Effect of damaged starch on the pasting
characteristics and tandoori roti making quality of whole wheat flour
Dharmesh C. SAXENA*, Punaroor H. RAO
RÉSUMÉ Effet de l’amidon endommagé de la farine de blé entière sur ses caractéris- tiques d’empesage et son aptitude à la fabrication de tandoori roti.
Les caractéristiques d’empesage de farine de blé entière à différents taux d’amidon endommagé ont été mesurées à différentes vitesses de chauffage à l’aide d’un « Rapid Visco Analyser ». Les résultats montrent que la hauteur du pic d’empesage, la viscosité de l’empois à chaud et sa viscosité à froid sont significativement corrélées aux taux d’amidon endommagé de la farine. Ce taux est également significativement corrélé à la qualité globale du tandoori roti, laquelle dépend principalement de la consistance telle qu’elle est appré- ciée en analyse sensorielle. Celle-ci est fortement corrélée à la force de cisaille- ment mesurée au texturomètre. Le taux optimum d’amidon endommagé dans la farine entière pour la fabrication du tandoori roti se trouve entre 14 et 15 %.
Mots clés : amidon endommagé, empesage, texture, tandoori roti.
SUMMARY
The pasting characteristics of whole wheat flour having different contents of damaged starch measured at different heating rates in rapid visco analyzer are reported. The studies indicated that damaged starch content was correla- ted significantly to peak viscosity (r = + 0.73, P < 0.01), hot paste viscosity (r = – 0.88, P < 0.01) and cold paste viscosity (r = – 0.91, P < 0.01). Starch damage was also significantly correlated to overall quality of tandoori roti (r = 0.91, P < 0.01). The overall quality of roti was mainly influenced by sen- sory texture. The shear value measured using texturometer well indicated the sensory texture (r = – 0.89, P < 0.01). The optimum damaged starch content in whole wheat flour for the preparation of tandoori roti was found in the range of 14-15%.
Key-words: damaged starch, gelatinization, tandoori roti, sensory score, shear value, correlation.
Department of Flour Milling, Baking and Confectionery Technology, Central Food Technological Research Institute, Mysore, India.
* Correspondence
1 - INTRODUCTION
Tandoori roti is a staple food item of a large number of populations in India and its neighboring countries. Of late, it is gaining popularity among western countries. Tandoori roti is made from whole wheat flour obtained either by grin- ding wheat in a plate mill or from a resultant atta, a by-product of Roller Flour Milling Industry (SAXENAand RAO, 1995). The dough made from flour is sheeted traditionally by palm to a size of 15 cm diameter and 3 mm thick and baked in a special type of oven known as tandoor oven. The preparation of tandoori roti has been restricted to households and restaurants. There is very little scientific information available on tandoori roti, which is as popular as chapati. Conside- rable information is available on chapati with respect to the type of wheat requi- red (CHOPRA and BHAT, 1975), method of processing wheat into whole wheat flour (RAOet al., 1986), optimum rheological parameter (LEELAVATHIet al., 1986), and desired quality characteristics of chapati (RAOet al., 1987).
The role of damaged starch in whole wheat flour in relation to rheological characteristics and quality of chapati has been well understood (RAO et al., 1989). SAXENA and RAO (1996) reported that flour obtained by processing in plate mill is more suitable for the preparation of tandoori roti due to its high damaged starch content. Damaged starch in flour also influences the rate of starch gelatinization (ATWELLet al., 1988).
There is no information on the influence of damaged starch on the pasting characteristics and quality of tandoori roti. Such information is necessary to arrive at optimum damaged starch content needed to produce good and consistent quality product. The present study deals with the above aspects.
2 - MATERIALS AND METHODS
2.1 Materials
Commercially available medium hard wheat was procured from the local market.
2.1.1 Whole wheat flour
Whole wheat flour of different damaged starch content was obtained by grinding wheat in a disc mill by varying clearances of the discs. The coarser flour was again ground in a pestle and mortar to reduce the particle size to that of finely ground flour having maximum damaged starch content. The particle size of such reground flour of various damaged starch content was almost simi- lar as indicated by 15.8 to 16.7% overtailings in 6XX sieve, 22.5 to 23.7% in – 6XX+ 10XX sieve and 57.4 to 58.6% in – 10XX +12XX sieve. This was done to minimize the influence of particle size.
2.2 Sieve analysis
The standard Rotap sieve shaker and U.S. standard sieves made by the W.S. Tyler Company were used for the sieve analysis. Two hundred gram sample was used for sieve analysis and sieving was done for 5 min. The amount of flour retained over the sieve was converted into the percentage.
2.3 Chemical analysis
Moisture, ash, wet and dry gluten, sedimentation value and damaged starch content were determined according to AACC procedures (AACC, 1983).
2.4 Farinograph characteristics
Farinograph characteristics of flours varying in damaged starch content was determined at optimum tandoori dough consistency of 850 BU at a lever posi- tion of 1:1 (SAXENAand RAO, 1995).
2.5 Pasting characteristics
The pasting characteristics of whole wheat flours obtained from different mills were determined using the Rapid Visco Analyzer (RVA) (Newport Scientific Analyzer, model RVA-3D, Sydney, Australia) as per the procedure described in the manual using 4 g (on 14% moisture basis) sample of whole wheat flour added to 25 ml water. The heating rate in RVA alters the duration of the experi- ment and may affect the pasting characteristics of flour. Therefore, in the pre- sent study, the heating rate was varied from 1.5 to 12°C per min to determine the effect of heating rates on the pasting characteristics of whole wheat flour.
2.6 Preparation of tandoori roti
Tandoori roties were prepared by the process developed by SAXENA and RAO (1995) and cooled for 30 min before further analysis for their sensory as well as objective quality characteristics.
2.7 Evaluation of tandoori roti
2.7.1 Sensory analysis
The sensory analysis of tandoori roti was carried out by a panel of six expe- rienced judges and was evaluated for appearance, colour, handfeel, mouthfeel, texture, taste and aroma by arriving a score sheet describing all the desirable attributes (SAXENAand RAO, 1996).
2.7.2 Instrumental method
The shear value of roti was determined by measuring the force required to shear its rectangular piece (3 cm wide and 8 cm long), using the Instron tex- turometer under the following conditions: load cell-500 N; plunger speed — 100 mm/min; and cutter — Warner Bratzler shear attachment. The above conditions were arrived at after several preliminary experiments carried out on two roti samples varying in sensory texture.
2.7.3 Moisture and sugar content
The moisture content in roti was determined by two-stage method of AOAC (PEARSON, 1976).
The sugar content was estimated by the standard AACC procedure (AACC, 1983).
2.8 Statistical evaluation
Data were tested for their significance using Duncan’s Multiple Range Test and the correlation coefficients among different characteristics were calculated as described by STEELand TORRIE(1960).
3 - RESULTS AND DISCUSSION
3.1 The quality characteristics of whole wheat flour
The wheat used for processing into whole wheat flour had the following qua- lity characteristics on 14% moisture basis: ash 1.77%, protein 10.8%, falling number 390, and sedimentation value 30 mL. The protein content and sedimen- tation value indicated the medium hard nature of wheat and hence its suitability for the preparation of tandoori roti.
It was observed in the trial experiments that the whole wheat flour having higher damaged starch of 15.9 and 16.9% were unacceptable for carrying further analyses due to stickiness in sheeting the dough made from them, hence non- uniform thickness of sheeted dough, and the prepared roti had undesirable sur- face due to more dusting of flour. Therefore, the experiments and the analyses were restricted to flours with damaged starch contents below or equal to 15%.
3.2 Farinograph characteristics of dough
The farinograph water absorption increased from 65.1 to 72.7% when the damaged starch increased from 7 to 15.0% as shown in table 1. Similar trend was observed by several workers (AUSTINand RAM, 1971; FARIDIand FAUBION, 1997; MILLERet al., 1967; RAOet al., 1989; TARAet al., 1972). The high value is due to the use of same wheat for obtaining flours of different damaged starch content, as the flour will have the same level of pentosans and protein which are also reported to influence the water absorption capacity (TARA et al., 1972;
SAXENAet al., 1997). The dough development time decreased as well as dough stability with increase in damaged starch content.
3.3 Effect of heating rates
The increase in the heating rate (from 1.5, 3.0, 6.0 to 12.0°C/min) increased the peak viscosity in all the flours irrespective of damaged starch content. DOU- BLIER (1987) and DOUBLIER et al. (1987) also conducted the similar study on wheat starch pastes at two heating rates and found that wheat pastes at 1°C/min heating rate were much less viscous than those at high heating rate.
Table 1 Rheological characteristics of different whole wheat flours varying in damaged starch content DamagedFarinograph CharacteristicsaRapid Visco Analyser Characteristics (SNU)b StarchFarinographDoughDoughPeak Hot PasteCold PasteBreakSetTotal Set (%)WaterDevelopmentStabilityViscosityViscosityViscosityDownBackBack Absorption (%)Time (min)(min) 7.065.15.54.01581242243466100 8.166.05.54.0163118215455297 8.666.35.54.0163115208484593 10.768.55.03.5169111203583492 11.970.65.03.5174105195692190 12.471.14.53.5177106196711990 12.871.44.53.0178104194741690 13.672.14.03.018310219181889 14.372.33.53.018310118982688 15.072.73.53.018510018885388 a At a dough consistency of 850 BU with the lever in the 1:1 position. b At 6°C/min heating rate; SNU - Stirring Number Unit.
Similar observations were reported by WONG and LELIEVRE (1981) in a study of the viscoelasticity of wheat starch pastes who has shown that the variation in rheological properties of pastes at different heating rates is due to the extent of starch swelling and solubility in pastes. This implies that it is impossible to accurately predict the performance of a starch prepared under other conditions (i.e., the heating rates) without actually carrying out the appropriate experiment.
The damaged starch content, as such, had little effect on the changes in peak viscosity with heating rate. However, in general, at all heating rates, the slurry made from flour having higher damaged starch content, showed higher peak viscosity (figure 1).
Figure 1
Effect of heating rate on pasting behaviour of whole wheat flours:
Peak viscosity (7.0% damaged starch) Peak viscosity (15.0% damaged starch) Hot paste viscosity (7.0% damaged starch) Hot paste viscosity (15.0% damaged starch) Cold paste viscosity (7.0% damaged starch) Cold paste viscosity (15.0% damaged starch)
Similar to peak viscosity, the hot paste viscosity also increased with increa- sing heating rates. However, the rate of increase was lower as compared to that observed for peak viscosity. Flour having high damaged starch content has a low value of hot paste viscosity at any heating rate. The cold paste viscosity also exhibited a similar pattern as hot paste viscosity, with flours having low damaged starch content showing higher value for cold paste viscosity at any heating rate. In case of both, hot paste viscosity as well as peak viscosity, the maximum difference among the flours having different damaged starch content was observed when the heating rate was maintained at 6°C/min. On this basis, the heating rate of 6°C/min as judged as optimum heating rate for carrying out further experiments in Rapid Visco Analyzer.
3.4 Pasting characteristics
The pasting curves for whole wheat flour having the highest, medium and lowest damaged starch content have been shown in figure 2. The peak viscosity increased from 158 to 185 SNU with increase in damaged starch content from 7.0 to 15.0% as shown in table 1. On the other hand, the hot paste viscosity decreased from 124 to 100 SNU and cold paste viscosity from 224 to 188 SNU with increase in damaged starch content from 7.0 to 15.0%. These large diffe- rences in hot paste viscosity are a mixed effect of swollen starch granules, gra- nule fragments, colloidally and molecularly dispersed starch molecules (LEELAVATHIet al., 1987). The set - back value decreased, gradually, from 66 to 3 SNU as well as total set-back value from 100 to 88 and break-down value increased from 34 to 85 SNU as the damaged starch content increased from 7.0 to 15.0% (table 1). This suggested greater breakdown of starch in RVA due to continuous stirring of the slurry containing flour having higher damaged starch content. The greater breakdown indicates the fragility of granules at higher damaged starch.
Figure 2
Effect of damaged starch on the pasting behaviour of whole wheat flour: Damaged starch (7.0%) - - - - -; (8.1%) — - — -; (11.9%) · · · ·; (15.0%) ———
3.5 Quality of tandoori roti
3.5.1 Sensory evaluation
The appearance of tandoori roti improved with increase in damaged starch content in flour (table 2). The desired light brown coloured spots were found in tandoori roti made from a flour containing 15.0% damaged starch content. A gradual improvement in mouthfeel was observed when damaged starch content increased in flour up to 15.0% while it became slightly doughy and moist at higher damaged starch containing flour. The texture as well as taste improved
Table 2 Effect of damaged starch content of different whole wheat flours on the quality of tandoori roti DamagedSensory QualityShear StarchAppearanceColourHandfeelMouthfeelTextureTaste &OverallValue (%)(7)(7)(7)(7)(7)Aroma (7)Quality (42)(Kg) 7.03.5a4.0a3.7a4.3a4.1a4.2a23.8a20.2a 8.14.0b4.6b4.1b4.8b4.3a4.4a26.2b17.1b 8.64.2b5.0c4.5c5.0b4.7b4.8b28.2b16.8b 10.74.5c5.2c5.3d5.9c5.1c5.0b31.0c13.4c 11.94.8d5.1c5.7e5.8c5.6d5.7b32.7d10.7d 12.45.3e5.9d6.0f6.0c,d5.8d6.0d35.0e9.0e 12.85.7f6.0d6.2f,g5.9c6.1e6.1d36.0f8.6e 13.66.1g6.6e,f6.1f6.2d6.0e6.3e37.3g5.4f 14.36.4h6.4e6.4g6.7e6.6f6.5e,f39.0h5.0f 15.06.5h6.7f6.3g6.7e6.7f6.7f39.6h4.3g SEM (df = 29)±0.21±0.17±0.12±0.16±0.20±0.25±0.51±0.43
with increase in the damaged starch content. Similar improvement was also observed in chapati and optimum content was found to be 18-19% (RAOet al., 1989). The roti made from flour having lower damaged starch content was hard and slightly brittle. The higher overall sensory quality score was found for roti made from flour containing 14.3 to 15.0% of damaged starch. Therefore, it can be inferred that the damaged starch content of 14.0 to 15.0% is optimum for flour used for the preparation of tandoori roti.
3.5.2 Instrumental method
As seen from table 2, the shear value measured using Instron Texturometer decreased continuously from 20.2 to 4.3 kg when damaged starch content in flour increased from 7.0 to 15.0%. The decrease was considerable when the damaged starch content increased upto 14.3%. Thereafter, the decrease was gradual. This could be due to greater water absorption and holding capacity of damaged starch.
Figure 3
Effect of damaged starch on moisture and sugar content of tandoori roti:
moisture (%) and sugar content (%)
3.5.3 Moisture content
It is evident from figure 3, that with an increase in damaged starch content from 7.0 to 15.0%, the moisture in tandoori roti increased from 22.16 to 30.62%. This increase is due to greater water retention capacity of damaged starch during baking. The higher amount of water present in roti imparts softer texture to roti.
3.5.4 Sugar content
The sugar content in roti increased from 4.30 to 6.81% with increase in the damaged starch content from 7.0 to 15.0%, causing an increase in diastatic
activity (mg maltose), thereby imparting sweetish taste to roti (RAO, 1982). The similar observations were reported in the study of starch gelatinization in bread making (YASUNAGA et al., 1968) and relation of starch damage and diastatic activity in chapati making (RAOet al., 1989).
3.6 Correlation between damaged starch, pasting characteristics and tandoori roti quality
A good correlation has been found between damaged starch and various rheological parameters (table 3). Damaged starch was positively correlated to farinograph water absorption (r = 0.92, P < 0.01) and negatively correlated to dough development time (r = – 0.89, P < 0.01) and stability (r = – 0.86, P < 0.01).
Similar observation was obtained for whole wheat flour used for chapati (RAOet al., 1989). The peak viscosity was positively correlated to damaged starch (r = 0.73, P < 0.05) while hot paste viscosity (r = – 0.88, P < 0.01) and cold paste viscosity (r = – 0.91, P < 0.01) were negatively correlated.
Table 3
Correlation coefficients between damaged starch, rheological characteristics and tandoori roti quality
Variables correlated Correlation
coefficient Starch damage vs. Farinograph Water Absorption + 0.92**
Starch damage vs. Dough Development Time – 0.89**
Starch damage vs. Dough Stability – 0.86**
Starch damage vs. Peak Viscosity + 0.73*
Starch damage vs. Hot Paste Viscosity – 0.88**
Starch damage vs. Cold Paste Viscosity – 0.91**
Starch damage vs. Overall quality of roti + 0.91**
Starch damage vs. Shear value – 0.87**
Sensory score vs. Shear value – 0.89**
* P < 0.5; ** P < 0.01
Damaged starch also influenced considerably the sensory score of tandoori roti and the correlation coefficient was found to be highly significant (r = 0.91, P < 0.01). Damaged starch was negatively correlated to shear value (r = – 0.87, P < 0.05). A good correlation (r = – 0.89, P < 0.01) obtained between sensory score and shear value indicated that an objective method of measuring the tex- ture of tandoori roti could be conveniently used to predict the overall quality of tandoori roti.
4 - CONCLUSION
Heating rate of 6.0°C/min in RVA was optimum to differentiate the flour from different damaged starch content. The optimum level of damaged starch was found to be 14-15% in whole wheat flour for obtaining good quality tandoori roti. Damaged starch was found to be highly correlated to overall quality parti- cularly the texture of tandoori roti.
ACKNOWLEDGEMENTS
The first author acknowledges the Senior Research Fellowship provided by Council of Scientific and Industrial Research, New Delhi for carrying out these investigations.
Receveid 11 January 2000, accepted 4 September 2000.
REFERENCES
AACC, 1983. Approved methods of the Ame- rican Association of Cereal Chemists. The American Association of Cereal Chemists. St.
Paul, Minneapolis.
AUSTIN A., RAM A., 1971. Studies on cha- pati making quality of wheat. Indian Council of Agricultural Research, Tech. Bull., 31.
ICAR, New Delhi, India.
ATWELL W.A., HOOD L.F., LINEBACK D.R., 1988. The terminology and methodology associated with basic starch phenomenon.
Cereal Foods World, 33, 306.
CHOPRA K., BHAT C.M., 1975. Acceptability of chapaties prepared from high yielding varieties of wheat. Indian Miller, 6, 38-44.
DOUBLIER J.L., 1987. A rheological compari- son of wheat, maize, faba bean and smooth pea starches. J. Cereal Sci., 5, 247-262.
DOUBLIER J.L., LLAMAS G., LE MEUR M., 1987. A rheological investigation of cereal
starch pastes and gels. Effect of pasting pro- cedures. Carbohydr. Polymers, 7, 251-275.
FARIDI H., FAUBION J.M., 1997. Dough rheology and baked product texture. CBS Publishers and Distributers, New Delhi, India.
LEELAVATHI K., RAO P.H., SHURPALEKAR S.R, 1986. Studies on the functional charac- teristics of differently milled whole wheat flour. J. Food Sci. Technol., 23, 10-14.
LEELAVATHI K., INDRANI D., SIDHU J.S., 1987. Amylograph pasting behaviour of cereal and tuber starches. Starch/Starke, 39, 378-381.
MILLER B.S., TRIMBO H.B., POWELL K.R., 1967. Effect of flour granulation and starch damage on the cake making quality of soft wheat flour. Cereal Sci. Today, 12, 245-252.
PEARSON D., 1976. The chemical analysis of foods. Churchill Livingstone, Edinburgh, Lon- don and New York.
RAO P.H., 1982. Studies on chapati and similar traditional foods. Ph.D. Thesis. Uni- versity of Mysore, Mysore, India.
RAO G.C.P., RAO P.H., LEELAVATHI K., SHURPALEKAR S.R, 1986. Effect of heat developed during grinding wheat in a disc mill on some chemical, rheological and cha- pati making characteristics of flour. J. Food Sci. Technol., 23, 29-32.
RAO P.H., LEELAVATHI K., SHURPALEKAR S.R, 1987. Objective measurement of the consistency of chapati dough using
“Research Water Absorption Meter”. J. Tex- ture Stud., 17, 401-420.
RAO P.H., LEELAVATHI K., SHURPALEKAR S.R, 1989. Effect of damaged starch on the chapati-making quality of whole wheat flour.
Cereal Chem., 66, 329-333.
SAXENA D.C., RAO P.H., 1995. Survey of the quality characteristics of dough and the tan- doori roti. J. Food Sci. Technol., 32, 74 -76.
SAXENA D.C., RAO P.H., 1995. Optimization of ingredients and process conditions for the preparation of tandoori roti using response surface methodology. Int. J. Food Sci. Tech- nol., 31, 345-351.
SAXENA D.C., RAO P.H., 1996. Effect of dif- ferent baking modes on the physico-chemi-
cal and sensory characteristics of tandoori roti. Z. Lebensm. Unters. Forsch., 203, 262- 267.
SAXENA D.C., RAO P.H., 1997. Influence of grinding methods on some physico-chemical characteristics of whole wheat flour and its suitability for the preparation of tandoori roti.
Sci. Aliments, 17, 183-191.
SAXENA D.C., PRASADA RAO U.J.S., RAO P. H., 1997. Indian wheat cultivars: Correla- tion between quality of gluten proteins, rheo- logical characteristics of dough and tandoori roti. J. Sci. Food Agric., 74, 265-272.
STEEL G.D.R., TORRIE J.H., 1960. Principles of Statistics. Mc-Graw Hill Book Company, Inc., New York.
TARA K.A., FINNEY P.L., BAINS G.S., 1972.
Damaged starch and protein contents in rela- tion to water absorption of flours of Indian wheats. Starch/Staerke, 24, 342-345.
WONG R.B.K., LELIEVRE J., 1981. Viscoe- lastic behaviour of wheat starch pastes.
Rheol. Acta, 20, 299-307.
YASUNAGA T., BUSHUK W., IRVINE G.N., 1968. Gelatinization of starch during bread- baking. Cereal Chem., 45, 269-279.
