a comparative study of physicochemical and rheological properties of iranian tomato pastes

Volume 6, Issue 1 2010 Article 5

International Journal of FoodEngineering

A Comparative Study of Physicochemical andRheological Properties of Iranian Tomato

Pastes

Asgar Farahnaky, Shiraz University, Shiraz, IranMarjan Majdinasab, Shiraz University, Shiraz, Iran

Mahsa Majzoobi, Shiraz University, Shiraz, IranGholamreza Mesbahi, Shiraz University, Shiraz, Iran

Recommended Citation:Farahnaky, Asgar; Majdinasab, Marjan; Majzoobi, Mahsa; and Mesbahi, Gholamreza (2010) "AComparative Study of Physicochemical and Rheological Properties of Iranian Tomato Pastes,"International Journal of Food Engineering: Vol. 6: Iss. 1, Article 5.DOI: 10.2202/1556-3758.1571

Brought to you by | University of SussexAuthenticated | 139.184.30.135

Download Date | 9/20/12 10:37 PM

A Comparative Study of Physicochemical andRheological Properties of Iranian Tomato

PastesAsgar Farahnaky, Marjan Majdinasab, Mahsa Majzoobi, and Gholamreza

Mesbahi

Abstract

In this study, the physicochemical properties and rheological behavior of a number of tomatopastes manufactured by Iranian food processors were compared. Chemical composition tests, colormeasurement, consistency and rotational viscometry were performed. There were significantdifferences among the samples in terms of Brix, salt level, vitamin C and Hunter color parameters(L and a/b). Some of the parameters did not pass the standard requirements set by the Institute ofStandards and Industrial Research of Iran (ISIRI), e.g. Brix, color and salt. The rotationalviscometry tests and shear stress–shear rate curves at 30, 45 and 60°C indicated the existence ofvariations among the samples in terms of apparent viscosity and yield stress. All tomato pastesamples in this study were non-Newtonian fluids and the apparent viscosity of the pastesdecreased with temperature increase. The rheological data obtained were fitted using a Power Lawequation. The differences were attributed to raw material variations and processing conditions.

KEYWORDS: Iranian tomato pastes, physicochemical properties, rheological behavior



Introduction

Tomato (Lycopersicon esculentum) is the world’s second largest vegetable crop in terms of annual value, with world production of about 70 million tones in 1993 (12). Tomatoes may be consumed fresh or processed to canned whole peeled tomatoes. It may also be processed to produce juice, concentrated tomato juice, puree or paste. In tomato processing operations, tomatoes are first crushed and filtered to remove the seeds, skin and mucilage. The process results in the production of two products, tomato juice and tomato waste. The waste mainly consisting of skin and seeds is called tomato pulp or pomace (18). The amount of tomato processing wastes in tomato producing countries is notable, and this is estimated to be around 150,000 tons/year in Iran. Tomato pomace contains mainly fiber, protein, sugar and ash. It contains a large amount of polysaccharides such as fiber and pectin (1, 15).

The main processing steps in the production of a tomato paste are: washing, sorting, trimming, breaking, juice extraction, concentration, pasteurization, filling, and cooling. After washing and sorting, the chopped tomatoes are subjected to cold break (60 °C) or hot break (90-95 °C). A hot break paste has a higher consistency compared to the cold break one, the reason is that in hot break pectinolytic enzymes are denatured and more pectin will be extracted into the resulting paste. During juice extraction the heated tomato pulp is passed thorough two extractors (pulper and finisher) to separate the seeds and skin. The type of extractors (paddle or screw) and screen size of extractors affect the quality of the final product in particular its texture and consistency (12).

The tomato juice is concentrated under a partial vacuum to minimize the heat damage to the product. The type of process (batch or continuous), process time and temperature and final concentration all affect chemical composition, color, viscosity and flavor of the end products (14).

According to the FDA (Food and Drug Administration of the USA) “tomato paste is strained tomatoes concentrated by evaporation with or without the addition of salt and with or without the addition of basil leaf, and contains not less than 24% salt free tomato solids” (14).

The physicochemical and rheological properties of a tomato paste depend on the quality of starting raw materials (variety and ripening stage), processing conditions (process design, time, temperature and process pressure), storage time and conditions. Tomato paste contains both water soluble materials and insoluble components. The consistency of a tomato paste is mainly controlled by the amount of pectin, total soluble solids, and size distribution of insoluble constitutes (14). The main quality parameters of tomato pastes perceived by the consumers are color, consistency, and flavor, in addition there are compositional standards. One of the problems facing the companies for exporting tomato pastes is

1

Farahnaky et al.: Physicochemical & Rheological Properties of Iranian Tomato Paste



variations in color and consistency of their products. The first step in solving these problems is to characterize this specific type of foods, and classify them based on the criteria set by the international recognized organizations e.g. FDA.

The main aim of this study was to compare the physicochemical properties and rheological behavior of a number of tomato pastes manufactured by Iranian food processors and to evaluate the variations in their properties e.g. consistency, colour and composition.

Materials and methods

Materials

Tomato pastes (eight 1 kg cans of each brand) from ten different tomato paste producing companies with nearly the same production dates were locally purchased (Shiraz, Iran). The sealed cans were kept in a cold room set at 4 °C for further experiments. The manufacturers were selected systematically to represent the main tomato growing areas of the country. The tomato pastes were from Dadfar, Mahram Urumada, Delpazir, 1&1, Shohreh, Tabarok, 95, Madlin and Chinchin companies and the customer price of each 1kg can of different brands was: 10500, 11500, 12500, 9900, 12000, 8500, 11000, 10000, 8950, 10600 Rials, respectively.

All chemicals used in this research were of analytical grade, unless otherwise mentioned.

Chemical Analysis of Tomato Pastes

Total soluble solid (Brix), reducing sugar, ascorbic acid, salt content and pH of the tomato pastes were quantitatively determined according to the Association of Official Analytical Chemists (AOAC) methods (reducing sugar, 42.1.16; Brix, 42.1.10; ash content, 42.1.12; pH, 42.1.04; NaCl concentration, 42.1.15; ascorbic acid concentration 45.1.16 (2).

Physicochemical Properties of Tomato Pastes

Color measurement of tomato pastes

The color of tomato paste samples was evaluated using a modified method of Yam et al. (20). Each sample was carefully poured into a Petri dish to avoid formation of any air bubbles on the surface. The Petri dish was covered using a layer of clear cling film. The Petri dish was then reversed over the scanner glass and the image was scanned using a Genius scanner (Color page-HR7X Slim). To

2

International Journal of Food Engineering, Vol. 6 [2010], Iss. 1, Art. 5

DOI: 10.2202/1556-3758.1571



avoid interference of any background effect on the images scanned, the scanner was covered with a layer of thick-black plastic wrap during the scanning process. Resolution, contrast and lightness of all images were set to 200 (dpi), 62 (%) and 62 (%), respectively. The pictures were saved in JPEG format and analyzed quantitatively using the Adobe Photoshop 8 software and the color parameters of L, a and b were determined in the “Lab” mode of the software. The a/b ratio, commonly used as a suitable index to report the quality of the color of tomato and its products was calculated and reported (3, 16).

Determination of Rheological Properties of Tomato Pastes

Rheological properties of tomato paste samples were studied using a controlled shear stress rheometer (Deer rheometer, Model PDR, 81, UK) at three temperatures (30, 45 and 60 °C). The tests were performed in triplicate using a cone and plate geometry with the cone angle of 4°. The geometry edges were covered by applying a small amount of a low viscosity oil for tests performed at high temperatures to minimize moisture loss. The obtained empirical data (torque and angular velocity) were converted into shear stress and shear rate parameters using Equations 1 and 2 (4). The values for the flow behavior index n; and the apparent viscosity (μ) were obtained by fitting the experimental data into a “Power Law equation” (Equation 3) using the “Solver” in Excel program (Microsoft Office, 2003). Apparent viscosities of the samples were then calculated at shear rate of 15 s-1 and compared.

γ= A.V/ tan θ (1)

where γ is the shear rate (s-1), A.V is angular viscosity (Rad . s-1) and θ is the cone angle of the geometry.

(2)

the σ is shear stress (dyne . cm-2), τ is torque (dyne . cm) and R (cm) is the radius of cone and plate geometry.

(3)

where η is viscosity (centiPoise, cP), n is flow behavior index and σ0 is yield stress.

σ= 3τ / 2ΠR3

σ = ηγn + σ0

3




Statistical Analysis

All data were analyzed by randomized plot and were subjected to analysis of variance, followed by a Duncan’s multiple-range test analysis based on triplicate samples. Significance level was set at α = 0.05. The COSTAT program was used for all statistical analysis. All tests were performed at least in triplicate.

Results and discussion

Chemical Composition of Tomato Pastes

According to the FDA, tomato pastes are divided into three types: heavy, medium and light. Heavy tomato pastes contain not less than 33% of salt free tomato solids. Pastes of medium concentration contain from 29 to 33% of salt free tomato solids and light pastes, 25 to 29% (14). The results of chemical analysis tests (Table 1) indicate that the total Brix of tomato pastes varied from 25.5 to 31.3% and there was a significant difference between the samples under study. However in the FDA and the Institute of Standards and Industrial Research of Iran (ISIRI), the “salt free Brix” is regarded as the standard criterion for tomato paste. The salt free Brix of the tomato pastes ranged from 22.73 to 30.68% and most of the samples were in the range of 25-26%. According to the ISIRI report number 671 (13) the salt free Brix of tomato paste should be in the range of 25 to 35%.

Most of the Iranian tomato paste samples were “light”, only one sample was “medium” and the Brix of one sample was too low to be considered as a tomato paste (Brix=22.73). The significant difference in the Brix of the samples indicates high variations in terms of process conditions (temperature, time and pressure) and the raw materials used.

The pH of the pastes was in the range of 4.04 to 4.48 and there was a significant difference between the samples. The maximum pH of tomato paste per Iranian Standard is 4.3. Since tomato pastes are pasteurized and not sterilized, low pH is an important factor for microbial stability in preventing the growth of pathogenic microorganisms and a proper and routine checking of pH of the final products by the manufacturers is required.

Because of the concerns over health-related issues regarding high intake of salt by the consumers, the level of salt in different foods has recently become the focus of many research projects (7). As an important issue the salt content of the samples was measured. The salt content of the samples was very different and ranged from 0.62 to 3.34% (w/w, Table 1). According to the ISIRI (13) the maximum salt content of tomato pastes is 2% (w/w). The salt levels reveal that the total intake of salt by the consumption of tomato pastes can be considerable if

4


DOI: 10.2202/1556-3758.1571



a large quantity is consumed and only one of the tomato pastes in this study can be considered as a low salt product.

Tomato fruit is a good source of vitamin C (about 140mg/100 g) and it is of great importance to investigate the level of residual vitamin C in tomato pastes. Heat and oxygen are amongst the main factors causing loss of vitamin C in tomato processing (9). Nutritionally a food manufacture would try to minimize the loss of vitamins during processing and storage. Therefore the concentration of vitamin C in a tomato paste can be counted upon as an indicative of processing conditions as well as raw material quality. The level of vitamin C in tomato pastes was very different and ranged from 10.67 to 57.79 mg/100g. A severe and long heat processing during the evaporation of water from the tomato juice can be one of the main reasons for this large difference. The comparison of the level of vitamin C in tomato fruit and the levels of vitamin C found for the tomato paste samples of this study show that a large quantity of the vitamin C in tomato fruit is degraded during the processing and storage. The reducing sugar content of the samples varied from 11.51 (w/w) (with lowest Brix of 25.5%) to 15.93 % (with highest Brix of 31.3%) which is determined by the reducing sugar content of the tomato fruits used and the Brix of the tomato pastes. Nearly half of the dry matter of tomato is reducing sugars (glucose and fructose) (14).

Color of Tomato Pastes

Lightness and a/b ratio (reported as the indicative and quality parameters for the color of tomato products) (12) of the samples were measured to quantify the extent of the color difference between tomato paste samples. The L values of the samples (Table 2) were significantly different and ranged from 53.2 (the darkest) to 59 (the lightest). A one unit difference in L values of two samples can be detected by the human eyes. There was also a significant difference between the tomato pastes in terms of a/b ratio which varied from 1.6 to 2 (Table 2).

5




Table 1. Chemical composition* of tomato pastes (g/100 g, wet basis).

Sample (%)Brix Salt free Brix (%) (%)Salt

Bostwick value

(cm/30s)pH Reducing

(%)SugarVitamine C(mg/100ml)

Dadfar 0.2±25.5 f

22.7±0.2 f

0.06±2.77 b

0.17±5.60 h

0.03±4.14 ef

0.11±11.51 g

0.14±14.70 f

Mahram 0.3±27.4 e

25.1±0.3 e

0.07±2.28 c

0.46±8.03 cd

0.03±4.14 ef

0.00±14.13 d

0.01±14.06 g

Urum ada 0.4±31.3 a

30.7±0.4 a

0.02±0.62 d

0.11±6.07 g

0.04±4.48 a

0.23±15.93 a

0.00±27.11 d

Delpazir 0.2±28.0 d

25.6±0.2 cd

0.09±2.44 bc

0.21±7.77 d

4.17±0.03 de

0.14±13.03 e

0.01±12.03 i

1&1 0.2±28.7 c

26.1±0.2 b

0.41±2.61 bc

0.00±7.00 e

0.02±4.20 cd

0.00±14.50 c

0.01±23.72 e

Shohreh 0.1±27.3 e

25.0±0.1 e

0.26±2.31 c

0.23±8.37 c

0.03±4.31 b

0.13±14.80 b

0.00±57.79 a

Tabarok 0.3±28.4 dc

25.6±0.3 cd

0.05±2.83 b

0.25±8.83 b

0.05±4.11 f

0.13±12.45 f

0.02±30.84 b

95 0.1±29.5 b

26.2±0.1 e

0.35±3.30 a

0.06±6.73 fe

0.03±4.04 g

0.09±12.93 e

0.01±27.96 c

Madlin 0.2±28.6 c

25.9±0.2 bc

0.11±2.71 cb

0.06±6.53 f

0.01±4.19 cd

0.09±14.44 c

0.01±10.67 j

Chin Chin 0.1±28.6 c

25.3±0.1 de

0.32±3.34 a

0.57±9.87 a

0.03±4.20 c

0.10±13.98 d

0.00±13.72 h

*Data are an average (±1SD) of triplicate trials. Different letters in each column indicate that the values differ significantly at α=0.05.

6


DOI: 10.2202/1556-3758.1571

Brought to you by | University of Sussex

Authenticated | 139.184.30.135D

ownload D

ate | 9/20/12 10:37 PM

Table 2. L a, b and a/b color parameters* of tomato paste samples.

*Data are an average (±1SD) of triplicate trials. Different letters in each column indicate that the values differ significantly at α=0.05. According to Goose et al. (11), an a/b ratio of 1.9 or greater represents a top quality product in terms of color and an a/b ratio of less than 1.80 indicates that the paste may be unacceptable. The data in Table 2 show that the minimum requirements for a quality product were not met for some samples.

Rheological Behavior of Tomato Pastes

Shear stress-shear rate curves (Figure 1) obtained from the rheological tests indicated that all tomato pastes in this study were non-Newtonian fluids and the flow behavior index values obtained (Table 3) indicate that the examined fluids were all pseudoplastic (shear thinning). The apparent viscosities of the samples decreased with increasing shear rate (Figure 1), therefore all tomato pastes were susceptible to shear thinning, a characteristic of pseudoplastic foods. Similar results have been reported by Dale et al (5) who showed that the viscosity of tomato products depends on fiber, protein, fat contents and total soluble solids.

a/bbaLSample

1.6±0.0b

6.9±0.1h

11.0±0.0i

53.2±0.0h

Dadfar

1.8±0.0ab

6.2±0.0i

11.1±0.1i

53.8±0.1g

Mahram

0.0±1.9ab

10.2±0.0d

19.8±0.1d

56.4±0.0c

Urum ada

0.0±1.8ab

9.8±0.1e

16.6±0.2g

55±0.0e

Delpazir

2.0±0.0a

8.6±0.1f

16.8±0.0f

54.4±0.1f

1&1

1.7±0.0ab

15.6±0.1a

26±0.0a

59±0.2a

Shohreh

0.0±1.8ab

13.4±0.2b

24.3±0.1b

58.4±0.1b

Tabarok

2.0±0.0a

10.9±0.0c

21.4±0.1c

56.5±0.1c

95

2.0±0.0a

9.7±0.3e

19.1±0.2e

55.5±0.2d

Madlin

0.1±1.7ab

8.1±0.1g

14.0±0.0h

55.0±0.0e

Chin Chin

7




They also developed an empirical equation for apparent viscosity of the products depending on the chemical composition. The results presented in Table 4 also show that increase in temperature resulted in a significant reduction in the apparent viscosity.

0,00

0,05

0,10

0,15

0,20

0,25

0,30

0,35

0,40

0,45

0,50

0 20 40 60 80 100 120 140 160 180 200

Shear rate (1/s)

Shea

r stre

ss(d

yn/c

m2)

Dadfar" MahramUrum Ada Delpazir1&1 ShohrehTabarok 95Madlin Chin Chin

Fig. 1. The plot of shear rate versus shear stress for different tomato pastes at 45 °C.

8


DOI: 10.2202/1556-3758.1571



Table 3. Flow behavior index (n) and yield stress (c, dyne.cm-2) of tomato paste samples at different temperatures.*

04530Temperature (°C)

cncncnSample

1.340±119.380g

0.002±0.259g

1.020±214.645j

0.010±0.215e

1.230±255.047h

0.001±0.356bc

Dadfar

1.021±78.064b

0.016±0.471a

1.120±100.220b

0.002±0.424a

1.120±231.893f

0.000±0.295e

Mahram

1.000±157.02i

0.021±0.384e

2.011±195.954g

0.021±0.358c

1.050±168.710b

0.010±0.415a

Urum Ada

1.052±108.453e

0.012±0.457b

1.101±200.516i

0.023±0.279d

1.030±207.687e

0.015±0.359bc

Delpazir

1.151±150.207h

0.101±0.300f

1.212±148.594e

0.001±0.359c

1.031±197.311d

0.000±0.370b

1&1

1.012±87.945c

0.014±0.433d

1.171±137.339d

0.011±0.355c

1.000±182.032c

0.010±0.376b

Shohreh

2.150±259.999j

0.011±0.138h

1.042±114.541c

0.101±0.365c

1.420±259.999i

0.012±0.182f

Tabarok

1.061±98.807d

0.023±0.450bc

1.001±153.893f

0.015±0.387b

1.230±253.154g

0.001±0.341cd

95

1.650±117.909f

0.003±0.452bc

1.011±199.071h

0.000±0.363c

306.012±1.260j

0.020±0.332d

Madlin

1.000±59.342a

0.001±0.441cd

1.000±92.022a

0.001±0.398b

1.01±156.990a

0.111±0.303e

Chin Chin


9


Brought to you by | University of Sussex

Authenticated | 139.184.30.135D

ownload D

ate | 9/20/12 10:37 PM

Analysis of the rheology data showed that “Power Law equation” was a suitable model for describing the flow behavior of the samples. Dervisoglu et al. (6) reported similar results for the flow behavior indices of their ketchups. As shown in Table 3 and reported by Fito et al. (8), Gómez-Díaz et al. (10), Sahin et al. (17) and Tanglertpaibul et al. (19) concentration and temperature do not have a strong effect on the n factor, as the flow behavior index.

Table 4. The apparent viscosity* (cP) of tomato paste samples at different temperatures at shear rate 15 (1/s).

at shear rate 15/sViscosity of tomato pastes(cP)604530Temperature(ºC)

Sample12.0±0.1

f18.0±0.1

f32.0±0.1

gChin Chin

26.0±0.1b

21.0±0.1ef

33.0±0.2g

Tabarok

17.0±0.3e

25.5±0.2cd

45.0±0.1f

Dadfar

19.0±0.1e

21.0±0.1Ef

48.0±0.1e

Mahram

19.0±0.0e

24.0±0.0de

54.0±0.0d

Shohreh

23.0±0.2cd

26.0±0.0bcd

62.0±0.3c

1&1

25.5±0.1bc

28.5±0.2bc

63.0±0.1c

Delpazir

30.0±0.1a

34.5±0.1a

64.0±0.1c

Urum ada

22.5±0.2d

29.0±0.2b

72.0±0.0b

95

26.5±0.1b

36.0±0.1a

90.0±0.1a

Madlin


When a tomato paste sample is subjected to a low shear stress the matter does not flow and only after reaching a certain level of stress (called yield stress) it starts to flow. The yield stress of tomato-based products is of great importance as an important consumer (e.g. for pouring behavior) and processing design (e.g. material handling) parameter. As expected, the yield stress of the samples was affected by temperature, the higher the temperature the lower the yield stress (Table 3).

10


DOI: 10.2202/1556-3758.1571



In Bostwick consistometer the distance traveled by a sample under its own weight is determined at a specified time, which has an inverse relationship with consistency. The plot of yield stress at 30 °C (obtained using rotational viscometry) versus Bostwick value at room temperature (Figure 2) of the samples shows that there was an inverse relationship between these two parameters. However the regression coefficient found for a linear fit was low (r2=0.16).

Fig. 2. The plot of yield stress, dyne .cm-2 (at 30 °C) versus Bostwick value obtained for tomato pastes at room temperature. R2 of 0.13 was found.

Figure 3 gives the relationship between the viscosity at 30 °C and the Bostwick values (measured at room temperature). The comparison of Figures 2 and 3 shows that Bostwick values have a much stronger dependence on viscosity than yield stress. Bostwick and viscosity both measure the behavior of a sample when it flows under an applied stress but the yield stress is an indication of the behavior of a sample before flowing.

y = -13.012x + 318.99R2 = 0.1302

150

200

250

300

350

5 6 7 8 9 10Bostwick value (cm/ 30 sec)

Yie

lds

stre

ss

11




Fig. 3. The plot of viscosity (at 30 °C and shear rate of 15 s-1) versus Bostwick value obtained for tomato pastes at room temperature. R2 of 0.69 was found.

There was a positive relationship between Brix and viscosity. The slopes of the linear plots of Brix of tomato pastes versus apparent viscosity at shear rate 15 (1/s) were 3.5, 2 and 1.9 at 30, 45 and 60 °C, respectively. This indicates that at 30 °C there is a greater dependence of Brix on viscosity than the dependence of viscosity measured at higher temperatures. However there was not any relationship between the Brix and the yield stress of tomato pastes (plots not shown).

Conclusions

The tomato pastes studied in this research were representative of most manufacturing areas of the country. In terms of composition there were significant differences between the samples particularly in terms of Brix, salt concentration and vitamin °C content. According to the FDA definitions for tomato pastes, this work showed that some of the tomato pastes studied in this research did not meet the Brix criteria to be called “tomato paste” and most of them are categorized as “light” tomato pastes. If vitamin C is taken as an indicator of the level of all vitamins remained in the pastes, after heat processing and storage, it can be concluded that the level of vitamins is low compared to starting raw materials (i.e. fresh tomatoes). In terms of color and rheological properties there were significant differences between the samples. The variations in the raw materials and the lack of a standard operating procedure with consistent process conditions would be the main reasons for such a wide variations in the quality of tomato pastes in Iran market.

y = -12.738x + 155.78R2 = 0.6925

0

20

40

60

80

5 6 7 8 9 10Bostwick value (cm/30 sec)

Vis

cosi

ty a

t 30

C (c

P)

12


DOI: 10.2202/1556-3758.1571



References

1. Al-Wandawi, H., M. Abdul-Rahman, and K. Al-Shaikhly. 1985. Tomato processing waste as essential raw materials source. J. of Agric. and Food Chem. 33:804-807.

2. A.O.A.C. (2002). Official Methods of Analysis. 17th ed. Association of Official Analytical Chemists, Inc. Washington D.C., USA.

3. Arias, R., T. C. Lee, L. Logendra, and H. Janes 2000. Correlation of lycopene measured by HPLC with the L, a, b colour readings of a hydroponic tomato and the relationship of maturity with colour and lycopene content. J. of Agric. and Food Chem. 48:1697–1702.

4. Bourne, M. 2002. Food Texture and Viscosity. Academic Press, New York. 5. Dale, K. B., M. R. Okos, and P. E. Nelson 1984. Concentration of tomato

products: analysis of energy saving process alternatives. J. of Food Sci. 47:1853-1858.

6. Dervisoglu, M., and J. L. Kokini. 1986. Steady shear rheology and fluid mechanics of four semisolid foods. J. of Food Sci. 51:541-546.

7. Farahnaky A., and S.E. Hill 2007. The effect of salt, water and temperature on wheat dough rheology. J. of Texture Studies. 38:499-510.

8. Fito, P. J., G. Clemente, and F. J. Sanz 1983. Rheological behavior of tomato concentrate. J of Food Eng. 2:51-62.

9. Gloria, S. Z., E. M. Yahia, K. Jeffrey, and A. Gardea. 2005. Effects of post harvest hot air treatments on the quality and antioxidant levels in tomato fruit. LWT. 38:657-663.

10. Gómez-Díaz, D., and J. M. Navaza. 2003. Rheology of aqueous solutions of food additives: Effect of concentration, temperature and blending. J. of Food Eng. 56:387–392.

11. Goose, P. G., and R. Binsted. 1964. Tomato paste definition, characteristics and quality. Chap. 1 in Tomato Paste, Puree, Juice and Powder. Food Trade Press Ltd, London.

12. Hayes, W. A., P. G. Smith, and A. E. J. Morris. 1998. The production and quality of tomato concentrates. Crit. Rev in Food Sci. and Nutr. 38:537-564.

13. ISIRI, Institute of Standards and Industrial Research of Iran. Standard of tomato paste, Report number: 761.

14. Luh, B. H., and C.E. Kean. 1998. Canning of Vegetables In: Commercial Vegetable Processing. Luh, B.H and J. G. Woodroof (ed).Van Nostrand Reinhold, New York. Pp. 195-285.

15. Osman, S. F., P. Irwin, W. F. Fett, J. V. O’Connor, and N. Parris. 1999. Preparation, isolation, and characterization of cutin monomers and oligomers from tomato peels. J. of Agric. and Food Chem. 47:799-802.

13




16. Sahin, H., and F. Ozdemir. 2004. Effect of some hydrocolloids on the rheological properties of different formulated ketchups. Food Hydro. 18: 1015–1022.

17. Shi, J., M. Le Maguer, Y. Kakuda, A. Liptay, and F. Niekamp. 1999. Lycopene degradation and isomerization in tomato dehydration. Food Res. Int. 32:15–21.

18. Suzuki, T., K. Tomita-Yokotani, H. Tsubura, S. Yoshida, I. Kusakabe, K. Yamada, Y. Miki., and K. Hasegawa. 2002. Plant growth-promoting oligosaccharide produced from tomato waste. Bioresource Tech. 81:91-96.

19. Tanglertpaibul, T., and M. A. Rao. 1987. Flow properties of tomato concentrates: effect of serum viscosity and pulp content. J. of Food Sci. 52:318-321.

20. Yam, K. L., and S. E. Papadakis. 2004. A simple digital imaging method for measuring and analyzing color of food surfaces. J. of Food Eng. 61: 137-142.

14


DOI: 10.2202/1556-3758.1571



a comparative study of physicochemical and rheological properties of iranian tomato pastes

Documents