Eric O. Amonsou

Physicochemical properties of starches with variable amylose contents extracted from bambara groundnut genotypes

The physicochemical properties of starches extracted from five bambara genotypes were investigated. Bambara starch granules were predominantly oval shaped with a smooth surface and an average size of 26±0.2μm. The amylose contents (20-35%) varied significantly among genotypes. X-ray diffraction revealed the C-type pattern for all starches with relative crystallinity range: 29-35%. FTIR spectra of bambara starches showed variable peak intensities at 2931, 1655 and 860cm(-1), which corresponds to CH stretching, H2O bending vibrations and CO stretching, respectively. Bambara genotype with the highest amylose content showed the lowest intensity at wavenumber 2931cm(-1). With the exception of oil absorption which was similar, swelling power, water absorption and paste clarity of starches were significantly different among genotypes. Genotype with high amylose content showed restricted swelling, low paste clarity and great ability to absorb water. All bambara starches displayed a shear thinning behaviour (n<1).

In vitro digestibility and some physicochemical properties of starch from wild and cultivated amadumbe corms

Amadumbe, commonly known as taro, is an indigenous underutilised tuber to Southern Africa. In this study, starch functional properties and in vitro starch digestibility of processed products from wild and cultivated amadumbe were determined. Starch extracts from both amadumbe types had similar contents of total starch (approx. 95%). Wild and cultivated amadumbe starch granules were polygonal and very small in size (2.7 ± 0.9 μm). Amylose content of wild amadumbe (20%) was about double that of cultivated (12%). By DSC, the peak gelatinisation temperatures of wild and cultivated amadumbe starches were 81 and 85°C, respectively. The slowly digestible starch (SDS); 20% and resistant starch (RS); 64% contents of wild amadumbe appeared slightly higher than those of cultivated. Processing amadumbe into boiled and baked products did not substantially affect SDS and RS contents. Estimated glycaemic index of processed products ranged from 40 to 44%. Thus, amadumbe, both wild and cultivated, present some potential in the formulation of products for diabetics and weight management.

Effects of amadumbe starch nanocrystals on the physicochemical properties of starch biocomposite films

The influence of amadumbe starch nanocrystals (SNCs) at varying concentrations (2.5, 5 and 10%) on the physicochemical properties of biocomposite films prepared using two starch matrices, amadumbe and potato starches were investigated. Amadumbe SNCs exhibited square-like platelets morphology, typical of SNC derived from A-type starches. In general, the inclusion of SNCs significantly decreased water vapour permeability (WVP) of composite films whilst thermal stability and opacity were increased. Amadumbe starch films showed substantially high tensile strength (TS) compared to potato starch in the presence of SNCs. At 2.5% SNCs, TS of composite amadumbe film (8MPa) was about four times that of composite potato films. However, SNCs≥5% generally decreased TS of both potato and amadumbe films. Amadumbe SNCs can potentially be used as fillers to improve the properties of biodegradable starch films. Amadumbe starch has better film forming properties compared to potato starch.

Microstructure, thermal properties and crystallinity of amadumbe starch nanocrystals

Amadumbe (Colocasia esculenta), commonly known as taro is a tropical tuber that produces starch-rich underground corms. In this study, the physicochemical properties of starch nanocrystals (SNC) prepared by acid hydrolysis of amadumbe starches were investigated. Two varieties of amadumbe corms were used for starch extraction. Amadumbe starches produced substantially high yield (25%) of SNCs. These nanocrystals appeared as aggregated and individual particles and possessed square-like platelet morphology with size: 50-100nm. FTIR revealed high peak intensities corresponding to OH stretch, CH stretch and H2O bending vibrations for SNCs compared to their native starch counterparts. Both the native starch and SNC exhibited the A-type crystalline pattern. However, amadumbe SNCs showed higher degree of crystallinity and slightly reduced melting temperatures than their native starches. Amadumbe SNCs presented similar thermal decomposition property as their native starches. Amadumbe starch nanocrystals may have potential application in biocomposite films due to their square-like platelet morphology.

Effects of amaranth addition on the pro-vitamin A content, and physical and antioxidant properties of extruded pro-vitamin A-biofortified maize snacks

BACKGROUND Pro-vitamin A-biofortified maize snacks with added leafy vegetable may have a potential as nutritious and health-promoting products, especially in addressing vitamin A deficiency, which is prevalent in developing regions. The objective of the study was to determine the effects of adding amaranth leaf powder on the physical, antioxidant properties and pro-vitamin A content of extruded pro-vitamin A-biofortified maize snacks. Extruded snacks were processed using four pro-vitamin A-biofortified maize varieties that were composited with amaranth leaf powder at 0%, 1% and 3% (w/w) substitution levels. RESULTS At higher amaranth concentration, the expansion ratio of the snacks decreased, while their hardness increased by as much as 93%. The physical quality of the snacks may therefore need improvement. As amaranth was increased, the phenolic content and antioxidant activity of the snacks increased as well as the pro-vitamin A content. CONCLUSION Pro-vitamin A-biofortified maize with added amaranth has a potential for use in nutritious and healthy extruded snacks. There are limited studies reporting on processing pro-vitamin A maize with complementary plant foods, which is common with white maize in southern Africa; thus the current study serves as a baseline.

Effect of Amaranth addition on the nutritional composition and consumer acceptability of extruded provitamin A-biofortified maize snacks

The objective of this study was to determine the effect of adding Amaranth leaf powder on the nutrient content and consumer acceptability of extruded provitamin A-biofortified (PVA) maize snacks. Flours of four varieties of PVA maize were composited with Amaranth leaf powder at 0, 1 and 3% (w/w) substitution of, respectively, and extruded into snacks. The ash content of the snacks increased from 0.53 g/100 g-0.58 g/100 g to 0.650 g/100g-89 g/100 g and protein content increased from 9.12 g/100 g-10.94 g/100 g when Amaranth was increased from 0% to 3%. Similarly, lysine content increased from 0.10 g/100 g to 0.17 g/100 g, whilst methionine increased from 0.14 g/100 g to 0.19 g/100 g. The provitamin A content of the snacks ranged from 1.29 µg/g to 1.40 µg/g at 0% Amaranth and 1.54 µg/g to 1.78 µg/g at 3% Amaranth. The acceptability of the snacks decreased with increasing Amaranth concentration, only a very small proportion (2-8%) of the panel liked the snacks extremely. PVA maize with added Amaranth leaf powder has a potential for use in nutritious and healthy extruded snacks, but the consumer acceptability of the snacks should be improved.

Inhibitory properties of bambara groundnut protein hydrolysate and peptide fractions against angiotensin‐converting enzymes, renin and free radicals

BACKGROUND An increased rate of high blood pressure has led to critical human hypertensive conditions in most nations. In the present study, bambara protein hydrolysates (BPHs) obtained using three different proteases (alcalase, trypsin and pepsin) and their peptide fractions (molecular weight: 10, 5, 3 and 1 kDa) were investigated for antihypertensive and antioxidant activities. RESULTS Alcalase hydrolysate contained the highest amount of low molecular weight (LMW) peptides compared to pepsin and trypsin hydrolysates. LMW peptides fractions (<1 kDa) exhibited the highest inhibitory activity against angiotensin-converting enzyme (ACE) for all the enzymes hydrolysates. For renin inhibition, alcalase hydrolysate showed the highest inhibition at 59% compared to other hydrolysates and their corresponding membrane fractions. The antioxidant power of bambara protein hydrolysates and peptide fractions was evaluated through the inhibition of linoleic acid peroxidation and ABTS scavenging activity. Among the hydrolysates, alcalase exhibited the highest inhibition of linoleic acid oxidation. Furthermore, all BPHs were able to scavenge ABTS•+ to a three-fold greater extent compared to the isolate. CONCLUSION BPH and LMW peptide fractions could potentially serve as useful ingredients in the formulation of functional foods and nutraceuticals against high blood pressure and oxidative stress.

Physicochemical and Mechanical Properties of Bambara Groundnut Starch Films Modified with Stearic Acid

The physicochemical and mechanical properties of biofilm prepared from bambara starch modified with varying concentrations of stearic acid (0%, 2.5%, 3.5%, 5%, 7%, and 10%) were studied. By scanning electron microscopy, bambara starch films modified with stearic acid (≥3.5%) showed a progressively rough surface compared to those with 2.5% stearic acid and the control. Fourier transform infrared spectroscopy spectra revealed a peak shift of approximately 31 cm-1 , suggesting the promotion of hydrogen bond formation between hydroxyl groups of starch and stearic acid. The addition of 2.5% stearic acid to bambara starch film reduced water vapor permeability by approximately 17%. Bambara starch films modified with higher concentration of stearic acid were more opaque and showed significantly high melting temperatures. However, mechanical properties of starch films were generally negatively affected by stearic acid. Bambara starch film may be modified with 2.5% stearic acid for improved water vapor permeability and thermal stability with minimal effect on tensile strength.

Effect of high-pressure homogenization on structural, thermal and rheological properties of bambara starch complexed with different fatty acids

The effect of high-pressure homogenization (HPH) on the degree of complexation of different fatty acids with bambara starch was studied. HPH significantly increased the complexation of bambara starch with palmitic, stearic, oleic and linoleic acids. However, saturated fatty acids generally showed higher complexing ability than unsaturated ones. For all fatty acids, bambara starch showed a higher complex index than corn and potato starches, which could be associated with the variation in amylose contents (22.5–31.5%). The formation of V-amylose crystalline materials was confirmed by XRD with peaks at 2θ = 7.4, 12.9 and 19.9°. Bambara starch–fatty acid complexes displayed significantly higher melting temperatures (95.74–103.82 °C) compared to native uncomplexed starch (77.32 °C). Homogenized bambara starch complexes were non-gelling while unhomogenized complexes produced weak gels, with G′ > G′′ in the range of 0.1–10 Hz. Complexation of bambara starch with fatty acids using HPH may be employed in the production of modified starch with non-gelling properties and higher thermal stability suitable for certain industrial applications.

Provitamin A retention and sensory acceptability of amahewu, a non‐alcoholic cereal‐based beverage made with provitamin A‐biofortified maize

BACKGROUND Vitamin A deficiency is a major public health problem in sub-Saharan Africa. Amahewu is a popular southern African lactic acid fermented non-alcoholic maize-based beverage, which is deficient in vitamin A. In this study, provitamin A retention and sensory acceptability of amahewu processed using provitamin A-biofortified maize and three types of inoculums during fermentation (malted maize, wheat bran and Lactobacillus starter culture) were investigated. RESULTS The total provitamin A content of amahewu samples, estimated as β-carotene, β-cryptoxanthin and α-carotene content, ranged from 3.3 to 3.8 g kg(-1) (dry weight). Provitamin A was substantially retained (79- 90% β-carotene equivalent) in amahewu after fermentation. Amahewu samples prepared with added starter cultures had the lowest retention of provitamin A. Consumers (approx. 69%) liked provitamin A-biofortified amahewu either moderately or very much. Principal component analysis of amahewu sensory data showed that 71% of variation was due to maize types and 18% of variation could be due to the inoculum used during fermentation. Amahewu samples prepared using provitamin A-biofortified maize were slightly more liked (mean score: 7.0 ± 1.2) compared to those of white maize reference samples. The use of starter culture combined with either malted maize or wheat bran as inoculum during fermentation improved the taste and aroma of amahewu and hence its acceptability. CONCLUSION Provitamin A is substantially retained in amahewu after fermentation. The slightly high acceptability of amahewu prepared using provitamin A-biofortified maize compared to that of white maize thus suggests that fermented product like amahewu can potentially be used to deliver provitamin A to vulnerable individuals.