IMPROVING THE TEXTURE AND DELAYING STALING IN RICE

FLOUR CHAPATI WITH HYDROCOLLOIDS AND α-AMYLASE

Hardeep Singh Gujral†, Monica Haros, Cristina M. Rosell*

Laboratorio de Cereales, Instituto de Agroquímica y Tecnología de Alimentos (IATA-

CSIC), P.O. Box 73, 46100 Burjassot, Valencia, Spain.

† Department of Food Science and Technology. Guru Nanak Dev University, Amritsar –

143005, India

Running Title: Development of rice flour chapati

Corresponding author:

Dr Cristina M. Rosell

Instituto de Agroquimica y Tecnologia de Alimentos (IATA)

POBox 73, Burjasot-46100. Valencia. Spain

Tel: 34-96-390 0022, Fax: 34-96-363 6301

e-mail: crosell@iata.csic.es

ABSTRACT

Chapaties were prepared from rice flour so as to make this product available to the patients

suffering from gluten intolerance (celiac disease). The textural properties of the fresh and

24 h stored rice flour chapati were determined using a tensile deformation test. The

extensibility and energy to rupture decreased whereas the peak force to rupture and tensile

deformation modulus increased during storage. Different hydrocolloids like guar gum,

xanthan, locust bean gum and hydroxypropylmethylcellulose were added to the rice flour

at levels of 0.25 and 0.5% flour basis and it was observed that they improved the texture of

chapati by keeping it more extensible during storage. Fungal α-amylase was also

incorporated into the rice flour alone and in combination with the hydrocolloid and this

resulted in further improvement in the texture. The retrogradation in the chapati after 24 h

of storage was also studied using differential scanning calorimetry. Chapaties containing

hydrocolloid and/or α-amylase showed lower retrogradation after storage. Rice flour

chapaties can be made available to celiac disease patients and the undesirable textural

changes, which take place in chapati as a result of starch retrogradation, can be delayed by

the incorporation of hydrocolloids and α-amylase.

Key words: rice flour, chapati, hydrocolloids, α -amylase, texture, DSC, staling.

INTRODUCTION

Celiac disease is a gluten-sensitive entheropathy with genetic, immunologic and

environmental basis. People suffering gluten intolerance (celiac disease) are diagnosed

everywhere in the world, with Asia being no exception (Bitar, Salem & Nasr, 1970; Al-

Hassany, 1975). The prevalence of this food allergy in India has also been reported

(Horvath & Mehta, 2000). The cause of the disease is the ingestion of cereal proteins,

namely prolamins, especially from wheat leading to the inflammation of the small intestine

and to the mal-absorption of important nutrients like calcium, iron, folic acid and fat

soluble vitamins (Feihery, 1999). The only effective treatment is to keep the diet of the

patient as gluten free as possible. As a result foods containing wheat, rye, barley, triticale

and oats and all foods containing gluten derivatives as thickeners, fillers and binders have

to be avoided.

Over 85% of the wheat consumption in India is in the form of chapati, which is unleavened

flat bread made from whole wheat flour (atta) (Shurpalekar & Prabhavathi, 1976). It has

served as the staple food of the Indian subcontinent and parts of the Middle East for

centuries. There have been some approaches to nutritionally improved the value of

chapaties by mixing wheat flour with soy flour (Lindell & Walker, 1984; Gandhi &

Bourne, 1988), barley flour (Sood, Dhaliwal, Kalia & Sharma, 1992; Anjum, Ali &

Chaudhry, 1991; Leelavathi & Haridas Rao, 1988), black gram flour, corn flour, millet

(Gujral & Pathak, 2002).

However, due to the prevalence of celiac disease in this region, patients have to be

provided with chapaties made from an alternative gluten free cereal. Rice has been found

to be the most suitable cereal in this regard as it possesses no gluten. Nevertheless, the

utilization of rice flour for making chapaties becomes very complicated because rice flour

does not form viscoelastic dough when it is kneaded with water and thus cannot be sheeted

as in the case of wheat dough. Production of rice flour bread is a bigger technological

challenge since it is a leavened product and the CO2 produced needs to be retained in the

dough in the absence of gluten, although different approaches using hydrocolloids and

enzymes have partially solved the problem (Kang, Choi & Choi, 1997; Sanchez, Osella, &

Torre, 2002; Gujral, Guardiola, Carbonell & Rosell, 2003; Gujral & Rosell, 2003).

Chapaties are an unleavened product thus there is no CO2 that needs to be retained, but

flour dough requires some viscoelasticity for sheeting with a rolling pin.

The production of rice chapati, apart from being very suitable for the celiac disease

patients, might be economically viable since rice flour is a by product from the rice milling

industry. Rice flour is obtained from the brokens produced during the milling process,

which fetch a lower price in the market as compared to the head rice. In fact, the use of rice

flour to partially replace the wheat flour in chapati has been reported (Gujral & Pathak,

2002).

The objectives of the present investigation were to explore the possibilities of making

chapaties from rice flour and study the textural changes during storage. With this aim some

hydrocolloids and α−amylase have been tested in order to improve the extensibility of the

rice chapati.

MATERIALS AND METHODS

Commercial rice flour obtained from Huici Leidan S.A (Navarra, Spain) was used in this

study. The rice flour had moisture, ash, and protein of 12.8, 0.57, 8.83% respectively, and

the amylose content was 21.9%. Hydroxypropylmethylcellulose (HPMC) Methocel K4M

was obtained from Dow Chemical Company (Michigan, USA). Xanthan, guar gum (GG)

and locust bean gum (LBG) were obtained from Ingavasa, Spain. The fungal α-amylase

(Fungamyl 1500MG) was provided by Novo Nordisk (Madrid, Spain)

Procedure for making chapati

Rice flour (500g) was mixed with optimum water (360 mL) in the bowl of the laboratory

mixer (Hobart N-50, Ontario, Canada). The optimum water was subjectively determined

till it gave a smooth non sticky dough, easy to handle and suitable for sheeting without

cracking (Gujral & Pathak, 2002; Gujral & Gaur, 2002). Hydrocolloids when added were

incorporated at two levels 0.25 and 0.5% (flour weight basis) to the flour before the

mixing, and in the case of α-amylase 0.01% (flour weight basis) was used. Mixing was

done with the U arm for 5 min at speed 1 and then dough was allowed to rest for 0.5 hours.

It was not possible to sheet the rice dough ball with a rolling pin due to the lack of

viscoelasticity. This problem was overcome by pressing the dough ball between two

parallel metal plates instead of sheeting with a rolling pin (Shurpalekar & Prabhavathi,

1976). Dough portions (50g) were rounded and placed on the bottom platform of the press

that was fitted with a 1.75 mm thick frame for ensuring uniform thickness of the chapati.

Chapati was then baked in a baking oven (Eurofours, Gommegnies, France) at 340oC for

140 seconds. The baking trials were carried out beforehand to select the optimum time and

temperature of baking. The chapati was allowed to cool for 10 min at 25oC and then sealed

in coextruded polypropylene pouches and stored at 25 oC.

Determination of chapati texture

The texture of fresh chapati was measured after 1 hour of baking and for stored chapati the

texture was measured after 24 hours of storage at 25°C. Rectangular strips of 20mm × 50

mm were cut from the center of the chapati using a metal template. The strip was clamped

on the extensibility cell and tested for extensibility on the Texture Analyzer TA-XT2i

(Stable Micro Systems, Surrey, UK). The clamps were properly aligned and set at 30 mm

apart. The chapati strip was pulled apart at a crosshead speed of 1 mm/sec until it ruptured.

The peak force (N, peak load to rupture) and distance to rupture (mm, extensibility) were

recorded. The parameters like modulus of deformation (MPa, tensile modulus) and energy

to rupture (J) were calculated as described by Gujral and Pathak (2002). The mean of at

least ten replicates from each treatment has been used. The chapati after 24 hrs of storage

was similarly tested for texture. Samples from fresh and stored chapati were freeze dried

for further differential scanning calorimetry studies.

Differential scanning calorimetry (DSC) analysis

DSC studies were carried out on a DSC-7 (Perkin-Elmer). Indium (enthalpy of fusion

28.41 J/g, melting point 156.4oC) was periodically used to calibrate the calorimeter. The

experimental values of enthalpy of fusion and melting point agreed within +2.0 and +1.3%,

respectively. About 12 mg of the freeze dried powdered rice chapati were weighted

directly into DSC stainless steel pans (PE 0319-0218) and distilled water was added by a

micropipette to obtain a water:chapati ratio of 2:1. After sealing, the pan was heated at a

rate of 10oC/min from 25 to 120oC. An empty pan was used as a reference. The parameters

measured were the onset temperature (To), the peak temperature (Tp) and the conclusion

temperature (Tc). Straight lines were drawn between To and Tc and enthalpy associated

with starch retrogradation (∆H) was calculated as the area enclosed by the straight line and

the endotherm curve. It was expressed in J/g of dry sample. Four replicates were run for

each sample.

Statistical analysis

Multiple sample comparison was statistically analysed with the Statgraphics Plus 5.0.

Fishers least significant differences (LSD) test was used to describe means at the 5%

significance level.

RESULTS AND DISCUSION

Effect of hydrocolloids and α -amylase on fresh rice chapati texture

Different trials were performed in order to set the optimal time and temperature of baking

the rice chapati. The baking trials showed that a higher temperature (340oC) and short time

(140 sec) resulted in a properly baked chapati with a better texture (results not showed).

Lower temperatures for longer time resulted in excessive drying of the chapati and a hard

texture.

A method to objectively describe the textural changes occurring in wheat and composite

flour chapati has been already described (Gujral & Pathak, 2002). The same extensibility

test can be used to study the texture of rice flour chapati. The force needed to extend the

chapati strip increased during tensile deformation and reached a peak before the strip

ruptured. The control chapati had an extensibility of 7.40 mm and also was soft and

extensible as indicated by the lower peak force values required to deform, lower

deformation modulus and higher extensibility (Table 1). When different hydrocolloids

were incorporated into the rice flour dough at levels of 0.25 and 0.5%, they increased the

extensibility and that effect was more pronounced with increasing hydrocolloid

concentration. Xanthan at 0.5% brought about the highest increase in the extensibility

followed by LBG, HPMC and GG. An increase in the extensibility of wheat flour dough

chapati by carboxymethylcellulose (CMC) has been reported earlier (Gujral & Pathak,

2002). Fresh chapati containing hydrocolloids had higher peak force to rupture (N) and

energy to rupture (J) control chapati, with the exception of GG and LBG at the lowest

concentration. Hydrocolloid addition lowered the deformation modulus of the chapati.

α-Amylase is usually added in bakery for improving specific volume and retard the bread

staling. In this study the effect of amylase on texture of rice chapati was tested. The level

of α -amylase added was taken from a recent work carried out by the authors on the

antistaling effect of this enzyme in rice bread (Gujral, Haros & Rosell, 2003). In case of

chapati the α-amylase must have acted on the starch during the short period of mixing and

resting (5 min and 30 min respectively at 25oC) and during the 140 seconds baking stage.

The action of the enzyme is evident on the increased extensibility of fresh chapati. The

combination of the enzyme along with the hydrocolloid also resulted in chapati with better

texture.

Influence of hydrocolloids and α-amylase on rice chapati texture after storage

Chapaties are generally consumed fresh (within an hour) but an industrially produced

product would need a longer time to reach the consumer. Chapaties should have a pleasing

color and should retain their soft and pliable structure during storage. The textural changes

that occur in chapati during storage (loss of extensibility and increased deformation

modulus) need to be minimized.

The extensibility of the rice chapati decreased to 2.50 mm after 24 hours of storage (Table

2). Decrease in the extensibility of wheat flour chapati has been reported earlier (Gujral &

Pathak, 2002, Gujral & Gaur, 2002) and was attributed to the staling of chapati. After 24

hours of storage the chapati became hard and brittle as indicated by the higher peak force

values, higher deformation modulus and lower extensibility. The energy required to break

the chapati decreased during storage, this was because the peak force of staled chapati

increases and its extensibility decreases. The area under the force displacement curve

decreased lowering the energy required to rupture the chapati strip that indicates an

increase in the brittleness of the chapati.

The chapaties containing the hydrocolloids remained more extensible after 24 hours

storage. The hydrocolloid concentration (0.25 and 0.5%) more significantly affected the

extensibility in fresh chapati as compared to the extensibility of 24 h stored chapati.

Chapati stored for 24 h and containing hydrocolloid had higher peak force to rupture and

energy to rupture and lower deformation modulus. The extensibility tests showed that the

chapati containing hydrocolloids were more extensible (pliable and less brittle) and

remained more extensible during storage. The ability of hydrocolloids to prevent firming

and retrogradation of starch in bread is well known (Martinez, Andreu & Collar, 1999;

Rojas, Rosell & Benedito, 1999), and it is due to their ability to bind water and physically

hinder the amylopectin retrogradation. The moisture absorption in the chapati dough with

and without the hydrocolloids was kept constant. It was observed that the chapaties

containing hydrocolloid showed lower bake loss (Table 3) after baking and as a result had

higher moisture. An inverse relationship of water and rate of firming has been reported

(Rogers, Zeleznak, Lai & Hoseney, 1988) and this could have lead to the better texture of

chapaties containing hydrocolloid.

The purpose of addition of α-amylase to the rice flour dough was to bring about some

depolymerization of the rice starch so as to delay the retrogradation and staling process.

The action of the enzyme was also evident on the extensibility of stored chapati that was

more extensible than the control. The combination of the enzyme along with the

hydrocolloid also resulted in chapati with better texture, which remained more extensible

after 24 h storage.

Retrogradation of rice starch in chapati

The chapati starch was completely gelatinized during baking, which was evident from the

lack of traditional endothermic transition at 65-75ºC of rice flour in fresh chapatti (data not

shown). On the other hand, after the first hour of storage at 25ºC no staling endotherm

appears on the DSC termogram, whereas after 24 hours of storage it appeared the peak as

the result of melting of crystallized amylopectin. The hydrocolloids and their combination

with α-amylase exhibited different results in their effect on starch retrogradation (Table 4).

The onset temperature (To) and enthalpy for endothermic melting of starch chapati varied

according to the hydrocolloid type and concentration, in ranges 41.7-47.2ºC and 0.52-1.42

J/g (Table 4). In control sample the retrogradation peak temperature appeared at 49.9ºC,

whereas the addition of hydrocolloids brought about slight delay of this temperature (1.4-

2.0ºC), with the exception of the sample added with xanthan. The chapati with α-amylase

(with or without hydrocolloids) showed higher displacement in the peak temperature (3.2-

4.8ºC). Addition of hydrocolloid and/or α-amylase lowered the amylopectin retrogradation

enthalpy (Table 4). The major effects were due to addition of xanthan at 0.25% and GG at

the same concentration. The stabilizing effects of the hydrocolloids on starch

retrogradation result from the interactions of them cooperatively with water as well as with

starch chains in the mixture (Lee, Baek, Cha, Park & Lim, 2002), therefore the water

content and its mobility have strong participation in this process (Zeleznak & Hoseney,

1987, Czchajowska & Pomeranz, 1989). Xanthan and GG may act as strong water binder

effectively depriving the starch chain of usable water for recrystallization. The

hydrocolloids seemed to better inhibit the retrogradation at lower concentration (0.25%) as

compared to the effect at higher concentration (0.5%). However, the addition of HPMC

and LBG at 0.25 or 0.5% had not produced significant difference on the retrogradation

enthalpy.

The incorporation of α-amylase significantly lowered the retrogradation (Table 4). The

enzyme can partially degrade the starch to produce smaller polysaccharides; therefore

decrease the amount of available starch for retrogradation (Duran, Leon, Barber &

Benedito, 2001). Some of branched-chain products (maltooligosaccharides) also inhibit the

starch interaction by their great hygroscopicity (Min, Yoon, Kim, Lee, Kim & Park, 1999).

The combination of the enzyme and the hydrocolloids also lowered the enthalpy of

retrogradation but did not give significant reduction compared with the sample added with

α-amylase alone, thus no summative effects were produced by the amylase and

hydrocolloids.

CONCLUSION

Hydrocolloids can be used for improving the texture of rice flour chapati. They contribute

to keep the chapati extensibility during storage. Hydrocolloid addition does not prevent

rice amylopectin retrogradation but it inhibits the recrystallization. Xanthan, GG and/or α-

amylase are especially effective in retarding starch recrystallization in rice chapati.

ACKNOWLEDGEMENTS

This work was financially supported by Comisión Interministerial de Ciencia y Tecnología

Project (MCYT, AGL2002-04093-C03-02 ALI) and Consejo Superior de Investigaciones

Científicas (CSIC), Spain. H.S. Gujral would also like to thank Ministerio de Educación,

Cultura y Deporte, Secretaría de Estado de Educación y Universidades (Spain) for his

grant.

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Table 1. Textural properties of fresh chapati as affected by hydrocolloids and enzyme. GG,

guar gum; LBG, locust bean gum; AM, α -amylase.

Sample Extensibility

(mm)

Peak force

(N)

Deformation

modulus (MPa)

Energy to

rupture (J)

Control 7.40a 4.035a,b 0.411c 0.015a

HPMC (0.25%) 10.60c,d,e 5.783c,d 0.408c 0.030c,d

HPMC (0.5%) 12.80f,g 5.038b,c 0.296a,b 0.032c,d

Xanthan (0.25%) 11.70e,f 4.973b,c 0.312a,b 0.030c,d

Xanthan (0.5%) 14.10g 6.518d,e 0.349b,c 0.045e

GG(0.25%) 9.90b,c,d 3.720a,b 0.282a,b 0.018a,b

GG (0.5%) 11.00d,e 5.915c,d 0.406c 0.032c,d

LBG (0.25%) 8.50a,b 3.180a 0.284a,b 0.013a

LBG (0.5%) 13.40f,g 4.300a,b 0.242a 0.028b,c

AM 8.96a,b,c 3.355a 0.281a,b 0.015a

AM + Xanthan (0.25%) 11.74e,f 6.250c,d,e 0.400c 0.037c,d,e

AM + GG (0.25%) 10.92d,e 7.302e 0.503d 0.039d,e

Different letters within a column mean significant differences (P≤0.05).

Table 2. Textural properties of stored (24 h) chapati as affected by hydrocolloids and

enzyme. GG, guar gum; LBG, locust bean gum; AM, α -amylase.

Samples Extensibility

(mm)

Peak force

(N)

Deformation

modulus (MPa)

Energy to

rupture (J)

Control 2.50a 9.698a 2.951d,e,f 0.012a

HPMC (0.25%) 3.20a,b 10.408b,c 2.463b,c,d,e 0.016a,b

HPMC (0.5%) 3.80b 14.340a,b,c 2.872d,e,f 0.027b,c,d

Xanthan (0.25%) 5.90d 13.443a,b,c 1.766a,b 0.039d

Xanthan (0.5%) 8.70e 12.653a,b,c 1.114a 0.055e

GG(0.25%) 5.00c,d 14.540a,b,c 2.200b,c,d 0.036c,d

GG (0.5%) 4.20b,c 13.328a,b,c 2.531b,c,d,e 0.028b,c,d

LBG (0.25%) 3.50a,b 16.360c 3.611f 0.028b,c,d

LBG (0.5%) 3.70b 12.700a,b,c 2.526b,c,d,e 0.024a,b,c

AM 3.69b 15.440c 3.109e,f 0.029b,c,d

AM + Xanthan (0.25%) 5.78d 14.445a,b,c 1.954a,b,c 0.041d,e

AM + GG (0.25%) 4.04b,c 15.075b,c 2.774c,d,e,f 0.031b,c,d

Different letters within a column mean significant differences (P≤0.05).

Table 3. Bake loss during chapati baking measured as a weight difference. GG, guar

gum; LBG, locust bean gum; AM, α -amylase.

Sample Bake loss (%)

Control 28.20c

HPMC (0.25%) 26.70a,b,c

HPMC (0.5%) 25.95a

Xanthan (0.25%) 27.05a,b,c

Xanthan (0.5%) 26.75a,b,c

GG (0.25%) 26.75a,b,c

GG (0.5%) 26.15a,b

LBG (0.25%) 26.50a,b,c

LBG (0.5%) 25.80a

AM 27.85b,c

AM + Xanthan(0.25%) 26.55a,b,c

AM + GG (0.25%) 26.20a,b

Different letters within a column mean significant differences (P≤0.05).

Table 4. Thermal properties of 24 h stored chapati as affected by hydrocolloids and

enzyme. To: onset temperature, Tp: peak temperature, Tc: conclusion temperature, ∆H:

retrogradation enthalpy.

Sample To (°C) Tp (°C) Tc (°C) ∆H (J/g)

Control 41.70a 49.90a 59.20a 1.42e

HPMC (0.25%) 43.60a,b,c 51.50b,c 60.70a,b 1.23d,e

HPMC (0.5%) 44.90a,b,c 51.90b,c 60.80a,b 1.08c,d,e

Xanthan (0.25%) 43.40a,b 50.90a,b 61.20a,b 0.52a

Xanthan (0.5%) 43.10a,b 50.90a,b 59.60a,b 1.05c,d

GG (0.25%) 46.10b,c 51.90b,c 61.30a,b 0.56b

GG (0.5%) 44.60a,b,c 51.30b 60.40a,b 0.80a,b,c

LBG (0.25%) 43.80a,b,c 51.50b 60.50a,b 1.07c,d,e

LBG (0.5%) 44.60a,b,c 51.80b,c 60.10a,b 1.26d,e

AM 45.60b,c 53.10c,d 61.70a,b 0.77a,b,c

AM + Xanthan(0.25%) 45.90b,c 53.90d,e 62.80a,b 0.99b,c,d

AM + GG (0.25%) 47.20c 54.70e 63.70b 0.64a,b

Different letters within a column mean significant differences (P≤0.05).