DOUGH CHARACTERISTICS AND BAKING STUDIES OF WHEAT FLOUR FORTIFIED WITH XANTHAN GUM

ABSTRACT

Incorporation of 0.1 to 0.5% of xanthan gum was investigated to evaluate its effect on the rheological, dough development, gas formation/gas retention and baking properties of wheat flour. Addition of 0.2% xanthan gum increased water absorption from 59 to 60.8%. Mixing tolerance index and degree of softening decreased by 40 BU each at 0.2% level of gum. Gelatinisation temperature and pasting peak remained statistically unaffected by all the levels of gum. Tenacity increased by 1.8 mm, extensibility by 2.0 mm, surface area by 1.23 cm², maximum dough height by 4.1 mm, time at which maximum height occurred by 1 min, total volume of gas production by 56 ml, retention volume by 79 ml and retention coefficient by 2.7% at 0.2% level as compared to control. There was increase in yield and softness of bread crumb with increase in the level of xanthan gum up to 0.5%. Firmness values indicated that the breads containing xanthan gum was softer even after 96 h of storage as compared to control under similar conditions.

INTRODUCTION

Bread is consumed by majority of population all over the world as a part of daily diet, due to various advantages, like, being ready to eat, convenient, cost effectiveness and its better nutritive quality. Gums have been used in baked goods, confectionary and food beverages as binding and emulsifying agents [1] and to monitor rheological properties of wheat flour 2-3. Specific additives have been incorporated as improvers to wheat flour and gums from various sources are one such important agent 4-6. Xanthan gum, a high molecular weight polysaccharide is produced by the plant pathogen Xanthomonas campestris [7]. The xanthan gum is composed of D-glucuronic acid, D-mannose and D-glucose units [8]. It has been used in conjugation with emulsifiers in the preparation of glutenless bread [9], high protein breads [10], bakery fillings and icings 11-12, syrups, toppings, desserts and dairy products [13], cakes [14] and pie fillings [4]. Considering the wide spread use of xanthan gum, present investigation was undertaken to determine the effect of xanthan gum on rheological, alveographic, dough development, gas formation and gas retention, baking and firmness properties of bread from flour of wheat variety WH 542.

MATERIALS AND METHODS

Preparation of Sample

Forty kg of wheat (WH 542) was obtained from Punjab Agricultural University Ludhiana out of the 1996–97 harvest. Sample was conditioned to 14% moisture content for 24 hours and milled using a laboratory mill (Brabender Quadrumat Junior) to get wheat flour of 70% extraction rate. Milled sample was stored in pearl pet containers for further use. Fresh (Tower Brand) compressed yeast was procured from the local market as and when required. Xanthan gum was procured from M/S John Baker Inc, Colorado, USA.

Chemical Characteristics

Moisture, total ash, dry and wet gluten, falling number (Perten, Sweden), damaged starch and diastase activity in the flour were determined according to [15] procedures. The gluten strength was determined using SDS-Sedimentation method [16].

Farinographic Characteristics

Constant flour weight method [15] was followed to study the effect of xanthan gum incorporation at 0.1, 0.2, 0.3, 0.4 and 0.5% levels on farinograms using Farinograph (Brabender, Germany). The amount of water required to center the farinogram curve at 500 BU line was measured as percent water absorption (WA)

where x=ml water added

Pasting Properties

Brabender Visco-Amylograph was used to study the pasting behavior of the flour [15]. Samples (60 g) containing optional ingredient (Xanthan gum of 0.1 to 0.5%) were mixed with 450 ml distilled water. The contents were mixed to smooth dispersion, transferred to the Visco-Amylograph bowl, brought to 30°C, then heated to 95°C at the rate of 1.5°C/min, held at 95°C for 15 min and cooled at the same rate to 50°C.

Alveographic Properties

Alveograph (Chopin, Tripette and Renaud, France) was used to study the effect of interaction between wheat flour and xanthan gum on the parameters like tenacity, elasticity, surface area, deformation energy and swelling index [2].

Gas Formation and Gas Retention Properties

The Rheofermentometer (Chopin, Tripette and Renaud, France) as described earlier [17] was used to study the effect of various levels of xanthan gum on dough development, gas formation and gas retention properties of wheat flour.

Baking Performance

Straight dough method [15] was used in bread making. Breads were prepared after adding 0.1, 0.2, 0.3, 0.4 and 0.5% xanthan gum on the flour weight basis. Loaf volume was measured using rapeseed displacement method [18] one h after baking. Evaluation of bread was carried out for crust and crumb characteristics i.e. texture, freshness score and eating quality by a panel of six judges 24 h after preparation as per procedure described [19]. The texture was evaluated in terms of softness and freshness on a scale of 1 to 6, with 6 for very fresh and 1 for stale and eating quality as normal or gummy. The unsliced loaves were placed on polyethylene bags, coded and stored at 24°C.

Firmness Measurement

After discarding the two out side portions (approximately 6 cm at each end), the loaves were sliced into 25 mm thick slices and used immediately for measuring firmness on Instron (Model 4464) Universal Testing Machine (Instron Corp., Canton, MA, USA). The rate of compression or crosshead speed was set at 100 mm/min., Flat aluminum plunger with a diameter of 36 mm (1017.9 mm²), was used to compress the 25 vmm thick slice. Slices were compressed to a total compression of 25% according to [15] procedure: The whole procedure was repeated on three different slices and the firmness values were averaged. The bread firmness measurements were also carried out at 24, 48, 72 and 96 hours after baking [20].

Statistical Analysis

Analysis of variance was conducted on the data obtained, using Sigma statistical software [21] to evaluate the effect of levels of xanthan gum for statistical significance. Least significant difference (LSD) was calculated for the significant effects (p<0.05).

RESULTS AND DISCUSSIONS

Chemical Characteristics

Chemical characteristics of the flour indicated that the wheat was medium strong. 70% extraction rate milled flour contained 0.5% ash, 9.8% protein, 30% wet and 11.2% dry gluten and showed 34 ml SDS sedimentation value. The flour also had low alpha amylase activity as revealed by falling number (712), diastase activity (192 mg per 10 g flour) and damaged starch content (5.3%).

Rheological Properties

All the dough characteristics except dough development time (DDT) were significantly affected by the various levels of xanthan gum. The data (Table 1) indicated a gradual but significant increase in water absorption by 1.4 to 3.0% with the increase in level of gum from 0.1 to 0.5% as compared to control. The useful properties of gum are largely due to the physical effects and primarily involve its interaction with water. Gum interacts with protein molecules to provide suspension and solution stability while the viscous and emulsification effects are due to the lipid molecules. By such interactions, gums perform their useful functions related to viscosity, solution stability and suspendability [22]. The dough development time remained statistically unaffected while stability of the dough and departure time decreased significantly by 1 min at 0.1 to 0.4% levels of xanthan gum. A significant (p<0.05) decrease of 40 BU each was observed in the mixing tolerance index and degree of softening at 2% and above levels of xanthan gum. Valorimeter value increased significantly by 2 BU at 0.3% addition of xanthan gum.

Table 1. Effect of Xanthan Gum on Dough Characteristics and Pasting Properties of Wheat Flour (WH 542)

	Xanthan Gum %
	0	0.1	0.2	0.3	0.4	0.5	LSD
Dough Characteristics Water absorption, %	59.0^a	60.4^a	60.8^b	61.2^bc	61.6^cd	62.0^de	1.42
Dough development time, min	1.5^a	1.5^a	1.5^a	1.5^a	2.0^a	2.0^a	0.68
Stability, min	12.0^a	11.0^b	11.0^b	11.0^b	11.0^b	11.5^a	0.88
Departure time, min	13.0^a	12.0^b	12.0^b	12.0^b	12.0^b	12.5^a	0.88
Mixing tolerance index after 5 min, BU	60^a	40^b	20^c	20^c	20^c	20^d	6.26
Degree of softening index after 10 min BU	80^a	40^b	40^b	40^c	40^c	40^c	5.34
Valorimeter value	54^a	52^b	53^a	56^c	53^a	54^a	1.61
Pasting Properties Gelatinisation temp, °C	61.5^a	61.0^a	60.5^a	59.5^b	58.5^bc	58.5^bc	1.56
Pasting peak, °C	87.0^a	87.0^a	86.5^a	86.5^a	87.5^a	87.0^a	0.84
Peak viscosity, BU	320^a	320^a	350^b	360^c	400^d	430^e	9.15
Viscosity at 95°C, BU	230^a	230^a	260^b	260^b	280^c	290^d	7.01
Viscosity after 15 min cooking at 95°C, BU	220^a	230^b	230^b	230^b	230^b	260^c	5.28
Viscosity at 50°C, BU	540^a	560^b	560^b	560^b	560^b	580^c	5.02
Setback on cooling, BU	320^a	330^b	340^c	330^b	330^b	320^a	3.93

Means superscripted with different alphabets in the same row differ significantly (p<0.05).

The statistical analysis showed that various xanthan gum levels affected all the pasting characteristics significantly (p<0.05) except pasting peak. As evident from Table 1 there was decrease in the gelatinisation temperature with the increase in level of xanthan gum. Peak viscosity and viscosity at 95°C increased significantly by 30 BU each at 0.2% level followed by further significant increase with levels. Christianson et al. (1981) have also reported the increase in peak viscosity of wheat starch with the addition of the xanthan gum. Viscosity after 15 min cooking at 95°C and viscosity at 50°C increased significantly by 10 and 20 BU at 0.2% level of xanthan gum, followed by further increase with levels of gum. The difference in the viscosity values between hot paste and paste cooled to 50°C referred to as the set back value [24] and reflects the retrogradation behavior of starch 25-26 which increased significantly with the increase in level of gum up to 0.4%.

Alveographic Properties

The statistical analysis of data in Table 2 indicated a significant (p<0.05) increase in the tenacity (resistance to extension) at 0.2% level of xanthan gum, however with further addition there was decrease in tenacity. Extensibility increased with an increase in level of gum but a significant (p<0.05) increase of 3.60 mm was observed only at 0.5% level as compared to control. Elasticity of the dough and pressure at bubble breaking point decreased with the increase in level of gum. Surface area which is an index of the baking strength of dough, increased with an increase in level of gum giving a significant increase of 3.17 cm² at 0.5% level only as compared to control, Swelling index remained constant with the increase in level of gum. As reported earlier [27] that xanthan gum imparted structural coherence to starch granules which is necessary to retain the gas.

Table 2. Effect of Xanthan Gum on Alveographic Characteristics of Wheat Flour (WH 542)

	Xanthan Gum %
Characteristic	0	0.1	0.2	0.3	0.4	0.5	LSD
P, tenacity (mm)	39.16^a	40.9^b	41.00^bc	40.04^b	40.00^b	38.82^a	1.29
L, extensibility (mm)	93.0^a	93.4^a	95.0^a	92.2^a	95.0^a	96.60^b	0.75
P/L, configuration ratio	0.42^a	0.43^b	0.43^a	0.43^a	0.42^a	0.40^a	0.04
p200, pressure at 4 cm from start of curve (mm)	17.6^a	19.8^b	19.0^a	18.7^a	15.0^c	13.2^cd	2.20
le, elasticity (p200/P)	0.45^a	0.48^a	0.46^a	0.46^a	0.38^b	0.34^b	0.10
P, pressure at bubble breaking point (mm)	11.0^a	11.0^a	11.0^a	10.0^a	9.0^b	9.0^b	1.36
S, Surface area (cm^2)	17.48^a	17.60^a	18.71^a	18.74^a	18.84^a	20.65^b	1.47
W, deformation work W=6.54×S (in 10^−4 Joules per g)	114.32^a	115.10^a	122.36^b	122.55^bc	123.21^bc	135.05^d	3.76
G, swelling index (mm)	21.40^a	21.45^a	21.60^a	21.25^a	21.60^a	21.80^a	0.60

Means superscripted with different alphabets in the same row differ significantly (p<0.05).

Gas Formation and Gas Retention Properties

The data in Table 3 revealed that all the dough development, gas formation and gas release parameters except the time at which gas permeability started from the dough, were significantly (p<0.05) affected by the levels of xanthan gum. Maximum dough height (Hm) increased significantly (p<0.05) by 3.9 mm at 0.2% level of xanthan gum as compared to control, followed by further significant (p<0.05) increase in height at 0.5% level. The development volume of the dough (h) increased significantly (p<0.05) by 3.3 mm at 0.1% level of xanthan gum, followed by further significant increase at 0.4 and 0.5% levels. The percent drop in development at 3 h from t ₁ decreased significantly (p<0.05) by 6.2% at 0.1% level of xanthan gum as compared to control, with no further significant change at higher levels of xanthan gum. The time (t ₁) at which dough reaches its maximum height (Hm) increased significantly (p<0.05) at each progressive level of xanthan gum upto 0.5% as compared to control.

Table 3. Effect of Xanthan Gum on Dough Development, Gas Formation, and Gas Release Characteristics of Wheat Flour (WH 542)

	Xanthan Gum %
Characteristic	0	0.1	0.2	0.3	0.4	0.5	LSD
	Dough Development Characteristics
Hm, (mm)	30.6^a	32.4^a	34.5^b	36.6^b	38.9^b	44.7^c	3.10
h (mm)	22.1^a	25.4^b	26.6^b	27.9^b	30.6^c	34.8^d	2.88
(Hm-h)/Hm (%)	27.8^a	21.6^b	22.9^b	23.7^b	21.3^b	22.1^b	2.13
t 1 (min)	73^a	74^a	74^a	81^b	98^c	124^d	6.32
	Gaseous Release Characteristics
Hm′ (mm)	58.5^a	56.2^a	56.8^a	58.7^a	62.3^b	64.5^c	2.48
t 1 (min)	174^a	165^b	157^c	148^d	142^d	137^e	5.18
t x (min)	13	13	13	13	13	13	NS
Total vol (ml)	1352^a	1388^b	1408^c	1433^d	1452^e	1489^f	9.60
CO2 lost (ml)	379^a	366^b	358^c	337^d	321^e	307^f	7.25
Retention volume (ml)	971^a	1022^b	1050^c	1096^d	1131^e	1182^f	12.05
Retention coefficient (%)	71.9^a	73.6^a	74.6^b	76.5^b	77.9^c	79.4^c	2.30

Means superscripted with different alphabets in the same row differ significantly (p<0.05).

Maximum height of the gas release curve (Hm′) showed a significant (p<0.05) increase by 3.8 and 6 mm respectively at 0.4 and 0.5% levels of xanthan gum as compared to control. The time of maximum gas formation (t′₁) decreased significantly (p<0.05) by 9 min at 0.1% level of xanthan gum as compared to control, followed by a further decrease with level up to 0.5%. The time at which gas permeability started from the dough (t _x ) remained unaffected with the increase in level of xanthan gum up to 0.5%. The total volume of the dough increased significantly (p<0.05) by 36 ml for 0.1% as compared to control, with successive significant increase in total volume at each of the levels up to 0.5%. The CO₂ lost volume decreased significantly (p<0.05) with increase in level of xanthan gum as compared to control. The gas retention volume also increased significantly (p<0.05) with the increase in the level of xanthan gum up to 0.5% as compared to control while the retention coefficient increased significantly (p<0.05) at 0.2 and 0.4% levels of xanthan gum. As reported earlier [27] that xanthan gum imparted structural coherence to starch granules which is necessary to retain the gas.

Baking Characteristics

The statistical analysis of the data (Table 4) indicated that there was a significant (p<0.05) increase in weight of bread by 2 to 6 g at 0.1 to 0.5% level of xanthan gum. Bread volume increased significantly (p<0.05) by 55 to 160 ml at 0.1 to 0.5% level of gum incorporation as compared to control. There was increase in specific volume of bread as compared to control. Texture of bread remained soft up to 0.2% level of gum and further increase in level resulted in a very soft bread. Bread texture scores remained constant while the eating quality changed to slightly gummy with 0.3 to 0.5% level of gum incorporation. The stability of xanthan gum to high temperature appears to increase the retention of moisture in the bread. The advantages of the increase in retained moisture coupled with the capability of the xanthan gum to complex with starch are of importance and may inhibit retrogradation and consequently lead to extension of the shelf-life of the baked goods [7]. The results highlight the increase in the yield of bread and improvement in softness of crumb by the incorporation of xanthan gum due to its highest water binding capacity among other food gums [28].

Table 4. Effect of Xanthan Gum on Loaf Volume and Crumb Characteristics of Bread from Wheat Flour for WH 542 (n=3)

	Loaf			Crumb (n=6)
Xanthan Gum %	Weight g	Volume ml	Specific Volume ml/g	Extra Yield %	Texture	Score	Eating Quality
0.0	302^a	9258^a	3.06^a	–	Soft	5	Normal
0.1	304^b	980^b	3.22^a	0.7^a	Soft	5	Normal
0.2	305^bc	1015^c	3.33^a	1.0^a	Soft	5	Normal
0.3	306^cd	1025^cd	3.35^a	1.3^b	Very soft	5	Slightly gummy
0.4	307^de	l040^e	3.39^a	1.7^b	Very soft	5	Slightly gummy
0.5	308^ef	1085^f	3.52^a	2.0^c	Very soft	5	Slightly gummy
LSD	2.00	10.17	0.53	0.5

Means superscripted with different alphabets in the same column differ significantly (p<0.05).

Firmness Characteristics

As evident form Fig. 1, mean firmness values decreased with the increase in level of gum to 0.5%. Storage resulted in an increase in firmness values, however the storage effect on firmness could be reduced with the increase in level of xanthan gum. The ability of xanthan gum to retain moisture and form complex with starch is of importance and inhibited retrogradation, consequently leading to extension in shelf life of baked goods [7]. This decrease in firmness of bread by incorporation of gum could be due to increased water absorption [17], having highest water binding capacity (232 ml/g) [25] and prevention of movement of moisture from gluten to starch by diffusion, which otherwise is responsible for staling [29]. Xanthan gum is tolerant to electrolytes and acids, its water binding in cake and bread systems results in improved shelf life [30].

Figure 1. Effect of level of xanthan gum and storage and bread firmness.

CONCLUSION

The findings of this study highlight an increase in extensibility, maximum gas formation/retention, extra yield of bread and decrease in firmness with levels of xanthan gum as compared to control sample. It is concluded that xanthan gum can be used at 0.2% level to get acceptable quality bread with extended softness from a medium strong wheat flour.

Acknowledgments