Effect of processing on the microstructure and composition of Bambara groundnut (Vigna subterranea (L.) Verdc.) seeds, flour and protein isolates
Claudine F. Diedericks, Paul Venema, Juliet Mubaiwa, Victoria A. Jideani, Erik van der Linden
Abstract
Pre-processing treatments are generally employed to circumvent negating effects, such as the hard-to-cook and hard-to-mill properties, associated with legume seeds. Several studies have investigated the effects of soaking and roasting on the macroscopic qualities of Bambara groundnut (Vigna subterranea (L.) Verdc.) [BGN] seeds, yet knowledge is lacking on the effects of these treatments on the microstructural and molecular properties of the seeds and resulting fractions (i.e. flour and protein isolates). Size-exclusion chromatography coupled with light scattering results have shown that roasting induces thermal aggregation in BGN proteins, resulting in the formation of insoluble aggregates. To that end, the molecular composition of the roasted and soaked-roasted samples were comparable, yet different to the control (untreated seeds), whereas the samples which were subjected to soaking compared favourably to the control. The morphology of the seeds were also well characterized by microscopic techniques, including a confocal imaging technique which appears novel for legume seeds, revealing cotyledon cells with several starch granules embedded in a matrix of protein bodies. The findings of this study provide valuable insights on the microstructural and molecular compositional changes occurring in BGN seeds and fractions when subjected to soaking and/or roasting, which could be linked to some macroscopic properties as previously reported.