that ethanol altered mass-transfer behavior, yielding a mixed regime governed by both internal diffusion and external convection. Ethanol pretreatment coupled with temperature control thus optimizes papaya-seed drying, supporting their use as a sustainable ingredient for the food and pharmaceutical industries. PRACTICAL APPLICATIONS: This study demonstrates that ethanol pretreatment prior to convective drying of papaya seeds is an effective strategy to reduce drying time and energy consumption while preserving functional properties such as phenolic compounds and antioxidant activity. The dried seeds exhibit microbiological stability and potential for use in functional foods, dietary supplements, and cosmetics. Moreover, the technique offers a sustainable solution for agro-industrial waste valorization, contributing to circular economy practices and adding value to the papaya supply chain.