Rheological properties of mucilage extracted from Alyssum homolocarpum seed as a new source of thickening agent

Journal of Food Engineering 91 (2009) 490–496

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Rheological properties of mucilage extracted from Alyssum homolocarpum seed as a new source of thickening agent A. Koocheki a, S.A. Mortazavi a, F. Shahidi a, S.M.A. Razavi a, A.R. Taherian b,* a b

Department of Food Science and Technology, Ferdowsi University of Mashad (FUM), P.O. Box: 91775-1163, Mashhad, Iran Food Research and Development Centre, Agriculture and Agri-Food Canada, 3600 Casavant West, St-Hyacinthe, Quebec, Canada, J2S-8E3

a r t i c l e

i n f o

Article history: Received 22 July 2008 Received in revised form 20 September 2008 Accepted 25 September 2008 Available online 7 October 2008 Keywords: Alyssum homolocarpum Rheology Salt Sugar pH Temperature

a b s t r a c t The rheological properties of Alyssum homolocarpum seed mucilage as influences of gum concentrations (1.5%, 2%, 2.5%, 3%, 3.5% and 4%) and temperatures (5, 25, 45, and 65 °C) were investigated. Effects of pH (3–9), salts concentrations (CaCl2 and MgCl2 from 0 to 0.049 M; NaCl and KCl from 0 to 0.17 M) and sucrose concentration (0% to 40%) were also evaluated at 3% weight/weight (w/w) of A. homolocarpum seed gum. The power law model well described the rheological behavior of the A. homolocarpum seed mucilage solutions with high determination coefficients, R2. The gum exhibited non-Newtonian, pseudoplastic behavior at all temperatures and concentrations. An increase in concentration, decreased the flow behavior indices, n, and increased the consistency coefficients; k. Increasing temperature decreased the viscosity and pseudoplasticity. The temperature effect was described using Arrhenius equation and as the activation energy (Ea) decreased the gum concentration increased. The apparent viscosity varied according to variation in pH, the highest viscosity was obtained at pH of 9 and the lowest at pH of 3, nevertheless there were no significant difference between pH ranging from five to nine. The apparent viscosity decreased with addition of Na+, K+, Ca2+ (<0.01 M) and Mg2+ (<0.039 M), whereas it increased with the addition of Ca2+ and Mg2+ at concentration higher than 0.01 M and 0.039 M, respectively. An increase in concentration was accompanied with an increase in pseudoplasticity (increase in k and decrease in n). Ó 2008 Elsevier Ltd. All rights reserved.

1. Introduction Hydrocolloids btained from different sources are widely used in food systems for various purposes such as thickening and gelling agents, stabilizers, and texture modifiers. From a chemical point of view, they are polysaccharides (gum arabic, guar gum, carboxymethylcellulose, carragenan, starch, pectin) or protein (gelatin). Hydrocolloids are polymers interacting strongly with water. Their caloric value is quite low and making them useful, particularly, in the development of diet foods. Even though they do not have direct influence on the taste and flavor of foodstuffs, but they are significantly effective on gel formation, water retention, emulsifying and aroma retention (Bai et al., 1978; Krumel and Sarkar, 1975; Speers and Tung, 1986). Hydrocolloids are also used in the food industry because of their ability to modify the rheological and functional properties of food systems. Many food products such as breads, sauces, syrups, ice cream, instant foods, beverages and ketchups might have hydrocolloids in their formulations (Rosell et al., 2001; Dogan and Kaya-

* Corresponding author. Tel.: +1 450 768 3329; fax: +1 450 773 8461. E-mail address: [email protected] (A.R. Taherian). 0260-8774/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2008.09.028

cier, 2004; Kayacier and Dogan, 2006; Taherian et al., 2007; Koocheki et al., 2008a). Starches, cellulose derivatives, are extracted from seaweeds, plant exudes, seed gums, plant extracts and microbial gums. Starches are commonly used in processed foods and other important industrial processes and products (Lillford and Norton, 1991; Whistler, 1993). Polysaccharides from plant extracts are the interesting source of additives for several industries and in particular for the food industries. These polymers have the advantage of being regarded as totally natural for many consumers (Lai et al., 2000). Mucilages and plant polysaccharidic exudates represent an easy and cheap access to the stock of polysaccharides and most of them are important in food formulation. Alyssum is a genus of about 100–170 species of flowering plants in the family of Cruciferae, native to Egypt, Arabia, Iraq, Iran and Pakistan. Alyssum homolocarpum has two rounds, broad, pale pink and very narrowly margined seeds with 1.5–2.5 mm long. Alyssum homolocarpum seed is known under the local name of Qodume shirazi, or Toderi in Iran. Qodume is produced mainly for its mucilage content and the seeds adsorb water quickly when soaked in water and produce a sticky, turbid and tasteless liquid. The seeds are known to contain a large amount of mucilaginous substance (Koocheki et al., 2008b) and have been used as a traditional herbal medicine in Iran. Qodume seeds are especially recommended by

A. Koocheki et al. / Journal of Food Engineering 91 (2009) 490–496

herbalists for dry coughs, whooping cough, asthma, lung infections, demulcent and kidney stone (Amin, 2005). The seeds have been used for hundreds of years in traditional Iranian medicinal prescriptions to be soaked in water and swallowed at once. Because of its pharmacological effects, foods fortified with A. homolocarpum mucilage gum may have a superior consumer acceptance. Furthermore, the rheological behavior of hydrocolloids is of special importance when they are used to modify the textural attributes of food (Patmore et al., 2003). It is also well recognized that rheological properties of fluid food should be carefully taken into account for designing and modeling purposes. Food hydrocolloids are compositionally and structurally complex materials and can exhibit a wide range of rheological properties at different conditions. Calculations in the processes involving fluid flows such as pump sizing, extraction, filtration, extrusion and purification requires knowledge of rheological data, and the rheology of the product is necessary for the analysis of flow conditions in various food processes (Marcotte et al., 2001a,b). The rheological properties of hydrocolloids in solution depends on many factors: concentration of the active compound, temperature, degree of dispersion, dissolution, electrical charge, previous thermal and mechanical treatment, presence or absence of other lyophilic colloids, and the presence of electrolytes and non-electrolytes (Marcotte et al., 2001a,b; Rao and Anantheswaran, 1982). The demand for hydrocolloids with specific functionality has been recently increased and food scientists and technologists are always searching for new sources of polysaccharides. Accordingly, there is still place for the new sources of plant hydrocolloids to meet this demand (Williams and Phillips, 2000; Yadav et al., 2007). Although A. homolocarpum mucilage has been used for centuries in Iran but no scientific work has been done on its functional and rheological properties. Thus, the objectives of this study were to first evaluate the flow behavior of gum extracted from A. homolocarpum, as a new source of hydrocolloid gum, and second to study the effect of gum concentration, temperature, solution pH, sucrose concentrations and salt concentrations on steady state shear viscosities of this solutions, and third to determine the shear rate and temperature dependencies of this gum.

491

and was dispersed in deionized water. The dispersion stored overnight at 4 °C with continuous stirring. Ultimately, the dispersion was dried in a conventional oven (overnight at 45 °C), milled and sieved using a mesh 18 sifter. 2.3. Rheological measurement Rheological measurements were carried out using a rotational viscometer (Bohlin Model Visco 88, Bohlin Instruments, UK) equipped with C14, C25 or C30 measuring spindles (based on viscosity of dispersion) and a heating circulator (Julabo, Model F12MC, Julabo Labortechnik, Germany). For each test, approximately 15–25 ml sample was transferred to sample compartment (bob and cup) following by 3 min pre-shearing at 100 s1 to obtain uniform solution. The instrument was programmed to set temperature and equilibrate for 10 min followed by two-cycle shear in which the shear rate was increased linearly from 0 to 300 s1 in 3 min and immediately decreased to 0 s1 in the next 3 min. The flow behavior index (n) and consistency index (k) values were computed by fitting the power law model (Eq. (1)):

s ¼ kc_ n

ð1Þ

where s is the shear stress (Pa), (c_ ) is the shear rate (s1), k is the consistency coefficients (Pa sn) and n is the flow behavior index (dimensionless). 2.4. Evaluation of temperature dependency of gum solutions Gum solutions were prepared at concentrations of 1.5%, 2%, 2.5%, 3%, 3.5% and 4% (w/w) by dispersing the required amount of gum in deionized water (Milli-Q, Millipore, Bedford, USA), under slow stirring at room temperature, and stored for 18 h at 4 °C for complete hydration prior to assessment. Prepared samples were loaded into the cup and maintained for 10 min at measurement temperatures of 5, 25, 45 or 65 °C. The temperature dependency of consistency coefficient (indicator of the viscous nature of the sample) was assessed by fitting the Arrhenius model (Eq. (2)) as was suggested by Sengul et al., 2005:

k ¼ k0  eðEa =RTÞ

ð2Þ

2. Materials and methods 2.1. Materials The Qodume shirazi seed was obtained from the local medical plant market, Mashad, Iran. The seeds were manually cleaned to remove all foreign matter such as dust, dirt, stones, chaff, immature and broken seeds. All chemicals used in this study were of analytical grade and purchased from Merck (Darmstadt, Germany) company. 2.2. Gum extraction Qodume shirazi seed gum was prepared according to the revised method of our pervious work (Koocheki et al., 2008b). In brief, Qodume shirazi seed gum was dispersed in preheated deionized water (Milli-Q, Millipore, Bedford, USA) at a water/seed ratio of 60:1. The pH was monitored continuously and adjusted at seven using 0.1 mol/L NaOH and/or HCl at a constant temperature of 55 ± 1.0 °C. The seed-water slurry was stirred continuously with a mechanical mixing paddle throughout the entire extraction period (1 h). The seeds were discarded, and the rest of the supernatant was subjected to ethanol precipitation (97% ethanol/mixture ratio of 3:1). The precipitate was then kept in the solvent for approximately 10 min with occasional gentle stirring. Later, the precipitate was recovered using a sieve to allow the drainage of excess solvent

where k0 is the proportionality constant (or consistency coefficient at a reference temperature, Pa sn), Ea the activation energy (J/mol), R the universal law gas constant (J/mol K), and T the absolute temperature (°K). 2.5. Determination of flow properties at different pH The viscosity and flow properties were measured for 3% Qodume shirazi seed gum solutions with pH ranging from 3.0 to 9.0 (2.0 increment, adjusted using 0.1 mol/L NaOH and HCl) at different shear rates and constant temperature of 25 °C. 2.6. Examination of viscosity at different salt concentrations Hydrocolloid solutions were prepared at 3%. Monovalent (NaCl and KCl) and divalent (CaCl2 and MgCl2) salts were added to give final concentrations of 0.035 to 0.172 M and 0.01 to 0.049 M, respectively. Viscosity measurements were performed at a shear rate of 46.16 s1 and temperature of 25 °C. 2.7. Assessment of flow properties at selected sugar concentrations Sugar was dissolved over a range of 0–40% into the solutions 3% gum. The flow behavior index (n) and consistency index (k) values were measured at 25 °C.

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3. Results and discussion 3.1. Effect of concentration and temperature on flow properties The consistency coefficient (k) and flow behavior index (n) values obtained by fitting the shear stress versus shear rate data to the power law model as influences of gum concentration and temperature are shown in Table 1. The coefficients of determination (R2) were 0.99 or higher for all tested samples indicating the appropriateness of the power low model to describe the flow properties of the A. homolocarpum seed gum. Examination of flow properties as a function of shear rate also designated the non-Newtonian behaviors for different concentrations and temperatures. The values of flow behavior indices, n, were less than 1, indicating the pseudoplastic (shear thinning) nature of the gum at different measuring conditions. Increasing the gum concentration decreased the flow behavior index values and increased the consistency coefficient. Temperature, on the other hand, indicated an inverse effect on power law parameters as flow behavior index increased and consistency coefficient decreased by increasing the temperature. These phenomena are in agreement with the work done by Marcotte et al. (2001a,b) on xanthan gum, carrageenan, pectin and starch. Mothe and Rao (1999), Vardhanabhuti and Ikeda (2006), and Farhoosh and Riazi (2007) also observed similar experimental behavior for cashew gum, monoi and salep. Furthermore, no differences were found between the flow behaviors indices (n) of the upward and downward curves and ranged between 0.33 to 0.42 and 0.32 to 0.43, respectively. Comparatively, the flow behavior index (n) of A. homolocarpum seed gum was lower than CMC, salep, carrageenan, pectin and

Table 1 The power law parameters for A. homolocarpum seed gum solutions at different concentrations and temperatures. Temperature (°C) Upward curve k

n

R2

k

n

R2

1.5% 5 25 45 65

2.83 ± 0.43 2.61 ± 0.53 2.14 ± 0.73 1.48 ± 0.21

0.39 ± 0.02 0.39 ± 0.04 0.41 ± 0.04 0.42 ± 0.04

0.99 0.99 0.99 0.99

2.86 ± 0.27 2.85 ± 0.01 2.77 ± 0.31 1.47 ± 0.16

0.40 ± 0.01 0.40 ± 0.01 0.41 ± 0.01 0.43 ± 0.03

0.99 0.99 0.99 0.99

2% 5 25 45 65

6.43 ± 0.99 4.46 ± 0.52 4.10 ± 0.84 3.32 ± 0.26

0.38 ± 0.02 0.38 ± 0.03 0.39 ± 0.02 0.39 ± 0.01

0.99 0.99 0.99 0.99

6.54 ± 0.41 4.60 ± 0.18 3.93 ± 0.63 2.95 ± 0.36

0.38 ± 0.01 0.38 ± 0.02 0.38 ± 0.01 0.41 ± 0.05

0.99 0.99 0.99 0.99

2.5% 5 25 45 65

10.42 ± 0.19 8.99 ± 0.35 7.72 ± 0.62 6.17 ± 0.54

0.36 ± 0.02 0.36 ± 0.03 0.37 ± 0.01 0.38 ± 0.01

0.99 10.55 ± 0.20 0.36 ± 0.01 0.99 9.20 ± 0.17 0.35 ± 0.02 0.99 7.93 ± 0.11 0.36 ± 0.01 0.99 5.61 ± 0.33 0.39 ± 0.01

0.99 0.99 0.99 0.99

3% 5 25 45 65

14.82 ± 0.45 11.24 ± 0.12 9.88 ± 0.65 8.91 ± 0.60

0.35 ± 0.02 0.36 ± 0.01 0.37 ± 0.01 0.38 ± 0.01

0.99 15.25 ± 0.67 0.34 ± 0.01 0.99 12.04 ± 0.10 0.35 ± 0.01 0.99 9.38 ± 0.57 0.36 ± 0.01 0.99 7.45 ± 0.23 0.38 ± 0.01

0.99 0.99 0.99 0.99

3.5% 5 25 45 65

23.12 ± 0.70 19.25 ± 0.28 18.27 ± 0.78 15.47 ± 0.66

0.34 ± 0.03 0.34 ± 0.02 0.36 ± 0.01 0.36 ± 0.07

0.99 0.99 0.99 0.99

24.03 ± 0.57 18.33 ± 0.26 14.84 ± 0.53 13.36 ± 0.75

0.33 ± 0.01 0.34 ± 0.01 0.34 ± 0.02 0.37 ± 0.02

0.99 0.99 0.99 0.99

4% 5 25 45 65

29.80 ± 0.24 26.30 ± 0.35 22.19 ± 0.37 21.51 ± 1.37

0.33 ± 0.02 0.33 ± 0.01 0.36 ± 0.05 0.37 ± 0.07

0.99 0.99 0.99 0.99

31.07 ± 1.13 27.23 ± 0.95 22.22 ± 1.96 21.86 ± 1.51

0.32 ± 0.02 0.33 ± 0.02 0.35 ± 0.06 0.36 ± 0.06

0.99 0.99 0.99 0.96

4

3

lnk (Pa. sn)

Concentration

Downward curve

starch at similar concentrations and temperatures, indicating that this gum is more pseudoplastic. Conversely, n, was higher than guar and xanthan gum (Riazi et al., 2006; Marcotte et al., 2001a). The low values of flow behavior indices represent the great departure of flow from the Newtonian behavior and like many other shear-thinning hydrocolloids, they have a high viscosity at law shear rates which decreases dramatically as the shear is increased. It has been reported that a non-Newtonian behavior became important when the flow behavior index is less than 0.6 (Muller et al., 1994; Chhinnan et al., 1985). This property is important, particularly, in formulation of oil in water emulsions and it means that the droplets are prevented from gravitational separation, but that the emulsion still flows easily when poured from a container as it has been reported by Taherian et al. (2007). In addition, gum solution with high value of flow behavior index (n) tends to feel slimy in the mouth (Szczesniak and Farkas, 1962). Thus, for a provision of a high viscosity and good mouth feel, hydrocolloid characterized by a low n value would be required (Marcotte et al., 2001a). The effect of temperature on flow behavior index (n) was negligible until 45 °C at gum concentration of 1.5% and 2%. As a result, 4% of gum solution at 5 °C was more pseudoplastic among other samples (Table 1). The values of consistency coefficient (k) vary between 1.48 to 29.80 Pa sn for upward and 1.47 to 31.07 Pa sn for downward curves as gum increases from 1.5% to 4% and the temperature from 5 to 65 °C. A decrease in consistency coefficient was observed with increasing temperature, indicating a decrease in apparent viscosity at higher temperatures (Table 1, Fig. 1). In addition, the consistency coefficients increased with the concentration of hydrocolloids at all temperatures. These results also are in agreement with the other studies by Vardhanabhuti and Ikeda (2006), Farhoosh and Riazi (2007) and Marcotte et al. (2001a,b) who also reported that temperature had a large effect on the consistency coefficient of different hydrocolloids and the consistency coefficient increased with the concentration of starch, pectin, carrageenan and xanthan gum. Nevertheless, A. homolocarpum seed gum has lower k value compare to carrageenan and xanthan at similar concentrations and higher value compare to that of pectin, starch and rounded-tuber salep (Marcotte et al., 2001a; Farhoosh and Riazi, 2007). Gomez-Diaz and Navaza (2003) related the increase of k values to the increase of water binding capacity. Wanchoo et al. (1996) reported that the coefficient k is a strong function of the concentration of the solution and the temperature, whereas index n does not

2 1.5% 2% 2.5% 3% 3.5% 4%

1

0 2.50

2.80

3.10

3.40

3.70

4.0

1000/T (1/K) Fig. 1. Consistency index as a function of temperature for A. homolocarpum seed gum solutions at concentrations of 1.5–4%.

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have a strong dependency on the concentration and temperature of the polymeric solutions. The relationship between apparent viscosity (ga) and shear rate of different gum concentrations at 25 °C is shown in Fig. 2a. It is evident that the apparent viscosity of all samples decreased with increasing shear rate as well as apparent direct dependency of the gum concentration. After a sharp reduction the viscosity change was smoothened at high shear rates. Shear thinning is the result of an orientation effect. As shear rate is increased, the long chain of polymer molecules and randomly positioned chains become increasingly aligned in the direction of flow resulting in less interaction between adjacent polymer chains. The values of viscosity at the weak shear rate could permit to appreciate the consistency of the product in the mouth (Morris and Taylor, 1982), while the values of viscosity at the high shear rate allow to understand the viscosity of the product during certain processing operations such as pumping and spray drying. Accordingly, as the viscosity of solution decreases as shear rate increases, pumping efficiency increases as pump flow rate increases (Race, 1991). The concentration of polysaccharide in solution is known to affect directly the viscosity and the degree of pseudoplasticity (Sutherland, 1994). Increasing the A. homolocarpum hydrocolloid concentration increased the viscosity as shown in Fig. 2a. This is due to the higher solid contents which generally cause an increase in the viscosity resulting from mainly molecular movements and interfacial film formation (Maskan and Gogus, 2000).

Apparent viscosity (Pa.s)

a

4 1.5%

2%

2.5%

3%

3.5%

4%

3

2

1

Fig. 2b shows the decrease of viscosity for 3% gum solution as an influence of temperature. Similar results were obtained for the other concentrations. This effect, according to Garcia-Ochoa and Casas (1992), is reversible and it is due to the interactions of the molecules in solution which become weaker at higher temperature. Hassan and Hobani (1998) also reported that the viscosity of a solution is a function of the intermolecular forces and water solute interactions that restrict the molecular motion. Therefore, as temperature increases, the thermal energy of the molecules increases and the intermolecular distances raise as a result of thermal expansion. These results also are in agreement with the previous published studies (Vardhanabhuti and Ikeda, 2006; Marcotte et al., 2001a; Feng et al., 2007), representing the identical outcomes. The temperature dependence of the viscosity, shown in Table 2, was assessed by applying the Arrhenius-type model (Barbosa Canovas and Peleg, 1983; Singh and Eipeson, 2000). Activation energy (Ea) for the flow process is related to chain flexibility (Nielsen, 1977) and high R2 values indicate that the apparent viscosity of solutions in relation with temperature obey the Arrhenius type equation. It can be seen that the Ea values for A. homolocarpum hydrocolloid decreased from 8229.81 J/mole at 1.5% concentration to 4520.57 J/mole at 4% concentration, meaning that solution with lower concentration had the grater viscosity dependency to the temperature. A higher Ea value signifies a more rapid change in viscosity (Medina-Torres et al., 2000). The outcomes imply that temperature control will be more critical for A. homolocarpum hydrocolloid with 1.5% concentration. Furthermore, these results could be explained by the Eyring’s reaction rate theory of viscosity (Eyring 1936). The Eyring theory postulates that the activation energy of a flow process is due to formation of some extra space for a molecule to flow into. With increase in concentration, the space for a molecule to flow and thus the activation energy decreases. However, k0 (as a viscosity index) increased with hydrocolloid concentration. It has also been reported that the activation energy increases with soluble content (Farhoosh and Riazi, 2007). Marcotte et al. (2001a) also pointed out that the apparent viscosity for carrageenan, xanthan, pectin and starch in relation with temperature generally obey the Arrhenius model. 3.2. Effect of pH

0 0

60

120

180

240

300

Shear rate (1/s)

Apparent viscosity (Pa.s)

b

3

5°C

25°C

45°C

65°C

2

The flow behavior index (n) and consistency coefficient (k) values, obtained by fitting the shear stress versus shear rate data to the power law model, are given in Fig. 3a. Increasing the pH of the solution, from three to seven, augmented the pseudoplasticity and consistency coefficient. These occurrences have been explained as induction of the electrostatic repulsion by functional group that tends to keep the molecules in an extended form, thus producing a high viscous solution and thus the k values increases (Launay et al., 1986; Onweluzo et al., 1994). The consistency coefficient will be at a maximum when its molecular chains are in a state close to the rod conformation in the solution (Feng et al., 2007). This presumably occurs in the

1 Table 2 Consistency index as a function of temperature for A. homolocarpum seed gum at different concentrations based on the Arrhenius equation.

0

Gum concentration (%)

0

60

120

180

240

300

Shear rate (1/s) Fig. 2. Effect of different gum concentrations (a, temperature: 25 °C) and temperatures (b, gum concentration: 3%) on apparent viscosity of A. homolocarpum seed gum.

1.5 2 2.5 3 3.5 4

k0 (Pa sn) 3

8.70  10 1.83  101 5.89  101 8.41  101 2.74 4.19

Ea (J/mole)

R2

8229.81 8123.11 6698.36 6550.27 4915.28 4520.57

0.88 0.95 0.97 0.97 0.96 0.96

494

12 11

0.4

10 n

k (Pas )

Table 3 The power law parameters for A. homolocarpum seed gum solutions with different salt concentrations.

0.45

9

0.35

8 7

k

6

0.3

n

5 2

4

6

Salt

n

a

A. Koocheki et al. / Journal of Food Engineering 91 (2009) 490–496

0.25 10

8

pH

Apparent viscosity (Pa.s)

b

2.50

3

5

7

9

2.00 1.50 1.00 0.50 0.00 0

60

120

180

240

300

Upward curve

Downward curve

k

n

R2

k

n

R2

NaCl 0 0.035 0.069 0.103 0.138 0.172

11.24 ± 0.12 10.66 ± 0.39 10.18 ± 0.24 9.95 ± 0.17 9.85 ± 0.28 8.42 ± 0.19

0.36 ± 0.01 0.36 ± 0.02 0.37 ± 0.01 0.37 ± 0.02 0.38 ± 0.01 0.39 ± 0.01

0.99 0.99 0.99 0.99 0.99 0.98

12.04 ± 0.10 10.15 ± 0.30 9.66 ± 0.31 9.48 ± 0.16 9.33 ± 0.25 8.10 ± 0.18

0.35 ± 0.01 0.37 ± 0.02 0.38 ± 0.01 0.39 ± 0.01 0.39 ± 0.01 0.40 ± 0.02

0.99 0.99 0.99 0.99 0.99 0.99

KCl 0 0.035 0.069 0.103 0.138 0.172

11.24 ± 0.12 9.62 ± 0.95 8.16 ± 0.70 7.98 ± 0.83 7.93 ± 0.72 7.98 ± 0.91

0.36 ± 0.01 0.37 ± 0.01 0.40 ± 0.01 0.41 ± 0.02 0.40 ± 0.02 0.40 ± 0.01

0.99 0.99 0.99 0.99 0.99 0.99

12.04 ± 0.1 9.12 ± 0.41 8.12 ± 0.63 7.92 ± 0.34 7.84 ± 0.45 7.99 ± 0.11

0.35 ± 0.01 0.38 ± 0.01 0.40 ± 0.01 0.40 ± 0.02 0.40 ± 0.04 0.41 ± 0.02

0.99 0.99 0.99 0.99 0.99 0.99

CaCl2 0 0.01 0.02 0.03 0.039 0.049

11.24 ± 0.12 10.36 ± 0.42 10.76 ± 0.32 10.76 ± 0.47 10.79 ± 0.72 10.77 ± 0.87

0.36 ± 0.01 0.40 ± 0.01 0.38 ± 0.01 0.38 ± 0.02 0.39 ± 0.03 0.38 ± 0.01

0.99 0.99 0.99 0.99 0.98 0.97

12.04 ± 0.1 10.47 ± 0.19 9.88 ± 0.56 9.59 ± 0.71 9.59 ± 0.65 9.50 ± 0.56

0.35 ± 0.01 0.39 ± 0.01 0.39 ± 0.01 0.39 ± 0.02 0.39 ± 0.01 0.39 ± 0.01

0.99 0.99 0.99 0.99 0.99 0.99

MgCl2 0 0.01 0.02 0.03 0.039 0.049

11.24 ± 0.12 10.77 ± 0.70 10.22 ± 0.40 10.22 ± 0.59 9.45 ± 0.62 10.45 ± 0.42

0.36 ± 0.01 0.36 ± 0.02 0.38 ± 0.04 0.38 ± 0.02 0.39 ± 0.01 0.38 ± 0.01

0.99 0.99 0.99 0.99 0.95 0.95

12.04 ± 0.1 10.96 ± 0.66 10.23 ± 0.17 9.42 ± 0.19 8.49 ± 0.15 9.52 ± 0.25

0.35 ± 0.01 0.35 ± 0.01 0.39 ± 0.03 0.39 ± 0.01 0.41 ± 0.05 0.40 ± 0.01

0.99 0.99 0.99 0.99 0.99 0.99

Shear rate (1/s) Fig. 3. Effect of different pH on flow behavior (a) and viscosity (b) of 3% A. homolocarpum seed gum.

vicinity of pH 7, where carboxyl groups are ionized so much that the consistency index reaches a maximum. Therefore, in the alkaline region, k values show a tendency to a constant value. The effect of pH on the viscosity of A. homolocarpum hydrocolloid at different shear rates is shown in Fig. 3b. Similar to consistency coefficient, increasing the pH up to 7 resulted in an increase in the viscosity values and remained constant afterwards. The pH had relatively little effect on apparent viscosity over the range of 7–9. A number of hydrocolloids such as galactomannans, CMC and gum karaya lose their viscosity at low pH (Glicksman, 1982). The viscosity of the A. homolocarpum seed gum also decreased gradually at more acidic conditions that may be explained by the ionization of the mucilage carboxyl groups above the pH 7. A comparable argument was given by Trachtenberg and Mayer (1982) who explained the increase in the intrinsic viscosity of mucilage with the pH. Medina-Torres et al. (2000) also studied the pH effect on apparent viscosity of Opuntia ficus indica and concluded that such increase was related to conformational changes in the molecule of the mucilage. Huei Chen and Yuu Chen (2001) as well reported that increase in pH, increased the apparent viscosity of the green laver mucilage. 3.3. Effect of salt The effect of salt concentration on viscosity is important in order to determine whether the mucilage behaves as polyelectolyte and also to estimate functional rheological properties. The effect of different salt concentration on the flow properties of A. homolocarpum seed gum solution are given in Table 3. The flow behavior indices increased progressively when the salt concentration was

increased from 0.035 to 0.172 M for NaCl and KCl. Addition of CaCl2 at 0.01 M and MgCl2 at 0.039 M augmented the flow behavior index but afterward decreased and remained constant at higher salt concentrations. The k values decreased from 11.24 Pa sn to 8.42 and 7.98 Pa sn with addition of NaCl and KCl, respectively. Increase in CaCl2 concentration from 0 to 0.01 M and MgCl2 from 0 to 0.039 M decreased the k values from 11.24 Pa sn to 10.36 and 9.45 Pa sn, correspondingly. These results confirm that KCl has more ability to decrease the apparent viscosity of A. homolocarpum seed hydrocolloid than other tested salts. As shown in Fig. 4a, NaCl and KCl greatly affected the viscosity of A. homolocarpum seed hydrocolloid and the viscosity decreased as the concentration of salts increased. Higher salt concentration had little additional effect on reducing the viscosity of mucilage solution. Study on flax seed mucilage by Mazza and Biliaderis (1989) indicated that addition of NaCl resulted in reduced viscosities at all shear rates. The authors concluded that this behavior arises from increasing association of counter-ions whit the polymer molecule which leads to a diminution in electrostatic repulsion of charged groups on the polymer chains. Since the exudates gum behaves as a polyelectrolyte, the solution viscosity is affected by the addition of salt. If no intermolecular interaction occurs, the viscosity of a dilute gum solution decreases due to the screening of charge and contraction of the macromolecule in presence of the counter ions. In a more concentrated solution, the presence of multivalent ions may promote interaction between chains and thus an increase in viscosity. For CaCl2 a rapid decrease in apparent viscosity (from 1.09 to 0.92 Pa s) was observed with addition of 0.01 M salt (Fig. 4b). Increasing the CaCl2 concentration up to 0.02 M augmented the viscosity to 0.99 Pa s. The MgCl2 concentration up to 0.039 M decreased the apparent viscosity from 1.087 to 0.90 Pa s but increased afterwards. It was assumed that this phenomenon might result from different interactions of cations with gum molecular chains. The presence of low amounts of salts, CaCl2 at 0.01 M and

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0.4

1.15

NaCl

20

KCl

18

n

Viscosity (Pa.s)

1.05

k 0.85

12

n

0.2

10 0

0

0.03

0.06

0.09

0.12

0.15

10

20

30

40

50

Sucrose Concentration (%)

0.18

Fig. 5. Effect of sucrose concentration on flow behavior of 3% A. homolocarpum hydrocolloid.

Salt concentration (M) 1.15

in agreement with Cancela et al. (2005) who investigated the effects of sucrose concentration and temperature on the rheological behavior of carboxymethylcellulose. The authors reported that, in general, an increase in concentration of sucrose was accompanied by an increase in consistency coefficient and a decrease in flow behavior index.

1.05

Viscosity (Pa.s)

14

0.95

0.75

b

16

0.3

k (Ps.sn)

a

0.95

4. Conclusion

0.85

MgCl2

CaCl2

0.75 0

0.01

0.02

0.03

0.04

0.05

Salt concentration (M) Fig. 4. Effect of different NaCl and KCl (a) and MgCl2 and CaCl2 (b) concentrations on apparent viscosity of 3% (w/w) A. homolocarpum hydrocolloid solution at shear rate 46.16-1 and 25 °C.

MgCl2 at 0.039 M, Ca2+ and Mg2+ resulted in the least contracted conformation of polysaccharide molecules and decrease of apparent viscosity. However, in the presence of high amount of salts, Ca2+ and Mg2+ promoted interchain interactions between gum molecules and the apparent viscosities increased. It has been reported that solution of carboxymethyl cellulose (CMC) and diluted pectin solution lose their viscosity after addition of salt and monovalent cations. The reason is the suppression of charges on carboxyl groups, thus weakening repulsion between adjacent chains and allowing closer association (Nussinovitch, 1997; Towle and Christensen, 1973). Studies by Mazza and Biliaderis (1989), Lai et al. (2000), Medina-Torres et al. (2000), and Huei Chen and Yuu Chen (2001) also indicated that an increase in salt concentration resulted in a decrease in viscosity of flax seed, hsian-tsao leaf, Opuntia ficus indica mucilage and green laver, respectively. In contrast, Cui and Eskin (1992) and Vardhanabhuti and Ikeda (2006) reported that increase in salt concentration, increased the viscosity of yellow mustard and monoi leaves hydrocolloids, respectively. 3.4. Effect of sucrose Changes in consistency coefficient (k) and flow behavior index (n) as a function of sucrose concentration are illustrated in Fig. 5. Both parameters were influenced by sucrose concentration. The k value increased from 11.24 ± 0.12 Pa sn to 17.68 ± 1.56 Pa sn while the n value decreased from 0.35 ± 0.0071 to 0.31 ± 0.014. The lower flow behavior index indicated that at higher concentration of sucrose, the solutions were less pseudoplastic. These results are also

Alyssum homolocarpum seed gum behaved as non- Newtonian, shear thinning fluid in concentrations from 1.5% to 4% and temperature range of 5–65 °C. The power law model well described the rheological behavior of the solutions. Because of the shear thinning nature of its dispersions, A. homolocarpum seed gum could be suitable for application as a thickening agent. Increasing the solution concentrations increased the viscosity and pseudoplasticity while increasing temperature resulted in a decrease in viscosity and pseudoplasticity. As the temperature of the solution increased, k decreased and n increased whereas increase in concentration resulted in higher k increased and lower n. Temperature dependency of the consistency index for the gum solutions was well described by the Arrhenius model. The apparent viscosities of A. homolocarpum seed gum was also affected by changes in pH of solutions and salts concentrations in different manners. Addition of sugar also increased consistency coefficient and viscosity. The results of this study could be useful in practical application in order to achieve a superior quality for new and existing gum added products. References Amin, G.H., 2005. Medicinal Plants of Iran, first ed. Tehran University Publication, Tehran, Iran, p. 106 (in Persian language). Bai, H.M., Ahn, J.K., Yoon, Y.H., Kim, H.U., 1978. A study of the development of the mixed stabilizer for ice cream manufacture. Korean Journal Animal Science 20, 436–445. Barbosa Canovas, G.V., Peleg, M., 1983. Flow parameters of selected commercial semi-liquid food products. Journal of Texture Studies 14, 213–234. Cancela, M.A., Alvarez, E., Maceiras, R., 2005. Effects of temperature and concentration on carboxymethylcellulose with sucrose rheology. Journal of Food Engineering 71, 419–424. Chhinnan, M.S., McWaters, K.H., Rao, V.N.M., 1985. Rheological characterization of grain legume pastes and effect of hydration time and water level on apparent viscosity. Journal of Food Science 50, 1167–1171. Cui, W., Eskin, N.A.M., 1992. Chemical and physical properties of yellow mustard (Sinapis alba L.) mucilage. Food Chemistry 46, 169–176. Dogan, M., Kayacier, A., 2004. Rheological properties of reconstituted hot salep beverage. International Journal of Food Properties 7, 683–691. Eyring, H., 1936. Viscosity, plasticity and diffusion as examples of absolute reaction rates. The Journal of Chemical Physics 4, 283–291. Farhoosh, R., Riazi, A., 2007. A compositional study on two current types of salep in Iran and their rheological properties as a function of concentration and temperature. Food Hydrocolloids 21, 660–666.

496

A. Koocheki et al. / Journal of Food Engineering 91 (2009) 490–496

Feng, T., Gu, Z.B., Jin, Z.Y., 2007. Chemical composition and some rheological properties of Mesona Blumes gum. Food Science and Technology International 13, 55–61. Garcia-Ochoa, F., Casas, J.A., 1992. Viscosity of locust bean gum solutions. Journal of the Science of Food and Agriculture 59, 97–100. Glicksman, M., 1982. Food Hydrocolloids, Vols. 2 and 3. CRC Press Inc, FL. Gomez-Diaz, D., Navaza, J.M., 2003. Rheology of aqueous solutions of food additives effect of concentration, temperature and blending. Journal of Food Engineering 56, 387–392. Hassan, B.H., Hobani, A.I., 1998. Flow properties of Roselle (Hibiscus sabdariffa L.) extract. Journal of Food Engineering 35, 459–470. Huei Chen, R., Yuu Chen, W., 2001. Rheological properties of the water-soluble mucilage of a green laver, Monostroma nitidium. Journal of Applied Phycology 13, 481–488. Kayacier, A., Dogan, M., 2006. Rheological properties of some gums-salep mixed solutions. Journal of Food Engineering 72, 261–265. Koocheki, A., Ghandi, A., Razavi, S.M.A., Mortazavi, S.A., Vasiljevic, T., 2008a. Effect of different temperature and hydrocolloids on rheological properties of ketchup. In: Proceedings of the 9th International Hydrocolloids Conference, Singapore. Koocheki, A., Mortazavi, S.A., Shahidi, F., Razavi, S.M.A., Kadkhodaee, R., Milani, J., 2008b. Optimization of mucilage extraction from Qodume shirazi seed (Alyssum homolocarpum) using response surface methodology. Journal of Food Process Engineering, doi:10.1111/j.1745-4530.2008.00312.x. Krumel, K.L., Sarkar, N., 1975. Flow properties of gums useful to the food industry. Food Technology 29, 36–44. Lai, L.S., Tung, J., Lin, P.S., 2000. Solution properties of hsian-tsao (Mesona procumbens Hemsl) leaf gum. Food Hydrocolloids 14, 287–294. Launay, B., Doubiler, I., Cavalier, G., 1986. Flow properties of aqueous solution and dispersions of polysaccharides. In: Mitchell, J.A. (Ed.), Functional Properties of Food Macromolecules. Elsevier Applied Science Publishers, New York, pp. 1–78. Lillford, P.J., Norton, I.T., 1991. In: Phillips, G.O., Williams, P.A., Wedlock, D.J. (Eds.), Gums and Stabilizers for the Food Industry, vol. 3. IRL Press, Oxford, London, pp. 3–15. Marcotte, M., Taherian, A.R., Ramaswamy, H.S., 2001a. Rheological properties of selected hydrocolloids as a function of concentration and temperature. Food Research International 34, 695–704. Marcotte, M., Taherian, A.R., Ramaswamy, H.S., 2001b. Evaluation of rheological properties of selected salt enriched food hydrocolloids. Journal of Food Engineering 48, 157–167. Maskan, M., Gogus, F., 2000. Effect of sugar on the rheological properties of sunflower oil–water emulsions. Journal of Food Engineering 43, 173–177. Mazza, G., Biliaderis, C.G., 1989. Functional properties of flax seed mucilage. Journal of Food Science 54, 1302–1305. Medina-Torres, L., Brito-De La Fuente, E., Torrestiana-Sanchez, B., Katthain, R., 2000. Rheological properties of the mucilage gum (Opuntia ficus indica). Food Hydrocolloids 14, 417–424. Morris, E.R., Taylor, L.J., 1982. Oral perception of fluid viscosity. Progress in Food and Nutrition Science 6, 285–296. Mothe, C.G., Rao, M.A., 1999. Rheological behavior of aqueous dispersions of cashew gum and gum arabic: effect of concentration and blending. Food Hydrocolloids 13, 501–506. 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. Brighton, UK, pp. 285–290. Nielsen, L.E., 1977. Polymer Rheology. Marcel Dekker Inc., New York. Nussinovitch, A., 1997. Hydrocolloid Applications: Gum Technology in the Food and Other Industries. Blackie Academic and Professional, London. Onweluzo, J.C., Obanu, Z.A., Onuoha, K.C., 1994. Viscosity studies on the flour of some lesser known tropical legumes. Nigerian Food Journal 12, 1–10. Patmore, J.V., Goff, H.D., Fernandes, S., 2003. Cryo-gelation of galactomannans in ice cream model systems. Food Hydrocolloids 17, 161–169. Race, S.W., 1991. Improved product quality through viscosity measurement. Food Technology 45, 86–88. Rao, M.A., Anantheswaran, R.C., 1982. Rheology of fluids in food processing. Food Technology 36, 116–126. Riazi, A., Farhoosh, R., Razavi, S.M.A., 2006. An Investigation on Rheological Properties of the Gum from Two Current Varieties of Salep in Iran Compared to CMC, Xanthan and Guar Gum. MSc thesis, Ferdowsi University of Mashhad, Iran. (Abstract in English). Rosell, C.M., Rojas, J.A., Benedito de Barber, C., 2001. Influence of hydrocolloids on dough rheology and bread quality. Food Hydrocolloids 15, 75–81. Sengul, M., Ertugay, M.F., Sengul, M., 2005. Rheological, physical and chemical characteristics of mulberry pekmez. Food Control 16, 73–76. Singh, N.I., Eipeson, W.E., 2000. Rheological behaviour of clarified mango juice concentrates. Journal of Texture Studies 31, 287–295. Speers, R.A., Tung, M.A., 1986. Concentration and temperature dependence of flow behavior of xantham gum dispersions. Journal of Food Science 51, 96–98. Sutherland, I.W., 1994. Structure-function relationships in microbial exopolysaccharides. Biotechnology Advances 12, 393–448. Szczesniak, A.S., Farkas, E., 1962. Objective characterization of the mouthfeel of gum solutions. Journal of Food Science 27, 381–385. Taherian, A.R., Fustier, P., Ramaswamy, H.S., 2007. Effects of added weighting agent and xanthan gum on stability and rheological properties of beverage cloud emulsions formulated using modified starch. Journal of Food Process Engineering 30, 204–224. Towle, G.A., Christensen, O., 1973. Pectin. In: Whistler, R.L., BeMiller, J.N. (Eds.), Industrial Gums: Polysaccharides and Their Derivatives. Academic Press, New York, pp. 429–459. Trachtenberg, S., Mayer, A.M., 1982. Biophysical properties of Opuntia ficus-indica mucilage. Phytochemistry 21, 2835–2843. Vardhanabhuti, B., Ikeda, S., 2006. Isolation and characterization of hydrocolloids from monoi (Cissampelos pareira) leaves. Food Hydrocolloids 20, 885–891. Wanchoo, R.K., Sharma, S.K., Bansal, R., 1996. Rheological parameters of some water-soluble polymers. Journal of Polymer Materials 13, 49–55. Whistler, R.L., 1993. In: Whistler, R.L. BeMiller, J.N. (Eds.), Industrial Gums, Polysaccharides and Their Derivatives, vol. 1. Academic Press, New York, pp. 1–19. Williams, P.A., Phillips, G.O., 2000. Introduction to food hydrocolloids. In: Phillips, G.O., Williams, P.A. (Eds.), Handbook of Hydrocolloids. CRC Press, New York, pp. 1–19. Yadav, M.P., Johnston, D.B., Hotchkiss, A.T., Hicks, K.B., 2007. Corn fiber gum a potential gum Arabic replacer for beverage flavor emulsification. Food Hydrocolloids 21, 1022–1030.