Influence of sun drying and a combination of boiling and sun drying on the retention of nutrients and bioactive compounds in cowpea (Vigna unguiculata (L). Walp) leaves

Abstract

The nutrients and bioactive compounds retention of cowpea (Vigna unguiculata (L). Walp) leaves subjected to the two traditional processing methods of sun drying and a combination of boiling and sun drying was investigated. Findings revealed that the retention of carbohydrates (92.72%), proteins (97.41%) and ash (92.39%) was significantly higher among samples that were subjected to sun drying alone, than samples subjected to boiling and sun drying. Considerable reduction in lipids content of sun dried samples (20.24%) and boiled and sundried samples (17.16%) were registered. Significant (p < 0.05) loss of bioactive compounds was registered when fresh leaves were subjected to the two processing methods. For example only 7.13% and 8% of β-carotene was retained in boiled and sun-dried samples and in sun dried samples, respectively. Insignificant effect on minerals was observed with more than 92% of Fe, Ca and Zn retained in sun dried and in boiled and sun dried leaves. The study demonstrated that subjecting cowpea leaves to sun drying and a combination of boiling and sun drying, leads to insignificant loss of carbohydrates and proteins but leads to the loss of bioactive compounds. The two processing techniques had insignificant effect on minerals contents. The study results show that drying could be considered for cowpeas preservation, which would contribute to ensuring all year availability of the vegetable.