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Changes in the physical-chemical and organoleptic characteristics of parotta during storage
Food Research International 33 (2000) 323±329
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Changes in the physical-chemical and organoleptic characteristics of parotta during storage D. Indrani, S. Jyothsna Rao, K. Udaya Sankar, G. Venkateswara Rao * Flour Milling, Baking and Confectionery Technology Department, Central Food Technological Research Institute, Mysore-570 013, India Received 19 July 1999; accepted 13 January 2000
Abstract Studies on the changes in quality of parotta during storage from 0.25 to 48 h indicated a decrease in alkaline water retention capacity (AWRC) from 257.4 to 127.7%, in total water solubles (TWS) from 8.25 to 6.24%, in soluble starch (SS) from 2.11 to 1.19%, in solubilised amylose from 0.39 to 0.13% and in solubilised amylopectin from 1.72 to 1.06%. The pasting characteristics of stored parotta measured using a rapid visco analyser showed a decrease in maximum viscosity at 95 C from 54 to 37 RVU. The overall quality score of parotta based on colour, nature of spots, shape, oiliness, handfeel, texture, layers, mouthfeel, taste and aroma decreased from 75 to 43 while the shear and compression force of parotta increased from 12.3 to 21.6 N and 304 to 711 N respectively, with storage time. The AWRC, SS, amylopectin and viscosity at 95 C showed a highly signi®cant correlation (r50.956, P<0.001) with overall quality score. The dierential scanning calorimeter (DSC) characteristics of stored parotta samples indicated an increase in the enthalpy of the endotherms with storage time, implying dierent degrees of starch retrogradation. Avrami methodology was applied to determine Avrami exponents (index of crystal type) and time constants (reciprocal of rate constant); an Avrami exponent value of 1.18 and a time constant (k 103) of 24.56 hÿ1.18 was obtained for parotta. # 2000 Elsevier Science Ltd. All rights reserved. Keywords: Indian traditional food; Parotta; Storage; DSC; Avrami exponent
1. Introduction About 80% of the wheat produced in India is consumed in the form of traditional products like chapathi, puri, phulka, roti, nan and parotta. Even though they constitute the staple diet of the majority of the population of India, hardly any systematic study of these products Ð with the sole exception of chapathi (Haridas Rao, 1993; Haridas Rao, Leelavathi & Shurpalekar, 1986; Venkateswara Rao, Leelavathi, Haridas Rao & Shurpalekar, 1986; Venkateswara Rao, Seibel, Bretscheider & Shurpalekar, 1981) Ð has been made. There are two types of parotta in India; they are south Indian parotta and north Indian parotta. The main raw material in the preparation of parotta in south India is white wheat ¯our (maida) obtained from roller mills, while whole wheat ¯our (atta) from disc mills or atta from roller ¯our mills is used in north India. The methodology of preparation, taste and textural pro®les of north * Corresponding author. Fax: +91-821-517233. E-mail address: [email protected] (G.V. Rao).
and south Indian parotta are quite dierent. Qarooni (1996) mentioned south Indian parotta in his book ``Flat Bread Technology''. Various aspects of work on whole wheat ¯our based parotta (north Indian parotta) that have been reported are preservation and packaging (Kameswara Rao, Malathi & Mohan, 1969), stabilization by antimycotic agents (Arya, 1990) and storage in ¯exible pouches (Ghosh, Krishnappa, Srivatsa, Eapen & Vijayaraghavan, 1979). In-pack processing of stued parottas in ¯exible packaging materials was reported by a number of researchers (Ghosh, Krishnappa, Eapen, Mattada, Sharma & Nath, 1974; Ghosh, Krishnappa, Eapen, Sharma & Nath 1974; Ghosh, Krishnappa, Srivatsa, Eapen & Vijayarahavan 1979; Kannur, Eapen, Rao, Vijayaraghavan & Nath 1972). More than 50% of wheat ¯our produced by the roller ¯our mills in south India is utilised for the preparation of south Indian parotta Ð henceforth referred to simply as parotta. Parotta is basically prepared using wheat ¯our, salt, oil and water while sugar and egg form optional ingredients. The baked parotta is creamish white to light brown in colour, and possesses several
0963-9969/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved. PII: S0963-9969(00)00025-9
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distinct layers. It is a soft textured product with chewy characteristics, and is generally consumed along with vegetarian or non-vegetarian side-dishes. Parotta is generally prepared and consumed fresh in households and restaurants, as well as in road side shops. There exists, however, considerable potential for the large scale manufacture and marketing of parotta, as the demand for ready-to-eat convenience food products has been steadily increasing because of industrialisation. Large scale production and marketing of parottas requires mechanisation in the preparation and distribution in unit packs. For achieving the objective of commercial marketing, it is desirable that the parotta should have an adequate shelf life. No data are available on the changes that take place during storage of parotta. The physical, chemical and organoleptic changes occurring in parotta during storage are presented in this paper. 2. Experimental A commercial wheat ¯our procured from the local market was used in the studies. Moisture, ash, gluten content, Hagberg Falling Number, SDS Ð sedimentation value and Farinograph characteristics were determined using AACC methods (American Association of Cereal Chemists [AACC], 1995). Parotta dough was prepared according to the following formula: ¯our 100 g, sugar 0.5 g, egg 5 g, water 57.5 ml (Farinograph water absorption) and commercially available re®ned groundnut oil 15 g (Postman brand, Ahmed mills, Bombay). The procedure for the preparation of parotta is shown in Fig. 1. After baking, parottas were cooled for 15 min and four parottas weighing 75 g each were packed in polypropylene pouches and heat sealed. Parottas were stored separately, at room temperature (27 C) and relative humidity (65%), for 0.25, 2, 4, 8, 16, 24 and 48 h. Stored parottas were evaluated separately at intervals of 0.25, 2, 4, 8, 16, 24 and 48 h for moisture content. The shear value of parotta was determined by measuring the force required to shear a piece (6 cm) of parotta using an Instron Universal Testing Machine (Model 4301, Instron, High Wycombe Bucks, UK) under the following conditions: load cell, 10 kg; plunger speed, 100 mm/min; Warner±Bratzler shear attachment. Data are averages of quadruplicate determinations. The compression characteristics of parotta were determined by measuring the force required to compress a piece of parotta (3.5 cm diameter and 0.5 cm height) using an Instron Universal Testing Machine under the following conditions: load cell, 500 kg; plunger diameter, 8.5 cm; clearance between the base and the plunger, 1.5 cm; cross head speed, 100 mm/min. Each sample was given 50% compression. The sensory analysis of stored parotta samples was carried out by a panel of six experienced
Fig. 1. Processing conditions for the preparation of parotta.
judges by assigning scores for each quality attribute presented in Fig. 2. At intervals of 0.25, 2, 4, 8, 16, 24 and 48 h, parottas were cut into small strips (1 cm ) and freeze-dried to 2± 3g/100g moisture content and ground in a mini laboratory mill (Buhler Miag Model-204). Ground samples were stored at ÿ20 C in air tight containers until analysed. Water binding capacity (WBC) was measured by the Alkaline Water Retention Capacity test (AWRC) as reported by Yamazaki (1953). The AWRC was reported as the weight gain per 100 g dry solid. Total water solubles (TWS) and soluble starch (SS) were determined as described by Morad and D'Appolonia (1980). The amylose content of soluble starch was determined by the method of Sowbhagya and Bhattacharya (1971). The amylopectin content in the soluble starch was obtained by subtracting the amylose content from the total amount of soluble starch. All determinations were carried out in triplicate. Pasting characteristics of stored parotta samples were determined according to ICC standards using a rapid visco analyser, RVA (ICC International Association for Cereal Science and Technology, 1996). A dierential scanning calorimeter [(Model DSC (+), Rheometric Scienti®c, UK)] supported by version 5.42 thermal software with an autocool arrangement connected to an `Airliquide' LN2 (liquid nitrogen) system was used to study the characteristics of stored parotta.
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325
Ht ÿ H0 H1 ÿ H0
and `n' is the Avrami exponent (McIver, Axford, Colwell & Elton, 1968). In the equation Ht represents the enthalpy change after time t, H0 the enthalpy at zero time (or at t=0). The enthalpy value at zero time (H0) was taken as zero. The enthalpy value of a sample stored for 48 h was taken to be the limiting enthalpy value, H1 as generally, the parotta is consumed within 48 h. The rate constant, k, which indicates the rate of starch crystallisation in parotta was calculated (by regression analysis) from the graph obtained by using the software Microsoft Excel 97. 1 ÿ exp ÿktn 1n 1 ÿ ÿktn 1nÿ1n 1 ÿ 1nk n1nt
1
Statistical analyses were carried out as described by Steel and Torrie (1980). 3. Results and discussion
Fig. 2. Reference score sheet used by sensory panel.
The temperature in the DSC cell was controlled at a programmed rate even at subambient temperature using a proportional integral derivative control. The DSC cell was purged with N2 at a rate 10 ml/min to avoid thermal currents at subambient temperatures. The cell was calibrated using indium (Hf=6.79 m cal/mg, Tm=156.66 C), lead (Hf=5.50 m cal/mg, Tm= 327.42 C) and tin (Hf=14.24 m cal/mg, Tm=231.88 C) for temperature and enthalpy measurements. A freezedried parotta sample (2 g) of known moisture content was intimately mixed with distilled water to make a sample to water ratio of 1:3 on a dry basis. Portions (10±20 mg) were weighed into an aluminium crucible and hermetically sealed with an aluminium lid using an encapsulating press. Each DSC run was carried out at a scan rate of 10 C/min from 10 to 120 C against an empty sealed crucible. The enthalpy of the endotherm H was obtained for the gelatinisation of starch. The kinetics of the retrogradation was studied using the equation 1 ÿ exp ÿktn where , representing the crystallised portion of starch in the parotta, is given by
The ¯our sample had 0.45% ash, 10.1% dry gluten, a 60 ml SDS Ð sedimentation value, a Falling Number of 374, 10.8% damaged starch and 57.5% farinograph water absorption. This indicated that the ¯our used for the study was of medium strength, and fell in the range of typical values reported for Indian wheat ¯ours by Shurpalekar, Kumar, Venkateswara Rao, Ranga Rao, Rahim and Vatsala (1976). The eects of storage on the physical characteristics of parotta are presented in Fig. 3. The results show that the moisture content of parotta, which was 30.1% on the ®rst day, decreased by 0.3% after 48 h of storage. Venkateswara Rao et al. (1986) and Hebeda, Bowles and Teague (1990) have made a similar observation, viz., that moisture is redistributed within a baked product during storage, although water loss is not a requirement for staling. The actual moisture loss in a properly packaged product is insigni®cant. The ®rst day readings for texture of parotta, as shown by the values for shear force and compression force, were 12.3 and 304 N respectively, which after 48 h of storage, gradually increased by 9.3 and 407 N respectively. The eects of storage on some chemical characteristics of parotta are shown in Fig. 4. AWRC and the amounts of TWS, SS and its amylose and amylopectin content decreased by 129.7, 2.01, 0.92, 0.26 and 0.66%, respectively, after 48 h of storage. The amounts decreased greatly during the ®rst 24 h of storage, and,
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thereafter, the changes were small. Similar observations in AWRC values have been reported for white pan bread (Bechtel, Meisher & Brodley, 1953), chapathi (Venkateswara Rao et al., 1986), Egyptian balady bread (Faridi & Rubenthaler, 1984) and Arabic bread (Toufeili, Sleiman & Abu Salman, 1993). The decreasing trend in the amount of TWS as the parotta aged, agrees with the ®ndings of Morad and D'Appolonia (1980) and of Toufeili et al. (1993) for bread and Arabic bread respectively. The composition of soluble starch indicated that the soluble starch leached from the fresh
Fig. 3. Eect of storage on moisture and texture of parotta.
parotta was predominantly amylopectin (1.72%). Similar results were obtained for white pan bread (Kim & D'Appolonia, 1977), Arabic bread (Toufeili et al., 1993), Egyptian balady bread (Faridi & Rubenthaler, 1984) and chapathi (Venkateswara Rao et al., 1986). According to Toufeili et al. (1993) and Zobel and Kulp (1996) the predominance of amylopectin in the starch leached from the bread during ageing is attributed to the tendency of the linear amylose chains to crystallise into insoluble aggregates at a very early stage. Although the amylose content in the soluble starch leached from the parotta was small, it decreased progressively from 0.39 to 0.13%, while the amylopectin content decreased from 1.72 to 1.06% on storage from 0.25 to 48 h. This suggests that changes in both soluble amylose and amylopectin are involved in the staling of parotta. Maximum viscosity at 95 C, viscosity at 95 C after 15 min, and viscosity at 50 C, all decreased from 54 to 37, 46 to 35 and 96 to 80 RVU respectively, for the parottas stored from 0.25 to 48 h (Table 1). This is in accordance with the observations made with an amylograph on Egyptian balady bread (Faridi & Rubenthaler, 1984) and bread (Morad & D'Appolonia, 1980). Organoleptic evaluation by a panel of six judges indicated that the pliability of parottas decreased with time (Table 2). The parottas exhibited typical chewiness up to 4 h of storage; after 4 h of storage, there was a progressive loss of chewiness. The onset of staleness in parottas was detected after 16 h of storage, and the parottas were stale by 48 h of storage. The overall quality score gradually decreased from 75 to 43. Based on the sensory scores, parottas were graded as satisfactory up to 16 h of storage; after 24 and 48 h of storage the quality of the parotta was rated as `fair' and `poor', respectively. Mold growth was observed in parottas stored for 72 h in polypropylene pouches. The dierent parameters (Table 3) studied showed signi®cant correlations with overall quality score, with alkaline water absorption, soluble starch, amylopectin and viscosity at 95 C after 15 min showing highly signi®cant correlations (r50.956, P<0.001) with overall quality score. Toufeili
Table 1 Eect of storage on rapid visco analyser (RVA) characteristics of parotta
Fig. 4. Eect of storage on chemical characteristics of parotta.
Storage period (h)
Viscosity at 95 C (RVU)a
Viscosity at 95 C, after 15 min (RVU)
Viscosity at 50 C (RVU)
0.25 2.0 4.0 8.0 16.0 24.0 48.0
54 52 46 44 42 40 37
46 45 44 43 41 38 35
96 94 92 90 86 84 80
a
RVU: Rapid visco analyser units.
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Table 2 Changes in organoleptic qualitya of parotta during storage Storage period (h)
Handfeel (10)
Texture (15)
Layers (15)
Mouthfeel (10)
Taste and aroma (10)
Overall quality score (100)
0.25
Soft pliable (7)
Distinct (11)
Good (75)
Soft pliable (6.5)
Normal (8)
Good (74)
4.0
Soft pliable (6)
Normal (8)
Good (72)
8.0
Lacks pliability (4)
Normal (8)
Satisfactory (66)
16.0
Hard (3)
Normal (6)
Satisfactory (60)
24.0
Hard (2)
Less distinct (8)
Easy breakdown no residue (7) Easy breakdown no residue (7) Easy breakdown no residue (6) Dicult to breakdown (5) Dicult to breakdown (4) Dry (3)
Normal (8)
2.0
Slightly stale (3)
Fair (52)
48.0
Hard (1)
Soft and slightly chewy (11) Soft and slightly chewy (10.5) Soft and slightly chewy (10.5) Slightly soft and less chewy (8) Slightly tough and very less chewy (7) Tough and completely lacks chewiness (5) Tough (2)
Less distinct (6)
Dry (2)
Stale (1)
Poor (43)
Distinct (11) Distinct (11) Less distinct (10) Less distinct (9)
a The sensory scores for colour (8), nature of spots (8), shape (8) and oiliness (7), for the maximum score of 10 each, remained constant during 48 h of storage.
et al. (1993) also observed highly signi®cant correlation between alkaline water absorption capacity, total water solubles and organoleptic scores of Arabic bread. The endotherm of stored samples in the temperature range of 50±70 C are mainly due to the retrogradation of the amylopectin fraction of the starch. The size of the enthalpy of gelatinisation peak increased with storage time from 0.25 to 48 h showing dierent degrees of retrogradation. Table 4 shows the temperature of gelatinisation onset (To), peak (Tp) and completion (Te) of the gelatinisation endotherms. The gelatinisation of retrograded parotta samples occurred between 50 and 72.8 C and in a range of 6.4±12.6 C corroborating the earlier observations made on starch (Longton & LeGrys, 1981). The variation in the temperature of onset (58.54.8) C, peak (61.95.2) C, and completion (67.54.6) C is mainly due to the interaction of ingredients such as salt, sugar, egg and oil present in parotta similar to that reported by Donovan (1977) on the
interactions of ingredients in the gelatinisation transition of wheat starch during the baking of cake. The values of enthalpy for the gelatinisation endotherm of the starch increased from 0.01 to 1.96 m cal/g, when parottas were stored for 48 h. The experimental data were ®tted to Eq. (1) using Microsoft Excel 97 software and the constants `k' and `n' were evaluated on a logarithmic graph [-ln (1- fractional retrogradation of starch)] vs time (Fig. 5 ) to obtain a linear equation. The regression was found to ®t with a coecient of determination of 0.9337. The experimental data ®tted the equation with a high level of signi®cance (P<0.001). The time constant (k103) was found to be 24.56 hÿ1.18. The Avrami exponent value (n) was 1.18. Fearn and Russel (1982) reported values of Avrami exponent (0.75) and time constant (38 hÿ0.75) for bread. McIver et al. (1968) reported rate constant 11 hÿ1 when n=1 for 50% starch gel. Kim and D'Appolonia, (1977) reported Avrami exponent (0.92±1.04) and time constant (3.74± 18.73) values for bread made using ¯ours of
Table 3 Linear correlation coecients between variables and overall quality score of parotta during storage
Table 4 Eect of storage period on peak temperatures and enthalpy of parotta as determined by DSC
Variables
Correlation coecienta
Alkaline water retention capacity Total water solubles Soluble starch Amylose Amylopectin Viscosity at 95 C Viscosity at 95 C after 15 min Viscosity at 50 C
0.981*** 0.909** 0.956*** 0.836* 0.976*** 0.916** 0.991*** 0.938**
a *, **, *** signi®cant at P<0.05, P<0.01, P<0.001 respectively (d.f=5).
Storagea (h)
0.25 2.0 4.0 8.0 16.0 24.0 48.0 a
Temperature ( C) of peak Start
Max
End
57.9 58.9 66.4 56.8 62.7 56.4 50.1
60.4 62.3 70.3 60.1 66.9 60.4 52.6
64.4 68.9 72.8 66.2 72.6 69.2 58.6
At temperature of 28 C.
Range
Enthalpy (m cal/g)
6.5 10.0 6.4 9.4 9.5 12.6 8.5
0.01 0.05 0.42 0.73 0.78 1.12 1.96
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Fig. 5. Kinetics of retrogradation of starch in stored parotta.
dierent protein content and stored at 21 and 30 C. They concluded that higher time constants were valid indicators of decreased staling rate. Russel (1987) reported rate constant for waxy maize (46), potato (86), wheat (6) and amylomaize (24) starches when n=1. 4. Conclusions The eect of storage time on the quality characteristics of parotta indicated a decrease in the AWRC, TWS, SS, amylose, amylopectin, viscosity and overall quality score with increase in storage time. The overall quality score showed highly signi®cant correlation with soluble starch, amylopectin and RVA viscosity at 95 C after 15 min. The changes in the characteristics of parotta during storage were studied using DSC. An attempt was made to ®t the DSC data to the Avrami equation, and to determine the Avrami exponent and time constant. References American Association of Cereal Chemists. (1995) Approved methods. St. Paul, MN. AACC Nos. 44-19, 08-01, 38-10, 56-81B, 56-70, 5421. Arya, S. S. (1990). Grain based snack and convenience foods. Indian Food Packer, 44, 17±38. Bechtel, W. G., Meisher, D. F., & Brodley, W. B. (1953). Eect of the crust on the staling of bread. Cereal Chemistry, 30, 160±168. Donovan, J. W. (1977). A study of the baking process by dierential scanning colorimetry. Journal of the Science and Food and Agriculture, 28, 571±578.
Faridi, H. A., & Rubenthaler, G. L. (1984). Eect of baking time and temperature on bread quality, starch gelatinization, and staling of Egyptian balady bread. Cereal Chemistry, 61, 151±154. Fearn, T., & Russel, P. L. (1982). A kinetic study of bread staling by dierential sacanning calorimetry. The eect of loaf volume. Journal of the Science and Food and Agriculture, 33, 537±548. Ghosh, K. G., Krishnappa, K. G., Eapen, K. C., Mattada, R. R., Sharma, T. R., & Nath, H. (1974). In-pack processing of stued parottas in indigenous ¯exible packaging materials. II. Studies on alternative packaging and processing systems. Journal of Food Science Technology, 11, 128±131. Ghosh, K. G., Krishnappa, K. G., Eapen, K. C., Sharma, T. R., & Nath, H. (1974). In-pack processing of stued parottas in indigenous ¯exible packaging materials. I. Investigations on the eect of processing on the packaging materials. Journal of Food Science Technology, 11, 101±104. Ghosh, K. G., Krishnappa, K. G., Srivatsa, A. N., Eapen, K. C., & Vijayaraghavan, P. K. (1979). Recent developments in the production of retort foods in ¯exible pouches. In Proceedings of the ®rst Indian convention of food scientists and technologists, Association of Food Scientists and Technologists, India. Food Science and Technology, Abstracts, Vol. II (12), A 871. Ghosh, K. G., Krishnappa, K. G., Srivatsa, A. N., Eapen, K. C., & Vijayaraghavan, P. K. (1979). In-pack processing of stued parottas in indigenous ¯exible packaging materials. III. Studies on newer packaging materials capable of withstanding the processing temperature. Journal of Food Science Technology, 16, 198±201. Haridas Rao, P. (1993). Chapati and related products. In Encylopedia on food science technology and nutrition. London: Academic Press. (pp 795±801). Haridas Rao, P., Leelavathi, K., & Shurpalekar, S. R. (1986). Test baking of chapati. Development of a method. Cereal Chemistry, 63, 297±303. Hebeda, R. E., Bowles, L. K., & Teague, W. M. (1990). Development in enzymes for retarding staling of baked goods. Cereal Foods World, 35, 444±457. ICC International Association for Cereal Science and Technology. (1996). Rapid pasting method using the Newport Rapid Visco Analyser, ICC standards 162.
D. Indrani et al. / Food Research International 33 (2000) 323±329 Kameswara Rao, G., Malathi, M. A., & Mohan, M. S. (1969). Preservation and packaging of Indian foods III. Parottas. Journal of Food Science Technology, 6, 279±281. Kannur, S. B., Eapen, K. C., Rao, G. K., Vijayaraghavan, P. K., & Nath, H. (1972). Heat processing of ready-to-eat foods in ¯exible pouches. I. Stued parottas and cutlet. Journal of Food Science Technology, 9, 179±184 Kim, S. K., & D'Appolonia, B. L. (1977). Bread staling studies I. Eect of protein content on staling rate and bread crumb pasting properties. Cereal Chemistry, 54, 207±215. Longton, J., & LeGrys, G. A. (1981). Dierential scanning calorimetry studies on the crystallisation of ageing wheat starch gels. Die Starke, 33, 410±414. McIver, R. G., Axford, D. W. E., Colwell, K. H., & Elton, G. A. H. (1968). Kinetic study of the retrogradation of gelatinised starch. Journal of the Science of Food and Agriculture, 19, 560±563. Morad, M. M., & D'Appolonia, B. L. (1980). Eect of surfactants and baking procedure on total water-solubles and soluble starch in bread crumb. Cereal Chemistry, 57, 1417±144. Qarooni, J. (1996). Flat breads. In J. Qaroon, Flat Bread Technology (pp. 88±). New York: Chapman and Hall, International Thomson Publishing. Russell, P. L. (1987). The aging of gels from starches of dierent amylose/amylopectin content studied by dierential scanning calorimetry. Journal of Cereal Science, 6, 147±158. Shurpalekar, S. R., Kumar, G. V., Venkateswara Rao, G., Ranga
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Changes in the physical-chemical and organoleptic characteristics of parotta during storage D. Indrani, S. Jyothsna Rao, K. Udaya Sankar, G. Venkateswara Rao * Flour Milling, Baking and Confectionery Technology Department, Central Food Technological Research Institute, Mysore-570 013, India Received 19 July 1999; accepted 13 January 2000
Abstract Studies on the changes in quality of parotta during storage from 0.25 to 48 h indicated a decrease in alkaline water retention capacity (AWRC) from 257.4 to 127.7%, in total water solubles (TWS) from 8.25 to 6.24%, in soluble starch (SS) from 2.11 to 1.19%, in solubilised amylose from 0.39 to 0.13% and in solubilised amylopectin from 1.72 to 1.06%. The pasting characteristics of stored parotta measured using a rapid visco analyser showed a decrease in maximum viscosity at 95 C from 54 to 37 RVU. The overall quality score of parotta based on colour, nature of spots, shape, oiliness, handfeel, texture, layers, mouthfeel, taste and aroma decreased from 75 to 43 while the shear and compression force of parotta increased from 12.3 to 21.6 N and 304 to 711 N respectively, with storage time. The AWRC, SS, amylopectin and viscosity at 95 C showed a highly signi®cant correlation (r50.956, P<0.001) with overall quality score. The dierential scanning calorimeter (DSC) characteristics of stored parotta samples indicated an increase in the enthalpy of the endotherms with storage time, implying dierent degrees of starch retrogradation. Avrami methodology was applied to determine Avrami exponents (index of crystal type) and time constants (reciprocal of rate constant); an Avrami exponent value of 1.18 and a time constant (k 103) of 24.56 hÿ1.18 was obtained for parotta. # 2000 Elsevier Science Ltd. All rights reserved. Keywords: Indian traditional food; Parotta; Storage; DSC; Avrami exponent
1. Introduction About 80% of the wheat produced in India is consumed in the form of traditional products like chapathi, puri, phulka, roti, nan and parotta. Even though they constitute the staple diet of the majority of the population of India, hardly any systematic study of these products Ð with the sole exception of chapathi (Haridas Rao, 1993; Haridas Rao, Leelavathi & Shurpalekar, 1986; Venkateswara Rao, Leelavathi, Haridas Rao & Shurpalekar, 1986; Venkateswara Rao, Seibel, Bretscheider & Shurpalekar, 1981) Ð has been made. There are two types of parotta in India; they are south Indian parotta and north Indian parotta. The main raw material in the preparation of parotta in south India is white wheat ¯our (maida) obtained from roller mills, while whole wheat ¯our (atta) from disc mills or atta from roller ¯our mills is used in north India. The methodology of preparation, taste and textural pro®les of north * Corresponding author. Fax: +91-821-517233. E-mail address: [email protected] (G.V. Rao).
and south Indian parotta are quite dierent. Qarooni (1996) mentioned south Indian parotta in his book ``Flat Bread Technology''. Various aspects of work on whole wheat ¯our based parotta (north Indian parotta) that have been reported are preservation and packaging (Kameswara Rao, Malathi & Mohan, 1969), stabilization by antimycotic agents (Arya, 1990) and storage in ¯exible pouches (Ghosh, Krishnappa, Srivatsa, Eapen & Vijayaraghavan, 1979). In-pack processing of stued parottas in ¯exible packaging materials was reported by a number of researchers (Ghosh, Krishnappa, Eapen, Mattada, Sharma & Nath, 1974; Ghosh, Krishnappa, Eapen, Sharma & Nath 1974; Ghosh, Krishnappa, Srivatsa, Eapen & Vijayarahavan 1979; Kannur, Eapen, Rao, Vijayaraghavan & Nath 1972). More than 50% of wheat ¯our produced by the roller ¯our mills in south India is utilised for the preparation of south Indian parotta Ð henceforth referred to simply as parotta. Parotta is basically prepared using wheat ¯our, salt, oil and water while sugar and egg form optional ingredients. The baked parotta is creamish white to light brown in colour, and possesses several
0963-9969/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved. PII: S0963-9969(00)00025-9
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distinct layers. It is a soft textured product with chewy characteristics, and is generally consumed along with vegetarian or non-vegetarian side-dishes. Parotta is generally prepared and consumed fresh in households and restaurants, as well as in road side shops. There exists, however, considerable potential for the large scale manufacture and marketing of parotta, as the demand for ready-to-eat convenience food products has been steadily increasing because of industrialisation. Large scale production and marketing of parottas requires mechanisation in the preparation and distribution in unit packs. For achieving the objective of commercial marketing, it is desirable that the parotta should have an adequate shelf life. No data are available on the changes that take place during storage of parotta. The physical, chemical and organoleptic changes occurring in parotta during storage are presented in this paper. 2. Experimental A commercial wheat ¯our procured from the local market was used in the studies. Moisture, ash, gluten content, Hagberg Falling Number, SDS Ð sedimentation value and Farinograph characteristics were determined using AACC methods (American Association of Cereal Chemists [AACC], 1995). Parotta dough was prepared according to the following formula: ¯our 100 g, sugar 0.5 g, egg 5 g, water 57.5 ml (Farinograph water absorption) and commercially available re®ned groundnut oil 15 g (Postman brand, Ahmed mills, Bombay). The procedure for the preparation of parotta is shown in Fig. 1. After baking, parottas were cooled for 15 min and four parottas weighing 75 g each were packed in polypropylene pouches and heat sealed. Parottas were stored separately, at room temperature (27 C) and relative humidity (65%), for 0.25, 2, 4, 8, 16, 24 and 48 h. Stored parottas were evaluated separately at intervals of 0.25, 2, 4, 8, 16, 24 and 48 h for moisture content. The shear value of parotta was determined by measuring the force required to shear a piece (6 cm) of parotta using an Instron Universal Testing Machine (Model 4301, Instron, High Wycombe Bucks, UK) under the following conditions: load cell, 10 kg; plunger speed, 100 mm/min; Warner±Bratzler shear attachment. Data are averages of quadruplicate determinations. The compression characteristics of parotta were determined by measuring the force required to compress a piece of parotta (3.5 cm diameter and 0.5 cm height) using an Instron Universal Testing Machine under the following conditions: load cell, 500 kg; plunger diameter, 8.5 cm; clearance between the base and the plunger, 1.5 cm; cross head speed, 100 mm/min. Each sample was given 50% compression. The sensory analysis of stored parotta samples was carried out by a panel of six experienced
Fig. 1. Processing conditions for the preparation of parotta.
judges by assigning scores for each quality attribute presented in Fig. 2. At intervals of 0.25, 2, 4, 8, 16, 24 and 48 h, parottas were cut into small strips (1 cm ) and freeze-dried to 2± 3g/100g moisture content and ground in a mini laboratory mill (Buhler Miag Model-204). Ground samples were stored at ÿ20 C in air tight containers until analysed. Water binding capacity (WBC) was measured by the Alkaline Water Retention Capacity test (AWRC) as reported by Yamazaki (1953). The AWRC was reported as the weight gain per 100 g dry solid. Total water solubles (TWS) and soluble starch (SS) were determined as described by Morad and D'Appolonia (1980). The amylose content of soluble starch was determined by the method of Sowbhagya and Bhattacharya (1971). The amylopectin content in the soluble starch was obtained by subtracting the amylose content from the total amount of soluble starch. All determinations were carried out in triplicate. Pasting characteristics of stored parotta samples were determined according to ICC standards using a rapid visco analyser, RVA (ICC International Association for Cereal Science and Technology, 1996). A dierential scanning calorimeter [(Model DSC (+), Rheometric Scienti®c, UK)] supported by version 5.42 thermal software with an autocool arrangement connected to an `Airliquide' LN2 (liquid nitrogen) system was used to study the characteristics of stored parotta.
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325
Ht ÿ H0 H1 ÿ H0
and `n' is the Avrami exponent (McIver, Axford, Colwell & Elton, 1968). In the equation Ht represents the enthalpy change after time t, H0 the enthalpy at zero time (or at t=0). The enthalpy value at zero time (H0) was taken as zero. The enthalpy value of a sample stored for 48 h was taken to be the limiting enthalpy value, H1 as generally, the parotta is consumed within 48 h. The rate constant, k, which indicates the rate of starch crystallisation in parotta was calculated (by regression analysis) from the graph obtained by using the software Microsoft Excel 97. 1 ÿ exp ÿktn 1n 1 ÿ ÿktn 1nÿ1n 1 ÿ 1nk n1nt
1
Statistical analyses were carried out as described by Steel and Torrie (1980). 3. Results and discussion
Fig. 2. Reference score sheet used by sensory panel.
The temperature in the DSC cell was controlled at a programmed rate even at subambient temperature using a proportional integral derivative control. The DSC cell was purged with N2 at a rate 10 ml/min to avoid thermal currents at subambient temperatures. The cell was calibrated using indium (Hf=6.79 m cal/mg, Tm=156.66 C), lead (Hf=5.50 m cal/mg, Tm= 327.42 C) and tin (Hf=14.24 m cal/mg, Tm=231.88 C) for temperature and enthalpy measurements. A freezedried parotta sample (2 g) of known moisture content was intimately mixed with distilled water to make a sample to water ratio of 1:3 on a dry basis. Portions (10±20 mg) were weighed into an aluminium crucible and hermetically sealed with an aluminium lid using an encapsulating press. Each DSC run was carried out at a scan rate of 10 C/min from 10 to 120 C against an empty sealed crucible. The enthalpy of the endotherm H was obtained for the gelatinisation of starch. The kinetics of the retrogradation was studied using the equation 1 ÿ exp ÿktn where , representing the crystallised portion of starch in the parotta, is given by
The ¯our sample had 0.45% ash, 10.1% dry gluten, a 60 ml SDS Ð sedimentation value, a Falling Number of 374, 10.8% damaged starch and 57.5% farinograph water absorption. This indicated that the ¯our used for the study was of medium strength, and fell in the range of typical values reported for Indian wheat ¯ours by Shurpalekar, Kumar, Venkateswara Rao, Ranga Rao, Rahim and Vatsala (1976). The eects of storage on the physical characteristics of parotta are presented in Fig. 3. The results show that the moisture content of parotta, which was 30.1% on the ®rst day, decreased by 0.3% after 48 h of storage. Venkateswara Rao et al. (1986) and Hebeda, Bowles and Teague (1990) have made a similar observation, viz., that moisture is redistributed within a baked product during storage, although water loss is not a requirement for staling. The actual moisture loss in a properly packaged product is insigni®cant. The ®rst day readings for texture of parotta, as shown by the values for shear force and compression force, were 12.3 and 304 N respectively, which after 48 h of storage, gradually increased by 9.3 and 407 N respectively. The eects of storage on some chemical characteristics of parotta are shown in Fig. 4. AWRC and the amounts of TWS, SS and its amylose and amylopectin content decreased by 129.7, 2.01, 0.92, 0.26 and 0.66%, respectively, after 48 h of storage. The amounts decreased greatly during the ®rst 24 h of storage, and,
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thereafter, the changes were small. Similar observations in AWRC values have been reported for white pan bread (Bechtel, Meisher & Brodley, 1953), chapathi (Venkateswara Rao et al., 1986), Egyptian balady bread (Faridi & Rubenthaler, 1984) and Arabic bread (Toufeili, Sleiman & Abu Salman, 1993). The decreasing trend in the amount of TWS as the parotta aged, agrees with the ®ndings of Morad and D'Appolonia (1980) and of Toufeili et al. (1993) for bread and Arabic bread respectively. The composition of soluble starch indicated that the soluble starch leached from the fresh
Fig. 3. Eect of storage on moisture and texture of parotta.
parotta was predominantly amylopectin (1.72%). Similar results were obtained for white pan bread (Kim & D'Appolonia, 1977), Arabic bread (Toufeili et al., 1993), Egyptian balady bread (Faridi & Rubenthaler, 1984) and chapathi (Venkateswara Rao et al., 1986). According to Toufeili et al. (1993) and Zobel and Kulp (1996) the predominance of amylopectin in the starch leached from the bread during ageing is attributed to the tendency of the linear amylose chains to crystallise into insoluble aggregates at a very early stage. Although the amylose content in the soluble starch leached from the parotta was small, it decreased progressively from 0.39 to 0.13%, while the amylopectin content decreased from 1.72 to 1.06% on storage from 0.25 to 48 h. This suggests that changes in both soluble amylose and amylopectin are involved in the staling of parotta. Maximum viscosity at 95 C, viscosity at 95 C after 15 min, and viscosity at 50 C, all decreased from 54 to 37, 46 to 35 and 96 to 80 RVU respectively, for the parottas stored from 0.25 to 48 h (Table 1). This is in accordance with the observations made with an amylograph on Egyptian balady bread (Faridi & Rubenthaler, 1984) and bread (Morad & D'Appolonia, 1980). Organoleptic evaluation by a panel of six judges indicated that the pliability of parottas decreased with time (Table 2). The parottas exhibited typical chewiness up to 4 h of storage; after 4 h of storage, there was a progressive loss of chewiness. The onset of staleness in parottas was detected after 16 h of storage, and the parottas were stale by 48 h of storage. The overall quality score gradually decreased from 75 to 43. Based on the sensory scores, parottas were graded as satisfactory up to 16 h of storage; after 24 and 48 h of storage the quality of the parotta was rated as `fair' and `poor', respectively. Mold growth was observed in parottas stored for 72 h in polypropylene pouches. The dierent parameters (Table 3) studied showed signi®cant correlations with overall quality score, with alkaline water absorption, soluble starch, amylopectin and viscosity at 95 C after 15 min showing highly signi®cant correlations (r50.956, P<0.001) with overall quality score. Toufeili
Table 1 Eect of storage on rapid visco analyser (RVA) characteristics of parotta
Fig. 4. Eect of storage on chemical characteristics of parotta.
Storage period (h)
Viscosity at 95 C (RVU)a
Viscosity at 95 C, after 15 min (RVU)
Viscosity at 50 C (RVU)
0.25 2.0 4.0 8.0 16.0 24.0 48.0
54 52 46 44 42 40 37
46 45 44 43 41 38 35
96 94 92 90 86 84 80
a
RVU: Rapid visco analyser units.
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Table 2 Changes in organoleptic qualitya of parotta during storage Storage period (h)
Handfeel (10)
Texture (15)
Layers (15)
Mouthfeel (10)
Taste and aroma (10)
Overall quality score (100)
0.25
Soft pliable (7)
Distinct (11)
Good (75)
Soft pliable (6.5)
Normal (8)
Good (74)
4.0
Soft pliable (6)
Normal (8)
Good (72)
8.0
Lacks pliability (4)
Normal (8)
Satisfactory (66)
16.0
Hard (3)
Normal (6)
Satisfactory (60)
24.0
Hard (2)
Less distinct (8)
Easy breakdown no residue (7) Easy breakdown no residue (7) Easy breakdown no residue (6) Dicult to breakdown (5) Dicult to breakdown (4) Dry (3)
Normal (8)
2.0
Slightly stale (3)
Fair (52)
48.0
Hard (1)
Soft and slightly chewy (11) Soft and slightly chewy (10.5) Soft and slightly chewy (10.5) Slightly soft and less chewy (8) Slightly tough and very less chewy (7) Tough and completely lacks chewiness (5) Tough (2)
Less distinct (6)
Dry (2)
Stale (1)
Poor (43)
Distinct (11) Distinct (11) Less distinct (10) Less distinct (9)
a The sensory scores for colour (8), nature of spots (8), shape (8) and oiliness (7), for the maximum score of 10 each, remained constant during 48 h of storage.
et al. (1993) also observed highly signi®cant correlation between alkaline water absorption capacity, total water solubles and organoleptic scores of Arabic bread. The endotherm of stored samples in the temperature range of 50±70 C are mainly due to the retrogradation of the amylopectin fraction of the starch. The size of the enthalpy of gelatinisation peak increased with storage time from 0.25 to 48 h showing dierent degrees of retrogradation. Table 4 shows the temperature of gelatinisation onset (To), peak (Tp) and completion (Te) of the gelatinisation endotherms. The gelatinisation of retrograded parotta samples occurred between 50 and 72.8 C and in a range of 6.4±12.6 C corroborating the earlier observations made on starch (Longton & LeGrys, 1981). The variation in the temperature of onset (58.54.8) C, peak (61.95.2) C, and completion (67.54.6) C is mainly due to the interaction of ingredients such as salt, sugar, egg and oil present in parotta similar to that reported by Donovan (1977) on the
interactions of ingredients in the gelatinisation transition of wheat starch during the baking of cake. The values of enthalpy for the gelatinisation endotherm of the starch increased from 0.01 to 1.96 m cal/g, when parottas were stored for 48 h. The experimental data were ®tted to Eq. (1) using Microsoft Excel 97 software and the constants `k' and `n' were evaluated on a logarithmic graph [-ln (1- fractional retrogradation of starch)] vs time (Fig. 5 ) to obtain a linear equation. The regression was found to ®t with a coecient of determination of 0.9337. The experimental data ®tted the equation with a high level of signi®cance (P<0.001). The time constant (k103) was found to be 24.56 hÿ1.18. The Avrami exponent value (n) was 1.18. Fearn and Russel (1982) reported values of Avrami exponent (0.75) and time constant (38 hÿ0.75) for bread. McIver et al. (1968) reported rate constant 11 hÿ1 when n=1 for 50% starch gel. Kim and D'Appolonia, (1977) reported Avrami exponent (0.92±1.04) and time constant (3.74± 18.73) values for bread made using ¯ours of
Table 3 Linear correlation coecients between variables and overall quality score of parotta during storage
Table 4 Eect of storage period on peak temperatures and enthalpy of parotta as determined by DSC
Variables
Correlation coecienta
Alkaline water retention capacity Total water solubles Soluble starch Amylose Amylopectin Viscosity at 95 C Viscosity at 95 C after 15 min Viscosity at 50 C
0.981*** 0.909** 0.956*** 0.836* 0.976*** 0.916** 0.991*** 0.938**
a *, **, *** signi®cant at P<0.05, P<0.01, P<0.001 respectively (d.f=5).
Storagea (h)
0.25 2.0 4.0 8.0 16.0 24.0 48.0 a
Temperature ( C) of peak Start
Max
End
57.9 58.9 66.4 56.8 62.7 56.4 50.1
60.4 62.3 70.3 60.1 66.9 60.4 52.6
64.4 68.9 72.8 66.2 72.6 69.2 58.6
At temperature of 28 C.
Range
Enthalpy (m cal/g)
6.5 10.0 6.4 9.4 9.5 12.6 8.5
0.01 0.05 0.42 0.73 0.78 1.12 1.96
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Fig. 5. Kinetics of retrogradation of starch in stored parotta.
dierent protein content and stored at 21 and 30 C. They concluded that higher time constants were valid indicators of decreased staling rate. Russel (1987) reported rate constant for waxy maize (46), potato (86), wheat (6) and amylomaize (24) starches when n=1. 4. Conclusions The eect of storage time on the quality characteristics of parotta indicated a decrease in the AWRC, TWS, SS, amylose, amylopectin, viscosity and overall quality score with increase in storage time. The overall quality score showed highly signi®cant correlation with soluble starch, amylopectin and RVA viscosity at 95 C after 15 min. The changes in the characteristics of parotta during storage were studied using DSC. An attempt was made to ®t the DSC data to the Avrami equation, and to determine the Avrami exponent and time constant. References American Association of Cereal Chemists. (1995) Approved methods. St. Paul, MN. AACC Nos. 44-19, 08-01, 38-10, 56-81B, 56-70, 5421. Arya, S. S. (1990). Grain based snack and convenience foods. Indian Food Packer, 44, 17±38. Bechtel, W. G., Meisher, D. F., & Brodley, W. B. (1953). Eect of the crust on the staling of bread. Cereal Chemistry, 30, 160±168. Donovan, J. W. (1977). A study of the baking process by dierential scanning colorimetry. Journal of the Science and Food and Agriculture, 28, 571±578.
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