Proximate composition, histochemical analysis and microstructural localisation of nutrients in immature and mature seeds of marama bean (Tylosema esculentum) – An underutilised food legume

Marama bean (Tylosema esculentum) is a wild-growing legume adapted to semi-arid conditions in southern Africa. Both immature and mature seeds are used as food by locals and marama bean has potential as a crop plant. Physicochemical and histochemical methods were used to study the accumulation of nutrients and their localisation in immature and mature seeds. The immature seeds had a high content of moisture (67%) and protein (21%), and a low content of lipid (1.5%). At maturity, proteins formed spherical bodies that were embedded in a droplet lipid matrix. The mature seeds are exceptional as they have a high content of protein (32%) and lipid (40%) and no starch. Staining of polysaccharides indicated increases of pectin and cellulose during maturation, parallel with the general increase of cell wall thickness; however, lignin was absent. The content and distribution of protein, lipid and carbohydrates in immature and mature marama beans make this underutilised nutritive legume a prospective crop plant and interesting for food processing applications.

Research highlights
► Proteins and lipids increase with maturity of the cotyledons.
► At maturity, proteins form spherical bodies embedded in a droplet lipid matrix.
► At maturity, there is an increase of pectin and cellulose, and cell wall thickness.
► Lignin and starch are absent in the cotyledons.