Managing the hard-to-cook (HTC) phenomenon in bambara groundnut (Vigna subterranea (L.) Verdc.) processing for resource limited communities in Zimbabwe

Bambara groundnut (Vigna subterranea (L.) Verdc.) is a legume crop with great agronomic and nutritional potential to alleviate malnutrition and improve food security of many rural communities in semi-arid regions of sub-Saharan Africa. Optimal use of bambara groundnut is limited due to the hard-to-cook (HTC) phenomenon and the lack of adequate processing and cooking techniques. To optimise use, this thesis explored various methods of managing the hard-to-cook phenomenon in the context of resource-limited communities. Long cooking time, milling challenges and firewood and water shortages were the constraints to processing and consumption of bambara groundnut. Useful techniques to process HTC legumes found include cooking with alkaline salts; and soaking, roasting and milling in the production of grits and flour.

Results on reviewed published data implicated microstructural and compositional changes as factors leading to the development HTC phenomenon. Cooking bambara groundnut seeds with alkaline rock salts (0.5% NaHCO­3  and 0.5% gowa) caused 13 and 20% reduction in cooking time, respectively. The contribution of bambara groundnut phenolic compounds to salt softening effects was evaluated by monitoring phenolic compounds solubilisation pattern in relation to cooking time reduction. Protocatechuic acid, catechin and epicatechin were indicators of softening in relation to cooking time reduction. Grit production was an efficient sustainable way of circumventing the HTC phenomenon as shown by a better processing aptitude as compared to traditional boiling of whole seeds. Different methods of grit processing had a similar dehulling efficiency with no significant varietal influence. Both traditional boiling and grit production improved IVSD, IVPD and mineral bioaccessibility. Dry roasted grits had the lowest IVPD (42%), followed by the combined soaking and roasting (45%), soaking (48%) and boiling (68%). Additionally, grit production was superior in improving mineral bioaccessibility, i.e. Zn, K, P and Mg. Bambara groundnut grits were found to be healthy and sustainable as they contribute to dietary diversity and the RDI values for protein, starch and minerals. Bambara groundnut flour produced by different pre-treatment methods i.e., roasting, soaking and combined soaking and roasting was regarded as nutritious and comparable to other legume flours. The soaked and combined soaked and roasted flours was recommended for further research in product development and consumer acceptance of locally consumed food products such as porridge, soups, bread, cakes and fritters.

Overall, insights provided by this thesis is useful in designing effective interventions for sustainably managing processing problems for legume crops for resource-limited communities, thereby contributing to improved food and nutrition security.