Food Sci. Technol. Res., 16 (6), 593–598, 2010

Quality Characteristics and Acceptability of Bread Produced with Supplementation

of Dolichos lab lab Beans

C.N. kunyanga* and J.K. iMungi

Department of Food Science, Nutrition and Technology, College of Agriculture and Veterinary Sciences, University of Nairobi, P.O. Box 29053-00625, Nairobi, Kenya

Received January 9, 2009; Accepted July 31, 2010

The viability of production of good quality and acceptable bread with substitution of wheat flour with Dolichos lab lab (Lab lab purpureus) was investigated. The bread was analyzed for protein, moisture, gen-eral bread quality and sensory properties. The protein content of bread was elevated by up to about 20% and the moisture content reduced by about 10% without significant changes in bread taste, odor, volume and general bread quality. Substitution levels of up to 10% produced bread with quality characteristics not significantly different from the control. Sensory evaluation showed no significant differences between the control bread and the Dolichos supplemented breads up to 15% in the sensory attributes of aroma, crumb appearance, texture, crust colour, loaf shape, taste and general acceptability (p < 0.05). The crumb colour changed from creamish white to dull brown and a gradual hardening of crumb texture was ob-served as the addition of Dolichos lab lab bean flour increased. Above 15% substitution levels, the accept-ability declined because of the compact texture of the crumb and the strong beany flavor of the product. Results indicate that acceptable breads can be produced by substitution of up to 15% wheat flour with dolichos bean flour.

Keywords: Dolichos lab lab, wheat flour substitution, bread quality, sensory evaluation

*To whom correspondence should be addressed.E-mail: nkirotekatie@yahoo.com

IntroductionBread is becoming increasingly important in the diets of

Kenyans. The demand and consumption are steadily increas-ing. The high population growth rate has contributed to the high demand. However, the relatively high cost of the loaf makes it unaffordable by the low social economic group of the population. The high cost of bread is due to the fact that Kenya does not produce sufficient wheat and has to rely on importation to meet the demand deficit. Also the wheat flour is extensively demanded for use at the domestic level for preparation of chapatti (unleavened bread) and both at the domestic and commercial levels cakes, biscuits, cook-ies, mandazi (buns) and other baked goods. Wheat flour is again used industrially in the fiberboard and plywood industry. Studies have been carried out in Kenya to produce composite flours for production of bread and other baked goods. In these composites, flours of root crops like cas-

sava (Imungi and Onyango, 1990; Onyango et al., 1993) and potatoes (Kabira and Imungi, 1991) and cereals like maize have partially replaced wheat flour. In other places high pro-tein legumes flours have been used in similar replacements (Dhingra, 2002; Eggleston et al., 1992; Giami et al., 2004). Studies on the incorporation of non-wheat flour into wheat breads actually date as far back as the First World War (Mu-nyiri, 1993). Available information on composite bread tech-nology, however, indicates that at least 65-70% wheat flour is required in order to get good loaf volume (Eggleston et al., 1992). The great urge to provide adequate and quality protein in diets has led to attempts to incorporate vegetable proteins into wheat flour for bread manufacture. Legumes are the richest sources of plant proteins. They are also rich in car-bohydrates, dietary fiber and minerals also required in diets worldwide. In Kenya, legumes are grown and consumed by all communities and therefore their tastes are familiar. They are used to provide variety to diets, but also act as the main sources of proteins and some vitamins in diets. Dolichos lab lab (also known as the horse bean or the black bean) is one

equivalent of flour. It was molded into pans of about 30 cm and proofed for 70 min in a fermentation chamber at 32 ± 1℃ and 80% relative humidity. The breads were baked for 15 min at 240℃. The loaves were cooled overnight and stored in plastic bags to await the analyses.

General bread quality Breads fortified with different levels of Dolichos lab lab flour were baked with the same scaling weight (350 g), fermentation times, and baking times. Bread weight was determined and volumes were measured by rapeseed replacement method. This information was used to calculate the specific loaf volumes. For evaluation of gen-eral appearance (break and shred, crust and crumb color), grain and texture, and flavor the breads were given to a sen-sory panel of 12 food technologists.

Sensory evaluation The sensory attributes, including break and shred, color of crust and crumb, symmetry of form, texture, taste, aroma, and the general acceptability were ana-lyzed in triangular tests using a panel of 10-12 individuals consisting of food technologists. All panelists were familiar with the sensory evaluation procedures of foods. The breads were sliced mechanically to12 mm thickness. The slices were placed in coded plastic petri dishes for presentation to the panelists. Drinking cold water (23℃) was used for rins-ing the mouths after each tasting. For testing off-flavor, the bread samples were cut into approximately 1 cm cubes and stored in 200 mL covered glass jars at 37℃ for 30 min before presentation to the panelists. All the sensory evaluation tests were carried out in a room having individual compartments for each panelist and normal electric lighting was used.

A hedonic test was conducted to determine consumer degree of liking of the bread samples using a 7-point hedonic rating scale with 1 = like very much and 7 = dislike very much. After evaluation of the samples, the descriptive scales were converted to numerical scores and the mean scores calculated. The mean scores were tabulated and an analysis of variance carried out for each attribute to determine the differences, while the least significant test was used to detect differences among the means.

Test for beany flavor as off-flavor Ten previously trained panelists used the triangular test procedure for testing for beany flavor by comparison with all wheat bread. Verbal description of off-flavors of coded samples was given by the panelists. Breads were sliced approximately 21 h after bak-ing. The 11 centre slices were labeled with three-digit ran-dom numbers, placed in cellophane bags, closed with staples and distributed to the panel members for evaluation. Panel members were instructed to refrain from eating or smoking for 30 min before tasting, rinse their mouths before tasting, wash their hands, dim overhead lights, sit in a comfortable position and sample only the center bread crumb.

of the most common and popularly consumed legumes in Kenya. The bean is highly prized for the high quality of its protein. Analyses have shown the bean to be rich in protein, thiamine, niacin, calcium, iron, carbohydrates and energy with a Biological Value of 40-50 (Deka and Sarkar, 1990; Salimatha and Tharanathan, 1982). The legume has average protein content of 26% and starch content of 48% as well as fiber carbohydrates. This study was therefore designed to produce acceptable breads by partial substitution of wheat flour with dolicos lab lab bean flour to enhance the protein quantity and quality.

Materials and MethodsMaterials Commercial wheat flour was purchased

from the supermarkets in Nairobi. The flour had a moisture content of 14.0% and protein content of 13.4% (db). Two commercially grown varieties of Dolichos lab lab beans were purchased from open air markets in Nairobi.

Preparation of Dolichos Bean Flour for bread The Dol-ichos lab lab beans were processed by destoning and clean-ing manually. About 1 kg were placed in a pressure cooker, water added to just cover them and cooked for 30 min. The cooking was interrupted and sodium carbonate (Na2CO3) was added to the beans at the rate of 2 g per 100 g, then cooked for further 30 min. The cooking water was decanted, then the beans were cooled by flooding with cold tap water. They were then soaked in tap water overnight with bean to water ratio of 1:10 (w/v). The soak water was drained. The beans were then dehulled by rubbing between hands hulls sepa-rated from the beans. The hulls amounted to about 18% of dry weight of the beans. The beans were then dried at 60℃ to a moisture content of about 13% and milled into flour (Mill model 290, Merck, Germany). The flour was screened using a 0.1 mm sieve to obtain fine flour within the similar particle size distribution as the wheat flour.

Formulation and baking of the bread Four blends of wheat flour and Dolichos lab lab flour were prepared by mixing wheat flour and Dolichos lab lab bean flour in the proportions of 95:5, 90:10, 85:15 and 80:20 using a kitchen food processor. The four blend formulations were used to bake breads using the straight dough method (Chuahan et al., 1992). A simple baking recipe with the following ingre-dients was followed: wheat flour or blend 1020 g, water 600 mL, Yeast 10 g, sugar 10 g, shortening 12.5 g and Sodium chloride 15 g. The dough was mixed for 1 min and for 8 min at speed 2 in a mixer (mcDuffy bowl and hook, Nairobi). Dough temperature was adjusted to 28 ± 0.5℃. The dough was fermented for 45 min followed by knock back and thereafter fermentation was carried out for a further 20 min. The dough was then scaled to 550 g, corresponding to 100 g

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Salimatha and Tharanathan, 1982). This high protein content in the Dolichos lab lab supplemented breads would be of nutritional importance in most developing countries, such as Kenya, where majority of the people can hardly afford high proteinous foods due to their high costs. Soaking increased the moisture content. Cooking of the beans showed no sig-nificant difference in moisture content as compared to the raw. The protein content was similar to that reported by Al Othman (1999) but higher than those reported by Ahmed and Nour (1990). Soaking and cooking significantly decreased the protein content. The decrease in protein content during soaking and cooking might be attributed to the leaching of soluble proteins. The protein loss may nevertheless, be sig-nificantly reduced by heat treatment or conditioning of the beans in hot water or alkali solutions.

Soaking in hot water can also increase the water absorp-tion ratio thus resulting in decreased cooking times. Studies have shown that the antinutritional factors level of these beans shows that the trypsin inhibitors activity level ranges from 11.8 to 29.0 TIA/g, tannin content of untreated lab lab bean has been reported to be high and the phytic acid level varied from 100.0 to 313.4 mg/100 g (Devaraj and Man-junath, 1993; Deka and Sarkar, 1990; Al Othman, 1999; Ahmed and Nour, 1990). Generally, adequate heat processing inactivates the trypsin and chymotrypsin inhibitors (Osman et al., 2002). Heat stable compounds in cereals and legumes are easily removed after soaking, germination and fermenta-tion (Reddy et al., 1985; Osman, 2004).

General bread quality and sensory evaluation The mean sensory scores obtained for the Dolichos lab lab supplement-ed breads and whole wheat breads ranges between 1.9 and 4.2 (Table 3). The analysis of variance (ANOVA) showed that the whole wheat breads did not differ significantly from the 5-10% Dolichos lablab supplemented breads (p < 0.05) in the sensory attributes of flavor and aroma, color of crust, color of crumb, internal texture, and general acceptability. However, at higher Dolichos lab lab flour supplementation (20% and above), varying significant differences occurred

Analytical methods The chemical composition in-cluding moisture and protein contents were determined by AOAC methods (AOAC, 1984). Moisture content was deter-mined by drying about 5 g, weighed accurately in aluminium dishes for 60 min at 130℃. Protein was determined as total nitrogen by the Kjeldahl method. The percent nitrogen was multiplied by empirical factors 5.38 and 6.25 to convert the percent nitrogen in breads and composite flours, and the per-cent nitrogen in dolichos bean flour respectively to percent protein.

Data analysis Results obtained during the sensory evaluation tests and the analyses of the actual samples were analyzed separately by analysis of variance (ANOVA) to study the effects of samples and judges. The mean scores and standard deviations of different sensory properties were also analyzed and tabulated in the results. To check the reproduc-ibility of the panel, we analyzed the data collected in a pre-liminary session with four different bread samples replicated three times. Descriptive analysis by the panelists (assessors) was used to compare the sensory properties of the bread samples. The assessors were selected for detection of tastes, odours, flavors and physical characteristics, as well as for the use of classification scales or scores. This was done to ensure excellent data quality.

Results and DiscussionChemical composition and protein content The chemi-

cal composition, protein and moisture content results of the Dolichos lab lab supplemented bread samples are shown in Tables 1 and 2. The bread produced from 20% Dolichos lab lab blends had the highest crude protein of 14.4% (DM). The protein content was observed to increase with progressive in-crease in proportion of Dolichos lab lab flour supplemented in the blend formulations. This indicated that supplementa-tion of wheat flour with flour from Dolichos lab lab beans would greatly improve the protein nutritional quality of breads. This could be attributed to the significant quantity of protein in Dolichos lab lab beans (Deka and Sarkar, 1990;

Quality of Bread Supplemented with Dolichos lab lab Beans

Table 1. Chemical Composition (per 100g dry matter edible portion) of Dolichos Lablab beans.

Parameter Protein (N×6.25) Carbohydrate Calories Moisture Fat Total Ash Crude FiberComposition (g) 22.8 62.1 340 11 1 3.1 4.6

Table 2. Protein and moisture content of dolichos lablab supplemented breads compared to wheat bread.

Parameter (DM)/Bread Samples 100% wheat 5 % dolichos 10% dolichos 15% dolichos 20% dolichosCrude protein (%) 11.2 ± 0.2 12.7 ± 0.8 13.3 ± 0.1 13.9 ± 0.8 14.4 ± 1.8

Moisture content (%) 84.0 83.5 83.0 76.5 75.0* Values are mean ± SD of three independent determinations.

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a good and acceptable sensory attributes with no significant differences from the whole wheat bread. Hoseney (1994) suggested that the appearance of bread was an important sensory characteristic on which the acceptability of bread de-pends. The loaf volume, crust and crumb appearance of the breads supplemented with Dolichos lab lab beans and rated as acceptable by panelists are shown in the figures below.

Loaf volume A significant reduction in loaf volume was observed as the level of substitution with Dolichos lab lab bean flours increased (Figure 1). The highest reduction in loaf volume was in bread made from wheat flour blended with Dolichos lab lab bean flour at and above the 20% level. This could be that a dilution effect on gluten with the addi-tion of non-wheat flour to wheat flour and less retention of CO2 gas caused the depression in loaf volume (Sharma and

in comparison to the whole wheat breads at the same prob-ability level. The whole wheat bread and Dolichos lab lab supplemented bread with 5-10% produced acceptable flavor, taste and color compared to the other samples Tables 4 (a) and 4 (b). However, it was noted that breads made from the composite flour generally had a rough feel.

Taste evaluation suggested that control and various supplemented breads had most satisfactory taste scores at the 5% level. However, wheat and Dolichos lab lab bean flour supplemented breads had a satisfactory taste score up to 15% level of substitution. Results indicated that the taste score decreased with increased level of substitution with Dolichos lab lab flour as compared with control bread. Hence, supple-mentation of wheat flour with Dolichos lab lab at 5-10% substitution levels in bread making would therefore, make

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Table 3. Mean sensory scores of the breads*.

Attribute/Bread Sample 100% wheat 5% dolichos 10 % dolichos 15% dolichos 20% dolichosFlavor 4.2 a 3.9 a 3.3 a 2.4 a 2.9 ab

Color of crust 3.9 a 3.6 a 3.1 a 1.9 ab 2.3 ab

Color of crumb 3.8 a 2.9 a 2.7 a 2.5 a 2.7 ab

Texture 3.8 a 2.0 a 2.1 a 2.4 a 2.3 ab

General acceptability 4.0 a 2.9 a 3.1 a 2.7 a 2.6 ab

* Mean scores with the same superscripts are not significantly different from each other (p < 0.05).

Table 4. Scores for general quality characteristics of the breads.a) External appearance

Scores*

Characteristics ofBread sample

Loaf A5% dolichos

Loaf B10% dolichos

Loaf C15 % dolichos

Loaf D20% dolichos

Color of crust 8 7 8 7Evenness of bake 3 3 3 3Symmetry of form 3 2 2 2Break and shred 3 3 2 2Character of crust 3 3 3 2Loaf volume 9 9 8 7Subtotal 29 27 26 23

b) Internal appearance

Scores*

Characteristics ofBread sample

Loaf A5% dolichos

Loaf B10% dolichos

Loaf C15 % dolichos

Loaf D20% dolichos

Grain 10 10 8 8Color of crumb 10 10 10 9Texture 15 12 12 10Aroma 10 10 10 10Taste 18 18 18 18Subtotal 63 60 58 55Total bread score (out of 100%) 92 87 84 78

* Using a 100-point scoring system: Volume, 10; crust color, 8; symmetry of form, 3; evenness of bake, 3; crust character, 3; break and shred, 3; grain, 10; color of crumb, 10; texture, 15; Aroma, 10; taste, 20, developed by the American Institute of Baking.Loaf A – 5% Dolichos beans, Loaf B – 10% Dolichos, Loaf C – 15% Dolichos and Loaf D – 20% Dolichos lab lab beans.

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Dolichos lab lab bean flour (Figure 3). Above 15% substitu-tion levels, the crumb texture hardened sufficiently to signifi-cantly affect the acceptability because the hardening of the crumb texture was also accompanied by development of a strong beany flavor of the product.

Off-flavor description The lowest levels of substitution (0%-15%) did not significantly affect the flavor of the breads except the substitution levels above 20%. Detailed studies of bread flavor were not undertaken. However, evaluations us-ing the triangle tests revealed that bread flavor did not differ statistically, although breads with higher proportions of the bean flour (≥ 20%) were rated low due to presence of a beany flavor (Table 5). The off-flavor descriptions for the Dolichos

Chauhan, 2000). The decrease in loaf volume could also be due to the presence of relatively high concentrations of low molecular weight thiols, especially reduced glutathione, which activates proteolytic enzymes, thereby causing a detri-mental effect on loaf volume (Indrani and Rao, 1992).

Crust appearance As the level of Dolichos lab lab flour in blends was increased, the crust colour of the breads changed from creamy white to dull brown (Figure 2). The data indicated that the darkest colour was observed in breads prepared from Dolichos lab lab blends at 20% levels and above. The darkening of crust colour was attributed to the higher rate of the maillard reactions between reducing sugars and proteins (Raidi and Klein, 1983). The two substances in-creased with the incorporation of the Dolichos lab lab flour. The crust texture was related to the external appearance of the bread top i.e. smoothness or roughness of the crust. Crust texture score also decreased with increase in the substitution of Dolichos lab lab bean flour in wheat flour as compared with the control bread. Among the blended breads, the high-est scores were observed for bread containing the bean flour at the 5-15% substitution and these breads were also the smoothest. The lowest scores were obtained for blended breads at levels from 20% substitution.

Crumb appearance The crumb colour changed from creamish white to dull brown and a gradual hardening of crumb texture was generally observed with the addition of

Quality of Bread Supplemented with Dolichos lab lab Beans

Fig. 1. Loaf volumes for breads A, B, C and D supplemented with Dolichos lablab.

Fig. 2. Crust appearance of breads A, B, C and D supplemented with Dolichos lablab.

Fig. 3. Crumb appearance of breads A, B, C and D supplemented with Dolichos lablab.

Table 5. Tests of difference for beany flavor due to substitution with Dolichos lab lab bean flour.

No. of judgments for breads supplemented with Dolichos lablaba

Substitution level (%)a Correct/total b Significance c

5 2/14 Not significant10 4/14 Not significant15 6/10 Significant20 8/10 Significant

a Proportion of Dolichos lablab bean flour added to the blend formulations.

b No. of judgment correct divided by total in triangle tests.c Level of significance *p = 0.05.

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lab lab supplemented breads of 20% and above were insipid, bland, sour, musty and flat. The public awareness of the nu-tritional importance of bread fortified with Dolichos lab lab would help enhance the acceptability of the Dolichos lab lab supplemented breads.

ConclusionResults of the study show that acceptable and high qual-

ity bread can be produced by substitution of wheat flour with flour from Dolichos lab lab beans. The breads would be nu-tritionally superior in protein content compared with the pure wheat breads. Beyond 15% substitution, the quality of the breads would be delimited by low loaf volumes, beany flavor and crumb appearance. Adoption of this bread manufactur-ing technology can accrue in great savings in the scarce re-sources in the country, and increase the protein content of the breads.

Acknowledgements The results in this study were part of a Mas-ter’s project by the author as a requirement for the degree of MSc of the University of Nairobi. We wish to acknowledge the financial assistance provided by the University of Nairobi.

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