Cowpea Protein Research Articles

Functional properties of acetylated and succinylated cowpea protein concentrate and effect of enzymatic hydrolysis on solubility

The present study was undertaken to improve functional properties of cowpea protein concentrate by acylation and partial hydrolysis with pepsin. The acylated concentrate showed significant improvement in protein solubility and water solubility index, at neutral pH. In addition, acylation increased fat absorption capacity compared with the untreated concentrate, and the maximum was obtained at 0.75 g succinic anhydride/g concentrate. Acetylation at concentrations of 0.25–0.50 g/g led to the higher emulsifying activity, and a markedly improvement in emulsifying stability was observed at 1.0 g anhydride/g concentrate. Foaming activity increased following acylation, particularly at 0.25 and 1.00 g/g succinic anhydride/g concentrate, while foam stability decreased. At pH 3.5, protein solubility of the acylated concentrates was low ( < 8%). Partial hydrolysis of cowpea protein concentrate with pepsin increased protein solubility at the isoelectric and neutral pH.

Purification of angiotensin I-converting enzyme inhibitory peptides from a cowpea ( Vigna unguiculata) enzymatic hydrolysate

Angiotensin I-converting enzyme (ACE) inhibitory peptides were isolated and characterized from cowpea ( Vigna unguiculata L. walp). Cowpea protein isolate was prepared by wet fractionation, extensively hydrolyzed with Flavourzyme ® and filtered through four molecular weight cut-off (MWCO) membranes in a high performance ultrafiltration (UF) cell. The ultrafiltered fraction with the highest ACE inhibitory activity was purified using gel filtration chromatography followed by reverse-phase high performance liquid chromatography (RP-HPLC). The cowpea peptide inhibition (IC 50) values were similar to those reported for many other natural ACE inhibitory peptides. The <1 kDa ultrafiltered fraction exhibited the highest biological activity. The observed amino acid composition suggests a substantial contribution of hydrophobic residues to the peptides’ inhibitory potency, which potentially acts via blocking of angiotensin II production. When hydrolyzed with the protease Flavourzyme ®, cowpea V. unguiculata protein is a good source of ACE inhibitory peptides with potential applications in physiologically functional foods with antihypertensive activity.

Nutritional and Functional Properties of Some Promising Legumes Protein Isolates

Proteins are essential component of diet performing multifarious role in human body. Present project was an attempt to extract and characterize legumes protein isolates for their functional properties. Four different legumes i.e. cowpea, pigeon pea, peas and mungbean were evaluated for protein content, functional properties and their ability to improve nutritional quality of foods. Cowpea exhibited maximum protein content 27.88±1.95% followed by mungbean, peas and pigeon pea. As for as functional properties are concerned, cowpea protein isolates showed highest bulk density 0.71±0.05 g/cm however, maximum 3 protein solubility 82±4.97 was observed in pea protein isolates. Maximum water and oil absorption capacity 163±10.05, 168±11.72% was observed in mungbean and pigeon pea protein isolates, respectively. Likewise different legumes protein isolates showed significant results for emulsifying, foaming and gelling properties.

English

A three-factorial field experiment was carried out at the University of Limpopo experimental Research farm during two planting seasons (2005/06 and 2006/07) to examine the effect of cowpea-leaf removal on cowpea performance. Three treatment factors namely cowpea varieties (Pan 311 and Red Caloona), cropping systems (sole and intercropping) and cowpea-leaf pruning regimes (pruned and un-pruned) were combined and arranged in a randomized complete block design (RCBD). Sole cowpea and sweet corn treatments were included and all treatments replicated four times. Fully expanded cowpea leaves on all cowpea plants in the two middle rows were harvested once at seven weeks after seed sowing prior to flowering. Growth and yield component data were collected from component crops while the protein content of harvested leaves and green pods as well as those of grains and the fodders at harvest were determined. The results of the study revealed that cowpea leaf protein content ranged from 24.1 to 28.1% and 26.0 to 30.7% for Red Caloona and Pan 311, respectively. The protein content of green cowpea pods obtained from Pan 311 cowpea variety ranged from 18.8 to 25.1% while that of Red Caloona varied between 17.9 and 20.7%. Similarly, the protein content of the fodder obtained after grain harvest varied between 9.3 and 9.4% and 9.9 and 12.3%, respectively for Pan 311 and Red Caloona during the two seasons. The protein content of cowpea grain obtained from intercropped plots (23.7 to 26.3%) was similar to that from sole plots (23.7 to 25.7%). In 2005/06, grain yield was 1704 kg ha-1 and 1480 kg ha-1 respectively for Pan 311 and Red Caloona while 1291 and 512 kg ha-1 were obtained for Pan 311and Red Caloona, respectively in 2006/07. There was a significant season x varietal effects on pod and seed protein content. These results reveal that Pan 311 would be better suited for both vegetable and grain production purposes for human consumption while Red Caloona would better serve as a fodder crop for animal production. The results also show that neither cropping system nor cowpea leaf pruning did have consequential effects on the nutritional value of cowpea plant parts and grains. Key words: Cropping systems, leaf pruning, cowpea protein, grain yield, dryland farming.

Legumes seeds protein isolates in the production of ascorbic acid microparticles

Abstract This study evaluated the use of pea ( Pisum sativum ) and cowpea ( Vigna unguiculata ) protein isolates (PPI and CPI) in the microencapsulation of ascorbic acid (AA), by spray drying. PPI and CPI were used pure or mixed with maltodextrin (M) as wall materials of AA. The process yield was improved from 66% to 86% by the addition of M (CPI/M and PPI/M); also, AA particles yield was 79%. The AA retention from the drying process was higher in PPI/M (69%) than in CPI/M (66%), and this was attributed to PPI proteolysis profile, demonstrated by the SDS–PAGE electrophoresis. Scanning electron microscopy revealed that AA particles were similarly spherical and shriveled. Mean particle sizes of PPI/M/AA and CPI/M/AA were 7 and 8 μm, respectively. This study showed the exploration of protein isolates from legumes in the development of a microparticulate system containing AA with great potential for use in human health.

Cholesterol‐Lowering Properties of Whole Cowpea Seed and Its Protein Isolate in Hamsters

Hypercholesterolemic hamsters were fed for 4 wk on diets rich in saturated fatty acids and cholesterol, differing only in protein source (20 %): casein (control group, HC), whole cowpea seed (HWS), and cowpea protein isolate (HPI). Hamsters fed on HWS and HPI presented significant reductions in plasma total cholesterol and non-HDL cholesterol. HPI and HC presented similar protein digestibility, which were significantly higher than that of HWS. Animals fed on HWS presented significantly higher levels of bile acids and cholesterol in feces than did the animals fed on casein or HPI diets. Histological analyses of the liver showed that HC diet resulted in steatosis widely distributed throughout the hepatic lobule, while HWS and HPI diets promoted reductions in liver steatosis. The effectiveness of HWS for modulating lipid metabolism was greater than that of HPI, as measured by plasma cholesterol reduction and liver steatosis.

Effect of micronisation temperature (130 and 170 °C) on functional properties of cowpea flour

Functional properties of cowpea flour from seeds micronised at two different surface temperatures (130 and 170 °C) were studied. Micronisation (130 and 170 °C) significantly ( P ⩽ 0.05) increased the water absorption capacity and least gelation concentration of the flour. The treatment significantly ( P ⩽ 0.05) reduced the water solubility and swelling indices, gel strength and foaming capacity of the flour. The changes in cowpea flour functional properties, such as the loss of foaming capacity in flours from micronised (130 and 170 °C) seeds, were associated with significant ( P ⩽ 0.05) increase in the surface hydrophobicity and cross-linking of the cowpea protein. SDS–PAGE of the protein-rich fractions revealed changes in the protein subunit profile which included the formation of disulphide bonds and possibly Maillard cross-links. The flour from M-170 °C seeds was significantly ( P ⩽ 0.05) darker than was the flour from unmicronised and M-130 °C seeds.

Gamma irradiation of cowpea ( Vigna unguiculata L. Walp) flours and pastes: Effects on functional, thermal and molecular properties of isolated proteins

In a previous study irradiation of cowpea flours and pastes at medium (10 kGy) and high (50 kGy) doses resulted in significant changes in protein-related functional properties. To understand some of the effects of gamma irradiation on cowpea proteins in particular, we isolated proteins from cowpea flours (FPC) and pastes (PPC) treated with gamma irradiation at 2, 10, and 50 kGy and analyzed their functional, thermal and molecular properties. Nitrogen solubility index of both FPC and PPC decreased, whereas oil absorption and emulsion capacities increased significantly with increasing irradiation dose. Differential scanning calorimetry showed decreases in transition temperatures ( T d) and enthalpies (Δ H), indicating a progressive denaturation of cowpea proteins with increasing irradiation. Size exclusion HPLC revealed increases in protein molecular weights, probably due to protein–protein cross-linking with irradiation in a dose-dependent manner. Reducing SDS-PAGE of FPC and PPC samples seems to suggest that the contribution of disulphide bonds to irradiation-induced cowpea protein–protein cross-linking is small.

Functional Properties of Protein Isolate from Cowpea (Vigna unguiculata L. Walp.)

ABSTRACT: Functional properties of protein isolates prepared from 3 cowpea varieties and 2 soybean varieties in each of 2 y were determined. Both cowpea protein isolate (CPI) and soy protein isolate (SPI) showed a u‐shaped curve for solubility with the minimum solubility occurring at pH 4.5. The CPI had lower emulsifying activity than SPI but was similar in stability. Foaming capacity and foaming stability ranged from 58.6 to 60.2 mL and 63.7 to 64.4 min for CPI and from 31.9 to 33.0 mL and 43.4 to 45.0 min for SPI, respectively. Gels were formed at 70 °C for 40 min and 30 min for CPI (12%) and SPI (10%), respectively. The CPI needs modification to enhance functional properties for potential application in food products.

Biological evaluation of a protein isolate from cowpea ( Vigna unguiculata) seeds

The present work was carried out to determine the nutritive quality of a protein isolate from cowpea ( Vigna unguiculata) seeds. Previous data from our laboratory showed that cowpea protein isolate (CPI) presents good functional properties, including solubility, emulsifying and foaming activities. In this work, rats were divided into three groups that received, during 16 days, liquid diets containing casein or CPI as protein sources or a protein-free diet. The nutritional parameters measured for the diet containing CPI showed a positive nitrogen balance (NB=0.5), a net protein retention (NPR) of 0.7 and digestibility of 87%. Furthermore, CPI did not present detectable hemagglutinating activity and very low trypsin inhibitory activity (18 TIU/mg protein) after heat treatment. In terms of its essential amino acid content, CPI presented a better composition than purified cowpea vicilin. No significant histological differences were found in several internal organs of the rats that were fed a diet containing CPI when compared to the group fed with a casein-containing diet. Taken together, these results suggest that CPI may provide a new, inexpensive source of protein for use as a potential functional and nutritional agent in the food industry.

Functional properties of purified vicilins from cowpea (Vigna unguiculata) and pea (Pisum sativum) and cowpea protein isolate.

The major storage globulins (vicilins) of cowpea (Vigna unguiculata) and pea (Pisum sativum) seeds were purified by ammonium sulfate precipitation, and a semipurified cowpea protein isolate (CPI) was prepared by isoelectric precipitation. Some of the functional properties of these proteins, including solubility, foaming, and emulsifying capacities, were investigated and compared. The solubility of purified cowpea vicilin was reduced at pH 5.0, increasing markedly below and above this value. Pea vicilin exhibited poor solubility between pH 5.0 and pH 6.0, and CPI was little soluble in the pH range from 4.0 to 6.0. At neutral pH, the emulsifying activity indexes (EAI) of purified pea vicilin and CPI were 194 and 291 m(2)/g, respectively, which compare quite favorably to EAIs of 110 and 133 m(2)/g for casein and albumin, respectively. Remarkably, purified cowpea vicilin exhibited an EAI of 490 m(2)/g, indicating a very high emulsifying activity. Purified cowpea and pea vicilins exhibited lower foaming capacities and foam stablity indexes (FSI) than CPI. FSI values of 80 and 260 min were obtained for purified pea and cowpea vicilin, respectively, whereas a FSI value of 380 min was obtained for CPI. These results are discussed in terms of the possible utilization of purified vicilins or protein isolates from pea and cowpea in the food processing industry.

Fractionation, solubility and functional properties of cowpea ( Vigna unguiculata) proteins as affected by pH and/or salt concentration

The content, fractionation, solubility and functional properties of cowpea proteins were determined. The effects of pH and/or NaCl concentration on some of these functional properties were also investigated. The protein content of the seed was found to be 26.8%. Albumin is the major fraction of cowpea seed proteins. The minimal protein solubility was observed at pHs 4, 5 and 6, and the maximum was at pH 10. The emulsifying capacity, activity and emulsion stability, as well as foaming capacity and foam stability, were greatly affected by pH levels and salt concentrations. Lower values were observed at a slightly acidic pH and high salt concentration. The least gelation concentration of cowpea proteins was found to be 6% when the proteins were dissolved in 0.5 or 1.0 M NaCl. The total protein was highly viscous and dispersable with a water holding capacity of 2.20 ml H 2O/g protein, oil-holding capacity of 1.10 ml oil/g protein and bulk density of 0.82 g/ml, while dispensability was found to be 72.0%.

Influence of altered solvent environment on the functionality of pigeonpea (Cajanus cajan) and cowpea (Vigna unguiculata) protein isolates

Functional properties of pigeonpea and cowpea isolates were determined as a function of pH and NaCl concentrations. At low pH, nitrogen solubility decreased with increasing NaCl concentration whereas, at high pH, it increased. Addition of NaCl to the solvent medium resulted in a marginal improvement and a significant improvement, in the emulsifying activity and emulsion stability of pigeonpea isolate, respectively. The above treatment decreased these properties for the cowpea isolate. Varying both the pH and NaCl concentrations resulted in significant improvements in the emulsifying properties of the isolates relative to the control treatment. NaCl concentrations higher than 0.1 M significantly (P<0.05) increased the expansion of pigeon and cowpea protein–stabilized foams but reduced foam stability, and adjusting pH from 2 to 8 improved foam expansion but decreased foam stability. Varying both the pH and salt concentration had similar effects on the foaming properties of the isolates. The least gelation concentration (LGC) of the isolates decreased with increasing salt concentration. Adjusting the pH to values away from the apparent isoelectric point, elicited similar responses in LGC. In 0.5 M NaCl solution, adjusting the pH to 2, 6 and 8 resulted in significant reductions in LGC relative to the distilled water protein suspensions.

Effects of isolation technique and conditions on the extractability, physicochemical and functional properties of pigeonpea (Cajanus cajan) and cowpea (Vigna unguiculata) protein isolates. I. Physicochemical properties

Physicochemical properties of pigeonpea and cowpea protein isolates were determined as a function of extraction technique and pH of the extracting medium. Protein extractability by the isoelectric point precipitation (IP) technique was positively correlated within the pH of the NaOH solution used in the pH range 8.5–12.5. The micellization (MP) technique extracted significantly (P<0.05) less protein than the IP technique when extraction pH of the NaOH was 9.5 or higher, and 10.5 or higher from cowpea and pigeonpea, respectively. The subunit composition and electrical mobility of the isolates were not affected by extraction technique and pH conditions. However, it was observed that the IP isolate extracted at pH 12.5 had the lowest proportion of hydrophilic amino acids, suggesting that the pH of the extracting medium exerted a major influence on the hydrophilicity of the isolates. Pigeonpea MP isolate exhibited significantly (P<0.05) higher exposed hydrophobicity than the IP isolates except for those extracted at pH 9.5 and 10.5. However, the cowpea MP isolate exhibited significantly lower exposed hydrophobicity than the IP isolate extracted at pH 8.5 but this was higher than the rest of the IP isolates. For IP isolates, an inverse relationship was apparent between the extraction pH and hydrophobicity. The MP isolates from both legume seeds were significantly lighter in colour than the corresponding IP isolates and, for the latter, the lightness value (L) was inversely correlated with extraction pH. Differential scanning calorimetry showed that the MP isolates exhibited higher transition enthalpy (ΔH) than the IP. For the IP isolates, ΔH decreased with increasing extraction pH.

Effects of isolation technique and conditions on the extractability, physicochemical and functional properties of pigeonpea (Cajanus cajan) and cowpea (Vigna unguiculata) protein isolates. II. Functional properties

The functional properties of pigeonpea and cowpea protein isolates were determined as a function of extraction technique and pH conditions of the extraction medium. The isolates extracted using the micellization technique (MP) showed significantly (P<0.05) higher solubility than those extracted using the isoelectric point precipitation technique (IP) and, for the latter, solubility was negatively correlated with the extraction pH. The MP isolates exhibited significantly higher water absorption than the isoelectric isolates extracted at pH 8.5 but lower than the isolates extracted at pH 11.5 and 12.5. Cowpea MP exhibited higher oil absorption than the IP but pigeonpea MP was lower in this property than the IP extracted at pH 8.5 and higher than those extracted at pH 9.5–11.5. The MP isolates exhibited better emulsifying properties than the corresponding IP isolates and this property was drastically impaired at extraction pH 12.5. Pigeonpea MP exhibited lower foam expansion than the IP isolates except for the isolate extracted at pH 12.5, but was higher in foam stability. Cowpea MP showed higher foam expansion than the IP isolates which decreased with increasing extraction pH for the latter, but foam stability was only slightly affected. The MP isolates exhibited better gelation properties than the IP isolates extracted at pH above 9.5 and the least gelation concentration increased with increasing extraction pH. The solubility and exposed hydrophobicity best predicted the whipping properties, emulsion stability, and least gelation concentration of the isolates.

Cowpea (Vigna unguiculata) protein concentrate as replacement for fish meal in diets for tilapia (Oreochromis niloticus) fry

This study provides information on the dietary efficiency of protein concentrate from cowpea seed, as an ingredient for practical diets of tilapia fry. Five experimental diets were prepared in which animal protein (fish meal) was replaced by increasing amounts of plant protein, and fed to tilapia during a nine-week period to assess the effect on growth, survival and feed efficiency. The highest growth rate and feed utilization was observed with 20–30% replacement of fish meal with cowpea protein concentrate, while the protein efficiency was best at 40% inclusion level. No mortalities related to the dietary plant protein were recorded. It is concluded that cowpea seed protein concentrate is a potential ingredient for use in feeding tilapia fry, and its use is recommended at the inclusion levels described in this paper.

Calorimetric and rheological behavior of cowpea protein plus starch (cowpea and corn) gels

Thermal transition and gel formation in dispersions (10% solids) of cowpea protein, and in mixtures of the protein and corn starch and cowpea starch, were examined using a differential scanning calorimeter (DSC) and dynamic rheometry, respectively. In mixtures of the protein and corn starch, two DSC peaks due to starch gelatinization and protein denaturation were observed. A single peak observed during the heating of the proteinlcowpea starch mixtures appeared to be an overlap of the starch and protein endotherm peaks. With an increase in the proteinl starch ratio (R), the starch gelatinization onset and peak temperatures shifted to higher values, while endotherm enthalpy decreased proportionally. G of the protein/starch gels increased with aging time at 20°C and attained plateau levels that decreased with increase in proteinl starch ratio (R). For proteinl cowpea starch gels, G growth with time was adequately described by a first-order kinetic model. In the early stages of structure development, a faster increase in G for the proteinl cowpea starch mixture ensured higher levels of G after 1 h of aging compared with that for starch gel at the same starch concentration. In comparison to corn starch gels, there was no significant increase in G of gels of protein/corn starch.

The effect of nematicides on the nutritive value and functional properties of cowpea seeds ( Vigna unguiculata L. Walp)

The effect of nematicides on the nutritive value and functional properties of cowpea seeds ( Vigna unguiculata L. Walp) has been evaluated with respect to proximate chemical, amino-acid and mineral compositions and protein solubility properties. The cowpea seeds produced with the application of nematicides have crude protein contents in the range of 23.6–27.3%, which is slightly higher than the crude protein (23.3%) in the control sample. The amino-acid composition of the control sample and those produced by the application of nematicides were not significantly different. The amino-acid composition showed that cowpea seeds contained nutritionally useful quantities of essential amino-acids of between 38.9 and 44.1 g aminoacid/100 g protein. However, they are highly deficient in methionine. The predominant mineral was potassium which varied from 1171 to 2753 mg/100 g sample. It was found that the nematicides do not inhibit the uptake of minerals from the soil by the cowpea plants, since there were no marked differences in the mineral compositions of the samples. It was also found that the cowpea protein has minimum solubility at pH 4.0. The solubility curves of the samples and the control were found to be similar. The industrial application of cowpea protein is discussed.

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

AbstractThe 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.

Proximate and amino acid composition of cowpea ( Vigna unguiculata, walp) protein concentrate prepared by isoelectric point precipitation

A cowpea protein concentrate (CPC) was extracted from decoated seeds, by the method of isoelectric point precipitation using dilute hydrochloric acid. Proximate analysis revealed that the CPC had a protein content (N × 6·25) as high as 82%. Amino acid analysis indicated that the profile of amino acids in CPC was similar to that found in the raw material. The potential use of CPC to supplement foods that are low in protein is discussed.