Relationship of hydrophobicity and solubility with some functional properties of cowpea (Vigna unguiculata) protein isolate

The relationship of hydrophobicity and solubility with some functional properties of cowpea protein isolate was determined. Cowpea protein isolate was prepared by alkali extraction followed by precipitation at pH 4.5. The precipitated proteins were then neutralized to pH 7. Heating of the protein isolate to 100°C for 10 min followed by cooling to room temperature resulted in a significant (P ≦ 0.05) decrease in aromatic hydrophobicity (ARH) when compared to the native protein isolate. The inclusion of sodium dodecyl sulfate (SDS) during heating gave a significant (P ≦ 0-05) 1.7-fold increase while inclusion of mercaptoethanol (ME) gave a significant (P ≦ 0.05) 2.5-fold increase in ARH of the cooled protein solution. Protein solubility (PS), foam expansion (FE) and emulsification activity index (EAI) of the isolate generally increased significantly (P ≦ 0.05) upon heating or treatment with urea or SDS or a combination of SDS and ME. Backward stepwise multiple regression was used to obtain equations for predicting emulsifying and foaming properties of the protein isolate from solubility and hydrophobicity parameters. PS, ARH and aliphatic hydrophobicity (ALH) were important in predicting foam stability and emulsion stability, while PS and ALH were important for predicting FE. ALH alone was important for predicting EAI.     

Effect of a microbial calcium‐independent transglutaminase on functional properties of a partially purified cowpea (vigna unguiculata) globulin

A partially purified globulin from cowpea seeds was polymerised by calcium‐independent microbial transglutaminase. The level of free amino groups in the globulin decreased with increase in enzyme concentration, suggesting that the cross‐linking reaction involved participation of the amino residues. At transglutaminase concentrations of 6–18 μg ml⁻¹ emulsifying activity decreased with increasing enzyme concentration and degree of cross‐linking, while a similar trend was observed for the foaming property at 6–12 μg ml⁻¹ transglutaminase concentrations. The resultant emulsions and foams formed by the cross‐linked proteins were more stable than those formed by the untreated protein. Sodium dodecyl sulphate polyacrylamide gel electrophoresis showed that of the two major polypeptides, the 55 kDa protein was more susceptible to transglutaminase action than the 50 kDa protein. Scanning electron microscopy revealed an amorphous structure for the control protein gel while a more defined and cross‐linked gel structure was observed for the protein treated with transglutaminase. The results suggest that protein products differing in functionalities can be obtained by controlling the degree of enzymatic protein cross‐linking. © 1999 Society of Chemical Industry     

Effect of milling method on selected physical and functional properties of cowpea (Vigna unguiculata) paste

Particle size distribution (PSD) of cowpea meal is an important determinant of paste functionality and end product quality. Samples from various mills and screen sizes were used to determine PSD, water‐holding capacity (WHC) and swelling capacity (SWC). Hammer mill (1.73 mm screen) meal had a geometric mean diameter (d_gw) of 221 microns, whereas PM‐360 [plate mill with one complete turn (360°) of clearance] meal had a d_gw of 1559 microns. All other milling processes resulted in meal with an intermediate particle size. To reduce the particle size of cowpea pastes, cowpea meals were hydrated to pre‐determined moisture contents, held for 15 min, and then blended in a blender before whipping. Blending increased the WHC and SWC of all samples.     

挤压温度对火麻蛋白理化、加工功能特性的影响

目的 探究不同挤压温度(60、80、100、120、140℃)对火麻蛋白的理化、加工功能特性的影响。方法 以火麻蛋白饼粕为原料,经过挤压前处理后,使用碱溶酸沉法从火麻蛋白饼粕中提取火麻蛋白,测定其提取率、等电点、氮溶解指数、体外消化率、巯基和二硫键含量、持水性和持油性,并利用傅里叶红外光谱、内源性荧光光谱、差式扫描量热仪、十二烷基硫酸钠-聚丙烯酰胺凝胶电泳、扫描电镜对火麻蛋白进行表征。结果 挤压处理会导致火麻蛋白的提取率、体外消化率和游离巯基含量提高,但在140℃时游离巯基含量降低,等电点、持水性、总巯基和二硫键含量均有所下降,随着挤压温度的升高,火麻蛋白的氮溶解指数先下降再升高后下降,持油性先降低后升高;傅立叶红外光谱和内源性荧光光谱结果表明挤压不会引起火麻蛋白生成新的吸收峰,挤压温度的升高会使其荧光强度先增加后减少;差式扫描量热仪结果表明在挤压温度为120℃时,火麻蛋白氢键断裂,热焓值升高;十二烷基硫酸钠-聚丙烯酰胺凝胶电泳结果显示挤压处理使火麻蛋白形成了大的聚集体,条带较未挤压的火麻蛋白颜色变浅;观察扫描电镜发现挤压处理导致火麻蛋白表面孔隙减小,并且随着挤压温度的升高逐渐形成了致...     

紫皮豇豆(Vigna unguiculata L.)花色苷的研究

首次应用高效液相色谱-二极管阵列检测器-质谱联用技术(HPLC-DAD-MS)鉴定出紫皮豇豆主要含有三种花色苷,分别为飞燕草色素、矢车菊色素、天竺葵色素的葡萄糖苷,其中矢车菊葡萄糖苷相对百分含量达到93.4%;应用pH示差法测定出其单体花色苷的含量为57.15mg/100g鲜重;应用DPPH法测定结果显示,花色苷粗提液有较强的抗氧化能力。     

Dehulling characteristics,sensory and functional properties of flours from selected cowpea varieties

BACKGROUND: The knowledge of dehulling characteristics is very important in the selection of cowpeas for flour production. In this study the sensory and functional properties of cowpea flour as influenced by dehulling method (wet and dry/mechanical dehulling) and cowpea variety (white, maroon and mottled) were investigated. RESULTS: White cowpea showed a significantly different (P < 0.05) and higher dehulling rate (DR > 97%) for all dehulling methods. Maroon and mottled cowpeas were poorly dehulled (DR < 10%) when using the wet method (WD). Dry dehulling (DD) was effective on all three varieties (DR > 94%). The highest yield of flour was observed with white cowpea (80% for DD and 96% for WD). The beany odour intensity of flours was dependent on the method of dehulling used. Flour functionality was more significantly influenced by cowpea variety than by dehulling method. CONCLUSION: Dry dehulling could be recommended for cowpea flour production, as this method was found to be more effective on the selected cowpea varieties. Owing to the observed variation in flour functionality among cowpea varieties, the choice of a particular variety for flour production will depend on the intended use of the flour. Copyright © 2009 Society of Chemical Industry     

Gamma irradiation of cowpea (Vigna unguiculata L. Walp) seeds: effect on colour,cooking quality and pasting characteristics

Cowpea seeds were treated to various gamma irradiation doses, and their colour, cooking quality and pasting properties studied. Irradiation at 50 kGy resulted in significant browning (indicated by decreases in L colour value) of cowpea seeds. At 2 and 10 (but not at 50) kGy, irradiation led to significant reduction in cooking time of cowpea seeds possibly through irradiation‐induced degradation of starch and pectic substances (indicated by decreases in peak and final viscosities) leading possibly to enhanced heat and mass transfer within the seed cotyledon and cell wall, respectively. At 50 kGy, the cooking time of cowpea seeds was prolonged significantly owing possibly to extensive polymer cross‐linking occurring within the seeds at this high dose. Splitting of cowpea cotyledons during cooking decreased significantly at 50 kGy, but was unaffected at 2 and 10 kGy. Irradiation resulted in significant leaching of nutrients from cowpea seeds during cooking in a dose‐dependent manner.     

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.     

A review on the physicochemical properties and potential food applications of cowpea (Vigna unguiculata) starch

Cowpea is a food legume with high protein and carbohydrate contents, which could be explored in addressing food and nutritional challenges in many parts of the world. However, some cowpea varieties are difficult to cook, resulting in high energy requirements and greater loss of nutrients. Since the bulk of carbohydrate in cowpea is starch, this component may be explored as an alternative starch source for various industrial applications, especially because cowpea starch is rich in resistant starch with several beneficial physiological effects. Hence, this review summarises the present knowledge on the isolation, composition, physicochemical properties and modification methods of cowpea starch. Future studies that are required to produce cowpea starch with novel properties were highlighted and the need to apply modified cowpea starch in food systems were also noted.     

Changes in the biochemical and functional properties of the extruded hard‐to‐cook cowpea (Vigna unguiculata L. Walp)

Changes in the biochemical and functional properties of the hard‐to‐cook cowpea bean after treatment by the extrusion process are reported. The extrusion was carried out at 150 °C, with a compression ratio screw of 3:1, a 5‐mm die, and a screw speed of 150 r.p.m. The extrusion caused the complete inactivation of the α‐amylase and lectin and it also reduced the trypsin inhibitor activity (38.2%) and phytic acid content (33.2%). The functional properties were also modified by the process, an increase of 2.5 times in the water absorption index and 3.1% in the water solubility were observed. The digestibility of the hard‐to‐cook flour of the cowpea bean was improved after the extrusion, with a 55.9% increase in protein digestibility and a 5.9% increase in starch digestibility.     

Inheritance of protein content in seeds of selected crosses of cowpea (Vigna unguiculata)

The inheritance pattern of protein content in seeds of two crosses of cowpea (Vigna unguiculata (L) Walp) was studied. It was observed that, in both crosses, inheritance of the character involved both additive and non-additive gene effects. Heritability in the broad sense was 0·70–0·78. A significant effect of pollen source was detected in one of the two crosses. In both crosses, comparison of seed protein content of reciprocal segregating generations indicated the influence of cytoplasmic factors.     

Influence of cowpea (Vigna unguiculata L Walp) variety on protein quality and sensory properties of akara,a popular West African cowpea‐based food

The influence of newly developed cowpea varieties (IT81D‐699, IT82E‐18, IT84S‐2246‐4 and TV_x3236) on the proximate composition, protein quality and sensory properties of akara, a popular West African cowpea‐based food, was investigated and the results obtained were compared with those for akara prepared from a local blackeye cowpea variety. Protein quality was evaluated using weanling albino rats fed diets which were formulated to supply 10% protein using defatted akara samples, with casein as a control. Akara samples prepared from IT81D‐699 and TV_x3236 had crude protein contents, texture and overall acceptability comparable to those of akara prepared from the blackeye variety. Also, akara diets formulated using IT81D‐699 and TV_x3236 showed significantly (p < 0.05) higher values for weight gain, protein efficiency ratio, net protein ratio and true digestibility than diets formulated with IT82E‐18, IT84S‐2246‐4 and blackeye, suggesting an improvement in the nutritional quality of akara produced using these (IT8ID‐699 and TV_x3236) newly developed cowpea varieties. Copyright © 2004 Society of Chemical Industry     

Evaluation of cooking time and quality of seven diverse cowpea (Vigna unguiculata (L.) Walp.) varieties

Seven cowpea ( Vigna unguiculata (L.) Walp.) varieties, which were part of a larger collection evaluated in agronomic field trials in Botswana, were selected for characterization of cooking time and quality. Newly harvested seed was kept in the open air for 2 weeks, then stored at 4°C and 40% relative humidity for 3 months. Duplicate samples were tested for cooking time with and without 12-h prior soaking. Varieties showed differences ( P < 0.01) in cooking time and response to soaking, although the overall effect of soaking was insignificant. Cooking times ranged from 29 to 64 min without soaking and 36 to 56 min after soaking, with small-seeded varieties having the longer cooking times. The seed coat of some varieties readily became soft, but others remained tough or split before finally softening.     

Genetic and environmental variability in starch,fatty acids and mineral nutrients composition in cowpea (Vigna unguiculata (L) Walp)

Fifteen cowpea cultivars grown in three locations (Kano (12°00′N 8°31′E), Mokwa (9°17′N 5°04′E) and Ago-Iwoye (6°58′N 4°00′)) between 1993 and 1994 were analysed for genotype, environmental and genotype×environment variability for starch (g kg⁻¹), fatty acids (% of total oil) and mineral nutrients (g kg⁻¹) composition. There were significant environmental as well as genetic effects on these nutritional qualities. The environmental effect accounted largely for the variability observed in starch (60%), palmitic acid (80%), arachidic acid (100%), potassium (100%), phosphorus (81%) and manganese (86%), while the genotypic effect accounted largely for the variability observed in linoleic acid (50%), linolenic acid (50%) and copper (68%) contents. Correlation coefficient (pooled data) from the three locations indicated that starch was positively correlated to palmitic acid (r = 0·21, 0·01< P < 0·05), potassium (r = 0·80, P < 0·001) and phosphorus (r = 0·65, P < 0·001), but negatively correlated to oleic (r = −0·23, 0·01< P < 0·05), linoleic (r = −0·67, P < 0·001) and linolenic acid (r = −0·74, P < 0·001) contents. Starch showed a strong positive correlation with magnesium content (r = 0·75) and a strong negative correlation with copper (r = −0·73) and iron (r = −0·62) at the genetic level. This research established the degree of variability for these characters in cowpea. © 1998 Society of Chemical Industry.     

Assessment of average exposure to organochlorine pesticides in southern Togo from water,maize (Zea mays) and cowpea (Vigna unguiculata)

Drinking water, cowpea and maize grains were sampled in some potentially exposed agro-ecological areas in Togo and analysed for their contamination by some common organochlorine pesticides. A total of 19 organochlorine pesticides were investigated in ten subsamples of maize, ten subsamples of cowpea and nine subsamples of drinking water. Analytical methods included solvent extraction of the pesticide residues and their subsequent quantification using gas chromatography-mass spectrometry (GC/MS). Estimated daily intakes (EDIs) of pesticides were also determined. Pesticides residues in drinking water (0.04–0.40 µg l^?1) were higher than the maximum residue limit (MRL) (0.03 µg l^?1) set by the World Health Organization (WHO). Dieldrin, endrin, heptachlor epoxide and endosulfan levels (13.16–98.79 µg kg^?1) in cowpea grains exceeded MRLs applied in France (10–50 µg kg^?1). Contaminants’ levels in maize grains (0.53–65.70 µg kg^?1) were below the MRLs (20–100 µg kg^?1) set by the Food and Agriculture Organization (FAO) and the WHO. EDIs of the tested pesticides ranged from 0.02% to 162.07% of the acceptable daily intakes (ADIs). Population exposure levels of dieldrin and heptachlor epoxide were higher than the FAO/WHO standards. A comprehensive national monitoring programme on organochlorine pesticides should be undertaken to include such other relevant sources like meat, fish, eggs and milk.     

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     

Physico‐chemical and functional properties of proteins from green mussel (Perna viridis) during ice storage

The effect of ice storage on the properties of proteins from green mussel (Perna viridis) has been investigated. Ice storage of green mussel for a period of 19 days revealed a marginal increase in moisture and decrease in total nitrogen content. There was significant reduction (P < 0.05) in non‐protein nitrogen content and calcium activated adenosine triphosphatase enzyme activity. The solubility of the total proteins in high ionic strength buffer decreased marginally. The ice storage of green mussel had a significant effect on association‐dissociation/denaturation phenomenon of proteins as revealed by gel filtration profile, reduced viscosity values and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS‐PAGE) pattern. The dynamic viscoelastic behaviour of green mussel meat in the temperature range of 30–90 °C revealed higher storage modulus (G′) values at a later part of ice storage. The emulsion capacity of green mussel did not show significant variation (P < 0.05) during ice storage. Copyright © 2006 Society of Chemical Industry     

In vitro and in vivo digestibility of the albumin and globulin fractions of eight Brazilian cowpea [Vigna unguiculata (L) Walp] cultivars

Cowpea (Vigna unguiculata) is a very important crop for people living in the north‐east of Brazil where it constitutes the principal source of protein and carbohydrate. In this study, it was observed that the in vitro digestibility of the seed albumin and globulin fractions extracted from eight Brazilian cowpea cultivars was high when treated with pepsin but resistant to degradation by trypsin or chymotrypsin even after 3 h of treatment. When the albumin and globulin fractions were given to rats by intragastric intubation it was observed that intact proteins or their fragments were immunodetected in the faeces. Immunohistochemical analyses of the gut sections of these rats showed that a proportion of the albumin fraction (or its fragments), but not the globulin one, was bound to the brush border enterocytes in the duodenum. Thus the incomplete enzymatic degradation of both globulin and albumin fractions as well as the albumin binding to the gut may have a bearing upon the growth depression, malabsorption and diarrhoea observed on rats fed on cowpea seeds. Copyright © 2004 Society of Chemical Industry