Effect of some hydrocolloids on the rheological

Food Hydrocolloids 18 (2004) 1015–1022 www.elsevier.com/locate/foodhyd

Effect of some hydrocolloids on the rheological properties of different formulated ketchups Hilal Sahin, Feramuz Ozdemir* Department of Food Engineering, Faculty of Agriculture, Akdeniz University, 07070 Antalya, Turkey Received 12 November 2003; revised 26 January 2004; accepted 1 April 2004

Abstract Five different hydrocolloids (tragacanth gum, guar gum, carboxy methyl cellulose, xanthan gum and locust bean gum) were added, at levels of 0, 0.5, and 1 g/100 g (w/w), respectively, to three different formulated ketchups which were processed from cold-break tomato paste dilutions, having total soluble solid (TSS) contents of 7.5, 10, and 12.5 g/100 g (w/w), in sequence, and the effect of these hydrocolloids on the rheological properties of tomato ketchups was investigated using a viscometer with smooth surface wide-gap coaxial cylinders. All hydrocolloids increased the consistency of the tested samples; however, guar gum and locust bean gum caused the maximum increase, followed by xanthan gum, tragacanth gum and carboxy methyl cellulose (CMC). Both the ketchup formulation and the hydrocolloid concentration were found to affect the consistency of ketchups. The highest consistency index was obtained by processing dilutions with a TSS content of 12.5%, and the addition of hydrocolloids at the level of 1%. The fluidity of the ketchups decreased with both the addition of all hydrocolloids and the increase in hydrocolloids concentration. Furthermore, the fluidity of the ketchups was also affected by ketchup formulation, and it was found to be the lowest for the samples prepared from the tomato paste dilutions having a TSS content of 12.5%. q 2004 Elsevier Ltd. All rights reserved. Keywords: Hydrocolloids; Gums; Tomato ketchup; Rheological properties

1. Introduction Hydrocolloids are water-soluble, high molecular weight polysaccharides that serve a variety of functions in food systems, such as enhancing viscosity, creating gel-structures, formation of a film, control of crystallization, inhibition of syneresis, improving texture, encapsulation of flavors and lengthening the physical stability, etc. (Dickinson, 2003; Dziezak, 1991; Garti & Reichman, 1993; Glicksman, 1991). These functional ingredients are widely used in dairy products, canned foods, bakery products, salad dressings, beverages, sauces, soups and other processed foodstuffs to improve textural characteristics, flavour and shelf life. Several authors have reviewed various applications of food hydrocolloids in the food industry (Anderson & Andon, 1988; Niederauer, 1998; Ward, 1997). Tragacanth gum is obtained from a certain species of the Astragallus (A. microcephalus, A. gummifier * Corresponding author. Tel.: þ90-242-310-24-34; fax: þ 90-242-22745-64. E-mail address: [email protected] (F. Ozdemir). 0268-005X/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodhyd.2004.04.006

and A. kurdicus) bush, and it is a mixture of two polysaccharides, of which the water-soluble component is called tragacanthin, and the insoluble polymer is called bassorin. The gum swells rapidly, in either cold or hot water, to form highly viscous dispersions, up to 4000 mPa s at 1% solids, depending on the grade (Alexander, 1999a; Anderson & Bridgeman, 1985). Guar and locust bean gums (LBG) are galactomannans, and their chemical structure is based on a 1,4-linked b-D mannan backbone with 1,6-linked a-D -galactose side groups (Richardson, Willmeir, & Foster, 1998; Schorsch, Garnier, & Doublier, 1997; Wang, Ellis, & Ross-Murphy, 2000) with a mannose to galactose ratio of about 1.8 and 3.5, respectively. They have different water solubility due to the difference in the degree of galactose substitution (Ko¨k, Hill, & Mitchell, 1999). Guar gum from Cyamopsis tetragonolobus has a higher galactose content and swells and disperses almost completely in both cold and hot water, whereas LBG from Cerotonia siliqua needs to be heated for complete solubility (Dunstan et al., 2001; Dziezak, 1991; Garti, Madar, Aserin, & Sternheim, 1997; Lundin & Hermansson, 1997; Wang et al., 2000). Viscosity usually

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ranges from 6000 to 7500 and 3000 to 3500 mPa s for guar and LBG solutions at 1% solids, respectively (Alexander, 1999a). Xanthan gum is microbial heteropolysaccharide produced by the aerobic fermentation of Xanthomonas campestris (Bresolin, Milas, Rinaudo, & Ganter, 1998). It has a cellulose backbone substituted on every second residue, with a side chain consisting of two mannose units separated by a glucuronic acid residue. The mannose residue attached to the cellulosic backbone is variably acetylated, and the terminal mannose can contain a pyruvate group (Schorsch et al., 1997). The gum is soluble either in hot or cold water, has a high viscosity at low concentrations (at 1% solids of 1000– 4300 mPa s) (Alexander, 1999b) and shows excellent stability in heat and acid systems (Casas, Santosa, & Garcıá-Ochoa, 2000). Carboxy methyl cellulose (CMC) is obtained by the reaction of alkali cellulose with sodium chloroacetate, and it is soluble in either cold or hot water. Commercial products have degree of substitution (DS) from 0.7 to 1.5. The concentration, molecular weight and DS are important factors for flow behaviour of CMC in aqueous solutions. Solutions of the gum show shear thinning properties, but products of lower DS are thixotropic, and viscosity decreases with an increase in temperature. Commercial products range in viscosity from 25– 50 mPa s at 2% solids, to 3 –6000 mPa s at 1% solids, depending on the molecular weight and DS (Alexander, 1999b; Feller & Wilt, 1990; Kulicke, Kull, Kull, & Thielking, 1996). Tomato is one of the most important vegetable products and is mainly marketed as a processed product, i.e. pastes, concentrates, ketchup, salsa, etc. Viscosity is one of the most important quality parameters of such tomato products (Vercet, Sańchez, Burgos, Montan˜e´s, & Buesa, 2002). Knowledge of the rheological properties of fluid and semisolid foodstuffs is important in the design of flow processes in quality control, in storage and processing stability measurements, and in understanding and designing texture. Tomato ketchup is a heterogeneous, spiced product, produced basically from either cold or hot extracted tomatoes; or directly from concentrates, purees and tomato paste. Consistency/viscosity of ketchup is an important attribute from the engineering and consumer viewpoints (Rani & Bains, 1987). Therefore, reliable and accurate rheological data are necessary for designing and optimization of various unit operations (pumping, mixing, heating, etc.), and ensuring product acceptability since the products with improper consistency may be graded as unacceptable, or sold at a lower price. Tomato ketchup obtains its viscosity from naturally occurring pectic substances in fruits. Tomato varieties with less pectin may result in reduced consistency, and other factors such as enzymatic degradations, pectin/ protein interaction, pulp content, homogenization process and concentration may also affect the consistency of tomato products (Crandall & Nelson, 1975; Stoforos & Reid, 1992;

Tanglertpaibul & Rao, 1987a; Vercet et al., 2002). However, the consistency can be maintained by adding polysaccharides such as starch, gum, etc. (Sidhu, Bawa, & Singh, 1997). There are few published articles about the effects of some hydrocolloids on the consistency of tomato ketchup processed directly from hot extracted tomatoes (Gujral, Sharma, & Singh, 2002; Sidhu et al., 1997). The primary objective of the present study was to investigate the effect of hydrocolloids from different sources, and at different concentrations, on the rheological properties of tomato ketchups processed from cold-break tomato paste in three different formulations.

2. Materials and methods 2.1. Materials Fifty kilograms of cold-break, double concentrated tomato paste having a total soluble solids (TSS) content of 28 – 30%, with ingredients typically used in ketchup preparation (sugar, salt, apple vinegar, onion, garlic and spices), were purchased from local markets in Antalya, Turkey. Five different commercial hydrocolloids (tragacanth gum, guar gum, CMC, xanthan gum and LBG) were obtained from the company of Incom Inc. (Mersin, Turkey). The tomato ketchup was prepared in accordance with various formulations, using the ingredients shown in Table 1. 2.2. Preparation of tomato ketchup The tomato paste dilutions, having TSS contents of 7.5, 10, and 12.5%, respectively, were prepared according to Table 1 Recipes used for the preparation of three different formulated tomato ketchups Ingredients

Tomato pastea (g) Sugar (g) Salt (g) Apple vinegar (ml) Onion (g) Garlic (g) Spice mix (g) Paprika extract (ml) Sodium benzoate (mg/kg) Hydrocolloidsb a

Formulation 1

2

3

3250 448 58.5 204 22.5 10 4.75 0.8 500

3250 366 58.5 204 22.5 10 4.75 0.8 500

3250 286 58.5 204 22.5 10 4.75 0.8 500

TSS contents of the tomato paste were adjusted to 7.5, 10, and 12.5% for formulation 1, 2, and 3, respectively. The final TSS content of ketchups was 28.08 ^ 0.02%. b Hydrocolloids were added into ketchups at the concentration of 0, 0.5, and 1 g/100 g.


the formulation. Each tomato paste dilution with an adjusted TSS content was put into an open pan. Spices (mace, cloves, cinnamon, black pepper fruits, and cardamom) were wrapped in a cloth and dipped into the tomato paste dilution. Onion and garlic pulp were added directly to the dilution. The mixture was then heated on a hot plate, set at a moderate temperature, and stirred constantly until the mixture reached a temperature between 75 and 80 8C. At this point, sugar and salt were added, and heating was continued until the mixture attained a TSS content of 25%. Then, apple vinegar and paprika extract were added to the mixture, and the ketchup was heated until a TSS of 26.5% was obtained. Finally, sodium benzoate was added as a preservative, and the ketchup was immediately portioned into three samples of 1 kg each. The hydrocolloids were then added into each 1 kg of ketchup, at different levels, and stirred for 2 min at 5000 rpm with an electric hand blender having a rotational blade with a diameter of 0.035 m (BKK2160, Beko). A ketchup TSS content of 28.08 ^ 0.02% was obtained during mixing, due to evaporation. The final levels of each hydrocolloid by weight in ketchup samples were 0, 0.5, and 1%. Each ketchup sample was then immediately poured into the glass jar, while still hot, sealed with screw caps, and then stored at ambient temperature (20 – 22 8C) for 24 h before the analyses. 2.3. Determination of rheological properties of ketchup Torque measurements were carried out on the ketchup samples after 1 day of storage at ambient temperature, with a Brookfield viscometer (Brookfield Engineering Inc., Model RV 2 DV þ I) at a controlled temperature of 25 8C, with six spindle speeds (2.5, 5, 10, 20, 50, 100 rpm). The samples in 500 ml of beaker were kept in a thermostatically controlled water bath for about 15 min before measurements in order to attain desirable temperature of 25 8C. First measurements were taken 2 min after the spindle was immersed in each sample, so as to allow thermal equilibrium in the sample, and to eliminate the effect of immediate time dependence. All data were then taken after 40 s in each sample, with a rest in time between the measurements at the different spindle speeds. The spindles (spindle nos: 3, 4, 5 and 6) were used in accordance with the sample nature to get all readings within the scale (Gujral et al., 2002). Each measurement was duplicated on the same sample. The obtained empirical data were converted into shear stress and shear rate data (Mitschka, 1982). The shear rate versus shear stress data were interpreted using the power law expression (t ¼ kgn ; where t is the shear stress (N/m2), g is the shear rate (s21), n is the flow behaviour index, and k is the consistency index (Nsn/m2)). The values for the flow behaviour index n; and the consistency index k were obtained from plots of log shear stress versus log shear rate, according to the power law equation ðlog t ¼ log k þ n log gÞ: Apparent viscosity of the sample was then calculated as in I˙banog˘lu and ˙Ibanog˘lu (1998).

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2.4. Measurement of consistency of ketchup The consistency of the ketchup at the temperature of 25 8C was also measured using a Bostwick consistometer with a flow range of 24 cm (Paul N. Gardner Company, Inc.), by measuring the flow of the undiluted product in 30 s (Porretta, 1991). The Bostwick flow values were taken at the edge of the ketchup, and did not include any of the free serum that exudes from the ketchup. The data were obtained as the average of parallel readings for each sample. 2.5. Statistical analysis The experiment was performed as a randomized plot, with a factorial design in the ketchup formulation, type of hydrocolloids and addition levels of hydrocolloids (3 £ 5 £ 3), using duplicate samples. The data were then subjected to analysis of variance, and appropriate means separation was conducted using Duncan’s multiple-range test analysis in SAS software.

3. Results and discussion Viscosity functions data showed that all ketchups under examination were non-Newtonian fluids, since the values for flow behaviour index, n were , 1, which was indicative of the pseudoplastic (shear thinning) nature of tomato ketchups. The power law equation was found to be an adequate model to describe the flow behaviour of the samples in this study. Values of R2 were found to vary from 0.960 to 0.999. The flow behaviour index ðnÞ of the power law model ranged between 0.114 and 0.298. Similar results for the flow behaviour index of ketchups have been reported by Bottiglieri et al. (1991) and Rani and Bains (1987). Although n does not have a strong dependence on the concentration and temperature of the polymeric solutions (Go´ mez-Dıáz & Navaza, 2003; Wanchoo,

Table 2 Mean squares from analysis of variance of rheological properties of ketchups at 25 8C Source of variation

DF

Flow behaviour index ðnÞ

Apparent viscosity ðha ; 2 s21 Þ

Bostwick flow value (cm)

Hydrocolloid (H) Formulation (F) Concentration (C) H£F H£C F£C H£F£C Error

4 2 2 8 8 4 16 45

0.002072** 0.003101** 0.042246** 0.000954** 0.005075** 0.002426** 0.000743** 0.000296

272.06** 1092.58** 4686.87** 8.73* 170.22** 26.68** 4.64NS 3.93

14.43** 191.28** 165.86** 0.58NS 3.74** 7.38** 0.34NS 0.33

NS, nonsignificant at P . 0:05; *, significant at P , 0:05; **, significant at P , 0:01:

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Table 3 Changes in the rheological properties of the ketchups added five different hydrocolloids CMC Flow behaviour index ðnÞ

Apparent viscosity ðhapp;2 Þ


Xanthan a

b

Guar

Tragacanth b

b

LBG

0.228 ^ 0.009

0.211 ^ 0.008

0.205 ^ 0.013

0.203 ^ 0.009

0.202b ^ 0.014

LBG

Guar

Xanthan

Tragacanth

CMC

23.64a ^ 3.781

23.31a ^ 3.424

21.63b ^ 3.220

17.47c ^ 2.057

14.77d ^ 1.733

CMC

Tragacanth

LBG

Guar

Xanthan

7.59a ^ 0.645

6.30b ^ 0.704

5.59c ^ 0.667

5.56c ^ 0.741

5.48c ^ 0.838

Values in a row followed by different superscript letters are significantly ðP , 0:05Þ different (Duncan’s multiple-range test). Mean value ^ standard error ðn ¼ 18Þ:

Sharma, & Bansal, 1996), it was significantly ðP , 0:01Þ affected by both the main factors (type of hydrocolloids, ketchup formulation and hydrocolloids concentration) and all interactions of these factors in present study (Table 2). It has been shown in Tables 3– 5 that there were significant ðP , 0:05Þ differences in the flow behaviour index of ketchup samples. Both the addition of hydrocolloids and the increase in the amount of tomato paste in the formulation increased the shear thinning properties of the ketchup samples. These results further indicated that addition of LBG, tragacant gum, guar gum and xanthan gum caused greater shear thinning properties, whereas CMC showed little effect on the shear thinning behaviour of the ketchup samples. The addition of different hydrocolloids led to a significant increase in the consistency index, and thereby resulted in an increase in the apparent viscosity of the tomato ketchups. The increase in the consistency index, and the apparent viscosity (at the shear rate of 2 s21), was highest with the addition of both guar gum and LBG, followed by the addition of xanthan gum and tragacanth gum, and the least with the addition of CMC (Table 3). The relationship between apparent viscosity and shear rate of different formulated tomato ketchups with added hydrocolloids was plotted as in Figs. 1– 5. As shown from the figures, all the ketchups were susceptible to shear thinning, a characteristic of pseudoplastic foods, and therefore the apparent viscosities decreased with increasing shear rate. Due to their high-water binding capacity (Garti et al., 1997), high molecular weights and more functional structures that combine the properties of both linear and branched polysaccharides, the highest consistency and apparent viscosity were imparted both by guar and LBG. Although guar gum, with a high galactose content, swells and dissolves readily in cold water, and LBG needs heating to 80 8C for complete solubility (Ko¨k, Hill, & Mitchell, 1999), considering the temperature of 92 –95 8C at which hydrocolloids were added to ketchup, there could be no significant difference in the solubility of both guar gum

and LBG. Therefore, LBG could be as effective as guar gum in increasing the consistency of tomato ketchup. Xanthan gum also caused a significant ðP , 0:05Þ increase in the apparent viscosity of the tomato ketchup. Table 4 Changes in the rheological properties of the ketchups prepared in three different formulations

Flow behaviour index (n)



1

2

3

0.221a ^ 0.007

0.208b ^ 0.008

0.201b ^ 0.009

3

2

1

26.19a ^ 2.276

20.18b ^ 2.327

14.12c ^ 1.868

1

2

3

8.79a ^ 0.563

5.74b ^ 0.375

3.78c ^ 0.295


Table 5 Changes in the rheological properties of the ketchups according to the hydrocolloids concentrations

Flow behaviour index (n)



0.0%

1.0%

0.5%

0.250a ^ 0.004

0.203b ^ 0.008

0.176b ^ 0.006

1.0%

0.5%

0.0%

34.03a ^ 2.038

16.68b ^ 1.027

9.78c ^ 0.780

0.0%

0.5%

1.0%

8.38a ^ 0.527

6.26b ^ 0.441

3.68c ^ 0.363



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Fig. 1. Changes in the apparent viscosity with shear rate in ketchups added tragacanth gum at three different concentrations (0, 0.5 and 1%): ketchups prepared from tomato paste dilutions having TSS content of 7.5% (A); 10% (B) and 12.5% (C). Bars indicate error limits, P , 0:05:

Its branching nature provided its unusual rheological characteristics, better than tragacanth gum and CMC. Linear cellulosic backbone, shielded by the trisaccharide side chains, provides the xanthan molecule with a rather stiff, rod-like structure that shows excellent stability to heat, enzymes, acid and alkali. Because of its solubility either in hot or cold water, xanthan molecules are extended in solutions, and thus achieves high viscosity at low concentrations, and its solutions show thickening properties with a pseudoplastic behaviour (Alexander, 1999b; Casas et al., 2000; Schorsch et al., 1997). Although xanthan gum, an ionic gum, has a higher viscosity than galactomannans at the same gum concentration (Liu & Eskin, 1998), it was found to cause the lower increase in the apparent viscosity of the ketchup samples than galactomannans. Gum tragacanth is a complex, highly branched molecule that is closely packed (Alexander, 1999a), and these characteristics may have resulted in its lower contribution to the consistency of tomato ketchup.

The least increase in the apparent viscosity with the addition of CMC could be resulted from the characteristics of the commercial one used, with the lower molecular weight and DS. The apparent viscosity of the ketchups was significantly changed by the formulation used. The ketchups produced according to the third formulation had the highest apparent viscosity, followed by the second formulation, with the least consistency rate being produced in the first formulation (Table 4). Rani and Bains (1987) have reported that the apparent viscosity of the ketchups was related to soluble pectin and pulp content of the ketchups and was less dependent on total solids. Regarding formulations, it can be stated that apparent viscosity of the ketchups increased when more tomato paste was used in the formulation, since the third formulation consisted of the highest amount of tomato paste. This finding could be attributed to the consequent higher pulp content that results from the increase in the amount of tomato paste in the ketchups. Tanglertpaibul and Rao (1987b) have reported

Fig. 2. Changes in the apparent viscosity with shear rate in ketchups added guar gum at three different concentrations (0, 0.5 and 1%): ketchups prepared from tomato paste dilutions having TSS content of 7.5% (A); 10% (B) and 12.5% (C). Bars indicate error limits, P , 0:05:

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Fig. 3. Changes in the apparent viscosity with shear rate in ketchups added CMC at three different concentrations (0, 0.5 and 1%): ketchups prepared from tomato paste dilutions having TSS content of 7.5% (A); 10% (B) and 12.5% (C). Bars indicate error limits, P , 0:05:

that the increase in the insoluble solids, being the pulp content of the tomato concentrate, caused an increase in the apparent viscosities of the samples. There was also a significant increase in the apparent viscosity of the tomato ketchup with the increase in concentration of the added hydrocolloids (Table 5). Because of the higher water binding capacity that occurs when increasing the concentration (Go´mez-Dıáz & Navaza, 2003), ketchups with the addition of hydrocolloids at a level of 1% had the highest consistency. There was a significant ðP , 0:01Þ effect of the formulation used, the type of hydrocolloids, and the hydrocolloids concentration, on the fluidity of the ketchup (Table 2). The addition of hydrocolloids, and an increase in their concentration, caused a decrease in the fluidity (Tables 3 and 5). Gujral et al. (2002) have been reported that, this could be resulted from the binding of water by hydrocolloid molecules, leading to an increase in the resistance to flow of the sample. The addition of xanthan gum in tomato ketchup caused the maximum decrease in fluidity, followed by guar gum, LBG, tragacanth gum and CMC, respectively (Table 3).

However, there was no significant ðP , 0:05Þ difference between the averages of fluidity for the ketchups when xanthan gum, guar gum and LBG were added. When analyzing the fluidities of the ketchups, from highest to lowest, an inverse relationship was noted between the fluidities and consistency indexes of the samples. Since the resistance of a fluid to flow increased with both the addition of hydrocolloids and the increase in their concentration gradually from 0 to 1%, the Bostwick flow values decreased in this way. Furthermore, the increase in the amount of tomato paste in the ketchup formulations caused a significant ðP , 0:05Þ decrease in the fluidity of the samples (Table 4). The Bostwick flow value was found to be the lowest for the ketchups prepared according to the third formulation, which included the tomato paste dilution having a TSS content of 12.5%. Tanglertpaibul and Rao (1987a,b) stated that the Bostwick consistency of tomato concentrates is affected by changes in soluble and insoluble solids. Since there was no significant ðP . 0:05Þ difference between the averages of TSS content of the ketchup samples (the average TSS content of ketchups was 28.08 ^ 0.02%), the decrease in the fluidity of the ketchups with the increase

Fig. 4. Changes in the apparent viscosity with shear rate in ketchups added xanthan gum at three different concentrations (0, 0.5 and 1%): ketchups prepared from tomato paste dilutions having TSS content of 7.5% (A); 10% (B) and 12.5% (C). Bars indicate error limits, P , 0:05:


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Fig. 5. Changes in the apparent viscosity with shear rate in ketchups added LBG at three different concentrations (0, 0.5 and 1%): ketchups prepared from tomato paste dilutions having TSS content of 7.5% (A); 10% (B) and 12.5% (C). Bars indicate error limits, P , 0:05:

in the amount of tomato paste in the formulation could be resulted from the stronger dependence of the fluidity on the insoluble, pulp, content of the finished product.

4. Conclusions The present study showed that all tested hydrocolloids can be used to improve consistency/viscosity of tomato ketchups. While the consistency index and the apparent viscosity increased with the addition of hydrocolloids and the increase in their concentrations, the Bostwick flow value decreased. The composition of the ketchup samples was also found to affect the rheological properties of the products. According to the results, when tomato ketchup is prepared from tomato paste, preparation of the ketchups from the tomato paste dilution having at least 10% of TSS and the addition of 0.5% of hydrocolloids was found to be effective in providing the optimum consistency. When excess hydrocolloid (1% in this study) was used, however, xanthan addition caused a slimy texture and the addition of guar gum resulted in unpleasant smelling. Therefore, the sensory assessments of the ketchups should be also taken into consideration. The other part of this study about sensory evaluation is under preparation for publication.

Acknowledgements The authors wish to thank the Scientific Research Fund of Akdeniz University for a grant (Project Number: 2002.0121.12).

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