Instrumental and Sensory Textural Properties of Fura Made from Different Cereal Grains

Abstract

A uniaxial compression test and sensory textural analysis were conducted on fura samples from rice, millet, acha, maize, and sorghum flours. Maize fura had significantly higher firmness, energy per unit mass (EPM), breaking stress, and hardness values than the other fura samples. Fura from rice and maize had brittle type of failure at compression having a shear plane. Fura from millet, acha, and sorghum had plastic failure having barreling. Based on the calculated gradient, maize fura was significantly more brittle (i.e., less cohesive) than the other samples; whereas sorghum fura was more cohesive than the others. The panelists detected significant differences (p ≤ 0.05) among the samples for gumminess (denseness and cohesion persisting during mastication) and springiness (the rate at which fura returns to its original condition after deformation). Maize fura was scored the lowest for gumminess and springiness. Hence, acceptability of maize for fura production among consumers of fura may be very poor. Acha and sorghum fura with a plastic characteristic would, therefore, be acceptable as good alternatives to millet for fura production in terms of the texture of the product.

Introduction

In tropical Africa, cereal grains are milled and used to produce thick porridges, which are known by various names in different parts of the continent. In West Africa, particularly in Nigeria, Ghana, and Burkina Faso, one such thick porridge is called “fura,” a semi-solid dumpling cereal meal.[1] Fura is produced mainly from moist pearl millet flour blended with spices and compressed into balls and boiled for 30 min. While still hot, the cooked dough is worked in a mortar with the pestle (with the addition of hot water) until a smooth, slightly elastic and cohesive lump (fura) is formed. The fura dough is rolled into a 25–30 g ball by hand and dusted with flour. The fura is made into porridge by crumbling the fura balls into fermented whole milk (kindrimo) or fermented skim milk (nono). Sugar may be added to taste. The mixture is called “fura da nono” in Nigeria. It is a popular mid-day meal.[2]

Texture, moisture, and color are critical factors in food processing, product quality, and consumer preference. Quality optimization requires consideration of various parameters affecting a food product, particularly a ready-to-eat food like fura. The fate of sorbic acid in millet dough (fura) has been investigated.[1] [3] A color change during storage of fura has been reported.[4] Jideani et al.[5] identified the hazards and critical control points in traditional fura manufacturing. Jideani et al.[6] reported the mathematical modeling of odor deterioration of fura as affected by time-temperature and product packaging parameters. Jideani[7] also reported instrumental and sensory textural properties of fura from pearl millet. However, there is no information on the textural properties of fura made from other cereal grains. Such information is necessary since texture affects processing and handling, influences food habits, and affects shelf-life and consumer acceptance of foods. Furthermore, millet grain is the major cereal used for making fura.[2] Consumers of fura in none millet producing areas may find it difficult to produce fura that is cost–effective. It is, therefore, necessary to analyze other cereals to determine which of them would be a good substitute for fura production. The objective of this study was to evaluate the instrumental and sensory properties of fura prepared from different cereal grains, with the aim of finding an alternative grain for fura production that will not affect its texture adversely.

Materials and Methods

Source of Materials

Spices (cloves and ginger) as well as different cereals—maize (Zea mays), rice (Oryza sativa), acha (Digitaria exilis), sorghum (Sorghum bicolor), and millet (Pennisetum glaucum)—were purchased from a local market in Bauchi metropolis, Bauchi State, Nigeria.

Grain and Spice Milling

The cereal grains were cleaned and dehulled (except acha) using a commercial dehulling machine, Amuda Superfine Huller No. 12031. The dehulled grains and acha were washed separately and dried in a cabinet dryer at 100°C for 30 min, milled into flour, and sieved with 425 µm sieve. The flour obtained from each grain was individually packaged in polyethylene bags and stored in the refrigerator until needed.

Cloves and dried ginger rhizomes were cleaned, washed, dried at 100°C for 1 h, milled into flour, and sieved with a 425 µm mesh sieve. The ground spices were separately packed in polyethylene bags and stored in a dry place until needed.

Preparation of Fura

Fura was prepared from the different cereal grains using the modified traditional method reported by Jideani.[8] The details of the procedure are given in Fig. 1. Cereal flour (300 g), 9 g ginger, and 1.5 g cloves were dry mixed and moistened with 200 mL of water and was allowed to stand for 30 min. The moist flour was compressed between the palms into a ball, and the weight was noted before, dropping it into boiling water. The balls were cooked for 30 min. The cooked flour balls were weighed then pounded to a cohesive dough while still hot. Hot water was added, while pounding if necessary. The dough was then rolled by hand into balls producing the fura.

Figure 1 Fura production process.

Proximate Analysis

The flour and fura samples from each cereal grain were dried and analyzed for moisture, crude protein, crude fat, and ash using the AOAC methods.[9] The carbohydrate content of the samples was estimated by difference. Food energy (kJ/100 g) was calculated using the Atwater factor,[10]

where protein, carbohydrate, and fat contents of the sample were expressed in g/100 g sample: 4, 4, and 9 kilocalories from protein, carbohydrate, and fat, respectively (4.2 is a factor for converting from calories to joules). The determinations were carried out in triplicate.

Quality of the Cereal Flours for Fura Production

The quality of fura produced from each cereal flour was assessed by calculating the cooking yield and the water-added cooking yield.[11] The cooking yield (%) is the ratio of the finished product mass (fura) to mass of hydrated flour expressed in percentage. The water added cooking yield or water holding capacity is the finished product mass (fura) divided by the flour mass, which is expressed as a percentage.

Instrumental Textural Measurement of Fura

Compression tests as described by Jideani[7] were performed on cylindrical sample (75 mm height, 38.9 mm diameter) on the ELE International Tritest 10 (10 KN load frame) at an unconfined testing mode. The method reported by Head[12] was used to calculate the strain and stress. A plot of stress against strain was obtained. From the stress–strain curve, the strength of fura was calculated in terms of breaking stress (maximum stress at failure, force per unit area); deformation at failure (an indication of the brittleness of the sample) showing how far a sample can be deformed before fracture; and the gradient of the slope at the point of failure (indicates samples toughness: the higher the gradient, the tougher the sample i.e., ease of chewing). From the force–strain curve, the firmness of fura was calculated in terms of hardness (maximum force of the force-deformation curve); the energy per unit of sample mass (EPM) required to shear the compressed fura was calculated by integrating the area under the force deformation curve up to the maximum force of the second peak and dividing by the mass of the fura. Firmness was expressed as maximum force divided by the mass of fura.[7] Each sample was tested in triplicate.

Sensory Textural Assessment of Fura Samples

The method reported by Jideani[7] was adopted to evaluate the sensory textural properties of the fura samples. The characteristics evaluated include hardness, cohesiveness, chewiness, and springiness. The texture of fura was evaluated by a ten-member, trained sensory panel. The panel consisted of students and staff from Federal Polytechnic, Bauchi, Nigeria. Panel-training consisted of two 1-h sessions. In the first session, the purpose of the project was explained and the panelists were familiarized with texture terminology such as hardness, cohesiveness, chewiness, gumminess, springiness, adhesiveness, viscosity, and fracturability. During the second session, panelists were allowed to discuss the textural terms and develop a ballot for fura. The final ballot consisted of hardness, cohesiveness, chewiness, gumminess, and springiness. The characteristics evaluated and the guidelines for evaluating each characteristic and the anchor terms for each are presented in Table 1. Panelists received the samples on white plastic plates. Each characteristic was evaluated on a 10 cm unstructured line scale anchored 1 cm from each end with terms representing extremes of the characteristics. Panel members scored the perceived intensity of each attribute by placing a vertical line across the unstructured lines. Panel scores were measured in centimeters from the left end of the line scale to the mark of the panelist.

Table 1 Sensory texture profile procedure for fura (panel techniques and definition of terms)

Characteristics, scoring criteria, and guidelines for evaluation		Scale anchora
Stage 1	Place a piece of fura in the mouth; chew the fura once between molars. Evaluate for:
Hardness—Force required to compress the sample between molar teeth.	Soft to hard
Springiness—The rate at which fura returns to its original condition after pressure is released.	Stays compressed to quickly returns
Stage 2	Place one fura ball in mouth and chew until ready to swallow. Evaluate for:
Cohesiveness—Extent to which sample falls apart during chewing.	Not cohesive to very cohesive
Chewiness—Number of chews to reach final swallowing point.	Low to high
Gumminess—Denseness and cohesion persisting during mastication.	Not gummy to very gummy
Starchiness—Feeling of free starch.	Not starchy to very starch

^aFirst term anchors left end of scale; second term anchors right.

Results and Discussion

Proximate Composition of the Cereal Flours and Their Fura

Tables 2 and 3 show the proximate composition of the cereal flour and fura produced from different cereal grains. The moisture content of the flours ranged from 8.97 to 11.04%. The fura prepared from these flours gave a moisture range of 45.35 to 50.66%. There was no significant difference (p ≥ 0.05) in moisture among the flour and fura from the different grains.

Table 2 Proximate composition of the cereal flours on dry-weight basis* ,#

Proximate composition (%)
Cereal	Moisture	Crude protein (N 2 × 6.25)	Crude fat	Ash	Carbohydrate	Energy (kJ/100 g)
Rice	10.97 ± 0.08	9.87^a	4.43 ± 0.01^a	0.741 ± 0.001^a	73.99^a	1,576^a
Millet	11.04 ± 0.06	11.43^b	8.32 ± 0.01^b	0.852 ± 0.003^a	68.36^b	1,655^b
Acha	10.17 ± 0.24	9.25^a	2.93 ± 0.01^c	0.700 ± 0.001^a	76.95^a	1,559^a
Maize	8.97	11.43^b	1.80 ± 0.01^c	0.404^b	77.40^a	1,560^a
Sorghum	9.44 ± 0.02	15.73^c	7.64^b	1.031 ± 0.001^c	66.16^b	1,665^b

*Mean standard deviation.

^#Any two values not followed by the same letter in the same column are significantly different (p ≤ 0.05).

Table 3 Proximate composition of fura from the different cereals on dry-weight basis* ,#

Proximate composition (%)
Cereal	Moisture	Crude protein (N 2 × 6.25)	Crude fat	Ash	Carbohydrate	Energy (kJ/100 g)
Rice	47.49 ± 0.01	9.31^a	5.06 ± 0.01	0.510 ± 0.014^a	37.63^a	980
Millet	50.66 ± 0.24	11.25^b	5.15	0.633 ± 0.011^a	32.31^b	927
Acha	47.13 ± 0.01	9.25^a	6.15	0.701 ± 0.001^b	36.77^a	1,006
Maize	45.35	11.06^b	6.20	0.445^c	36.95^a	1,041
Sorghum	50.22 ± 0.31	12.50^b	4.47	0.766 ± 0.028^b	32.04^b	917

*Mean standard deviation.

^#Any two values not followed by the same letter in the same column are significantly different (p ≤ 0.05).

The protein content of the cereal flours—rice, millet, acha, maize, and sorghum—ranged from 9.25 to 15.73%. There was significant difference (p ≤ 0.05) in protein among the cereal flours, sorghum being significantly higher in protein than the other flours. The protein content of the fura from the flours ranged from 9.25 to 12.50%. The range of protein content of the fura samples was in agreement with that reported for cereal and cereal products.[13]

The fat content of the cereal flours ranged from 1.80 to 8.32%, with millet flour being significantly higher (p ≤ 0.05) in fat than the other cereal flours. The fat content of the fura samples ranged from 4.47 to 6.20%. The presence of fat in cereals is reported to modify the process of gelatinization by helping to control gelatinization of the starch granules by coating the granules.[14] It is suspected that the gelatinization of the starch in millet flour may be incomplete since the high fat content may modify the gelatinization process. The ash content of the cereal flours ranged from 0.40 to 1.03%. There was a significant difference (p ≤ 0.05) in ash among the cereal flours. The ash content of the fura from the flours ranged from 0.45 to 0.77%. Significant differences (p ≤ 0.05) in ash content exist among the fura samples.

The carbohydrate content of the cereal flours ranged from 66.16 to 77.40%. The carbohydrate content of the fura from the cereal flours ranged from 32.04 to 37.63%. There was significant difference (p ≥ 0.05) in carbohydrate content among the fura samples. The energy content of the fura from the cereal flours ranged from 917 to 1041 kJ/100 g. There was significant difference in energy among the samples.

Quality of Cereal Flours for Fura Production

Table 4 shows the quality of cereal flours for fura production based on the cooking and water added cooking yield. Maize flour had a significantly (p ≤ 0.05) higher cooking yield (122%) followed by sorghum flour (113%). The hydrophilic group in the starch molecules causes it to take up moisture in proportion to the relative humidity of the atmosphere. Swelling of the granules is slight in cold water, but on heating, some of the intermolecular hydrogen bonds are disrupted and swell. The gelatinization of starch is very important in cooking flour goods because it contributes to the desired crumb structure and texture of the product.[15] Maize and sorghum flour may be more profitable in fura production in terms of yield. The water added cooking yield (%) ranged from 172 to 178%. Although there was no significant difference (p ≥ 0.05) in the water-added cooking yield among the flours, maize and sorghum flours had higher water-added cooking yield.

Table 4 Cooking yield and water added cooking yield of flour from the cereal grains

Cereal	Cooking yield (%)	Water-added cooking yield (%)
Rice	105	172
Millet	108	174
Acha	106	176
Maize	122	177
Sorghum	113	178

Instrumental Textural Characteristics of Fura from Different Cereal Flours

Typical force-deformation curves of fura from the different grains are shown in Fig. 2. The force-deformation curve of fura peaked when the shear-compression force reached the maximum. Fura prepared from rice and maize, underwent brittle type of failure having a shear plane. Fura prepared from millet, acha, and sorghum underwent plastic failure having barreling. The differences in failure mode of the samples during compression may be a result of the varying ratios of amylose and amylopectin in the different cereal flours, which will influence the strength of gelatinization of these flours.[14] Amylose enhances gelling by forming a more regular network in the gel.

Figure 2 Force deformation curve for the different cereal fura.

Table 5 shows the instrumental textural characteristics of fura from the different cereals. Fura firmness ranged from 0.30 to 0.69 kN/g. The energy per unit mass of fura (EPM) ranged from 1.842 to 5.581 J/g. The peak force of the fura samples ranged from 29.5 to 67.7 kN. Maize fura had significantly higher firmness, EPM, and hardness values than the other fura samples.

Table 5 Strength and firmness of fura samples from different cereals*

Strength			Firmness
Cereal	Breaking stress (N/m^2)	Deformation at failure (%)	Gradient	Firmness (kN/g)	EPM (J/g)	Hardness (kN)
Rice	30.4^a	15.8^a	199^a	0.408^a	3.377^a	41.0^a
Millet	27.8^a	15.4^a	210^a	0.453^a	ND	45.5^a
Acha	24.6^a	10.0^b	236^a	0.304^a	1.842^b	29.5^b
Maize	50.9^b	14.7^a	314^b	0.689^b	5.581^c	67.7^c
Sorghum	22.4^c	15.8^a	153^c	0.309^a	2.709^a	30.2^b

ND—Not determined.

*Any two values not followed by the same letter in the same column are significantly different (p ± 0.05).

The breaking stress of the fura samples ranged from 22.4 to 50.9 N/m². Maize fura was significantly higher (p ≤ 0.05) in breaking stress than all the other fura samples. Sorghum fura was significantly lower in breaking stress than the other samples. Deformation at failure ranged from 10.0 to 15.8%. Acha fura differed significantly in deformation at failure from other fura samples. The toughness (ease of chewing) of fura measured as the gradient of the stress-strain curve ranged from 153 to 314. The ease with which these fura samples yielded under an increasing compression load is quite low. The smaller the deformation under a given load, the lower the cohesiveness and the greater the brittleness of the product.[16] Szczesniak[16] defined brittleness as the force required to deform a substance. Both crispness and brittleness are measures of the force required to deform a substance. Materials exhibiting greater slope and lower resistance to deform are considered to be more brittle (i.e., less cohesive). Based on the calculated gradient, maize fura is significantly more brittle (i.e., less cohesive) than the other samples; whereas sorghum fura is more cohesive than the others.

Jideani[7] had devised a fura quality scale based on the peak force: soft and poor quality fura will have a peak force of <10 kN; acceptable fura has a peak force of 19–24 kN; a firm and good quality fura, 24–25 kN; very hard and very poor quality fura will have a peak force of >25 kN. Fura prepared in this study can be said to be very hard in texture.

Sensory Textural Characteristics of Fura from Different Cereals

The mean sensory scores for the sensory textural characteristics of the samples are shown in Table 6. The panelists could not detect any difference in the fura samples for chewiness (the length of time required to prepare the sample for swallowing), hardness (force required to compress sample between molar teeth), and cohesiveness (extent to which sample falls apart during chewing). However, significant differences (p ≤ 0.05) existed among the samples for gumminess (denseness and cohesion persisting during mastication) and springiness (the rate at which fura returns to its original condition after deformation). The denseness and cohesion persisting during mastication for millet fura was higher when compared to the other grain fura. Maize fura was scored the lowest for gumminess and springiness.

Table 6 Mean sensory scores of textural attributes of fura from different cereal grains

Sensory texture attributes* ,#
Fura sample	Hardness	Springiness	Cohesiveness	Chewiness	Gumminess
Rice	4.4^a	4.2^a	3.6^a	4.9^a	4.4^a
Millet	2.2^a	4.1^a	4.7^a	5.2^a	4.5^a
Acha	3.9^a	3.2^a	4.5^a	5.4^a	4.4^a
Maize	3.6^a	2.8^b	3.3^a	5.1^a	2.3^b
Sorghum	2.8^a	4.2^a	3.4^a	4.3^a	2.7^b

*The maximum full scale of score is 10 cm (0 the weakest and 10 the strongest).

^#Different letters in the same column designate statistical differences (p ≤ 0.05) among samples.

Relationship Between Instrumental and Sensory Texture of Fura

Table 7 provides details of the relationship between sensory and instrumental texture of fura. Correlations between sensory and instrumental tests revealed that a significant relationship exists between springiness and gradient (r = −0.90, p < 0.05). This result agrees with that reported by Jideani.[7] Strong negative, though not significant, relationships exist between springiness and breaking stress; cohesiveness and energy per unit mass; gumminess and energy per unit mass; deformation at failure and chewiness. Correlations between the instrumental textural properties of fura revealed that significant positive relationships exist between breaking stress and gradient, firmness, energy per unit mass and hardness; and energy per unit mass and firmness and hardness.

Table 7 Relationship between sensory and instrumental textural characteristics of furaa

Texture parameter	Breaking stress	Deformation at failure	Gradient	Firmness	EPM	Instrumental hardness
Sensory hardness	0.229	−0.321	0.279	0.022	0.023	0.016
(0.711)	(0.598)	(0.649)	(0.972)	(0.977)	(0.980)
Springiness	−0.688	0.576	−0.903b	−0.564	−0.454	−0.537
(0.199)	(0.309)	(0.036)	(0.322)	(0.546)	(0.351)
Cohesiveness	−0.466	−0.488	−0.097	−0.355	−0.727	−0.343
(0.429)	(0.404)	(0.877)	(0.557)	(0.273)	(0.571)
Chewiness	0.255	−0.640	0.631	0.255	0.033	0.256
(0.679)	(0.245)	(0.254)	(0.679)	(0.967)	(0.677)
Gumminess	−0.546	−0.297	−0.298	−0.486	−0.657	−0.462
(0.341)	(0.628)	(0.626)	(0.406)	(0.343)	(0.434)
Breaking stress	1.000	0.161	0.880b	0.968b	0.954b	0.960b
—	(0.796)	(0.049)	(0.007)	(0.046)	(0.009)
Deformation at failure	0.161	1.000	−0.298	0.294	0.489	0.316
(0.796)	—	(0.626)	(0.631)	(0.511)	(0.604)
Gradient	0.880	−0.298	1.000	0.822	0.697	0.808
(0.049)	(0.626)	—	(0.088)	(0.303)	(0.098)
Firmness	0.968	0.294	0.822	1.000	0.975b	0.999b
(0.007)	(0.631)	(0.088)	—	(0.025)	(0.000)
EPM	0.954	0.489	0.697	0.975b	1.000	0.978b
(0.046)	(0.511)	(0.303)	(0.025)	—	(0.022)
Instrumental hardness	0.960	0.316	0.808	0.999b	0.978b	1.000
(0.009)	(0.604)	(0.098)	(0.000)	(0.022)

^aFigures in parentheses are significant probability values; EPM = energy per unit mass.

^bCorrelation is significant at the 0.05 level (2-tailed).

Conclusion

A good fura is a slightly elastic cohesive lump. Consumers of fura prefer to chew fura that creates a sticky feeling in the gums.[2] Maize flour gave a harder, firmer, tougher, and more brittle fura than the fura from the other cereal grains. Obviously, maize fura, being brittle, will not give the consumers the satisfaction of an elastic cohesive fura with the sticky feeling in the gums. Hence, acceptability of maize for fura production among consumers of fura may be very poor. Acha and sorghum fura have a plastic characteristic and would, therefore, be acceptable as good alternatives to millet for fura production in terms of the texture of the product.