Effect of Acha (Digitaria exilis) Grain Flour on the Physico-Chemical and Sensory Properties of Bread

Abstract

Different levels of acha (Digitaria exilis) grain flour (0–100%) were mixed with wheat flour (golden penny) and other ingredients (1.0 g salt, 2.5 g fat, 1.5 g yeast, 12.0 g sugar, and 56.0 g water, per 100 g of flour) fermented, molded, pan-proved and baked to produce bread. The baked products were evaluated for loaf volume, moisture content, and sensory qualities (taste, odor, color, texture, outward appearance) and compared with bread made from 100% wheat flour. The water absorption and the amylograph unit of the flour and dough increased from 0.66 to 2.27 and decreased from 2405 to 1460 Au, respectively. The loaf volume index decreased from 4.19 to 1.62 and moisture content increased from 31.1 to 44.45% with increasing acha grain flour (0–100%). The sensory mean scores for the taste, odor, color of crust, color of crumb, texture of crumb and outward appearance decreased from 7.8 to 2.95, 7.35 to 3.5, 6.60 to 2.70, 7.70 to 2.95, 7.65 to 2.90 and 7.95 to 2.2, respectively. Generally, addition of more than 30% (w/w) acha grain flour caused a significant difference (p ≤ 0.05) in the evaluated qualities and product poorly.

Keywords:

• Acha
• Flour
• Physico-chemical
• Sensory
• Bread

Introduction

The tendency to eat bread is increasing among populations in many parts of the world even where previously bread was not an item of daily diet. This is due to increase in population, urbanization and the convenience factor of bread. Many tropical countries in Africa can no longer afford to pay for wheat or wheat flour—the base ingredient in bread. This has caused the price of bread to increase over 400% and ceased to be a common man's food it once used to be in some African countries.1

Indeed, Nigeria obviously has to proceed at a much faster pace in order to redress the very grave situation implied by the current virtual dependence on imported raw materials.2 Many of the under-utilized food crops indigenous to the third world areas, particularly Nigeria are neglected by researchers and policy makers.3 They may however be of great potential particularly in improving the quality of our foods, hence the nutrient intake of the populace.

Acha, (Digitaria exilis) also known as Fundi, fonio, Hungry rice, Fonio blanc and Petit mil, is a grass indigenous to West Africa.4 5 6 7 Acha, though neglected, is probably the oldest African cereal.6 Lacking the interest and support of authorities (most of non-African colonial authorities, missionaries, and agricultural researchers) the local grain; acha could not keep pace with the up-to-the minute foreign cereals, which were made especially convenient to consumers by the use of mills and processing. The old grains languished and remained principally as the food of the poor and rural areas.6

The proteins [8–11%] in acha grains are not easily extractable however, their digestibility are better than those of sorghum and millet. It is among the most nutritious of all grains because they are rich in methionine and cysteine.1 8 9 The high levels of residue protein in it may have important functional properties. Acha is also among the world's best cereal, which has good taste.6 This combination of nutrition and taste has outstanding potentials for the acha. It is known that products based on intact cereal kernel evoke small increase in blood glucose. Millet is also known to contain a relatively high proportion of unavailable carbohydrate and the release of sugar from millet based diets.10 These factors could be best utilized in developing special foods for diabetics.11 Acha showed a high water absorption capacity,12 a property that could be linked to appreciable amounts of pentosans.22 Acha contains 33 g/kg pentosan.13 The high water absorption capacity of acha could be utilized in baked goods. However, bread making with acha has not been investigated.11 This research, as a preliminary work, is aimed to examine the effect of acha on the physical and sensory properties of bread.

Materials and Methods

The acha (Digitaria exilis) grain was purchased from Jos, Nigeria, while wheat flour (golden penny), yeast, (Ferminpan Instant), baking fat (Holsum-Lever Brothers PLC), salt and sugar were purchased from Wunti market—Bauchi, Nigeria.

Preparation of Materials

The acha grain was washed (using tap water), de-stoned (manually using sedimentation method), dried (carbinet—APV-drier at 50°C for 3 h); milled (Hammer mill), and sieved (0.4 mm sieve aperture) to obtain acha flour, packed heamatically in polythene bags till usage.

Preliminary Investigations

The moisture, protein content, water absorption capacity, and the gelatinization characteristics (amylogram) of the wheat and acha grain flour were determined. Also the water absorption of the composite flour and its amylogram were evaluated. The moisture content was determined using FDA method.14 Two grams of the acha–wheat composite samples were oven dried at 105°C for 3 h and the weight difference determined. The protein content was determined using AOAC method.15 Water absorption capacity was estimated using the method described elsewhere.16 Two (2.0 g) gram of the flour was weighed and 10 mL of deionized water was added. The mixture was periodically stirred manually by swirling, in a centrifuge tube for 30 min. The contents were centrifuged for 15 min at 8500 rpm, decanted and the difference in weight of sample estimated as the water absorption capacity. The amylograms was evaluated by mixing 80.0 g of the acha and acha–wheat composite flour samples with 450 mL distilled water and poured into the amylograph bowl (Brabender, DGH, Duisburg, Germany) under constant stirring and at a constant temperature of 1.5°C per minute (from 30 to 90°C).

Production of Acha–Wheat Flour Composite Bread

The straight Dough method16 17 and the recipe shown in Table 1 was used in producing the dough. The dough was baked at 200°C in an Air-Rotary (BCH) oven for 15 min, cooled down to room temperature (32°C) and packed in a polythene bag until usage.

Table 1 Acha-wheat flour composite bread recipe

	Samples
Ingredients	A	B	C	D	E	F	G
Wheat floura (g)	200	180	160	140	120	100	—
Acha grain flourb (g)	—	20	40	60	80	100	200
Water (mL)	104	104	104	104	104	104	104
Salt (g)	2	2	2	2	2	2	2
Sugar (g)	24	24	24	24	24	24	24
Fat (g)	5	5	5	5	5	5	5
Yeast (g)	3	3	3	3	3	3	3

^aMoisture content 9.6%, protein content 9.8%.

^bMoisture content 9.2% protein 8.1%.

Methods

Loaf Volume/Loaf Volume Index

The mass of the bread was determined and the respective volume estimated using seed displacement method. A rectangular wooden box was used. The box was filled with cleaned millet grams, leveled, and poured out. The bread was placed in the same box and filled with the measured millet grain and leveled. The volume of the remaining grains from the same measured grains was taken as the volume of the loaf. The loaf volume index was calculated using a standard formula.3

Moisture Content

The moisture content of the bread was determined using FDA and calculated on dry weight basis.14

Sensory Qualities Assessment

The sensory evaluation of the baked acha–wheat composite bread was carried out for consumer acceptance and preference using twenty (20) untrained judges randomly selected (students and staff of the Dept. of Food Science and Technology, Federal Polytechnic, Bauchi) using a nine (9) point Hedonic Scale (1 and 9, representing extremely dislike and extremely like, respectively). The qualities assessed included—taste, odor, color (crust and crumb), texture (crumb), outward appearance, and overall acceptance. Coded samples of the same size, at the same temperature (32°C) were served in a white colored plate of the same size to judges in each panel cupboard under the florescent light. Each of the booths was painted white with ceiling fan, under the same temperature. Only one sensory attribute was tested in one sitting. Data collected were subjected to Analysis of Variance.17 Unless otherwise mentioned, all the measurements were made in triplicate and the values represent the average of three.

Results and Discussion

Preliminary Observations

The moisture and protein contents of the wheat and acha grain flours were 9.6, and 9.8, 9.2, and 8.1 (kg/100 kg flour), respectively. The protein content of the wheat flours agrees with earlier reports on Nigerian wheat flours of range values 9–14.5%.19 20 The protein content of acha is slightly lower than that (7.6–8.5%) observed by Lasekan13 and Jideani.11 This could be due to the influence of some environmental and soil factors as also observed by Babalola and Babalola.20 The water absorption capacity of the acha–wheat composite flour increased 0.66–2.27 with increase in the percentage of added acha grain flour as shown in Table 2. The increase in the water absorption capacity could be due to the substantial amount of pentosan (33 g/kg) in acha grain flour as earlier substantiated by Lasekan13 and Hoseney.21 The higher water absorption capacity in 100% acha (2.27) than that of wheat flour (0.66) could be due to lower pentosan (2 g/kg) and the presence of polymeric pentose sugars rather than hexose sugar in wheat flour.23 The gelatinization characteristics as revealed by the amylogram showed a decrease from 2405 to 1460 Au and increase in the gelling temperature (62.5–70.2°C) with increasing the added acha grain flour (0–100%). The value 1460 Au for 100% acha grain flour agrees with Jideani et al.23 The increase in the gelling temperature could be due to the high amylopectins (59.3–70.3%) from acha starch.25 26 The increase in the gelling temperature could also help in increasing the amount of moisture absorbed as observed (Table 2). The long chain component of amylopectin has been found to increase gelling temperature, viscosity etc.27 These properties are important for use in food products and industrial applications of starch. The decrease in the amylogram (2405–1460 Au) could be due to the poor quality protein in acha which could not form a similar complex as with gluten on hydration.

Table 2 Effect of acha/wheat flour on the physical quality of bread

	Physical properties of acha–wheat composite flour
	Wheat–acha composite flour			Wheat–acha composite bread
Acha grain flour (%)	Water absorption capacity	Gelling temp (^oC)	Amylograph unit	Moisture content	Specific volume
0	0.66 ± 0.01	62.5	2405	31.1 ± 4.2	4.19 ± 1.10
10	0.95 ± 0.01	62.8	1850	31.8 ± 3.5	3.89 ± 1.10
20	1.02 ± 0.05	63.8	1740	33.8 ± 4.2	3.51 ± 0.75
30	1.17 ± 0.08	65.4	1690	34.4 ± 4.6	3.30 ± 0.80
40	1.20 ± 0.55	68.2	1600	38.8 ± 6.1	2.79 ± 0.50
50	1.26 ± 0.05	68.8	1600	40.2 ± 5.0	2.50 ± 0.45
100	2.27 ± 0.85	70.2	1460	44.5 ± 3.1	1.62 ± 0.46
LSD (0.05)a	0.25	—	—	3.5	0.75

^aMean values with difference equal to or greater than the corresponding LSD in the same column is significantly different at p ≤ 0.05.

Effect of Acha Grain Flour on Physical Qualities

Loaf Volume Index

The loaf volume index of the acha–wheat composite bread decrease from 4.19 to 1.62 with increase in the percentage of acha grain flour (0–100%) as shown in Table 2. There is a strong but negative correlation relationship (r = −0.95) between the acha grain flour and the loaf volume index of the acha–wheat composite bread. The effect was significant (p < 0.05) at above 30% added acha grain flour. The decrease in the loaf volume index (4.19–1.62) with increase in the acha grain could be due to poor rheological property of the dough and baking quality of the inherent proteins of the acha flour. The high positive correlation coefficient (r = 0.94) between the loaf volume index and that of amylogram of the acha–wheat composite flour agree with the poor quality of the inherent protein.

Acha grain flour has a relatively lower effect on the loaf volume of bread, compared to that of amaranth grain flour with similar size compactness of grain, with poor baking quality protein. These findings agree with the earlier report on amaranth.3 The loaf volume indices of acha–wheat and amaranth–wheat composite bread at 50% addition of flour were 2.50 and 1.90 respectively. The difference could be due to the high content of pentosan (33 g/kg flour) in acha grain flour.13

Moisture Content

The moisture content increased from 31.1 to 44.5% with increase in added acha grain flour (0 to 100%) in the composite bread as shown in Table 2. The moisture content of the acha–wheat composite bread had a high correlation coefficient of r = 0.90, r = 0.87 with added acha grain flour and the water absorption capacity of the composite flour, respectively. The increase in moisture content of the composite bread could be due to the increase in the pentosan content of the acha flour,13 extremely small particle size of the flour6 8 as increase in the surface area of particles improves moisture absorption.28

Effect of Acha–Grain Flour in Sensory Properties

Taste and Odor

The mean scores for the taste and odor of the acha–wheat composite bread decrease from 7.8 to 2.95, and 7.35 to 3.5, respectively, with increase in the percentages of added acha flour (0–100%) as shown in Table 3. The effect was significant (p < 0.05) at above 30% added acha flour for the two attributes (taste and odor). The unacceptable effect at above 30% added acha flour could be due to characteristic flavor of acha.6

Table 3 Effect of acha grain flour on the sensory properties of bread

	Sensory quality
Acha grain flour (%)	Taste	Odor	Color of crust	Color of crumb	Texture of crumb	Outward appearance	General acceptance
0	7.8±0.9	7.35±0.7	6.60±0.9	7.70±1.1	7.65±1.2	7.95±0.9	7.95±0.8
10	7.55±0.9	7.0±1.1	5.95±0.9	7.50±1.0	7.25±1.0	7.6±0.9	7.70±0.7
20	6.95±0.8	6.40±0.9	5.91±0.8	6.85±0.9	6.55±1.0	7.0±1.0	7.05±1.0
30	6.55±1.1	6.10±0.9	5.10±0.5	6.95±0.7	6.10±0.85	6.95±0.9	6.60±0.7
40	6.15±0.9	5.6±0.4	4.95±0.3	6.00±0.5	5.15±0.8	6.25±0.7	5.60±0.6
50	5.65±0.4	5.50±0.3	4.30±0.4	5.5±0.7	4.35±0.6	5.2±0.6	4.30±0.6
100	2.95±0.3	3.5±0.4	2.70±0.3	2.95±0.5	2.90±0.5	2.2±0.3	2.49±0.5
LSD (0.05)a	1.30	1.30	1.76	1.10	1.10	1.30	1.85

^aMean scores with difference equal to or greater than the corresponding LSD in the same column is significantly different at p ≤ 0.05.

Color (Crust and Crumb)

The mean scores for the color of the crust and that of crumb decreased from 6.60 to 2.70 and 7.70 to 2.95, respectively, as shown in Table 3. The decrease was significant at above 40% and 30% added acha flour for the crust and crumb respectively (p ≤ 0.05). The low mean scores of the crust at high percentage of acha could be due to poor color development–pale white as a result of too high moisture content which do not favor Browning reaction. The relative high mean scores for the color of the crumb could be due to the cream color of the acha grain flour which is similar to that of wheat normally used for bread production.

Texture (Crumb)

The mean scores of the crumb texture decreased from 7.65 to 2.90 with increase in the added acha grain flour (0–100%). The effect was significant (p < 0.05) above 20% added acha grain flour. The decrease could be due to development of closed or collapse crumbs as a result of too rising of the dough prior to baking. The absence of gluten-protein has been identified to cause poor formation of the crumb.29

Outward Appearance

The mean scores of the outward appearance of the acha–wheat composite bread decrease from 7.95 to 2.2 with increase in the acha grain flour (0–100%). The effect was significant at above 30% added acha grain flour (p ≤ 0.05). The means score of the outward appearance has a high positive correlation relationship of r = 0.91 and r = 0.88 with the volume index and means score of the crust color, respectively. The two qualities (loaf volume and crust color) have been noted to determine the acceptability of bread at foresight.

Conclusion

Acha grain flour has effect on the physical and sensory properties of acha–wheat composite bread. The acha grain flour can be used up to 30% in the production of acha–wheat composite bread without any significant effect. In this blend the high methionine and cysteine content of acha grain could improve the protein quality of the bread. A follow up work to improve the rhelogical properties of the acha grain flour could produce 100% acha bread.