article · FUDMA Journal of Sciences
Conventional drying methods often degrade the nutritional and bioactive quality of leafy vegetables. Comparing Refractance Window drying and oscillatory hot-air drying on bitter leaf (Vernonia amygdalina) reveals distinct performance differences. Refractance Window drying achieved a lower residual moisture content of 6.57 percent alongside superior nutrient retention, maintaining higher levels of crude protein, fat, fibre, and ash. It also preserved bioactive properties more effectively, yielding higher total phenolic content, total antioxidant capacity, and radical scavenging activity. In addition, the Refractance Window method preserved the natural green colour of the leaves better than oscillatory drying. The resulting powder demonstrated enhanced techno-functional attributes, including superior water absorption capacity, a higher rehydration ratio, and higher bulk density, confirming its structural integrity and ease of reconstitution for downstream applications.
Drying green vegetables without destroying their beneficial nutrients, antioxidant qualities, and appearance is a persistent difficulty in food processing. Demonstrating that Refractance Window drying retains critical nutrients and antioxidant properties in bitter leaf offers a viable processing alternative for producing stable, high-value vegetable powders that reconstitute well and retain natural colour.
The findings suggest applications in functional food manufacturing and nutraceutical formulations, targeting food processors seeking nutrient-dense ingredient powders. The work represents applied laboratory research comparing two drying techniques. Real-world adoption would depend on scaling up Refractance Window drying equipment and evaluating process economics against standard commercial drying methods.
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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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DOI: 10.33003/fjs-2026-1014-5648
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