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Title: Rheological behaviour of Bambara groundnut starch-soluble dietary fibre nanocomposite for delivering active compounds in food systems
Authors: Maphosa, Yvonne 
Keywords: Bambara groundnut -- Composition;Rheology;Food -- Fiber content -- Analysis;Nanotechnology;Biopolymers
Issue Date: 2022
Publisher: Cape Peninsula University of Technology
Abstract: This aim of this study was to assess the effect of Bambara groundnut (BGN) (Vigna subterranea (L.) Verdc) starch-soluble dietary fibre nanocomposite (STASOL) on the functional, physicochemical and rheological properties of orange oil beverage emulsions. STASOL was composed of 11.5% Bambara groundnut starch (BGNS) and 88.5% Bambara groundnut soluble dietary fibre (BGN-SDF). STASOL had a mean particle size of 74.01 nm and conductivity of -57.3 mV which qualified it as a nanocomposite and a very stable compound, respectively. STASOL and BGN-SDF were amorphous in nature while BGNS was crystalline, showing strong peaks at 15, 17 and 23° (2θ), thus classifying it as type C starch. STASOL, BGN-SDF and BGNS had functional groups in the regions 3600-2900, 1641.71, 1200-900, 1300-800 cm-1 which were attributed to the vibrations of C-H and OH, C=O and OH, C-C and C-H-O as well as C-O and C-C bonds, respectively. BGNS had smooth, oval structures while BGN-SDF and STASOL exhibited irregular, polygonal morphologies. STASOL was the most thermally stable biopolymer suggesting its suitability for high-temperature food applications. STASOL was high in carbohydrates (78.69%) and proteins (6.96%), low in fat (0.84) and had a considerable amount of ash (4.88%). BGNS, BGN-SDF and STASOL showed significant (p = 0.00) differences in solubility with BGNS being insoluble in water. The emulsion activity index (EAI) and emulsion stability index (ESI) of BGNS, BGN-SDF and STASOL were 23.25 and 23.33%, 85.71 and 87.13%, 90.65 and 87.49%, respectively. The significantly (p = 0.000) higher EAI and ESI of STASOL suggested its suitability as a stabiliser in emulsions. The oil binding capacities of BGNS, BGN-SDF and STASOL differed significantly (p = 0.000) and were 1.13, 3.78 and 1.61 g/g, respectively. STASOL had a substantial amount of antioxidant compounds with 1.45 μmol AAE/g ferric reducing antioxidant power and 0.46 mg GAE/g. Colour characteristics described all studied biopolymers as light (L*), reddish (+a*) and yellowish (+b*). The mean initial backscattering (BSAVO) of STASOL stabilised emulsions was in the range 50.73-70.47% for emulsions composed of 14:30:56 and 20:30:50 (STASOL:oil:water), respectively. The turbiscan stability index (TSI) of the emulsions ranged from 0.0005 to 0.1000 for formulation 11 (20:30:50 STASOL:oil:water) and formulation 5 (8:42:50 STASOL:oil:water), respectively. Low TSI values indicate a low probability of phase separation. The hysteresis loop area (HLA) of emulsions ranged from 2.04 Pas-1 [Formulation 10 (12:34:54 STASOL:oil:water)] to 43.09 Pas-1 [Formulation 2 (20:30:50 STASOL:oil:water)]. The first-order stress decay with a zero equilibrium stress value and Herschel-Bulkley models were the best predictors of time-dependent and time-independent rheological flow behaviour, respectively. The most stable emulsion system was characterised by the highest STASOL (20%), lowest orange oil (30%) and lowest water (50%) concentrations and had the highest BSAVO, lowest TSI and highest HLA. All emulsions were non-Newtonian, time-dependent, thixotropic, shear-thinning and possessed yield stress. Both temperature and time largely affected the extent of destabilisation, with emulsions stored at 5 and 45°C showing the least and most destabilisation over time, respectively. The viscosity of emulsions stored at 5°C started significantly (p = 0.000 decreasing after the 9th day while that of emulsions stored at 20 and 45°C significantly (p = 0.000) decreased after the 3rd day. Emulsions stored at 5 and 45°C for 20 days were the most and least stable, respectively. STASOL stabilised emulsions should be refrigerated to prolong their shelf life.
Description: Thesis (Doctor of Food Science and Technology)--Cape Peninsula University of Technology, 2022
Appears in Collections:Food Technology - Doctoral Degrees

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