Abstract
Bambara groundnut (BGN) starch-soluble dietary fibre nanocomposite (STASOL) was manufactured by grafting 1.95 g BGN soluble dietary fibre (BGN-SDF) onto 15 g BGN starch (BGNS). The particle sizes, functional groups, crystallinity, morphology and thermal properties of BGNS, BGN-SDF and STASOL were studied using a Zetasizer, Fourier transform infrared, X-ray diffraction, scanning electron microscope and differential scanning calorimetry, respectively. STASOL had a particle size and conductivity of 74.01 nm and −57.3 mV, respectively. BGN-SDF and STASOL were amorphous and BGNS was classified as type C starch, typical of legumes. The biopolymers had functional groups in the regions 2900–3600, 1600–1642, 900–1200 and 800–1300 cm−1, which could be attributed to the vibrational stretching of OH groups, vibration of OH groups in the non-crystalline region of starch, vibration of C-O, C-C and C-H-O bonds and the vibration of 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, disintegrating at 293 °C, therefore suggesting that it would find use in high-temperature food applications such as baking.
Highlights
1400–3380 cm−1 are characteristic of stretching vibrations and deformation of the OH bond of water while the peak at 1641.71 cm−1 is characteristic of C=O of carboxyl groups as well as the vibration of OH of water molecules in the non-crystalline region of starch [31]
BGN starch (BGNS) and starch-soluble dietary fibre nanocomposite (STASOL) had peaks in the region 434.37–571.59 cm−1 while no peaks were detected in the Bambara groundnut (BGN)-soluble dietary fibre (SDF)
BGN soluble dietary fibre (BGN-SDF) and STASOL did not exhibit any crystallinity as both compounds were thereby increasing the solubility of compounds in water [7]
Summary
The choice of modification method is dependent on several factors such as end-use, desired functional properties, toxicity levels as well as permitted chemical residues in the final modified starch. Another way of mitigating these limiting properties involves modification by complexing starch with a more robust biopolymer such as SDF. Bambara groundnut SDF are prebiotic [11], have high oil binding capacities and are rich in bioactive compounds, namely, uronic acids and polyphenols, with crucial physiological and functional benefits [12] Both BGN-SDF and BGNS currently have no reported uses in the food industry. The particle size, conductivity, functional groups, crystallinity, morphology and thermal properties of STASOL were characterised
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