Refractance Window versus Oscillatory Drying: Effects on Vernonia amygdalina Nutritional, Bioactive, and Techno-Functional Properties
DOI:
https://doi.org/10.33003/fjs-2026-1014-5648Keywords:
Vernonia amygdalina, Refractance Window Drying, Oscillatory Hot-Air Drying, Antioxidant Activity, Techno-Functional PropertiesAbstract
The preservation of nutritional and bioactive compounds during the drying of leafy vegetables remains a major challenge, as conventional drying methods often cause quality deterioration due to thermal degradation. This study compared the effects of Refractance Window drying (RWD) and oscillatory hot-air drying (OD) on the nutritional composition, bioactive compounds, colour characteristics, and techno-functional properties of Vernonia amygdalina (bitter leaf). Fresh leaves were dried under controlled conditions using both techniques, and the resulting powders were analyzed using standard methods. RWD produced a lower residual moisture content (6.57%) than OD (9.04%) and resulted in higher retained levels of protein (15.60%), fat (3.34%), fiber (4.57%), and ash (7.24%). The technique also demonstrated superior preservation of bioactive compounds, yielding a total phenolic content of 40.54 mg GAE/100 g, total antioxidant capacity of 54.39 mg AAE/g, and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity of 58.65%. Furthermore, RWD better maintained colour quality by preserving leaf greenness compared with OD. Improved techno-functional properties were also observed, including higher water absorption capacity, a rehydration ratio of 3.51, and a bulk density of 0.42 g/cm³, indicating enhanced structural integrity and reconstitution characteristics. This study demonstrates that RWD is a promising drying technology for producing high-quality V. amygdalina powders with improved nutritional, functional, and bioactive properties, making it suitable for application in functional foods and nutraceutical formulations.
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Copyright (c) 2026 Mayowa Saheed Sanusi, Hafsat Funmilayo Bankole, Sodiq Ayinde Olaleye, Joyce Titilayo Madamori, Musiliu Olushola Sunmonu
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