Development And Characterization of Extruded Fura From Mixtures of Pearl Millet and Grain Legumes Flours

Abstract

Dehulled pearl millet flour (100%) and blends of pearl millet, cowpea, groundnut and soybean flours at 80:20, 70:30 were extruded at 30 g moisture/100 g sample using a Brabender Laboratory single screw extruder to develop extruded fura products. The fura extrudates and fura produced in the traditional way were analyzed for their physical and chemical and sensory properties. There were significant differences (p < 0.05) in the puff ratio of the extruded fura products. Pearl millet: cowpea (80:20) fura had the highest puff ratio (4.71) while the pearl millet: groundnut (80:20) fura had the lowest (2.90). The bulk density of the pulverized extruded fura was lower than that of the dried and pulverized traditional fura. The hydration power of the extrudates increased significantly (p < 0.05) at 28°C and 50°C. Extrusion increased the hydration power of products. Fura extrudate containing 100% pearl millet flour had the highest hydration power of 63.9% at 28°C, while the traditional fura had the lowest of 15.8% at 28°C. Protein content of samples increased with supplementation of pearl millet with grain legumes. Sensory evaluation results showed that there were no significant differences among the fura extrudates and the traditional fura with respect to color, texture and overall acceptability except for flavor. Extruded products were still acceptable after 12 weeks storage in polyethylene and cellophane bags at 30 ± 2°C. Extrusion and supplementation processes are therefore one way of producing a convenient shelf stable nutrient rich fura in the areas where fura is commonly consumed.

Keywords:

• Millet
• Fura
• Extrusion
• Legumes
• Puff-ratio
• Development

INTRODUCTION

Fura is unfermented millet dough that is steam cooked. It is a traditional staple food in West Africa particularly in Nigeria, Burkina Faso, Niger, Mali, and Ghana.[1–3] Fura is a popular breakfast and mid-day meal taken with nono, kindrimo, or yogurts. It is sometimes mashed in water before consumption. Fura is prepared primarily from pearl millet. During preparation, dehulled grain is pounded in a mortar, shaped into balls and placed in boiling water, and cooked for 30 to 40 minutes. The cooked balls are repounded with hot water and spices until smooth slightly cohesive dough is formed. The dough is reshaped into small balls.[3,4] The major problem of fura is its short storage life of 3 to 6 days.

Extrusion cooking is a process, which combines several unit operations and provides great opportunities in the creation new food products. Extrusion cooking has been used to produce a wide range of foods including snacks, ready-to eat cereals, confectioneries, texturized foods, meat substitutes, and extruded crisp bread. The main purpose of extrusion is to increase the variety of foods in the diet by producing a wide range of quality products with different shapes, texture, color, flavor, and excellent storage life from basic ingredients.[5–7] Therefore, extrusion cooking of fura will provide a great potential for a shelf stable product.

Fura is also a single cereal based product with low nutritional quality especially when consumed with water alone. The addition of grain legume flours in fura production will improve its nutrient composition and possibly alleviate the protein energy malnutrition problem in areas where fura is consumed.[8] Extruded blends of finger millet and legume flours are already being used in India to form nutritionally balanced foods that can be used as supplementary foods for malnourished children.[9] The objective of this article was to develop an extruded fura from pearl millet flour and mixtures of pearl millet-grain legume flour and to determine the physicochemical and sensory properties of the extrudates.

MATERIALS AND METHODS

Materials

The pearl millet (Pennisetum glaucum) var. Ex-Borno used in this study was obtained in bulk from Lake Chad Research Institute, Maiduguri, Nigeria. The grain legumes (cowpea, groundnut and soybean) and spices (ginger and black pepper) used were purchased from Jimeta Main Market, Yola, Nigeria.

Preparation of Pearl Millet and Grain Legumes Flour

Millet flour

The pearl millet was first cleaned using Vegvari Ferenc aspirator (Vegvari Ferenc, OB125, Hungary). The cleaned grain was treated with 4 g water/100 g sample and dehulled using No. IA Amuda type rice huller (Amuda, India). The dehulled grain was washed then dried to 14 g moisture/100 g sample (wet basis) in an air oven (Chirana type HS 20IA, Czechoslovakia) set at 50°C. The dried grain was milled using the Brabender OHG DUISBURG Roller mill equipped with a 70 μm screen.

Cowpea flour

The cowpea sample was soaked in water for 30 minutes at room temperature to soften the seed coat. The seeds were then dried at 50°C for 3 hours in air oven to 14 g moisture/100 g seed. The dried cowpea kernel was cooled and dehulled using the local pestle and mortar. The seed coats were removed by aspiration using the Vegvari Ferenc aspirator, and the kernels ground in a laboratory disc attrition grinder (Amuda, India) and then sieved to past B.S. No. 28 mesh sieve.

Soybean flour

The soybean seeds were soaked in tap water for 24 hours at room temperature, dried, dehulled, ground, and sieved as previously described for cowpea.

Groundnut paste

The groundnut kernels were soaked in water for 30 minutes, followed by drying in an air oven set at 90°C for 3 hours. After drying the skins were removed by rubbing between the palms of the hand. The seed coat was removed by aspiration as described for cowpea. The kernels were ground into a paste using a local laboratory disc attrition grinder.

Spices

Back pepper and ginger were sorted and cleaned manually and further dried in a convection air oven (Chirana Type HS201A, Czechoslovakia) set at 50°C for 5 hours. They were then individually ground with a pestle and mortar and sieved using a 20-mesh screen (Brabender OHG Duisburg Type).

Formulation of Fura Flour Blends

The pearl millet flour and legume flours (cowpea, soybean, and groundnut paste) were blended in ratios of 80:20 and 70:30 pearl millet flour to grain legume flour. One gram of mixed spices was added to each formulation. The control sample was 100% pearl millet flour containing one gram of mixed spices.

Traditional Fura Production

The pearl millet sample was first dehulled and washed to remove the bran layer. It was then pounded using wooden pestle and mortar. The flour was sifted, then shaped into balls after dampening with water and placed in boiling water to cook for 30 minutes. The cooked balls were removed from the boiling water and re-pounded with hot water. Mixed spices (1 g) were added and the pounding continued until smooth slightly cohesive dough was formed. The dough was reshaped into small balls (30 g) and dusted with pearl millet flour.[4]

Extrusion Conditions

The extrusion was performed in a laboratory single screw extruder (Brabender Duisburg DCE–330 model), powered by a Decoder drive, which enabled torque to be continuously measured. The barrel had a diameter of 20 mm with a 20:1 length to diameter ratio. As temperature, feed moisture, die configuration, and screw speed account for most of the variation in texturization by extrusion,[10] these variables were optimized for consistent experimental conditions. The runs were performed at feed moisture content of 30 g /100 g sample, screw speed 180 rpm, hopper screw speed 80 rpm, and barrel temperatures of 150, 170, and 150°C for the three heating zones respectively. The die temperature was maintained at 150°C during extrusion. The extrusion data is shown is Table 1. They were variations in the pressure, torque and mass flow rate of samples during extrusion.[11]

Table 1 Extrusion conditions.

	Moisture content of feed(% wb)	Barrel Temp. (°C)			Die Temp. (°C)	Pressure N/m^2	Torque Nm	Mass flow rate g/min	Screw speed rpm	Feed hopper speed rpm
Samples		1	2	3
Extruded fura (100%) millet	30	150	170	150	150	1.75 × 10^6	15	65	180	80
Millet: Cowpea fura
80:20	30	150	170	150	150	1.8 × 10^6	16	64	180	80
70:30	30	150	170	150	150	2.3 × 10^6	18	62	180	80
Millet: Soybean fura
80:20	30	150	170	150	150	1.4 × 10^6	14	68	180	80
70:30	30	150	170	150	150	1.3 × 10^6	13	72	180	80
Millet: Groundnut fura
80:20	30	150	170	150	150	1.2 × 10^6	13	76	180	80
70:30	30	150	170	150	150	1.1 × 10^6	15	82	180	80
wb: wet basis.

Chemical Analysis

The moisture, crude protein, crude fat, ash, and crude fiber of samples were determined according to AOAC[12] methods. The percentage carbohydrate was determined by difference Egan et al.[13]

Expansion Ratio (Puff Ratio)

Puff ratio was determined according to Zasypkin and Tung-ching Lee[14] procedures. This was determined by dividing the average diameters of the extrudates by the diameter of the extruder nozzle. Ten separate readings for each sample was taken and their mean recorded.

Bulk Density

The bulk densities of flour samples and ground extrudates were determined according to Jao et al.[15] method. 10 g of pulverized extrudates and flour samples placed in 100 ml measuring cylinders were firmly tapped 30 times on a bench top to settle the sample volume. Measurements were then made in triplicate for each sample.

Hydration Power

The Bhattacharya et al.[16] method was used. 80 ml of tap water at 28 and 50°C were added to 10 g pulverized extrudates and allowed to stand for 1 hour in 150 ml beaker. The hydrated extrudate was collected by inverting the beaker over a B.S. No. 20 mesh screen for 60 seconds. The percentage hydration was defined as:

Where, W₁ is initial weight of sample before hydration, W₂ wet weight of sample after hydration. Ten separate readings were made for each sample and their means recorded.

Sensory Evaluation

Fura samples for sensory evaluation were prepared as follows. 100 g of pulverized extruded fura and traditional fura were added to 500 ml of nono (traditional local yogurt) in 1000 ml beaker. 50 g of granulated sugar was added to each preparation before serving. Portions of the fura preparations were served to 20 untrained panelists familiar with fura seated in air conditioned individual boots in the sensory evaluation laboratory of the Department of Food Science and Technology, Federal Polytechnic, Mubi, Nigeria. Samples were served in clean plastic bowls. The panelists were provided with clean potable water for oral rinsing between samples. They were asked to rate the color, flavor, texture, and overall acceptability of samples on a 9-point hedonic scale (1 = disliked extremely and 9 = liked extremely).[17] Fura prepared as per the traditional process served as the control. The attributes assessed belong to different categories, those perceived visually such as color, those perceived by mouth feel such as texture (grittiness), taste, and flavor and finally overall acceptability.

Statistical Analysis

The results of the proximate composition, puff ratio, bulk density, hydration and sensory properties were statically analyzed by analysis of variance and means separated by Duncan Multiple Range Test (DMRT).[18]

RESULTS AND DISCUSSION

Proximate Composition

There were significant variations (p < 0.05) in the proximate composition of flour samples and pearl millet-grain legume flour blends (Table 2). Protein content increased with supplementation of pearl millet flour with grain legume flour as would be expected. Pearl millet-soybean flour blends had the highest protein content, while pearl millet—groundnut blends had the highest fat content. Other workers have reported similar increases in protein and fat contents of cereal—legume blends.[19,9]

Table 2 Proximate composition raw flour samples and flour blends.

Sample	Moisture (%)	Protein (%)	Crude fat (%)	Ash (%)	Crude fiber (%)	Carbohydrate (%)
Millet	11.2^bc	10.8^f	3.8^g	1.6^b	1.8^b	70.8^a
Cowpea	12.6^a	20.7^c	1.8^h	2.0^ab	2.1^ab	60.8^b
Soybean	11.6^bc	38.6^a	21.8^b	2.4^a	2.3^a	23.3^d
Groundnut	7.2^e	24.4^b	42.1^a	1.8^b	1.1^c	23.4^d
Millet: Cowpea
80:20	11.3^bc	13.0^e	3.4^g	1.7^b	1.9^b	69.2^a
70:30	11.5^bc	13.8^e	3.2^g	1.7^b	1.9^b	67.8^a
Millet: Soybean
80:20	11.3^bc	16.4^d	7.4^f	1.8^b	0.9^b	61.3^bc
70:30	11.3^bc	19.1^c	9.2^e	1.8^b	2.0^b	56.6^c
Millet: Groundnut
80:20	10.8^cd	13.7^e	11.5^d	1.5^c	1.6^b	61.4^bc
70:30	10.0^d	14.9^e	15.3^c	1.5^c	1.8^b	56.6^c
Means within a column not having same superscript are significantly different (p < 0.05) values are means of triplicate determinations.

The proximate composition of extruded fura from pearl millet, and pearl millet-grain legume flour blends and traditional dried fura are presented in Table 3. There were significant differences (p < 0.05) in protein, fat, ash, crude fiber, and ash contents of fura samples. Protein content for all fura samples increased after extrusion. This may be due to the lower moisture content of the extruded fura, which ranged from 5.3 to 6.5%. As would be expected crude fat was highest in the millet—groundnut flour fura extrudate and lowest for millet—cowpea flour fura one.

Table 3 Proximate composition of extruded fura products and traditional fura.

Sample	Moisture (%)	Protein (%)	Fat (%)	Ash (%)	Crude fiber (%)	Carbohydrate (%)	Energy value (kcal)
Millet: Cowpea
80:20	6.0	14.5^d	3.6^e	1.8	2.0	72.0^b	378^d
70:30	5.8	15.7^d	3.3^e	1.9	2.4	71.0^c	376^d
Millet: Soybean
80:20	5.3	18.0^c	6.9^d	1.9	2.0	65.0^d	398^bc
70:30	6.0	21.1^a	9.0^c	1.9	2.1	59.0^e	405^b
Millet: Groundnut
80:20	5.9	15.8^d	9.4^b	1.7	1.9	65.3^d	409^b
70:30	5.3	18.5^bc	11.2^a	1.9	2.0	60.7^e	417^a
100% Millet Fura
Extrudate	6.7	11.5^e	4.0^e	1.6	1.9	74.6^a	380^d
Traditional	7.8^a	11.3^e	3.9^e	1.4	1.7	73.9^a	376^d
Means within a column not having same superscript are significantly different (p < 0.05). Values are means of triplicate determinations.

Puff Ratio, Bulk Density and Hydration Properties

There were significant differences (p < 0.05) in the puff ratio of extruded fura products (Table 4). Pearl millet-cowpea fura extrudate (80:20) had the highest puff ratio (4.7), while pearl millet groundnut fura extrudate had the least (2.9). Samples with high fat content appeared to have lower puff ratio. When food materials leave the extruder nozzle a change in pressure and normal forces in the dough causes substantial expansion of the cooked product resulting in the loss of moisture.[17] The presence of water vapor, which flashes off at the extruder die, causes the formation of vacuoles giving a porous structure of fibers and laminated sheaths (Table 4).

Table 4 Puff ratio, bulk density and hydration properties of extruded fura.

	Puff ratio Products	Bulk density (g/cm^3		Hydration power (g water/10g) sample for 60 sec
Sample		Raw sample	Products	At 28°C	At 50°C
Millet: Cowpea
80:20	4.71^a	0.81^a	0.31^c	58.70^b	60.84
70:30	4.00^ab	0.52^c	0.32^c	56.56^c	58.32
Millet: Soybean
80:20	3.25^c	0.50^c	0.35^b	56.30^c	64.82
70:30	3.64^c	0.52^c	0.34^b	54.76^d	63.36
Millet: Groundnut
80:20	3.72^bc	0.57^c	0.33^bc	52.28^c	61.10
70:30	2.90^d	0.67^b	0.34^bc	51.32^c	56.32
100% Millet Fura
Extrudate	4.09^b	0.63^b	0.32^c	63.92^a	67.54
Traditional	ND	ND	0.48^a	15.81	20.63
ND: Not determined
Means within a column not having same superscript are significantly different (p < 0.05) values are means of triplicate determinations.

The hydration power of fura extrudates varied significantly (p < 0.05) for some samples at 28 and 50°C (Table 4). Fura extrudate from 100% pearl millet flour had the highest hydration power (63.9%) at 28°C and the traditional fura had the lowest hydration power (15.8%) at 28°C. Hydration power was found to increase slightly with increase in temperature for all samples. Generally extrusion increased the hydration power of products. The increases in the levels of cowpea flour and groundnut paste appear to have negative effect on hydration power of products. Mensah and Sefa-Deddeh[20] reported similar results. Increase in water absorption of sorghum extrudates was reported by Gomez et al.[21] It has been suggested that water absorption index of starch paste could be used as indices of extent of starch hydrolysis under different extrusion conditions. The results of the hydration power of fura extrudates at 28 and 50°C suggest that extruded fura could be reconstituted in cold and warm water with nearly similar results. This is an advantage extruded fura would have over the traditional fura. Extrusion process brings about numerous reactions for example protein denaturation, starch gelatinization and net work formation which tend to modify product characteristics.[22] This influences such physico-chemical properties as solubility, water binding capacity, swelling and apparent viscosity, gel formation, and strength.

Sensory Properties

There were no significant differences (p > 0.05) in color and texture for all fura samples. However, there were significant differences (p < 0.05) in flavor among fura extrudates (Table 5). The traditional fura was rated better than extruded fura from millet: cowpea (80:20) blend. There were no significant differences (p > 0.05) in overall acceptability among extruded fura products, but the traditional fura was rated better than extruded fura from millet: cowpea (80:20) in overall acceptability (Table 5)6.

Table 5 Sensory properties of extruded fura samples a day after production.

Sample	Flavor	Color	Texture (Grittiness)	Overall acceptability
Millet: Cowpea
80:20	5.10^b	5.7^a	5.5^a	4.5^b
70:30	5.45^ab	6.35^a	57^a	5.6^ab
Millet: Soybean
80:20	6.35^ab	6.15^a	6.35^a	6.7^ab
70:30	6.15^ab	5.85^a	5.9^a	6.25^ab
Millet: Groundnut
80:20	5.70^ab	5.85^a	6.05^a	6.65^ab
70:30	6.95^ab	6.85^a	6.7^a	7.15^ab
100% Millet Fura Extrudate	6.0^ab	6.35^a	6.15^a	6.2^ab
Traditional	7.6^a	7.01^a	6.55^a	7.4^a

Table 6 Sensory properties of extruded fura samples after 12 weeks storage at room temperature (28 ± 2°C).

Sample	Flavor	Color	Texture (Grittiness)	Overall acceptability
Millet: Cowpea
80:20	4.35^b	5.46^a	5.48^a	5.15^a
70:30	5.60^b	6.28^a	5.67^a	5.46^a
Millet: Soybean
80:20	6.28^ab	6.05^a	6.20^a	6.80^a
70:30	6.22^ab	5.88^a	6.10^a	6.04^a
Millet: Groundnut
80:20	5.45^ab	5.64^a	6.10^a	6.40^a
70:30	6.84^ab	6.14^a	6.35^a	7.25^a
100% Millet Fura Extruded	6.10^ab	6.18^a	6.35^a	5.95^a
Traditional	7.10^a	6.81^a	5.40^a	6.70^a
Means within a column not having same superscript are significantly different (p < 0.05).

After packaging into low density polyethylene and cellophane bags and storage for 12 weeks (temperature 28 ± 2°C, RH 64%) there were still no significant differences (p > 0.05) in term of color and texture for all fura products. There were also no significant differences (p > 0.05) in flavor between the traditional fura and extruded fura samples, except for extruded fura from millet: cowpea blends. The overall acceptability for all fura samples after 12 weeks storage was similar. The beany flavors of fura from millet: cowpea may have led to its low rating in relation to the other products. No fura sample was rated poor or unacceptable an indication that an acceptable fura can be produced through extrusion cooking. Shelf life studies (results not shown) reveal that extruded fura can store for up to 6 months in low-density polyethylene and cellophane packaging materials at 30°C and RH 64%.

CONCLUSION

It can be concluded that extruded fura showed instantization tendency and had good hydration power compared to the traditional fura. The addition of grain legumes to fura enhanced its nutrient density which means that extruded fura supplemented with grain legumes can be recommended for areas prone to protein energy malnutrition and those living in war torn and famine ravaged areas of West Africa. All extruded fura had good puff ratio and were acceptable even after 12 weeks storage at room temperature.

ACKNOWLEDMENT

This study was supported in part by a grant from the Swiss corporation to West and Central African Millet Research Network (ROCAFREMI-WCAMRN) through Lake Chad Research Institute.