Microscopic, Nutritional and Functional Properties of Cowpea Flours and Protein Concentrates During Storage

During storage for 6 mo at 64% RH, whole seed flour, dehulled seed flour and air-classified protein concentrate from cowpeas showed little change in nutritional or sensory properties but there were improvements in functional properties. However, wet-processed protein concentrate, after drum-drying, darkened and had reduced functionality by the 6th mo. When storaged at 79% RH, all cowpea products darkened significantly, showed decreased lysine contents and lower nitrogen, solubility, all emulsification and foaming characteristics. Both dehulling and air classification improved the storage properties of cowpea products but drum drying of a wet-processed product had an adverse effect on functionality and nutritive value, especially when stored at 79% RH.     

Cowpea flour: A potential ingredient in food products

Cowpeas (Vigna unguiculata L. Walp) are an important grain legume in East and West African countries as well as in other developing countries. The U.S. is the only developed country producing large amounts of cowpeas. High protein (18 to 35%) and carbohydrate (50 to 65%) contents, together with an amino acid pattern complementary to that of cereal grains, make cowpeas potentially important to the human diet from a nutritional standpoint. Despite their potential as an inexpensive source of protein and energy, cowpeas are underutilized in the U.S. and other industrialized countries. A simple technology for preparing cowpea flour would stimulate increased consumption of this legume. This paper reviews the status of cowpea flour production technologies and uses of cowpea flour in various food products.     

Functional characterization of flour of selected cowpea (Vigna unguiculata) varieties: canonical discriminant analysis

Characterization of 28 varieties of cowpea flour, based on Brabender pasting properties of flour slurry (12% w/w flour: water), was achieved by canonical discriminant analysis. Pasting viscosities at various points on the amyiogram, pasting temperature and paste viscosity ratios were obtained for each variety of flour. Significant varietal influence on pasting properties was indicated by ANOVA (P<0.01) and MANOVA. The hot paste viscosity at 95 °C (HTPV) and the hot paste capacity index (HPCI) had the highest correlations with the 1st and 2nd canonical variables and together accounted for 78% of total variance in the whole dataset. A plot of the second canonical variable against the 1st canonical variable showed that varieties situated together had HTPV values within close ranges. The hot paste viscosity (HTPV) was the most discriminating paste viscosity and could become an important index of functionality of cowpea flour.     

Effect of Soy Flour and Maize Flour Addition on Phase Separation in Moi-Moi from Soaked Cowpea (Vigna unguiculata) and Cowpea Flour from Different Cowpea Varieties

Two improved varieties of cowpea (IT89KO and IT90K-76) and one local variety (lsiocha) were used to investigate the effects of added soyflour and maize flour on the phase separation in moi-moi made from soaked cowpea and cowpea flour. Different levels (5%, 10%, 15%, 20% and 25%) of maize flour, soyflour and a 1:1 blend of soyflour and maize flour (soy/maize flour) were separately added. The moi-moi from the different combinations was evaluated for phase separation and per cent height of the upper layer calculated. Soaking of cowpea reduced the size of the upper layer in moi-moi compared with the use of cowpea flour. The addition of maize flour or the soy/maize flour reduced the upper layer compared with when either flour was added alone. The upper layer of moi-moi made from cowpea flour with added soy flour (21.20%) was significantly higher (p < 0.05) than moi-moi from soaked cowpea with added soy flour (15.2%). Moi-moi with added maize flour made from cowpea flour produced a significantly (p < 0.05) higher mean per cent upper layer (19.72%) compared with that from soaked cowpea (8.95%). Addition of soyflour produced the greatest upper layer for all varieties used. There were no significant (p > 0.05) differences in the per cent upper layers for moi-moi from all cowpea varieties when maize flour was added. Increasing the proportion of added flours increased the size of the upper layer. Complete prevention of the occurrence of phase separation in moi-moi by addition of soy flour and maize flour alone is not feasible.     

Automatic, rapid screening of seed resistance in cowpea, Vigna unguiculata (L.) Walpers, to the seed beetle Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) using acoustic monitoring

The biomonitor technique was investigated as a rapid and automatic method for measuring the resistance of cowpea varieties to the seed beetle Callosobruchus maculatus. This technique measures the activity of internally feeding insect larvae by counting ultrasonic emissions produced as they feed. Activity throughout the development of C. maculatus larvae in known susceptible and resistant cowpea varieties was recorded. This showed details of the development of each larval instar, and showed clear differences between the resistant and susceptible cowpeas. A rapid method for comparing cowpeas was proposed in which the activity of larvae was recorded for 24 h starting 14 days after oviposition. Using this method, significant differences in activity were apparent between one susceptible and two resistant cowpea varieties. Further comparisons using a randomised block experimental design also showed a clear difference in activity between one susceptible and one known resistant cowpea variety. This experimental protocol took 21 days. It is suggested that the biomonitor offers a promising method for screening seeds for resistance to insect pests with a reduction in the time and effort required over conventional bioassay methods.     

Soaking Studies on Winged Bean (Psophocarpus tefragonolobus L.DC) to Process Full-Fat Flour and Determine It's Shelf-Life Stability

Suitable methods to process full-fat flour from dried winged bean seeds, their effect on trypsin-inhibitor activity and keeping qualities of the flour were studied. Soaking in 0.5% or 1% sodium bicarbonate solution and boiling for 30 – 45 min was found to be suitable process for hull removal. Dry dehulling methods resulted in only 14 – 22% hull separation, while wet processing treatments were not effective. Soaking the winged bean seeds (12 hr) in 0.5% sodium bicarbonate, sodium carbonate and sodium chloride solutions reduced 30 – 40% of the trypsin inhibitor activity. Winged bean full-fat flour could be stored for 4 wk under ambient conditions.     

不同品种豇豆发酵过程中质构品质变化及产植物细胞壁降解酶微生物种类分析

以4种不同品种豇豆为研究对象,探究发酵过程中菌群和质构特性变化,分析造成不同品种发酵豇豆软腐的产植物细胞壁降解酶(Plant cell wall degradation enzymes,PCWDEs)微生物的主要种类。采用质构分析仪测定发酵过程中豇豆质构的变化,用鉴别培养基筛选产PCWDEs微生物并进行16S rDNA或18S rDNA分子生物学鉴定。结果表明:豇豆品种A(成豇10号)在发酵过程中表现出的质构品质最好,与豇豆品种A相比,豆品种B(红嘴胖豇)、品种C(成豇9号)和品种D(挂面红)的硬度、弹性、咀嚼力下降得更快,尤其是豇豆品种B。对产PCWDES微生物种类分析得知,品种B发酵豇豆中产PCWDEs微生物数量和种类最多且产酶类别多样,微生物分属于肠杆菌属(Enterobacter)、柠檬酸杆菌属(Citrobacter)、假单胞菌属(Pseudomonas)、葡萄球菌属(Staphylococcus)、粘菌属(Myroides)、泛菌属(Pantoea)和克雷伯氏菌属(Klebsiella)等属;品种A、品种C、品种D中产PCWDEs微生物及产酶种类较少,仅在品种D中发现产PCWDEs的解鸟氨酸拉乌尔菌(Raoultella ornithinolytica);4种发酵豇豆中均分离得到产蛋白酶的植物乳杆菌(Lactobacillus plantarum)和产淀粉酶的异常威克汉姆酵母(Wickerhamomyces anomalus)。综上所述,不同品种豇豆在发酵过程中微生物群体及质构品质变化具有品种特异性,发酵后期豇豆的软腐与产PCWDEs微生物的种类和数量有关。     

Seed coat has no value in protecting cowpea seed against attack by Callosobruchus maculatus (F.)

Experiments were conducted to compare the oviposition preference of the cowpea seed beetle Callosobruchus maculatus (F.) on 22 cowpea varieties, with and without seed coat. The cowpeas included five resistant, four moderately resistant and 13 susceptible varieties. Ten of the varieties had smooth seed coats while 12 were wrinkled. Mean numbers of eggs laid on smooth and wrinkled varieties were not significantly different. The survival of the bruchid was also assessed on intact and decorticated seeds of five varieties, comprising two resistant varieties “Kanannado” and “IT89KD-288”, a moderately resistant variety “IT93K-513-2” and two susceptible varieties “IT87K-941-1” and “IT89KD-374-57”. There was no correlation of resistance level with the number of eggs oviposited on cowpea varieties. Under limited and free-choice conditions, cowpea seeds with intact seed coats were preferred to decorticated seeds for oviposition. Adult emergence, mean development periods and pre-adult mortality were similar when seed coats were removed or left intact. It is concluded that the seed coat may not be a useful aspect to consider for breeding of bruchid resistance into cowpea varieties.     

Environmental conditions affect the response of West African Callosobruchus maculatus (Coleoptera: Bruchidae) populations to susceptible and resistant cowpeas

Development and release of resistant cowpea varieties represents an attractive alternative to conventional chemical methods for control of Callosobruchus maculatus (F.), a major pest of stored cowpea, Vigna unguiculata (L.) Walpers, across sub-Saharan West Africa. However, laboratory studies on geographically distinct populations have repeatedly highlighted significant intraspecific variation in performance on resistant cowpeas, which could interfere with their effectiveness as a control method. In this study, the effect of different environmental conditions on population performance on susceptible and resistant cowpeas was investigated to determine whether they could also affect the degree of control achieved in different areas. Seven Nigerian populations were screened against cowpeas under two environmental regimes (Condition A—26°C, 75±5% relative humidity (r.h.), LD11.5:12.5 h, and Condition B—30:15°C (11.5:12.5 h), 30±5% r.h., LD11.5:12.5 h), designed to simulate field conditions during the storage period in different regions of Nigeria. Independent of environmental conditions and seed variety, significant differences among populations were expressed in terms of embryonic mortality, post-embryonic mortality, development time and adult weight. Resistant seeds delayed development, resulted in protracted adult emergences and increased post-embryonic mortality. Environmental conditions are shown for the first time to have a significant effect on population performance on resistant seeds, principally on development time and post-embryonic mortality. Effects on these parameters were not the same; rapid development was favoured under Condition A, although mortality was higher under this regime. The effects of resistant seeds and environmental conditions on performance could not be generalised across biological traits. Furthermore, significant interactions between environment and seed variety and between environment and population, were identified in certain parameters, suggesting performance on a resistant variety may vary significantly across populations, with seed variety and in response to differences in environmental conditions. It is suggested that the only reliable way of predicting the effectiveness of resistant varieties in the field would be to test them against local populations in the areas targeted for release, under local environmental conditions.     

Fungi and mycotoxins in cowpea (Vigna unguiculata L) on Nigerian markets

ABSTRACT

In this study, 81 samples of two cowpea varieties (brown: 54; white: 27) collected from various markets in southwestern Nigeria were examined for fungal and mycotoxin contamination. Moulds belonging to Aspergillus, Fusarium, and Penicillium were recovered from 99% of the samples. In both cowpea varieties, Aspergillus (52–53%) dominated Fusarium (29–30%) and Penicillium (17–20%). The interactive effect of cowpea variety and sampled location was significant (p = .013) on the occurrence of Fusarium species. Aflatoxins were detected in one brown and two white cowpea samples at concentrations reaching 209 and 84 µg/kg, respectively. Additionally, beauvericin was found in two samples of each cowpea variety, albeit at low concentrations. Cowpea presents as an alternative vegetable protein source to groundnuts in household nutrition with respect to mycotoxin contamination. Simple techniques to prevent mycotoxins in dry cowpeas are discussed.     

Comparative studies of some properties of undehulled, mechanically dehulled and manually dehulled cowpea (Vigna unguiculata Walp. L.) flours

A comparative evaluation was made of some physico‐chemical and rheological characteristics of undehulled, manually dehulled and mechanically dehulled cowpea (Vigna unguiculata Walp. L.) flours from brown and white varieties of the legume. The flours were used to prepare steamed bean paste, ‘Moinmoin’, which was analysed for some sensory parameters. Dehulling and dehulling methods had no appreciable influence on the physical characteristics and proximate composition of the flours, except ash content, which was slightly higher in undehulled flour samples. Amylograph pasting characteristics of the flours showed varying trends because of dehulling method and/or presence of seed coats. ‘Moinmoin’ samples prepared from the flours received similar ratings for all sensory attributes, with no significant differences (P < 0.01 and P < 0.05), except for the low‐rated (poorer) colour of the undehulled brown product.     

Nutrients and antinutrients in cowpea and horse gram flours in comparison to chickpea flour: Evaluation of their flour functionality

The nutrient composition, antinutritional factors and flour functionality of cowpea and horse gram flours were evaluated in comparison to chickpea flour characteristics. Protein content of these flours was in the range of 22.5−24.1%. Fat content was highest in chickpea (4.8%) and lowest in horse gram (1.4%). Resistant starch and phytic acid were significantly higher in cowpea flour. Compared to chickpea and cowpea, horse gram has more carbohydrate, dietary fibre, polyphenols and trypsin inhibitor activity and less oligosaccharides. Horse gram and chickpea flours had the highest water and oil absorption capacities with values of 148.1% and 109.3%, respectively. Although emulsion activity (58.1%) and stability (52.0%) were superior in horse gram, foaming capacity and foam stability were significantly higher in chickpea and cowpea flours, respectively. These results suggest the potential utility of cowpea and horse gram flours as substitutes for chickpea flour in some food products formulations.     

Cowpea cooking characteristics as affected by micronisation temperature: a study of the physicochemical and functional properties of starch

Bechuana white cowpeas were micronised to three temperatures (130, 153 and 170 °C). Cooking properties of the cowpea seeds and the role of starch‐related properties were studied. In all cases, micronisation significantly reduced the cooking time and thus the time required for the cowpea seeds to attain a suitably soft texture. This was attributed in part to the significant improvement in rate of water absorption during cooking and starch pre‐gelatinisation, as evidenced by loss of birefringence and increased susceptibility of the cowpea starch to α‐amylase digestion. However, micronisation to 170 °C resulted in a severe deterioration in pasting properties of the cowpea flour, possibly due to starch depolymerisation and/or amylose‐associated crosslinking. Owing to these changes, cowpea seeds micronised to 170 °C required a longer cooking time than the other two micronised samples. Flour prepared from cowpea seeds micronised to 170 °C may have limited starch functionality. Copyright © 2006 Society of Chemical Industry     

Fat reduction affects quality of akara (fried cowpea paste)

Akara, a fried finger food made from cowpeas (Vigna unguiculata), is popular in West Africa and has been shown to be acceptable to American consumers. Akara is, however, a high‐fat food (about 31%, dry wt basis). We determined the effects of incorporating two modifiers, high amylose cornstarch or extruded cowpea flour, on akara fat content and consumer acceptability. The modifiers were used at the 10% level. Akara fat content was reduced by 26.1% with cornstarch and by 36.8% with extruded cowpea flour. There were no significant differences in sensory ratings among samples, and all samples received acceptable ratings (6 = like slightly) for overall liking.     

Changes in fatty acid,simple sugar,and oligosaccharide content of cowpea (Vigna unguiculata) flour as a result of soaking,boiling, and fermentation with Rhizopus microsporus var. oligosporus

Changes in fatty acid, simple sugar, and oligosaccharide content of cowpea flour as a result of soaking, boiling, and fermentation with Rhizopus microsporus var. oligosporus were investigated. The major fatty acids in flour made from both nonfermented and fermented cowpeas were linoleic, palmitic, and linolenic. With the exception of lower amounts of lauric, palmitic, linoleic, and linolenic acids and slightly higher amounts of lignoceric acid, the remaining fatty acids in flour made from soaked cowpeas were essentially unchanged from the control flour made from cowpeas that were not soaked, boiled or fermented. Soaking followed by boiling generally increased amounts of fatty acids in flour compared to the control. Rhizopus microsporus did not utilize lipid during 24 h of fermentation. Soaking decreased the amount of sucrose and stachyose by 39% and 18.4%, respectively, whereas soaking followed by boiling caused decreases of 58.3% and 49.3%. Complete elimination of sucrose, raffinose, and stachyose was achieved after 15 h of fermentation.     

Hydrothermal treatments of two cowpea (Vigna unguiculata L. Walp) varieties: effect of micronisation on physicochemical and structural characteristics

The effects of a hydrothermal treatment consisting of tempering (to 41% moisture) and heating to 153 °C (micronisation) on the structural and physicochemical characteristics of two cowpea varieties were studied. The untreated varieties had similar cooking times, although cooked Bechuana white cowpeas were significantly (P ≤ 0.05) softer and had a higher incidence of splitting than Var. 462 cowpeas. This may be due in part to differences in cotyledon structure affecting water uptake during cooking. The hydrothermal treatment changed the physical structure and chemical properties of the cowpea seeds. This led to significant (P ≤ 0.05) reductions in the cooking time of micronised Bechuana white and Var. 462 cowpeas, by 47 and 36% respectively, as compared with control samples. Micronisation caused physical fissuring of the seed coat and cotyledon and significantly (P ≤ 0.05) reduced the bulk density of treated seeds. These changes in the physical structure significantly (P ≤ 0.05) improved the initial water uptake during soaking and cooking, increased the enzyme‐susceptible starch and reduced the protein solubility and hydration capacity of the cowpea seeds. Cooked (60 min) micronised cowpeas also had significantly (P ≤ 0.05) more splits and a significantly (P ≤ 0.05) softer texture than control samples. Copyright © 2005 Society of Chemical Industry     

Effect of Processing on Certain Antinutrients in Cowpeas (Vigna unguiculata)

Four Nigerian cultivars of cowpeas were analyzed for raffinose, stachyose, phytic acid, tannins, and trypsin inhibitory activity after dehulling, cold-soaking, hot-soaking, and cooking as ewa-ibeji and moin-moin (two popular Nigerian cowpea foods). Dehulling decreased stachyose and removed the tannins. Hot-soaking caused a significant reduction in stachyose and trypsin inhibitory activity. Ewa-ibeji and moin-moin contained similar quantities of antinutrients, except for tannins which were absent in moin-moin.     

EFFECTS OF INFESTATION BY BRUCHID BEETLES (CALLOSOBRUCHUS MACULATUS) ON THE NUTRITIONAL QUALITY AND SENSORY PROPERTIES OF COWPEAS (VIGNA UNGUICULATA)

The effects of insect infestation by Callosobruchus maculatus (Fabricus) on the chemical, nutritional and sensory properties of three cowpea varieties were investigated. Proximate analysis showed that infestation led to an increase in moisture content of seeds by 28.6% on the average. Decreases of 10.6%, 46.5% and 11.4% in crude protein, ash and soluble carbohydrate contents, respectively, were observed. For the three cowpea varieties, the minerals sodium, calcium and magnesium decreased by 6.7%, 10.0% and 1.3%, respectively. Indices of fat deterioration, peroxide value and free fatty acids, increased by 175% and 242%, respectively. Infestation decreased the weight gain, Protein Efficiency Ratio (PER), Feed Efficiency Ratio (FER) and blood glucose levels of experimental rats by 28.5%, 19%, 63.5% and 1.46%, respectively. Infestation also led to significant deterioration of the sensory attributes of food products developed from cowpeas. The color, aroma, taste and texture of these cowpea products were less acceptable than the sensory parameters of products made with uninfested cowpeas .