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Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Acknowledgments
  9. References

Drying effect on functional properties of two plantain and cowpea varieties and suitability of their flour blends in extruded snacks was determined. The functional and rheological behaviors of (plantain : cowpea): 90:10, 80:20, 70:30, 60:40 and 50:50 blends were evaluated. The extrusion product melt temperatures were set to 90C for half-products, and 140C for fully expanded snack products. The differences in rheological properties depended on plantain and cowpea varieties. The peak viscosity for plantain flour decreased from 595.5 to 281.5 BU when blended with cowpea flour (75:25%); cowpea peak viscosities were 6 BU (Nhyira means blessings) and 13 BU (Asetenapa means good living). Paste value decreased as amount of cowpea flour blended with plantain flour increased. Pasting properties of the extrusion blends were significantly different (P < 0.05) depending on the blend ratios. The level of cowpea added affected the paste, hardness properties and the expansion height of the extruded products.

Practical Application

The purpose of this work was to develop a long-term storage of indigenous local raw materials, to reduce postharvest losses and add economic value. The cowpea was used as a protein source to fortify the high carbohydrate plantains, with the aim of developing local snack industries in Ghana and other sub-Saharan Africa countries. Perishable raw materials will be processed into shelf-stable flours and extruded snacks, enhancing food security.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Acknowledgments
  9. References

Plantain (Musa paradisiacal normalis) and cooking bananas (Musa acuminata) are very similar to unripe dessert bananas (M. Cavendish AAA) in exterior appearance, although often larger in size; the characteristic difference with plantains is that their flesh is starchy rather than sugary and sweet. Plantains are used ripe or unripe and require cooking (Happi Emaga et al. 2007). Plantains are among the green vegetables with the richest iron and other nutrient contents (Aremu and Udoessien 1990). Plantains are however highly perishable and subjected to fast deterioration because of their moisture content and high metabolic activity even after harvest (Demirel and Turhan 2003). Traditionally, air-drying alone or together with sun-drying is used for preserving unripe plantain in tropical countries of Africa. Drying adds value to plantain because the milled flour can be stored for later use. A modern process involves crushing plantain after mashing and drying the pulp in drum or hot air or spray dryers. The dried product is pulverized and sifted through a 100-mesh sieve to produce a free-flowing powder that is stable for at least 1 year after packaging. The plantain powders are used in bakery and confectionery products for the functional benefits of treating intestinal disorders in infants (Adeniji et al. 2006).

Cowpeas (Vigna unguiculata) are the most popular grain legumes in West Africa. Unlike other legumes, which are oil-protein seeds, cowpeas are starch-protein seeds, and therefore offer a wide possibility of utilization than other legumes. Cowpeas are a major source of vegetable proteins containing 20–23% crude protein and 50–67% starch (Quin 1997). Cowpeas are an excellent source of niacin, thiamine, riboflavin and other water-soluble vitamins, and essential minerals such as calcium, magnesium, potassium and phosphorus (Phillips and McWatters 1991). The important role grain legumes play in the diet of billions of people from many protein-deficient countries has prompted research increasing their utilization (Sefa-Dedeh and Yiadom-Farkye 1988).

One area of legume protein research is converting them into products with desirable functionality using processes like extrusion to make products acceptable to consumers. Extrusion cooking is efficient in combining starch and protein materials into viscous, plastic-like dough and expanded snacks (Ganjyal and Hanna 2002). Although grains and vegetable proteins such as soy are dominant extruded products, different proteins such as whey proteins are now being extruded into various foods. The incorporation of cheese whey into extruded products is a relatively new area of extrusion research (Onwulata et al. 1998). In general, the incorporation of whey into starch-based snacks affected the physical properties of extrudates; the quality of the extrudates depending on the processing conditions and ingredient characteristics (Onwulata et al. 2001).

The addition of proteins to starches increases sites for cross-linking and affects textural quality. Ideally, proteins are denatured, realigned and complexed to form expanded matrices; however, the degree of expansion depends on the concentration of protein (Aboagye and Stanley 1987).

The development of low-cost, energy and nutrient-rich infant foods is a constant challenge in developing countries with encouraging successes since the early 1980s. The use was for mitigating malnutrition problems (Harper 1989). However, these early applications research did not include resources local to developing countries such as root tubers, bananas and plantains.

Extending extrusion technology to non-grain starch staples like plantain and cowpeas would help broaden the protein sources. Therefore, the present work was aimed at using unripe plantain flours from two varieties of plantains, Apantu (False horn) and Apem (French horn), and two varieties of cowpeas, CSIR-Asetenapa and CSIR-Nhyira, developed by the Council for Scientific and Industrial Research (CSIR)-Crops Research Institute, Ghana. The proximate composition, functional and rheological characteristics of the prepared flours were evaluated. The suitability of blends of a commercial plantain flour, white bean flour and oat fiber for extruded snacks was determined.

Materials and Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Acknowledgments
  9. References

The raw materials used were two varieties of unripe (green) plantains (M. paradisiacal normalis) named Apantu (False horn) and Apem (French horn), obtained from a local market (Agbogbloshie) in Accra, Ghana. The plantain fruits chosen were unripe mature stage (grade 1 maturity) of acceptable appearance for consumption as described by Dadzie and Orchard (1997). Two varieties of cowpeas from CSIR, CSIR-Asetenapa (Asetenapa) and CSIR-Nhyira (Nhyira), were obtained from the CSIR-Crops Research Institute, Fumesua, Kumasi, Ghana.

The plantain fruits were cleaned and peeled with a stainless steel knife, and then rinsed with 150 mL potable water. A total of 400 kg of plantains were sliced into 12.5–25 mm thickness. Two hundred kilograms (200 kg) was mechanically sliced with a slicer (Fold-up electric Food Slicer model CFE 1954, Philips, Atlantis, FL) into 2–5 mm thick for the production of flours. The sliced plantain chips were dried in a mechanical dryer (Apex Royce Ross, London, UK) at 60C for 7 h. The dried chips were milled with a laboratory Hammer mill (Milomat Laboratory Mill, Pfeuffer, Germany) and sifted with a 250-μ sieve. The flour obtained was stored at 27 ± 3C and relative humidity of 79 ± 2% in a hermetically sealed glass container until further analysis (Barbosa-Canovas and Vega-Mercado 1996; Singh and Heldman 2001). Cowpeas were processed into flour by first soaking for 36 h, and then dehulling by rubbing with the bare hands in the soaked water. The cotyledons were washed, blanched in water for 6 min at 100C, dried at 60C for 8 h in mechanical dryer (Apex Royce Rolls, London, UK), milled with a laboratory Hammer mill and sifted in a 250-μ sieve. The cowpea flours were packaged in airtight polyethylene bags and stored at 27 ± 3C for further analysis.

Proximate Composition and Functional Properties Measurement

The proximate composition and chemical characteristics of the plantain and cowpeas measured were moisture content, protein (N × 6.25), crude fiber, fat, ash from the fresh edible portions of the plantains and the cowpea varieties following AOAC (2000) methods. Total crude fiber was determined using the methodology described by Kirk and Sawyerr (1990). The protein, fat and crude fiber content of the blends was determined according to standard methods (AOAC 2000). Caloric content (energy) was determined using the Atwater factor (Kirk and Sawyerr 1990), and total carbohydrate was determined by difference. Water activity was measured in triplicate with a Rotronic Hygrolab 2 m (Rotronic, Huntington, NY).

In functional properties, water absorption index (WAI) was measured using the methods developed by Jin et al. (1995) with minor modifications. Plantain flours (Apantu and Apem) and cowpea flours (Asetenapa and Nhyira), each of 5 g were passed through a 250-mesh screen and combined with 30 mL of distilled water in a tarred centrifuge tube. The mixture was sealed, mixed and allowed to hydrate for 10 min. The sealed tube was inverted two times at both 5- and 10-min intervals to ensure proper mixing. After 10 min, specimens were centrifuged for 15 min at 3,000 rpm using a Sorvall RC-5B fixed angle rotor (DuPont Instruments, Wilmington, DE). The supernatant was decanted into a preweighed aluminum dish. The tube was inverted for 5 min over the dish to drain the residual moisture; the centrifuge tubes were reweighed to determine the weight of the sediment. The dish with the decantate was dried overnight at 70C in a forced-air hotbox oven (BS Gallenkamp, London, England). WAI was calculated by dividing the sediment weight by the dry sample weight while water solubility index was calculated by dividing the dried supernatant weight by the dry sample weight (Jin et al. 1995).

Pre-Extrusion Analysis

The rapid visco analyzer (RVA) (Newport Scientific, Warriewood, Australia) was used to characterize the rheological properties of the plantain and cowpea flour blends before extrusion processing. A 2.5-g specimen of flour blend was adjusted to 14% moisture basis before adding to 25 g distilled water. The time-temperature profile used was the RVA general pastry method #1 (ICC Standard Method #162) and included initially holding the sample at 50C for 4 min with the paddles rotating at 160 rpm, to investigate the cold-swelling starch peak. The specimen was heated to 95C at a constant rate of 12C/min, held at that temperature for 3 min and then cooled to 50C in 4 min at the same rate. Stimulation of extrusion processing was conducted at the United States Department of Agriculture-Agricultural Research Service–Eastern Regional Research Center, USA, using 100 kg of commercially processed plantain flour obtained from Raymond-Hadley Corp. (Spencer, NY 14883), white bean flour (Bob's Red Mill Natural Foods, Inc., Milwaukie, OR) and oat fiber from Sun Opta Ingredient Group (Chelmsford, MA). The blends were formulated as follows: (1) 100% plantain; (2) 100% white bean flour; (3) 75% plantain and 25% white bean flour; (4) 75% plantain and 25% oat fiber; and (5) 50% plantain, 25% white bean flour and 25% oat fiber.

Extrusion Processing

Extrusion processing of half-products was conducted using 10 kg each of the five individual blends with the following extrusion parameters: A ZSK-30 twin-screw extruder (Krupp Werner Pfleiderer Co., Ramsey, NJ) with a smooth barrel, and nine heating zones. The effective product forming zones 6, 7, 8 and 9 temperatures were set to 90, 90, 75 and 60C, respectively; zones 1 and 2 were set to 35C, zone 3 to 45C, zone 4 to 50C and zone 5 to 80C. Product melt temperature was monitored behind the die. The die plate was fitted with a single slit die of 3 × 30 mm. The screw elements were selected to provide low shear at 300 rpm as published earlier (Onwulata et al. 1998). Feed was conveyed into the extruder with a series 6,300 digital feeder, type T-35 twin-screw volumetric feeder (K-tron Corp., Pitman, NJ). The feed screw speed was set at 600 rpm, corresponding to a rate of 6.3 kg/h for all products. Water was added into the extruder at the rate of 1.0 L/h with an electromagnetic dosing pump (Milton Roy, Acton, MA). Half-products were collected and immediately cut into 30 mm × 25 mm pieces and then frozen for future processing.

The half-products were thawed at room temperature either baked or fried to complete cooking. One portion of extruded half-products was baked at 176C for 20 min (Despatch Industrial Oven, Minneapolis, MN) and the other specimens were fried in 0.5 L vegetable oil at 190C for 3 min using DeLonghi Fryer Bedford Heights, OH. The samples were cooled, packaged in air-tight plastic containers and stored at 20C for further analysis.

The extrusion of expanded product was similar except for the change in melt temperatures in zones 6, 7, 8 and 9: 90, 110, 120 and 140C, respectively. Zones 1–3 were set to 35C, 4 to 50C and 5 to 75C. Product melt temperature was monitored behind the die. The die plate was fitted with two round 5-mm die opening. The screw profile was the same (Onwulata et al. 1998). Expanded products were collected and dried at 60C for 1 h in an industrial dryer (Corbett Industries, Waldwick, NJ) and stored in plastic bags at 20C until analyzed.

Texture Analysis of Extruded Snacks

The texture analysis of the extruded, baked and fried half-products snack was determined using a TA-XT2 Texture Analyzer (Stable Micro Systems, Surrey, England) outfitted with a 500 N load cell, running at a cross-head speed of 2.0 mm/s and fitted with a 6.35-mm spherical probe. Hardness (N), and maximum compression force, required to puncture the samples was measured. Because the samples varied in height, the force values were normalized using the height (mm) as measured for each piece analyzed. Data reported are averages of 10 specimens. The normalized hardness value was obtained by dividing the hardness value (N) of the extrudate by its height (mm).

Statistical Analysis

The data generated for the studies were analyzed using Statistical Analysis Systems version 9.1 (SAS Developer, San Diego, CA) software package. Significance of treatment means was tested at 5% probability level using Duncan's new multiple range test.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Acknowledgments
  9. References

The proximate composition of plantain fruits and cowpea seeds is presented in Table 1. The proximate compositions of the plantain and cowpea flours are shown in Table 2.

Table 1. Proximate Composition of Plantain and Cowpea Seeds
Product Moisture (g/100 g)Ash (g/100 g)Fat (g/100 g)Protein (g/100 g)Carbohydrate (g/100 g)Crude fiber (g/100 g)Energy (kcal/100 g)
  1. Pooled standard deviation for mean testing: moisture (2.75), ash (0.007), fat (0.013), protein (0.017), crude fiber (0.019).

Plantain Apantu 57.21.00.021.338.00.6157.3
Apem 57.90.90.041.539.70.2165.0
Cowpea Nhyira 13.73.21.931.158.63.7341.9
Asetenapa 13.82.71.928.360.43.9343.5
Table 2. Proximate Composition and Water Activity of Plantain and Cowpea Flour
Flours Moisture (g/100 g)Ash (g/100 g)Fat (g/100 g)Protein (g/100 g)Carbohydrate (g/100 g)Crude fiber (g/100 g)Energy (kcal/100 g)Water activity
  1. Pooled standard deviation for mean testing: moisture (0.021), ash (0.0005), fat (0.073), protein (0.021), crude fiber (0).

Plantain Apantu 8.22.11.71.785.60.6364.80.49
Apem 8.71.62.12.684.40.6366.80.56
Cowpea Nhyira 6.11.34.022.765.20.7387.80.50
Asetenapa 7.81.603.523.462.31.4374.50.44

The Apantu flour had high Brabender values for all parameters measured such as viscosity at 95 and 50C compared with the Apem plantain flour (Table 3). The Asetenapa cowpea flours were higher in pasting parameters compared with the Nhyira cowpea flour (Table 3).

Table 3. Brabender Analysis of Plantain and Cowpea Flour
Flours Pasting temperature (C)Peak viscosity (BU)Viscosity at 95C (BU)Viscosity after 15 min at 95C (BU)Viscosity at 50C (BU)Pasting stability at 50C (BU)Breakdown (BU)Setback (BU)
  1. Values in the same column with different letters are significantly different at P < 0.05.

Plantain Apantu 73.6b 629.0d 607.5c 515.0b 776.0c 750.0115.0d 252.0c
Apem 74.9c 595.5c 591.0b 509.0b 764.5c 747.086.5c 252.5b
Cowpea Nhyira 50.2a 6.0a 2.5a 6.0a 19.5a 18.00.5a 13.5a
Asetenapa 94.3d 13.0b 6.5a 12.5a 35.0b 32.50.5a 22.5a

The summary of the Brabender amylograph analyses of the formulated blends of plantain and cowpea flour is presented in Table 4. In all cases, the 100% plantain without cowpea had high peak viscosity values, viscosity at 95C and setback at 50C. The 50/50% blends of plantains and cowpea had the lowest values for peak viscosity, viscosity at 95C and setback at 50C. The pasting parameters decreased as the amount of cowpea added to the plantain increased. The protein, fat and fiber content of the Apem and Nhyira plantain blends increased as the proportion of cowpea added increased. The same trend applied for other combinations of the plantains Apantu and Apem with cowpeas, Nhyira and Asetenapa.

Table 4. Brabender Analyses of Plantain and Cowpea Flour Blends
Apantu plantainCowpea Nhyira cowpeaSetback Asetenapa cowpeaSetback
Pasting temperature (°C)Peak viscosity (BU)Viscosity at 95C (BU)Pasting temperature (°C)Peak viscosity (BU)Viscosity at 95C (BU)
  1. Values in the same column with different letters are significantly different at P < 0.05. Mean of duplicates: 100 AP + 0 − 100% Apem flour – protein 3.20 g/100 g, fat 0.30 g/100 g, crude fiber 0.20 g/100 g; 90:10APN − 90% Apem + 10% Nhyira – protein 5.50 g/100 g, fat 0.60 g/100 g, crude fiber 0.30 g/100 g; 80:20APN − 80% Apem + 20% Nhyira – protein 7.80 g/100 g, fat 0.70 g/100 g, crude fiber 0.70 g/100 g; 70:30APN − 70% Apem + 30% Nhyira – protein10.40 g/100 g, fat 0.90 g/100 g, crude fiber 0.8 g/100 g; 60:40AP − 60% Apem + 40% Nhyira – protein 12.4 g/100 g, fat 1.0 g/100 g, crude fiber 0.90 g/100 g; 50:50APN − 50% Apem + 50% Nhyira – protein 14.10 g/100 g, fat 1.4 g/100 g, crude fiber 1.10 g/100 g.

100073.6a 629.0f 607.5f 252.0f 73.6a 629.0f 607.5f 252.0f
901074.5b 459.0e 453.0e 159.0e 74.3b 485.0e 476.0e 169.0e
802074.6b 371.0d 366.5d 118.5d 75.8b 197.5d 196.5d 26.5d
703074.8b 290.5c 289.5c 77.5c 75.1c 318.0c 317.5c 62.5c
604075.6c 246.0b 245.0b 62.5b 75.4c 245.5b 245.0b 41.0b
505075.5c 169.5a 169.0a 34.5a 74.7c 386.0a 382.0a 99.5a
Apem
100074.9a 595.5a 591.0a 252.5f 74.9a 595.5f 591.0f 252.5f
901075.9a 452.5a 422.5a 135.5e 75.9b 425.5e 425.0e 130.5e
802075.7b 365.0c 364.0c 107.0d 76.2b 328.0d 326.5d 77.5d
703075.7b 281.5d 280.5d 68.5c 76.3b 271.0c 269.5c 57.0c
604077.1c 182.0e 180.5e 37.5b 76.8c207.5b 205.0b 39.0b
505077.7d 151.5f 148.5f 33.5a 77.6d 151.0a 146.0a 25.5a

The RVA properties of blended flours used for extrusion processing are presented in Table 5. The physical properties of moisture, and hardness of the extruded, baked and fried extrudates for plantain and cowpea blends are presented in Table 6.

Table 5. Rva Properties of Raw Powders for Extruded Products
Plantain (wt %)Cowpea (wt %)Oat fiber (wt %)Peak1 (cP)Trough (cP)Breakdown (cP)Final viscosity (cP)Setback (cP)Peak time (min)
  1. Values in the same column with different letters are significantly different at P < 0.05. RVA, rapid visco analyzer.

100006,719.5e 4,001.5e 2,718.0e 5,346.5e 1,345.0d 4.9a
01000804.5a 763.0a 41.5a 1,200.5a 437.5a 7.0a
752504,511.0c 3,090.0c 1,421.0c 4,511.5c 1,421.5c 5.1a
750253,269.5e 2,300.5d 969.0d 3,313.5d 1,013.0e 4.8a
5025251,981.0b 1,515.5b 465.5b 2,145.5b 630.0b 5.2a
Table 6. Physical Properties of Extruded Plantain and Cowpea Blends
ProcessingPlantain (wt %)Cowpea (wt %)Oat fiber (wt %)Moisture content (%)Hardness (N)Normalized hardness (N/mm)Expansion height (mm)
  1. Pooled standard deviation for mean testing: moisture (0.10), hardness (224.7), normalized hardness (6.73), height (0.46).

Extruded (half-product)1000038.653.810.25.2
7525035.530.26.04.9
7502536.538.410.53.7
50252531.956.613.84.2
Baked1000012.797.910.49.9
7525010.962.308.57.9
750257.586.211.27.8
5025256.381.710.67.8
Fried1000022.2115.114.78.0
7525016.178.210.18.2
7502513.4108.614.18.8
50252512.545.85.59.3

The moisture content for extruded half-products was higher than baked or fried samples (Table 6). The moisture contents of the blends decreased as white bean and oat fiber were blended with plantain in the following amounts (plantain : white bean : oat fiber, 75:25:0, 75:0:25, 50:25:25). Plantain extrudates retained the highest moisture while the 50:25:25 blend had the lowest (Table 6).

Initial hardness values of extruded blends were slightly lower than the values recorded for baked and fried extruded blends. The hardness of extruded plantain 100:0:0 and 50:25:25 is presented in Table 6. The baked plantain hardness was 97.9 ± 48.4 and 62.3 ± 36.2 N for 75:25:0 blend. For fried extrudates, plantain (100:0:0) recorded the most hard value of 115.1 ± 46.8 N whereas 50:25:25 was the softest with a value of 45.8 ± 48.7 N. The height of each piece of extrudates varied; baked extrudates ranged from 3.7 ± 0.7 to 5.2 ± 0.7 mm, and fried extrudates ranged from 7.80 ± 0.7 to 9.9 ± 1.2 mm. The height of fried extrudates ranged from 8.04 ± 0.8 to 9.3 ± 1.2 mm. The normalized hardness values for extruded half-product ranged from 5.9 ± 1.9 to 13.8 ± 1.7 N/mm; for baked extrudates 8.5 ± 1.2 to 11.2 ± 4.8 N/mm, and fried extrudates hardness ranged from 5.5 ± 6.4 to 14.7 ± 6.5 N/mm (Table 6).

The water absorption indices of plantain and cowpea flours are presented in Fig. 1. The WAI for the Apantu plantain flour was higher than Apem flour. The WAI was higher for the Asetenapa cowpea compared with Nhyira. Figure 2 shows the half-products from the five different extruded formulations. The 100% plantain extrudates were dark and gummy. The 100% white bean extrudates were cream in color with a dough-like texture. The 75% plantain and 25% oat fiber were lighter in color than the 100% plantain; the 75% plantain and 25% white bean flour was brownish. The 50% plantain, 25% oat fiber and 25% bean extrudate was deep brown in color. The 100% white bean extrudate was very attractive (Fig. 2). The extrudates puffed out, pillow-like after frying. After frying, the color of extrudates toned down making the product more attractive. For the baked products, there was more puffing in all the extrudates except for the 100% white bean. The color of extruded half-product did not change after baking; however, the products looked more appealing. The products from the three blends were light brown in color. The expanded product from white bean flour alone was cream in color, whereas the others were dark brown in color. Expanded product from plantain was very dark in color.

figure

Figure 1. Water Absorption Index of Plantain and Cowpea Flours

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figure

Figure 2. Pictures of Extruded Half- Product (Top) and Extruded Baked Half-Products (Bottom) of Plantain, White Bean Flour And Oat Fiber

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Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Acknowledgments
  9. References

Chemical Composition of Plantain Fruits and Cowpea Seeds

The average moisture content of the two varieties of plantain Apantu and Apem was 57.6 g/100 g, similar to values (58.0 g/100 g) reported for plantains by Akomolafe and Aborisade (2007). Moisture conditions may vary due to differences in variety, maturity and environmental conditions. The fat content for the plantains was 0.03 g/100 g compared with 0.08 g/100 g reported by Akomolafe and Aborisade (2007). The average protein content was 28.6 g/100 g for Nhyira and Asetenapa cowpeas. This value is similar to literature values in the range of 24.1–25.4 g/100 g (Bressani 1985). Deshpande and Damodaran (1990) reported cowpea protein content of 24%. Nhyira and Asetenapa cowpeas had the same fat content of 1.9 g/100 g, compared with literature values in the range of 1.3 g/100 g reported by Deshpande and Damodaran (1990). Deshpande and Damodaran (1990) reported ash content for cowpeas in the range of 3.4–3.9 g/100 g, but we reported a value of 2.9 g/100 g for Nhyira and Asetenapa cowpeas, which is comparable to literature values.

The average moisture content of the plantain varieties was 8.4 g/100 g (Table 2). This value is lower than the value of 11.8 g/100 g reported by Pacheco-Delahaye et al. (2008). The average ash content for Apantu and Apem plantain flours was 2.1 g/100 g, which is comparable with a value of 2.02 g/100 g reported by Pacheco-Delahaye et al. (2008). Pacheco-Delahaye et al. (2008) reported a value of 3.1 g/100 g for protein content of plantain flour, but the value for both Apantu and Apem is 2.1 g/100 g, which is significantly lower. But others such as Morton (1987) reported values for plantain protein ranging from 1.2 to 1.5 g/100 g, which is similar to our results. The fat content of the plantain flours 1.8 g/100 g is much higher compared with 0.3 g/100 g reported by Pacheco-Delahaye et al. (2008). The moisture contents of Nhyira and Asetenapa cowpea flours were 6.1 ± 0.06 g/100 g and 7.8 ± 0.2 g/100 g, respectively.

Physicochemical Properties of Plantain and Cowpea Flour

The water activity values for both plantain and cowpea flours were in the range of 0.44–0.50, making them safe from microbial proliferation. Beuchat (1997) showed that products are safe if water activity level was between 0.7 and 0.9. The low moisture contents of plantain and cowpea flours coupled with low water activity will favor long-term storage stability.

The WAI is the ability of flour to absorb water for uniform consistency. The WAI of both plantain flours Apantu and Apem was high, and low for cowpea flours, Asetenapa and Nhyira (Fig. 1). High WAI values are due to the starch length and gelatinization; WAI is also dependent on starch content and not protein (Li et al. 2004). Water absorption is an important parameter to be considered in the mashing, extrusion and baking of snack products. Higher WAI is preferred for improved mashing properties while lower WAI values are more desirable for making thinner gruels. It is an important functional characteristic in development of ready-to-eat foods because high water absorption capacity may assure product cohesiveness (Kulkani et al. 1991).

Rheological Analysis of Formulated Commercial Raw Powder Using RVA

High peak paste values were recorded for commercial plantain flour (6,719.5 cp). This could be due to the structural differences of the starch. The white bean flour however had a low value of 804.5 cp indicating less starch granules but more amino acid units and different starch granules.

The commercial plantain flour had a highest setback value of 1,345.0 cP, which is a degree of retrogradation of amylose unit during cooling of starch paste. The 75% plantain and 25% white bean flour had a setback value of 421.5 cP. The 75% plantain and 25% oat fiber blend setback value was 1,013 cP. RVA results indicated that as the proportion of cowpea and oat fiber added to plantain increased, the peak viscosity, final viscosity, the trough and setback values decreased. The peak times were however smaller compared with the rest of the blends. Apantu plantain flour setback value was 1,488.0 cP and Apem flour was 1,592.5 cP. Setback values for Asetenapa and Nhyira cowpea flours were 1,137 and 1,076 cP, respectively. This implied that starch granules in the plantain flour can easily form pastes. Significant differences were observed at (P < 0.05) for all measured rheological parameters for all samples. Studies by Haase et al. (1995) comparing RVA and Brabender viscograms showed a close correlation of r = 0.94 for both peak and trough viscosity. Doublier (1987) observed that differences in starch and flour pasting properties between the Brabender and RVA could be attributed to different pasting conditions that lead to quite different swelling and solubilization.

Extrusion Processing of Half-Products

About 100% plantain extrudate appearance was dark and gummy due to easily gelatinized iron-rich starch, when cooked becomes dark brown (Fig. 2). The 100% white bean extrudate was cream in color and had a dough-like texture. The 75% plantain and 25% oat fiber extrudate was slightly lighter in color than 100% plantain. The 75% plantain and 25% white bean flour was brownish in color. This was because white bean flour mitigated the dark color of cooked plantain flour. The 50% plantain, 25% oat fiber and 25% bean were deep brown in color. The 100% white bean was comparatively very attractive (Fig. 2). The extrudates puffed out a bit when fried; also color of extrudates toned down making the product more attractive after the frying process.

There was significant puffing in all baked extrudates except for 100% white bean extrudate. The color of extruded half-products did not change much after baking; however, they looked more appealing. Similar expansion and puffing characteristics were reported for cassava, barley and quinoa products (Onwulata et al. 2010). Drying after the extrusion process reduced the moisture content in the extrudates.

Texture Analysis of Extruded Half-Products, Extruded Baked and Extruded Fried Products

The hardness level of the extruded half samples ranged from 30.2 for 75:25 to 56.6 N for 50:25:25 as presented in Table 6. The hardness values increased from 62.3 for 75:25 to 81.7 N when extruded samples were baked; however, 50:25:25 hardness reduced to 45.8 N when fried, 75:25 combination recorded hardness of 78.2 N. The increase in hardness was the result of reduced moisture as samples were dried and further baked and fried. Drying the extrudates reduced the moisture content (Table 6). Moisture content of baked products was lower ranging from 6.3 to 12.7%, fried half-products from 12.5 to 22.2%, because the oil absorbed during frying. The moisture in baked product evaporated during the baking period. The height of the extruded snack was lower compared with the baked and fried.

Conclusion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Acknowledgments
  9. References

Differences in rheological properties of extruded plantain and cowpea flours depended on the varieties and amount of cowpea added. Addition of cowpea flour boosted protein content of plantain flour formulation. The expanded extrudates have a potential for scaling up plantain and cowpea flour process using local raw materials for use in extrusion of high-protein snacks in developing countries.

Acknowledgments

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Acknowledgments
  9. References

We are grateful to Raymond-Hadley Corp., Spencer, NY 14883, Bob's Red Mill Natural Foods, Inc., Milwaukie, OR, and Sun Opta Ingredient Group (Chelmsford, MA) for the supply of the plantain flour, oat fiber and white bean flour. The contribution of United States Department of Agriculture-Agricultural Research Service–Eastern Regional Research Center and CSIR-Food Research Institute is appreciated. Grant Agreement -58-1935-9-174F.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Acknowledgments
  9. References
  • Aboagye, Y. and Stanley, D.W. 1987. Thermoplastic extrusion of peanut flour by twin-screw extruder. Can. Inst. Food Sci. Technol. 20, 148153.
  • Adeniji, T.A., Barimalaa, I.S. and Achinewhu, S.C. 2006. Evaluation of bunch characteristics and flour yield potential in black Sigatoka resistant plantain and banana hybrids. Glob. J. Pure Appl. Sci. NGA 12, 4143.
  • Akomolafe, O.M. and Aborisade, A.T. 2007. Effects of simulated rural storage conditions on the quality of plantain (Musa paradisiaca) fruits. Int. J. Agric. Res. 2, 10371042.
  • AOAC. 2000. Official Methods of the Association of Official Analytical Chemists, 17th Ed., The Association, Arlington, VA.
  • Aremu, C.Y. and Udoessien, E.I. 1990. Chemical estimation of some inorganic elements in selected tropical fruits and vegetables. Food Chem. 37, 229240.
  • Barbosa-Canovas, G. and Vega-Mercado, H. 1996. Cabinet and bed dryer. In Dehydration of Foods, 1st Ed. (Chapman Hall ITP, ed.) pp. 157184, 256–257, EEUU, Thompson, NY.
  • Beuchat, L. 1997. Water activity and microbial stability. Center for Food Safety and Department of Food Science and Technology. University of Georgia, USA.
  • Bressani, R. 1985. Nutritive value of cowpea. In Cowpea Research, Production and Utilization ( S.R. Singh and K.O. Rachie , eds.) pp. 353359, John Wiley and Sons, Chichester.
  • Dadzie, B.K. and Orchard, E. 1997. Routine post-harvest screening of banana/plantain hybrids: Criteria and methods. Inibap Technical Guidelines. www.ipgri.cgiar.org/publications%20pdf/235.pdf (accessed October 28, 2007).
  • Demirel, D. and Turhan, M. 2003. Air drying behavior of Dwarf Cavendish and Gros Michel banana slices. J. Food Eng. 59, 111.
  • Deshpande, S.S. and Damodaran, S. 1990. Food legumes: Chemistry and technology. In Advances in Cereal Science and Technology ( X.Y. Pomeranz , ed.) pp. 147241, Am. Assoc. Cereal Chemists, St. Paul, MN.
  • Doublier, J.L. 1987. A rheological comparison of wheat, maize, faba bean and smooth pea starches. J. Cereal Sci. 5, 247262.
  • Ganjyal, G. and Hanna, M.A. 2002. A review on residence time distribution (RTD). In Zhang, W. and Hoseney, R.C. 1998. Factors affecting expansion of corn meals with poor and good expansion properties. Cereal Chem. 75, 639643.
  • Haase, N.U., Mintus, T. and Weipert, D. 1995. Viscosity measurements of potato starch paste with the rapid visco analyzer. Starch/Stärke 47, 123126.
  • Happi Emaga, T., Herinavalona Andrianaivo, R., Wathelet, B., Tchango Tchango, J. and Paquot, M. 2007. Effects of the stage of maturation and varieties on the chemical composition of banana and plantain peels. Food Chem. 103, 590600.
  • Harper, J.M. 1989. Food extruders and their applications. In Extrusion Cooking ( C. Mercier , P. Linko and J.M. Harper , eds.) pp. 116, Pub. American Association of Cereal Chemistry, St. Paul, MN.
  • Jin, Z., Hseih, F. and Huff, H.E. 1995. Effects of soy fiber, salt, sugar and screw speed on physical properties and microstructure of corn meal extrudate. J. Cereal Sci. 22, 185194.
  • Kirk, R.S. and Sawyerr, R. 1990. Pearson's Composition and Analysis of Foods, 9th Ed., p. 578, Longman Scientific and Technical, Harllow, Essex.
  • Kulkani, K.D., Noel, G. and Kulkani, D.N. 1991. Sorghum malt-based weaning food formulations preparation, functional properties and nutritive value. Food Nutr. Bull. 17(2), 322327. The United Nations University Press.
  • Li, P.X., Campanella, O.H. and Hardacre, A.K. 2004. Using an in-line slit-die viscometer to study the effects of extrusion parameters on corn melt rheology. Cereal Chem. 81, 7076.
  • Morton, J. 1987. Breadfruit. In Fruits of Warm Climates, Julia F. Morton, Miami, FL, pp. 50–58 ( J.P.R. Cannell , ed.) pp. 329363, Humana Press Inc., Totowa, NJ. Tomas-Barberan.
  • Onwulata, C.I., Konstance, R.P. and Holsinger, V.H. 1998. Physical properties of extruded products as affected by cheese whey. J. Food Sci. 63, 814818.
  • Onwulata, C.I., Konstance, R.P., Smith, P.W. and Holsinger, V.H. 2001. Co-extrusion of dietary fiber and milk proteins in expanded corn products. Lebensm. Wiss. Technol. 34, 424429.
  • Onwulata, C.I., Thomas, A.E., Cooke, P.H., Phillips, J.G., Carvalho, C.W.P., Ascheri, J.L.R. and Tomasula, P.M. 2010. Production of extruded barley, cassava, corn and quinoa enriched with whey proteins and cashew pulp. Int. J. Food Prop. 13(12), 122.
  • Pacheco-Delahaye, E., Maldonado, R., Pérez, E. and Schroeder, M. 2008. Production and characterization of unripe plantain (Musa paradisiaca L.) flours. Interciencia 33(4), 290294.
  • Phillips, R.D. and McWatters, K.H. 1991. Contribution of cowpeas to nutrition and health. Food Technol. 45(9), 127130. J Food Sci 67:1996–2001.
  • Quin, F.M. 1997. Introduction. In Advances in Cowpea Research ( B.B. Singh , D.R. Mohan Raj , K.E. Dashiel and L.E.N. Jackai , eds.) pp. ixxv, Co-publication of International Institute of Tropical Agriculture (IITA) and Japan International Centre for Agriculture, Ibadan, Nigeria.
  • Sefa-Dedeh, S. and Yiadom-Farkye, N.A. 1988. Some functional characteristics of cowpea (Vigna unguiculata), bambara beans (Voandzeia subterranea) and their products. Can. Inst. Food Sci. Technol. J. 21, 266270.
  • Singh, R.P. and Heldman, D.R. 2001. Introduction to Food Engineering, 3rd Ed., pp. 565567, Academic Press, San Diego, CA.