Chemical processing of Bambara Groundnut Flour (Vigna subterranea)

Kremmyda, Alexandra (2020) Chemical processing of Bambara Groundnut Flour (Vigna subterranea). MRes thesis, University of Nottingham.

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The first aim of this thesis was the determination of the crude protein content (21%), the fat (6.69%) and the moisture (8.85%) of a Bambara Groundnut Flour (BGF) trace called Ex - Sokoto. The microstructure of the BGF showed starch granules in the cotyledon cells surrounded by a protein matrix and fibrous material. Subsequently, BGF was treated with various solvents / pH conditions (H2O pH=6, alkalinised H2O pH=9 and 0.1M NaOH pH=13) in order to investigate the effect of different solvents on its physicochemical characteristics. Water Absorption Index (WAI) increase with lower pH treatment (H2O > alkalinised H2O > 0.1M NaOH) while the Solubility Index (SI) was higher at higher pH (0.1M NaOH > alkalinised H2O > H2O). The starch gelatinisation peak of the pellets resulting from the BGF treatment with different solvents, found at 80 - 85 oC. The particle size of the same samples showed a trimodal distribution with peaks at ≈ 50 µm (starch), 100 μm and 150 - 1,000 μm. The sample treated with alkalinised H2O presented the highest ability to solubilise the proteins. This was confirmed by SDS - PAGE and elemental analysis where the supernatant of this sample revealed the greatest number of bands and intensity and the highest crude protein content (45.45%). Protein isolates were prepared from BGF using alkalinised H2O (pH=9) and 0.1M NaOH (pH=13). The BCA assay test showed that the protein isolate extracted with 0.1M NaOH had higher content in “water soluble proteins” than the isolate extracted with alkalinised H2O. Elemental analysis showed that alkalinised H2O had higher crude protein content (86.08%) and greater intensity of bands at the SDS -PAGE profile in comparison to 0.1M NaOH protein isolate.

The effect of 0.1M to 0.3M NaOH on BGF was tested and it was indicated that BGF gel when ≥ 0.3M NaOH was applied. The phenomenon was attributed to starch gelatinisation because the starch gelatinisation peak was not displayed in the micro DSC thermograph. The starch peak was also absent from the particle size analysis graph, and swelling, aggregation and loss of the starch granules birefringence was observed under the microscope. This property of the BGF starch was used for the development of a non thermal cooking method, resulting to a self - standing gel. The same gel showed a homogeneous starch - rich microstructure where proteins (21%), fibers and lipids were present. The BGF and the gel SDS - PAGE profile displayed minor differences and the WAI (≈ 6 g), the SI (36.5%) and the moisture (97%) of the gel were also measured. In order to understand the microstructural changes, occur during the non - thermal cooking of the BGF the following experiments were conducted. The non - thermal cooking method was applied on starch sources (potato flakes, maize starch) and resulted to a non- self - standing gel. BGF was also dispersed in different solvents prior to non – thermal cooking (deionised H2O, alkalinised H2O and 0.1M NaOH) in order to provide evidence of the changes occur to the constituents of the samples during further processing and subsequent to a non - self standing gel (viscous fluid).

Overall, the thesis confirmed that BGF trace had high nutritional value and showed that different solvents could drive physicochemical changes. It was also indicated that 0.3M NaOH gelatinise starch and this property was used for the development of a non - thermal method resulting to a self - standing gel. Finally, the starch had the major role on this processing method, yet proteins and possibly other compounds (lipids) also played a role on it.

Item Type: Thesis (University of Nottingham only) (MRes)
Supervisors: Foster, Timothy John
Keywords: Bambara groundnut, Vigna subterranea, Non-thermal cooking, Chemical processing, Novel technology, Legumes
Subjects: T Technology > TP Chemical technology > TP 368 Food processing and manufacture
Faculties/Schools: UK Campuses > Faculty of Science > School of Biosciences
Item ID: 59618
Depositing User: Kremmyda, Alexandra
Date Deposited: 24 Jan 2023 10:38
Last Modified: 24 Jan 2023 10:39

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