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NIGERIAN ANNALS OF NATURAL SCIENCES, VOLUME 12 (1) December 2011 (pp 8 15) PRINTED IN NIGERIA

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THE EFFECT OF DIFFERENT PARTICLE SIZES OF AFRICAN YAMBEAN (SPHENOSTYLIS STENOCARPA) SEED FLOUR ON ITS FUNCTIONAL PROPERTIES

AZEKE, M. A., EKPO 1, K. E. AND IHIMIRE I. G. 1

Department of Biochemistry, Ambrose Alli University, P. M. B. 14, Ekpoma, Edo State

1Corresponding author; e-mail: [email protected]

ABSTRACT This study was conducted to determine the effect of particle sizes on some important functional properties of seed flour of the underutilized African yambean. The seeds were milled after which flour was separated into different particle sizes using meshes of different pore sizes (10, 20, 40, 60, 80 and 100 mesh respectively). The functional properties determined were ptotein solubility, bulk density, water and oil absorption capacities, emulsion properties (emulsion activity and stability) and foaming properties (foam capacity and stability). From the results obtained, it was found that the smaller particle size flour had the lower protein solubility, while the flour with larger particle size had the higher protein solubility (p


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particle size of the flour. Akara made fromcowpea flour in which 48% of the particledistribution was in the 400 mesh range was dryand dense, and exhibited a tough outer surface.Flour in which 42% of the particles were from the100 mesh screen produced a more acceptableproduct. Ngoddy et al . (1986) studied the effectsof successive milling of cowpea flour through a 1mm screen, and observed that if fine flours wereused to prepare akara or moin-moin, the foodswere less hydrated, denser, and exhibited anundesirable spongy texture as well as anunacceptable appearance. This work wasconducted to evaluate the effect of particle sizeson the functional properties of African Yambeanseed flour.

MATERIALS AND METHODS African yambean seeds ( Sphenostylis stenocarpa ), purchased from the Ekpoma mainmarket, were decorticated as described by Hunget al . (1991) and ground in a Thomas-Wileylaboratory mill (Model 4, Arthur H. Thomas Co.,Philadelphia, PA). The yambean seed flour wasthen passed through a series of sieves (20, 30,40, 60, 80, 100 mesh screens) to separate it intofractions of various particle size.

Functional propertiesProtein solubility: The pH-dependent protein

solubility was determined by the method Were et al . 1997. 25 mg of seed flour was blended with25 ml distilled water and the pH of solution wasadjusted to 6.0, 7.0 or 9.0 using 0.5 M NaOH or HCl. The solutions were mixed thoroughly andcentrifuged. The supernatant was filtered and

nitrogen was estimated by Kjeldahls method(Humphries, 1956). The soluble protein (%)profile was thus determined (nitrogen solubility X6.25)

Bulk DensityThe bulk density was determined according tothe method of Okaka and Potter (1977). A 50-gsample was put into a 100 mL graduatedcylinder. The cylinder was tapped about 30 timesuntil there was no further change in volume. Thebulk density was calculated as weight per unitvolume of the sample.

Water and Oil Absorption CapacitiesWater and oil absorption capacities (WAC andOAC) were determined in triplicate according tothe method Beuchat (1977). One gram of flour was mixed by shaking with 10 ml distilled water or refined vegetable oil for 30 s in centrifugetubes. The solution was allowed to stand at roomtemperature for 30 min, centrifuged (5000g, 30min) and volume of supernatant was determined.Water and oil absorption capacities wereexpressed as ml/g flour.

Emulsion PropertiesEmulsion Activity (EA) and Stability (ES) weredetermined in triplicate following the methods of Neto et al . (2001). Five millilitre of flour

dispersion in distilled water (10 mg/ml) washomogenized (1 min) with 5 ml refined vegetableoil. The emulsions were centrifuged (1100g, 5min) and the height of the emulsified layer andthe total contents in the tube was determined.The emulsifying activity was calculated:


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Emulsion stability was determined by heating the emulsion (80 oC, 30 min) before centrifuging (1100g, 5min)

Foaming propertiesFoaming Capacity and Stability of flour wasdetermined in triplicate according the methodoutlined by Seena and Sridhar (2005). Twograms of the flour was dispersed in 100 ml

distilled water and whipped vigorously for 2 minin a kitchen blender at speed 1. The volumes of foam were recorded before and after whippingand the percentage volume increase wascalculated:

Foam stability was determined as the volume of foam that remained after 8 h at room temperature

(27 2 o C) and expressed as the percentage of initial foam volume

RESULTS AND DISCUSSION

The protein solubility profile of yambean seedflour is as shown in table 1. Particle size had asignificant effect on protein solubility. It wasfound that the smaller the particle size, the lower the protein solubility. This is unexpected anddifficult to explain considering the fact that thesmaller particle size flour has larger surface area

of contact with the extracting solvent. This resultis contrary to the report of Kerr et al . (2000) whoworked on the effect of particle size on proteinsolubility of cowpea seed flour and found thatthere was an increase in solubility as particle sizedecreased. One possible reason for this contrastcould be that more of the protein is present in theflour with larger particle size

Emulsifying Activity (%) =Height of the emulsified layer

Height of the total contentX 100

Foam Capacity (%) =Volume after whipping Volume before whipping

Volume before whipping X 100

Emulsifying Stability (%) =Height of the emulsified layer after heating

Height of emulsified layer before heating X 100

Foam Stability (%) = Volume after 120 min

Initial foam volumeX 100


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Table 1: Protein Solubility Index (%) of yambean bean flour as affected by pH and particle size.

MeshSizes

Particlesize (mm)

Water (pH7.0)

pH 6.0 pH 7 pH 9

10 2.0 10.41 3.40a 6.02 0.01a 5.42 0.01a 5.82 0.01a

20 0.84 10.27 3.35a 6.63 0.01a 4.22 0.01b 5.71 0.09a

40 0.42 9.73 3.17ab 8.12 0.01b 2.12 0.01c 6.72 0.01b

60 0.297 9.51 3.10b 8.73 0.01b 1.82 0.01cd 6.91 0.01b

80 0.177 9.29 3.03bc 4.82 0.09cd 2.12 0.01c 6.93 0.01b

100 0.149 8.82 2.88c 4.51 0.09c 2.43 0.01c 9.02 0.09c

> 100 < 0.149 - 5.13 0.01d 1.52 0.09d 9.92 0.01c

Results are means of three independent determinations Standard Deviation; Values in a column withdifferent alphabets are significantly different

The effect of particle size on protein solubilitywas found to be pH dependent. While therewas a gradual reduction in PSI as particle sizedecreased at pH 7.0, the reverse was the caseat pH 9.0. At both acidic and alkaline pH, theflour recorded a higher PSI than at pH 7.0

regardless of particle size. Similar trend wasreported for Canavalia species (Seena andSridhar, 2005) bambarra ground nut andMucuna beans (Adebowale and Lawal, 2004).

At acidic and alkaline pH the protein gets netpositive and negative charge, respectively,which favours the repulsion of molecules andthereby increasing the solubility of proteins(Adebowale and Lawal, 2004). The proteinconcentrates of seeds that are soluble at pH 4 7 are normally suitable for use as additives inbe verages such as vegetable milk.

The effects of particle size on some functionalproperties of yambean seed flour are shown intable 2. With the exception of water absorptioncapacity, foam capacity and emulsion activity,most functional properties did not show anypattern of effect with particle size. The bulkdensities of yambean seed flour of different

particle sizes ranged from 0.57 0.66 g/ml.These results are similar to that reported for cowpea (0.6 g/ml) by Okaka and Porter (1979)and that reported for bambara groundnut (0.6 0.75 g/ml) by Onimawo et al . (1998) but higher than that reported for pigeon pea (0.27 g/ml) by

Onimawo and Akpojovwo (2006). Bulk densityis a reflection of the load the flour samples cancarry if allowed to rest directly on one another (Onimawo and Akpojovwo, 2006).

Water absorption capacity (WAC) of yambeanflour decreased with decrease in particle sizefrom 6.47 5.84 ml/g (table 2). The oilabsorption capacity (OAC) of the flour wasfound to be 6.02 6.22 ml/g. These values arehigh compared to earlier reports from other legumes. For example Onimawo and

Akpojovwo (2006) reported WAC and OAC of 4.47 and 2.50 respectively for pigeon pea.Seena and Sridhar (2005) reported WAC andOAC of 2.3 and 1.4 respectively for Canavaliaspecies. Khattab and Arntfield (2009) workingwith different legumes reported a range of 3.2 7.9 and 2.1 2.6 g/ml for WAC and OACrespectively

.


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Table 2: Some functional properties of yambean seed flour as affected by particle size

MeshSize

ParticleSize (mm)

Bulk density(g/ml)

Waterabsorption

(ml/g)

Oil absorption(ml/g)

Foam capacity(%)

Foam stability(%)

Emulsionactivity (%)

Emulsionstability (%)

10 2.0 0.57 0.004a 6.47 0.06a 6.22 0.13a 14.00 1.00a 5.67 1.20a 52.00 4.58a 8.63 0.11a

20 0.84 0.61 0.005a 6.57 0.02a 6.13 0.06a 15.67 0.88b 12.67 3.71b 57.00 5.13b 8.22 0.15a

40 0.42 0.66 0.006a 6.17 0.10ab 6.11 0.14a 30.67 0.88c 11.67 1.20b 65.67 4.06c 8.62 0.40a

60 0.297 0.57 0.004a 5.97 0.04b 6.25 0.11a 33.67 1.76c 13.67 1.76c 70.33 4.09d 8.85 0.06a

80 0.177 0.61 0.018a 5.95 0.11b 6.02 0.03a 37.67 0.88d 9.67 0.88d 77.33 3.76e 8.70 0.06a

100 0.149 0.60 0.005a 5.86 0.12b 6.20 0.03a 40.00 1.16e 10.33 1.45d 81.67 3.84f 8.77 0.05a

> 100 - 0.58 0.016a 5.84 0.04b 6.18 0.13a 40.00 0.58e 14.00 3.06e 86.67 4.06g 8.92 0.02a

Results are means of three independent determinations Standard Deviation; Values in a column with different alphabets are significantly different


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The differences in the WAC and OAC may bedue to the variation in the presence of non-polar side chains, which bind the hydrocarbon sidechain of oil. The enhanced ability of the meal toabsorb and retain water and oil may help toimprove binding of the structure, enhance flavor retention, improve mouth feel and reducemoisture and fat losses of food products(Sreerama et al ., 2008). WAC enabled bakers toadd more water to doughs so as to improvehandling characteristics and maintain freshnessin bread. Oil absorption capacity is desired inground meat formulations, flavour retention,improvement of palatability, extension of shelf lifeof bakery or meat products, meat replaces andextenders, doughnuts, pancake, baked goodsand soups.

The foaming capacities of flour were found toincrease from 14 40 % with decrease in particlesize. Owing to a large increase in the surfacearea in the liquid/air interphase, proteinsdenature and aggregate during whipping. This isimportant for flour used in many leavening foodproducts such as baked goods, cakes andbiscuits (Sreerama et al ., 2008). There are widevariations in the foaming capacities reported for different flours. While Onimawo and Akpojovwo(2006) reported 600 % foam capacity for pigeonpea flour, Khattab and Arntfield (2009) reported

17 56 % for different legume varieties. Thefoam from the yambean flour of smaller particleswas found to be more stable than that from flour of larger particle.

Emulsifying activity (EA) increased from 52 to 86% with decrease in particle size while emulsionstability (ES) was not dependent on particle size(table 2). These values agree with previousreports for other legumes (Seena and Sridhar,2005; Onimawo and Akpojovwo, 2006; Khattaband Arntfield, 2009). EA and ES are important

functional properties of food proteins. They varywith the type of protein, its concentration, pH,ionic strength, and viscosity of the system. Manychemical and physical factors are involved in theformation, stability, and textural properties of protein fat water emulsions (Khattab and

Arntfield, 2009). Superior emulsifying propertiesare desired to make milk like beverages andmeat analogues.

CONCLUSION

Milling and subsequent sieving of Africanyambean seeds into flours of different particlesizes had various effects on the functionalproperties of yambean seed flour. When high

water absorption is desired, yambean flour of larger particle size would be appropriate whilethe flour of smaller particle size would beappropriate in food formulations where higher foam capacity and emulsion activity are desired.Therefore, the present study shows the potentialof yambean flour for incorporation into newvalue-added products. The detailed toxicologicalproperties of this meal still remain to beevaluated and further research is needed on thereaction of protein of yambean seeds with other constituents of food products such as starch and

lipids

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