Instrumental Texture of Chapati as Affected by Barley Flour, Glycerol Monostearate and Sodium Chloride

Abstract

Chapaties from wheat flour were prepared by incorporating barley flour (0, 10, and 20%w/w), glycerol monostearate (GMS, 0, 0.25, and 0.5%w/w) and sodium chloride (0, 0.5, and 1%w/w). The instrumental texture of fresh and 24 h-stored chapati were evaluated. An objective method to measure, the instrumental texture of chapati, based on tensile deformation, has been presented. The extensibility decreased whereas load to rupture and deformation modulus increased upon storage of chapati. GMS, barley flour, and sodium chloride at all levels significantly affected the instrumental texture of chapati. All the three ingredients prevented staling of chapati as exhibited by higher extensibility values after 24 h of storage. A regression model was developed, and the coefficients had high R² values (≥0.83) and can be used to predict the textural behaviour of chapati.

Keywords:

• Chapati
• Extensibility
• Deformation Modulus
• Instrumental texture
• Barley flour

INTRODUCTION

People in India have been using wheat from times immemorial as chapati (unleavened flat bread). At present, about 85 to 90%[1] of wheat consumption in India is in the form of chapati and its culinary variations such as tandoori roti, nan, parantha, and poori. The traditional method of milling is carried out by grinding wheat into flour with a chakky, which consists of two heavy granite stones of equal diameter (one rotating and the other stationary). The ground whole wheat flour (atta) is collected and sieved to remove the coarsest particles of bran giving a flour of over 95% extraction rate. This flour is an excellent source of nutrition and dietary fiber.

Whole wheat flour (atta) is kneaded thoroughly by adding an adequate quantity of water until a dough of moderately stiff consistency is obtained. The dough is allowed to rest for about 30 min, which facilitates a uniform distribution of moisture in the dough, hydration of proteins and starches, and allows the dough to develop more completely.[2] A portion of the dough is rolled and flattened and then baked on hot flat iron plates (tawa). Chapati dough should be moderately strong, elastic, and extensible. The chapati should have a pleasing colour and should retain its soft and pliable structure during storage. It must tear smoothly and easily and should not be brittle or leathery. Unless eaten immediately after baking, chapatis become stale and difficult to chew, which poses a problem especially to geriatrics and infants.

Wheat flour is traditionally mixed with flours of other cereals and pulses to enhance palatability and nutritional quality. Barley has a high β-glucan content.[3,4] β-glucan is an economical and palatable ingredient that can be added to processed food products formulated to modify glycemic and insulin response.[5,6] The effect of composite flours and additives on the instrumental texture of chapati has been reported and barley can be blended with wheat flour to yield acceptable quality of chapati.[1] Sodium chloride is used in almost every baked product at levels of 1–2% where it gives taste and strengthens the dough.[7] Glycerol monostearate (GMS), a commonly used emulsifier, decreases recrystallization of starch in bread.[8,9] Incorporation of additives like sodium chloride and GMS and use of composite flours appear feasible as a means to restrain staling in chapati. The objectives of the present investigation were to ascertain the combined effects of barley flour, sodium chloride, and GMS incorporation on chapati instrumental texture and to develop a mathematical model to predict the instrumental texture of the resulting chapati.

MATERIALS AND METHODS

Common wheat (Triticum aestivum) obtained from Punjab Agriculture University was cleaned and milled into whole wheat flour (atta) in a stone mill. Barley flour was obtained by milling ‘PL-426’ variety in a stone mill and flour was sifted through 60-mesh sieve. Sodium chloride and glycerol monostearate (AR grade) were obtained from CDH Chemicals, New Delhi.

Chapati Making

Composite wheat flour, 150 gm containing barley flour (0, 10 and 20%w/w) and GMS (0, 0.25 and 0.5%w/w) and sodium chloride (0, 0.5 and 1% w/w) were mixed with optimum water for three minutes in a laboratory mixer (National Manufacturing Company, Lincoln, NE). The optimum water absorption was the one which resulted in a well developed non sticky viscoelastic dough which was easy to sheet.[7,10] The dough was left to rest for half an hour. Dough (50 gm) was rounded and then placed on the rolling board and was sheeted to a diameter of 155 mm and a thickness of 2 mm using a rolling pin. The dough was rolled in one direction, inverted, and then rolled in a perpendicular direction. The raw chapati was immediately placed on a hot plate (250^o C) and baked for a total of 1 minute on both sides. The chapati was allowed to cool for 10 min at 25°C (80% relative humidity) and then packed in polyethylene pouches and placed in an air tight container at 25°C.

Instrumental Texture of Chapati

Rectangular strips of 90 mm × 18 mm were cut from the center of the chapati using a metal template. Each strip of chapati was then tested for extensibility on the Instron Universal Testing Machine (Model - 4464, Buckinghamshire, England). The chapati strip was placed between two clamps. One clamp was attached to the moving arm of the Instron and the other was attached to the platform. Both clamps were properly aligned and set at 40 mm apart. A load cell of 100 N was used at a crosshead speed of 50 mm/min to pull the chapati strip apart until it ruptured. Only the chapati strips that ruptured from the center were considered; those that ruptured close to the clamps were discarded. The force-displacement curve was obtained, and from this curve various parameters such as the modulus of deformation (tensile modulus, MPa), load to rupture (kN), energy to rupture (J), and extensibility (mm) were calculated.[11,12]

(1)

where F is the load (peak force, N) to rupture, A is cross section area (m²), L is initial length (m) of chapati, and △L is change in length (extensibility, m). The chapatis were stored for 24 h in an airtight container at room temperature (25°C) and later subjected to the extensibility test. A sensory panel comprised of students of the department was asked to evaluate the instrumental texture of chapati on a nine point Hedonic scale, but the panel was unable to differentiate subjectively between the samples.

Statistical Analysis

Regression analysis was performed using Excel (Microsoft) software. A full factorial screening design with 11 treatments was used,[13] in which barley flour, GMS, and sodium chloride were taken as the independent variables. These variables had values of X₁ (barley flour concentration: 0, 10, and 20%), X₂ (GMS concentration: 0, 0.25, and 0.5%) and X₃ (Sodium chloride concentration: 0, 0.5, and 1%). The data for all the parameters were the average of ten replications. The following equation was used to measure the dependent variable:

(2)

where, Y is either extensibility, load to rupture, energy to rupture, or deformation modulus.

RESULTS AND DISCUSSION

The whole wheat flour had an extraction rate, protein content, and ash content of 95, 9.2, and 1.86%, respectively. The particle size distribution of the flour was such that 11, 2, 44, and 29% was retained by 44, 52, 72, and 100 mesh sieves and 14% passed through 100 mesh sieve. The wheat flour had water absorption of 61.4%. All the three ingredients increased water absorption, with barley flour incorporation having the most significant effect (Table 1). The water absorption increased to 65.4% when barley flour was incorporated at 20% level.

Table 1 Experimental design and responses

					Extensibility (mm)		Load to rupture (kN)		Energy to rupture (J)		Deformation modulus (MPa)
S.No.	Barley flour (%w/w)	GMS (%w/w)	Sodium chloride (%w/w)	Dough water absorption (%)	Fresh	24 h storage	Fresh	24 h storage	Fresh	24 h storage	Fresh	24 h storage
1	0	0	0	61.4	8.18	3.20	0.0023	0.0028	0.0297	0.0087	0.250	0.790
2	20	0	0	65.4	9.22	4.33	0.0020	0.0003	0.0237	0.0105	0.195	0.635
3	0	0.5	0	64.0	14.14	3.91	0.0025	0.0046	0.0313	0.0150	0.160	1.043
4	20	0.5	0	66.7	12.60	2.72	0.0027	0.0035	0.0340	0.0081	0.193	1.148
5	0	0	1.0	64.0	14.52	3.06	0.0023	0.0038	0.0030	0.0088	0.145	1.103
6	20	0	1.0	64.0	12.64	3.80	0.0021	0.0041	0.0232	0.0110	0.147	0.964
7	0	0.5	1.0	63.4	12.84	4.29	0.0026	0.0046	0.0358	0.0151	0.179	0.956
8	20	0.5	1.0	66.0	14.95	4.50	0.0030	0.0048	0.0385	0.0177	0.181	0.963
9	10	0.25	0.5	65.4	14.02	3.46	0.0030	0.0038	0.0430	0.0134	0.191	0.988
10	10	0.25	0.5	65.4	10.59	4.04	0.0024	0.0046	0.0341	0.0157	0.208	1.011
11	10	0.25	0.5	65.4	12.30	3.75	0.0027	0.0042	0.0385	0.0145	0.199	0.999
Values are mean of ten replications.

Extensibility

Fresh control chapati (0% barley flour, 0% sodium chloride, and 0% GMS) had an extensibility of 8.18 mm, which decreased to 3.20 mm after 24 h of storage. This decrease can be attributed to recrystallization and retrogradation of starch in the chapati, a very common phenomenon which occurs in bread.[14,15] Extensibility of fresh chapati was most significantly affected by sodium chloride followed by GMS and barley, as indicated by p values (Table 2). Barley flour at the 20% levels increased the extensibility to 9.22 mm in fresh chapati and 4.33 mm in chapati stored for 24 h.

Table 2 Regression coefficients for instrumental textural properties of chapati

Term	Extensibility				Load to rupture
	Fresh		24 h storage		Fresh		24 h storage
	Coefficient	p-value	Coefficient	p-value	Coefficient	p-value	Coefficient	p-value
Constant (a)	8.1582		3.211		0.0024		0.0030
X1 (b1)	0.0522	0.634	0.0566	0.043	−1.3 × 10^−5	0.600	−0.0001	0.063
X2 (b2)	11.9200	0.057	1.4240	0.124	0.0005	0.626	0.0035	0.141
X3 (b3)	6.3425	0.049	−0.1450	0.695	7.5 × 10^−5	0.881	0.0009	0.359
X1X2 (c2)	−0.2581	0.424	−0.2322	0.016	4.7 × 10^−5	0.524	0.0001	0.324
X1X3 (c3)	−0.1462	0.372	−0.0195	0.472	−2.5 × 10^−7	0.994	0.0001	0.105
X2X3 (d)	−15.270	0.072	1.0510	0.349	−5.0 × 10^−5	0.971	−0.0019	0.511
X1X2X3 (e)	0.6563	0.195	0.1782	0.076	2.65 × 10^−5	0.793	−0.0002	0.446
R^2	0.87		0.94		0.85		0.92
	Energy to rupture				Deformation modulus
	Fresh		24 h storage		Fresh		24 h storage
	Coefficient	p-value	Coefficient	p-value	Coefficient	p-value	Coefficient	p-value
Constant (a)	0.0328		0.0094		0.2549		0.8233
X1 (b1)	−0.0003	0.701	9.37 × 10^−5	0.627	−0.0027	0.105	−0.0364	0.015
X2 (b2)	0.0033	0.916	0.0127	0.166	−0.1793	0.032	0.5069	0.181
X3 (b3)	−0.0268	0.158	1.0 × 10^−4	0.978	−0.1046	0.021	0.3134	0.121
X1X2 (c2)	0.0009	0.696	−0.0009	0.171	0.0088	0.078	0.0832	0.027
X1X3 (c3)	0.0013	0.285	1.88 × 10^−5	0.944	0.0028	0.190	0.0294	0.065
X2X3 (d)	0.0624	0.221	−6.0 × 10^−5	0.995	0.2483	0.034	−0.8014	0.147
X1X2X3 (e)	−0.0026	0.427	0.0009	0.276	−0.0088	0.159	−0.0686	0.100
R^2	0.85		0.83		0.90		0.96
Where, X1 is barley flour (0, 10 & 20%), X2 is GMS (0, 0.25 & 0.5%) and X3 is sodium chloride (0, 0.5 & 1%).

Chapati containing barley flour showed a smaller decrease in extensibility after storage, suggesting that β-glucan in barley flour may be involved in retarding firming. Glucans improve the extensibility of dough by structuring a large amount of water in the dough phase, improving the mechanical strength of the liquid film, and by associating with the continuous protein phase in dough.[16,17] β-glucans reduce starch recrystallization because they absorb large amounts of water and decrease the amount of starch available for retrogradation. 18]

Rate of firming has an inverse relationship to water content.[19] Sodium chloride at 1% level increased the extensibility to 14.52 mm in fresh chapati, which decreased to 3.06 mm on storage for 24 h. Sodium chloride is known to bind or tighten the water and proteins in the dough. Sodium ions compete with hydrogen ions for loci on gluten molecules reducing the hydrogen binding that tends to tie the molecules together.[20] This phenomena was seen as a coagulation or hardening of the gluten with release of water; the gluten molecules are bent and interlocked so that work in the form of additional mixing is required to unwind or unravel the gluten strands into more nearly linear alignments.[21] GMS at the 0.5% level increased the extensibility to 14.14 mm in fresh chapatti, which decreased to 3.91 mm in chapati stored for 24 h (Table 1). GMS is widely used for maintaining bread crumb softness for longer periods by retarding the process of staling. The formation of a monoglyceride and amylose complex contributes to a decrease in initial crumb firmness, while complexing with amylopectin results in a distinct reduction in the rate of firming during storage.[22] The same phenomenon may be occurring in chapati. Barley flour, GMS, and sodium chloride, when added in combination at their highest levels, resulted in an extensibility of 14.95 mm in fresh chapati and 4.50 mm in 24 h stored chapati. The extensibility of fresh and stored chapati at varying levels of barley flour, GMS, and sodium chloride has been predicted using the regression coefficients from Table 2. As observed, the predicted values (Fig. 1 –3) are very close to the actual values. Increasing levels of barley flour and GMS improved chapati extensibility in both fresh and 24 h stored chapati (Fig. 1 and 2). The addition of sodium chloride improved the extensibility of fresh chapati but lowered the extensibility of stored chapati (Fig. 3), which agrees with the actual values in Table 1. This negative effect of sodium chloride was reversed in the presence of barley flour and GMS (Fig. 3).

Figure 1 Predicted effect of barley flour on chapati extensibility.

Figure 2 Predicted effect of GMS on chapati extensibility.

Figure 3 Predicted effect of sodium chloride on chapati extensibility.

Peak Load to Rupture

The load to rupture is the peak force of the force-displacement curve. Load to rupture increased with storage, indicating an increase in brittleness/toughness and a decrease in extensibility of chapati. The load to rupture for the control fresh chapati was 0.0023 kN and increased to 0.0028 kN after 24 h of storage. Load was most significantly affected by barley flour followed by GMS and sodium chloride for both fresh and stored, as indicated by p values (Table 2). Barley flour at 20% levels decreased the load to 0.0020 kN in fresh chapati and 0.0003 kN in chapati stored for 24 h. Sodium chloride at 1% levels increased the load to 0.0023 kN in fresh chapati and 0.0038 kN in chapati stored for 24 h. GMS at 0.5% level increased the load to 0.0025 kN in fresh chapati and 0.0046 kN in chapati stored for 24 h. Load to rupture fresh chapati was 0.0030 kN and increased to 0.0048 kN in chapati stored for 24 h when the three additives were present in combination at their highest levels.

Energy to Rupture

Energy to rupture is the area under the force-displacement curve up to the rupture point. Energy to rupture fresh control chapati was 0.0297 J, which decreased to 0.0087 J on storage. Sodium chloride followed by barley and GMS most significantly affected the energy to rupture fresh chapati, as indicated by p values (Table 2). Increasing levels of barley flour decreased the energy to rupture because the corresponding load to rupture decreased, resulting in a lower area under the force-displacement curve. Sodium chloride at the 1% level increased the energy required to rupture to 0.0030 J in fresh chapati and 0.0088 J in chapati stored for 24 h. GMS at 0.5% level increased the energy to rupture to 0.0313 J in fresh chapati and 0.015 J in chapati stored for 24 h. When barley flour, GMS, and sodium chloride were added at levels of 20, 0.5, and 1%, respectively the energy to rupture increased to 0.0385 J in fresh chapati and 0.0177 J in stored chapati.

Deformation Modulus

Fresh chapati had lower deformation modulus (0.250 MPa) as compared to that of chapati stored for 24h (0.790 MPa). Sodium chloride most significantly affected the deformation modulus of fresh chapati followed by GMS and barley flour (p values, Table 2). At their highest levels of incorporation, barley flour, GMS, and sodium chloride resulted in fresh chapati having deformation modulus of 0.195, 0.160, and 0.145 Mpa, which increased to 0.0635, 1.043, and 1.103, respectively, after 24 h storage. In combination at their highest levels, the modulus was 0.181 MPa for fresh chapati, which increased to 0.963 MPa after storage for 24 h. The extensibility of chapati, both fresh and stored, was significantly improved by barley incorporation. Additions of GMS and sodium chloride were also helpful in restraining the changes that normally occur during storage. In combination, the three additives—barley flour (10-20%), GMS (0.25-0.5%), and sodium chloride (0.5-1%)—can restrain staling and help bring the quality of stored chapati closer to that of fresh chapati.