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Effect of barley husk addition on rheological, textural, thermal and sensory characteristics of traditional flat bread (chapatti)
Journal of Cereal Science 79 (2018) 376e382
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Journal of Cereal Science journal homepage: www.elsevier.com/locate/jcs
Effect of barley husk addition on rheological, textural, thermal and sensory characteristics of traditional flat bread (chapatti) Tooba Mehfooz a, Tahira Mohsin Ali a, *, Saqib Arif b, Abid Hasnain a a b
Department of Food Science and Technology, University of Karachi, 75270, Karachi, Pakistan Food Quality and Safety Research Institute, Pakistan Agricultural Research Council (PARC), University of Karachi Campus, 75270, Pakistan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 7 June 2017 Received in revised form 24 November 2017 Accepted 26 November 2017
The present study suggested utilization of barley husk obtained as a by-product during extraction of starch from barley grains in preparation of unleavened flat bread (chapatti). The barley husk was added at (5e30) % level to wheat flour. These flour and husk blends were then turned into dough by adding water based on farinograph water absorption. It was observed that gluten index reduced with addition of fiber suggesting weakened gluten network. This was also confirmed with increase in mixing tolerance index (MTI) values on addition of barley fiber. The correlation between percent fiber and MTI was found to be 0.899 (p < 0.01). Alveograph showed reduction in “L” values on addition of husk suggesting reduction in dough extensibility. The doughs with reduced elasticity led to formation of chapattis which were less elastic and harder as observed through Universal Testing Machine. For all doughs (with and without fiber) storage modulus (G0 ) was found to be higher than loss modulus. The slopes measured through linear regression of log G’ vs. log (frequency) declined with increase of fiber in dough. Interestingly, it was observed that the sensory panelists were unable to perceive the differences in quantity of fiber in various chapattis. © 2017 Elsevier Ltd. All rights reserved.
Keywords: Chapatti Barley husk Rheology Texture
1. Introduction In Pakistan, India, Middle East and North Africa, wheat (Triticumaestivum) flour is extensively used for flat bread production (Rehman et al., 2007). Flat bread is a staple food of Pakistan. There are several types of flat breads namely chapatti/roti, Paratha, Kulcha, Puri and Tandoori roti (Gocmen et al., 2009). Flat breads are generally made from whole wheat flour, refined flour or using blends of different flours (Gujral and Pathak, 2002). Unleavened flat bread that is chapatti/ roti is made from wheat flour majorly after kneading with suitable quantity of water. Oil and salt are optional ingredients in chapatti. According to a study 90% of the wheat produced in Pakistan is consumed as roti (Safdar et al., 2009). It is usually prepared twice a day and consumed immediately. Texture and flavor are the two most important parameters to judge quality of chapatti (Shalini and Laxmi, 2007). A chapatti consists mainly of crust, with little crumb. Some qualities of good chapatti are softness, pliability, folding of chapatti in spoon shape and should be easy to tear, without being excessively brittle or leathery. However, slight chewiness in mouth
* Corresponding author. E-mail address: [email protected] (T. Mohsin Ali). https://doi.org/10.1016/j.jcs.2017.11.020 0733-5210/© 2017 Elsevier Ltd. All rights reserved.
feel is desirable (Dhaliwal et al., 1996). Food and Agriculture Organization (FAO) in 1998 recommended to increase the intake of low glycemic index foods. Cereal grains like wheat, barley, oats and rye are rich in bioactive components such as dietary fibers, antioxidants, phenolic compounds, vitamins and minerals. These bioactive compounds aid in reduction of cardiovascular diseases, certain cancers, diabetes, obesity and some other chronic diseases (Estruch et al., 2009). Several studies have been reported regarding types of fiber breads with different flour blends. Some of the reported fibers are insoluble date fiber (Ahmed et al., 2013), hull and cotyledon fibers from peas, lentils and chickpeas (Dalgetty and Baik, 2006), microcrystalline cellulose, pea, cocoa, coffee, orange mez et al., 2003), carob fibers, oat whole meal (Mis et al., 2012) (Go have also been successfully added. Incorporation of barley b-glucan (Skendi et al., 2010) has also been reported. Dietary fiber is of two types: water soluble dietary fiber (SDF) and water insoluble dietary fiber (IDF). Water insoluble dietary fiber is metabolically inert, provides bulking, act as prebiotic and ferments in large intestine. These absorb water while moving in digestive tract easing defecation (Table, 2005). Insoluble dietary fiber also regulates blood sugar level, which may reduce glucose and insulin levels in diabetic people and may lower risk of diabetes, alleviates constipation by bulking stool, balances intestinal pH, stimulates production of short chain fatty acids in the intestine
T. Mehfooz et al. / Journal of Cereal Science 79 (2018) 376e382
which subsequently reduces the risk of colorectal cancer. Cellulose, hemicellulose and lignin are the three major chemical constituents in barley husk (Moldes et al., 2002). Further analysis of the barley husk revealed that about 66% of the dry matter content consisted of polysaccharides, the main sugars being glucan (30.1%), xylan (28.7%) and arabinans (6.2%) (Palmarola-Adrados et al., 2005). Different application of barley husks have been proposed including steam processing for further ethanol production, dye removal (Robinson et al., 2002), and xylooligosaccharide production by autohydrolysis (Garrote et al., 2008). This fiber was obtained as a by-product during extraction of starch from barley grains. The by-product is a rich source of insoluble fiber. Since, the flatbread (chapatti) is a staple food of Pakistan and it is frequently consumed with every meal. Therefore, incorporation of barley husk in chapatti will substantially increase the consumption of insoluble fiber in daily diet as usually people are reluctant to consume fiber directly with water. Thus, the present study incorporated barely fiber at (10e30%) levels in chapatti followed by evaluation of its compositional, thermal (percent freezable water content), textural and sensory characteristics. 2. Material and methods All purpose wheat flour was purchased from Ashrafi Food Industries, Karachi, Pakistan. All chemicals in the present study were analytical grade. 2.1. Pretreatment of by-product after starch isolation Barley grains were purchased from local market for starch isolation. Barley starch was isolated by the method of Yangsheng and Seib (1990) with some modifications. Five hundred grams of barley grains were slightly ground to rupture the kernels. The ruptured kernels were steeped in 1000 mL of 0.2% sodium metabisulphite solution and 5 mL of lactic acid overnight at room temperature. The steeping water was decanted and barley kernels were washed extensively with water in order to remove excess chemicals. The kernels were ground with ample amount of water and screened through nylon bolting cloth. The overs on sieve were regrounded in blender with water and sieved again. This step was repeated several times to remove residual starch. The obtained starch slurry was centrifuged at 1200 g for 5 min. The liquid was decanted carefully and the brown tailing pigment on top was removed using spatula. The crude starch was suspended in 0.15% NaOH and centrifuged again at 1200 g for 5 min. This step was repeated several times. The starch slurry was neutralized using 1 M HCl followed by washing and centrifugation for removal of supernatant. Starch palate obtained was forced air dried in oven at 40 C. Dried starch was finely grounded to powder form. After isolation of starch the remaining husk was washed with water and oven dried at 65 C until the moisture content reached 8%. Dried husk was then ground finely using hammer mill. The ground husk was passed through 100 size mesh sieve to obtain uniform particle size for incorporation in wheat flour. The particle size distribution of barley husk was found to be 58%, 30%, 9% and 3% on 100, 200, 325 and 400 mesh sieves, respectively. Whereas, the particle size of flour used for present study were 33%, 52%, 13% and 2% on 100, 200, 325 and 400 mesh sieves, respectively. 2.2. Compositional analysis Flour with and without fibers were chemically analyzed by using standard methods. Protein was estimated using Inframatic 8620 NIR (Perten, Sweden). Gluten index, dried gluten and wet gluten
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were determined by Glutomatic 2200, (Perten, Sweden) using AACC (38-12) method. Damaged starch content was evaluated by using AACC (58e81 B) method while ash content was found using AACC (08-01) assay. The crude fiber of control and husk added chapattis was estimated using AACC (32-10) method (AACC, 2000). 2.3. Preparation of dough All purpose wheat flour was used to make dough for chapatti. Barley husk (5 g, 10 g, 20 g and 30 g) were added separately to 100 g wheat flour. The flour without any barley fiber was considered as control. Prior to addition of water, flour and husk were mixed with 1% salt and 5% oil, based on flour weight. The amount of water added to dough was based on percent water absorption evaluated using farinograph (D-47055 Duisburg Brabender, Germany). The dough was kneaded using Braun Mixer Model K650 (Kronberg/Germany). After the formation of dough, it was covered with polyethylene film and was allowed to rest for 10 min. A 50 g portion of dough was taken and rolled out using a wooden roller into a thin circular sheet of 1 mm thickness. It was then cut into an 11.5 cm diameter round sheet of dough using petri plate followed by cooking on a round hot iron plate at a temperature of 270 C. The chapatti was cooked on both sides. Chapattis were cooled and stored in a desiccator (containing silica gel beads as desiccant to obtain a dry atmosphere) before further analysis. Chapattis were stored at 20 C. 2.4. Rheological testing of dough using farinograph, alveograph and rheometer 2.4.1. Farinograph The composite dough behaviour was measured using a Farinograph (D-47055 Duisburg Brabender, Germany) according to AACC method 54-24. Water absorption (WA), dough development time (DDT), dough stability (DS), breakdown (B) and mixing tolerance index (MTI) were calculated directly using Brabender® Farinograph software (Version: 3.2.6). 2.4.2. Alveograph The viscoelastic behaviour of dough was also studied through Alveograph by AACC method 54-30A. Parameters monitored were deformation in energy (W), tenacity or resistance to extension (P), dough extensibility (L), and curve configuration ratio (P/L ratio) of dough with and without fibers. 2.4.3. Rheometer Rheological measurements of blended dough were performed on Discovery HR-1 hybrid rheometer (TA Instruments, USA). The geometry used was plate-plate with 40 mm diameter. The dough sample was placed in a 2 mm gap between two stainless steel parallel plates. The sample temperature was set at 25 C and was controlled via lower peltier plate. Optimum dough was prepared based on farinograph water absorption. Dough after placement on peltier plate was sealed between two parallel plates using a thin film of silicon oil so as to prevent moisture loss during analysis. Amplitude sweep measurements were first conducted to determine the linear viscoelastic range (LVR). Strain sweep tests in oscillatory shear rate were made over a range of 0.01%e100% at a fixed frequency of 1 Hz. Frequency sweep measurements were performed within LVR over a frequency of (0.1e100) Hz at a temperature of 25 C. The dough was given a soak time of 800 s. The mechanical spectra were characterized by G’ (storage modulus), G” (loss modulus) and complex viscosity. The effects of different levels of barley husk on G0 , G” and complex viscosity were also reported separately at 1 Hz.
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The frequency dependency of G’ was approximated for dough using following equation: logG’ ¼ logA þ n log u Where, G0 is storage modulus, n is the slope (dimension less), A is intercept (Pa.s), and u is frequency.
2.8. Statistical analysis One way ANOVA (Analysis of variance) and t-test were used to calculate significant differences between the means, and Duncan's test at p 0.05 was used to separate means using SPSS software (version 17, SPSS Inc., USA). 3. Results and discussion
2.5. Percent freezable water content in chapattis A Differential scanning calorimeter (DSC Q10 calorimeter, TA Instruments, USA) was used to determine the amount of freezable water in chapattis with reference to an empty pan. Method of Lodi and Vodovotz (2008) was used with some modifications. Freshly prepared flatbread sample (4 mg) was placed in an aluminum pan and sealed hermetically before analysis. The samples were scanned from 30 C to (50 C) at a scan rate of 10 C/min using DSC refrigerated cooling system with liquid nitrogen flowing at a rate of 100 mL/min. Samples were held at (50 C) for 1 min, and were then heated to 130 C at a rate of 10 C/min. Frozen water content (FWC) was calculated using following equation: % FW ¼ A/ l. Mc Where, % FW is percent freezable water content, A is the integrated area under the endothermic peak of water fusion, l is the specific latent heat of fusion of water (334 J/g) and Mc is the % moisture content of the sample under analysis (Lodi and Vodovotz, 2008).
2.6. Textural analysis of fresh and stored chapattis Textural measurements of chapatti were performed using Universal Testing Machine (Zwick/Roell, GmbH, Germany). Freshly prepared chapatti was cut into bone shaped strips from center of flat bread. The total length of the strip was 10 mm whereas width was 5.5 mm from edges and 3.5 mm at the center. The strips of flatbread were then held between two clamps (screw grips) of Universal Testing Machine (Zwick/Roell, GmbH, Germany). One clamp was attached to the moving arm while the other was fixed on the platform. The load cell used was of 1 KN. Grip to grip separation was 50 mm. The test speed of the upper moving clamp was 50 mm/ min whereas force shutdown threshold was kept at 30%. The upper clamp stretched the chapatti strip until it was ruptured. Those strips ruptured from the center were considered whereas those rupturing from the edges of the strip were not included in the mean values. The Fmax or maximum force required to rupture was measured in MPa and extensibility was measured in mm. All parameters were directly calculated by Test Xpert software.
2.7. Sensory analysis of chapattis A sensory panel consisting of 12 members evaluated freshly prepared chapattis with and without addition of fiber for general acceptance using nine-point hedonic scale from like extremely to dislike extremely from 9 to 1, respectively. Appearance, hardness, spooning like shape, aroma and overall acceptability were some parameters analyzed by panelists. Spooning is an important parameter that allows flatbread to form a spoon like shape by folding. The panelists included the students and faculty members of Department of Food Science and Technology, University of Karachi. Since, chapatti is a staple food and is eaten in everyday meals therefore, no training sessions were conducted.
3.1. Effect of barley husk addition on compositional characteristics of wheat flour and crude fiber content of chapattis It could be observed from Table 1 that total protein content reduced with the increase in bran content of flour. Similarly, wet gluten and dry gluten also reduced. The decrease in total protein content is an expected outcome as percentage of protein dilutes when fiber is added to 100 g of wheat flour (Ognean et al., 2010). Secondly, gluten index which is measurement of gluten strength reduced significantly with the progressive increase of fiber percentage in flour. The value of gluten index close to 100 indicates gluten of high quality. Since fiber absorbs water and also interferes with aggregation of gliadin and glutenin during formation of dough, therefore, gluten index drastically reduced on addition of barley husk. The husk of barley also contains damaged starch as an outcome of wet milling of barley grains. Therefore, addition of barely husk increased the damaged starch content of flour blends. Similar to wheat bran, barley husk is also a source of ash. The aleurone cells, together with testa and germ contains essential minerals required for the growth of embryo (Clydesdale, 1994). According to Krawczyk et al. (2008) barley husk contains 9.1 g ash in 100 g of husk. Therefore, barley husk addition led to increase in ash content of wheat flour. The crude fiber content of chapattis significantly increased with the addition of barley husk in flour. The Pearson coefficient of correlation between % husk in chapatti and % crude fiber was found to be 0.991 (p < 0.05) (not shown). The % fiber content in control chapatti was found to be 1.91%, which increased to 21.76% in chapatti made through the addition of 30% barley husk. Since, chapatti is usually consumed 2 to 3 times daily; therefore, addition of barley husk to chapattis will significantly increase fiber consumption per day which will subsequently improve bowel movement. 3.2. Effect of barley husk addition on farinograph indices of dough The effect of fiber addition on the rheological properties of dough is presented in Table 2a. It is a known fact that water absorption increases with the increase in fiber content (Sudha et al., 2007). The increase in tendency of flour to hold water with the increase in fiber is due to higher number of hydroxyl groups present in fiber structure, allowing more water interaction through hydrogen bonds (Rosell et al., 2001). Percent water absorption of flour and husk blends increased progressively with addition of barley husk with Pearson coefficient of correlation of 0.965, p < 0.05. Addition of barley husk also increased damaged starch content which is another reason for increase in percent water absorption as damaged starch is supposed to be more hydrophilic than undamaged starch (Bushuk, 1966). Addition of 30% barley husk in flour resulted in almost 10% higher water absorption compared to control dough. Dough development time shortened with the addition of barley husk. The reduction in time for optimum development of dough is due to dilution of wheat protein which subsequently reduces the extent of gluten network formed (Sroan et al., 2009). Dough stability is defined as the difference between time when the curve first intercepts the 500 BU line and the time when it leaves the 500 BU line. Longer the time, the better is the
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Table 1 Characteristics of wheat flour/barely husk blends and crude fiber content of chapattisa. Barley husk (%)
Protein (%)
Control (0%) 5% 10% 20% 30%
9.77 9.55 9.43 9.04 8.66
± ± ± ± ±
Ash (%)
0.03e 0.02d 0.03c 0.05d 0.05a
0.29 0.81 0.83 0.91 1.02
DS (%) ± ± ± ± ±
0.02a 0.02b 0.02b 0.02c 0.01d
WG (%)
11.11 12.05 14.06 17.00 21.12
± ± ± ± ±
0.09a 0.05b 0.06c 0.11d 0.15e
DG (%)
26.10 25.03 23.10 21.50 19.48
± ± ± ± ±
0.11e 0.03d 0.12c 0.05d 0.04a
8.04 7.94 7.70 7.25 7.02
GI ± ± ± ± ±
0.05e 0.05d 0.04c 0.04b 0.03a
81.43 79.43 79.05 70.05 66.42
CFC (%) ± ± ± ± ±
0.09e 0.07d 0.05c 0.05b 0.17a
1.91 ± 0.01a 3.89 ± 0.01b 7.72 ± 0.02c 16.07 ± 0.03d 21.76 ± 0.01e
a Means with different superscript lowercase letters within a column are significantly different at p < 0.05. n ¼ 3. DS: Damaged starch; WG: Wet gluten; DG: Dry gluten; GI: Gluten index; CFC: Crude fiber content of chapatti.
Table 2a Farinograph indices for wheat flour and husk blendsa. Barley husk (%)
DDT (min)
Control (0%) 5% 10% 20% 30%
3.80 3.20 3.50 3.30 2.70
± ± ± ± ±
WA (%) 1.41c 0.18b 0.14bc 0.14b 0.21a
61.40 61.20 65.80 67.40 70.07
Stability (min) ± ± ± ± ±
0.84a 0.98a 0.35b 0.43b 0.14c
4.00 3.00 2.20 2.50 1.30
± ± ± ± ±
0.14d 0.11c 0.14b 0.14b 0.17a
MTI (FU)
Breakdown (min)
56.00 ± 2.82a 110.00 ± 0.37b 157.00 ± 4.24c 155.00 ± 4.24c 192.00 ± 2.28d
5.80 4.51 3.40 4.20 3.48
± ± ± ± ±
0.14c 0.49b 0.14a 0.14b 0.17a
a Means with different superscript lowercase letters within a column are significantly different at p < 0.05. n ¼ 2. DDT: Dough development time; WA: Water absorption; MTI: Mixing tolerance index.
dough stability. It could be observed in Table 2a that dough stability reduced as barley husk increased, suggesting easy disruption of starch-gluten network owing to fiber particles. Mixing tolerance index (MTI) is also an indicator of dough stability as it measures the drop in peak viscosity of dough after 5 min. Lower MTI or smaller drop in viscosity suggested stronger strength of dough. The control flour with no barley husk showed the least MTI whereas, as fiber increased MTI also increased showing the least tendency of dough to resist over mixing in the presence of barley husk. Similar results were also reported by Elkhalifa and El-Tinay (2002) on addition of sorghum and wheat flour. The correlation between percent fiber and MTI of flour was found to be 0.899, p < 0.01. Like MTI, breakdown also reduced with increasing fiber levels. 3.3. Effect of barley husk addition on alveograph indices of dough Dough resistance to deformation/tenacity (P value) indicates ability of dough to retain gas. The P-value showed a progressive decline on addition of fiber up to 10% and thereafter it became constant. Similar results were also observed by Wang et al. (2002). Extensibility of dough (L) informs about the processing characteristics i.e. dough's capacity to extend without breakdown. The fiber added flours were found to have lower ‘L’ values compared to control which indicates the reduction in dough extensibility. This result was expected as fiber not only competes for water with gluten protein but also curtails the formation of strong gluten network. The ‘G’ is defined as the index of bubble swelling or in other words size of bubble after inflation. It could be seen in Table 2b that G value of control sample without fiber was significantly higher than other samples suggesting strong gluten network in control dough. Similar to G-value, energy required to blow up the bubble i.e. W was higher for control dough. The higher ‘W’ value indicates strong gluten network. Above 10%, the Wevalue was insignificantly different from each other. Wang et al. (2002) also observed decrease in W-value with the addition of pea fiber. 3.4. Effect of barley husk addition on dynamic frequency sweep measurements of dough The G0 and G00 mechanical spectra measured from 0.1 to 100 Hz is presented in Fig. 1a and b respectively while values of viscosity, G’
(storage modulus), G” (loss modulus) observed at 1 Hz is presented in Table 2c. It could be observed from Table 2c that storage modulus of all the doughs were greater than the loss modulus emphasizing the fact that dough made with and without addition of barley husk tend to have more solid like elastic characteristics. This type of response is shown by a typical cross-linked network. Such behaviour is also reported by Ahmed et al. (2013). With the increase in barley husk a progressive increase was found in G0 , G00 and viscosity values of dough with Pearson correlation coefficient of 0.915, 0.942 and 0.859 at p < 0.05, respectively at 1 Hz. The increase in viscosity is due to less availability of water as a plasticizer as water is absorbed/bound to fibers added to flour. Thus, limited effect of water plasticization led to overall increase in mechanical property of the dough. No cross over between G0 and G00 was observed for any of the dough blends (results not shown). However, on addition of 20% and 30% barley husk, the G0 and G00 approached quite close to each other at 100 Hz. At all frequencies (0.1e100) Hz, G0 was observed to be greater than G” for all dough blends (Fig. 1). The viscoelastic nature of dough was further evaluated by calculating slopes from linear regression of plots between log of frequency and log of (G’). Usually a true gel has zero slope for a power law. It could be observed from Table 2d, that slopes of blended dough declined with the increase in percentage of barley husk. Similar observation was also made by Ahmed et al. (2013) and Bonnand-Ducasse et al. (2010). Incorporation of barley husk 10% in wheat flour led to significant decline in the magnitude of slope suggesting a more solid like character of dough with rise in barley fiber. The doughs with higher amount of fibers were stiffer and rigid compared to control dough. Georgopoulos et al. (2004) reported decrease in frequency dependency with decrease in water content of dough. Since, presence of fiber reduces the availability of water, therefore frequency dependence reduced with the increase in barley husk content of flour blends. 3.5. Effect of barley husk addition on percent freezable water content of chapattis Results for freezable water content are presented in Table 3. Fiber as an additive binds available water that is required for starch gelatinization. With the increment in fiber level, freezable water content tends to decrease. Possible reasons for this decrease could
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Table 2b Alveograph indices of wheat flour and husk blendsa. Barley husk (%)
P (mm H2O)
Control (0%) 5% 10% 20% 30%
94.60 68.60 45.00 45.03 44.60
± ± ± ± ±
L (mm)
4.50d 9.47b 3.80a 3.00a 5.31a
66.20 35.40 31.82 20.80 21.40
G ± ± ± ± ±
6.37d 12.73b 2.28b 4.49a 0.55a
18.08 12.95 13.02 10.10 10.28
± ± ± ± ±
0.89c 2.78b 0.43b 1.12a 0.10a
W (10e4J)
P/L
186.60 ± 16.07d 76.80 ± 17.82b 43.00 ± 5.14a 31.40 ± 4.03a 29.40 ± 4.83a
1.44 2.33 1.31 2.25 2.08
± ± ± ± ±
0.14ab 1.42c 0.10a 0.54bc 0.26abc
a Means with different superscript lowercase letters within a column are significantly different at p < 0.05. n ¼ 3. P: Tenacity; L: Dough extensibility; W: Deformation energy; P/L ratio: curve configuration; G: Index of swelling.
b)
G"(Pa)
G'(Pa)
a) 500000 450000 400000 350000 300000 250000 200000 150000 100000 50000 0 0
20
40
60
80
100
200000 180000 160000 140000 120000 100000 80000 60000 40000 20000 0
120
0
20
Frequency (Hz)
40
60
80
100
120
Frequency (Hz)
Fig. 1. Effect of frequency on storage modulus (a) and loss modulus (b) of wheat flour and husk blends. (-) Wheat flour Control (0%); () Wheat flour with 5% husk blend; () Wheat flour with 10% husk blend; (þ) Wheat flour with 20% husk blend; (C) Wheat flour with 30% husk blend.
be due to lower availability of free water in chapatti, as fiber having higher number of hydroxyl groups binds more water through hydrogen bonding (Rosell et al., 2001). According to Zeleznak and Hoseney (1986), the amount of water of present in bread determines the extent of amylopectin retrogradation. The results presented in Table 3 ascribed to the fact that fiber fortified flatbreads tend to form fewer amount of ice crystals during freezing because of less availability of free water (Leray et al., 2010). 3.6. Effect of barley husk addition on textural characteristics of chapattis The results of textural characteristics of fresh and stored chapattis are presented in Table 4. It could be observed from the results that fresh chapatti in the absence of fiber required higher amount of force to tear the chapatti. On addition of fiber to the chapattis, the force reduced by 50%. However, there was no significant difference in the rupturing force with increasing levels of fiber in chapatti. These results suggested that addition of fiber interferes with the formation of extensible gluten network. The fiber particles thwart the association of glutenin and gliadin protein. Secondly, barely fibers absorb water from the dough, making it less available for the development of elastic gluten network and subsequently a weak gluten network is formed which is easily teared off during textural
analysis. A high degree of similarity was observed between the subjective (sensory analysis Table 4) and objective analysis (hardness of chapatti Table 5) as both reflected insignificant difference in hardness in terms of quantity of fiber present in chapatti. Chapattis when stored for two days at room temperature showed significant increase in rupturing force. This increase is assumed to be due to retrogradation of starches which is the major component of wheat flour. During cooking of chapatti on hot iron plate, the gelatinization of starch takes place. For gelatinization to take place, two key factors i.e. water and temperature greater than 50 C are necessary. Water is added during preparation of dough, while the temperature of hot plate is around 270 C leading to gelatinization of starch. These gelatinized starch granules when stored for two days retrograde and eventually imparts hardness to chapattis. Elasticity is yet another quality parameter of flat bread which denotes the length of extension of bread before it gets teared up. More the extensibility, the higher will be the length recorded at the time of rupture. The results clearly depicted the fact that control chapatti had significantly higher elasticity compared to chapattis made with addition of fiber to flour. The appreciable amount of water bound to fiber makes scanty water available for development of starch gluten network which subsequently reduces elasticity (Brennan and Cleary, 2007). Moreover, addition of fiber also dilutes down the gluten content resulting in increased hardness and
Table 2c Rheological parameters at 1 Hz for doughs made with different percentages of barley huska. Barley husk (%)
G’ (Pa)
G’’ (Pa)
Viscosity (Pa.s)
Control (0%) 5% 10% 20% 30%
22378.30 ± 4556.30a 36213.21 ± 808.93b 52686.40 ± 2504.51c 86796.42 ± 237.72d 211319 ± 5433.40e
6299.80 ± 200.50a 7760.73 ± 300.65a 20015.92 ± 996.52a 22353.41 ± 1600.51a 127521.61 ± 1300.53b
3712.10 ± 869.50a 5895.32 ± 100.21b 8970.51 ± 302.22c 14289.74 ± 345.40d 43464.90 ± 1312.00e
a Means with different superscript lowercase letters within a column are significantly different at p < 0.05. n ¼ 2. G’: Storage modulus, G”: Loss modulus.
T. Mehfooz et al. / Journal of Cereal Science 79 (2018) 376e382
3.7. Effect of barley husk addition on sensory characteristics of chapattis
Table 2d Slope of linear regression of (logG’) vs (log u) for doughs made with different percentages of barley huska. Barley husk (%)
Slope
Control (0%) 5% 10% 20% 30%
0.22 0.21 0.19 0.17 0.16
R2
± ± ± ± ±
0.01d 0.00cd 0.01bc 0.00ab 0.01a
The results of sensory characteristics are presented in Table 5. In terms of all sensory traits the control chapatti without any fiber received the highest scores as they were whiter and softer compared to fiber added chapattis. It could be observed from Table 5 that incorporation of higher quantity of barley fiber (greater than 5%) resulted in less preferred appearance as fiber imparts its own brownish color to chapattis. Interestingly, it was observed that all chapattis with added fiber were insignificantly different from each other in terms of hardness, spooning and aroma. This suggests that the sensory panelists were unable to perceive the differences in quantity of fiber in different chapattis. Though the addition of fiber significantly affected hardness and spooning capability of chapatti compared to control chapatti but they still received scores higher than 5. This shows that incorporation of fiber in chapatti does not make chapattis completely undesirable to consumer. Fiber being gritty gives slightly off-flavor to chapattis and also increases hardness and reduces elasticity as fiber interferes with gluten network and distribution of moisture in chapattis. This is also reflected in overall acceptability, as it could be observed that it reduced due to fiber addition. However, none of the chapattis were completely disliked by the panelists in terms of overall acceptability.
0.99 0.98 0.98 0.97 0.99
a
Means with different superscript lowercase letters within a column are significantly different at p < 0.05. n ¼ 2.
Table 3 Percent freezable water content of chapatti made with different percentages of barley huska. Barley husk (%)
%FW
Control (0%) 5% 10% 20% 30%
54.08e 18.33d 14.13c 12.27b 9.45a
381
a
Means with different superscript lowercase letters within a column are significantly different at p < 0.05. n ¼ 3. %FW: Percent freezable water.
4. Conclusion
reduction in elasticity (Collar et al., 2007). Storage of chapatti resulted reduced elasticity of all chapattis. On storage, the amylose chains in short term and amylopectin on long term storage reassociates or interact in close proximity to form crystallites, which confer hard/rigid structures, therefore, elasticity of dough reduces as starch granules form the major matrix along with gluten network. This phenomenon is called bread staling and reduces sensorial characteristics of flatbread. Apart from starch retrogradation, the altered water distribution is also a reason for decline in chapatti elasticity. According to Gray and Bemiller (2003) and HugIten et al. (2003), on retrogradation of amylopectin, the water molecules from gluten network are shifted towards starch linkages formation involved in formation of amylopectin crystallites. Also the plasticizing effect of water is less, leading to less extensible gluten network and less extensible chapattis.
From overall results, it could be concluded that the addition of barley husk fiber modified the chemical and rheological properties of flour blends and dough simultaneously. Chemical composition of all purpose wheat flour altered significantly as the level of husk increases. Addition of fiber up to 30% also affected farinograph indices. Flour blends with 30% husk showed higher water absorption and mixing tolerance index while rest of the parameters tend to decline. Flour blends at increasing level of husk showed decline in alveograph parameters except for P/L ratio which did not behave significantly different. Frequency sweep measurements exhibited development of stiffer dough with the increase in barley husk due to more amount of water being absorbed by fiber. Though panelists preferred chapattis with no fiber at all but none of the chapattis with added fibers were disliked by panelists.
Table 4 Texture of fresh and stored chapattis made with different percentages of barley huska. Samples
Fmax (g)
Barley husk (%)
Day 0
Control (0%) 5% 10% 20% 30%
4.50 2.54 2.47 2.41 2.71
± ± ± ± ±
Ɛ-Fmax (mm) Day 2
0.50c,1 0.38b,1 0.31b,1 0.56b,1 0.13b,1
6.58 4.26 3.49 4.19 3.70
± ± ± ± ±
0.38b,2 0.20a,2 0.71a,2 1.11a,2 0.84a,2
Day 0
Day 2
23.94 ± 2.62d,1 11.27 ± 2.10b,1 10.58 ± 1.66ab,1 8.44 ± 1.70a,1 8.20 ± 1.34a,1
3.83 2.45 1.44 1.70 1.27
± ± ± ± ±
0.59c,2 0.29b,2 0.28a,2 0.32a,2 0.26a,2
a Means with different superscript lowercase letters within a column and different numbers within a row are significantly different at p < 0.05. n ¼ 3. Fmax: Force to tear; Ɛ-Fmax: Extensibility.
Table 5 Sensory characteristics of chapatti containing different percentages of barley huska. Barley husk (%)
Appearance
Control (0%) 5% 10% 20% 30%
8.17 7.31 5.92 6.17 6.17
± ± ± ± ±
0.84c 1.34bc 1.93a 1.40ab 1.16a
Hardness 8.50 5.92 5.67 5.75 6.25
± ± ± ± ±
0.52b 1.66a 2.43a 1.36a 0.96a
Spooning 8.67 6.54 6.67 6.17 6.75
± ± ± ± ±
0.49b 1.89a 1.87a 1.19a 0.86a
a Means with different superscript lowercase letters within a column are significantly different at p < 0.05. O.A: Overall acceptability.
Aroma 9.00 6.15 6.58 6.58 6.42
± ± ± ± ±
O.A 0.00b 1.95a 1.88a 2.06a 1.78a
9.00 6.69 6.58 6.17 6.00
± ± ± ± ±
0.00c 1.18b 1.38b 1.47b 1.21b
382
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Journal of Cereal Science journal homepage: www.elsevier.com/locate/jcs
Effect of barley husk addition on rheological, textural, thermal and sensory characteristics of traditional flat bread (chapatti) Tooba Mehfooz a, Tahira Mohsin Ali a, *, Saqib Arif b, Abid Hasnain a a b
Department of Food Science and Technology, University of Karachi, 75270, Karachi, Pakistan Food Quality and Safety Research Institute, Pakistan Agricultural Research Council (PARC), University of Karachi Campus, 75270, Pakistan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 7 June 2017 Received in revised form 24 November 2017 Accepted 26 November 2017
The present study suggested utilization of barley husk obtained as a by-product during extraction of starch from barley grains in preparation of unleavened flat bread (chapatti). The barley husk was added at (5e30) % level to wheat flour. These flour and husk blends were then turned into dough by adding water based on farinograph water absorption. It was observed that gluten index reduced with addition of fiber suggesting weakened gluten network. This was also confirmed with increase in mixing tolerance index (MTI) values on addition of barley fiber. The correlation between percent fiber and MTI was found to be 0.899 (p < 0.01). Alveograph showed reduction in “L” values on addition of husk suggesting reduction in dough extensibility. The doughs with reduced elasticity led to formation of chapattis which were less elastic and harder as observed through Universal Testing Machine. For all doughs (with and without fiber) storage modulus (G0 ) was found to be higher than loss modulus. The slopes measured through linear regression of log G’ vs. log (frequency) declined with increase of fiber in dough. Interestingly, it was observed that the sensory panelists were unable to perceive the differences in quantity of fiber in various chapattis. © 2017 Elsevier Ltd. All rights reserved.
Keywords: Chapatti Barley husk Rheology Texture
1. Introduction In Pakistan, India, Middle East and North Africa, wheat (Triticumaestivum) flour is extensively used for flat bread production (Rehman et al., 2007). Flat bread is a staple food of Pakistan. There are several types of flat breads namely chapatti/roti, Paratha, Kulcha, Puri and Tandoori roti (Gocmen et al., 2009). Flat breads are generally made from whole wheat flour, refined flour or using blends of different flours (Gujral and Pathak, 2002). Unleavened flat bread that is chapatti/ roti is made from wheat flour majorly after kneading with suitable quantity of water. Oil and salt are optional ingredients in chapatti. According to a study 90% of the wheat produced in Pakistan is consumed as roti (Safdar et al., 2009). It is usually prepared twice a day and consumed immediately. Texture and flavor are the two most important parameters to judge quality of chapatti (Shalini and Laxmi, 2007). A chapatti consists mainly of crust, with little crumb. Some qualities of good chapatti are softness, pliability, folding of chapatti in spoon shape and should be easy to tear, without being excessively brittle or leathery. However, slight chewiness in mouth
* Corresponding author. E-mail address: [email protected] (T. Mohsin Ali). https://doi.org/10.1016/j.jcs.2017.11.020 0733-5210/© 2017 Elsevier Ltd. All rights reserved.
feel is desirable (Dhaliwal et al., 1996). Food and Agriculture Organization (FAO) in 1998 recommended to increase the intake of low glycemic index foods. Cereal grains like wheat, barley, oats and rye are rich in bioactive components such as dietary fibers, antioxidants, phenolic compounds, vitamins and minerals. These bioactive compounds aid in reduction of cardiovascular diseases, certain cancers, diabetes, obesity and some other chronic diseases (Estruch et al., 2009). Several studies have been reported regarding types of fiber breads with different flour blends. Some of the reported fibers are insoluble date fiber (Ahmed et al., 2013), hull and cotyledon fibers from peas, lentils and chickpeas (Dalgetty and Baik, 2006), microcrystalline cellulose, pea, cocoa, coffee, orange mez et al., 2003), carob fibers, oat whole meal (Mis et al., 2012) (Go have also been successfully added. Incorporation of barley b-glucan (Skendi et al., 2010) has also been reported. Dietary fiber is of two types: water soluble dietary fiber (SDF) and water insoluble dietary fiber (IDF). Water insoluble dietary fiber is metabolically inert, provides bulking, act as prebiotic and ferments in large intestine. These absorb water while moving in digestive tract easing defecation (Table, 2005). Insoluble dietary fiber also regulates blood sugar level, which may reduce glucose and insulin levels in diabetic people and may lower risk of diabetes, alleviates constipation by bulking stool, balances intestinal pH, stimulates production of short chain fatty acids in the intestine
T. Mehfooz et al. / Journal of Cereal Science 79 (2018) 376e382
which subsequently reduces the risk of colorectal cancer. Cellulose, hemicellulose and lignin are the three major chemical constituents in barley husk (Moldes et al., 2002). Further analysis of the barley husk revealed that about 66% of the dry matter content consisted of polysaccharides, the main sugars being glucan (30.1%), xylan (28.7%) and arabinans (6.2%) (Palmarola-Adrados et al., 2005). Different application of barley husks have been proposed including steam processing for further ethanol production, dye removal (Robinson et al., 2002), and xylooligosaccharide production by autohydrolysis (Garrote et al., 2008). This fiber was obtained as a by-product during extraction of starch from barley grains. The by-product is a rich source of insoluble fiber. Since, the flatbread (chapatti) is a staple food of Pakistan and it is frequently consumed with every meal. Therefore, incorporation of barley husk in chapatti will substantially increase the consumption of insoluble fiber in daily diet as usually people are reluctant to consume fiber directly with water. Thus, the present study incorporated barely fiber at (10e30%) levels in chapatti followed by evaluation of its compositional, thermal (percent freezable water content), textural and sensory characteristics. 2. Material and methods All purpose wheat flour was purchased from Ashrafi Food Industries, Karachi, Pakistan. All chemicals in the present study were analytical grade. 2.1. Pretreatment of by-product after starch isolation Barley grains were purchased from local market for starch isolation. Barley starch was isolated by the method of Yangsheng and Seib (1990) with some modifications. Five hundred grams of barley grains were slightly ground to rupture the kernels. The ruptured kernels were steeped in 1000 mL of 0.2% sodium metabisulphite solution and 5 mL of lactic acid overnight at room temperature. The steeping water was decanted and barley kernels were washed extensively with water in order to remove excess chemicals. The kernels were ground with ample amount of water and screened through nylon bolting cloth. The overs on sieve were regrounded in blender with water and sieved again. This step was repeated several times to remove residual starch. The obtained starch slurry was centrifuged at 1200 g for 5 min. The liquid was decanted carefully and the brown tailing pigment on top was removed using spatula. The crude starch was suspended in 0.15% NaOH and centrifuged again at 1200 g for 5 min. This step was repeated several times. The starch slurry was neutralized using 1 M HCl followed by washing and centrifugation for removal of supernatant. Starch palate obtained was forced air dried in oven at 40 C. Dried starch was finely grounded to powder form. After isolation of starch the remaining husk was washed with water and oven dried at 65 C until the moisture content reached 8%. Dried husk was then ground finely using hammer mill. The ground husk was passed through 100 size mesh sieve to obtain uniform particle size for incorporation in wheat flour. The particle size distribution of barley husk was found to be 58%, 30%, 9% and 3% on 100, 200, 325 and 400 mesh sieves, respectively. Whereas, the particle size of flour used for present study were 33%, 52%, 13% and 2% on 100, 200, 325 and 400 mesh sieves, respectively. 2.2. Compositional analysis Flour with and without fibers were chemically analyzed by using standard methods. Protein was estimated using Inframatic 8620 NIR (Perten, Sweden). Gluten index, dried gluten and wet gluten
377
were determined by Glutomatic 2200, (Perten, Sweden) using AACC (38-12) method. Damaged starch content was evaluated by using AACC (58e81 B) method while ash content was found using AACC (08-01) assay. The crude fiber of control and husk added chapattis was estimated using AACC (32-10) method (AACC, 2000). 2.3. Preparation of dough All purpose wheat flour was used to make dough for chapatti. Barley husk (5 g, 10 g, 20 g and 30 g) were added separately to 100 g wheat flour. The flour without any barley fiber was considered as control. Prior to addition of water, flour and husk were mixed with 1% salt and 5% oil, based on flour weight. The amount of water added to dough was based on percent water absorption evaluated using farinograph (D-47055 Duisburg Brabender, Germany). The dough was kneaded using Braun Mixer Model K650 (Kronberg/Germany). After the formation of dough, it was covered with polyethylene film and was allowed to rest for 10 min. A 50 g portion of dough was taken and rolled out using a wooden roller into a thin circular sheet of 1 mm thickness. It was then cut into an 11.5 cm diameter round sheet of dough using petri plate followed by cooking on a round hot iron plate at a temperature of 270 C. The chapatti was cooked on both sides. Chapattis were cooled and stored in a desiccator (containing silica gel beads as desiccant to obtain a dry atmosphere) before further analysis. Chapattis were stored at 20 C. 2.4. Rheological testing of dough using farinograph, alveograph and rheometer 2.4.1. Farinograph The composite dough behaviour was measured using a Farinograph (D-47055 Duisburg Brabender, Germany) according to AACC method 54-24. Water absorption (WA), dough development time (DDT), dough stability (DS), breakdown (B) and mixing tolerance index (MTI) were calculated directly using Brabender® Farinograph software (Version: 3.2.6). 2.4.2. Alveograph The viscoelastic behaviour of dough was also studied through Alveograph by AACC method 54-30A. Parameters monitored were deformation in energy (W), tenacity or resistance to extension (P), dough extensibility (L), and curve configuration ratio (P/L ratio) of dough with and without fibers. 2.4.3. Rheometer Rheological measurements of blended dough were performed on Discovery HR-1 hybrid rheometer (TA Instruments, USA). The geometry used was plate-plate with 40 mm diameter. The dough sample was placed in a 2 mm gap between two stainless steel parallel plates. The sample temperature was set at 25 C and was controlled via lower peltier plate. Optimum dough was prepared based on farinograph water absorption. Dough after placement on peltier plate was sealed between two parallel plates using a thin film of silicon oil so as to prevent moisture loss during analysis. Amplitude sweep measurements were first conducted to determine the linear viscoelastic range (LVR). Strain sweep tests in oscillatory shear rate were made over a range of 0.01%e100% at a fixed frequency of 1 Hz. Frequency sweep measurements were performed within LVR over a frequency of (0.1e100) Hz at a temperature of 25 C. The dough was given a soak time of 800 s. The mechanical spectra were characterized by G’ (storage modulus), G” (loss modulus) and complex viscosity. The effects of different levels of barley husk on G0 , G” and complex viscosity were also reported separately at 1 Hz.
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The frequency dependency of G’ was approximated for dough using following equation: logG’ ¼ logA þ n log u Where, G0 is storage modulus, n is the slope (dimension less), A is intercept (Pa.s), and u is frequency.
2.8. Statistical analysis One way ANOVA (Analysis of variance) and t-test were used to calculate significant differences between the means, and Duncan's test at p 0.05 was used to separate means using SPSS software (version 17, SPSS Inc., USA). 3. Results and discussion
2.5. Percent freezable water content in chapattis A Differential scanning calorimeter (DSC Q10 calorimeter, TA Instruments, USA) was used to determine the amount of freezable water in chapattis with reference to an empty pan. Method of Lodi and Vodovotz (2008) was used with some modifications. Freshly prepared flatbread sample (4 mg) was placed in an aluminum pan and sealed hermetically before analysis. The samples were scanned from 30 C to (50 C) at a scan rate of 10 C/min using DSC refrigerated cooling system with liquid nitrogen flowing at a rate of 100 mL/min. Samples were held at (50 C) for 1 min, and were then heated to 130 C at a rate of 10 C/min. Frozen water content (FWC) was calculated using following equation: % FW ¼ A/ l. Mc Where, % FW is percent freezable water content, A is the integrated area under the endothermic peak of water fusion, l is the specific latent heat of fusion of water (334 J/g) and Mc is the % moisture content of the sample under analysis (Lodi and Vodovotz, 2008).
2.6. Textural analysis of fresh and stored chapattis Textural measurements of chapatti were performed using Universal Testing Machine (Zwick/Roell, GmbH, Germany). Freshly prepared chapatti was cut into bone shaped strips from center of flat bread. The total length of the strip was 10 mm whereas width was 5.5 mm from edges and 3.5 mm at the center. The strips of flatbread were then held between two clamps (screw grips) of Universal Testing Machine (Zwick/Roell, GmbH, Germany). One clamp was attached to the moving arm while the other was fixed on the platform. The load cell used was of 1 KN. Grip to grip separation was 50 mm. The test speed of the upper moving clamp was 50 mm/ min whereas force shutdown threshold was kept at 30%. The upper clamp stretched the chapatti strip until it was ruptured. Those strips ruptured from the center were considered whereas those rupturing from the edges of the strip were not included in the mean values. The Fmax or maximum force required to rupture was measured in MPa and extensibility was measured in mm. All parameters were directly calculated by Test Xpert software.
2.7. Sensory analysis of chapattis A sensory panel consisting of 12 members evaluated freshly prepared chapattis with and without addition of fiber for general acceptance using nine-point hedonic scale from like extremely to dislike extremely from 9 to 1, respectively. Appearance, hardness, spooning like shape, aroma and overall acceptability were some parameters analyzed by panelists. Spooning is an important parameter that allows flatbread to form a spoon like shape by folding. The panelists included the students and faculty members of Department of Food Science and Technology, University of Karachi. Since, chapatti is a staple food and is eaten in everyday meals therefore, no training sessions were conducted.
3.1. Effect of barley husk addition on compositional characteristics of wheat flour and crude fiber content of chapattis It could be observed from Table 1 that total protein content reduced with the increase in bran content of flour. Similarly, wet gluten and dry gluten also reduced. The decrease in total protein content is an expected outcome as percentage of protein dilutes when fiber is added to 100 g of wheat flour (Ognean et al., 2010). Secondly, gluten index which is measurement of gluten strength reduced significantly with the progressive increase of fiber percentage in flour. The value of gluten index close to 100 indicates gluten of high quality. Since fiber absorbs water and also interferes with aggregation of gliadin and glutenin during formation of dough, therefore, gluten index drastically reduced on addition of barley husk. The husk of barley also contains damaged starch as an outcome of wet milling of barley grains. Therefore, addition of barely husk increased the damaged starch content of flour blends. Similar to wheat bran, barley husk is also a source of ash. The aleurone cells, together with testa and germ contains essential minerals required for the growth of embryo (Clydesdale, 1994). According to Krawczyk et al. (2008) barley husk contains 9.1 g ash in 100 g of husk. Therefore, barley husk addition led to increase in ash content of wheat flour. The crude fiber content of chapattis significantly increased with the addition of barley husk in flour. The Pearson coefficient of correlation between % husk in chapatti and % crude fiber was found to be 0.991 (p < 0.05) (not shown). The % fiber content in control chapatti was found to be 1.91%, which increased to 21.76% in chapatti made through the addition of 30% barley husk. Since, chapatti is usually consumed 2 to 3 times daily; therefore, addition of barley husk to chapattis will significantly increase fiber consumption per day which will subsequently improve bowel movement. 3.2. Effect of barley husk addition on farinograph indices of dough The effect of fiber addition on the rheological properties of dough is presented in Table 2a. It is a known fact that water absorption increases with the increase in fiber content (Sudha et al., 2007). The increase in tendency of flour to hold water with the increase in fiber is due to higher number of hydroxyl groups present in fiber structure, allowing more water interaction through hydrogen bonds (Rosell et al., 2001). Percent water absorption of flour and husk blends increased progressively with addition of barley husk with Pearson coefficient of correlation of 0.965, p < 0.05. Addition of barley husk also increased damaged starch content which is another reason for increase in percent water absorption as damaged starch is supposed to be more hydrophilic than undamaged starch (Bushuk, 1966). Addition of 30% barley husk in flour resulted in almost 10% higher water absorption compared to control dough. Dough development time shortened with the addition of barley husk. The reduction in time for optimum development of dough is due to dilution of wheat protein which subsequently reduces the extent of gluten network formed (Sroan et al., 2009). Dough stability is defined as the difference between time when the curve first intercepts the 500 BU line and the time when it leaves the 500 BU line. Longer the time, the better is the
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Table 1 Characteristics of wheat flour/barely husk blends and crude fiber content of chapattisa. Barley husk (%)
Protein (%)
Control (0%) 5% 10% 20% 30%
9.77 9.55 9.43 9.04 8.66
± ± ± ± ±
Ash (%)
0.03e 0.02d 0.03c 0.05d 0.05a
0.29 0.81 0.83 0.91 1.02
DS (%) ± ± ± ± ±
0.02a 0.02b 0.02b 0.02c 0.01d
WG (%)
11.11 12.05 14.06 17.00 21.12
± ± ± ± ±
0.09a 0.05b 0.06c 0.11d 0.15e
DG (%)
26.10 25.03 23.10 21.50 19.48
± ± ± ± ±
0.11e 0.03d 0.12c 0.05d 0.04a
8.04 7.94 7.70 7.25 7.02
GI ± ± ± ± ±
0.05e 0.05d 0.04c 0.04b 0.03a
81.43 79.43 79.05 70.05 66.42
CFC (%) ± ± ± ± ±
0.09e 0.07d 0.05c 0.05b 0.17a
1.91 ± 0.01a 3.89 ± 0.01b 7.72 ± 0.02c 16.07 ± 0.03d 21.76 ± 0.01e
a Means with different superscript lowercase letters within a column are significantly different at p < 0.05. n ¼ 3. DS: Damaged starch; WG: Wet gluten; DG: Dry gluten; GI: Gluten index; CFC: Crude fiber content of chapatti.
Table 2a Farinograph indices for wheat flour and husk blendsa. Barley husk (%)
DDT (min)
Control (0%) 5% 10% 20% 30%
3.80 3.20 3.50 3.30 2.70
± ± ± ± ±
WA (%) 1.41c 0.18b 0.14bc 0.14b 0.21a
61.40 61.20 65.80 67.40 70.07
Stability (min) ± ± ± ± ±
0.84a 0.98a 0.35b 0.43b 0.14c
4.00 3.00 2.20 2.50 1.30
± ± ± ± ±
0.14d 0.11c 0.14b 0.14b 0.17a
MTI (FU)
Breakdown (min)
56.00 ± 2.82a 110.00 ± 0.37b 157.00 ± 4.24c 155.00 ± 4.24c 192.00 ± 2.28d
5.80 4.51 3.40 4.20 3.48
± ± ± ± ±
0.14c 0.49b 0.14a 0.14b 0.17a
a Means with different superscript lowercase letters within a column are significantly different at p < 0.05. n ¼ 2. DDT: Dough development time; WA: Water absorption; MTI: Mixing tolerance index.
dough stability. It could be observed in Table 2a that dough stability reduced as barley husk increased, suggesting easy disruption of starch-gluten network owing to fiber particles. Mixing tolerance index (MTI) is also an indicator of dough stability as it measures the drop in peak viscosity of dough after 5 min. Lower MTI or smaller drop in viscosity suggested stronger strength of dough. The control flour with no barley husk showed the least MTI whereas, as fiber increased MTI also increased showing the least tendency of dough to resist over mixing in the presence of barley husk. Similar results were also reported by Elkhalifa and El-Tinay (2002) on addition of sorghum and wheat flour. The correlation between percent fiber and MTI of flour was found to be 0.899, p < 0.01. Like MTI, breakdown also reduced with increasing fiber levels. 3.3. Effect of barley husk addition on alveograph indices of dough Dough resistance to deformation/tenacity (P value) indicates ability of dough to retain gas. The P-value showed a progressive decline on addition of fiber up to 10% and thereafter it became constant. Similar results were also observed by Wang et al. (2002). Extensibility of dough (L) informs about the processing characteristics i.e. dough's capacity to extend without breakdown. The fiber added flours were found to have lower ‘L’ values compared to control which indicates the reduction in dough extensibility. This result was expected as fiber not only competes for water with gluten protein but also curtails the formation of strong gluten network. The ‘G’ is defined as the index of bubble swelling or in other words size of bubble after inflation. It could be seen in Table 2b that G value of control sample without fiber was significantly higher than other samples suggesting strong gluten network in control dough. Similar to G-value, energy required to blow up the bubble i.e. W was higher for control dough. The higher ‘W’ value indicates strong gluten network. Above 10%, the Wevalue was insignificantly different from each other. Wang et al. (2002) also observed decrease in W-value with the addition of pea fiber. 3.4. Effect of barley husk addition on dynamic frequency sweep measurements of dough The G0 and G00 mechanical spectra measured from 0.1 to 100 Hz is presented in Fig. 1a and b respectively while values of viscosity, G’
(storage modulus), G” (loss modulus) observed at 1 Hz is presented in Table 2c. It could be observed from Table 2c that storage modulus of all the doughs were greater than the loss modulus emphasizing the fact that dough made with and without addition of barley husk tend to have more solid like elastic characteristics. This type of response is shown by a typical cross-linked network. Such behaviour is also reported by Ahmed et al. (2013). With the increase in barley husk a progressive increase was found in G0 , G00 and viscosity values of dough with Pearson correlation coefficient of 0.915, 0.942 and 0.859 at p < 0.05, respectively at 1 Hz. The increase in viscosity is due to less availability of water as a plasticizer as water is absorbed/bound to fibers added to flour. Thus, limited effect of water plasticization led to overall increase in mechanical property of the dough. No cross over between G0 and G00 was observed for any of the dough blends (results not shown). However, on addition of 20% and 30% barley husk, the G0 and G00 approached quite close to each other at 100 Hz. At all frequencies (0.1e100) Hz, G0 was observed to be greater than G” for all dough blends (Fig. 1). The viscoelastic nature of dough was further evaluated by calculating slopes from linear regression of plots between log of frequency and log of (G’). Usually a true gel has zero slope for a power law. It could be observed from Table 2d, that slopes of blended dough declined with the increase in percentage of barley husk. Similar observation was also made by Ahmed et al. (2013) and Bonnand-Ducasse et al. (2010). Incorporation of barley husk 10% in wheat flour led to significant decline in the magnitude of slope suggesting a more solid like character of dough with rise in barley fiber. The doughs with higher amount of fibers were stiffer and rigid compared to control dough. Georgopoulos et al. (2004) reported decrease in frequency dependency with decrease in water content of dough. Since, presence of fiber reduces the availability of water, therefore frequency dependence reduced with the increase in barley husk content of flour blends. 3.5. Effect of barley husk addition on percent freezable water content of chapattis Results for freezable water content are presented in Table 3. Fiber as an additive binds available water that is required for starch gelatinization. With the increment in fiber level, freezable water content tends to decrease. Possible reasons for this decrease could
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T. Mehfooz et al. / Journal of Cereal Science 79 (2018) 376e382
Table 2b Alveograph indices of wheat flour and husk blendsa. Barley husk (%)
P (mm H2O)
Control (0%) 5% 10% 20% 30%
94.60 68.60 45.00 45.03 44.60
± ± ± ± ±
L (mm)
4.50d 9.47b 3.80a 3.00a 5.31a
66.20 35.40 31.82 20.80 21.40
G ± ± ± ± ±
6.37d 12.73b 2.28b 4.49a 0.55a
18.08 12.95 13.02 10.10 10.28
± ± ± ± ±
0.89c 2.78b 0.43b 1.12a 0.10a
W (10e4J)
P/L
186.60 ± 16.07d 76.80 ± 17.82b 43.00 ± 5.14a 31.40 ± 4.03a 29.40 ± 4.83a
1.44 2.33 1.31 2.25 2.08
± ± ± ± ±
0.14ab 1.42c 0.10a 0.54bc 0.26abc
a Means with different superscript lowercase letters within a column are significantly different at p < 0.05. n ¼ 3. P: Tenacity; L: Dough extensibility; W: Deformation energy; P/L ratio: curve configuration; G: Index of swelling.
b)
G"(Pa)
G'(Pa)
a) 500000 450000 400000 350000 300000 250000 200000 150000 100000 50000 0 0
20
40
60
80
100
200000 180000 160000 140000 120000 100000 80000 60000 40000 20000 0
120
0
20
Frequency (Hz)
40
60
80
100
120
Frequency (Hz)
Fig. 1. Effect of frequency on storage modulus (a) and loss modulus (b) of wheat flour and husk blends. (-) Wheat flour Control (0%); () Wheat flour with 5% husk blend; () Wheat flour with 10% husk blend; (þ) Wheat flour with 20% husk blend; (C) Wheat flour with 30% husk blend.
be due to lower availability of free water in chapatti, as fiber having higher number of hydroxyl groups binds more water through hydrogen bonding (Rosell et al., 2001). According to Zeleznak and Hoseney (1986), the amount of water of present in bread determines the extent of amylopectin retrogradation. The results presented in Table 3 ascribed to the fact that fiber fortified flatbreads tend to form fewer amount of ice crystals during freezing because of less availability of free water (Leray et al., 2010). 3.6. Effect of barley husk addition on textural characteristics of chapattis The results of textural characteristics of fresh and stored chapattis are presented in Table 4. It could be observed from the results that fresh chapatti in the absence of fiber required higher amount of force to tear the chapatti. On addition of fiber to the chapattis, the force reduced by 50%. However, there was no significant difference in the rupturing force with increasing levels of fiber in chapatti. These results suggested that addition of fiber interferes with the formation of extensible gluten network. The fiber particles thwart the association of glutenin and gliadin protein. Secondly, barely fibers absorb water from the dough, making it less available for the development of elastic gluten network and subsequently a weak gluten network is formed which is easily teared off during textural
analysis. A high degree of similarity was observed between the subjective (sensory analysis Table 4) and objective analysis (hardness of chapatti Table 5) as both reflected insignificant difference in hardness in terms of quantity of fiber present in chapatti. Chapattis when stored for two days at room temperature showed significant increase in rupturing force. This increase is assumed to be due to retrogradation of starches which is the major component of wheat flour. During cooking of chapatti on hot iron plate, the gelatinization of starch takes place. For gelatinization to take place, two key factors i.e. water and temperature greater than 50 C are necessary. Water is added during preparation of dough, while the temperature of hot plate is around 270 C leading to gelatinization of starch. These gelatinized starch granules when stored for two days retrograde and eventually imparts hardness to chapattis. Elasticity is yet another quality parameter of flat bread which denotes the length of extension of bread before it gets teared up. More the extensibility, the higher will be the length recorded at the time of rupture. The results clearly depicted the fact that control chapatti had significantly higher elasticity compared to chapattis made with addition of fiber to flour. The appreciable amount of water bound to fiber makes scanty water available for development of starch gluten network which subsequently reduces elasticity (Brennan and Cleary, 2007). Moreover, addition of fiber also dilutes down the gluten content resulting in increased hardness and
Table 2c Rheological parameters at 1 Hz for doughs made with different percentages of barley huska. Barley husk (%)
G’ (Pa)
G’’ (Pa)
Viscosity (Pa.s)
Control (0%) 5% 10% 20% 30%
22378.30 ± 4556.30a 36213.21 ± 808.93b 52686.40 ± 2504.51c 86796.42 ± 237.72d 211319 ± 5433.40e
6299.80 ± 200.50a 7760.73 ± 300.65a 20015.92 ± 996.52a 22353.41 ± 1600.51a 127521.61 ± 1300.53b
3712.10 ± 869.50a 5895.32 ± 100.21b 8970.51 ± 302.22c 14289.74 ± 345.40d 43464.90 ± 1312.00e
a Means with different superscript lowercase letters within a column are significantly different at p < 0.05. n ¼ 2. G’: Storage modulus, G”: Loss modulus.
T. Mehfooz et al. / Journal of Cereal Science 79 (2018) 376e382
3.7. Effect of barley husk addition on sensory characteristics of chapattis
Table 2d Slope of linear regression of (logG’) vs (log u) for doughs made with different percentages of barley huska. Barley husk (%)
Slope
Control (0%) 5% 10% 20% 30%
0.22 0.21 0.19 0.17 0.16
R2
± ± ± ± ±
0.01d 0.00cd 0.01bc 0.00ab 0.01a
The results of sensory characteristics are presented in Table 5. In terms of all sensory traits the control chapatti without any fiber received the highest scores as they were whiter and softer compared to fiber added chapattis. It could be observed from Table 5 that incorporation of higher quantity of barley fiber (greater than 5%) resulted in less preferred appearance as fiber imparts its own brownish color to chapattis. Interestingly, it was observed that all chapattis with added fiber were insignificantly different from each other in terms of hardness, spooning and aroma. This suggests that the sensory panelists were unable to perceive the differences in quantity of fiber in different chapattis. Though the addition of fiber significantly affected hardness and spooning capability of chapatti compared to control chapatti but they still received scores higher than 5. This shows that incorporation of fiber in chapatti does not make chapattis completely undesirable to consumer. Fiber being gritty gives slightly off-flavor to chapattis and also increases hardness and reduces elasticity as fiber interferes with gluten network and distribution of moisture in chapattis. This is also reflected in overall acceptability, as it could be observed that it reduced due to fiber addition. However, none of the chapattis were completely disliked by the panelists in terms of overall acceptability.
0.99 0.98 0.98 0.97 0.99
a
Means with different superscript lowercase letters within a column are significantly different at p < 0.05. n ¼ 2.
Table 3 Percent freezable water content of chapatti made with different percentages of barley huska. Barley husk (%)
%FW
Control (0%) 5% 10% 20% 30%
54.08e 18.33d 14.13c 12.27b 9.45a
381
a
Means with different superscript lowercase letters within a column are significantly different at p < 0.05. n ¼ 3. %FW: Percent freezable water.
4. Conclusion
reduction in elasticity (Collar et al., 2007). Storage of chapatti resulted reduced elasticity of all chapattis. On storage, the amylose chains in short term and amylopectin on long term storage reassociates or interact in close proximity to form crystallites, which confer hard/rigid structures, therefore, elasticity of dough reduces as starch granules form the major matrix along with gluten network. This phenomenon is called bread staling and reduces sensorial characteristics of flatbread. Apart from starch retrogradation, the altered water distribution is also a reason for decline in chapatti elasticity. According to Gray and Bemiller (2003) and HugIten et al. (2003), on retrogradation of amylopectin, the water molecules from gluten network are shifted towards starch linkages formation involved in formation of amylopectin crystallites. Also the plasticizing effect of water is less, leading to less extensible gluten network and less extensible chapattis.
From overall results, it could be concluded that the addition of barley husk fiber modified the chemical and rheological properties of flour blends and dough simultaneously. Chemical composition of all purpose wheat flour altered significantly as the level of husk increases. Addition of fiber up to 30% also affected farinograph indices. Flour blends with 30% husk showed higher water absorption and mixing tolerance index while rest of the parameters tend to decline. Flour blends at increasing level of husk showed decline in alveograph parameters except for P/L ratio which did not behave significantly different. Frequency sweep measurements exhibited development of stiffer dough with the increase in barley husk due to more amount of water being absorbed by fiber. Though panelists preferred chapattis with no fiber at all but none of the chapattis with added fibers were disliked by panelists.
Table 4 Texture of fresh and stored chapattis made with different percentages of barley huska. Samples
Fmax (g)
Barley husk (%)
Day 0
Control (0%) 5% 10% 20% 30%
4.50 2.54 2.47 2.41 2.71
± ± ± ± ±
Ɛ-Fmax (mm) Day 2
0.50c,1 0.38b,1 0.31b,1 0.56b,1 0.13b,1
6.58 4.26 3.49 4.19 3.70
± ± ± ± ±
0.38b,2 0.20a,2 0.71a,2 1.11a,2 0.84a,2
Day 0
Day 2
23.94 ± 2.62d,1 11.27 ± 2.10b,1 10.58 ± 1.66ab,1 8.44 ± 1.70a,1 8.20 ± 1.34a,1
3.83 2.45 1.44 1.70 1.27
± ± ± ± ±
0.59c,2 0.29b,2 0.28a,2 0.32a,2 0.26a,2
a Means with different superscript lowercase letters within a column and different numbers within a row are significantly different at p < 0.05. n ¼ 3. Fmax: Force to tear; Ɛ-Fmax: Extensibility.
Table 5 Sensory characteristics of chapatti containing different percentages of barley huska. Barley husk (%)
Appearance
Control (0%) 5% 10% 20% 30%
8.17 7.31 5.92 6.17 6.17
± ± ± ± ±
0.84c 1.34bc 1.93a 1.40ab 1.16a
Hardness 8.50 5.92 5.67 5.75 6.25
± ± ± ± ±
0.52b 1.66a 2.43a 1.36a 0.96a
Spooning 8.67 6.54 6.67 6.17 6.75
± ± ± ± ±
0.49b 1.89a 1.87a 1.19a 0.86a
a Means with different superscript lowercase letters within a column are significantly different at p < 0.05. O.A: Overall acceptability.
Aroma 9.00 6.15 6.58 6.58 6.42
± ± ± ± ±
O.A 0.00b 1.95a 1.88a 2.06a 1.78a
9.00 6.69 6.58 6.17 6.00
± ± ± ± ±
0.00c 1.18b 1.38b 1.47b 1.21b
382
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