The authors have declared that no competing interest exists.
The effects of 55-70% teff (Eragrostis tef), 20-30% sorghum (
At present
Grain sorghum (
Faba bean (
To get sufficient nutrition, cereals have been found to have nutrient potentials that could complement one another if properly processed and blended with legumes
Since, Sorghum and faba bean is less expensive in Ethiopia, there is great interest to blend with
The experimental materials such as white tef, faba bean and sorghum were collected from Debre Zeit Agricultural Research Center (DZARC); Holeta Agricultural Research Center (HARC) and Haramaya University Research Center (HURC) respectively.
The experimental design was used in this study to determine the ratio of the blends cereals (tef and sorghum) with legume faba bean, and to optimize the fermentation time using mixture design. A mixture design is appropriate when the response depends on the component proportions of the mixture and not on the component quantities. In this study the effect of three mixtures of products, namely tef (T), sorghum (S) and faba bean (F) flour was studied to determine appropriate formulation. The proportion of tef from 55 to 70%, sorghum from 20 to 30% and faba bean from 5 to 15% were used. The constrained proportion was planned after doing preliminary test. Thus to compare the blend Injera, 100 % tef flour was used
The tef, sorghum, faba bean grains was manually cleaned. Then tef grain was milled by the disk attrition mill to whole flour to the finenest level traditionally used for Injera processing at Haramaya University public grain milling house. The sorghum grain was milled after debraning using mortar and pestle. Faba bean was milled after seed coat was removed on a disc attrition mill. The flour was kept in an airtight sealed plastic bucket at room temperature
Tef, sorghum and faba bean blended injera was prepared using standard recipes. The process involved dough processing and fermentation and then baking of the batter (thin fermented dough). Prior to fermentation 1 kg of the blend flour (tef, sorghum and faba bean flour) was mixed with about 2L water and about 80 ml of
During 24 hrs fermentation, notably vigorous gas evolution and maximum dough expansion were observed. Acidic yellowish liquid on dough surface were observed during 48 hrs and 72 hrs fermentation time. The layer of the liquid was then removed. For Injera baking of dough fermented for 24 hrs, 48 hrs and 72 hrs, about 10% of fermenting dough was withdrawn for absit preparation. 10% of the fermented dough of the blend flour (for each fermentation time: 24 hrs, 48 hrs and 72 hrs) was taken and boiled at 100°C and then after the absit was cool at 46°C mixed back to the fermented dough. After the 2nd fermentation (2 to 3 hrs) injera was baked
Injera was baked after fermentation by diluting the batter slightly with water to uniform consistency. Then it was poured using circular motion from the outer perimeter towards the center, onto a hot-round smooth baking griddle called
Mineral contents such as Iron, Zinc and Calcium of both control and blended injera samples were carried out using the method
In order to determine consumer acceptability of tef, sorghum and faba bean blended injeras, a sensory evaluation was conducted. A total of 50 male and female panelists were selected from Haramaya University Food Science and Postharvest Technology staffs and students, who have knowledge on sensory analysis.
At least a triplicate data were analyzed and modeled using the statistical software JMP™ 8, 2008 (by SAS Institute Inc., Cary, NC, USA). Mixture response surface methodology was applied to the experimental data using JMP version 8. A polynomial equation was fitted to the data to obtain a regression equation. Statistical significance terms in the models were identified. Summary of fit, ANOVA, lack of fit and parameter estimates were generated by the JMP 8. Data were also analyzed by ANOVA and mean comparison was done using Duncan’s Multiple Range Test (DMRT) by SAS 9.1.3. Significance was judged if the probability level of the
The effect of tef, sorghum and faba bean blending ration and fermentation time had significant (P<0.05) effect on the proximate composition of the blend Injera.
The iron content of the blend injera made by blending sorghum and faba bean flour in to tef flour was shown in
The control 100% tef injera had the lowest iron content 18.83 mg/100 g as compared to the blend injera.The result has shown that the addition of more faba bean and sorghum flour into tef flour is important to boost the iron content of the blend injera as compared to the control (100% tef injera). All the interaction terms (tef and faba bean) and (tef and sorghum) had significant (P<0.05) effect on the iron content of the blend injera. Thus, when the proportion of faba bean and sorghum flour increased in the mixture the iron content was also increased. The following model (Eq. 1) was developed to predict the iron content.
Fe=0.253T+0.219S-1.869FB-0.008(T*S)-0.028(T*Fb)+0.134FTx (1)
Where Fe = predicted iron (mg/100g), T =the proportion of raw tef flour (%), S =is the raw sorghum flour (%), and FB =is the raw faba bean flour (%), and FT x = is the batter fermentation time at (x=24, 48 and 72hrs).
When the proportion of tef, sorghum, and faba bean flour and fermentation time substituted into equation 19 the predicted iron content would be determined. For example the predicted value of the blend injera obtained by blending 15% faba bean and 30% sorghum into 55% tef flour was 22.22%, which is equivalent to the actual data (22.66±4.48). This indicates that the model was sufficient enough in describing the data.
The shaded region of
The zinc content of the blend injera was shown in
The addition of both sorghum and faba bean flour in to tef flour had significantly (P<0.05) increased the zinc content of blend injera. This might be attributed to more zinc content in faba bean and sorghum flour. The interaction effect of sorghum and tef had no significant (P>0.05) effect on the zinc content of the blend injera. This indicates that the blend of sorghum and tef flour has not an important contribution for the increment of zinc content. However, the interaction effect of tef and faba bean had a significant (P<0.05) effect on the zinc content of the blend injera.
With respect to fermentation time, the zinc content of the blend injera was significantly (P<0.05) affected by fermentation. By increasing the fermentation period there was a gradual increase in zinc content. This is due to the reduction of antinutritional factors present in the raw flour. The model used to predict zinc content was presented in the (Eq. 2) as follows.
Zn=0.312T+1.678S-1.438Fb-0.029 (T*S)+0.021(T*Fb)+0.115FT x (2)
Where: Zn is zinc predicted (mg/100g), T is the proportion of raw tef flour (%), S is the proportion of raw sorghum flour (%), FB is the proportion of raw faba bean flour (%), and FT x is the batter fermentation time at (x= 24, 48 and 72 hrs)
The range of tef, sorghum and faba bean was depicted in the shaded region of the contour plots (
The calcium content of the blend injera was shown in
All fermentation time had a significant (P<0.05) effect on the calcium content of the blended injera. Thus, fermentation had significantly (P<0.05) increased the calcium content of the blend injera. This is probably due to fermentation, which reduces the content of antinutritional factors such as phytates and tannins and is therefore likely to enhance mineral absorption
Ca=1.829T+5.456S+1.409Fb-0.086 (T*S) + 0.115 (T*Fb)+0.508 FT x (3)
Where: Ca is calcium predicted (mg/100g), T is the proportion of raw tef flour (%), S is the proportion of raw sorghum flour (%), FB is the proportion of raw faba bean flour (%), and FT x is the batter fermentation time at (x= 24, 48 and 72 hrs).
The range of tef, sorghum and faba bean was depicted in the shaded region of the contour plot (
The condensed tannin of the control and the blend was presented in
The result revealed that fermentation time had a significant (P<0.05) effect on the tannin content of the blend
CT=-0.056T-0.347S+0.372FB+0.0069(T*S)-0.0034(T*FB)-0.0007FTx (4)
Where: CT is predicted condensed tannin (mg catechin eq/kg), T is the proportion of raw tef flour (%), S is the proportion of raw sorghum flour (%), and FB is the proportion of raw faba bean flour (%), and FT x is the batter fermentation time at (x=24, 48 and 72 hrs).
The range of tef, sorghum and faba bean was depicted in the shaded region of the contour plot (
The phytic acid content of the blend injera was shown in
BlendingRatio | FT | Fe (mg/100g) | Zn(mg/100g) | Ca(mg/100g) | Tannin(mg/kg) | Phyticacid(mg/100g) |
55% T +30% S +15% FB | 24 h | 16.74±0.04h | 18.33±0.04g | 172.89±0.01d | 0.606±0.00a | 203.86±0.03f |
48 h | 17.62±0.02g | 21.44±0.04d | 173.17±5.79c | 0.595±0.00c | 174.99±0.00j | |
72 h | 22.66±4.48a | 23.81±0.01a | 187.25±0.02a | 0.581±0.00e | 120.76±0.02o | |
65% T +20% S +15% FB | 24 h | 15.34±0.01j | 18.14±0.05h | 166.44±0.02g | 0.603±0.00b | 208.65±0.03e |
48 h | 16.45±0.01i | 21.35±0.01e | 170.26±0.04f | 0.584±0.00d | 195.59±0.28g | |
72 h | 21.65±0.05b | 22.88±0.01b | 182.57±0.02b | 0.576±0.00f | 140.12±0.01k | |
65% T +30% S +5% FB | 24 h | 11.56±0.04m | 15.66±0.04j | 129.55±0.02l | 0.110±0.00g | 190.56±0.01h |
48 h | 13.73±0.04k | 21.15±0.04f | 152.42±0.02j | 0.074±0.00i | 132.56±0.05l | |
72 h | 18.55±0.01f | 21.75±0.03c | 170.43±0.02e | 0.066±0.00j | 124.54±0.02n | |
70% T +20% S +10% FB | 24 h | 13.44±0.03l | 17.85±0.04i | 149.56±0.01k | 0.098±0.00h | 290.84±0.02b |
48 h | 16.76±0.02h | 21.13±0.02f | 165.45±0.04h | 0.066±0.00j | 179.73±0.02i | |
72 h | 18.83±0.01e | 21.75±1.79c | 162.25±0.01i | 0.061±0.00k | 130.65±0.04m | |
Control | 24 h | 18.83±0.04e | 14.27±0.03m | 123.86±0.04o | 0.015±0.00l | 295.46±0.03a |
48 h | 19.05±0.01d | 14.55±0.03l | 126.97±0.03n | 0.008±0.00m | 282.24±0.04c | |
72 h | 19.18±0.01c | 14.66±0.02k | 136.86±0.03m | 0.008±0.00m | 234.46±0.03d |
Values in the column are means of three replicates and same column with different letters are significantly different at 0.05 probability level according to Duncan Multiple Range Test. T - Tef, S - Sorghum, FB - Faba bean, FT - Fermentation time, h – hours, Control - 100% Tef flour.
There were also significant differences between fermentation time (P<0.05) on phytic acid content of the blend injera as well as the control injera. The highest phytic acid (295.46mg/100g) was obtained at 24h while the lowest phytic acid was obtained at 72 hours.This might be attributed to enzymatic hydrolysis of phytic acid by endogenous phytase of sorghum and/or by phytase, which was produced by the microorganism, may account for most of the reduction of phytic acid during fermentation
The results also found that fermentation time had a significant reduction effect on the phytic acid content of the blend
PA=11.835T+50.38S-29.96Fb-1.019(T*S)+0.268 (T*FB)-1.713FTx (5)
Where: PA is predicted phytic acid (mg/100g), T is the proportion of tef flour in percent (%), S the proportion of sorghum flour in percent (%), FB is the proportion of faba bean flour in percent (%), and FTx is batter fermentation time (x=24, 48 and 72 hrs).
The range of tef, sorghum and faba bean was depicted in the shaded region of the contour plot (
Sensory evaluation is used in food science to objectively analyze food quality through the evaluation of the attributes traceable by one or more of the five human senses— taste, smell, touch, sight, and hearing
In the current study, a panel of 50 judges was used to describe the degree of consumer acceptance and satisfaction to the injera prepared using different combinations of teff flour combined with sorghum and faba bean flour, and fermentation time. Fermentation time and Blending of tef, sorghum and faba bean had a significant (P<0.05) effect on the sensory acceptability of the blend injera. Acceptability test result for flavor, aroma, sourness, color, appearance and rollability of the control and blended injera product was given in
The addition of faba bean and fermentation time had a significant (P<0.05) effect on the rollability of the blend injera. Rollability is associated with the less staling property of the baked product. The staling in the product will increase crumb firmness and deterioration of the baked product during storage
Sourness is the sharp acidic taste of fermented foods. The blending ratios and fermentation time caused significantly (P˂0.05) differences on sourness; Injera from 70% tef with 20% sorghum and 10% faba bean exhibited the highest acceptability scores of 6.96 followed by 6.84 was obtained from the injera containing 65% tef, 30% sorghum and 5% faba bean fermented at 24 hrs respectively (
A strong, pleasant smell (odor) usually from food is called as aroma and is sensed by receptors in the nose. The highest scores of aroma were 6.94 belonged to
Flavor is the sense of taste and smell combined. Taste of injera is associated with the sensation of saltiness, sweetness, sourness and bitterness triggered in the mouth by contact with the injera
The color of injera also affects the consumer acceptability of the injera. People mostly prefer the white color injera is consumed as a staple food
The appearance of injera is one of the most important parameters, which refers to the quality of the eyes and underneath the appearance of injera. The eyes of injera are the honeycomb-like structure of the top surface formed during cooking due to escaping CO2 bubbles
The maximum acceptability scores recorded for underneath appearance of the
Based on the present findings, the addition of sorghum and faba bean with tef, and fermentation time significantly increased sensory score of rollability, sourness, aroma, flavor and underneath the appearance, and decreased the score color and eyes formation of injera. All blends scored a mean rating well above average, which is an indicative of the goodness as products (
The injera made from 55% tef with 30% sorghum and 15% faba bean had the maximum amount of moisture, protein, ash, fiber, iron, zinc and calcium content. The high amount of ash, fat, fiber, carbohydrate, energy and sensory score were obtained from 70% tef, 20% sorghum and 10% faba bean blended injera. Significant (P<0.05) increased in moisture, protein, iron, zinc, calcium and sensory attributes were shown on long fermentation time (72 hrs). However, ash, fat, fiber, carbohydrate and energy were shown at short fermentation time. On the two dimensional mixtures contour plot the optimum value of chemical composition of injera was observed when 55% tef, 30% sorghum and 15% faba bean were blended and fermented at 72 hrs.
The present findings revealed that the optimum value of all chemical composition and sensory acceptability of blended injera was obtained when 30% sorghum and 15% faba bean were mixed in to tef flour and fermented for 72 hrs. The blending of sorghum and faba bean with tef is not only increased the nutritional properties and sensory acceptability of injera and also reduces the utilization of expensive cereal such as tef for injera making. Generally, this study demonstrated the potential of incorporating sorghum and faba bean flour into sour bread injera, thereby creating opportunity for food producers to provide more healthy nutritional enriched products.
Great deal thanks to MOE for granting us financial support. We also thank Holeta Agricultural Research Center for providing us faba bean. Heartfelt thanks go to Shewangezaw Teketel and Dechasa Bersissa for their technical support and assistance during laboratory work. I would like to appreciate all the staff and department of Food Science and Postharvest Technology, Haramaya University for providing us all the necessary services. Center of Research on Grain Quality, Processing and Technology Transfer (CRGQPTT) at the Food Science and Postharvest Technology department, Haramaya University is acknowledged for supporting with facilities.