Abstract
Vegetable overproduction and high moisture content lead to significant food waste and fast deterioration. Drying is an effective circular economy strategy to valorise these surpluses, extending shelf-life and reducing losses. This process transforms perishable biomass into stable, value-added ingredients, promoting a more sustainable agri-food system. This study evaluated the effect of drying on moisture content, colour attributes and drying kinetics of two kale cultivars, Brassica oleracea L. var. acephala DC and B. oleracea L. var. costata, produced in Northern Atlantic Portugal, with the aim of supporting sustainable valorisation pathways for leafy vegetable surpluses. Fresh leaves, subjected or not to hot water blanching, were dried at 60, 70 and 80 °C in a laboratory-scale oven until reaching 2% moisture. Moisture content was determined and colour was characterised using the CIELab system (L*, a*, b*, ?E), and drying behaviour was described through thin-layer models fitted to moisture ratio data. Drying caused a marked darkening of var. acephala, whereas brightness of var. costata was largely preserved, in both cultivars, b* increased, indicating more intense yellow tones, while a* remained in the green region. Among the empirical models tested, the Page equation showed the best fit, with coefficients of determination (R²>0.999) across all temperatures and pretreatments, confirming faster moisture removal at higher temperatures and in non-blanched samples. Overall, the results demonstrate that appropriate combinations of blanching and drying temperature can control colour changes while ensuring efficient moisture removal, contributing to the sustainable processing and circular economy-based valorisation of kale leaves.
