evaluation of rheological properties of selected salt enriched food hydrocolloids

Evaluation of rheological properties of selected salt enriched foodhydrocolloids

Mich�ele Marcotte a,1, Ali R. Taherian a, Maher Trigui a, Hosahalli Swamy Ramaswamy b,*

a Food Research and Development Centre, Agriculture and Agri-Food Canada, 3600 Casavant Blvd West, St. Hyacinthe, Qu�ebec, Canada J2S 8E3b Department of Food Science and Agricultural Chemistry, Macdonald Campus of McGill University, 21, 111 Lakeshore, Sainte-Anne-de-Bellevue,

Qu�ebec, Canada H9V 3V9

Accepted 4 September 2000

Abstract

Rheological properties of hydrocolloids are important for the design and operation of continuous processes such as ohmic

heating. Addition of salt to hydrocolloids may be desirable to enhance the e�ciency of ohmic heating. A rotational viscometer was

used to characterize the ¯ow behavior of pectin, starch, xanthan and carrageenan solutions at four temperatures

(20°C; 40°C; 60°C and 80°C) and three concentrations. Salt was added at 1%. Samples were subjected to a programmed shear rate

increasing from 0 to 300 sÿ1 in 3 min, held constant at 300 sÿ1 for 10 min and linearly decreasing to 0 during 3 min. The power law

model was ®tted to shear stress vs. shear rate data to obtain the consistency coe�cient (m) and the ¯ow behavior index (n) for starch

and pectin whereas the Herschel±Bulkley model was used for carrageenan and xanthan. Both m and n were sensitive to changes in

temperature and concentration. Ó 2001 Elsevier Science Ltd. All rights reserved.

Keywords: Rheological properties; Salt enriched food hydrocolloids; Ohmic heating

1. Introduction

Thermal process design for liquid foods with orwithout particulate require accurate information on the¯ow behavior to arrive at processing conditions whichensure safety and improve quality. In these continuousprocesses, rheological properties play a major role indescribing the heat transfer or in the design, evaluationor/and modeling of the continuous treatment, as ¯owcharacteristics of pumpable liquid, viscous and semi-liquid foods are dependent on ¯uid viscosity and den-sity.

Hydrocolloids are commonly used as thickeningagents to give product proper qualities, mostly texturalcharacteristics. They are used in a variety of food ¯uidssuch as fruit-based (e.g., sauces, jams, juice concentrateetc.) or milk-based products (e.g., pudding, yoghurtetc.). They may be incorporated in meat products.Moreover, hydrocolloids in solutions need to be ma-

nipulated in various food processing unit operations,playing a major role in the transportation of solid par-ticles in aseptic processing equipment (Palmer & Jones,1976; McCoy, Zuritz, & Sastry, 1987; Berry, 1989; Lee &Singh, 1991a,b, 1993; Dutta & Sastry, 1990; Abdelrahim& Ramaswamy, 1995; Abdelrahim, Ramaswamy, & vande Voort, 1995) including ohmic heating (Khalaf &Sastry, 1996; Kim et al., 1996) as carrier ¯uids for par-ticulate foods. During ohmic heating, carrier ¯uids willbe subjected to di�erent shear rates in di�erent sectionsof the process. Usually, low shear rates will be observedin straight heating tubes and high shear rates whilepassing through pumps.

It has been recognized that the rheological propertiesof hydrocolloids in solution depend on many factors:concentration of the active compound, temperature,degree of dispersion, dissolution, electrical charge, pre-vious thermal and mechanical treatment, presence orabsence of other lyophilic colloids, age of the lyophilicsolution and the presence of electrolytes and non-elec-trolytes (Rao, 1986, 1992; Rao & Kenny, 1975). At anindustrial scale, real food formulations will usually in-volve the addition of other ingredients. For example,Kim et al. (1996) have reported that the salt content of atypical gravy or sauce of a typical particulate food such

Journal of Food Engineering 48 (2001) 157±167

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* Corresponding author. Tel.: +1-514-398-7919; fax: +1-514-398-

7977.

E-mail addresses: [email protected] (M. Marcotte), Ramasw-

[email protected] (H.S. Ramaswamy).1 Tel.: +1-450-773-1105 (219); fax: +1-450-773-8461.

0260-8774/01/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved.

PII: S 0 2 6 0 - 8 7 7 4 ( 0 0 ) 0 0 1 5 3 - 9

as beef stew, to be used in the ohmic heating context, isbetween 0.6% and 1%. Rheological properties of these¯uids also depend on the shear rate, the duration of theshear as well as the previous shear history (Rao, 1977).Also, di�erent temperatures are usually encounteredduring ohmic processing of hydrocolloids, therefore,their rheological properties should be studied as afunction of temperature. For the measurement of rhe-ological properties to be useful, a representative modelshould be developed. As well as, a proper measurementtechnique should be used to cover a wide range of shearrate, temperature and concentration of hydrocolloids insolution. Finally, there should be an investigation of thetime dependency on rheological properties.

Solutions of hydrocolloids are usually known to benon-Newtonian pseudoplastic ¯uids (Rha, 1978) whichmeans that the apparent viscosity decreases when theshear rate is increased or that the ¯uid is shear thinningin nature. Several models have been used to representthe ¯ow behavior of gum solutions. The power law orOstwald-de-Waele has been the most widely used modelto describe the ¯ow behavior of solutions of hydrocol-loids because of its compatibility with engineering cal-culations (Lalande, Leuliet, & Maingonnat, 1991).Either an exponential or power relationship (Speers &Tung, 1986) usually describes the e�ect of concentrationon apparent viscosity. An Arrhenius type equation(Speers & Tung, 1986) generally expresses the e�ect oftemperature on the apparent viscosity at a speci®edshear rate. However, Abdelrahim et al. (1995) foundthat it was not the best for Thermo-¯o starch particu-larly at lower concentrations, and the combined e�ect oftemperature and concentration on the consistency co-e�cient (m) and ¯ow behavior index (n) was evaluatedby a modi®ed Turian approach (Turian, 1964) using amultiple regression analysis. Hydrocolloid solutionsmay also exhibit time-dependent properties mainly thi-xotropy, which means that the apparent viscosity, orconsistency will decrease with time. Abdelrahim,Ramaswamy, Doyon, and Toupin (1994) andRamaswamy and Basak (1992) used a modi®edWeltmann logarithmic model to describe the thixotropicbehavior of CMC solutions and pectin in ¯avoredyoghurt. Muller, Pain, and Villon (1994) have reportedon the modeling of the behavior of non-Newtonianliquids in a continuous ohmic heater. They found thatthe e�ect of non-Newtonian rheological properties wasimportant when the ¯ow behavior index was less than 0.6.

The importance of salt (an ionic species) to be addedto hydrocolloid solutions in order to improve the e�-ciency of ohmic heating, was reported by Yon-gsawatdigul, Park, and Kolbe (1995). Typically, a foodsauce would contain between 0.5% and 1% salt (Kimet al., 1996). However, rheological properties of somehydrocolloids were found to be a�ected by saltconcentration (Kelco, 1994). Data on the rheological

characteristics of hydrocolloid solutions are needed forthe selection of the proper hydrocolloid for the beste�ciency of the ohmic heating process and for theoptimization of continuous thermal processes such as acontinuous ohmic heating.

The objectives of this study were: (1) to evaluate the¯ow behavior of selected hydrocolloid solutions in thepresence of 1% salt, (2) to study the e�ect of temperatureand concentration on the power law (plastic or not)parameters (m and n) and apparent viscosities of thesesolutions, and (3) to determine the shear rate and tem-perature dependency on m and n and the apparent vis-cosities of selected hydrocolloids. Data generated couldbe used to design continuous ohmic heating processes.

2. Materials and methods

2.1. Preparation of solutions

Four types of hydrocolloids were studied: carragee-nan (Grinsted Carrageenan, CL210, Danisco Ingredi-ents Canada, Rexdale, ON, Canada), xanthan(Rhodigel, lot # 9635001, Rhone-Poulenc Food Ingre-dients, Fort Washington, PA, USA), pectin (GrinstedPectin, RS400 lot # 701J547, Danisco IngredientsCanada, Rexdale, ON, Canada), starch (Thermo-¯ostarch, NFPA 0934 lot # LF5919, National Starch andChemical Co., Bridgewater, NJ, USA). Three levels ofconcentrations: carrageenan (1.5%, 1.7% and 1.9%),xanthan (1.6%, 1.8% and 2.0%), pectin (2.3%, 2.5% and2.7%) and starch (3.8%, 4.0% and 4.2%) were tested toobtain an apparent viscosity around 0.2 Pa s at a shearrate of 300 sÿ1 and 20°C so that these solutions couldsubsequently be compared at similar viscosity levels.The selected concentrations of carrageenan, xanthan,pectin and starch were 1.5%, 2.0%, 2.5% and 4.0%, re-spectively. These were used to study the e�ect of tem-perature on rheological characteristics. In each solution,1% salt was added as a typical concentration used infood sauces (Kim et al., 1996).

Batches of 20 l of solution were prepared in duplicate.Dry ingredients (salt and hydrocolloid powders) andwater were accurately weighed. Water, placed in adouble-jacketed tank, was pumped in a closed circuit.Salt was ®rst added to the water through a butter¯yvalve until it was thoroughly dissolved. Then, the pre-weighed quantity of hydrocolloid powder was slowlyadded in the same manner and circulated to obtain atotal dissolution. For carrageenan, xanthan and pectin,the solutions were then heated in the double-jacketedtank ®lled with hot water at 100°C. The solution washeated until it reached 100°C and was cooled to 20°C.Starch solutions were heated at 140°C after dissolutionin the scraped surface heat exchanger of an asepticsystem to allow for complete gelatinization.

158 M. Marcotte et al. / Journal of Food Engineering 48 (2001) 157±167

2.2. Rheological measurement

Rheological properties of hydrocolloid solutions wereevaluated using a rotational viscometer (Rotovisco,Model RV20, Haake Mess-Technik, Karlsruhe, Ger-many) equipped with an M5 OSC measuring head andan MV2 rotor. Solution samples were loaded into thecylindrical cup and allowed to equilibrate at a set-pointtemperature for 20 min in a water bath. Experimentswere carried out in triplicate at four temperatures:20°C; 40°C; 60°C and 80°C. A computer controlledprogram (Rheocontroller, RC20 module, Haake Mess-Technik, Karlsruhe, Germany) in a rotational mode wasused to shear samples at a linear rate from 0 to 300 sÿ1

in 3 min. This was followed by a stress decay at a con-stant shear rate of 300 sÿ1 for 10 min and ®nally by alinearly decreasing shear to 0 during 3 min. Silicone oilstandards (Cannon Instrument Company, State College,PA, USA) were used to calibrate the rheometer. Shearstress (s)±shear rate ( _c) data were gathered as rheo-grams. Apparent viscosities were calculated at 100, 200,

and 300 sÿ1 in Pa s for each combination of hydrocol-loid type, concentration and temperature.

2.3. Data analysis

Flow curves or rheograms were evaluated using thepower law (Eqs. (1) and (2)) and the Herschel±Bulkley(Eq. (3)) rheological models. The e�ect of temperatureon the consistency coe�cient (m) and ¯ow behaviorindex (n) was evaluated using a modi®ed Turian ap-proach (Turian, 1964) through a regression analysis(Eqs. (4) and (5)). The temperature dependency of theapparent viscosity was evaluated using an Arrheniusmodel (Eq. (6)). The time dependency of the shear stresswas determined using the Weltmann model (Eq. (7)).

s � m _cn �1�or

ga �s_c� m _cnÿ1; �2�

Fig. 1. Typical ¯ow behavior of selected hydrocolloids at 20°C.

M. Marcotte et al. / Journal of Food Engineering 48 (2001) 157±167 159

sÿ s0 � m _cn; �3�log m � log m0 ÿ A1T ; �4�n � n0 � A2T ; �5�

ga � g0 exp

�ÿ Ea

RT

�; �6�

s � B1 ÿ B2 log�t�: �7�

3. Results and discussion

3.1. Characterization of ¯ow curves

Typical ¯ow curves for selected hydrocolloids at aconstant temperature of 20°C under dynamic and steadyshearing are presented in Fig. 1. The ¯ow curves of all

samples showed a shear thinning behavior �n < 1� withyield stress for xanthan and carrageenan. Yield stressfor carrageenan solutions was observed only at20°C and 40°C, while ¯ow curves of xanthan exhibitedlarge yield stress values at all temperatures. It should benoted that a stress decay at a steady shear rate wasobserved for carrageenan solutions at lower tempera-tures (20°C and 40°C) only. There was no yield stressfor starch and pectin solutions at any test temperature.The yield value, or `the shear stress that must be ex-ceeded before ¯ow can begin', is consistent with thepseudoplastic behavior and particular suspensoidproperty of xanthan solutions over a wide range oftemperatures. For instance, xanthan gum was reportedto increase the stability of mayonnaise and emulsion(Hibberd, Howe, Mackie, Purdy, & Robins, 1987) aswell as its structure by the formation of larger sizeaggregates (Yilmazer & Kokini, 1992).

Table 1

The power law parameters for pectin (2.5%) and starch (4%) at selected temperatures

Upward curve Downward curve

n m r2 n m r2

20°C

Pectin 0:827� 0:004 0:68� 0:01 0.99 0:82� 0:02 0:68� 0:10 0.99

Starch 0:516� 0:006 1:84� 0:02 0.99 0:59� 0:004 1:58� 0:02 0.99

40°C

Pectin 0:851� 0:019 0:32� 0:03 0.99 0:893� 0:01 0:26� 0:02 0.99

Starch 0:531� 0:003 1:46� 0:08 0.98 0:60� 0:009 1:24� 0:11 0.99

60°C

Pectin 0:913� 0:012 0:13� 0:005 0.98 0:95� 0:01 0:106� 0:01 0.99

Starch 0:558� 0:011 1:03� 0:07 0.99 0:63� 0:01 0:82� 0:05 0.99

80°C

Pectin 0:92� 0:01 0:06� 0:003 0.97 0:99� 0:015 0:03� 0:004 0.99

Starch 0:585� 0:02 0:61� 0:014 0.98 0:65� 0:01 0:65� 0:07 0.99

Table 2

The Herschel±Bulky parameters for xanthan (2%) and carrrageenan (1.5%) at selected temperatures

s0 Upward curve Downward curve

n m r2 n m r2

20°C

Xanthan 36 0:247� 0:005 7:52� 0:67 0.95 0:22� 0:02 7:14� 1:10 0.99

Carrageenan 35 0:332� 0:02 7:64� 0:21 0.97 0:74� 0:04 0:29� 0:009 0.99

40°C

Xanthan 30 0:259� 0:02 6:75� 0:08 0.99 0:26� 0:01 5:77� 0:13 0.99

Carrageenan 4.5 0:338� 0:01 1:99� 0:04 0.98 0:76� 0:05 0:06� 0:004 0.99

60°C

Xanthan 28 0:275� 0:004 5:90� 0:08 0.99 0:35� 0:03 4:75� 0:02 0.99

Carrageenan 0.03 0:874� 0:009 0:02� 0:002 0.98 0:94� 0:02 0:01� 0:001 0.99

80°C

Xanthan 23 0:288� 0:02 5:56� 0:08 0.98 0:37� 0:01 4:54� 0:16 0.99

Carrageenan 0.02 0:879� 0:02 0:02� 0:002 0.92 0:98� 0:01 0:008� 0:0007 0.99


3.2. Rheological models and e�ect of temperature on ¯owparameters

The power law model was applied to characterize the¯ow behavior of pectin and starch, while the ¯ow be-havior of xanthan and carrageenan, which denoted theyield stresses (power law plastic model), was described bythe Herschel±Bulkley model for both upward and

downward curves. Tables 1 and 2 show the means andstandard deviations of the power law and Herschel±Bulkley parameters associated with selected hydrocol-loids at the mid-concentration levels. Coe�cients ofvariation were calculated and for most cases were less than5%, with few exceptions not exceeding 15%. Obtainedhigh values for coe�cient of determination (r2) indicateda good ®t for both models for each hydrocolloid.

Fig. 2. E�ect of temperature on consistency coe�cient (m) of hydrocolloid solutions using the Turian approach.


The ¯ow behavior index of pectin (2.5%) variedbetween 0.82 and 0.99 whereas for starch (4%) it wassituated between 0.51 and 0.65. Lowest values (0.22±0.37) of ¯ow behavior index were observed for xanthan(2%) at all temperatures. The ¯ow behavior indices of

carrageenan (1.5%) were lower at 20°C and 40°C butthe highest i.e., 0.874 and 0.98 at 60°C and 80°C, re-spectively. In their study on the modelling of a contin-uous ohmic heating process for non-Newtonian liquids,Muller et al. (1994) reported that a non-Newtonian

Fig. 3. E�ect of temperature on ¯ow behavior index (n) of hydrocolloid solutions using the Turian approach.


behavior became important when the ¯ow behavior in-dex was less than 0.6. If pectin (2.5%) was to be used forcontinuous ohmic heating, the contribution of the non-Newtonian behavior would not be signi®cant. However,for starch (4%) and xanthan (2%), the contribution ofthe viscosity is expected to be important.

Large di�erences between upward and downwardcurves were found for the ¯ow behavior index of car-rageenan because of the time dependency of rheologicalproperties. The intercept value (B1) and the slope (B2),

based on the Weltmann model (Weltmann, 1943), werefound to be 96.8 and 26.3 at 20°C and 15.9 and 3.3 at40°C for carrageenan.

The Turian approach showed a decrease in consis-tency coe�cient at higher temperatures with an in-crease in ¯ow behavior index (Figs. 2 and 3) for allhydrocolloids. Values of Turian parameters are tabu-lated in Table 3. These values can be used as inputs forpredicting the ¯ow behavior in a continuous ohmicheater.

Table 3

The Turian parameters for selected hydrocolloids

Sample log m0 A1 n0 A2

Carrageenan (1.5%)

Upward 1.89 )0.049 0.06 0.0108

Downward )0.12 )0.027 0.63 0.0044

Pectin (2.5%)

Upward 0.18 )0.017 0.79 0.0017

Downward 0.30 )0.022 0.74 0.0038

Starch (4%)

Upward 0.46 )0.008 0.49 0.0012

Downward 0.34 )0.007 0.57 0.0011

Xanthan (2%)

Upward 0.92 )0.002 0.23 0.0007

Downward 0.91 )0.003 0.16 0.0027

Fig. 4. Arrehnius plots for selected hydrocolloids.


3.3. Temperature dependency of apparent viscosity

The e�ect of temperature on the viscosity of hydro-colloids must also be known as, in most continuousheating processes, they will be subjected to a range oftemperatures. The Arrhenius relationship has been usedby many researchers (Ramaswamy & Basak, 1991; Rao& Anantheswaran, 1982; Hernandez, Chen, Johnson, &Carter, 1995) to describe the temperature dependency ofrheological parameters. In this study, the Arrheniusapproach was used to compare changes in apparentviscosity of selected hydrocolloids at di�erent tempera-tures (Fig. 4).

It is evident from the curves that there was a minortemperature in¯uence for xanthan and accordingly thelowest activation energies (Ea 100 sÿ1 � 1:75 kJ=molewith r2 � 0:97, Ea 200 sÿ1 � 1:33 kJ=mole with r2 �0:95, and Ea 300 sÿ1 � 1:08 kJ=mole with r2 � 0:92)were obtained. The apparent viscosity of xanthan wasmostly a�ected by the shear rate. As mentioned earlier,xanthan was the only hydrocolloid, which exhibited asigni®cant yield stress for all measuring temperatures.This means that xanthan solutions have the ability toretain their gel network and viscosity at higher tem-peratures. An investigation (Kelco, 1994) also showedthat xanthan gum solutions maintain their viscositiesuntil a speci®c `melting temperature' is reached. Theirdata showed that the melting temperature in thepresence of 0.5% salt is greater than 80°C and anaddition of salt concentration (up to 5%) increases themelting temperature to over 110°C. A structural studyby Sanderson (1981) showed that xanthan exhibited

the viscosity stability at elevated temperatures, high at-rest or low-shear viscosity accompanied with yieldvalue as a result of weak intermolecular associations,even at very low hydrocolloid concentration and highpesudoplasticity. This results from the progressivealignment of the rigid molecules with the shearingforce.

Carrageenan solutions, which only denoted theyield stresses at 20°C and 40°C, showed the highestlevel of activation energies indicating a lower resis-tance at elevated temperatures. Activation energiesranged from 55 kJ/mole with r2 � 0:95, 49 kJ=molewith r2 � 0.95 and 45 kJ/mole with r2 � 0:95 at 100,200 and 300 sÿ1, respectively. Pectin showed lowertemperature sensitivity than carrageenan but higherthan xanthan. Activation energies for pectin were 27kJ/mole with r2 � 0:99 at 100 sÿ1, 26 kJ=mole withr2 � 0:99 at 200 sÿ1 and 26 kJ/mole with r2 � 0:99 at300 sÿ1. The activation energy values for starch werelower than pectin solutions, ranging from 11, 10, and9.9 kJ/mole with r2 � 0:93 at 100, 200 and 300 sÿ1,respectively. It should be noted that a decrease inactivation energy is always associated with an increasein the shear rate.

3.4. E�ect of concentration on ¯ow parameters

The relationship between rheological parameters,evaluated at 20°C, and concentration is shown inTable 4. The power law model described the upward anddownward curves for starch and pectin and the Herschel±Bulkley model was used to characterize the ¯ow behavior

Table 4

E�ect of concentration on upward and downward curves for selected hydrocolloids at 20°C

so Upward curve Downward curve

n m r2 n m r2

Xanthana

1.6% 29 0:276� 0:004 3.46�0.06 0.98 0:41� 0:01 2:93� 0:15 0.99

1.8% 33 0:259� 0:007 5.35�0.19 0.97 0:34� 0:01 3:31� 0:13 0.99

2% 36 0:241� 0:003 7.26�0.12 0.98 0:33� 0:007 4:05� 0:09 0.99

Carrageenana

1.5% 33 0:338� 0:010 7.69�0.18 0.97 0:81� 0:03 0:28� 0:02 0.99

1.7% 45 0:327� 0:008 15.3�0.29 0.95 0:69� 0:01 1:17� 0:10 0.99

1.9% 48 0:281� 0:008 21.3�0.94 0.99 0:60� 0:008 2:03� 0:08 0.99

Starchb

3.8% ) 0:600� 0:013 1.04�0.03 0.99 0:64� 0:02 1:18� 0:06 0.99

4% ) 0:514� 0:021 1.89�0.08 0.98 0:62� 0:01 1:51� 0:04 0.99

4.2% ) 0:494� 0:026 2.72�0.27 0.98 0:58� 0:03 2:11� 0:14 0.99

Pectinb

2.3% ) 0:820� 0:015 0.56�0.06 0.99 0:83� 0:02 0:52� 0:04 0.99

2.5% ) 0:821� 0:007 0.71�0.04 0.99 0:82� 0:02 0:73� 0:09 0.99

2.7% ) 0:823� 0:005 0.81�0.04 0.99 0:79� 0:007 0:93� 0:07 0.99

a Herschel±Bulkyley model.b Power law model.


for xanthan and carrageenan. It is evident that concen-tration had a considerable e�ect on the ¯ow behavior ofhydrocolloid solutions. All samples at lower concentra-tion displayed a lower consistency coe�cient (m) and anincrease in concentration was accompanied with a pro-gressive upward shifting of the curve. The apparent vis-cosity (ga) depended on both m and n within theconcentration ranges studied: the ¯ow behavior indexeswere only marginally di�erent and did not show anyspeci®c trend. However, a shear thinning behavior wasobserved for all selected hydrocolloids. Similar trendswere observed with the downward curves.

3.5. E�ect of concentration and shear rate on apparentviscosity

The e�ect of shear rate and concentration at 20°C onapparent viscosity is shown in Fig. 5. It should be noted

that each curve represents the mean of six measure-ments (two separate batches � three rheological mea-surements) using the power law and Herschel±Bulkley models to express the results. As expected, theviscosity of all samples increased with increasing con-centration.

The concentration e�ect was quite dominant forcarrageenan solution and showed 88% and 112% in-creases in apparent viscosity, as the concentration wasincreased from 1.5% to 1.7% and 1.9%, respectively.Xanthan was less a�ected by concentration and dis-played 43% and 79% increases in apparent viscosity, asthe concentration changed from 1.6% to 1.8% and 2%.The apparent viscosity of pectin increased by 20% and39% as the concentration increased from 2.3% to 2.5%and 2.7%. As compared to other hydrocolloids, starchshowed an intermediate behavior as a function of con-centration. Apparent viscosities were increased by 22%

Fig. 5. E�ect of concentration and shear rate on apparent viscosity.


and 59% as concentration increased from 3.8% to 4%and 4.2%.

Increasing the shear rate from 100 to 200 and 300 sÿ1

resulted in a decrease of apparent viscosity of carra-geenan by 37% and 52%. Xanthan was mostly a�ectedby the shear rate and showed 39% and 55% reductions inapparent viscosity as the shear rate increased from 100to 200 and 300 sÿ1. When increasing shear rate up to 200and 300 sÿ1 for pectin, the apparent viscosity of pectindecreased by 11% and 17%. For starch, shifting theshear rate from 100 to 200 and 300 sÿ1 resulted in lossesof 24% and 36% in apparent viscosities.

4. Conclusions

Rheological properties of carrageenan, pectin, starchand xanthan solutions were investigated at varioustemperatures (20±80°C), concentrations (carrageenan1.5%, 1.7% and 1.9%; pectin 2.3%, 2.5% and 2.7%;starch 3.8%, 4% and 4.2%; xanthan 1.6%, 1.8% and 2%)and shear rate 100, 200 and 300 sÿ1 in the presence of1% salt. For the study of the e�ect of temperature onrheological properties, only one concentration of eachhydrocolloid in water solutions was selected (carragee-nan, 1.5%; pectin, 2.5%; starch, 4% and xanthan, 2%) toobtain an apparent viscosity of 0.2 Pa s at 300 sÿ1 and20°C.

A shear thinning behavior was observed for all se-lected hydrocolloids for the upward and downwardcurves of rheograms. Concentration, temperature andshear rate e�ects on rheological properties were di�erentdepending on the type of hydrocolloids. Flow curveswere well described by the power law model for starchand pectin. Yield stresses were observed for carrageenanat 20°C and 40°C only and for xanthan at all tempera-tures. For these, Herschel±Bulkely models were moreappropriate. If starch (4%) and xanthan (2%) were to beused as carriers during continuous ohmic heating, it isexpected that there will be an important contribution ofthe non-Newtonian behavior because their n values wereless than 0.6 at all temperatures. Pectin (2.5%) exhibitedvalues of ¯ow behavior index greater that 0.6 at alltemperatures. At low temperature (20°C and 40°C, nvalues for carrageenan were low whereas at high tem-peratures (60°C and 80°C), the ¯ow behavior index washigher than 0.9.

The temperature dependency of m and n was modeledusing a modi®ed Turian approach. Both the consistencycoe�cient (m) and the ¯ow behavior index (n) weresensitive to changes in temperature and concentration.As the temperature of the solution increased, m de-creased and n increased. As the concentration of thesolution was increased, m increased and n decreased.

The concentration e�ect on apparent viscosity wasmore important for starch and carrageenan and less for

the pectin and xanthan. It was quite dominant for car-rageenan solutions. Xanthan was less a�ected by con-centration but mostly by the shear rate. Carrageenansolutions showed the highest level of activation indi-cating a lower resistance of decreasing the apparentviscosity at elevated temperatures. Pectin resulted in alower temperature sensitivity of the apparent viscositythan carrageenan and higher than xanthan.

A time dependency was found only for carrageenanand a modi®ed Weltmann model was used to evaluatethe e�ect of time on the shear stress.

Acknowledgements

The authors would like to thank sincerely NicolasElazhary, Kim Ouellet and Kathia Charland for theirtechnical assistance in carrying out the experimentalwork.

References

Abdelrahim, K. A., & Ramaswamy, H. S. (1995). High temperature/

pressure rheology of carboxymethyl cellulose (CMC). Food Re-

search International, 28, 285±290.

Abdelrahim, K. A., Ramaswamy, H. S., Doyon, G., & Toupin, C. J.

(1994). Rheology of carboxymethyl cellulose as in¯uenced by

concentration and temperature. International Journal of Food

Science and Technology, 29, 243±253.

Abdelrahim, K. A., Ramaswamy, H. S., & van de Voort, F. R. (1995).

Rheological properties of starch solutions under aseptic processing

temperatures. Food Research International, 28, 473±480.

Berry, M. F. (1989). Predicting the fastest residence time. First

International Conference on Aseptic Processing Technologies.

Indianapolis, IN, 19±21 March.

Dutta, B., & Sastry, S. K. (1990). Velocity distributions of food

particle suspensions in holding tube ¯ow: Experimental and

modeling studies on average particle velocities. Journal of Food

Science, 55, 1448±1453.

Hernandez, E., Chen, C. S., Johnson, J., & Carter, R. D. (1995).

Viscosity changes in orange juice after ultra®ltration and evaporation

(pp. 387±395). G.B.: Elsevier.

Hibberd, D. I., Howe, A. M., Mackie, A. R., Purdy, P. W., & Robins,

M. M. (1987). Measurements of creaming pro®les in oil-in-water

emulsions. In E. Dickenson (Ed.), Food Emulsions and Foams.

London: The Royal Society of Chemistry.

Kelco. (1994). Xanthan gum natural biogum for scienti®c water control

(5th ed.). USA.

Khalaf, W. G., & Sastry, S. K. (1996). E�ect of ¯uid viscosity on the

ohmic heating rate of solid±liquid mixtures. Journal of Food

Engineering, 27, 145±158.

Kim, H. J., Choi, Y. M., Yang, T. C. S., Taub, I. A., Tempest, P.,

Skudder, P., Tucker, G., & Parrot, D. L. (1996). Validation of

ohmic heating for quality enhancement of food products. Food

Technology, 50(5), 253±261.

Lalande, M., Leuliet, J. C., & Maingonnat, J. F. (1991). HTST

processing of viscous liquid foods. In P. Zeuthen et al. (Eds.),

Processing and quality of foods (Vol. 1, pp. 123±127). New York:

Elsevier.

Lee, J. J., & Singh, R. K. (1991a). Process parameter e�ects on particle

residence time in a vertical scraped surface heat exchanger. Journal

of Food Science, 56, 869±870.


Lee, J. H., & Singh, R. K. (1991b). Particle residence time distributions

in a model horizontal scraped surface heat exchanger. Journal of

Food Process Engineering, 14, 125±146.

Lee, J. H., & Singh, R. K. (1993). Residence time distribution

characteristics of particle ¯ow in a vertical scraped surface heat

exchanger. Journal of Food Engineering, 18, 413±424.

McCoy, S. C., Zuritz, C. A., & Sastry, S. K. (1987). Residence time

distribution of simulated particles in a holding tube. ASAE Paper

No. 87-6536.

Muller, F. L., Pain, J. P., & Villon, P. (1994). On the behaviour of non-

Newtonian liquids in collinear ohmic heaters. In Proceedings of the

10th international heat transfer conference. Freezing, melting,

internal forces convection and heat exchangers (Vol. 4, pp. 285±

290). Brighton, UK.

Palmer, J. A., & Jones, V. A. (1976). Prediction of holding times for

continuous thermal processing of power law ¯uids. Journal of Food

Science, 41, 1233±1244.

Ramaswamy, H. S., & Basak, S. (1991). Rheology of stirred yogurt.

Journal of Texture Studies, 22, 231±241.

Ramaswamy, H. S., & Basak, S. (1992). Time dependent stress decay

rheology of stirred yogurt. International Dairy Journal, 1, 17±31.

Rao, M. A. (1977). Rheology of liquid foods ± A review. Journal of

Texture Studies, 8, 135±168.

Rao, M. A. (1986). Rheological properties of ¯uid foods. In M. A.

Rao, & S. S. H. Rizvi, Engineering properties of foods (pp. 1±47).

New York: Marcel Dekker.

Rao, M. A. (1992). Rheology of ¯uids in food processing. Food

Technology, 46(2), 116±126.

Rao, M. A., & Anantheswaran, R. C. (1982). Rheology of ¯uids in

food processing. Food Technology, 36(2), 116±126.

Rao, M. A., & Kenny, J. F. (1975). Flow properties of selected food

gums. Canadian Institute Food Science Technology Journal, 8(3),

142±148.

Rha, C. (1978). Rheology of ¯uid foods. Food Techology, 32(7),

77±82.

Sanderson, G. R. (1981). Polysaccharides in food. Food Technology,

7(4), 50±56.

Speers, R. A., & Tung, M. A. (1986). Concentration and temperature

dependence of ¯ow behavior of xanthan gum dispersions. Journal

of Food Science, 51, 96±98, 103.

Turian, R. M. (1964). Thermal phenomena and non-Newtonian visco-

metry. Ph. D. Thesis. Madison: University of Wisconsin.

Weltmann, R. N. (1943). Breakdown of thixotropic structure as

function of time. Journal of Applied Physics, 14, 343±350.

Yilmazer, G., & Kokini, J. L. (1992). E�ect of salt on the

stability of propylene glycolalginate/xanthan gum/polysorbate-60

stabilized oil-in-water emulsions. Journal of Texture Studies, 23,

195±213.

Yongsawatdigul, J., Park, J. W., & Kolbe, E. (1995). Electrical

conductivity of Paci®c Whiting surimi paste during ohmic heating.

Journal of Food Science, 60, 922±925, 935.


evaluation of rheological properties of selected salt enriched food hydrocolloids

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