Effects of gamma-irradiation on cotyledon cell separation and pectin solubilisation in hard-to-cook cowpeas.

BACKGROUND: Cowpeas stored under high temperature and humidity develop the hard-to-cook defect (HTC). This defect greatly increases cooking times and energy costs. To better understand the mechanisms involved in the HTC defect development, the effects of gamma-irradiation on cotyledon cellular structure and pectin solubility in two cowpea cultivars with different susceptibility to HTC defect were investigated. RESULTS: Gamma-irradiation decreased cotyledon cell wall thickness, increased cell size, and intercellular spaces in both cowpea cultivars and reduced cooking time of the less HTC susceptible cultivar. However, it did not reverse the HTC defect in the susceptible cultivar. Gamma-irradiation also increased the levels of cold water- and hot water-soluble pectin. The irradiation effects were thus mainly due to hydrolysis of pectin fractions in the cell walls. However, chelator-soluble pectin (CSP) solubility was not affected. CONCLUSION: As the cell wall changes brought about by gamma-irradiation were associated with pectin solubilisation, this supports the phytate-phytase-pectin theory as a major cause of the HTC defect. However, the non-reversal of the defect in HTC susceptible cowpeas and the absence of an effect on CSP indicate that other mechanisms are involved in HTC defect development in cowpeas, possibly the formation of alkali-soluble, ester bonded pectins. © 2017 Society of Chemical Industry.

Influence of extraction pH on the foaming, emulsification, oil-binding and visco-elastic properties of marama protein.

BACKGROUND: Marama bean protein, as extracted previously at pH 8, forms a viscous, adhesive and extensible dough. To obtain a protein isolate with optimum functional properties, protein extraction under slightly acidic conditions (pH 6) was investigated. RESULTS: Two-dimensional electrophoresis showed that pH 6 extracted marama protein lacked some basic 11S legumin polypeptides, present in pH 8 extracted protein. However, it additionally contained acidic high molecular weight polypeptides (∼180 kDa), which were disulfide crosslinked into larger proteins. pH 6 extracted marama proteins had similar emulsification properties to soy protein isolate and several times higher foaming capacity than pH 8 extracted protein, egg white and soy protein isolate. pH 6 extracted protein dough was more elastic than pH 8 extracted protein, approaching the elasticity of wheat gluten. CONCLUSION: Marama protein extracted at pH 6 has excellent food-type functional properties, probably because it lacks some 11S polypeptides but has additional high molecular weight proteins. © 2017 Society of Chemical Industry.

Stability of ß-carotene during baking of orange-fleshed sweet potato-wheat composite bread and estimated contribution to vitamin A requirements.

Orange-fleshed sweet potato (OFSP) is known to be a rich source of ß-carotene, a precursor of vitamin A and a potential tool for fighting vitamin A deficiency (VAD) in developing countries. OFSP flour was incorporated into wheat flour at 10, 20 and 30% (w/w) substitution levels. The stability of ß-carotene during baking and the contribution of OFSP-wheat composite breads to vitamin A requirements were evaluated. The retention of all-trans-ß-carotene in breads containing 10, 20 and 30% OFSP flour was 62.7, 71.4 and 83% respectively, after baking. Breads containing 20% and 30% OFSP flour could be used for the eradication of vitamin A deficiency as they were found to meet 29 and 89.2% (100g portion) respectively, of the recommended dietary allowance (RDA) of vitamin A amongst children aged 3-10years. The latter would meet nearly a half of the RDA of vitamin A for pregnant and lactating women.

Effects of micronisation and dehulling of pre-soaked bambara groundnut seeds on microstructure and functionality of the resulting flours.

Functional properties of flours from pre-soaked and micronised (130°C) whole and dehulled bambara seeds (5, 10 and 15min) were determined. An increase in micronisation time significantly reduced the pasting viscosity of the flours. Significant reductions in the differential scanning calorimetry endothermic peak enthalpies and loss of birefringence in the starch were found, indicating starch pre-gelatinisation when micronised. The low viscous paste of resultant flours seems to be related to protein denaturation as shown by decrease in nitrogen solubility index. Starch was embedded in a protein matrix as shown by confocal laser scanning microscopy. This denatured protein matrixes could be in part preventing starch hydration and dispersion during pasting and thus reduced viscosity. Dehulling reduced the pasting viscosity suggesting higher effect of micronisation for dehulled than whole samples. Resulting flours can be useful ingredients in protein energy-dense foods due to low viscosity.

Emerging Early Actions to Bend the Curve in Sub-Saharan Africa's Nutrition Transition.

BACKGROUND: Sub-Saharan Africa is the last region to undergo a nutrition transition and can still avoid its adverse health outcomes. OBJECTIVE: The article explores emerging responses to "bend the curve" in sub-Saharan Africa's nutrition transition to steer public health outcomes onto a healthier trajectory. METHODS: Early responses in 3 countries at different stages of food system transformation are examined: South Africa-advanced, Ghana-intermediate, and Uganda-early. By comparing these with international experience, actions are proposed to influence nutrition and public health trajectories as Africa's food systems undergo rapid structural change. RESULTS: Arising from rapid urbanization and diet change, major public health problems associated with overweight are taking place, particularly in South Africa and among adult women. However, public health responses are generally tepid in sub-Saharan Africa. Only in South Africa have policy makers instituted extensive actions to combat overweight and associated noncommunicable diseases through regulation, education, and public health programs. Elsewhere, in countries in the early and middle stages of transition, public health systems continue to focus their limited resources primarily on undernutrition. Related pressures on the supply side of Africa's food systems are emerging that also need to be addressed. CONCLUSIONS: Three types of intervention appear most feasible: maternal and child health programs to simultaneously address short-term undernutrition problems while at the same time helping to reduce future tendencies toward overweigh; regulatory and fiscal actions to limit access to unhealthy foods; and modernization of Africa's agrifood food system through job skills training, marketing reforms, and food industry entrepreneurship.

Sorghum-cowpea composite porridge as a functional food, Part II: Antioxidant properties as affected by simulated in vitro gastrointestinal digestion.

The effect of compositing red non-tannin sorghum with brownish-cream cowpea and in vitro gastrointestinal digestion on total phenolic and flavonoid contents and antioxidant properties of a sorghum-cowpea composite porridge was studied. Maize-soybean composite porridge was used as a reference sample. Antioxidant properties were studied using radical scavenging activities against the 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid), peroxyl and NO radicals as well as inhibition of low density lipoprotein (LDL) oxidation and oxidative damage of vector DNA. Hydroperoxide content of the samples was also measured. All the samples demonstrated radical scavenging activity. Simulated duodenal digests of the porridges had hydroperoxides and therefore caused LDL oxidation. The undigested porridges and simulated gastric digests inhibited LDL oxidation. Compositing the cereals with legumes increased total phenolic and flavonoid contents and NO scavenging activity of their porridges. In vitro gastrointestinal digestion of the porridges increased their total phenolic and flavonoid contents, radical scavenging activities and LDL oxidation inhibitory activity.

Effects of stearic acid and gamma irradiation, alone and in combination, on pasting properties of high amylose maize starch.

The effects of stearic acid and gamma irradiation on pasting properties of high amylose maize starch (HAMS) were studied. Stearic acid (0%, 1.5%, and 5%) was added to HAMS, and then irradiated at 0, 30, and 60 kGy before pasting. Stearic acid increased the paste viscosity of un-irradiated HAMS from 420 mPas to 557 and 652 mPas for 1.5% and 5% stearic acid, respectively. This observation related well with the formation of type II amylose-lipid complexes, with melting temperatures of about 100-120 °C. Gamma irradiation (30 and 6 0kGy) reduced pasting viscosity of HAMS. Pasting of gamma irradiated HAMS resulted in the formation of type I amylose-lipid complexes, with melting temperatures and enthalpies ranging from 82 to 102 °C and 0.22 to 1.85 J/g, respectively. Stearic acid addition followed by irradiation creates means of producing different types of amylose-lipid complexes from HAMS for industrial utilization.

Sensory and physicochemical analyses of roasted marama beans [Tylosema esculentum (Burchell) A. Schreiber] with specific focus on compounds that may contribute to bitterness.

The role of phenolics and saponins in contributing to bitterness in marama beans, an underutilized legume, especially when roasted, was investigated. Marama beans were roasted at 150°C for 20, 25 or 30 min, then dehulled to separate cotyledons, and pastes were prepared from these. Water extracts were prepared from full fat and defatted flours from roasted and unroasted marama cotyledons. A sensory panel evaluated the sensory attributes of marama pastes and water extracts. Marama water extracts were analysed for total phenolic content, phenolic composition and saponin content. Roasting of marama beans for more than 20 min resulted in negative properties, such as bitterness. The major extractable phenolic acids present in marama water extracts were gallic and protocatechuic acids which increased as a function of roasting time. Saponin content of the water extracts was in the range of 55-63 mg/l. The identified phenolic acids, saponins and other as yet unidentified compounds may contribute to the perceived bitterness.

Novel in situ evaluation of the role minerals play in the development of the hard-to-cook (HTC) defect of cowpeas and its effect on the in vitro mineral bioaccessibility.

Cowpea is a nutritionally important drought-resistant legume in sub-Saharan Africa. It is, however, underutilised, in part due to the hard-to-cook (HTC) defect caused by adverse storage conditions resulting in seeds not softening during cooking. This study introduced a novel evaluation of the potential role that minerals play in the development of the HTC defect. The mineral distribution in the cotyledons of normal and HTC cowpeas were analysed by Proton Induced X-ray Emission (PIXE) spectrometry. The phytate, tannin and total phenolic contents were analysed together with in vitro mineral bioaccessibility. In HTC cowpeas, Ca and Mg were more concentrated in the cell wall-middle lamella area of the parenchyma cells. This, together with the reduction in phytate content, confirmed the 'phytase-phytate-mineral' hypothesis as a mechanism for development of the HTC defect. Despite the phytate reduction in stored cowpeas, the HTC defect decreased the bioaccessibility of Ca, Fe and Zn in cowpeas.

Does a sorghum-cowpea composite porridge hold promise for contributing to alleviating oxidative stress?

The effect of compositing red non-tannin sorghum with cream-coloured cowpea and porridge preparation on phenolic profile and radical scavenging activity was studied. A maize-soybean composite porridge representing a similar product on the South African market was used as reference sample. UPLC-QToF-MS-ESI was used to determine phenolic composition of the grain flours, their composites and porridges. Total phenolic content was determined using Folin-Ciocalteu method while radical scavenging activity was determined using the ABTS, DPPH and NO radical scavenging assays. Four benzoic acid derivatives and five cinnamic acid derivatives were identified in the samples. The predominant flavonoid subclasses identified in sorghum were flavan-3-ols, flavanones and flavones while cowpea had mainly flavan-3-ols and flavonols with soybean having mainly isoflavones. Compositing the cereals with legumes significantly (p<0.01) increased their total flavonoid content and radical scavenging activities. Sorghum-cowpea composite porridge showed better promise in contributing to alleviating radical induced oxidative stress than maize-soybean composite porridge.

Relating physico-chemical properties of frozen green peas (Pisum sativum L.) to sensory quality.

BACKGROUND: The acceptability of frozen green peas depends on their sensory quality. There is a need to relate physico-chemical parameters to sensory quality. In this research, six brands of frozen green peas representing product sold for retail and caterer's markets were purchased and subjected to descriptive sensory evaluation and physico-chemical analyses (including dry matter content, alcohol insoluble solids content, starch content, °Brix, residual peroxidase activity, size sorting, hardness using texture analysis and colour measurements) to assess and explain product quality. RESULTS: The sensory quality of frozen green peas, particularly texture properties, were well explained using physico-chemical methods of analysis notably alcohol insoluble solids, starch content, hardness and °Brix. Generally, retail class peas were of superior sensory quality to caterer's class peas although one caterer's brand was comparable to the retail brands. Retail class peas were sweeter, smaller, greener, more moist and more tender than the caterer's peas. Retail class peas also had higher °Brix, a(*) , hue and chroma values; lower starch, alcohol insoluble solids, dry matter content and hardness measured. CONCLUSIONS: The sensory quality of frozen green peas can be partially predicted by measuring physico-chemical parameters particularly °Brix and to a lesser extent hardness by texture analyser, alcohol insoluble solids, dry matter and starch content.

Phenolic composition and inhibitory effect against oxidative DNA damage of cooked cowpeas as affected by simulated in vitro gastrointestinal digestion.

Cowpeas contain phenolic compounds with potential health benefits. The effect of simulated gastrointestinal digestion on phenolic composition of cooked cowpeas and the ability of the digests to inhibit radical-induced DNA damage was determined. A red and a cream-coloured cowpea type were used. The phenolic composition of acetone extracts and enzyme digests of cooked cowpeas was determined using UPLC-MS. Compounds such as p-hydroxybenzoic acid, p-coumaric acid, coumaroylaldaric acid and feruloylaldaric acid were present in the acetone extracts of the cooked cowpeas but were not detected in the enzyme digests. Glycosides of quercetin and myricetin decreased upon in vitro gastrointestinal digestion of cooked cowpeas whereas flavan-3-ols were hardly present except catechin glucoside. The enzyme digest of the red cowpea type was about thrice as effective as that of the cream cowpea type in protecting DNA from oxidative damage. The observation that enzyme digests of cooked cowpeas inhibited radical-induced DNA damage suggests that cowpea phenolics retain some radical scavenging activity after gastrointestinal digestion.

Effect of micronisation of pre-conditioned cowpeas on cooking time and sensory properties of cooked cowpeas.

BACKGROUND: Cowpea is mostly utilised as cooked whole seeds. This is often achieved only after boiling for up to 2 h, resulting in high energy consumption and a long time for food preparation. Micronisation of pre-conditioned cowpeas reduces their cooking time. Micronisation changes the physicochemical properties of cowpea seeds, which may affect the sensory properties of cooked cowpeas. Consumer acceptance and utilisation of micronised cowpeas depend on their sensory properties. Micronised and unmicronised samples of Blackeye, Bechuana white, Glenda and Dr Saunders cowpeas were subjected to cooking time, descriptive sensory and colour analyses. RESULTS: Micronisation significantly reduced cowpea cooking time by 28-49%. There were significant (P < 0.05) increases in roasted aroma and flavour, mushy texture and splitting in all micronised samples. Bechuana white was more mushy and split than others. There were significant decreases in firmness, mealiness and coarseness after micronisation for all cowpea types. Micronised cowpeas were darker (lower L* values) than unmicronised cooked cowpeas. Darkening was more evident in light-coloured than dark-coloured cowpeas. CONCLUSION: Micronisation reduces cowpea cooking time but also affects sensory properties of cowpeas such as introducing roasted flavours that may not be familiar to consumers. This might have an influence on consumer acceptance of micronised cowpeas.

Highly viscous dough-forming properties of marama protein.

Marama bean is an indigenous southern African oilseed legume with an unusual protein composition. Hence, its rheological properties were studied. Marama protein formed a highly viscous and extensible dough when compared to soya and gluten. With a dough of 38% moisture, marama protein extensibility was very high (304% of its original length), twice that of gluten and soya, and this increased considerably (>3-fold) when the moisture content was increased to 45%. With added peroxidase, the storage modulus (G') of marama protein dough increased with time, suggesting the formation of new and strong protein networks. Dityrosine crosslinks were detected in the doughs. Marama protein showed a single transition with a denaturation temperature higher than soya glycinin. Marama protein was more hydrophobic and contained more ß-sheet structure than did soya. Thus, the highly viscous and extensible rheological behaviour of marama protein is probably related to its high ß-sheet conformation, hydrophobic interactions and tyrosine crosslinks.

Micronisation and hot air roasting of cowpeas as pretreatments to control the development of hard-to-cook phenomenon.

BACKGROUND: Cowpeas stored under conditions of high temperature and high relative humidity (HTHH) develop the hard-to-cook (HTC) defect. Cowpeas with HTC defect require long cooking times, limiting their utilisation. Heat pretreatments are aimed at inactivating the enzymes responsible for HTC defect development. In this study, two heat pretreatments, micronisation and hot air roasting, were evaluated to assess their effectiveness in controlling the HTC defect development in cowpeas after storage under HTHH conditions. RESULTS: Micronisation and hot air roasting as pretreatments reduced the cooking time of cowpeas after storage under HTHH conditions compared with the control. The differences in the effectiveness of HTC defect control between micronisation and roasting were dependent on the degree of phytase inactivation on day 0. Phytase activity was reduced by 45 and 70% by roasting and micronisation pretreatments respectively. Reduced phytase activity was associated with higher phytate and soluble pectin contents in micronised cowpeas than in roasted cowpeas after HTHH storage. This observation is in agreement with the phytase-phytate-pectin theory. CONCLUSION: Micronisation was more effective than hot air roasting in controlling the development of HTC defect. This was due to a higher degree of phytase inactivation in micronisation when compared with roasting.

Effect of kafirin protein coating on sensory quality and shelf-life of 'Packham's Triumph' pears during ripening.

BACKGROUND: Pears are exported in large quantities from South Africa, resulting in large revenues. Minimisation of quality losses once the fruit has reached the export destination is as important as following strict export and distribution protocols. Kafirin can form edible films. In this study an edible coating made from 20 g kg(-1) kafirin coating solution was applied as a postharvest treatment to retard quality deterioration of 'Packham's Triumph' pears during storage at the typical ripening temperature (20 °C). Changes in physicochemical and sensory quality were monitored over a period of 24 days. RESULTS: The kafirin coating was unable to retard the onset of ripening but decreased the respiration rate and retarded the progression of senescence. However, moisture loss was exacerbated in the kafirin-coated fruit during ripening at 20 °C, especially towards the end of the shelf-life. CONCLUSION: The kafirin coating extended the eat-ripe quality of the pears by 1-2 weeks. However, the appearance of the fruit was unacceptable after 14 days of storage in terms of wrinkled skin. Further work is needed to improve the water barrier properties of the kafirin coating by incorporating a wax or triglyceride into the coating formulation or more simply by applying a kafirin coating to waxed fruit.

The morama bean (Tylosema esculentum): a potential crop for southern Africa.

The morama bean is an underutilized leguminous oilseed native to the Kalahari Desert and neighboring sandy regions of Botswana, Namibia, and South Africa (Limpopo, North-West, Gauteng, and Northern Cape provinces), and forms part of the diet of the indigenous population in these countries. It is also known as gemsbok bean, moramaboontjie, elandboontjie, braaiboonjie, marama, marumana, tsi, tsin, gami, and ombanui. It is reported as an excellent source of good quality protein (29-39%); its oil (24-48%) is rich in mono- and di-unsaturated fatty acids and contains no cholesterol. Morama is a good source of micronutrients such as calcium, iron, zinc, phosphate, magnesium, and B vitamins including folate. It is also reported to be a potential source of phytonutrients including phenolic compounds (e.g., tannins), trypsin inhibitors, phytates, and oligosaccharides, components which have been shown in other foods to contribute to health in particular, prevention of noncommunicable diseases such as cardiovascular diseases, diabetes, and some cancers. From a nutritional and health perspective, the morama bean has potential commercial value as a cash crop and value-added products, particularly in the communities where it is found.

Sensory quality of marama/sorghum composite porridges.

BACKGROUND: The edible seeds of marama beans are a good source of protein and fat and can potentially enhance the nutritional quality of sorghum products. Utilisation of marama flour in a composite porridge depends on sensory acceptance. Heating of marama beans before milling is used to inactivate trypsin inhibitors. Defatting of marama flour would improve shelf life. In this study, marama/sorghum composite porridges (10% solids) were prepared and subjected to descriptive sensory analysis, consumer acceptance testing, texture analysis, pasting and colour measurements. RESULTS: Composite porridges had less cooked sorghum aroma/flavour but more intense overall aroma/flavour and were less viscous and less firm than sorghum porridge. Composite porridges prepared with flour from heated marama beans had a roasted nut flavour and were darker in colour compared with porridges prepared with unheated marama beans, which had a strong boiled nut aroma/flavour. Composite porridges from full-fat marama flours tasted more buttery/creamy. A bitter aftertaste was perceived in porridges from defatted marama flours. The 100% sorghum porridge and the composite porridge with full-fat flour were more acceptable to consumers. CONCLUSION: Combining sorghum meal with full-fat marama bean flour has the potential to improve the sensory quality of sorghum porridge as a staple by providing acceptable sensory appeal.

Kafirin microparticle encapsulation of catechin and sorghum condensed tannins.

To exploit the porous nature of previously developed kafirin microparticles, encapsulation of the bioactive polyphenols, catechin and sorghum condensed tannins, was investigated. The antioxidant release profiles of the encapsulated substances were studied under simulated gastric conditions. Kafirin microparticles encapsulating catechin or sorghum condensed tannins were similar in size to control kafirin microparticles (5-6 mum). TEM showed that kafirin microparticles encapsulating catechin had a rough porous surface. Microparticles encapsulating sorghum condensed tannins were irregular in shape, some apparently joined together, with a mixture of rough and smooth surfaces. Over a period of 4 h, catechin and sorghum condensed tannin encapsulated kafirin microparticles showed virtually no protein digestion but released approximately 70 and 50%, respectively, of total antioxidant activity. Thus, the use of kafirin microparticles to encapsulate catechin and sorghum condensed tannins has potential as an effective method of controlled release of dietary antioxidants.

Preparation of free-standing films from kafirin protein microparticles: mechanism of formation and functional properties.

A method of preparing free-standing films using kafirin microparticles made by phase separation from acetic acid is described. Film preparation involved the suspension of the microparticles in acetic acid solution containing plasticizer. On evaporation of the acetic acid, a complete, smooth, flexible, transparent film was formed. A minimum concentration of acid was required to form a cohesive film relative to the concentration of kafirin. This was approximately 10.8:1, percent acetic acid to percent kafirin. Film formation appears to be by controlled aggregation of kafirin microparticles, followed by dissolution of the microparticles in acetic acid and drying into a cohesive film. The functional properties of microparticle films were generally superior to films cast directly from a solution of kafirin, at the same protein content. Kafirin microparticle films were very thin (<15 microm), relatively strong but not very extensible, with better water barrier properties and lower protein digestibility than conventionally cast kafirin films.