Impact of Partial Replacement of Wheat Flour with Chickpea Flour on Physico-Chemical and Sensory Properties of Tea Buns

ABSTRACT The present study aimed to identify the optimum substitution ratio of chickpea flour (CF) into ordinary tea buns with intention to improve the nutritional value and the best sensory properties while retaining their shape. Flour blends were prepared in the proportions of wheat flour WF: CF (w/w %) 80:20, 70:30, 60:40, and 50:50 while WF (100:0) as a control. The rheological properties of blends were determined by Brabender farinograph apparatus. The prepared buns were evaluated for color, loaf specific volume, proximate composition, amino acid profile, and the preference towards sensory properties. According to the farinograph results, WF and 20% substitution were strong dough while 30%, 40%, and 50% substitutions were medium-strength doughs. In higher incorporation ratios, the moisture contents of the buns were decreased and the crumb texture gets harder and less porous making the product unacceptable. Buns made with 40% and 50% substitution failed to exceed the minimum requirement of specific loaf volume. The levels of protein in the buns are gradually elevated, making the product more nutritious with complementing amino acid profiles. Although the higher incorporation is more healthy and nutritious, only 20% and 30% CF incorporated buns seem to be practical in the manufacturing industry.


Introduction
Bakery products have been a staple of the human diet for centuries and are becoming increasingly popular in all over world due to their low cost, ease of consumption, varied taste and texture profiles.Though the buns are available in many shapes and sizes, they can be generally considered as round, small loaf of bread which is softer and sweeter than ordinary bread.A variety of buns such as burger buns, tea buns, cream buns, hot dog buns, and so on, are widely consumed all over the world while children are considered as the most obsessed group.The most of the school-children in Sri Lankans prefer bread or WF based foods for breakfast over home cooked rice meals [1] .
The essential ingredients of the buns are flour, leavening agent, edible common salt, water, edible fat and sugar. [2]Other optional ingredients are commonly added to aid processing, enrich nutritional value or improve texture or sensory characteristics. [3,4]Being the basic ingredient, refined WF makes the bakery products in lack of some nutritional components such as protein, dietary fiber, vitamins and minerals which are essential in a healthy diet.It has been suggested that bakery products may contribute to increase certain unhealthy characteristics of children's diet, especially excess energy, saturated fats and sugars. [5]In addition, it can be a cause of obesity and other non communicable diseases when it is consumed in large quantities regularly and when it is a part of an unbalanced diet. [6]ue to these consequences, the consumption of white bread and bakery products is discouraged.
Health concerns play a main role in determining the consumers' quality perception of bread products. [7]10][11] However, unlike other bread and bakery products, very few attempts have been made to fortify buns.14] Supplementation of WF with legume flours is a potential way to increase the nutritional properties of cereal-based foods and have been successfully incorporated in bakery products [15].Grain Legumes receive much attention in nowadays because of its nutritional value which comprising a plentiful source of proteins, total amino acids and functioning as an excellent enhancer of protein quality when mixed with other cereal flours. [15,16]It is reported that the amino acid composition of pulses (high lysine and low methionine) complements that of cereals [17] and hence, provides a better amino acid profile in the new formulations.Further bioactive compounds in grain modulate the physiological functions in the body while facilitating reduction of obesity, lowering glycemic index of foods due to their high dietary fiber content and reducing of chronic diseases. [18]hickpea is a one of the nutritious pulse crop with low digestible carbohydrates (40-60%), protein (15-22%), essential fats (4-8%), and a range of minerals and vitamins [19] along with a variety of health benefits.It was grown in nearly 57 countries worldwide in varying climatic and growing conditions and chickpea ranks third in the global production of pulses at about 11.6 million tons annually. [19,20]ncorporation of CF would be an excellent method to improve the nutritional value and sensory properties of ordinary tea buns, which are often consumed by Sri Lankan children.However, it has been a challenge to incorporate pulse flours into yeast leavened products since it results a less viscoelastic dough which makes difficulty in the air incorporation and gas retention during leavening.This happens due to the inability to form gluten networks and weak interactions between pulse and wheat proteins. [21]Hence, incorporation proportion is reported to be limited.The present study was carried out to develop tea buns substituting WF with CF at different ratios to find out the optimum substitution ratio of CF, which gives the best nutritional value and sensory properties while retaining the desirable specific volume and shape of bun.

Materials, Chemicals and Reagents
Commercially available soft WF and CF with fine particle sizes was used.Flour and other ingredients used in the tea bun making process were obtained from the local super markets in Malabe, Sri Lanka.The packaged flour samples were kept in airtight containers and stored at room temperature (25°C to 28°C) until use.

Chemical Composition of Commercial Wheat and Chickpea Flours
Proximate composition of flours was determined as methods described in following AOAC, 2012. [22]oisture content was measured by the oven drying method at 105°C in an oven (MEMMERT NLE 500, Germany).Crude protein content was analyzed using macro-Kjeldahl method (950.36) which involved protein digestion followed by distillation using Kjeldahl apparatus (Auto Digester; VELP Scientifica DK 20, Italy and Kjeldahl semi distillation unit, VELP Scientifica DK 139, Italy).In calculating protein content, 5.71 were taken as the conversion factor. [9]Crude fat content was determined using solvent extraction method (922.06) using Fat extraction unit (Soxtherm, Gerhardt-SOX416, Germany).The crude fiber content was determined as method described (978.10)using Fibertec apparatus ((FOSS−1020 Hot extractor, Netherlands).Ash content was determined as method described (923.03)by igniting sample at 550°C in muffle furnace (LENTON Furnace, UK).Carbohydrate content and energy value were calculated as follows.All determinations were done in triplicates.

Rheological Properties of WF and Flour Blends
Rheological properties of blends prepared from replacement of WF with CF were determined by Farinograph apparatus (Brabender Farinograph, Model: 8 10 101, Duisburg, Germany).Farinograph curves were generated according to AACC method. [23]The 300 g samples were used, in conjunction with the standard operating speed of 63 rpm, temperature of 30°C, measuring range of 0-5 Nm and damping of 1s.Experiments were conducted in triplicates and the mean values and standard deviations were reported.The curves were read manually and several parameters were recorded.Percentage water absorption (WA) was determined by adjusting the water amount to center of the curve on the 500 BU line.Dough Development Time (t d ) was determined to the nearest 0.5 min as the time gap between the point of first water addition and the point in the maximum consistency range immediately before the first indication of weakening.Stability (S) was determined as the interval, to the closest 0.5 min, from the point where the top of the curve first intersects the 500 BU line (arrival time) to the point where the top of the curve leaves the 500 BU line (departure time).Mixing Tolerance Index (MTI) was determined by the difference in BU from the top of the curve at the peak to the top of the curve measured at 5 min after the peak was reached.Time to Breakdown (t b ) was determined by drawing a horizontal line through the center of the curve at its highest point and then drawing another parallel line at the 30 BU lower levels.The time from the start of the mixing until the center of the descending curve crosses this lower line was considered as the "time to breakdown." [23]uns Preparation Procedure The buns were prepared with the above said flour blends (Sec 2.2).The ingredients were weighed per 100 g of flour.Sugar (32 g), margarine (14 g), yeast (3 g for Formula F and F1: 3.8 g for F2, F3, and F4), skim milk powder (2 g), salt (1.5 g), ascorbic acid (150 ppm), calcium propionate (0.2 g), and water (40-45 ml).The dry ingredients were mixed with flour blends for 2 min.Next, the activated yeast dissolved in water was added followed by the addition of water to make the hard dough.Then, the dough was kneaded for 5 min.Finally, margarine was mixed with the dough and the kneading process was continued for another 10-15 min.From the dough, 60 ± 5 g of pieces were shaped and placed in baking pans then a proofing cabinet (Bolidt, Netherlands) at 30°C 75-80% relative humidity.After 2 1/ 2 h fermentation, the dough was baked at 200°C for 15 min in a table top electric oven (BEKO, Turkey).The buns were then cooled and packaged in polypropylene bags to prevent moisture loss at room temperature (approximately 25−28°C).

Evaluation of Physical Properties and Loaf Measurements
Color of the samples (fresh buns) were measured using a reflectance Chroma-meter (Konica Minolta, Japan) based on the L*(brightness/whiteness), a* (redness/greenness), and b*(yellowness/blueness) values.Samples were placed on a porcelain tile, the measuring probe was placed on the surface of the buns crust/cross-section and the values for L*, a*, and b* were recorded.The same procedure was followed 15 times to increase the accuracy.The loaves were weighed and the loaf volumes were measured by sesame seed displacement test according to Standards for white bread. [24]The loaf specific volume was calculated as the ratio between the volume of the bread and its weight.

Evaluation of Chemical Properties of Buns
Evaluation of chemical properties of buns were carried out as methods described in chemical composition of commercial wheat and chickpea flours

Amino Acid Composition
Sample preparation for total amino acid analysis was done according to the method stated by Liyanaarachchi et al. [25] Sieved dried powdered (0.2 g) sample was placed inside a screw capped glass tube and 5.00 mL of hydrolysis mixture (6 mol/L HCI containing 1 g of phenol per L) was added.The sample after vortexing for 5 min was placed inside a drying oven set at 110°C for 22 h to complete the hydrolysis.In order to minimize building up of pressure inside the screw capped tube containing the hydrolysis mixture, it was tightened only after an hour kept in the oven.
After completion of the hydrolysis, the mixture was transferred to an ice bath and the pH was adjusted to 2.2 using 10 M and 1 M sodium hydroxide solution using pH meter (EUTECH Instruments, PH510, pH/mv/ o C meter, USA).The pH adjusted solution was transferred to a 25 mL volumetric flask and made up to the mark with ultra pure water.
Amino acid analysis was performed using an Agilent 1260 infinity HPLC system (Agilent Technologies, USA), which consisted of a quaternary gradient pump, diode array detector (DAD), thermostated column compartment (TCC) and a programmable auto sampler.The chromatographic separation was achieved using an Agilent Zorbax Eclipse AAA column (4.6 × 150 mm, 3.5 μm) with gradient elution.Mobile phase consisted of A: 40 mM Na 2 HPO 4 , pH 7.8 aqueous buffer and B: Acetonitrile: Methanol: Water (45:45:10).The gradient elution started with 100% A for 1.9 min; increased to 57% B within next 18.1 min; increased to 100% B in 18.6 min and kept at 100% B till 22.3 min; then increased to 100% A in 23.2 min and maintained till 26 min.Total run time was set to 30 minutes with a flow rate of 2 mL/min.Column compartment was thermostated at 40°C.The automated pre-column derivatization with o-phthalaldehyde 3-mercaptopropionic acid (OPA−3MPA) and fluorenyl methyloxycarbonyl chloride (FMOC) for primary and secondary amino acids was performed prior to detection at 338 nm and at 262 nm, respectively, using the DAD detector.Agilent Open Lab Chem station software version 1.8.1 was used for the data acquisition and analysis.

Sensory Properties
The sensory preference of the buns (F1, F2, F3, and F4) was evaluated as a ranking test by 15 trained panelists in a sensory evaluation laboratory equipped with separate booths in the Food Technology Section, Industrial Technology Institute, Malabe.The panelists ranked the sensory attributes of color, aroma, overall texture, taste, and overall acceptability of each bun formulation.The panelists were asked to rinse their mouths with water between samples to reduce any residual effects.

Statistical Analysis
The results obtained were statistically analyzed by computer software package (SPSS, 2000).Descriptive data and significant differences among the various score were established using analysis of variance (ANOVA) and Turkey's multiple tests.Sensory data was analyzed using non-parametric statistics (Kruskal-Wallis and Friedmann).

Farinogram Parameters of WF and Flour Blends
After tried out several pre-farinograms to center of the curve on the 500 BU, following farinograph parameters were determined (Table 1).Optimum water level which needed to develop cohesive, viscoelastic dough with optimum gluten strength differs from flour to flour depending on the quantity of protein and other particles that they contained. [26]The water absorption values ranged from 58.1% to 60.4% with the ratios of flour blends of wheat: chick pea 50:50 to 80:20 having the lowest and highest values, respectively.Earlier studies have also reported that the water absorption capacity gradually decreased when increased in the quantity of pulse flour in a blend. [27]he rheological characteristics showed that the control (WF100 : CF0) arrived the 500 BU consistency line at the 1.68 min whereas the blends arrived at relatively longer times, indicating slower uptake of water and slower dough development as it is a measure of the rate at which water was taken up by the flour.All the blends except 50:50 had shorter departure times (DT) compared to the control.Moreover, the control had the highest dough development time (t d ) of 12.67 min whereas WF80: CF20 had the lowest of 5.3 min.The value has increased with the increasing of replacement level of chickpea flour.It is observed that the flour blends with low dough stability, had higher MTI values.Generally, flours with good tolerance to mixing have low MTI whereas the higher the MTI value showed the weaker the flour.The MTI values ranged from 27.5 to 65 BU with the control having the lowest values.Breakdown Time (t b ) is also an index of the relative strength of flours.The t b values ranged from 9 min to 13.3 min and conveyed the same pattern as the t d .Dough stability time indicated the tolerance of the  flour in between over or under mixing.With the increasing proportion of CF in WF blends from 0 to 50% led to progressive decrease in the dough stability which was decreased gradually from 9.27 min to 2 min.These results are complying with the previous studies carried out for pulse flour blends.It was suggested that the low gluten proteins and higher fiber content of CF makes the dough less stable, as compared with the WF. [27]ough development usually begins with addition of water and initiation of mixing operation.First, the ingredients are hydrated giving sticky dough.Then, more gluten protein gets hydrated and tends to align due to the shear and stretching forces applied along with further mixing.As a result, the viscosity and the dough strength get increased developing a non sticky mass at peak consistency (above the 500 BU of the farinogram).When the dough is mixed beyond this point, the monomeric proteins form a matrix within the long polymer networks minimizing the ability to extend by developing viscous dough with reduced elasticity.The dough again becomes stickier due to the existence of smaller chains of proteins. [28]The farinographic parameters classify the flour as very strong (WA > 63%, td >10 min, and MTI < 10 BU), strong (WA > 58%, t d between 4 min and 8 min, and MTI between 15 and 50 BU), Medium strength (WA from 54% to 60%, t d between 2.5 min and 4 min, and MTI between 60 BU and 100 BU), Weak (WA < 55%, t d <2.5 min and MTI > 100 BU). [29]he preferred flours for yeast-leavened products have high WA (62-64%), 4 to 6 min dough development time, 8-12 min dough stability and an MTI of approximately 40 BU. [29]The result revealed that the WF and WF 80: CF20 flour blends were strong flours while WF70:CF30 flour blend is medium strength.Except the values of t d , WF60:CF40 and WF50:CF50 also can be considered as medium strength flours.

Preparation of Buns
Except for the main ingredients, ascorbic acid and calcium propionate were used as additives.Ascorbic acid is used to strengthen the dough and has a beneficial effect on the volume, crumb structure and softness of the bread while Calcium Propionate is used as a mold and rope inhibitor.
In the process of preparation of buns, it was observed that the dough texture was sticky and hard to work with in incorporation ratios of 30% and above.The control was the easiest to form into dough.The appearance of the buns is given in Figure 1.In general, the buns had a golden brown crust and yellowish crumb and an appealing aroma.However the crumb texture got harder and less porous in higher incorporation ratios.

Average Loaf weight, Average Volume and Color of Buns
The physical characteristics of buns were measured to determine the effect of incorporation of CF on loaf weight, volume and color (Table 2) after baking.In the present study, all the buns met the requirement of minimum mass of 50 g as specified in local standard for buns [2] (Table 2).However, there was a reduction in Specific Loaf Volume (volume: mass ratio) when the incorporation rate is increasing compared to the control (F).If the value is too high the crumb can have an open grain and weak texture, and when it is lower there can be a weak gluten quality or incomplete dough development during fermentation. [30]Among all the samples of buns, 40% and 50% chickpea flour incorporated samples (i.e.F3 and F4) failed to retain the minimum requirement of specific loaf volume of 2.5 (ml/g) as specified in local standards for buns. [2]actors which affect the loaf weight are the amount of baked dough, moisture, and carbon dioxide released out of the loaf during baking, [31] which depends on the amount of gluten proteins develop in the matrix to retain gas.Replacing WF with CF reduces the amount of gluten in the blends due to the pulse proteins do not contain gluten.Increasing the level of the chickpea flours in the dough reduces the proportion of the gluten which is known as a gluten-dilution effect.This can be a cause of volume reduction in buns.The presence of fiber in CF (1.28 ± 0.19%, Table 3) might also be a significant reason in reducing loaf volume since fiber affects the behavior of gelatinized starch. [32]It was recorded that pulse starch has higher level of amylose in starch than wheat starch and the gelatinization temperature is different from that of wheat starch. [33]According to Kusunose et al. (1999) all the starch in bread should be gelatinized and set when the dough is completely expanded. [34]If not, the dough will not expand to its maximum.This can be another reason of volume reduction in buns.The results of the loaf measurements in the present study agree with the previous findings. [35,36]The reduction in loaf volume is considered as an undesirable quality characteristic as consumers usually prefer softer products.Unless the crumb structure is developed softer using additives, only 20% and 30% CF incorporated products seems to be practical.
while crust color depends on the baking temperature and the level of residual sugars. [30]The colorimetric values of crumb are given in Table 2.For crumb color, the values of L* ranged from 70.59 to 75.34.The lightest crumb was detected for the bun made with 50% addition of CF except control whereas the darkest crumb was observed for the bun made with 20% addition of chickpea flour.Even though the lightness (L*) values of samples were significantly different compared to the control (p < .05),no particular pattern was observed.The a* values, which correlate to the redness, ranged between 2.14 in control and in buns made with 50% addition of CF and F3 and F4 were significantly higher compared to the control (p < .05).The b* value s of all the samples (F1, F2, F3 and F4) were significantly different from the control and from each other indicating a noticeable increment in yellowness of the crumbs (p < .05)with increasing chick pea flour incorporation.Crust of all the buns observed were not even in color.The L*, a* and b* values were observed to have larger range possibly due to the difficulties in maintaining uniform baking conditions.The lightest crust was identified for the bun made with 40% addition of CF whereas the darkest crumb was observed for the bun made with 50% addition of chickpea flour.Both of these values are significantly different compared to the control (p < .05).The values of a* ranged from 16.9 to 23.06 while the values of b* ranged from 28.74 to 40.40.The buns made with 30%, 40% and 50% addition of CF were significantly different in a* values whereas 40% and 50% addition of CF were significantly different in b* values compared to the control (p < .05).Since there is no clear pattern identified, it is difficult to conclude the effect of CF addition into buns.

Proximate Composition of WF, CF and Formulated Buns
The proximate composition of WF and CF is presented in Table 3.The composition of commercial WF used in the present study is compatible with the previous research findings. [37,38]However, crude protein, crude fiber, crude fat and ash values of CF were remarkably higher than that of WF.The composition of CF is in line with those obtained by Khan et al., (1995) except ash and fiber values which are slightly different. [39]hemical properties of buns were evaluated in terms of proximate composition.The highest value for protein 12.96% was found in F4 (containing 50% CF) while the lowest value for protein 7.56% was found to be in F (control).It is explicable that due to addition of protein rich chickpea flour, the level of protein in the buns has gradually elevated and all are significantly differed (p < .05).
It was also observed that ash percentage in F4 is the highest (2.22%) and in F is the lowest (1.54%).However, the values of F1, F2, F3, and F4 were not significantly different when comparing with the control sample (p > .05).Crude fiber values were also increased along with the incorporation.Based on the results, incorporation of CF in the product formulation is encouraged to improve intake of minerals and fiber through consumption of the products.Addition of fiber into food has become a recent trend due to its physiological benefits.However, the fat content was found to be the highest in F2 while fat contents in formulations were held constant.The fat values in all other samples are significantly different than the control sample (p < .05).Those results may be due to the CF has more fat content than WF (Table 3).There was no consistent pattern among the carbohydrate values of the buns while the F1, F2, F3, and F4 samples shows no significant difference compared to the control (p > .05).
The moisture contents of the buns were gradually decreased (from 30.51% to 19.62%) along with increasing the CF.Incorporation of dehulled pulse flours lower the water absorption, resulting in loaves with extremely reduced volumes and dense crumb structures. [21]Even though the moisture content is important factor for longer shelf life, the low moisture levels can make the buns dryer than the control sample while making them undesirable.

Amino Acid Composition
Table 4 summarizes the mean Total Amino Acid (TAA) contents observed in the analyzed buns and flour samples.Total amino acid contents in formulated buns were in increasing order with an incorporation of CF (76.49-86.4μg per g of dry sample).Results showed that aspartate content in CF is higher than WF and the increasing incorporation of CF in buns formulations increases aspartate content.According to TAA profiles, glutamate showed the highest content in both WF and CF while tyrosine and methionine were the least present.Since the glutamate contents were high in both flours, the developed product of buns contained predominant content of glutamate.However the variation pattern of glutamate content is not clear with the incorporation of chick pea flour and may due to the technological problems such as improper mixing or the processing.It was observed that the most of the amino acids present in the formulations were not significantly differed (eg.Glycine, Threonine, Arginine, Alanine, Tyrosine, Valine, Phenylalanine, Isoleucine, Leucine and Lysine).Lysine contents in formulated buns were in increasing pattern with CF incorporation in complementing the essential amino acid profile in the buns.Although the histidine was detected in amino acid profiles of WF and CF it was not detected in the formulated buns.Those variations may be due to either in processing techniques or sample preparation technique.Buns made with different formulations of Wheat Flour (WF): Chickpea Flour (CF), F −100:0%, F1-80: 20%, F2-70: 30%, F3-60: 40%, F4-50: 50%, respectively.Numbers were assigned in each column in the order of their rank (p < .05)

Sensory Evaluation
Summary of the mean ranks given to each sample is given in Table 5.Most preferred sample was ranked as one while least preferred sample was ranked as five.Hence, the lower mean rank values indicate the most preferred samples in each attribute and vice versa.Texture is one of the most important sensory attributes with regard to the bakery products.Panelists graded the control sample as the most preferred texture while F4 is the least.This might be a result of dense crumb structure occurred due to the higher incorporation of CF.Though the preference for texture was reducing along with the incorporation ratios, F1 and F2 were not significantly different than the control (p < .05).The buns with 20% addition of CF were ranked first in taste and aroma even though there's no statistically significant difference in color, aroma and taste of the samples.Generally, panelists preferred the buns with 20% addition of CF over control and has been said that the taste is highly pleasing when CF is added.

Conclusion
Present study has been concluded that it is possible to incorporate CF to partially substitute WF in preparation of tea buns.According to the farinograph results, WF and 20% substitution were strong flours while 30%, 40%, and 50% substitutions were medium strength.Addition of CF will be an obstacle for the manufacturing process as the dough is sticky and hard to work with when incorporating more than 30%.The substitution percentage significantly affects the physical, chemical and sensory attributes of the final product.The moisture contents of the buns were decreased along with increasing substitution ratio.Crumb texture get harder and less porous in higher incorporation ratios and make the product unacceptable.Buns made with 40% and 50% substitution failed to exceed the minimum requirement of specific loaf volume.In sensory evaluation, the preference for texture was changed significantly at 40% and 50% substitution than the control (p < .05).However, the taste has been highly pleased at level 20% of chickpea substitution over control even though there's no statistically significant difference in color, aroma and taste of those samples.In addition, the levels of protein in the buns are gradually elevated making product more nutritious than the usual tea buns.Although the higher incorporation is more healthy and nutritious, only 20% and 30% CF incorporated buns seem to be practical in terms of physical and sensorial attributes of the product in the manufacturing industry.

Table 1 .
Farinograph parameters of WF replaced with different levels of CF.

Table 2 .
The average loaf weight, Average volume and color of buns.

Table 3 .
Proximate composition of different flours and bun formulations.

Table 4 .
Total amino acid composition of different bun formulations.

Table 5 .
Mean ranks of the preference toward sensory attributes of buns.