Microscopic Analysis on Structural Morphologies of Total Protein Isolates from Two Varieties (DAS and BS) of Nigerian CultivatedSolojo Cowpea (Vigna Unguiculata L. Walp)

Abstract

Structural morphologies of total protein isolate of two varieties of solojo cowpea were studied by scanning electron microscope (SEM). The morphological properties of raw and germinated protein isolates of DAS and BS are presented in Figures. 4.42 – 4.53. Results showed the apparent structural differences between them. The Raw DAS showed plate like structure with relatively smooth surface topography with large cavities while Raw BS showed flaky structure like that of Albumins. This pattern is similar to that of albumin shapes of the Great Northern Bean, field pea protein and that of Crotalaria pallida. The SEM micrographs results of DAS isolates revealed smooth lamella with flake-like structures on it, having large particle sizes and irregular geometry shapes. Large vacuum spaces were also observed. After six hours of modification, a change in morphology of the original isolate was observed with disappearance of the plate-like and flake-like structure and the vacuum space; DAS 24 h protein isolates then exhibited a spongy plate like structure. Rise in the germination period to 36 h led to disappearance of the cloudy mass and formation of smooth non homogeneous mass. Further increase in the germination time to 48 and 72 h led to smoother mass with a few dispersed particles with cracked surface. The observation of the microstructure presentation from 36 h is also comparable to that obtained for bitter vetch (Vicia ervilia) protein films strengthened by microbial transglutaminase, in this case, the images of BVPC films containing mTGase clearly indicate a more compact microstructure, with evident continuous zones. The BS isolates morphology which presented a thin wafer-like structure like that of albumin, possessing wide surface area could in part justify the great solubility of albumins in neutral environment, enabling better access to water molecules. The structure was observed to become more homogeneous and compact, with no cavities as germination proceeded. The DAS protein isolates presents micrograph similar to those of white bambarra (WB) and black bambarra (BB) surfaces which presented cracking. The micrograph of BS 6 h germinated protein isolate, which presents a flaky plate like structure is comparable to that of commercial textured Glycine max protein