P h t F oo& for Human Nutrition 58: 1-10.2003. 8 2004 Kluwer Academic Publishers. Printed in the Netherlands. Effect of processing method on the quality of cowpea (Vigna unguiculata) flour for akara preparation A.A. OLOPADE', J.O. AKINGBALA~*A*,. O. OGUNTUNDE~a nd K.O. F' A LADE^ Federal Institute of Industrial ResegM Oshaii, Nigeria; 2~hemicaEl ngineering Department, University of The West Indies St. Augustine, Trinidad & Tobago; 3L.ate, of Food Technology Department, University of Ibadan, Ibadan, Nigeria; 4 ~ o o dTe chnology Department, University of Ibadan, Ibadan, Nigeria (*authorf or correspondence; e-mail: jakingba@ uwi. n) Received 12 December 2000, accepted in revised form 21 August 2001 Abstract. Cowpeas were prepared into flour by wet dehulling, wet milling into paste and drying; wet dehulling, drying and milling; and wet dehulling, wet milling and foam mat drying. Proximate chemical composition and functional properties (water and fat absorption capacities, foaming capacity, foam stability, bulk density, gelation capacity and emulsification capacity) of flours and of paste prepared by wet dehulling, wet milling and no drying, were determined. Akara from fresh paste and pastes reconstituted from flours was organoleptically evaluated. Reconstituted paste of flour from ground dry cotyledons produced the best quality akara, compared with the control. Akara from reconstituted foam mat dried and ground dry paste flours were less acceptable. Key words: Akara, Cowpea flour, Processing quality, Sensory quality Introduction Cowpeas are the second important source of protein, next to meat in Nigeria [I, 21. They are cooked plain, mixed-with other foods or processed into for- mulated recipes such as moinmoira, a steamed paste, or akara, a deep fried paste product. These paste produc~moinmoina nd akara), ark still prepared using the traditional methods. The ~oductiono f fresh paste from cowpeas is a major constraint in cowpea utilization and considerable efforts have been made to produce ready-to-use cowpea flours which can be rehyderated to paste, thus reducing the time and labor of paste production [3-61. Previous research has shown that cowpea flour can be made into acceptable moinmoin [I]. However, the preparation of akara from reconstituted flour has not been as successful, due mainly to rehydration problems of the flours [1,2,4]. The objective of this work was to evaluate three processes viz. dry milling of coty- UNIVERSITY OF IBADAN LIBRARY ledons, dry milling of paste and foam mat drying of paste in the production of flour for akara preparation. Materials and methods White (Sokoto) and brown (Drum) varieties of cowpeas were purchased from Bodija market Ibadan, Nigeria. Refined vegetable oil and refined table salt were purchased from the samdmarket. Sodium palmitate (Lever Brothers Nigeria Ltd.) was used to stabilize paste foam for extrusion and drying. Preparation of cowpeajfour Cowpea flours were prepared as presented in Figure 1. The cowpeas (200 g) were steeped in 300 ml water for 10 min to soften the testa, which was re- moved manually and washed off. The cleaned cotyledons were converted into flour following the different processes (Figure 1). The dry cotyledons of flour A and the dry paste of flour B were ground using a hammer mill to pass through a screen of 0.8 mm opening. The paste of flour C, after mixing, was extruded on wire gauze, using a caterer's syringe, and dried at 70 OC for 2 h. The resultant dry foams were milled using a hammer mill to pass through 0.8 rnrn screen. Chemical analyses Proximate coinpositions of cowpeas and flours'(moisture, crude fiber, fat, ash and crude protein [Nx 6.25]), were determined by AOAC methods [7]. Carbohydrate content was determined by difference. Functional properties of JEours Foaming capacity and foam stability were determined as described by Sathe et al. [8]; water and fat absorptio~ca pacities were determined as described by Sosulski [19] and Sosulski et al. t10], respectively. Emulsion capacity was determined according to the method of Yasumatsu et al. [I I] and gelation capacity by the method of Coffman & Garcia [12]. Bulk density of the flour was determined according to the method described by Okaka & Potter [13]. UNIVERSITY OF IBADAN LIBRARY STEEP I A w J L L I SOAKING DRYING (W°C. 24h) I DECANT COTYLEDON WET MILLING SEE REDUCTION (0.8mm SCREEN) + 200ml H20 . PASTE WET MILLING PASTE A PASTE *DRY PASTE I MIXING I EXTRUSION SlZE REDUCTION @S.CRhEEN ) +DRYING (70°C. 24h) m', DRY PASTE FLOUR I SlZE REDUCTION (0.8mm SCREEN) Figure 1. Production of cowpea flow from dry milled cotyledon (A), wet milled cotyledon (B) and foam-mat dried paste (C). UNIVERSITY OF IBADAN LIBRARY Prepamtion of akara Akara was made from freshly prepared paste and paste from reconstituted flours. The freshly prepared paste was made by soaking 200 g cowpea in 300 ml water for 10 min to soften the testa for manual removal. The clean cotyledons were steeped in 300 ml water for 30 min; the water was drained, and the softened cotyledons blended in a Kenwood food mixer at speed 6 for 4 min.into a paste. Seasonings (20 g chopped pepper, 20 g onions and 10 g salt) were mixed in the paste.3gblespoon (15 ml) portions of the mixture were deep fried in vegetable oil at 190 OC for 4 min on each side. The akara was removed from the oil, drained of excess oil and stored in an incubator at 30 "C for sensory evaluation. Flours A, B, C (200 g), prepared as described in Figure 1, were each rehydrated with 300 ml water. The mixture was stirred manually using a plastic spatula, then whipped in a Kenwood food mixer at setting 6 for 4 rnin. Seasonings were added and the mixture fried into akara using the same procedure described for the paste. The akaras produced were stored at 30 "C for sensory evaluation. Sensory evaluation The akara samples were coded and presented to a ten person panel of judges who were familiar with the product for sensory evaluation. The ten person trained panel scored the color, flavor, texture and overall acceptability of the akara using a nine point scale, where 9 indicated 'liked extremely' and 1, 'dislike extremely'. Statistical analysis Means were tested for differences using Analysis of Variarice, and separated by the Duncan's Multiple Range Test [14] when a significant F value was noted. Significance was accepted at p 5 0.05. Results and discussion Proximate chemical composition The proximate composition of the flours was essentially similar (Table 1) and within the range generally reported [4,5, 151 for cowpeas (Table 1). Protein contents of the cowpeas were not different (p < 0.05). The fat content of cowpeas was small and not of much nutritional significance. The difference UNIVERSITY OF IBADAN LIBRARY Table I. ~ e a n lch?e~mi cal compositions of cowpea flour samples (dry weight basis) Sample Moisture (%) Protein (%) Fat (%) Crude fiber (%) Ash (%) Carbohydrate (%) Whole bean flour (white) 10.4a 23 .9d 1 . 7 ~ 2.6P 3.33a 68.Sa Whole bean flour (brown) 10.Sa 25.v 2.W 2.2gb Wet-dehulled and wet-gilled (white) flour (WWDW) 8SCd 25.F 1.82~ 2.08C 3 2cb c 67.2g6bC6 Wet-dehulled and wet^^ (brown) flour (BWDW) 8.9bC 25.2& 1.46' 1.92~ 3-16' 68.3ab Wet-dehulled and dry-milled (white) flour (WWDD) 8.9bC 25.9a 1.76~ 1.83d 3.14' 67.4ef Wetdehulled and dry-milled (brown) flour (BWDD) 8.4d 25.5* 2 . e 1.84~ 3.3Sa 66.9f Foam-mat dried (white) flour (WFD) 7.tie 25.ga 1.84~ 1.5@ 3.3P 67.6* Foam-mat dried (brown) flour (BFD) 7.7e 25.7a 1.55' 1.82~ 3.26b 6 7 . 7 ~ ~ Means of 3 replicates. Means with the same superscripts in a column are not different (p < 0.05). UNIVERSITY OF IBADAN LIBRARY in the crude fiber contents of the whole flour and the dehulled samples was due to the removal of the testa in the dehulled samples. The wet dehulled, dry milled flour had a greater ash content due to the greater amounts of minerals lost during steeping of the cotyledons for softening of the wet milled samples.The greater ash content of the foam mat dried sample was probably a function of the metal mesh on which the sample was dried. Foaming capacity Foaming capacity of the flour ranged from 17.0 in the foam mat dried flour to 41.0 in the wet dehulled dry milled flour (Table 2). Incorporation of air into the paste is essential for good crumb structure of akara [I]. Henshaw & Lawal [16] reported that processing involving soaking appears to lower gelation and foaming capacities of cowpea flour, which is consistent with the observation in this work. Water and fat absorption capacities Water absorption capacity of the flours ranged from 97% in the wet dehulled, dry milled flour to 151 % in the foam mat dried flour sample. The fat absorp- tion capacity of the foam mat dried flour was greater than that of the wet dehulled, wet milled flour, which was similar to the wet dehulled dry milled flour ( p -c 0.05). The high water and fat absorption capacities of the foam mat dried flour may have been due to the emulsifying property of monoglycerol palmitate used as a foam stabilizer, while the greater water and fat absorptions of the whole grain flour may have been due to the greater fiber content of this flour (Table 1). Henshaw & Lawal[16] attributed the increased fat absorption capacity of cowpea flour to the heat denaturation of protein, which could have occurred in the foam mat dried sample, which was dried at 70 "C. Gelation capacity The least gelation capacities of the flours ranged from 17 to 19% (Table 2). This was similar to 18% reported for cowpea flour by Abbey & Ibeh [17]. Sathe et al. [8] associated the &ling properties of legumes to the amounts of carbohydrates, protein and kidids present in the flours. Interactions among these components may have a significant role in the functional properties of the flours. The similarity in the gelation property of the flours may have been due to the similarity in their proximate chemical compositions (Table 1). UNIVERSITY OF IBADAN LIBRARY Tabb 2. ~ e a n lfu. n~ct ional properties of cowpea flours Flour sample FC (%) WAC (%) FAC (%) GC (%) EC (%) Bulk density (glml) Whole bean (white) ND 1 0 8 ~ 1 0 4 ~ ~ N D ND 0.6gbt Whole b a n (brown) ND 1 2 2 ~ 1 0 7 ~ ~ ND ND 0.67* ~d&adnd dwet- milled (white) 32Sb 1 2 7 ~ 8gb 19a 48.15~ 0.80a Wet-dehulled and wet-milled (brown) 43.Sa lood 95b 1 7 ~ 53.298 0.71b Wet-dehulled and dry-milled (white) 34.0~ 1 1 6 ~ ~ ~6~ 18& 54,8a 0.81a Wetdehulled and dry-milled (brown) 41.08 97d 92b 1 7 ~ 54.ga 0.69~ Foam-mat dried (white) 16.5' 150a 117a 18& 48.6b 0.59' Foam-mat dried (brown) 17.V 151a llSa lga 31.5' 0.57' Means of 3 replicates. Means in the same column with the same superscripts are not different p < 0.05. ND - Not determined; FC = foaming capacity; WAC = water absorption capacity; EC = emulsion capacity; FAC = fat absorption capacity; GC = gelation capacity. UNIVERSITY OF IBA AN LIBRARY + W D W 85 1 tB WDW -9-BWDD LE Figurn 2. Stability of m p e a flour foams. WWDD = 3-;W WDW = -C, BWDW = -A-; BWDD=-O-;WFD=+,BFD=+-. Emuls~caionc apacity The emulsification capacity of the foam mat dried flour was lower than those of wet dehulled, wet milled and wet dehulled, dry milled flours, which were similar (Table 2). Marayana & Rao [18] reported that heat reduced the emul- sification properties of winged bean. Bulk density Foam mat dried cowpea flour had the least bulk density due to the air in- corporated during foam formation. The greater porosity of the particles of this flour may have resulted in the greater water and fat absorption capacities observed. The objective of foam mat drying of the paste in this experiment was to improve the rehydration of the flour; thus, possibly through this, the foaming property, may have bee$negated by the heat (70 9C) used in drying the foam. The bulk density of thplwet dehulled, wet milled flour (0.81 glrnl), was greater than that of the wet &hulled, dry milled sample (0.69 glml), but the wet milled flour had greater water absorption capacity probably because the particles are aggregates of smaller particles. UNIVERSITY OF IBADAN LIBRARY Table 3. ~ e a n lse. n~so ry evaluation scored of akara Akara sample Color Flavor Texture Overall acceptability Cowpea paste (white) 6.6C 5.4b 6.1b 6.4C Cowpea paste (brown) 7.7ab 7.ga 8.0a 8.1a Wetdehulled and wet-milled (white) flour 8 . 0 ~ 7~.3 a 8.1a 7.8& Wetdehulled and wet-milled (brown) flour 8.4a 7.6a 7.8a 7.7ab Wet-dehulled and dry-milled W e ) fl our 4.3d 5 . 0 ~ 3.P 4.3d Wet-dehulled and dry-milled (brown) flour 7.0bC 7.1a 7.6a 7 . 0 ~ Foam-mat dried paste flour (white) 4.4d 4.7b 4.3= 4.3d Foam-mat dried paste flour (brown) 4.1d 3.5' 3.2' 3.Se Means of 3 replicates. Means with the same superscripts are not different p < 0.05. 1 = Dislike extremely; 9 = Like extremely. F m sta bility The foam mat dried flour produced the most stable foam (Figure 2). Foam from the wet dehulled, dry milled flour was greater up to 1 h when the foam is crucial in the production of akara. Generally during the production of akara, the paste is whipped to incorporate air just before frying. Thus, it appears that the foaming capacity of the paste would be a better index of akara texture than foam stability. Sensory evaluation The flavor, texture and overall acceptability scores of akara ma& from wet dehulled, dry milled and wet dehuhed, wet milled flours were rated similarly to those of akara made from hibas te (control). Akara made from the wet dehulled, dry milled flour had bettkr color ratings than akara made from the paste and from wet dehulled, wet milled flours (Table 3). Akara made from the foam mat dried flour had poor flavor, texture, color and overall acceptabil- ity. The foam mat dried flour had a grey color imparted by the foam stabilizing agent, which the panelists did not like. The poor texture rating of akara made from the foam mat dried flour was due to the dense, oily crumb, caused by the high water, high fat, and low foaming capacity of the flour. UNIVERSITY OF IBADAN LIBRARY Dovlo FE, W~lliamsC E, Zoaka L (1976) Cowpeas: Home Prepamtion and Use in West Africa. Ottawa, Canada: International Development Research Centre, pp 20-28. Williams CE (1980)C owpea flour Innovation in a Traditional Dish and Its Acceptability in Selected Areas of Oyo Division. PhD dissertation, University of Ibadan, Nigeria. MacWatters KH, Brentley BB (1982) Characteristic of akara prepared from cowpea paste and meal. J Food Tech 36: 66-69. MacWatters KH (1983) Compositional, physical and sensory characteristics of akara processed from cowpea p a s t e s Nigerian cowpea flour. Cereal Chem 60: 333-336. 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Whipping and emulsifying properties of soybean products. J Agric Biol Chem 36: 719-727. C o hC W,G arcia W (1977) Functional properties of amino acid content of protein isolate from mung bean flour. J Food Tech 12: 473. Okaka JC, Potter NN (1979) Physicochemical and functional properties of wwpea products processed to reduce beany flavour. J Food Sci 44: 1235-1238. Duncan DB (1955) Multiple range and multiple F-tests. Biometries 1 1 : 1 4 2 . Elias U;, Colindres R Bressani R (1%4) The nutritive values of eight varieties of cowpea (VigM sinensis). J Food Sci 29: 118-122. Henshaw FO, Lawal SA (1993) Effect of processing methods on the functional properties of cowpea flour. J Trp Sci 33: 377-385. Abbey BW, Ibeh GO (1988) Functional properties of raw and heat processed cowpea (VigM wrguiculafa)f lour. J Food Sci 49: 1534. Marayana N, Rao N (1982)F unctional properties of raw and heat processed winged bean (Phosphocarpus tetragonolobus) floqt. J Food Sci 49: 1554. 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