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Bread from composite cassava-wheat flour: I. Effect of baking time and temperature on some physical properties of bread loaf
Food Research International 40 (2007) 280–290 www.elsevier.com/locate/foodres
Bread from composite cassava-wheat flour: I. Effect of baking time and temperature on some physical properties of bread loaf T.A. Shittu a
a,*
, A.O. Raji b, L.O. Sanni
a,c
Department of Food Science and Technology, University of Agriculture, Alabata Road, Abeokuta, Ogun, Nigeria b Department of Agricultural and Environmental Engineering, University of Ibadan, Ibadan, Nigeria c International Institute of Tropical Agriculture, Ibadan, Nigeria Received 14 September 2006; accepted 23 October 2006
Abstract The use of composite cassava-wheat (CCW) flour for commercial breadmaking purposes and consumption of CCW bread are relatively new in Nigeria. This study investigated the effect of baking temperature and time on some physical properties of bread from composite flour made by mixing cassava and wheat flour at ratio of 10:90 (w/w). A central composite rotatable experimental design was used while the baking temperature and time investigated ranged from 190 to 240 C and 20 to 40 min, respectively. Loaf volume, weight and specific volume varied significantly (p < 0.001) from 440 to 920 cm3, 162 to 183 g and 3.31 to 5.32 cm3/g, respectively. The tristimulus color parameters such as L* (lightness) and brownness index (BI) of the crust varied significantly (p < 0.01) from 31 to 72 and 68 to 123, respectively. Moreover, Fresh crumb moisture, density, porosity and softness as well as the dried crumb hardness were also significantly (p < 0.01) affected by both the baking temperature and time with values ranging from 34% to 39%, 0.16 to 0.20 g/cm3, 0.69 to 0.80, 13.00 to 18.05 mm and 0.90 to 2.05 kgf, respectively. Due to the complex effect of temperature and time combination, most of the measured properties could not be reliably predicted from the second order response surface regression equations except the loaf weight and crumb moisture. Further studies are required to optimize the CCW bread baking process based on some storage and consumption qualities. 2006 Published by Elsevier Ltd. Keywords: Bread loaf properties; Composite flour; Cassava; Wheat; Response surface methodology
1. Introduction Bread has become the second most widely consumed non-indigenous food products after rice in Nigeria. Till date, most Nigerians have not been introduced to other types of bread apart from that made from 100% wheat flour. To cut the nation’s expense on wheat importation and find wider utilization for the increasingly produced cassava roots, the Federal Government mandated the use of composite cassava-wheat flour for baking by adding minimum of 10% cassava flour to wheat for a start. To
*
Corresponding author. Tel.: +234 803 538 8060. E-mail address: [email protected] (T.A. Shittu).
0963-9969/$ - see front matter 2006 Published by Elsevier Ltd. doi:10.1016/j.foodres.2006.10.012
ensure the commercial success of this composite cassavawheat flour technology, systematic studies need to be conducted to fully understand the best way to formulate product and to determine the optimal processing conditions required to realize high quality baked products. Most of the previous studies conducted on the use of composite flour for breadmaking purposes (Adeyemi & Idowu, 1990; Dhingra & Jood, 2004; Hsu, Hurang, Chen, Weng, & Cheng, 2004; Khalil, Mansour, & Dawood, 2000; McWatter et al., 2004) were devoted to determining the effect of biological origin of flour and level of wheat flour substitution on their bread making quality. The composite flours used were either binary or ternary mixtures of flours from some other crops with or without wheat flour. They generally observed reduction in loaf volume and
T.A. Shittu et al. / Food Research International 40 (2007) 280–290
impairment of sensory qualities (e.g. appearance, texture, and flavor) as the level of substitution of wheat with nonwheat flour increased. Some varietal differences within the same crop in terms of bread making potential were also reported. In the works of Defloor, Nys, and Delcour (1993, 1994, 1995) and Khalil et al. (2000), it was specifically reported that inclusion of CF into wheat flour up to about 30% could still give an acceptable fresh loaf depending on the source of flour. Very few studies have also been conducted on the effect of baking temperature on the quality of bread from 100% wheat flour (Bloksma, 1990; Singh & Bhattacharya, 2005; Therdthai, Zhou, & Adamzcak, 2002; Zhang & Datta, 2006) and virtually none has been reported on composite cassava-wheat (CCW) bread. The control of parameters like temperature and time combination during baking is basically an engineering problem that is critical to the successful implementation of commercial composite flour baking technology. Presently, bread baking in Nigeria is mostly practiced at cottage level with ovens that lack temperature-time control devices. Fewer small and medium scale bakeries that use automated devices exist presently in the country (Idowu, Atanda, Bankole, Uzochukwu, & Olaewe, 2002). Baking duration used varied widely while fueling of ovens and temperature control is done using highly subjective means developed by these bakers through long time baking experience; baking also spans over a period ranging from 20 to 60 min. At present, systematic studies to understand the behavior of CCW dough under the prevalent processing conditions encountered in these bakeries are lacking. Such studies will assist in the design and development of appropriate process for making baked product from CCW flour and also guide in the design of interim training program for successful application of CCW flour technology by the bakers in the country. This study was devoted to determine how various temperature–time combinations would influence the physical properties of CCW bread using the government approved 10% CF substitution into wheat flour as a basis. 2. Materials and methods 2.1. Preparation of composite flour Cassava flour (CF) used was obtained from Cassava Mosaic Disease (CMD) resistant clone (TMS 30572) of the International Institute of Tropical Agriculture (IITA), Ibadan. Hard red wheat flour was obtained from Honeywell Flour Mill, Lagos, Nigeria. Composite flour was made by mixing 10 parts of cassava flour (CF) and 90 parts wheat flour as approved by the Federal Government of Nigeria in November 2004. Other materials include granulated sugar (Dangote Groups (Nig.) Ltd., Lagos Nigeria), Fermipan baking yeast (DSM bakery ingredient, Dordrecht-Holland), baking fat (PT Intiboga Sejahtera, Jakarta, Indonesia).
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2.2. Baking experiment All ingredients (Table 1) were initially dry mixed in a Hobart mixing machine and later water was mixed with the original dry mix until soft dough that can easily be handled is produced. The straight dough method described in Eggleston, Omoaka, and Arowosegbe (1993) was followed. The whole mass was kneaded mechanically, divided into equal sizes of 100 g and then manually kneaded before molding into cylindrical shape, and placed in the bread baking tin. Dough proofing was carried for 30 min in tin in a thermostatically controlled chamber for 2 h under ambient conditions (32 C, 78–80% RH) before baking. 2.3. Experimental design The central composite rotatable design (Mason, Gunst, & Hess, 1989), consisting of a two-factor five-level pattern with 10 design points (8 combinations with two replication of the center point) was used. The combination of the two factors (baking temperature and time) studied in the response surface experiment, their coded and actual values are shown in Table 2. The bread samples were allowed to cool for about 6 h prior to use in analysis. For each trial, three samples were produced and analyzed separately. 2.4. Determination of physical properties 2.4.1. Loaf weight, volume and specific volume The weights of bread samples were determined after sufficient cooling using a digital balance (0.01 g accuracy) and the loaf volumes were determined using rapeseed displacement method. The specific volume of each loaf was then calculated as Specific volumeðcm3 =gÞ ¼
Loaf volume : loaf weight
ð1Þ
2.4.2. Crumb moisture The bread loaves were first cut into slices of 1.5 cm thick using a slicing machine. The outer crust of bread samples were carefully scrapped with kitchen type bread knife. Samples of bread crumb were cut from five points along the diagonal point of 3 separate slices. The 1 g cuts from each point were combined to make a final weight of about Table 1 Recipe used in dough formulation per loaf Material
Compositiona
Cassava flour Wheat flour Salt Sugar Yeast Vegetable oil EDC
30.0 g 270.0 g 1.5% 6.0% 5.0% 3.0% 0.3%
a
% values are based on the total flour weight (300 g).
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Table 2 Experimental design showing coded and actual values of baking temperature and time used in the experiment Trial
1 2 3 4 5 6 7 8 9 10
Variable codes
Actual values
X1
X2
Temperature (C)
Time (min)
1 1 1 1 0 1.414 0 0 0 1.414
1 1 1 1 0 0 0 1.414 1.414 0
233 197 197 233 215 240 215 215 215 190
41.0 24.0 41.0 24.0 32.5 32.5 32.5 45.0 20.0 32.5
Inc., USA). The instrument has spot diameter view of 15 mm. To determine the color of bread crust, the top crust was divided equally into three regions and the tristimulus color parameters L*, a*, b* were determined within each region in duplicate. The brownness index (BI) was calculated according to Maskan (2001): ½100ðx 0:31Þ ; 0:17 ða þ 1:75LÞ : x¼ ð5:645 L þ a 3:012bÞ
BI ¼
ð2Þ ð3Þ
The means of each duplicate measurement was reported as the crust color parameter. 2.5. Crumb density and porosity
5 g. The moisture content was determined by placing bread crumb samples on Petri dishes that were placed in a digital oven chamber. The oven temperature was thermostatically set at 75 ± 2 C while the samples were dried for about 72 h to allow for slow and non destructive drying process. 2.4.3. Crumb hardness (textural analysis) The textural analysis was carried out to determine both the dried crumb hardness and fresh crumb softness. The softness of fresh crumb was determined using a bench top cone penetrometer with a 35 g probe (Central Ignition Company, UK), while the hardness of dried crumb was also determined using a hardness tester (Kiya Seisakuso Ltd., Tokyo, Japan). To determine the crumb softness, 5 cm thick bread slices were used in the analysis. Care was taken to obtain very flat and undistorted surfaces on the slices. The tip if the cone was brought to touch the bread surface by adjusting the hanger position. The cone was later released to fall under gravity and penetrate the bread crumb. The extent of penetration (mm) was determined on the radial dial gauge attached to the instrument after 3 s of penetration. Measurement was done at three points along a diagonal line within the crumb. To determine dried crumb hardness, about 2.5 · 2.5 · 1.5 cm3 crumb slice was obtained from each loaf at the crumb center. The slices were dried in laboratory oven at about 35 C for about 48 h giving rise to samples with moisture levels below 3.0%. Each slice was then placed in the middle of a flat surfaced hardness tester receptacle. The plunger head was brought to touch the surface of the dried crumb slice. Thereafter, the plunger was driven 40 rpm into the crumb until it fractured. The maximum force required to cause the failure (measured in g) was read off the dial gauge attached to the instrument. Measurement was done in quintuplicate. 2.4.4. Crust color The tristimulus color parameters L* (Lightness), a* (Redness to Greenness), b* (Yellowness to Blueness) of the baked loaves crumbs were determined using a digital colorimeter (Color Tec PCM, Accuracy Micro census
A modified method of Saguy, Marabi, and Wallach (2005) was used in determining crumb porosity. In preparation for the analysis, bread samples were kept in ambient air (26–29 C, 72–75% RH) for 24 h to allow slow drying for proper setting of loaf in order to prevent possible deformation of loaf in subsequent handling, which can affect the true values of crumb porosity. A portion of each bread crumb [4.5 (length) · 4.5 (breadth) · 3.8 (thickness)] cm was cut from the central portion of loaves with a razor blade and dried at about 50 C for 12 h in an oven. The moisture content of dried crumb samples used was found to range between 2.0% and 3.0% while insignificant volumetric change (<0.5%) was observed due to shrinkage. The dried crumb slices were then cooled and weighed (W1) immediately using a sensitive balance (0.0001 g accuracy). The crumbs were ground in a laboratory sample mill (Analysenmuhle A10, Janke and Kunkel, IKA Labortechnik, Germany). The milled samples were sieved to 100 mesh size and the underflow was weighed (W2). The sample was then poured into a 20 cm3 measuring cylinder (accuracy = 0.5 cm3) and tapped 10 times. The volume occupied by the sample was determined (V2). The data were used to determine the crumb (qc) and solid density (qs) as follows: W1 V1 V2 qs ¼ W2
qc ¼
ð4Þ ð5Þ
V1 (Volume of rectangular sample) = Length · Breadth · Thickness. The crumb porosity was calculated as: q ec ¼ 1 c : ð6Þ qs 2.6. Rapid Visco-analysis of bread crumb The bread crumb was dried at 35 C overnight in a laboratory oven. The dried crumbs were carefully pulverized with a mild force to small grits. To determine the RVA viscosities, approximately 3 g of the grit were weighed into RVA canister; about 25 mL of distilled water was added
T.A. Shittu et al. / Food Research International 40 (2007) 280–290
to make slurry prior to viscosity analysis using a rapid visco analyzer (RVA) (Newport Scientific Pty. Ltd., Warriewood, Australia) to determine the peak, trough, breakdown, setback and final viscosities as well as the time to reach peak viscosity.
ied significantly (p < 0.001) with both baking time and temperature. A quick way to compare the effect of baking temperature and time on the loaf size from this experiment is to determine linear response of sample by varying one of the factors and making the other constant. Generally, Baking time had more significant linear effects compared to that of baking temperature. Some of these effects are displayed in Figs. 1–3. Higher loaf weight and volume have positive economic effect on bread at the retail end. Therefore, loaf weight reduction during baking is an undesirable economic quality to the bakers as consumers often get attracted to bread loaf with higher weight and volume believing that it has more substance for the same price. The specific volume, which is the ratio of the two properties, has been generally adopted in the literature as a more reliable measure of loaf size. Loaf volume is affected by the quantity and quality of protein in the flour (Ragaee & Abdel-Aal, 2006) as well as proofing time (Zghal, Scanlon, & Sapirstein, 2002). Whereas loaf weight is basically determined by the quantity of dough baked and the amount of moisture and carbon dioxide diffused out of the loaf during baking. In this study, higher temperature and longer baking period caused reduction of loaf weight (Fig. 1) while the opposite effect was shown on loaf volume and specific volume. Since the bread samples studied here have been produced from the same formulation, proofing time and dough size, the variation in loaf volume could be attributed mainly to different rate of gas evolution and the extent of starch gelatinization due to differences in baking temperature and time. It must also be mentioned that baking temperature and time parameters affects moisture retention capacity of bread crumb (Eggleston et al., 1993).
2.7. Data analyses Analysis of variance (ANOVA), correlations, and descriptive data analysis were carried out using the SPSS 11.0 (Michigan State University, USA) while the response surface regression was performed using S-PLUS 2000 Professional Release I (Mathsoft Inc., Seattle, WA, USA) statistical softwares as guided by Anon (1999). The accuracy of the response surface models developed for predicting each property was verified by calculating the absolute average deviation (AAD) (Bas & Boyaci, 2007) defined as: Pp jY i;exp Y i;cal j AAD ¼
i¼1
Y i;exp
p
ð7Þ
;
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where Yi,exp and Yi,cal are the experimental and calculated responses, respectively, and p is the number of experimental run. 3. Results and discussion 3.1. Loaf size The results of size-related parameters of the cassavawheat bread are shown in Table 3. Loaf volume, weight and specific volume ranged from 550 to 1125 cm3, 162 to 183 g and 3.0 to 6.6 cm3/g, respectively. These values var-
Table 3 Effect of baking temperature and time on size-related and color characteristics of composite cassava-wheat loaf Temperature (C)
Time (min)
Loaf weight (g)
Loaf volume (cm3)
Specific volume (g/cm3)
Crust L*
Crust a*
Crust b*
Brownness index
190.00 190.00 197.00 197.00 215.00 215.00 215.00 215.00 233.00 240.00
32.50 41.00 24.00 41.00 20.00 32.50 32.50 45.00 24.00 32.50
175.87 172.69 181.98 169.35 182.17 173.32 176.06 167.35 178.05 162.04
560.00 920.00 640.00 760.00 440.00 600.00 640.00 800.00 840.00 560.00
3.41 5.32 3.52 4.72 2.42 3.56 3.52 5.02 4.72 3.31
56.45 52.32 67.45 48.07 71.20 54.08 57.58 46.58 47.20 31.76
13.12 13.97 4.76 14.45 3.18 13.73 12.93 14.22 14.90 6.68
31.51 31.80 32.27 29.38 21.47 31.41 31.90 29.195 30.94 15.18
95.55 108.36 68.18 111.51 38.44 101.72 86.49 115.22 122.47 78.79
***
***
***
***
***
***
***
***
***
***
**
***
NS
***
***
***
***
**
***
*
***
Main effect: Temperature (T) Time (Tm) Interaction: T · Tm
Values are means of four replicate determinations. * Significant effect at p < 0.05. ** Significant effect at p < 0.01. *** Significant effect at p < 0.001.
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Crumb moisture (%)
Loaf weight (g)
180 175 170 165 160
40.0 39.0 38.0 37.0 36.0 35.0
155 190
215
190
240
38
Crumb moisture (%)
Loaf weight (g)
185 180 175 170 165 160 155 32.5
45
Baking time (min) Fig. 1. Effect of temperature (T) and time (Tm) on loaf weight [Tm: r2 = 0.978; T: r2 = 0.723].
60.0
Crust lightness, L
37 36 35 34 33 32 20
20
50.0 40.0 30.0 20.0 10.0 0.0 190
215
240
Baking temperature (deg C) 80
Crust Lightness, L
240
Baking temperature (deg C)
Baking temperature (deg C)
60 40 20 0 20
32.5
45
Baking time (min) Fig. 2. Effect of temperature (T) and Time (Tm) on crust lightness [Tm: r2 = 0.960; T: r2 = 0.561].
3.2. Crust color characteristics The values of the tristimulus color parameters L*, a* and of the bread crust as affected by various temperature– time combination in baking are shown in Table 3. These values ranged between 31 and 72, 3 to 15 and 15 to 33, b*
215
32.5
45
Baking time (min) Fig. 3. Effect of temperature (T) and time (Tm) on crumb moisture [Tm: r2 = 0.693; T: r2 = 0.333].
respectively. The values fall within the range obtained in previous works for various baked products. The crust color parameter L* reduced with increasing time and temperature (Fig. 2). This is expected because as the rate of brown pigment formation increase with temperature and time. The brownness index (BI) of the loaf crust ranged from 38.44 to 122.47. The BI was negatively affected by baking time (p < 0.01) while temperature effect was less significant (p > 0.05) (Table 3). The results also indicate that bread crust color can essentially be described as a composite of red and yellow pigments. Previous works have shown that instrumental measurement of baked products’ color is an inevitable quality check that could be used in determining the effects of ingredient or product formulation, process variable as well as storage conditions on baked products (Erkan, Celik, Bilgi, & Koskel, 2006; Gallagher, Gormley, & Arendt, 2003a, Gallagher, Kunkel, Gormley, & Arendt, 2003b; Sanchez, Klopfenstein, & Walker, 1995). Most of these works reported the tristimulus CIELAB color parameters (L*, a*, b*) for the respective products’ crust and crumb. Since the effect of baking formulation is not studied here, it is assumed crumb color characteristics are not liable to differ significantly in the samples. Thus, emphasis is placed on the changes in crust color characteristics. The crust color and thickness are two most emphasized in literature. In a very recent work by Jefferson, Lacey, and Sadd (2006) to understand the process of crust formation during bread baking, the effect of several process and product parameters were studied as they affect crust thickness, proportion of loaf mass in the crust and the final density at the bread
T.A. Shittu et al. / Food Research International 40 (2007) 280–290
surface. It was shown that 10% increase oven temperature caused about 12% increase in surface density, 3% increase in proportion of mass in crust and about 10% reduction in crust thickness. However, the combined effect of oven temperature and baking time was not studied. 3.3. Crumb properties The results showing the effect of baking temperature and time on crumb characteristics of composite cassava-wheat bread are shown in Table 4. The moisture content of bread crumbs ranged from 32% to 39%. It was found that effect of temperature on the residual moisture content in the loaves was more significant than that of time. The amount of moisture in bread crumb has some implication on the mechanical (Zghal et al., 2002) and keeping qualities (Defloor et al., 1993). It is also determined by the extent of gelatinization of starch in dough during baking. It was found that higher crumb moisture had a positive correlation with crumb softness. However, the relationship was not significant (Table 5, r = 0.443, p > 0.05). The crumb density is primarily affected by the volumetric expansion of dough due to gas evolution during proofing. However, early onset of gelatinization causes faster plasticization of the starch–protein network on gas cell walls formed and increases mechanical strength of dough near the surface thereby making further expansion difficult (Singh & Bhattacharya, 2005; Zhang & Datta, 2006). The highest crumb density (lowest gas cell formation) was found in bread baked at the highest baking temperature (240 C) and relatively longer time (32.5 min). Such loaf is characteristically heavy with ‘stony’ crumb. This is evident from the lowest porosity (0.634) of the same sample. Apart from the direct consumption of bread, breadcrumb is another bye-product of bread made by drying fresh bread crumb usually with near ambient conditions purposely to avoid further decomposition and gelatinization of starch. The dried stuff is then gently milled to avoid unwanted damage to starch granules. The particles may be sieved to desired sizes. Breadcrumb has found many applications as ingredients in processing of some other food products. For example, breadcrumb is used as breading materials in fries and coating in confectioneries. After appropriate drying, completely gelatinized crumb may be so difficult to mill gently as it becomes tough. A recent study (Ejiwumi, 2005) investigated the breadcrumb making quality of some flour for use as breading material in Scotch egg production. It was found that it is possible to replace 100% wheat breadcrumb with that made from maize– wheat composite flour to produce scotch-egg with a better overall acceptability. Similarly, breadcrumb from cassavawheat composite flour could be prospected. However, the influence of baking condition on the ease of milling must be established. Since gas filled cellular foods like bread are known to fail under mechanical force via brittle fracture (Warner, Thiel, & Donald, 2000), hardness test was therefore used
285
to establish the amount of energy that may be required to fracture a given volume of the dried crumb. It was found that baking time had more significant positive effect on the hardness of dried bread crumb (r = 0.611, p < 0.01). Dried crumb hardness correlated positively with loaf volume (and specific volume) (p < 0.01, Table 5). The presence of plasticizing agent like water, known to affect mobility of the food polymers, has also been reported to be responsible for differing mechanical behavior of solid foods (Luyten, Plijter, & Vliet, 2004). Also, higher moisture content is known to increase plasticization and reduce the tendency of solid foods to fail under brittle fracture, implying increased hardness. In order remove the effect of different crumb moisture on the hardness test, the crumb samples were dried under a slow and mild condition to moisture level below 3.0%. Since it has been shown earlier that bread with higher volume resulted from longer baking time, it is expected that such bread will undergo higher level of polymeric plasticization which takes place at the cell wall. The increased plasticization of the cell wall of bread crumb combined with moisture removal as experienced in this experiment, could have disposed the samples to higher brittle fracture hence the reduced hardness. Results further indicated that a soft crumb could give fairly brittle dried crumb as fresh crumb’s softness correlated negatively with dried crumb’s hardness as shown in Table 5 (r = 0.233, p > 0.05). The amylograph pasting viscosities (measured in RVU) of the dried bread crumb generally reduced with increasing baking temperature and time (Table 4). However, the singular effect of baking time and the interaction between temperature and time was significant on all the viscosity parameters. Lower peak and final viscosities directly indicate higher heat damage to the starch granule due to gelatinization and plasticization of starch–protein structure earlier mentioned. Specifically, the breakdown, final and setback viscosities were not affected by the baking duration. 3.4. Response surface models Response surface methodology (RSM) is an effective statistical technique which has been widely used to optimize processes or formulations with minimal experimental trials when many factors and their interactions may be involved. RSM was applied in studying combined effect of temperature and time on the physical properties of composite cassava-wheat bread produced in this study. Contour plots are 2D graphical outputs of RSM useful in showing how dependent variables respond to varying independent factors and identifying optimal points on a response surface. In order to appreciate how the measured bread properties respond to the process variable, contour plots were first generated using raw experimental data. Some of these plots are displayed in Figs. 4–9. Most of the contours plots show multiple asymmetric saddling, indicating a rather complex relationship between the
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Table 4 Effects of baking temperature and time on the CCW bread crumb properties Time (min)
Moisture (%)
Density (g/cm3)
Porosity
Hardness (kgf)a
Softness (mm)b
PKV(RVU)
TRGH(RVU)
BKDV(RVU)
FV(RVU)
SBV(RVU)
PKTM (min)
190.00 190.00 197.00 197.00 215.00 215.00 215.00 215.00 233.00 240.00
32.50 41.00 24.00 41.00 20.00 32.50 32.50 45.00 24.00 32.50
37.07 38.05 32.49 35.71 37.24 36.96 36.80 34.24 37.57 38.67
0.195 0.188 0.225 0.166 0.191 0.169 0.160 0.167 0.194 0.277
0.741 0.747 0.687 0.756 0.721 0.766 0.768 0.742 0.793 0.634
1.45 1.95 1.30 1.60 0.90 1.70 2.30 2.55 2.05 1.58
18.05 17.30 13.85 17.65 13.80 13.05 13.00 14.50 15.10 23.35
33.17 36.00 34.08 32.50 36.00 31.58 30.05 34.50 34.50 29.58
32.00 34.08 31.83 31.75 33.00 31.17 31.00 33.17 32.75 28.58
1.17 1.92 2.25 0.75 3.00 0.42 0.33 1.33 1.75 1.00
42.17 42.67 47.33 39.42 47.33 40.92 37.88 42.92 46.67 37.00
10.17 8.58 15.50 7.67 14.33 9.75 8.80 9.75 13.92 8.50
6.33 5.27 6.92 6.40 6.73 6.13 6.10 5.67 7.00 6.47
***
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***
**
***
*
**
NS
NS
NS
*
**
***
**
***
***
**
*
***
***
***
***
***
***
***
***
***
***
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***
***
Main effects: Temperature (T) Time (Tm) Interaction: T · Tm
PKV, peak viscosity; TRGH, trough; BKDV, breakdown viscosity; FV, final viscosity; SBV, setback viscosity; PKTM, time to reach peak viscosity. a Dried crumb. b Fresh crumb. * Significant effect at p < 0.05. ** Significant effect at p < 0.01. *** Significant effect at p < 0.001; NS, Not significant.
T.A. Shittu et al. / Food Research International 40 (2007) 280–290
Temperature (C)
**
*
b
a
LSV
1.000 0.091 0.074 0.401 0.406 0.674** 0.054 0.335 0.764** .481* 0.858**
LV 1.000 0.990** 0.123 0.055 0.457* 0.468* 0.646** 0.035 0.245 0.751** 0.552** 0.839**
Dried crumb. Fresh crumb within 12 h after baking. Correlation is significant at the 0.05 level (2-tailed). Correlation is significant at the 0.01 level (2-tailed).
1.000 0.227 0.358 0.259 0.006 0.311 0.308 0.405 0.680** 0.787** 0.335 0.333 0.423
36. 35 4 .6
35
3 7 .2
37.2
1.000 0.945** 0.441 0.686** 0.142 0.589** 0.489* 0.479*
9
1.000 0.564** 0.012 0.433 0.073
1.000 0.146 0.582** 0.601** 0.130 0.709**
1.000 0.404 0.586** 0.100 0.649** 0.529* 0.559*
37.
CS
CH
CP
20 190
31.8
20 190
32. 5 3 5 .6 3 6 .4
1.000 0.371 0.051 0.233 0.395 0.072 0.037 0.074 0.057
1.000 0.502 0.087 0.098 0.047 0.443* 0.383 0.125 0.391 0.046
CD
Baking time (min)
PD
CM
3 7 .9
LW
1.000 0.607** 0.947**
a
Baking time (min)
1.000 0.287 0.487* 0.462*
L
30
2 .7
3 .3 3 .0
Loaf weight (LW) Loaf volume (LV) Loaf specific volume (LSV) Crumb moisture (CM) Particle density (PD) Crumb density (CD) Crumb porosity (CP) Crumb hardness (CH)a Crumb softness (CS)b Crust lightness (L) Crust Redness (a) Crust yellowness (b) Brownness index (BI) 1.000 0.518
b
40
3 4 .9 3 4 .1 3 3 .3
Properties
35
3 .3
Table 5 Pearson’s correlation matrix between bread properties measured
1.000
CCS
T.A. Shittu et al. / Food Research International 40 (2007) 280–290 287
5.3
5.0 4 .7
4.5
3.9
4.2 3 .6
3 .6
25
4 .2 4 .5
4.7
200 210 220 230 Baking temperature (deg C)
Fig. 4. Combined effect of temperature and time on the loaf specific volume (cm3/g).
34.9
40
30
25
200 210 220 230 Baking temperature
Fig. 5. Effect of temperature and time on the crumb moisture content (%).
dependent and independent variables. This directly reflects the complexity of various changes that modified the bread properties during baking. This could have contributed to the low predictability of these properties. It also shows how critical is a step change in setting of baking temperature and time to the resultant quality of the product. To establish predictive models for the bread properties from the varying temperature and time used in baking, the experimental data for each response variable were fitted to the usual quadratic regression equation applied in most RSM studies (Bas & Boyaci, 2007). The regression parameters for these equations are shown in Table 6. Most of the properties were poorly predicted by a second order model.
288
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39
0 17.
9 15.
.7
.6
25
1 3 .6
20 190
200 210 220 230 Baking temperature (deg C)
Fig. 6. Effect of baking temperature and time on L-value of loaf crust.
Fig. 8. Effect of temperature and time on fresh crumb softness. 2.2
2 .4
1 .9
40
3 0 .6 5
0 .6 6
30
0. 0 68 0 .7 .7 0 2
0 .7 0 .7 3 5 0 .7 7 0.78
25 0 .7
30
25
2
5
0.80
1.0
200 210 220 230 Baking temperature (deg C)
20 190
1. 1 .2 3
1 .7 5 1.
0 .7
0
0 .7 3
0.68
0 .7
35
1 .7
35
Baking time (min)
40
0 .6
Baking time (min)
18 .1 17. 15. 0 9
200 210 220 230 Baking temperature (deg C)
2.1
20 190
.7
.3
14
67
71.2
.5 47 .5 51 4 . 55 .4 59 .3 63
20 190
30
.7
35
25
2 3 . 7 2 2 . 6 2 1 .5 2 0 .3
8
30
35
14
35
Baking time (min)
40
31.
Baking time (min)
40
1 .9
200 210 220 230 Baking temperature (deg C)
Fig. 7. Effect of temperature and time on the crumb porosity (%). Fig. 9. Effect of temperature and time on dried crumb hardness.
Though some had r2 values greater than 80%, the AAD values were extremely high (>50%). However, the crumb moisture and weight could be reliably predicted by the quadratic model. The r2 and AAD values were 0.677 and 3.51%, and 0.972% and 0.81%, respectively. It is worth noting that despite the low r2 value of moisture equation, it gave such an acceptable AAD value. We further tried to fit the experimental data to some third order models with a view to improving the predictability of the properties. We got equations with higher coefficient of determination (r2). However, the equations were too complex and their invalidity was established from the extremely higher values of AAD for all the dependent variables. The statistics showing the singular and interactive effects of the independent factors as well as the predictive powers of each regression equation have also been indicated (Table 6). The properties having the highest predictability are the
loaf weight, fresh crumb softness and crumb density while the least predictable was the crust lightness. Analysis of variance showed that baking temperature singularly had significant effects (p < 0.001) only on loaf weight and crust lightness (L*). On the other hand, singular effect of baking time was significant (p < 0.01) on all the properties except the bread crumb properties (moisture, density and porosity). This result is not unexpected since previous studies have shown that bread crumb properties are particularly more affected by pattern of starch gelatinization and process of cell formation, which are all time limited changes. Moreover, (Therdthai et al., 2002) have shown that the internal temperature of dough reaches a maximum at a time during baking. After this period the microstructure changes in the crumb will no longer be due to temperature changes but time.
5.6470 0.0191 0.3674 0.0297 14.3100 1.4020 **
***
0.7447 1.9580
Regression factor is significant at p < 0.05. Regression factor is significant at p < 0.01. Regression factor is significant at p < 0.001. *
6.48*** 8.37* 5.92E02* 7.89E03 0.832 34.09% 0.0000 5.90E02 1.22E04*** 1.06E04 2.44E04*** 0.797 >100% 0.0002 1.29*** 7.90E03** 3.93E03 1.06E03 0.927 0.81% 0.0000
0.75*** 3.88E03 3.53E04 4.32E03* 0.677 51.65% 0.0040
8.03 0.01 185.82 3.50***
Constant Temperature (T) Time (Tm) T2 Tm2 T · Tm R2 AAD Regression p-value RSE
3.15 1.12E02* 7.00E04 1.15E02* 0.605 3.57% 0.0141
10.21** 3.21E02*** 0.11 4.38E02 0.847 >100% 0.0000
8.98E02 1.34E04* 2.35E04 3.51E04*** 0.695 >100.0% 0.0027
0.25** 5.43E0 1.07E03 6.46E04 0.575 >100% 0.0223
83.63 2.85*** 7.40 5.94E02 32.06 0.26
Specific volume (g/cm3) (r2 = 0.677, AAD = 51.65%)
29.85 0.11
5257.94 47.22
7.88 6.81E02
Crumb density (g/ cm3)(r2 = 0.797, SE = 0.005) Crumb hardness (kgf) (r2 = 0.575, SE = 0.230) Crumb porosity (r2 = 0.695, SE = 0.017) Crumb softness (mm) (r2 = 0.847, SE = 4.398)
This study has been able to show that varying temperature–time combination during baking leads to significant differences in the quality of composite cassava-wheat bread produced. The results clearly reflect complex polymeric changes caused by the changing temperature–time combination in baking, which may be peculiar with the use of CCW flour in breadmaking. Consequently, it was found that most of the measured properties could not be reliably predicted with the usual quadratic model generally used for response surface model studies. The influence of baking temperature was specifically more significant on loaf volume and crumb moisture while baking time had more significant influence on loaf weight, dried crumb hardness and density. Therefore, further studies are required to accurately determine the response of sensory and storage properties of the CCW bread to changing baking temperature and time as they are more important for optimizing consumer acceptability. References
Weight (g) (r2 = 0.927, AAD = 0.81%)
Crumb moisture (%) (r2 = 0.605, AAD = 2.78%)
289
4. Conclusions
Regression factor
Table 6 Response surface regression equations predicting the effect of the independent baking factors on some cassava-wheat bread loaf properties
Crust lightness (r2 = 0.832 SE = 5.96)
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Adeyemi, I. A., & Idowu, M. A. (1990). Evaluation of pregelatinized maize in the development of maissa-a baked product. Nigerian Food Journal, 8, 63–73. Anon (1999). S-PLUS 2000 guide to statistics (vol. I). Seattle, Washintgon: Mathsoft Inc., p. 187–190. Bas, D., & Boyaci, I. H. (2007). Modeling and optimization I: usability of response surface methodology. Journal of Food Engineering, 78, 836–845. Bloksma, A. H. (1990). Rheology of the bread making process. Cereals Foods World, 35, 226–236. Defloor, I., Nys, M., & Delcour, J. A. (1993). Wheat starch, cassava starch, and cassava flour impairment of the bread making potential of wheat flour. Cereal Chemistry, 78, 525–530. Defloor, I., De Geest, C., Schellekens, M., Martens, A., & Delcour, J. A. (1994). Impact of genotype and cropdage on the breadmaking and physiochemical properties of flour produced from cassava (Manihot esculenta Crantz) planted in the dry season. Journal of the Science of Food and Agriculture, 66, 193–202. Defloor, I., Leijskens, R., Bokanga, M., & Delcour, J. A. (1995). Impact of genotype, crop age and planting season on the breadmaking and gelatinization properties of flour produced from cassava (Manihot esculenta Crantz). Journal of the Science of Food and Agriculture, 68, 167–174. Dhingra, S., & Jood, S. (2004). Effect of flour blending on the functional, baking and organoleptic characteristics of bread. International Journal of Food Science and Technology, 39, 213–222. Eggleston, G., Omoaka, P. E., & Arowosegbe, A. U. (1993). Flour starch and composite breadmaking quality of various cassava clones. Journal of the Science of Food and Agriculture, 62, 49–59. Ejiwumi, M.O. (2005). Comparative study of bread crumb making quality of different flours for making Scotch egg. Unpublished Postgraduate Diploma Thesis Submitted to the Department of Food Science and Technology, University of Agriculture, Abeokuta. Erkan, H., Celik, S., Bilgi, B., & Koskel, H. (2006). A new approach for the utilization of barley in food products: barley tarhana. Food Chemistry, 97, 12–18. Gallagher, E., Gormley, T. R., & Arendt, E. K. (2003a). Crust and crumb characteristics of gluten free breads. Journal of Food Engineering, 56, 153–163. Gallagher, E., Kunkel, A., Gormley, T. R., & Arendt, E. K. (2003b). The effect of dairy powder addition on loaf and crumb characteristics, and on shelf life (intermediate and long term) of gluten-free breads stored
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in a modified atmosphere. European Journal of Food Research, 218, 44–48. Hsu, C. L., Hurang, S. L., Chen, W., Weng, Y. M., & Cheng, C. Y. (2004). Qualities and antioxidant properties of bread as affected by incorporation of yam flour in the formulation. International Journal of Food Science and Technology, 39, 231–238. Idowu, M. A., Atanda, O. O., Bankole, M. O., Uzochukwu, S. V. A., & Olaewe, O. O. (2002). An assessment of the status and product quality of some breadmaking industries in Abeokuta. ASSET Series B, 1(1), 61–68. Jefferson, D. R., Lacey, A. A., & Sadd, P. A. (2006). Understanding crust formation during baking. Journal of Food Engineering, 75, 515–521. Khalil, A. H., Mansour, E. H., & Dawood, F. M. (2000). Influence of malt on rheological and baking properties of wheat-cassava composite flours. Lebensmittel Wissenchaf und Technologie, 33, 159–164. Luyten, H., Plijter, J. J., & Vliet, V. V. (2004). Crispy crunchy crust of cellular solid foods: a literature review with discussion. Journal of Texture Studies, 35, 445–492. Maskan, M. (2001). Kinetics of color change of kiwi fruit during hot air and microwave drying. Journal Food Engineering, 48, 169–176. Mason, R. L., Gunst, R. F., & Hess, J. L. (1989). Statistical design and analysis of experiments-with application to engineering and science. New York, USA: John Wiley and Sons. McWatter, K. H., Philips, R. D., Walker, S. L., McCullough, S. E., Mensah-Wilmot, Y., Saalia, F. K., et al. (2004). Baking performance
and acceptability of raw and extruded cowpea flour breads. Journal of Food Quality, 27, 337–351. Ragaee, S., & Abdel-Aal, E. S. M. (2006). Pasting properties of starch and protein in selected cereals and quality of their products. Food Chemistry, 95, 9–18. Saguy, S. I., Marabi, A., & Wallach, R. (2005). Liquid imbibition during rehydration of dry porous foods. Innovative Food Science and Technologies, 6, 37–43. Sanchez, C., Klopfenstein, C. F., & Walker, C. E. (1995). Use of carbohydrate fat substitute and emulsifying agents in reduced-fat shortbread cookies. Cereal Chemistry, 72, 25–29. Singh, A. P., & Bhattacharya, M. (2005). Development of dynamic modulus and cell opening of dough during baking. Journal of Texture Studies, 36, 44–56. Therdthai, N., Zhou, W., & Adamzcak, T. (2002). Optimization of the temperature profile in bread baking. Journal of Food Engineering, 55, 41–48. Warner, M., Thiel, B. L., & Donald, A. M. (2000). The elasticity and failure of fluid-filled cellular solids. Proceedings of the National Academy of Science, 97(4), 1370–1375. Zghal, M. C., Scanlon, M. G., & Sapirstein, H. D. (2002). Cellular structure of bread crumb and its influence on mechanical properties. Journal of Cereal Chemistry, 36, 167–176. Zhang, J., & Datta, A. K. (2006). Mathematical modeling of bread baking process. Journal of Food Engineering, 75, 78–89.
Bread from composite cassava-wheat flour: I. Effect of baking time and temperature on some physical properties of bread loaf T.A. Shittu a
a,*
, A.O. Raji b, L.O. Sanni
a,c
Department of Food Science and Technology, University of Agriculture, Alabata Road, Abeokuta, Ogun, Nigeria b Department of Agricultural and Environmental Engineering, University of Ibadan, Ibadan, Nigeria c International Institute of Tropical Agriculture, Ibadan, Nigeria Received 14 September 2006; accepted 23 October 2006
Abstract The use of composite cassava-wheat (CCW) flour for commercial breadmaking purposes and consumption of CCW bread are relatively new in Nigeria. This study investigated the effect of baking temperature and time on some physical properties of bread from composite flour made by mixing cassava and wheat flour at ratio of 10:90 (w/w). A central composite rotatable experimental design was used while the baking temperature and time investigated ranged from 190 to 240 C and 20 to 40 min, respectively. Loaf volume, weight and specific volume varied significantly (p < 0.001) from 440 to 920 cm3, 162 to 183 g and 3.31 to 5.32 cm3/g, respectively. The tristimulus color parameters such as L* (lightness) and brownness index (BI) of the crust varied significantly (p < 0.01) from 31 to 72 and 68 to 123, respectively. Moreover, Fresh crumb moisture, density, porosity and softness as well as the dried crumb hardness were also significantly (p < 0.01) affected by both the baking temperature and time with values ranging from 34% to 39%, 0.16 to 0.20 g/cm3, 0.69 to 0.80, 13.00 to 18.05 mm and 0.90 to 2.05 kgf, respectively. Due to the complex effect of temperature and time combination, most of the measured properties could not be reliably predicted from the second order response surface regression equations except the loaf weight and crumb moisture. Further studies are required to optimize the CCW bread baking process based on some storage and consumption qualities. 2006 Published by Elsevier Ltd. Keywords: Bread loaf properties; Composite flour; Cassava; Wheat; Response surface methodology
1. Introduction Bread has become the second most widely consumed non-indigenous food products after rice in Nigeria. Till date, most Nigerians have not been introduced to other types of bread apart from that made from 100% wheat flour. To cut the nation’s expense on wheat importation and find wider utilization for the increasingly produced cassava roots, the Federal Government mandated the use of composite cassava-wheat flour for baking by adding minimum of 10% cassava flour to wheat for a start. To
*
Corresponding author. Tel.: +234 803 538 8060. E-mail address: [email protected] (T.A. Shittu).
0963-9969/$ - see front matter 2006 Published by Elsevier Ltd. doi:10.1016/j.foodres.2006.10.012
ensure the commercial success of this composite cassavawheat flour technology, systematic studies need to be conducted to fully understand the best way to formulate product and to determine the optimal processing conditions required to realize high quality baked products. Most of the previous studies conducted on the use of composite flour for breadmaking purposes (Adeyemi & Idowu, 1990; Dhingra & Jood, 2004; Hsu, Hurang, Chen, Weng, & Cheng, 2004; Khalil, Mansour, & Dawood, 2000; McWatter et al., 2004) were devoted to determining the effect of biological origin of flour and level of wheat flour substitution on their bread making quality. The composite flours used were either binary or ternary mixtures of flours from some other crops with or without wheat flour. They generally observed reduction in loaf volume and
T.A. Shittu et al. / Food Research International 40 (2007) 280–290
impairment of sensory qualities (e.g. appearance, texture, and flavor) as the level of substitution of wheat with nonwheat flour increased. Some varietal differences within the same crop in terms of bread making potential were also reported. In the works of Defloor, Nys, and Delcour (1993, 1994, 1995) and Khalil et al. (2000), it was specifically reported that inclusion of CF into wheat flour up to about 30% could still give an acceptable fresh loaf depending on the source of flour. Very few studies have also been conducted on the effect of baking temperature on the quality of bread from 100% wheat flour (Bloksma, 1990; Singh & Bhattacharya, 2005; Therdthai, Zhou, & Adamzcak, 2002; Zhang & Datta, 2006) and virtually none has been reported on composite cassava-wheat (CCW) bread. The control of parameters like temperature and time combination during baking is basically an engineering problem that is critical to the successful implementation of commercial composite flour baking technology. Presently, bread baking in Nigeria is mostly practiced at cottage level with ovens that lack temperature-time control devices. Fewer small and medium scale bakeries that use automated devices exist presently in the country (Idowu, Atanda, Bankole, Uzochukwu, & Olaewe, 2002). Baking duration used varied widely while fueling of ovens and temperature control is done using highly subjective means developed by these bakers through long time baking experience; baking also spans over a period ranging from 20 to 60 min. At present, systematic studies to understand the behavior of CCW dough under the prevalent processing conditions encountered in these bakeries are lacking. Such studies will assist in the design and development of appropriate process for making baked product from CCW flour and also guide in the design of interim training program for successful application of CCW flour technology by the bakers in the country. This study was devoted to determine how various temperature–time combinations would influence the physical properties of CCW bread using the government approved 10% CF substitution into wheat flour as a basis. 2. Materials and methods 2.1. Preparation of composite flour Cassava flour (CF) used was obtained from Cassava Mosaic Disease (CMD) resistant clone (TMS 30572) of the International Institute of Tropical Agriculture (IITA), Ibadan. Hard red wheat flour was obtained from Honeywell Flour Mill, Lagos, Nigeria. Composite flour was made by mixing 10 parts of cassava flour (CF) and 90 parts wheat flour as approved by the Federal Government of Nigeria in November 2004. Other materials include granulated sugar (Dangote Groups (Nig.) Ltd., Lagos Nigeria), Fermipan baking yeast (DSM bakery ingredient, Dordrecht-Holland), baking fat (PT Intiboga Sejahtera, Jakarta, Indonesia).
281
2.2. Baking experiment All ingredients (Table 1) were initially dry mixed in a Hobart mixing machine and later water was mixed with the original dry mix until soft dough that can easily be handled is produced. The straight dough method described in Eggleston, Omoaka, and Arowosegbe (1993) was followed. The whole mass was kneaded mechanically, divided into equal sizes of 100 g and then manually kneaded before molding into cylindrical shape, and placed in the bread baking tin. Dough proofing was carried for 30 min in tin in a thermostatically controlled chamber for 2 h under ambient conditions (32 C, 78–80% RH) before baking. 2.3. Experimental design The central composite rotatable design (Mason, Gunst, & Hess, 1989), consisting of a two-factor five-level pattern with 10 design points (8 combinations with two replication of the center point) was used. The combination of the two factors (baking temperature and time) studied in the response surface experiment, their coded and actual values are shown in Table 2. The bread samples were allowed to cool for about 6 h prior to use in analysis. For each trial, three samples were produced and analyzed separately. 2.4. Determination of physical properties 2.4.1. Loaf weight, volume and specific volume The weights of bread samples were determined after sufficient cooling using a digital balance (0.01 g accuracy) and the loaf volumes were determined using rapeseed displacement method. The specific volume of each loaf was then calculated as Specific volumeðcm3 =gÞ ¼
Loaf volume : loaf weight
ð1Þ
2.4.2. Crumb moisture The bread loaves were first cut into slices of 1.5 cm thick using a slicing machine. The outer crust of bread samples were carefully scrapped with kitchen type bread knife. Samples of bread crumb were cut from five points along the diagonal point of 3 separate slices. The 1 g cuts from each point were combined to make a final weight of about Table 1 Recipe used in dough formulation per loaf Material
Compositiona
Cassava flour Wheat flour Salt Sugar Yeast Vegetable oil EDC
30.0 g 270.0 g 1.5% 6.0% 5.0% 3.0% 0.3%
a
% values are based on the total flour weight (300 g).
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Table 2 Experimental design showing coded and actual values of baking temperature and time used in the experiment Trial
1 2 3 4 5 6 7 8 9 10
Variable codes
Actual values
X1
X2
Temperature (C)
Time (min)
1 1 1 1 0 1.414 0 0 0 1.414
1 1 1 1 0 0 0 1.414 1.414 0
233 197 197 233 215 240 215 215 215 190
41.0 24.0 41.0 24.0 32.5 32.5 32.5 45.0 20.0 32.5
Inc., USA). The instrument has spot diameter view of 15 mm. To determine the color of bread crust, the top crust was divided equally into three regions and the tristimulus color parameters L*, a*, b* were determined within each region in duplicate. The brownness index (BI) was calculated according to Maskan (2001): ½100ðx 0:31Þ ; 0:17 ða þ 1:75LÞ : x¼ ð5:645 L þ a 3:012bÞ
BI ¼
ð2Þ ð3Þ
The means of each duplicate measurement was reported as the crust color parameter. 2.5. Crumb density and porosity
5 g. The moisture content was determined by placing bread crumb samples on Petri dishes that were placed in a digital oven chamber. The oven temperature was thermostatically set at 75 ± 2 C while the samples were dried for about 72 h to allow for slow and non destructive drying process. 2.4.3. Crumb hardness (textural analysis) The textural analysis was carried out to determine both the dried crumb hardness and fresh crumb softness. The softness of fresh crumb was determined using a bench top cone penetrometer with a 35 g probe (Central Ignition Company, UK), while the hardness of dried crumb was also determined using a hardness tester (Kiya Seisakuso Ltd., Tokyo, Japan). To determine the crumb softness, 5 cm thick bread slices were used in the analysis. Care was taken to obtain very flat and undistorted surfaces on the slices. The tip if the cone was brought to touch the bread surface by adjusting the hanger position. The cone was later released to fall under gravity and penetrate the bread crumb. The extent of penetration (mm) was determined on the radial dial gauge attached to the instrument after 3 s of penetration. Measurement was done at three points along a diagonal line within the crumb. To determine dried crumb hardness, about 2.5 · 2.5 · 1.5 cm3 crumb slice was obtained from each loaf at the crumb center. The slices were dried in laboratory oven at about 35 C for about 48 h giving rise to samples with moisture levels below 3.0%. Each slice was then placed in the middle of a flat surfaced hardness tester receptacle. The plunger head was brought to touch the surface of the dried crumb slice. Thereafter, the plunger was driven 40 rpm into the crumb until it fractured. The maximum force required to cause the failure (measured in g) was read off the dial gauge attached to the instrument. Measurement was done in quintuplicate. 2.4.4. Crust color The tristimulus color parameters L* (Lightness), a* (Redness to Greenness), b* (Yellowness to Blueness) of the baked loaves crumbs were determined using a digital colorimeter (Color Tec PCM, Accuracy Micro census
A modified method of Saguy, Marabi, and Wallach (2005) was used in determining crumb porosity. In preparation for the analysis, bread samples were kept in ambient air (26–29 C, 72–75% RH) for 24 h to allow slow drying for proper setting of loaf in order to prevent possible deformation of loaf in subsequent handling, which can affect the true values of crumb porosity. A portion of each bread crumb [4.5 (length) · 4.5 (breadth) · 3.8 (thickness)] cm was cut from the central portion of loaves with a razor blade and dried at about 50 C for 12 h in an oven. The moisture content of dried crumb samples used was found to range between 2.0% and 3.0% while insignificant volumetric change (<0.5%) was observed due to shrinkage. The dried crumb slices were then cooled and weighed (W1) immediately using a sensitive balance (0.0001 g accuracy). The crumbs were ground in a laboratory sample mill (Analysenmuhle A10, Janke and Kunkel, IKA Labortechnik, Germany). The milled samples were sieved to 100 mesh size and the underflow was weighed (W2). The sample was then poured into a 20 cm3 measuring cylinder (accuracy = 0.5 cm3) and tapped 10 times. The volume occupied by the sample was determined (V2). The data were used to determine the crumb (qc) and solid density (qs) as follows: W1 V1 V2 qs ¼ W2
qc ¼
ð4Þ ð5Þ
V1 (Volume of rectangular sample) = Length · Breadth · Thickness. The crumb porosity was calculated as: q ec ¼ 1 c : ð6Þ qs 2.6. Rapid Visco-analysis of bread crumb The bread crumb was dried at 35 C overnight in a laboratory oven. The dried crumbs were carefully pulverized with a mild force to small grits. To determine the RVA viscosities, approximately 3 g of the grit were weighed into RVA canister; about 25 mL of distilled water was added
T.A. Shittu et al. / Food Research International 40 (2007) 280–290
to make slurry prior to viscosity analysis using a rapid visco analyzer (RVA) (Newport Scientific Pty. Ltd., Warriewood, Australia) to determine the peak, trough, breakdown, setback and final viscosities as well as the time to reach peak viscosity.
ied significantly (p < 0.001) with both baking time and temperature. A quick way to compare the effect of baking temperature and time on the loaf size from this experiment is to determine linear response of sample by varying one of the factors and making the other constant. Generally, Baking time had more significant linear effects compared to that of baking temperature. Some of these effects are displayed in Figs. 1–3. Higher loaf weight and volume have positive economic effect on bread at the retail end. Therefore, loaf weight reduction during baking is an undesirable economic quality to the bakers as consumers often get attracted to bread loaf with higher weight and volume believing that it has more substance for the same price. The specific volume, which is the ratio of the two properties, has been generally adopted in the literature as a more reliable measure of loaf size. Loaf volume is affected by the quantity and quality of protein in the flour (Ragaee & Abdel-Aal, 2006) as well as proofing time (Zghal, Scanlon, & Sapirstein, 2002). Whereas loaf weight is basically determined by the quantity of dough baked and the amount of moisture and carbon dioxide diffused out of the loaf during baking. In this study, higher temperature and longer baking period caused reduction of loaf weight (Fig. 1) while the opposite effect was shown on loaf volume and specific volume. Since the bread samples studied here have been produced from the same formulation, proofing time and dough size, the variation in loaf volume could be attributed mainly to different rate of gas evolution and the extent of starch gelatinization due to differences in baking temperature and time. It must also be mentioned that baking temperature and time parameters affects moisture retention capacity of bread crumb (Eggleston et al., 1993).
2.7. Data analyses Analysis of variance (ANOVA), correlations, and descriptive data analysis were carried out using the SPSS 11.0 (Michigan State University, USA) while the response surface regression was performed using S-PLUS 2000 Professional Release I (Mathsoft Inc., Seattle, WA, USA) statistical softwares as guided by Anon (1999). The accuracy of the response surface models developed for predicting each property was verified by calculating the absolute average deviation (AAD) (Bas & Boyaci, 2007) defined as: Pp jY i;exp Y i;cal j AAD ¼
i¼1
Y i;exp
p
ð7Þ
;
283
where Yi,exp and Yi,cal are the experimental and calculated responses, respectively, and p is the number of experimental run. 3. Results and discussion 3.1. Loaf size The results of size-related parameters of the cassavawheat bread are shown in Table 3. Loaf volume, weight and specific volume ranged from 550 to 1125 cm3, 162 to 183 g and 3.0 to 6.6 cm3/g, respectively. These values var-
Table 3 Effect of baking temperature and time on size-related and color characteristics of composite cassava-wheat loaf Temperature (C)
Time (min)
Loaf weight (g)
Loaf volume (cm3)
Specific volume (g/cm3)
Crust L*
Crust a*
Crust b*
Brownness index
190.00 190.00 197.00 197.00 215.00 215.00 215.00 215.00 233.00 240.00
32.50 41.00 24.00 41.00 20.00 32.50 32.50 45.00 24.00 32.50
175.87 172.69 181.98 169.35 182.17 173.32 176.06 167.35 178.05 162.04
560.00 920.00 640.00 760.00 440.00 600.00 640.00 800.00 840.00 560.00
3.41 5.32 3.52 4.72 2.42 3.56 3.52 5.02 4.72 3.31
56.45 52.32 67.45 48.07 71.20 54.08 57.58 46.58 47.20 31.76
13.12 13.97 4.76 14.45 3.18 13.73 12.93 14.22 14.90 6.68
31.51 31.80 32.27 29.38 21.47 31.41 31.90 29.195 30.94 15.18
95.55 108.36 68.18 111.51 38.44 101.72 86.49 115.22 122.47 78.79
***
***
***
***
***
***
***
***
***
***
**
***
NS
***
***
***
***
**
***
*
***
Main effect: Temperature (T) Time (Tm) Interaction: T · Tm
Values are means of four replicate determinations. * Significant effect at p < 0.05. ** Significant effect at p < 0.01. *** Significant effect at p < 0.001.
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Crumb moisture (%)
Loaf weight (g)
180 175 170 165 160
40.0 39.0 38.0 37.0 36.0 35.0
155 190
215
190
240
38
Crumb moisture (%)
Loaf weight (g)
185 180 175 170 165 160 155 32.5
45
Baking time (min) Fig. 1. Effect of temperature (T) and time (Tm) on loaf weight [Tm: r2 = 0.978; T: r2 = 0.723].
60.0
Crust lightness, L
37 36 35 34 33 32 20
20
50.0 40.0 30.0 20.0 10.0 0.0 190
215
240
Baking temperature (deg C) 80
Crust Lightness, L
240
Baking temperature (deg C)
Baking temperature (deg C)
60 40 20 0 20
32.5
45
Baking time (min) Fig. 2. Effect of temperature (T) and Time (Tm) on crust lightness [Tm: r2 = 0.960; T: r2 = 0.561].
3.2. Crust color characteristics The values of the tristimulus color parameters L*, a* and of the bread crust as affected by various temperature– time combination in baking are shown in Table 3. These values ranged between 31 and 72, 3 to 15 and 15 to 33, b*
215
32.5
45
Baking time (min) Fig. 3. Effect of temperature (T) and time (Tm) on crumb moisture [Tm: r2 = 0.693; T: r2 = 0.333].
respectively. The values fall within the range obtained in previous works for various baked products. The crust color parameter L* reduced with increasing time and temperature (Fig. 2). This is expected because as the rate of brown pigment formation increase with temperature and time. The brownness index (BI) of the loaf crust ranged from 38.44 to 122.47. The BI was negatively affected by baking time (p < 0.01) while temperature effect was less significant (p > 0.05) (Table 3). The results also indicate that bread crust color can essentially be described as a composite of red and yellow pigments. Previous works have shown that instrumental measurement of baked products’ color is an inevitable quality check that could be used in determining the effects of ingredient or product formulation, process variable as well as storage conditions on baked products (Erkan, Celik, Bilgi, & Koskel, 2006; Gallagher, Gormley, & Arendt, 2003a, Gallagher, Kunkel, Gormley, & Arendt, 2003b; Sanchez, Klopfenstein, & Walker, 1995). Most of these works reported the tristimulus CIELAB color parameters (L*, a*, b*) for the respective products’ crust and crumb. Since the effect of baking formulation is not studied here, it is assumed crumb color characteristics are not liable to differ significantly in the samples. Thus, emphasis is placed on the changes in crust color characteristics. The crust color and thickness are two most emphasized in literature. In a very recent work by Jefferson, Lacey, and Sadd (2006) to understand the process of crust formation during bread baking, the effect of several process and product parameters were studied as they affect crust thickness, proportion of loaf mass in the crust and the final density at the bread
T.A. Shittu et al. / Food Research International 40 (2007) 280–290
surface. It was shown that 10% increase oven temperature caused about 12% increase in surface density, 3% increase in proportion of mass in crust and about 10% reduction in crust thickness. However, the combined effect of oven temperature and baking time was not studied. 3.3. Crumb properties The results showing the effect of baking temperature and time on crumb characteristics of composite cassava-wheat bread are shown in Table 4. The moisture content of bread crumbs ranged from 32% to 39%. It was found that effect of temperature on the residual moisture content in the loaves was more significant than that of time. The amount of moisture in bread crumb has some implication on the mechanical (Zghal et al., 2002) and keeping qualities (Defloor et al., 1993). It is also determined by the extent of gelatinization of starch in dough during baking. It was found that higher crumb moisture had a positive correlation with crumb softness. However, the relationship was not significant (Table 5, r = 0.443, p > 0.05). The crumb density is primarily affected by the volumetric expansion of dough due to gas evolution during proofing. However, early onset of gelatinization causes faster plasticization of the starch–protein network on gas cell walls formed and increases mechanical strength of dough near the surface thereby making further expansion difficult (Singh & Bhattacharya, 2005; Zhang & Datta, 2006). The highest crumb density (lowest gas cell formation) was found in bread baked at the highest baking temperature (240 C) and relatively longer time (32.5 min). Such loaf is characteristically heavy with ‘stony’ crumb. This is evident from the lowest porosity (0.634) of the same sample. Apart from the direct consumption of bread, breadcrumb is another bye-product of bread made by drying fresh bread crumb usually with near ambient conditions purposely to avoid further decomposition and gelatinization of starch. The dried stuff is then gently milled to avoid unwanted damage to starch granules. The particles may be sieved to desired sizes. Breadcrumb has found many applications as ingredients in processing of some other food products. For example, breadcrumb is used as breading materials in fries and coating in confectioneries. After appropriate drying, completely gelatinized crumb may be so difficult to mill gently as it becomes tough. A recent study (Ejiwumi, 2005) investigated the breadcrumb making quality of some flour for use as breading material in Scotch egg production. It was found that it is possible to replace 100% wheat breadcrumb with that made from maize– wheat composite flour to produce scotch-egg with a better overall acceptability. Similarly, breadcrumb from cassavawheat composite flour could be prospected. However, the influence of baking condition on the ease of milling must be established. Since gas filled cellular foods like bread are known to fail under mechanical force via brittle fracture (Warner, Thiel, & Donald, 2000), hardness test was therefore used
285
to establish the amount of energy that may be required to fracture a given volume of the dried crumb. It was found that baking time had more significant positive effect on the hardness of dried bread crumb (r = 0.611, p < 0.01). Dried crumb hardness correlated positively with loaf volume (and specific volume) (p < 0.01, Table 5). The presence of plasticizing agent like water, known to affect mobility of the food polymers, has also been reported to be responsible for differing mechanical behavior of solid foods (Luyten, Plijter, & Vliet, 2004). Also, higher moisture content is known to increase plasticization and reduce the tendency of solid foods to fail under brittle fracture, implying increased hardness. In order remove the effect of different crumb moisture on the hardness test, the crumb samples were dried under a slow and mild condition to moisture level below 3.0%. Since it has been shown earlier that bread with higher volume resulted from longer baking time, it is expected that such bread will undergo higher level of polymeric plasticization which takes place at the cell wall. The increased plasticization of the cell wall of bread crumb combined with moisture removal as experienced in this experiment, could have disposed the samples to higher brittle fracture hence the reduced hardness. Results further indicated that a soft crumb could give fairly brittle dried crumb as fresh crumb’s softness correlated negatively with dried crumb’s hardness as shown in Table 5 (r = 0.233, p > 0.05). The amylograph pasting viscosities (measured in RVU) of the dried bread crumb generally reduced with increasing baking temperature and time (Table 4). However, the singular effect of baking time and the interaction between temperature and time was significant on all the viscosity parameters. Lower peak and final viscosities directly indicate higher heat damage to the starch granule due to gelatinization and plasticization of starch–protein structure earlier mentioned. Specifically, the breakdown, final and setback viscosities were not affected by the baking duration. 3.4. Response surface models Response surface methodology (RSM) is an effective statistical technique which has been widely used to optimize processes or formulations with minimal experimental trials when many factors and their interactions may be involved. RSM was applied in studying combined effect of temperature and time on the physical properties of composite cassava-wheat bread produced in this study. Contour plots are 2D graphical outputs of RSM useful in showing how dependent variables respond to varying independent factors and identifying optimal points on a response surface. In order to appreciate how the measured bread properties respond to the process variable, contour plots were first generated using raw experimental data. Some of these plots are displayed in Figs. 4–9. Most of the contours plots show multiple asymmetric saddling, indicating a rather complex relationship between the
286
Table 4 Effects of baking temperature and time on the CCW bread crumb properties Time (min)
Moisture (%)
Density (g/cm3)
Porosity
Hardness (kgf)a
Softness (mm)b
PKV(RVU)
TRGH(RVU)
BKDV(RVU)
FV(RVU)
SBV(RVU)
PKTM (min)
190.00 190.00 197.00 197.00 215.00 215.00 215.00 215.00 233.00 240.00
32.50 41.00 24.00 41.00 20.00 32.50 32.50 45.00 24.00 32.50
37.07 38.05 32.49 35.71 37.24 36.96 36.80 34.24 37.57 38.67
0.195 0.188 0.225 0.166 0.191 0.169 0.160 0.167 0.194 0.277
0.741 0.747 0.687 0.756 0.721 0.766 0.768 0.742 0.793 0.634
1.45 1.95 1.30 1.60 0.90 1.70 2.30 2.55 2.05 1.58
18.05 17.30 13.85 17.65 13.80 13.05 13.00 14.50 15.10 23.35
33.17 36.00 34.08 32.50 36.00 31.58 30.05 34.50 34.50 29.58
32.00 34.08 31.83 31.75 33.00 31.17 31.00 33.17 32.75 28.58
1.17 1.92 2.25 0.75 3.00 0.42 0.33 1.33 1.75 1.00
42.17 42.67 47.33 39.42 47.33 40.92 37.88 42.92 46.67 37.00
10.17 8.58 15.50 7.67 14.33 9.75 8.80 9.75 13.92 8.50
6.33 5.27 6.92 6.40 6.73 6.13 6.10 5.67 7.00 6.47
***
***
***
**
***
*
**
NS
NS
NS
*
**
***
**
***
***
**
*
***
***
***
***
***
***
***
***
***
***
***
***
***
***
***
Main effects: Temperature (T) Time (Tm) Interaction: T · Tm
PKV, peak viscosity; TRGH, trough; BKDV, breakdown viscosity; FV, final viscosity; SBV, setback viscosity; PKTM, time to reach peak viscosity. a Dried crumb. b Fresh crumb. * Significant effect at p < 0.05. ** Significant effect at p < 0.01. *** Significant effect at p < 0.001; NS, Not significant.
T.A. Shittu et al. / Food Research International 40 (2007) 280–290
Temperature (C)
**
*
b
a
LSV
1.000 0.091 0.074 0.401 0.406 0.674** 0.054 0.335 0.764** .481* 0.858**
LV 1.000 0.990** 0.123 0.055 0.457* 0.468* 0.646** 0.035 0.245 0.751** 0.552** 0.839**
Dried crumb. Fresh crumb within 12 h after baking. Correlation is significant at the 0.05 level (2-tailed). Correlation is significant at the 0.01 level (2-tailed).
1.000 0.227 0.358 0.259 0.006 0.311 0.308 0.405 0.680** 0.787** 0.335 0.333 0.423
36. 35 4 .6
35
3 7 .2
37.2
1.000 0.945** 0.441 0.686** 0.142 0.589** 0.489* 0.479*
9
1.000 0.564** 0.012 0.433 0.073
1.000 0.146 0.582** 0.601** 0.130 0.709**
1.000 0.404 0.586** 0.100 0.649** 0.529* 0.559*
37.
CS
CH
CP
20 190
31.8
20 190
32. 5 3 5 .6 3 6 .4
1.000 0.371 0.051 0.233 0.395 0.072 0.037 0.074 0.057
1.000 0.502 0.087 0.098 0.047 0.443* 0.383 0.125 0.391 0.046
CD
Baking time (min)
PD
CM
3 7 .9
LW
1.000 0.607** 0.947**
a
Baking time (min)
1.000 0.287 0.487* 0.462*
L
30
2 .7
3 .3 3 .0
Loaf weight (LW) Loaf volume (LV) Loaf specific volume (LSV) Crumb moisture (CM) Particle density (PD) Crumb density (CD) Crumb porosity (CP) Crumb hardness (CH)a Crumb softness (CS)b Crust lightness (L) Crust Redness (a) Crust yellowness (b) Brownness index (BI) 1.000 0.518
b
40
3 4 .9 3 4 .1 3 3 .3
Properties
35
3 .3
Table 5 Pearson’s correlation matrix between bread properties measured
1.000
CCS
T.A. Shittu et al. / Food Research International 40 (2007) 280–290 287
5.3
5.0 4 .7
4.5
3.9
4.2 3 .6
3 .6
25
4 .2 4 .5
4.7
200 210 220 230 Baking temperature (deg C)
Fig. 4. Combined effect of temperature and time on the loaf specific volume (cm3/g).
34.9
40
30
25
200 210 220 230 Baking temperature
Fig. 5. Effect of temperature and time on the crumb moisture content (%).
dependent and independent variables. This directly reflects the complexity of various changes that modified the bread properties during baking. This could have contributed to the low predictability of these properties. It also shows how critical is a step change in setting of baking temperature and time to the resultant quality of the product. To establish predictive models for the bread properties from the varying temperature and time used in baking, the experimental data for each response variable were fitted to the usual quadratic regression equation applied in most RSM studies (Bas & Boyaci, 2007). The regression parameters for these equations are shown in Table 6. Most of the properties were poorly predicted by a second order model.
288
T.A. Shittu et al. / Food Research International 40 (2007) 280–290
39
0 17.
9 15.
.7
.6
25
1 3 .6
20 190
200 210 220 230 Baking temperature (deg C)
Fig. 6. Effect of baking temperature and time on L-value of loaf crust.
Fig. 8. Effect of temperature and time on fresh crumb softness. 2.2
2 .4
1 .9
40
3 0 .6 5
0 .6 6
30
0. 0 68 0 .7 .7 0 2
0 .7 0 .7 3 5 0 .7 7 0.78
25 0 .7
30
25
2
5
0.80
1.0
200 210 220 230 Baking temperature (deg C)
20 190
1. 1 .2 3
1 .7 5 1.
0 .7
0
0 .7 3
0.68
0 .7
35
1 .7
35
Baking time (min)
40
0 .6
Baking time (min)
18 .1 17. 15. 0 9
200 210 220 230 Baking temperature (deg C)
2.1
20 190
.7
.3
14
67
71.2
.5 47 .5 51 4 . 55 .4 59 .3 63
20 190
30
.7
35
25
2 3 . 7 2 2 . 6 2 1 .5 2 0 .3
8
30
35
14
35
Baking time (min)
40
31.
Baking time (min)
40
1 .9
200 210 220 230 Baking temperature (deg C)
Fig. 7. Effect of temperature and time on the crumb porosity (%). Fig. 9. Effect of temperature and time on dried crumb hardness.
Though some had r2 values greater than 80%, the AAD values were extremely high (>50%). However, the crumb moisture and weight could be reliably predicted by the quadratic model. The r2 and AAD values were 0.677 and 3.51%, and 0.972% and 0.81%, respectively. It is worth noting that despite the low r2 value of moisture equation, it gave such an acceptable AAD value. We further tried to fit the experimental data to some third order models with a view to improving the predictability of the properties. We got equations with higher coefficient of determination (r2). However, the equations were too complex and their invalidity was established from the extremely higher values of AAD for all the dependent variables. The statistics showing the singular and interactive effects of the independent factors as well as the predictive powers of each regression equation have also been indicated (Table 6). The properties having the highest predictability are the
loaf weight, fresh crumb softness and crumb density while the least predictable was the crust lightness. Analysis of variance showed that baking temperature singularly had significant effects (p < 0.001) only on loaf weight and crust lightness (L*). On the other hand, singular effect of baking time was significant (p < 0.01) on all the properties except the bread crumb properties (moisture, density and porosity). This result is not unexpected since previous studies have shown that bread crumb properties are particularly more affected by pattern of starch gelatinization and process of cell formation, which are all time limited changes. Moreover, (Therdthai et al., 2002) have shown that the internal temperature of dough reaches a maximum at a time during baking. After this period the microstructure changes in the crumb will no longer be due to temperature changes but time.
5.6470 0.0191 0.3674 0.0297 14.3100 1.4020 **
***
0.7447 1.9580
Regression factor is significant at p < 0.05. Regression factor is significant at p < 0.01. Regression factor is significant at p < 0.001. *
6.48*** 8.37* 5.92E02* 7.89E03 0.832 34.09% 0.0000 5.90E02 1.22E04*** 1.06E04 2.44E04*** 0.797 >100% 0.0002 1.29*** 7.90E03** 3.93E03 1.06E03 0.927 0.81% 0.0000
0.75*** 3.88E03 3.53E04 4.32E03* 0.677 51.65% 0.0040
8.03 0.01 185.82 3.50***
Constant Temperature (T) Time (Tm) T2 Tm2 T · Tm R2 AAD Regression p-value RSE
3.15 1.12E02* 7.00E04 1.15E02* 0.605 3.57% 0.0141
10.21** 3.21E02*** 0.11 4.38E02 0.847 >100% 0.0000
8.98E02 1.34E04* 2.35E04 3.51E04*** 0.695 >100.0% 0.0027
0.25** 5.43E0 1.07E03 6.46E04 0.575 >100% 0.0223
83.63 2.85*** 7.40 5.94E02 32.06 0.26
Specific volume (g/cm3) (r2 = 0.677, AAD = 51.65%)
29.85 0.11
5257.94 47.22
7.88 6.81E02
Crumb density (g/ cm3)(r2 = 0.797, SE = 0.005) Crumb hardness (kgf) (r2 = 0.575, SE = 0.230) Crumb porosity (r2 = 0.695, SE = 0.017) Crumb softness (mm) (r2 = 0.847, SE = 4.398)
This study has been able to show that varying temperature–time combination during baking leads to significant differences in the quality of composite cassava-wheat bread produced. The results clearly reflect complex polymeric changes caused by the changing temperature–time combination in baking, which may be peculiar with the use of CCW flour in breadmaking. Consequently, it was found that most of the measured properties could not be reliably predicted with the usual quadratic model generally used for response surface model studies. The influence of baking temperature was specifically more significant on loaf volume and crumb moisture while baking time had more significant influence on loaf weight, dried crumb hardness and density. Therefore, further studies are required to accurately determine the response of sensory and storage properties of the CCW bread to changing baking temperature and time as they are more important for optimizing consumer acceptability. References
Weight (g) (r2 = 0.927, AAD = 0.81%)
Crumb moisture (%) (r2 = 0.605, AAD = 2.78%)
289
4. Conclusions
Regression factor
Table 6 Response surface regression equations predicting the effect of the independent baking factors on some cassava-wheat bread loaf properties
Crust lightness (r2 = 0.832 SE = 5.96)
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