Influence of alkaline salt cooking on solubilisation of phenolic compounds of bambara groundnut (Vigna subterranea (L.) Verdc.) in relation to cooking time reduction

Bambara groundnut (Vigna subterranea (L.) Verdc.) is an underutilized crop native to sub-Saharan Africa. Its utilisation is limited due to the development of the hard-to-cook (HTC) phenomenon during storage. Various factors have been implicated in the development of the HTC phenomenon. Alkaline rock salts, such as gowa, are known to reduce cooking time. In this research, red bambara groundnuts were cooked in deionised water, 0.5 g/100 mL gowa and 0.5 g/100 mL NaHCO3. The salts caused 20 and 13% reduction in cooking time, respectively. The decrease of hardness and the kinetics of water absorption by the beans are even more influenced by the alkaline cooking. The comparative effect of NaHCO3 and deionised water on polyphenol profile in the beans and in the boiling water during cooking also showed clear differences among the samples. Catechin and epicatechin were the main polyphenols in bambara groundnuts for all treatments investigated and their release in water was faster in alkaline solutions. This study demonstrated that alkaline salts contribute to increased solubilisation of polyphenols in relation to cooking time reduction. Data indicate that the action of the salts favours polyphenol solubilisation thereby altering the structure of the lamellae and reducing hardness.