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Optimization of Bread Preparation from Wheat Flour and Malted Rice Flour
Rice Science, 2010, 17(1): 51−59 Copyright © 2010, China National Rice Research Institute. Published by Elsevier BV. All rights reserved DOI: 10.1016/S1672-6308(08)60104-3
Optimization of Bread Preparation from Wheat Flour and Malted Rice Flour Subajiny VELUPPILLAI1, Ketheeswary NITHYANANTHARAJAH2, Seevaratnam VASANTHARUBA1, Sandrasegarampillai BALAKUMAR2, Vasanthy ARASARATNAM2 (1Department of Agricultural Chemistry, Faculty of Agriculture, University of Jaffina, Sri Lanka; 2Department of Biochemistry, Faculty of Medicine, University of Jaffna, Sri Lanka) Abstract: The feasibility of partially replacing wheat flour with malted rice flour in bread making was evaluated in several formulations, aiming to find a formulation for the production of malted rice-wheat bread with better nutritional quality and consumer acceptance. The whole grains of a local rice variety (Oryza sativa L. subsp. indica var. Mottaikaruppan) were steeped in distilled water (12 h, 30°C) and germinated for 3 days to obtain high content of soluble materials and amylase activity in bread making. The quality of bread was evaluated by considering the physical and sensorial parameters. When the wheat flour was substituted with malted rice flour, 35% substitution level and the malted rice flour from 3 days of germination was the best according to the physical and sensory qualities of bread. The quality of bread was improved by the addition of 20 g of margarine, 20 g of baking powder and 20 g of yeast in 1 kg of flour. Among different ratios of yeast and baking powder, 2:1 was the best. Bread improver containing amylases and oxidizing agents at the concentration of 40 g/kg was selected as the best concentration. When comparing the final formulation made in the bakery with wheat bread, malted rice-wheat bread contains more soluble dietary fiber (0.62%), insoluble dietary fiber (3.95%), total dietary fiber (4.57%) and free amino acid content (0.64 g/kg) than those in wheat bread (0.5%, 2.73%, 3.23% and 0.36 g/kg, respectively). Key words: rice; bread; malted rice flour; wheat flour; physical parameters; sensorial parameters
Bakery foods are the major cereal products available to consumers and bread has been the principal food in over half of the countries around the world [1]. Due to the increase in the involvement of females in labour market, bread plays an important part as breakfast food among urban Sri Lankan populations. Wheat is not grown in Sri Lanka because the soil and climatic conditions are not suitable. Therefore, total requirement of wheat is fulfilled by importation. Nowadays the increasing price of wheat grain in the world market forces Sri Lanka to find other locally available raw materials for bread making. Alternatives for wheat flour such as germinated and non-germinated soy bean flour [2], malted and fermented sorghum [3], banana flour [4], composite flours of wheat, plantain and soybeans [5], maizesoybean flour blends [6], cassava [7], rice flour, corn starch and cassava starch [8-9], rice, corn and soy flour [10] and rice flour [11-14] have been reported. A part of wheat flour was substituted with rice flour at the levels of 50, 100, 150 and 200 g/kg for bread making Received: 17 June 2009; Accepted: 31 September 2009 Corresponding author: Vasanthy ARASARATNAM ([email protected])
and the overall acceptability of the product was the best when wheat flour was substituted with rice flour up to the 150 g/kg replacement [14]. Another study revealed that the incorporation of rice, corn and soy flour in wheat up to a level of 10% produced the bread without any negative effect in quality attributes, while 30% and 50% substitution levels had very low scores for the acceptability [10]. When the wheat flour was substituted with plantain flour at the levels of 5%, 10%, 20% and 30%, breads with acceptable qualities were formulated when the wheat flour was substituted with plantain flour only up to 20% level [4]. Wheat flour can be substituted with cassava flour only up to 20% [7]. Among the cereals, wheat and rye contain the protein called ‘gluten’, which makes them superior to other cereals for the production of porous baked goods. The main function of gluten in dough during dough mixing is to swell and hold water, forming cells with strong elastic walls which capture carbon dioxide formed during fermentation [15]. Therefore, when substituting wheat flour with other flours, the amount of gluten is reduced and there will be a lack of gluten net work to capture the carbon dioxide formed during fermentation.
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The rice flour is far from the ideal as the structural component of leavened bread rolls or loaves, and the rice grain contains none of the gluten which gives wheat flour its unique ability to form highly expanded, tender, white and flavorful yeast leavened or chemically leavened baked products [16]. However, it may be possible to use malted rice flour instead of raw rice flour in the preparation of bakery items since many changes occur in the grains during germination. During seed germination, the breakdown of seed reserves, carbohydrates and proteins takes place. Germination causes increase in several vitamins [17]. The natural process accompanying sprouting of grains creates or releases in active form relatively large quantities of enzymes and changes the original components of the grains in many other ways [16]. Therefore, addition of malted rice flour may improve not only the nutritional quality but also the texture of breads when the wheat flour is substituted with malted rice flour. The aim of the present study is to evaluate the possibility of substituting wheat flour with malted whole rice flour for the preparation of bread, improve the physical and sensorial properties of malted whole rice-wheat bread and statistically establish the optimal amounts of each ingredient in malted whole ricewheat bread, in order to produce the bread with good textural properties and nutritional value.
Evaluation of bread quality Evaluation of bread volume Volume of the bread was determined one hour after the end of baking process using the formula: specific volume (cm3/g) = Volume of bread (cm3) / Dough weight (g). After weighing, the volume of the sample was measured by the method of displacement of millet seeds [8]. Bread sensorial evaluation Bread preparations were submitted to a sensory analysis in order to evaluate flavor, crumb colour, crumb texture, crust colour, crust texture and degree of mouth satisfaction or acceptability. The bread samples were homogenously sliced and served with water. The samples were presented in identical containers. Ten untrained panel members were selected from students and staff of the Department of Biochemistry, Faculty of Medicine, Sri Lanka to perform the evaluation using a hedonistic scale of 5 points (Table 1). Breads prepared with different formulations were submitted Table 1. Scores assigned for the evaluation of flavor, mouth satisfaction, crumb colour, crumb texture, crust colour and crust texture of the breads under different treatments. Attribute Flavor
MATERIALS AND METHODS Mouth satisfaction
Materials for bread preparation Grains of rice (Oryza sativa L. subsp. indica var. Mottaikaruppan) were purchased from a local market and husked. The reagents used were of analytical grade. The ingredients used in bread making were: wheat flour, malted rice flour, table sugar, table salt (NaCl), margarine (AB Mauri Lanka, Sri Lanka), yeast (commercial strain of Saccharomyces cerevisiae of Fermipan bakers yeast from Gist-Brocades, Waterings-1, Delft-Holla, Netherlands), bread improver (SK 9000, ESS KAYE Enterprise, Kelaniya, Sri Lanka) which contains wheat flour, sugar, amylases and oxidizing agents as ingredients and baking powder (Motha Confectionary Works Ltd, Sri Lanka). All ingredients were purchased from a local market and the same trade products were used in all experiments.
Crumb colour
Crumb texture
Crust colour
Crust texture
Character
Score
Sweet Savor Fermented Raw dough Bitter Dislike very much Dislike Like nor Dislike Like Like very much Reddish Reddish brown Brown Light brown White Crumbling Buttery Floury Soft Sticky Reddish brown Brown Light brown Whitish brown White Brittle Hard Dry Soft Sticky
1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5
Subajiny VELUPPILLAI, et al. Optimization of Bread Preparation from Wheat Flour and Malted Rice Flour
to an acceptability test using proper questionnaire. Evaluation of proximate composition The contents of moisture (gravimetric method), total sugar [18], total protein [18], free amino acids [19], fat [18], fiber [20] and ash [18] of the final bread formulation were evaluated. Malting of rice grain Husked and unpolished rice grains were steeped in distilled water (grain to water ratio is 1:2) at 30°C for 12 h and germinated for 3 days in a sterile moistened cloth bag kept in dark. Moistened conditions were maintained throughout the germination period by spraying distilled water. The grains were dried under the sun to arrest germination and the dried grains were
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pulverized in a domestic grinder at 30°C to obtain malted rice flour. Bread making with traditional ingredients Bread making started from a basic formulation (BF) given in Table 2. Breads were baked for 40 min at 230°C. All the experiments were performed in triplicates. Bread making with malted rice flour by altering the formulation First the breads were prepared from wheat flour substituted with different amounts of malted rice flour, and then the malted rice flour obtained after different days of germination were tested to find out the effect of malting in the preparation of bread. Subsequently,
Table 2. Amount of ingredients used in different experiments. Factor changed in the formulation Basic formulation Malted rice flour
Days of germination
Fat
Baking powder
Yeast
Ratio between optimum amount of baking powder and yeast
Bread improver
Formulation Wheat flour Malted rice flour Baking powder No. (%) (%) (%) a BF I-a I-b I-c I-d I-e I-f II-a II-b II-c II-d II-e III-a III-b III-c III-d III-e IV-a IV-b IV-c IV-d IV-e V-a V-b V-c V-d V-e VI-a VI-b VI-c VI-d VI-e VI-f VII-a VII-b VII-c VII-d
100 100 90 80 70 65 60 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65
0 10 20 30 35 40 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35
a Percentage of flour. To all bread formulae, 1.67 g of salt and 3 g of sugar were added.
0 0 2 3 4 5 2 2 2 2 2 2 1 0 2 2 1 1 1 1 1
Yeast (%) a
Fat (%) a
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 3 4 5 2 2 2 0 1 1 2 2 2 2
2 2 2 2 2 2 2 2 2 2 2 2 1 2 4 6 8 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
Bread Days of germination improver (%) a (d) 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0.5 1 2 4
4 4 4 4 4 1 2 3 4 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
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different bread formulations were tested by changing the amount of an ingredient at a time to get optimum amount of each ingredient (Table 2). Breads were evaluated for the physical and sensorial properties. Specific volume and sensory qualities of the breads were determined. Comparison of malted rice-wheat bread with wheat bread Malted rice flour-wheat bread and wheat bread made in the bakery were compared by analyzing specific volume and proximate composition. Breads also were submitted to sensory evaluation to evaluate flavor, crumb colour, crumb texture, crust colour, crust texture, degree of mouth satisfaction and over all acceptability by asking the degree of likeness. The scores assigned for each attribute are: 1, Dislike very much; 2, Dislike; 3, Like nor Dislike; 4, Like and 5, Like very much. Statistical analysis Results obtained for specific volume, moisture content and proximate composition of breads were statistically analyzed by ANOVA and sensorial data were statistically analyzed by the Friedman test using the SAS analytical package.
RESULTS
difference in specific volume was significant (P<0.05) under all the different substitutions considered. The highest specific volume (4.71 cm3/g) was obtained for 100% wheat bread (Formula I-a) and the specific volume of the breads decreased significantly (P <0.05) from 4.57 to 2.95 cm3/g whereas the moisture content of the breads was increased as the substitution level increases. Regarding moisture content, significant increase (P<0.05) from 29.4% to 33.4% with increasing level of malted rice flour was seen. Extreme outliers in the results were omitted for the analysis. The sensory analysis showed no significant differences (P>0.05) for the attributes of flavor and crust texture of the malted rice flour-wheat bread compared with 100% wheat bread, while significant differences (P<0.05) for the attributes of crumb colour, crumb texture, crust colour and degree of mouth satisfaction (Fig. 1-A). Crumb colour and crust colour were increased from whitish to reddish with increasing level of malted rice flour substitution. Bread with the 40% (Formula I-f) substitution level produced sticky crumb texture and the lowest scores for mouth satisfaction. Even though the 35% substitution level (Formula I-e) had low level of mouth satisfaction and low specific volume, by considering the nutritional value, this formula was selected for further studies to improve the taste and specific volume. Effects of fat content on bread quality
Effects of different concentrations of malted rice flour on bread quality Malted rice flour from four days of germination was used for the preparation of bread. Considering the substitution of wheat flour with malted rice flour,
The specific volume was increased significantly (P<0.05) from 3.8 to 3.9 cm3/g when the fat content of flour was increased from 10 to 20 g/kg. After that, with increase in the amount of fat, the specific volume decreased, but the decrease was not significant
Fig. 1. Effects of different contents of malted rice flour (A) and fat (B) on the mean scores for the attributes of flavor, mouth satisfaction, crumb colour, crumb texture, crust colour and crust texture of breads.
Subajiny VELUPPILLAI, et al. Optimization of Bread Preparation from Wheat Flour and Malted Rice Flour
(P>0.05) for 40 g/kg (Formula III-c) and 60 g/kg of flour (Formula III-d). Moisture content of the breads under different treatments ranged from 29.47% to 29.88% and did not differ significantly (P>0.05) among treatments. Sensory analysis (Fig. 1-B) showed that a significant difference (P<0.05) was observed only for crumb texture. The crumb texture became sticky as the fat content increases. While other attributes such as flavor, crumb colour, crust colour, crust texture and mouth satisfaction did not differ significantly (P>0.05) among treatments. Based on these results, the fat content of 20 g/kg of flour (Formula III-b) was selected as the best one.
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Table 3. Effect of germination days of malted rice on the mean scores for the attributes of flavor, mouth satisfaction, crumb colour, crumb texture, crust colour and crust texture of breads. Germination time Mouth Crumb Crumb Crust Crust Flavor (d) satisfaction colour texture colour texture 0 1 2 3 4
3.0 3.0 3.0 3.0 3.0
3.6 3.5 3.7 3.8 3.9
4.0 4.1 4.1 4.0 4.1
4.1 4.0 4.0 4.1 4.1
2.9 2.9 3.0 2.9 2.9
1.0 1.0 1.1 1.2 1.0
The ratio of wheat flour and malted rice flour is 65:35.
Significant differences (P<0.05) in specific volumes were observed among the breads made from rice flour malted for 0 (raw rice) (Formula II-a), 1 (Formula II-b) and 2 days (Formula II-c), whereas the specific volume of breads made from rice flour malted for 3 (Formula II-d) and 4 days (Formula II-e) did not differ significantly (P>0.05). The specific volume increased from 2.3 to 3.8 cm3/g with the increase in the germination time. Moisture content (ranged from 29.82% to 30.05%) and all the attributes of sensory evaluation showed no significant difference (P>0.05) among different treatments. Mean score obtained for the attributes of different treatments are shown in Table 3.
(P<0.05) from 3.91 to 3.31 cm3/g with increasing levels of baking powder whereas the moisture content (ranged from 30.37% to 32.20%) did not differ significantly (P>0.05). Sensory evaluation showed no significant difference (P>0.05) for flavor and crumb colour among the treatments. Other attributes such as crumb texture, crust colour, crust texture and mouth satisfaction differed significantly (P<0.05) among the treatments (Fig. 2-A). Crust colour was increased towards reddish with increasing level of baking powder. Baking powder at the level of 20 g/kg of flour (Formula IV-b) produced soft crumb texture. Comments showed that baking powder at the levels of 30 (Formula IV-c), 40 (Formula IV-d) and 50 g/kg of flour (Formula IV-e) gave bitter taste. The Formula IV-b showed a higher score for the degree of mouth satisfaction than the control (without baking powder). Therefore, the Formula IV-b was selected as the best one.
Effects of baking powder on bread quality
Effects of yeast concentrations on bread quality
Effects of malting time of rice on bread quality
The specific volume showed a significant decrease
In order to find out the optimum concentration of
Fig. 2. Effects of addition of different amounts of baking powder (A), yeast (B) and different ratios between optimum amount of yeast (20 g/kg) and baking powder (20 g/kg) (C) on the mean scores for the sensory attributes of flavor, mouth satisfaction, crumb colour, crumb texture, crust colour and crust texture of breads.
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yeast for bread making, bread formulation developed from previous experiment was evaluated with different concentrations of yeast. The specific volume increased significantly (P<0.05) from 4.0 to 4.4 cm3/g when the amount of yeast increased from 10 to 20 g/kg of flour. After that, the specific volume was decreased with the increasing level of yeast, but the decrease was not significant (P>0.05). Moisture content was decreased from 34.3% to 29.6% with the increasing level of yeast. Regarding sensory analysis (Fig. 2-B), among the attributes evaluated, only the mouth satisfaction showed significant difference (P<0.05) among the treatments. Yeast used at the levels of 40 (Formula Vd) and 50 g/kg of flour (Formula V-e) showed a lower degree of mouth satisfaction than the levels of 10 (Formula V-a), 20 (Formula V-b) and 30 g/kg of flour (Formula V-c). Comments showed that the yeast levels of more than 30 g/kg of flour gave acid taste to bread. Therefore, bread made by using the yeast level of 20 g/kg of flour (Formula V-b) was selected as the best one for further studies. Effects of different ratios between yeast and baking powder on bread quality The optimum amounts of yeast and baking powder selected from previous experiments were examined with possible combinations. A significantly higher (P<0.05) specific volume (4.96 cm3/g) was obtained at the ratio of 2:1 (yeast:baking powder) (Formula VI-b) than other ratios. Moisture contents of the breads from different treatments ranged from 29.97% to 30.56% and did not differ significantly (P>0.05). Sensory analysis (Fig. 2-C) showed no significant difference (P<0.05) in flavor and crumb colour among the treatments. Higher degree of mouth satisfaction was obtained at the ratio of 2:1 (yeast:baking powder) (Formula VI-b). Based on these results, the Formula VI-b was selected as the best one.
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moisture content was decreased from 30.67 to 28.92% when the amount of bread improver was increased from 5 to 40 g/kg of flour. The sensory analysis (Fig. 3) showed a significant difference (P<0.05) among the treatments for the attribute of mouth satisfaction only, whereas others did not differ significantly (P>0.05). The highest score for mouth satisfaction was obtained for bread improver at the level of 40 g/kg of flour. Based on these results, the Formula VII-d was selected as the best one. Comparison of malted rice-wheat bread with wheat bread The specific volume of the 100% wheat (5.84 cm /g) was significantly higher (P<0.05) than that of malted rice-wheat bread (5.31 cm3/g). Proximate composition of malted rice-wheat bread and wheat bread are as follows: moisture, 35.44% and 33.11%; total protein, 6.62% and 7.62%; fat, 1.40% and 1.40%; ash, 1.76% and 1.73%; free amino acids, 0.06% and 0.03%; soluble dietary fiber, 0.62% and 0.50%; insoluble dietary fiber, 3.95% and 2.73%; total dietary fiber, 4.57% and 3.23%; total carbohydrate, 50.87% and 52.80%, respectively. Malted rice-wheat bread was compared with 100% wheat bread to evaluate flavor, mouth satisfaction, crumb colour, crumb texture, crust colour and crust texture by applying the five points scale (Fig. 4). The lowest score was assigned for ‘dislike’ and the highest for ‘like’ category for each attribute. Extreme outliers were omitted from the analysis. When comparing the sensory characters of wheat bread and malted rice3
Effects of different concentrations of bread improver on bread quality The specific volume increased with increase in the amount of bread improver. The highest specific volume (5.23 cm3/g) was obtained at the level of 40 g/kg of flour (Formula VII-d) and the lowest (5.00 cm3/g) at the 50 g/kg of flour (Formula VII-a). The
Fig. 3. Effects of bread improver concentration on the mean scores for the attributes of flavor, mouth satisfaction, crumb colour, crumb texture, crust colour and crust texture of breads.
Subajiny VELUPPILLAI, et al. Optimization of Bread Preparation from Wheat Flour and Malted Rice Flour
Fig. 4. Mean scores of the attributes of flavor, mouth satisfaction, crumb colour, crumb texture, crust colour and crust texture for the malted rice-wheat bread and 100% wheat bread made in the bakery.
wheat bread, only the crumb texture differed significantly (P<0.05).
DISCUSSION Rice bran fiber is very hydrophilic and can absorb almost its weight of water [21]. Since the rice grains used in this study were whole rice grains, the rice bran added from the malted rice flour may be the reason for the increase in the moisture content with the increase in the level of substitution of wheat flour with malted rice flour. From this study, 35% malted rice flour substitution level (Formula I-e) was selected for further studies considering the nutritional value, even though the specific volume of the bread was decreased. The increase in specific volume with increase in germination time might be due to the increase in hydrolytic enzymes (especially endogenous amylase) and soluble materials. The principal functional benefits of malted rice flour addition include an increased gas production in the dough and an improved crust colour formation, a better crumb moisture retention and an enhanced flavor development. Malt α-amylases acting on damaged starch granules rectify the deficiency of fermentable sugar which is necessary for optimal yeast growth and gas production [22]. Addition of germinated soy bean flour to wheat flour improved the overall bread quality and resulted in a higher specific volume [2]. The malt amylase present in the malted rice would also improve the bread quality when compared
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to that prepared from raw rice. Considering nutritional and sensory values, bread prepared from rice flour malted for 3 days (Formula II-d) was selected for further studies. Therefore, it could be concluded that the use of germinated rice flour has advantage over the use of raw rice flour for bread making. Also, with the increase in germination time, the physical and nutritional quality of bread could be improved. Fats and oils, widely known as shortenings, are used in baking to improve the quality of baked loaves [23]. Proper amount of fat in bread dough improves the volume, grain, texture and crust tenderness, keeps quality of bread and makes the dough more elastic [24]. During baking, fat crystals melt, thereby making it possible for the crystal-liquid interface to be incorporated into the surface of the bubble as it expands [25]. This transfer of interfacial material from crystals to bubble surface explains how the addition of shortening to dough allows bubbles to expand during baking without rupturing, thus producing high volume bread with fine crumb structure. However, in this study, the specific volume increased only up to the fat level of 20 g/kg of flour beyond which the specific volume decreased and the bread’s texture was sticky. Therefore, 2 g of margarine per 100 g of flour (Formula III-b) was selected to be the optimum amount for malted rice-wheat bread making. The majority of bakery products, principally breads are manufactured using yeast as a leavening agent. The yeasts used are strains of Saccharomyces cerevisiae which ferment the sugars present to produce ethanol and carbon dioxide when incorporated into dough. The ethanol is driven off during the subsequent baking stage. The production of carbon dioxide in the dough leads to the formation of a network of regularly shaped cavities so that, when the dough is baked, the bread has a more or less uniform honey comb-like texture. The principal alternative to using yeast is to produce carbon dioxide chemically by reacting sodium bicarbonate with an acid salt, the mixture of chemicals known as baking powder [26]. In this study even yeast was used as leavening agent in the basic bread formulation. The effect of addition of different amounts of baking powder and yeast and the effect of different ratios of optimum amount of baking powder and yeast levels were
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evaluated. Baking powder used in this study contained sodium bicarbonate and sodium acid pyrophosphate. When the mixture dissolves in water and the temperature rises, carbon dioxide is released. Addition of baking powder to bread produced an attractive reddish colour to breads. However, higher levels (above 20 g/kg of flour) of baking power produced bitter taste and unacceptable smell to breads. Therefore, it was decided to find out the optimum ratio among baking powder and yeast. From this experiment, the ratio of 1:2 (baking powder:yeast) (Formula VI-b) produced better taste, texture and colour to breads. Thus, the amount of baking powder and yeast selected were 10 g/kg and 20 g/kg, respectively (Formula VI-b). Bread improver used in this study mainly contained α-amylase (activity 2490 U/g). The α-amylase is an endo-enzyme that randomly hydrolyses the α-1,4glucosidic linkages in polysaccharides, resulting in short chains further fermented by yeast [27]. The αamylase is routinely added to bread dough in order to supply dextrins which are effective in decreasing bread hardness. The improved bread volume after addition of enzymatic preparations was caused by the increased amount of fermentable sugars. Usually wheat flour contains a sufficient amount of β-amylase. However, only α-amylases are able to hydrolyze native undamaged starch. During the dough making process, the damaged starch granules are quickly attacked by both α- and βamylases [28]. The same observation of increase in the volume of the bread was found with the increase in the germination time in which the amylase activity was increased. Therefore, the increase in the volume of bread with the increase in the amount of bread improver could be attributed to the increase in the amount of amylases. Also, it could be concluded that the inclusion of malted rice flour in bread making is advantageous and can be a natural alternative to artificial enzyme preparations. The contents of moisture, total protein, total digestible carbohydrate, soluble dietary fiber (SDF), insoluble dietary fiber (IDF), total dietary fiber (TDF) and free amino acids of the malted rice-wheat bread differed significantly (P<0.05) from the wheat bread while fat and ash contents did not (P>0.05). Total protein and total digestible carbohydrate contents of the wheat bread were higher than those of the malted
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rice-wheat bread. Free amino acids content of the malted rice-wheat bread is almost twice than that of the wheat bread. It could be due to the fact that the free amino acids content increases during germination. Dietary fiber plays a key role in maintaining human health. The glycemic index is an extension of the fiber hypothesis, suggesting that fiber consumption reduces the rate of nutrient influx from the gut. TDF consists of SDF and IDF. Among those properties, SDF has the highest correlation with glycemic response and affects blood glucose control. SDF directly decreases digestion rate by impeding access to digestive enzymes and absorption rate by slowing diffusion across unstirred layer. While indirect effect of SDF decreases absorption of dietary fat and regulates the appetite [29]. When the fiber contents of the wheat flour bread (prepared in bakery) and malted rice-wheat bread (final bread Formula VI-b) were considered, the malted rice-wheat bread contained more SDF (0.62%), IDF (3.95%) and TDF (4.57%) than the wheat flour bread (0.50%, 2.73% and 3.23%, respectively). The available carbohydrate in the foods for absorption might be made unavailable due to its SDF, IDF and TDF contents. The monosaccharide released by hydrolysis and available for absorption might be made unavailable. This could be due to the tendency of the fibers to absorb sugars and that the absorbed sugars released slowly. Soluble fibers slow down the digestion of starches and absorption of the glucose into the bloodstream [30]. The SDF, IDF and TDF contents of malted rice-wheat bread were higher than those of wheat flour bread. Therefore, the glycemic index of malted rice-wheat bread would be lower than that of wheat flour bread.
CONCLUSIONS A bread formulation containing rice flour obtained from malting of whole rice grains for 3 days was established considering both nutritional and sensory qualities of the bread based on the present study. The bread formulation is, malted rice flour 35%, wheat flour 65%, fat 2%, baking powder 1%, yeast 2%, bread improver 4%, sugar 3% and salt 1.67%. The results of the present study suggest that breads can be prepared from the inclusion of malted rice flour with
Subajiny VELUPPILLAI, et al. Optimization of Bread Preparation from Wheat Flour and Malted Rice Flour
better consumer acceptability and better nutritional value than wheat bread. Also, the inclusion of malted rice flour in bread can significantly reduce the glycemic index of bread. Thus the malted rice wheat bread can be a better choice for management of diabetics.
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ACKNOWLEDGEMENT
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Cawley R W, Howarth D T. The wheat industry. [2009-0617]. http://www.nzic.org.nz/ChemProcesses/food/6C.pdf.
Financial support from the University of Jaffna, Sri Lanka is highly acknowledged.
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Optimization of Bread Preparation from Wheat Flour and Malted Rice Flour Subajiny VELUPPILLAI1, Ketheeswary NITHYANANTHARAJAH2, Seevaratnam VASANTHARUBA1, Sandrasegarampillai BALAKUMAR2, Vasanthy ARASARATNAM2 (1Department of Agricultural Chemistry, Faculty of Agriculture, University of Jaffina, Sri Lanka; 2Department of Biochemistry, Faculty of Medicine, University of Jaffna, Sri Lanka) Abstract: The feasibility of partially replacing wheat flour with malted rice flour in bread making was evaluated in several formulations, aiming to find a formulation for the production of malted rice-wheat bread with better nutritional quality and consumer acceptance. The whole grains of a local rice variety (Oryza sativa L. subsp. indica var. Mottaikaruppan) were steeped in distilled water (12 h, 30°C) and germinated for 3 days to obtain high content of soluble materials and amylase activity in bread making. The quality of bread was evaluated by considering the physical and sensorial parameters. When the wheat flour was substituted with malted rice flour, 35% substitution level and the malted rice flour from 3 days of germination was the best according to the physical and sensory qualities of bread. The quality of bread was improved by the addition of 20 g of margarine, 20 g of baking powder and 20 g of yeast in 1 kg of flour. Among different ratios of yeast and baking powder, 2:1 was the best. Bread improver containing amylases and oxidizing agents at the concentration of 40 g/kg was selected as the best concentration. When comparing the final formulation made in the bakery with wheat bread, malted rice-wheat bread contains more soluble dietary fiber (0.62%), insoluble dietary fiber (3.95%), total dietary fiber (4.57%) and free amino acid content (0.64 g/kg) than those in wheat bread (0.5%, 2.73%, 3.23% and 0.36 g/kg, respectively). Key words: rice; bread; malted rice flour; wheat flour; physical parameters; sensorial parameters
Bakery foods are the major cereal products available to consumers and bread has been the principal food in over half of the countries around the world [1]. Due to the increase in the involvement of females in labour market, bread plays an important part as breakfast food among urban Sri Lankan populations. Wheat is not grown in Sri Lanka because the soil and climatic conditions are not suitable. Therefore, total requirement of wheat is fulfilled by importation. Nowadays the increasing price of wheat grain in the world market forces Sri Lanka to find other locally available raw materials for bread making. Alternatives for wheat flour such as germinated and non-germinated soy bean flour [2], malted and fermented sorghum [3], banana flour [4], composite flours of wheat, plantain and soybeans [5], maizesoybean flour blends [6], cassava [7], rice flour, corn starch and cassava starch [8-9], rice, corn and soy flour [10] and rice flour [11-14] have been reported. A part of wheat flour was substituted with rice flour at the levels of 50, 100, 150 and 200 g/kg for bread making Received: 17 June 2009; Accepted: 31 September 2009 Corresponding author: Vasanthy ARASARATNAM ([email protected])
and the overall acceptability of the product was the best when wheat flour was substituted with rice flour up to the 150 g/kg replacement [14]. Another study revealed that the incorporation of rice, corn and soy flour in wheat up to a level of 10% produced the bread without any negative effect in quality attributes, while 30% and 50% substitution levels had very low scores for the acceptability [10]. When the wheat flour was substituted with plantain flour at the levels of 5%, 10%, 20% and 30%, breads with acceptable qualities were formulated when the wheat flour was substituted with plantain flour only up to 20% level [4]. Wheat flour can be substituted with cassava flour only up to 20% [7]. Among the cereals, wheat and rye contain the protein called ‘gluten’, which makes them superior to other cereals for the production of porous baked goods. The main function of gluten in dough during dough mixing is to swell and hold water, forming cells with strong elastic walls which capture carbon dioxide formed during fermentation [15]. Therefore, when substituting wheat flour with other flours, the amount of gluten is reduced and there will be a lack of gluten net work to capture the carbon dioxide formed during fermentation.
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The rice flour is far from the ideal as the structural component of leavened bread rolls or loaves, and the rice grain contains none of the gluten which gives wheat flour its unique ability to form highly expanded, tender, white and flavorful yeast leavened or chemically leavened baked products [16]. However, it may be possible to use malted rice flour instead of raw rice flour in the preparation of bakery items since many changes occur in the grains during germination. During seed germination, the breakdown of seed reserves, carbohydrates and proteins takes place. Germination causes increase in several vitamins [17]. The natural process accompanying sprouting of grains creates or releases in active form relatively large quantities of enzymes and changes the original components of the grains in many other ways [16]. Therefore, addition of malted rice flour may improve not only the nutritional quality but also the texture of breads when the wheat flour is substituted with malted rice flour. The aim of the present study is to evaluate the possibility of substituting wheat flour with malted whole rice flour for the preparation of bread, improve the physical and sensorial properties of malted whole rice-wheat bread and statistically establish the optimal amounts of each ingredient in malted whole ricewheat bread, in order to produce the bread with good textural properties and nutritional value.
Evaluation of bread quality Evaluation of bread volume Volume of the bread was determined one hour after the end of baking process using the formula: specific volume (cm3/g) = Volume of bread (cm3) / Dough weight (g). After weighing, the volume of the sample was measured by the method of displacement of millet seeds [8]. Bread sensorial evaluation Bread preparations were submitted to a sensory analysis in order to evaluate flavor, crumb colour, crumb texture, crust colour, crust texture and degree of mouth satisfaction or acceptability. The bread samples were homogenously sliced and served with water. The samples were presented in identical containers. Ten untrained panel members were selected from students and staff of the Department of Biochemistry, Faculty of Medicine, Sri Lanka to perform the evaluation using a hedonistic scale of 5 points (Table 1). Breads prepared with different formulations were submitted Table 1. Scores assigned for the evaluation of flavor, mouth satisfaction, crumb colour, crumb texture, crust colour and crust texture of the breads under different treatments. Attribute Flavor
MATERIALS AND METHODS Mouth satisfaction
Materials for bread preparation Grains of rice (Oryza sativa L. subsp. indica var. Mottaikaruppan) were purchased from a local market and husked. The reagents used were of analytical grade. The ingredients used in bread making were: wheat flour, malted rice flour, table sugar, table salt (NaCl), margarine (AB Mauri Lanka, Sri Lanka), yeast (commercial strain of Saccharomyces cerevisiae of Fermipan bakers yeast from Gist-Brocades, Waterings-1, Delft-Holla, Netherlands), bread improver (SK 9000, ESS KAYE Enterprise, Kelaniya, Sri Lanka) which contains wheat flour, sugar, amylases and oxidizing agents as ingredients and baking powder (Motha Confectionary Works Ltd, Sri Lanka). All ingredients were purchased from a local market and the same trade products were used in all experiments.
Crumb colour
Crumb texture
Crust colour
Crust texture
Character
Score
Sweet Savor Fermented Raw dough Bitter Dislike very much Dislike Like nor Dislike Like Like very much Reddish Reddish brown Brown Light brown White Crumbling Buttery Floury Soft Sticky Reddish brown Brown Light brown Whitish brown White Brittle Hard Dry Soft Sticky
1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5
Subajiny VELUPPILLAI, et al. Optimization of Bread Preparation from Wheat Flour and Malted Rice Flour
to an acceptability test using proper questionnaire. Evaluation of proximate composition The contents of moisture (gravimetric method), total sugar [18], total protein [18], free amino acids [19], fat [18], fiber [20] and ash [18] of the final bread formulation were evaluated. Malting of rice grain Husked and unpolished rice grains were steeped in distilled water (grain to water ratio is 1:2) at 30°C for 12 h and germinated for 3 days in a sterile moistened cloth bag kept in dark. Moistened conditions were maintained throughout the germination period by spraying distilled water. The grains were dried under the sun to arrest germination and the dried grains were
53
pulverized in a domestic grinder at 30°C to obtain malted rice flour. Bread making with traditional ingredients Bread making started from a basic formulation (BF) given in Table 2. Breads were baked for 40 min at 230°C. All the experiments were performed in triplicates. Bread making with malted rice flour by altering the formulation First the breads were prepared from wheat flour substituted with different amounts of malted rice flour, and then the malted rice flour obtained after different days of germination were tested to find out the effect of malting in the preparation of bread. Subsequently,
Table 2. Amount of ingredients used in different experiments. Factor changed in the formulation Basic formulation Malted rice flour
Days of germination
Fat
Baking powder
Yeast
Ratio between optimum amount of baking powder and yeast
Bread improver
Formulation Wheat flour Malted rice flour Baking powder No. (%) (%) (%) a BF I-a I-b I-c I-d I-e I-f II-a II-b II-c II-d II-e III-a III-b III-c III-d III-e IV-a IV-b IV-c IV-d IV-e V-a V-b V-c V-d V-e VI-a VI-b VI-c VI-d VI-e VI-f VII-a VII-b VII-c VII-d
100 100 90 80 70 65 60 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65 65
0 10 20 30 35 40 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35
a Percentage of flour. To all bread formulae, 1.67 g of salt and 3 g of sugar were added.
0 0 2 3 4 5 2 2 2 2 2 2 1 0 2 2 1 1 1 1 1
Yeast (%) a
Fat (%) a
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 3 4 5 2 2 2 0 1 1 2 2 2 2
2 2 2 2 2 2 2 2 2 2 2 2 1 2 4 6 8 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
Bread Days of germination improver (%) a (d) 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0.5 1 2 4
4 4 4 4 4 1 2 3 4 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
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different bread formulations were tested by changing the amount of an ingredient at a time to get optimum amount of each ingredient (Table 2). Breads were evaluated for the physical and sensorial properties. Specific volume and sensory qualities of the breads were determined. Comparison of malted rice-wheat bread with wheat bread Malted rice flour-wheat bread and wheat bread made in the bakery were compared by analyzing specific volume and proximate composition. Breads also were submitted to sensory evaluation to evaluate flavor, crumb colour, crumb texture, crust colour, crust texture, degree of mouth satisfaction and over all acceptability by asking the degree of likeness. The scores assigned for each attribute are: 1, Dislike very much; 2, Dislike; 3, Like nor Dislike; 4, Like and 5, Like very much. Statistical analysis Results obtained for specific volume, moisture content and proximate composition of breads were statistically analyzed by ANOVA and sensorial data were statistically analyzed by the Friedman test using the SAS analytical package.
RESULTS
difference in specific volume was significant (P<0.05) under all the different substitutions considered. The highest specific volume (4.71 cm3/g) was obtained for 100% wheat bread (Formula I-a) and the specific volume of the breads decreased significantly (P <0.05) from 4.57 to 2.95 cm3/g whereas the moisture content of the breads was increased as the substitution level increases. Regarding moisture content, significant increase (P<0.05) from 29.4% to 33.4% with increasing level of malted rice flour was seen. Extreme outliers in the results were omitted for the analysis. The sensory analysis showed no significant differences (P>0.05) for the attributes of flavor and crust texture of the malted rice flour-wheat bread compared with 100% wheat bread, while significant differences (P<0.05) for the attributes of crumb colour, crumb texture, crust colour and degree of mouth satisfaction (Fig. 1-A). Crumb colour and crust colour were increased from whitish to reddish with increasing level of malted rice flour substitution. Bread with the 40% (Formula I-f) substitution level produced sticky crumb texture and the lowest scores for mouth satisfaction. Even though the 35% substitution level (Formula I-e) had low level of mouth satisfaction and low specific volume, by considering the nutritional value, this formula was selected for further studies to improve the taste and specific volume. Effects of fat content on bread quality
Effects of different concentrations of malted rice flour on bread quality Malted rice flour from four days of germination was used for the preparation of bread. Considering the substitution of wheat flour with malted rice flour,
The specific volume was increased significantly (P<0.05) from 3.8 to 3.9 cm3/g when the fat content of flour was increased from 10 to 20 g/kg. After that, with increase in the amount of fat, the specific volume decreased, but the decrease was not significant
Fig. 1. Effects of different contents of malted rice flour (A) and fat (B) on the mean scores for the attributes of flavor, mouth satisfaction, crumb colour, crumb texture, crust colour and crust texture of breads.
Subajiny VELUPPILLAI, et al. Optimization of Bread Preparation from Wheat Flour and Malted Rice Flour
(P>0.05) for 40 g/kg (Formula III-c) and 60 g/kg of flour (Formula III-d). Moisture content of the breads under different treatments ranged from 29.47% to 29.88% and did not differ significantly (P>0.05) among treatments. Sensory analysis (Fig. 1-B) showed that a significant difference (P<0.05) was observed only for crumb texture. The crumb texture became sticky as the fat content increases. While other attributes such as flavor, crumb colour, crust colour, crust texture and mouth satisfaction did not differ significantly (P>0.05) among treatments. Based on these results, the fat content of 20 g/kg of flour (Formula III-b) was selected as the best one.
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Table 3. Effect of germination days of malted rice on the mean scores for the attributes of flavor, mouth satisfaction, crumb colour, crumb texture, crust colour and crust texture of breads. Germination time Mouth Crumb Crumb Crust Crust Flavor (d) satisfaction colour texture colour texture 0 1 2 3 4
3.0 3.0 3.0 3.0 3.0
3.6 3.5 3.7 3.8 3.9
4.0 4.1 4.1 4.0 4.1
4.1 4.0 4.0 4.1 4.1
2.9 2.9 3.0 2.9 2.9
1.0 1.0 1.1 1.2 1.0
The ratio of wheat flour and malted rice flour is 65:35.
Significant differences (P<0.05) in specific volumes were observed among the breads made from rice flour malted for 0 (raw rice) (Formula II-a), 1 (Formula II-b) and 2 days (Formula II-c), whereas the specific volume of breads made from rice flour malted for 3 (Formula II-d) and 4 days (Formula II-e) did not differ significantly (P>0.05). The specific volume increased from 2.3 to 3.8 cm3/g with the increase in the germination time. Moisture content (ranged from 29.82% to 30.05%) and all the attributes of sensory evaluation showed no significant difference (P>0.05) among different treatments. Mean score obtained for the attributes of different treatments are shown in Table 3.
(P<0.05) from 3.91 to 3.31 cm3/g with increasing levels of baking powder whereas the moisture content (ranged from 30.37% to 32.20%) did not differ significantly (P>0.05). Sensory evaluation showed no significant difference (P>0.05) for flavor and crumb colour among the treatments. Other attributes such as crumb texture, crust colour, crust texture and mouth satisfaction differed significantly (P<0.05) among the treatments (Fig. 2-A). Crust colour was increased towards reddish with increasing level of baking powder. Baking powder at the level of 20 g/kg of flour (Formula IV-b) produced soft crumb texture. Comments showed that baking powder at the levels of 30 (Formula IV-c), 40 (Formula IV-d) and 50 g/kg of flour (Formula IV-e) gave bitter taste. The Formula IV-b showed a higher score for the degree of mouth satisfaction than the control (without baking powder). Therefore, the Formula IV-b was selected as the best one.
Effects of baking powder on bread quality
Effects of yeast concentrations on bread quality
Effects of malting time of rice on bread quality
The specific volume showed a significant decrease
In order to find out the optimum concentration of
Fig. 2. Effects of addition of different amounts of baking powder (A), yeast (B) and different ratios between optimum amount of yeast (20 g/kg) and baking powder (20 g/kg) (C) on the mean scores for the sensory attributes of flavor, mouth satisfaction, crumb colour, crumb texture, crust colour and crust texture of breads.
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yeast for bread making, bread formulation developed from previous experiment was evaluated with different concentrations of yeast. The specific volume increased significantly (P<0.05) from 4.0 to 4.4 cm3/g when the amount of yeast increased from 10 to 20 g/kg of flour. After that, the specific volume was decreased with the increasing level of yeast, but the decrease was not significant (P>0.05). Moisture content was decreased from 34.3% to 29.6% with the increasing level of yeast. Regarding sensory analysis (Fig. 2-B), among the attributes evaluated, only the mouth satisfaction showed significant difference (P<0.05) among the treatments. Yeast used at the levels of 40 (Formula Vd) and 50 g/kg of flour (Formula V-e) showed a lower degree of mouth satisfaction than the levels of 10 (Formula V-a), 20 (Formula V-b) and 30 g/kg of flour (Formula V-c). Comments showed that the yeast levels of more than 30 g/kg of flour gave acid taste to bread. Therefore, bread made by using the yeast level of 20 g/kg of flour (Formula V-b) was selected as the best one for further studies. Effects of different ratios between yeast and baking powder on bread quality The optimum amounts of yeast and baking powder selected from previous experiments were examined with possible combinations. A significantly higher (P<0.05) specific volume (4.96 cm3/g) was obtained at the ratio of 2:1 (yeast:baking powder) (Formula VI-b) than other ratios. Moisture contents of the breads from different treatments ranged from 29.97% to 30.56% and did not differ significantly (P>0.05). Sensory analysis (Fig. 2-C) showed no significant difference (P<0.05) in flavor and crumb colour among the treatments. Higher degree of mouth satisfaction was obtained at the ratio of 2:1 (yeast:baking powder) (Formula VI-b). Based on these results, the Formula VI-b was selected as the best one.
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moisture content was decreased from 30.67 to 28.92% when the amount of bread improver was increased from 5 to 40 g/kg of flour. The sensory analysis (Fig. 3) showed a significant difference (P<0.05) among the treatments for the attribute of mouth satisfaction only, whereas others did not differ significantly (P>0.05). The highest score for mouth satisfaction was obtained for bread improver at the level of 40 g/kg of flour. Based on these results, the Formula VII-d was selected as the best one. Comparison of malted rice-wheat bread with wheat bread The specific volume of the 100% wheat (5.84 cm /g) was significantly higher (P<0.05) than that of malted rice-wheat bread (5.31 cm3/g). Proximate composition of malted rice-wheat bread and wheat bread are as follows: moisture, 35.44% and 33.11%; total protein, 6.62% and 7.62%; fat, 1.40% and 1.40%; ash, 1.76% and 1.73%; free amino acids, 0.06% and 0.03%; soluble dietary fiber, 0.62% and 0.50%; insoluble dietary fiber, 3.95% and 2.73%; total dietary fiber, 4.57% and 3.23%; total carbohydrate, 50.87% and 52.80%, respectively. Malted rice-wheat bread was compared with 100% wheat bread to evaluate flavor, mouth satisfaction, crumb colour, crumb texture, crust colour and crust texture by applying the five points scale (Fig. 4). The lowest score was assigned for ‘dislike’ and the highest for ‘like’ category for each attribute. Extreme outliers were omitted from the analysis. When comparing the sensory characters of wheat bread and malted rice3
Effects of different concentrations of bread improver on bread quality The specific volume increased with increase in the amount of bread improver. The highest specific volume (5.23 cm3/g) was obtained at the level of 40 g/kg of flour (Formula VII-d) and the lowest (5.00 cm3/g) at the 50 g/kg of flour (Formula VII-a). The
Fig. 3. Effects of bread improver concentration on the mean scores for the attributes of flavor, mouth satisfaction, crumb colour, crumb texture, crust colour and crust texture of breads.
Subajiny VELUPPILLAI, et al. Optimization of Bread Preparation from Wheat Flour and Malted Rice Flour
Fig. 4. Mean scores of the attributes of flavor, mouth satisfaction, crumb colour, crumb texture, crust colour and crust texture for the malted rice-wheat bread and 100% wheat bread made in the bakery.
wheat bread, only the crumb texture differed significantly (P<0.05).
DISCUSSION Rice bran fiber is very hydrophilic and can absorb almost its weight of water [21]. Since the rice grains used in this study were whole rice grains, the rice bran added from the malted rice flour may be the reason for the increase in the moisture content with the increase in the level of substitution of wheat flour with malted rice flour. From this study, 35% malted rice flour substitution level (Formula I-e) was selected for further studies considering the nutritional value, even though the specific volume of the bread was decreased. The increase in specific volume with increase in germination time might be due to the increase in hydrolytic enzymes (especially endogenous amylase) and soluble materials. The principal functional benefits of malted rice flour addition include an increased gas production in the dough and an improved crust colour formation, a better crumb moisture retention and an enhanced flavor development. Malt α-amylases acting on damaged starch granules rectify the deficiency of fermentable sugar which is necessary for optimal yeast growth and gas production [22]. Addition of germinated soy bean flour to wheat flour improved the overall bread quality and resulted in a higher specific volume [2]. The malt amylase present in the malted rice would also improve the bread quality when compared
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to that prepared from raw rice. Considering nutritional and sensory values, bread prepared from rice flour malted for 3 days (Formula II-d) was selected for further studies. Therefore, it could be concluded that the use of germinated rice flour has advantage over the use of raw rice flour for bread making. Also, with the increase in germination time, the physical and nutritional quality of bread could be improved. Fats and oils, widely known as shortenings, are used in baking to improve the quality of baked loaves [23]. Proper amount of fat in bread dough improves the volume, grain, texture and crust tenderness, keeps quality of bread and makes the dough more elastic [24]. During baking, fat crystals melt, thereby making it possible for the crystal-liquid interface to be incorporated into the surface of the bubble as it expands [25]. This transfer of interfacial material from crystals to bubble surface explains how the addition of shortening to dough allows bubbles to expand during baking without rupturing, thus producing high volume bread with fine crumb structure. However, in this study, the specific volume increased only up to the fat level of 20 g/kg of flour beyond which the specific volume decreased and the bread’s texture was sticky. Therefore, 2 g of margarine per 100 g of flour (Formula III-b) was selected to be the optimum amount for malted rice-wheat bread making. The majority of bakery products, principally breads are manufactured using yeast as a leavening agent. The yeasts used are strains of Saccharomyces cerevisiae which ferment the sugars present to produce ethanol and carbon dioxide when incorporated into dough. The ethanol is driven off during the subsequent baking stage. The production of carbon dioxide in the dough leads to the formation of a network of regularly shaped cavities so that, when the dough is baked, the bread has a more or less uniform honey comb-like texture. The principal alternative to using yeast is to produce carbon dioxide chemically by reacting sodium bicarbonate with an acid salt, the mixture of chemicals known as baking powder [26]. In this study even yeast was used as leavening agent in the basic bread formulation. The effect of addition of different amounts of baking powder and yeast and the effect of different ratios of optimum amount of baking powder and yeast levels were
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evaluated. Baking powder used in this study contained sodium bicarbonate and sodium acid pyrophosphate. When the mixture dissolves in water and the temperature rises, carbon dioxide is released. Addition of baking powder to bread produced an attractive reddish colour to breads. However, higher levels (above 20 g/kg of flour) of baking power produced bitter taste and unacceptable smell to breads. Therefore, it was decided to find out the optimum ratio among baking powder and yeast. From this experiment, the ratio of 1:2 (baking powder:yeast) (Formula VI-b) produced better taste, texture and colour to breads. Thus, the amount of baking powder and yeast selected were 10 g/kg and 20 g/kg, respectively (Formula VI-b). Bread improver used in this study mainly contained α-amylase (activity 2490 U/g). The α-amylase is an endo-enzyme that randomly hydrolyses the α-1,4glucosidic linkages in polysaccharides, resulting in short chains further fermented by yeast [27]. The αamylase is routinely added to bread dough in order to supply dextrins which are effective in decreasing bread hardness. The improved bread volume after addition of enzymatic preparations was caused by the increased amount of fermentable sugars. Usually wheat flour contains a sufficient amount of β-amylase. However, only α-amylases are able to hydrolyze native undamaged starch. During the dough making process, the damaged starch granules are quickly attacked by both α- and βamylases [28]. The same observation of increase in the volume of the bread was found with the increase in the germination time in which the amylase activity was increased. Therefore, the increase in the volume of bread with the increase in the amount of bread improver could be attributed to the increase in the amount of amylases. Also, it could be concluded that the inclusion of malted rice flour in bread making is advantageous and can be a natural alternative to artificial enzyme preparations. The contents of moisture, total protein, total digestible carbohydrate, soluble dietary fiber (SDF), insoluble dietary fiber (IDF), total dietary fiber (TDF) and free amino acids of the malted rice-wheat bread differed significantly (P<0.05) from the wheat bread while fat and ash contents did not (P>0.05). Total protein and total digestible carbohydrate contents of the wheat bread were higher than those of the malted
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rice-wheat bread. Free amino acids content of the malted rice-wheat bread is almost twice than that of the wheat bread. It could be due to the fact that the free amino acids content increases during germination. Dietary fiber plays a key role in maintaining human health. The glycemic index is an extension of the fiber hypothesis, suggesting that fiber consumption reduces the rate of nutrient influx from the gut. TDF consists of SDF and IDF. Among those properties, SDF has the highest correlation with glycemic response and affects blood glucose control. SDF directly decreases digestion rate by impeding access to digestive enzymes and absorption rate by slowing diffusion across unstirred layer. While indirect effect of SDF decreases absorption of dietary fat and regulates the appetite [29]. When the fiber contents of the wheat flour bread (prepared in bakery) and malted rice-wheat bread (final bread Formula VI-b) were considered, the malted rice-wheat bread contained more SDF (0.62%), IDF (3.95%) and TDF (4.57%) than the wheat flour bread (0.50%, 2.73% and 3.23%, respectively). The available carbohydrate in the foods for absorption might be made unavailable due to its SDF, IDF and TDF contents. The monosaccharide released by hydrolysis and available for absorption might be made unavailable. This could be due to the tendency of the fibers to absorb sugars and that the absorbed sugars released slowly. Soluble fibers slow down the digestion of starches and absorption of the glucose into the bloodstream [30]. The SDF, IDF and TDF contents of malted rice-wheat bread were higher than those of wheat flour bread. Therefore, the glycemic index of malted rice-wheat bread would be lower than that of wheat flour bread.
CONCLUSIONS A bread formulation containing rice flour obtained from malting of whole rice grains for 3 days was established considering both nutritional and sensory qualities of the bread based on the present study. The bread formulation is, malted rice flour 35%, wheat flour 65%, fat 2%, baking powder 1%, yeast 2%, bread improver 4%, sugar 3% and salt 1.67%. The results of the present study suggest that breads can be prepared from the inclusion of malted rice flour with
Subajiny VELUPPILLAI, et al. Optimization of Bread Preparation from Wheat Flour and Malted Rice Flour
better consumer acceptability and better nutritional value than wheat bread. Also, the inclusion of malted rice flour in bread can significantly reduce the glycemic index of bread. Thus the malted rice wheat bread can be a better choice for management of diabetics.
12
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Nishita K D, Bean M M. Physiochemical properties of rice in relation to rice bread. Cereal Chem, 1979, 56(3): 183–189.
13
Gujral H S, Rosell C M. Improvement of the bread making quality of rice flour by glucose oxidase. Food Res Int, 2004, 37(1): 75–81.
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Noomhorm A, Bandola D C. Effect of rice variety, rice flour concentration and enzyme levels on composite bread quality. J Sci Food Agric, 1994, 64(4): 433–440.
ACKNOWLEDGEMENT
15
Cawley R W, Howarth D T. The wheat industry. [2009-0617]. http://www.nzic.org.nz/ChemProcesses/food/6C.pdf.
Financial support from the University of Jaffna, Sri Lanka is highly acknowledged.
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