Purification of cress seed (Lepidium sativum) gum: A comprehensive rheological study

Food Hydrocolloids 61 (2016) 358e368

Contents lists available at ScienceDirect

Food Hydrocolloids journal homepage: www.elsevier.com/locate/foodhyd

Purification of cress seed (Lepidium sativum) gum: A comprehensive rheological study Somayeh Razmkhah a, Seyed Mohammad Ali Razavi a, *, Mohammad Amin Mohammadifar b a

Food Hydrocolloids Research Centre, Department of Food Science and Technology, Ferdowsi University of Mashhad (FUM), PO Box: 91775-1163, Mashhad, Iran Research Group for Food Production Engineering, National Food Institute,Technical University of Denmark, SøltoftsPlads, 2800, Kgs. Lyngby, Denmark

b

a r t i c l e i n f o

a b s t r a c t

Article history: Received 1 March 2016 Received in revised form 26 May 2016 Accepted 29 May 2016 Available online 30 May 2016

In this paper, the effects of different purification methods (ethanol (sample E), isopropanol (sample I) and ethanol-isopropanol (sample EI)) on intrinsic viscosity, steady and dynamic rheological properties of cress seed gum were investigated. The gum dispersions exhibited viscoelastic properties, the storage modulus (G0 ) was higher than the loss modulus (G00 ), and mechanical spectra of the crude and purified cress seed gums were classified as weak gels. The purified samples had stronger and more elastic network structure than the crude gum (CSG) and the gel network got stronger along the series of I, EI and E. All the gum dispersions indicated shear-thinning behavior and the viscosity of the samples followed the order of E > EI > I > CSG. Herschel-Bulkley model was the best model to describe steady shear flow behavior and Arrhenius-type model was also applied to describe the effect of temperature. Crude cress seed gum and EI showed the highest and the lowest activation energy, respectively. The crude and purified gums indicated thixotropic behavior and CSG exhibited the lowest hysteresis loop area and the highest structural recovery. All the samples revealed random coil conformation in dilute regimes, and chain flexibility and intrinsic viscosity enhanced after purification. Intrinsic viscosity of the purified samples increased along the series of I, EI and E. © 2016 Elsevier Ltd. All rights reserved.

Keywords: Intrinsic viscosity Purification Seed gum Shear thinning Rheology Thixotropy

1. Introduction Lepidium sativum (Garden cress) seeds contain a large amount of mucilaginous substances, which are a good source of hydrocolloids with high molecular weight (Karazhiyan et al., 2009; Naji & Razavi, 2014; Razavi, Farhoosh, & Bostan, 2007). Extraction optimization, some physicochemical and functional properties of cress seed gum (CSG) have been recently studied (Karazhiyan, Razavi, & Phillips, 2011; Karazhiyan et al., 2011; Naji, Razavi, Karazhiyan, & Koocheki, 2012; Naji, Razavi, & Karazhiyan, 2012; Naji, Razavi, & Karazhiyan, 2013; Naji & Razavi, 2014; Razavi, Bostan, Niknia, & Razmkhah, 2011). Also, some researchers have investigated rheological properties of CSG. Shear thinning behavior in steady shear measurements and a weak gel type behavior in dynamic tests were observed for 1% solution of crude Lepidium sativum seed extract, and its rheological

* Corresponding author. E-mail address: [email protected] (S.M.A. Razavi). http://dx.doi.org/10.1016/j.foodhyd.2016.05.035 0268-005X/© 2016 Elsevier Ltd. All rights reserved.

properties was depended on many factors such as shear rate, temperature, time, pH, biopolymer concentration, concentration and type of salts and sugars (Behrouzian, Razavi, & Karazhiyan, 2013; Karazhiyan et al., 2009; Naji & Razavi, 2014). Behrouzian, Razavi, and Karazhiyan (2014) reported that the cress seed extract was Newtonian at dilute concentrations below 0.1% and had the conformation between random coil and rigid rod. Gum extraction methods usually result in solutions containing a mixture of components, which should be further purified to isolate the specific polysaccharide of interest. The purification of polysaccharides removes unacceptable flavors of the crude gums and the purified gums give clearer and more stable solutions due to the elimination of impurities and endogenous enzymes. Various procedures such as precipitation with ethanol, isopropanol, methanol, copper or barium complexes and etc have been used to purify gums (Bouzouita et al., 2007; Cui, 2005; da Silva & Gonçalves, 1990). Many researchers studied purification of hydrocolloids by various procedures and the results indicated that the purified gums had different physicochemical, functional and rheological properties

S. Razmkhah et al. / Food Hydrocolloids 61 (2016) 358e368

(Amid & Mirhosseini, 2012; Bouzouita et al., 2007; Cunha, Paula, & €k, 2007; Lubambo Feitosa, 2007; da Silva & Gonçalves, 1990; Ko et al., 2013; Youssef, Wang, Cui, & Barbut, 2009). Recently, we investigated the effect of purification methods on physicochemical and functional properties of cress seed gum (Razmkhah, Mohammadifar, Razavi, & Ale, 2016). Chemical composition and molecular weight of crude cress seed gum (CSG) varied significantly after purification with different methods (ethanol (sample E), isopropanol (sample I) and ethanolisopropanol (sample EI)). All the purification methods led to a reduction in ash and protein content and molecular weight of CSG, and molecular weight increased significantly along the series of I, EI and E. Monosaccharide composition of cress seed gum changed after purification and it was dependent on the method applied. In general, the crude and purified gums contained relatively high amounts of arabinose, xylose and rhamnose. The crude and purified gums exhibited different physicochemical and functional properties, so various rheological characteristics and application area are expected for them. The rheological behavior of the crude and purified cress seed gums is of special importance when they are used to improve functional properties of food. Therefore, the objective of this paper was to elaborate rheological properties of the crude and purified cress seed gums including: dynamic and steady shear rheological properties, temperature dependency, thixotropy and intrinsic viscosity. 2. Materials and methods 2.1. Cress seed gum extraction Seeds of Lepidium sativum were purchased from a local market in Tehran, Iran. Aqueous L. sativum seed gum was extracted from whole seeds using distilled water (water to seed ratio of 30:1, pH 7, soaking period: 15 min) at room temperature and based on the method as described by Karazhiyan, Razavi, and Phillips (2011a). Separation of the gum from the swollen cress seeds was achieved by passing the seeds through an extractor (Pars Khazar 700P, Rasht, Iran) equipped with a rotating plate that scraped the mucilage layer on the seed surface. Some of the extracted gum was dried at room temperature and the dried gum was ground and denoted as crude cress seed gum (CSG). 2.2. Cress seed gum purification 2.2.1. Purification using ethanol (sample E) Three volumes of 96% ethyl alcohol were added to one volume of the extracted gum and left for 2 h at room temperature. The collected precipitate was dried (at room temperature) and ground (Razmkhah et al., 2016). 2.2.2. Purification using isopropanol (sample I) In this method, three volumes of 99.5% isopropyl alcohol were added to one volume of the extracted gum and left for 2 h (at room temperature). After drying the collected precipitate at room temperature, the dried gum was ground (Razmkhah et al., 2016). 2.2.3. Purification using isopropanol and ethanol (sample EI) Two volumes of 96% ethyl alcohol were added to one volume of the extracted gum and left for 30 min. Then, the white fibrous precipitate was collected and kept overnight in 99.5% isopropanol (1/2 ethanol volume) at room temperature. The collected precipitate was dried (at room temperature) and ground (Razmkhah et al., 2016).

359

2.3. Preparation of gum solutions The crude and purified gum solutions (0.0015 g/ml for intrinsic viscosity, 1% for oscillatory and steady shear rheological measurements) were prepared by dispersing the gums in distilled water and stirring (500 rpm) with a magnetic stirrer for about 2 h at ambient temperature until full dissolution. The solutions were stored at 4  C overnight for complete hydration. 2.4. Rheological measurements Rheological evaluations of the crude and purified cress seed gums were performed with a Physica MCR 301 rheometer (AntonPaar, GmbH, Graz, Austria) using a serrated parallel plate system (PP40/S-SN16891; d ¼ 0.5 mm) with duplication measurements. The temperature was controlled with a Peltier system (Viscotherm VT2) equipped with a fluid circulator (Anton Paar, GmbH) with the accuracy of ±0.01  C, and the samples were left at rest for five minutes to allow structure recovery and temperature equilibration. All the samples were covered with a solvent trap to prevent evaporation during the measurements. Rheoplus software version 3.21 (Anton-Paar) was used to collect and analyze the rheological data. 2.4.1. Small dynamic oscillatory measurements Strain sweep tests were carried out (0.04e700%, 1 Hz, 25  C) to determine: 1)LVE (linear viscoelastic) range; 2) gL (critical strain which the G0 begins to decrease), 3) G0 LVE (storage modulus at LVE as an indicative of the structural strength); 3) ty or yield stress (the resistance to mechanical force that can be determined from the limiting value of LVE range in terms of shear stress); 4) tf or the flow point (the stress in which internal structure breaks to such an extent that it causes the material to flow (G0 ¼ G00 ); 5) tan d LVE or damping factor at LVE (a view of whether the samples behaved as liquids or solids and can be calculated from the ratio of loss modulus to elastic modulus) (Mezger, 2006; Balaghi, Mohammadifar, Zargaraan, AhmadiGavlighi, & Mohammadi, 2011; Yousefi & Razavi, 2015). Frequency sweep tests were then performed (1% strain, 0.05e50 Hz, 25  C) to evaluate the viscoelastic nature of the crude and purified cress seed gums. 2.4.2. Steady shear measurements The steady shear flow properties of the samples were measured at shear rate of 0.1e700 s1 (25  C) and different viscoplastic and shear-thinning models have been selected to fit the experimental flow curves (Rao, 1999; Steffe, 1996): 1. Power law (or Ostwald-Waele’s) model:

t ¼ kp g_ nP

(1)

where kP and nP are the power law consistency coefficient (Pa sn) and flow behavior index (dimensionless), respectively. 2. Bingham’s model:

t ¼ hB g_ þ t0B

(2)

where hB and t0B are Bingham plastic viscosity (Pa s) and Bingham yield stress (Pa), respectively. 3. Herschel-Bulkley’s model:

t ¼ kH ðg_ ÞnH þ t0H

(3)

360

S. Razmkhah et al. / Food Hydrocolloids 61 (2016) 358e368

where kH is the consistency coefficient (Pa sn), nH is flow behavior index (dimensionless) and t0H is the yield stress (Pa) for HerschelBulkley model. 4. Casson’s model:

_ 0:5 t0:5 ¼ k0:5 0c þ kc ðgÞ

(4)

where k20c is Casson yield stress (t0c, Pa) and k2c is Casson plastic viscosity (hc, Pa s). 5. Moore’s model (simplified Cross model):

h ¼ h∞ þ

h0  h∞ 1 þ tg_

(5)

where h0 is the limit viscosity at low shear rate or zero shear viscosity (Pa s), h∞ is the limit viscosity at high shear rate or infinite shear viscosity (Pa s) and t is relaxation time (s). 2.4.3. Temperature dependence Effect of temperature on apparent viscosity of the crude and purified cress seed gum solutions was determined in the range of 2e40  C at shear rate of 5 (s1) according to Arrhenius model (Steffe, 1996):

hrel ¼

h hs

(7)

hsp ¼

h  hs ¼ hrel  1 hs

(8)

Where, hs is the viscosity of the solvent (deionized water). The relative viscosity (hrel) was kept from 1.2 to 2.0, in order to assure good accuracy and linearity of extrapolation to zero concentration (Da Silva& Rao, 1992). The intrinsic viscosity [h] is usually estimated by double extrapolation to zero concentration of Huggins’ and Kraemer’s equations. Huggins’ equation (Huggins, 1942):

hsp C

¼ ½h þ k1 ½h2 C

(9)

Kraemer’s equation (Kraemer, 1938):

ln hrel ¼ ½h þ k2 ½h2 C C

(10)

Where, k1 and k2 are the Huggins’ and Kraemer’s constants, respectively, and C is the solution concentration. 2.6. Estimation of the molecular conformation

h ¼ h0exp (Ea/RT)

(6)

Where h0 is the proportionality constant (or apparent viscosity at a reference temperature, Pa s), Ea is the activation energy (kJ/ mol), R is the universal gas constant (kJ/mol K) and T is the absolute temperature (K). Activation energy is determined from the slope of ln h vs. 1/T plot.

The power-law relation was applied to estimate exponent b from the slope of a double logarithmic plot of hsp against concentration (Eq. (11)), and this parameter provides an indication of the conformation of polysaccharides (Higiro, Herald, Alavi, & Bean, 2007; Lai, Tung, & Lin, 2000).

hsp ¼ aC b

(11)

2.4.4. Thixotropy 2.4.4.1. In-shear structural recovery measurements. An in-shear structural recovery test was carried out through the modified procedures of Achayuthakan and Suphantharika (2008), Sikora € et al. (2015), Wang et al. (2009) and Wang, Li, Wang, & Ozkan,  (2010) at 25 C. The subsequent steps were as follows: (1) a constant shear rate at 1 s1 for 45 s, (2) a constant shear rate at 100 s1for 45 s, and (3) a constant shear rate at 1 s1 for 250 s. The results were used to calculate the degree of structure recovery (DSR) of the samples which was defined as the ratio of the average apparent viscosity obtained during the first 45 s of the third measurement step and the average apparent viscosity estimated in the first step. 2.4.4.2. Hysteresis loop test. Hysteresis loop test was consisted of a three step operation at25  C: the rate of shear was increased linearly from 2 to 50 s1 within 160 s, followed by the constant shear rate of 50 s1 for 45 s, and subsequent decrease (linear) to 2 s1 within 160 s. The area of the hysteresis loop(the area encircled between upward and downward flow behavior curves) was calculated using Rheoplus software. 2.5. Intrinsic viscosity Viscosity of dilute solutions was measured using an Ubbelohde viscometer (size 1, Fisher scientific, USA), which was suspended in a thermostatic water bath under precise temperature control (25  C ± 0.1  C). The flow time in seconds was measured at least three times. The sample viscosity (h) was converted to relative viscosity (hrel) and specific viscosity (hsp) using the following equations:

2.7. Statistical analysis The results were analyzed using a general linear model (GLM) procedure of the MINITAB ver.17. The level of significance (LSD) was preset at P < 0.05. 3. Results and discussion 3.1. Strain sweep From Fig. 1, it was possible to discriminate two different regions, namely a linear viscoelastic region in which G0 and G00 were practically constant with G0 > G00 (solid-like behavior), and a non-linear one in which G0 and G00 began to diminish with increasing strain. After the crossover point (flow point), G00 was higher than G0 and the samples showed more liquid-like behavior. Therefore, the crude and purified cress seed gums showed a gel-like structure (a weakgel) at 1 Hz and 25  C. Strain sweep parameters of the samples were summarized in Table 1. Critical strain (gL) was high for CSG (13.2%), which indicates the sample had longer LVE ranges and implied a higher stability of the viscoelastic material under the applied strain amplitude. Loss tangent (tan d ¼ G00 /G0 ) is a characteristic value for evaluation of the viscoelastic behavior, the low value of tan d (tan d < 1) indicates a predominantly elastic behavior, whereas tan d > 1 indicates a predominantly viscous behavior. Tan d values greater than 0.1 means that the sample is not true gel and the structure is between high concentrated biopolymer and real gel (Mandala, Savvas, & Kostaropoulos, 2004). As demonstrated in Table 1, tan dLVE values

S. Razmkhah et al. / Food Hydrocolloids 61 (2016) 358e368

361

presence of isopropanol, and sample I (purified with isopropanol) showed weaker gel network structure than sample EI (purified with ethanol and isopropanol) due to more polysaccharide chain degradation. Also, precipitation with ethanol had more impressive effect on reduction of protein content of the cress seed gum (11.29%), and protein content of the purified gums decreased from I (1.28%)to EI (1.27%)to E(0.91%) (Razmkhah et al., 2016), meaning that elimination of protein to lower levels could improve gel network strength and elasticity. 3.2. Frequency sweep

Fig. 1. Strain sweep dependency of storage modulus (G0 ) and loss modulus (G00 ) for crude and purified cress seed gums (CSG, crude cress seed gum; E, CSG purified by ethanol; I, CSG purified by isopropanol; EI, CSG purified by ethanol-isopropanol).

As shown in Fig. 2, the crude and purified cress seed gums indicated typical weak gel-like behavior showing G0 higher than G00 throughout the frequency range, with a slight dependence of G0 and G00 on frequency (Clark & Ross-Murphy, 1987). At low frequency, G00 was much lower than G0 ; with the increase of frequency, the value of G00 rose rapidly and they became closer. Such behavior was in good agreement with that reported by Karazhiyan et al. (2011b) for

Table 1 Structural strength G0 LVE, limiting value of strain gL, and loss-tangent value tan d LVE in the linear viscoelastic range, yield stress at the limit of the LVE range, ty, and flow-point stress with corresponding modulus Gf: G0 ¼ G00 for 1% dispersions of crude and purified cress seed gums, as determined by strain sweep tests at 25  C and a frequency of 1 s1. Parameter

CSG

E

EI

I

gL (%) tan d LVE

13.20 ± 0.65 a 0.580 ± 0.003 a 2.38 ± 0.05 d 1.20 ± 0.03 d 0.261 ± 0.021 d 1.447 ± 0.002 d

11.01 ± 0.89 bc 0.349 ± 0.009 c 18.10 ± 0.09 a 5.29 ± 0.03 a 1.910 ± 0.132 a 10.051 ± 0.003 a

9.46 ± 1.02 c 0.339 ± 0.008 c 15.31 ± 0.49 b 5.02 ± 0.14 b 0.764 ± 0.051 b 8.364 ± 0.020 b

12.49 ± 1.16 ab 0.421 ± 0.005 b 8.02 ± 0.15 c 2.93 ± 0.04 c 0.411 ± 0.032 c 4.412 ± 0.004 c

G0 LVE (Pa) Gf (Pa) ty (Pa) tf (Pa)

CSG, crude cress seed gum; E, CSG purified by ethanol; I, CSG purified by isopropanol; EI, CSG purified by ethanol-isopropanol. Different letters indicate significant differences between samples at p < 0.05 by LSD test.

a

of the crude and purified gums (0.339e0.580) were lower than 1, but higher than 0.1 which indicates the presence of elastic structure in weak biopolymer gel. Since all the samples were not real gel, therefore chains entanglements and macromolecules connections were temporary and could be disrupted by applying high shear rates (Naji-Tabasi & Razavi., 2016). Sample E exhibited the highest structural strength (G0 LVE ¼ 18.1), reflecting that it promoted higher intermolecular interactions and entanglements. The cross point of elastic and viscous moduli (Gf) is a suitable indicator of structure strength at flow point; With respect to Gf values, sample E had the highest strength (5.29 Pa). Also, sample E showed the highest yield stresses or resistance to mechanical force at the limiting value of LVE range (ty) and the flow point (tf). In general, the magnitude of Gf, G0 LVE, ty and tf increased, while tan d decreased after purification, meaning that the gel network got stronger which could be due to elimination of impurities, enzymes and protein fraction after purification. Molecular weight and structural characteristics are important factors which affect rheological behavior of the gum solutions (Xiu, Zhou, Zhu, Wang, & Zhang, 2011). Therefore, different viscoelastic parameters of the purified gums was related to their different chemical compositions (monosaccharide composition, ash, moisture, carbon, hydrogen, nitrogen and uronic acid content) and molecular weight (Razmkhah et al., 2016). Gf, G0 LVE, ty and tf increased significantly along the series of I, EI and E, which was in agreement with their molecular weight results, increasing the molecular weight could be resulted in more elastic behavior of the purified samples (Lin, Amidon, Weiner, & Goldberg, 1993; Tuvikene et al., 2015). The highest gel strength of sample E compared to samples I and EI, might be related to degradation of the polysaccharide chain in the

crude Lepidium sativum seed extract (1, 1.5 and 2% w/w). Frequency sweep pattern of polymer solutions depends on many factors like concentration of the polymer, molecular weight, dispersity, structural properties and quality of solvent (Fadavi, Mohammadifar, Zargarran, Mortazavian, & Komeili, 2014). The frequency dependency of G0 and G00 could be described by a power-law equation as follows: G0 ¼ k’(u)n0

(12)

Fig. 2. Frequency sweeps of storage modulus(G0 ) and loss modulus(G00 ) for crude and purified cress seed gums (CSG, crude cress seed gum; E, CSG purified by ethanol; I, CSG purified by isopropanol; EI, CSG purified by ethanol-isopropanol) at g ¼ 1% and T¼25  C.

362

S. Razmkhah et al. / Food Hydrocolloids 61 (2016) 358e368

G^00 ¼ k^00 (u)n^00

A perfectly elastic system shows a slope of 1 and for such an elastic system, G* is independent of u (h* ¼ G*/u), the greater the slope of log h* versus log u, the more elastic the gel (Shatwell, Sutherland, Ross-Murphy, & Dea, 1991). CSG showed the lowest slope (0.638) and the slope increased after purification, indicating the presence of more elastic gels after purification. There was no significant difference between samples E and EI (Table 3). The results of the frequency sweep tests suggested that all the purification methods significantly affected molecular structure of cress seed gum in a way which enhanced its rheological properties. It could be assumed that with elimination of impurities especially protein component, the polysaccharide chains closed to each other freely and more intermolecular interactions formed, which resulted in stronger and more ordered networks. Also, with increasing molecular weight much more junction zones were existed for intermolecular interactions, and more crosslinking networks of higher elasticity were formed which could sustain high mechanical deformation. So, with decreasing protein content and increasing molecular weight along the series of I, EI and E (Razmkhah et al., 2016), the gel network got stronger. Amid and Mirhosseini (2012) reported the same results for purified durian seed gums due to significant effect of purification process on chemical composition of the crude gum. Youssef et al. (2009) indicated that protein fraction influenced viscoelastic properties of purified and crude fenugreek gum.

(13)

Where k0 and k00 are constants, n0 and n00 may be referred to as the frequency exponents (can provide useful information regarding the viscoelastic nature of food materials),u is the angular frequency € (Ozkan, Xin, & Chen, 2002). The magnitudes of slopes (n0 and n00 ), intercepts (k0 and k00 ), and R2 (determination coefficient) were represented in Table 2. It was found that all the samples displayed gel-like behavior because the slopes (n0 ¼ 0.125e0.311 and n00 ¼ 0.288e0.417) were positive. The n0 value can be used as an indicator of the strength and nature of the gel, n0 ¼ 0 reflects a covalent gel, whereas for a physical gel n0 > 0. Low n0 values (near zero) means that G0 does not change with frequency, while for n0 values near to 1, the system behaves as a viscous gel (Balaghi et al., 2011; Khondkar, Tester, Hudson, Karkalas, & Morrow, 2007). According to low values of n0 and n00 determined for the crude and purified gums, they exhibited slight frequency dependency. The n00 was higher than n0 , indicating that G00 increased at a higher rate than the increases in G0 with increases in the frequency. CSG showed the highest value of n0 and n00 , reflecting the highest frequency sensitivity. The n0 value of CSG was 0.311, which represents weak polysaccharide chain interaction. The values of k0 were much higher than those of k00 , confirming again the weak gellike behavior of the crude and purified gums (Razavi, Cui & Ding, 2016). The ratio of k0 /k00 followed the order of E (3.792) >EI (3.397) >I (2.931) > CSG (2.379), and magnitudes of k0 also exhibited the same trend, reflecting that the gel network got stronger. As shown in Table 3, CSG showed the lowest G0 (2.495 Pa) and G00 (1.419 Pa) values, which indicates the weak ability of its molecular chain to form network. All the purification methods enhanced significantly (p < 0.05) both elastic modulus (G0 ) and viscous modulus (G00 ) of cress seed gum. The tan d values of the samples were smaller than unity and in the range of 0.328e0.569, meaning that the weak biopolymer gels were more elastic than viscous. The storage modulus increased significantly along the series of CSG, I, EI and E, whereas tan d decreased significantly, reflecting stronger and more elastic network structure. Therefore it is possible to conclude that the polysaccharide fraction played the main role in the elastic behavior of CSG, and with decreasing protein content (as troublous component) from CSG (11.29%) to I (1.28%) to EI(1.27%) to E(0.91%) (Razmkhah et al., 2016), a significant increment was observed in storage modulus, indicating improvement of elastic properties in absence of protein fraction. In addition, the lowest gel strength of sample I among the purified gums could be due to degradation of polysaccharide chain in the presence of isopropanol and its the lowest molecular weight (495 kDa) (Razmkhah et al., 2016). Sample EI showed molecular weight (664 kDa) and gel strength between those of samples I and E (928 kDa). All the samples exhibited a shear dependent flow behavior as the complex viscosity (h*) decreased linearly with increase in frequency on a double logarithmic scale (Fig. 3). Therefore, it could be resulted that the gum dispersions had non-Newtonian shear-thinning behavior.

3.3. Steady shear flow behavior The apparent viscosity of the dispersions was sharply decreased as an increase in shear rate, which indicates the high shear dependency (shear thinning) of the crude and purified cress seed gums (Fig. 3). For example, the results showed that the apparent viscosity of sample EI was decreased 17, 66, 219, 305, 543 times as the shear rate was increased from 0.1 to 3.45, 20.3, 119, 215 and 700 s1, respectively. The decrease in viscosity with increasing shear rate is mainly related to the disentanglement of macromolecular chains and alignment of microstructure in the direction of the shear flow (Chandra & Shamasundar, 2015; Dakia, Blecker, Robert, Wathelet, & Paquot, 2008). Shear-thinning hydrocolloids are extensively used to improve or modify food texture, and this behavior provides processing advantage during high-shear processing operations such as pumping and filling (Koocheki, Taherian, & Bostan, 2013). Crude cress seed gum showed the lowest apparent viscosity which might be due to the presence of the highest protein content (Amid & Mirhosseini, 2012; Razmkhah et al., 2016). It could be assumed that the purification processes reduced the content of main impurities (such as trace elements, tannin, natural pigments and protein) present in the crude cress seed gum and improved the solubility of the gum (Naji-Tabasi & Razavi., 2016). The different viscosities of the purified gums could be explained by their different chemical structures (i.e., monosaccharide composition, molecular weight and protein content). Apparent viscosity decreased from E to EI to I, due to degradation effect of isopropanol

Table 2 Frequency dependency of elastic and viscous modulus of crude and purified cress seed gums. Sample

Elastic modulus (G0 ) 0

CSG E EI I

Viscous modulus (G00 ) 0

k

n

1.589 ± 0.011 d 14.368 ± 0.096 a 10.934 ± 0.112 b 5.502 ± 0.072 c

0.311 0.165 0.125 0.181

R ± ± ± ±

0.008 0.001 0.001 0.003

a c d b

2

0.880 0.953 0.987 0.992

k00 0.668 3.789 3.219 1.877

n00 ± ± ± ±

0.003 0.009 0.012 0.005

d a b c

CSG, crude cress seed gum; E, CSG purified by ethanol; I, CSG purified by isopropanol; EI, CSG purified by ethanol-isopropanol. a Different letters indicate significant differences between samples at p < 0.05 by LSD test.

0.417 0.288 0.318 0.359

R2 ± ± ± ±

0.006 0.001 0.004 0.003

a d c b

0.971 0.969 0.978 0.976

S. Razmkhah et al. / Food Hydrocolloids 61 (2016) 358e368

363

Table 3 Storage modulus (G0 ), loss modulus (G00 ) and complex viscosity (h*) of crude and purified cress seed gums at f ¼ 1 Hz, g ¼ 1% and T ¼ 25 C. Sample

G0 (Pa)

G00 (Pa)

CSG E EI I

2.495 ± 0.030 d 18.380 ± 0.102 a 13.697 ± 0.093 b 7.552 ± 0.060 c

1.419 6.019 5.613 3.472

± ± ± ±

h* (Pa s) 0.011 0.005 0.110 0.042

d a b c

0.457 3.078 2.356 1.323

± ± ± ±

0.005 0.015 0.020 0.011

tan (d) d a b c

0.569 0.328 0.410 0.460

± ± ± ±

Slope of h* 0.002 0.002 0.005 0.002

a d c b

0.638 0.824 0.850 0.784

± ± ± ±

0.032 0.003 0.002 0.006

c a a b

CSG, crude cress seed gum; E, CSG purified by ethanol; I, CSG purified by isopropanol; EI, CSG purified by ethanol-isopropanol. a Different letters indicate significant differences between samples at p < 0.05 by LSD test.

Fig. 3. Cox-Merz plot of complex viscosity (h*) against apparent viscosity (ha) for crude and purified cress seed gums (CSG, crude cress seed gum; E, CSG purified by ethanol; I, CSG purified by isopropanol; EI, CSG purified by ethanol-isopropanol).

on polysaccharide chain and decrease of molecular weight along the same series (E: 928 kDa, EI: 664 kDa, I: 495 kDa), also protein content increased from E (0.91%) to EI (1.27%) to I (1.28%) (Razmkhah et al., 2016). Amid and Mirhosseini (2012)also indicated that purified durian seed gum containing the lowest protein content and the largest particle size showed the highest viscosity. Razavi et al. (2009) showed that purified basil seed gum (BSG) had higher apparent viscosity and lower protein content than crude BSG extracts. Cunha et al. (2007) also reported that the purified guar gum containing higher molecular mass induced more viscous solution. The analysis of flow behavior of the samples by different timeindependent rheological models (Eqns. (1)e(5)) is represented in Table 4. Generally, HerscheleBulkley model (Eq. (3)) showed high coefficients of determination (R2) for all the samples. The values of flow behavior index (nH) were less than 1, ranged from 0.456 to 0.533, reflecting shear-thinning (pseudoplastic) nature of the crude and purified cress seed gums. There was no significant difference for the values of nH among the purified samples. The yield stress values (0.174e4.368 Pa) suggested that the CSG samples solutions had coherent network structures which required a certain amount of force to initiate the flow. Totally, CSG had the lowest kH, t0H and the highest nH, meaning that all the applied purification methods increased pseudoplasticity (n), thickening (k) and stabilizing (t0) properties of the cress seed gum. As shown in Table 4, t0H decreased significantly in the order: E > EI > I, which might be related to degradation effect of isopropanol on polysaccharide chain and weaken the interactions of polymer chains with decreasing molecular weight (E: 928 kDa, EI: 664 kDa, I: 495 kDa). In addition, this different yield stress values of the purified gums could be attributed to differences in composition of them (Lv, Wang, Wang, Li, & Adhikari, 2013). The values of Herschel-

Bulkley parameters for CSG were different from those reported by Naji and Razavi (2014) and Behrouzian et al. (2013) for cress seed gum (1%), which could be explained by diversity of varieties, different plant growing conditions and extraction processes used (Razavi, Cui, Guo, & Ding, 2014; Razmkhah et al., 2016). In this paper, we also applied the Moore model to describe the very shear thinning behavior of the crude and purified cress seed gums over a wide shear rate range, since it incorporates terms for both zero shear rate (h0) and infinite shear rate (h∞) viscosities. As show in Table 4, the Moore model showed coefficients of determination higher than 0.947 for the purified gums, and was satisfactorily fitted to the experimental data over the applied shear rate range for CSG (R2 ¼ 0.999). The relaxation time (t) is defined as the typical time for macromolecules to return to equilibrium; higher relaxation time values of the purified gums could be related to increase in the entanglement density of the polymer chains after purification (Kurt &Kahyaoglu, 2015; Razavi et al., 2014). The magnitude of zero shear viscosity (h0) is related to the microstructural nature of biopolymer during storage, and a higher h0 value reveals a greater number of linkages between the polymer molecules (Razavi et al., 2014; Sun, Huang, & Wu, 2014). The zero shear viscosity and relaxation time of cress seed gum increased significantly after purification due to removal of impurities (Kurt &Kahyaoglu, 2015). The values of t and h0 increased from I to EI to E (Table 4), which could be due to decrease of protein content and increase of molecular weight along the same series (Razmkhah et al., 2016). Infinite-shear rate viscosity indicates the consistency of the product during processing (e.g. pumping, mixing, spraying); a higher h∞ value implies a greater energy required for processing (Razavi et al., 2014). All the purified gums exhibited higher infinite shear viscosity than crude cress seed gum. Razavi et al. (2009) reported different values for power law model parameters of crude and purified BSG gum. Power law and cross model parameters of salep showed different values after removal of impurities by ethanol treatment (Kurt &Kahyaoglu, 2015). 3.4. Relationship between steady and dynamic shear rheology According to the empirical Cox-Merz rule, the variation of complex viscosity (h*) as a function of angular frequency can be compared to apparent viscosity (ha) as a function of shear rate (Cox &Merz, 1958). If the polymer solutions are devoid of energetic interactions, dynamic and steady shear viscosities should be identical (Karazhiyan et al., 2011b; Razavi et al., 2014). Unlike irregular biopolymers, polysaccharides solutions with a rigid and ordered chain conformation, showing gel like behavior (e.g. xanthan, sage seed gum and gellan polysaccharides), violate the Cox-Merz rule (Chronakis & Kasapis, 1995; Miyoshi & Nishinari, 1999; Bot, Smorenburg, Vreeker, P^ aques, & Clark, 2001; Fang, Takemasa, Katsuta, & Nishinari, 2004; Razavi et al., 2014). As demonstrated in Fig.3, the complex dynamic viscosity was larger than steady shear viscosity which deviating from the Cox-Merz rule, indicating a tenuous network which remained intact under low amplitude oscillation but was disrupted under continuous shear (Miyoshi &

364

S. Razmkhah et al. / Food Hydrocolloids 61 (2016) 358e368

Table 4 Steady shear rheological parameters of crude and purified cress seed gums. Model Power law model kp (Pa sn) nP R2 Bingham model t0B (Pa) hB (Pa s) R2 HerscheleBulkley model t0H (Pa) kH (Pa sn) nH R2 Casson model t0c (Pa) hc(Pa s) R2 Moore model h0 (Pa s) h∞ (Pa s) t (s) R2

CSG

E

EI

I

0.690 ± 0.040 d 0.444 ± 0.003 a 0.941

6.206 ± 0.160 a 0.242 ± 0.007 d 0.885

5.616 ± 0.079 b 0.273 ± 0.004 c 0.906

2.953 ± 0.037 c 0.295 ± 0.003 b 0.892

0.345 ± 0.040 d 0.025 ± 0.002 d 0.830

6.184 ± 0.153 a 0.070 ± 0.003 b 0.857

5.491 ± 0.255 b 0.079 ± 0.001 a 0.839

2.812 ± 0.161 c 0.051 ± 0.001 c 0.850

0.174 ± 0.003 d 0.402 ± 0.020 d 0.533 ± 0.020 a 0.976

4.368 ± 0.250 a 1.581 ± 0.031 b 0.477 ± 0.010 b 0.993

3.429 ± 0.228 b 1.945 ± 0.167 a 0.456 ± 0.014 b 0.990

1.760 ± 0.160 c 1.044 ± 0.116 c 0.479 ± 0.019 b 0.985

0.356 ± 0.005 d 0.017 ± 0.001 d 0.926

5.260 ± 0.417 a 0.032 ± 0.001 b 0.967

4.661 ± 0.147 b 0.039 ± 0.001 a 0.954

2.367 ± 0.092 c 0.026 ± 0.001 c 0.962

3.174 ± 0.310 d 0.017 ± 0.000 d 1.024 ± 0.080 c 0.999

59.095 ± 2.095 a 0.050 ± 0.001 b 5.853 ± 0.303 a 0.959

37.663 ± 1.653 b 0.054 ± 0.001 a 3.163 ± 0.635 b 0.947

15.714 ± 2.679 c 0.035 ± 0.000 c 2.740 ± 0.509 b 0.949

CSG, crude cress seed gum; E, CSG purified by ethanol; I, CSG purified by isopropanol; EI, CSG purified by ethanol-isopropanol. Different letters indicate significant differences between samples at p < 0.05 by LSD test.

a

Nishinari, 1999). Therefore, it could be concluded that gel like structures of the crude and purified cress seed gums were sensitive to steady shear. All the purified gums showed similar trends, and for the crude gum the deviation from the rule was more considerable at low frequencies. This observation was consistent with Karazhiyan et al. (2011b) findings for hydrocolloid extract from the seeds of Lepidium sativum. 3.5. Effect of temperature The response of hydrocolloid viscosity to temperature is significant in food industries due to the wide range of temperatures encountered during processing and storage of food dispersions containing gums (Anvari et al., 2016; Wu, Ding, Jia, & He, 2015). As shown in Fig. 4, apparent viscosity of the samples decreased as the temperature increased. According to Eyring’s theory, there are spaces within fluids for the movement of molecules and they need energy to permanently move in these spaces; at high temperatures,

there is sufficient energy in the system to provide the activation energy needed for molecules to move freely and the fluid flows simply (Abbastabar, Azizi, Adnani, &Abbasi, 2015; Anvari et al., 2016). The corresponding values of Arrhenius model parameters are summarized in Table 5. The temperature dependent behavior of the gum solutions was well described by the Arrhenius relationship. Karazhiyan et al. (2009) also indicated that the change of apparent viscosity of lepidium sativum seed extract with temperature obeyed the Arrhenius model. Activation energy (Ea) indicates the energy required for an elementary flow process to occur, and is dependent on polymer concentration, ionic strength, polymer physicochemical characteristics and on the shear stress applied (Alves et al.,  n, Mun ~ oz, Ramírez, Gala n, &Alfaro, 2014). CSG and EI 2010; Rinco showed the highest and the lowest Ea, respectively. The microstructure of CSG was more sensitive to the temperature and the network structure formed by its molecules was gradually destroyed with increasing temperature (Xu, Gong, Dong, & Li, 2015). All the purification methods increased thermal stability of cress seed gum, which might be related to elimination of impurities (especially drastic reduction of protein) and formation of more stable and ordered polysaccharide structures. The effect of temperature on viscosity is closely related to characteristics of structure (Sun et al., 2014), so with respect to different structural characteristics (i.e.,

Table 5 Arrhenius model parameters, hysteresis area and degree of structure recovery (DSR) of crude and purified cress seed gums. Sample

Arrhenius model parameters Ea(kJ/mol)

CSG E EI I Fig. 4. Effect of temperature on the viscosity of crude and purified cress seed gums (CSG, crude cress seed gum; E, CSG purified by ethanol; I, CSG purified by isopropanol; EI, CSG purified by ethanol-isopropanol) at constant shear rate of 5s1.

0.167 0.096 0.031 0.103

± ± ± ±

0.012 a 0.008b 0.004c 0.014 b

Thixotropy parameters R2

Hysteresis area

0.995 0.994 0.975 0.993

10.83 21.94 46.23 26.72

± ± ± ±

0.33 1.01 2.23 0.72

d c a b

DSR 0.545 0.383 0.413 0.392

± ± ± ±

0.025 0.013 0.020 0.014

a b b b

CSG, crude cress seed gum; E, CSG purified by ethanol; I, CSG purified by isopropanol; EI, CSG purified by ethanol-isopropanol. Different letters indicate significant differences between samples at p < 0.05 by LSD test. a

S. Razmkhah et al. / Food Hydrocolloids 61 (2016) 358e368

365

monosaccharide composition, ash, carbon, protein content and molecular weight) of the purified gums (Razmkhah et al., 2016), different temperature sensitivity was observed. Cunha et al. (2007) reported that crude and purified guar gums (purification with different methods) showed different activation energy values. 3.6. Thixotropy Thixotropy is defined as the decrease in viscosity as a function of shear time, which is recovered when shearing is removed (Ma, Lin, Chen, Zhao, & Zhang, 2014; Souza et al., 2015; Wei et al., 2015). One of the methods that used to characterize thixotropic behavior is hysteresis loop test, the area between the up curve and the down curve is an index of the energy needed to eliminate the effect of time on flow behavior (Chandra & Shamasundar, 2015; Khodaei, Razavi, & Khodaparast, 2014). Even though the loop test is quick and qualitative, it has a certain limitation. Shear rate and time are coupled in this experiment, which cannot be resolved into the separate effects of these two parameters (Mewis & Wagner, 2009; Wang et al., 2010). The in-shear structural recovery test was carried out in order to investigate the capability of the crude and purified cress seed gum dispersions to recover their original structure under low shear conditions after decomposition under high-shear conditions (Mezger, 2006). As shown in Fig. 5, a hysteresis loop area was observed for CSG and the purified samples, which indicated time-dependent fluid behavior (Steffe, 1996). The corresponding areas of hysteresis loops and the quantitative results of the in-shear structural recovery test were given in Table 5. CSG showed the lowest hysteresis loop area and the highest structural recovery (DSR), reflecting that CSG returned to its original structure more quickly after deformation than the purified samples (Fig.6). This result was also consistent with the dynamic viscoelastic data in which the purified gums having more structured systems broke down partially with increasing shearing time and exhibited higher  pez, Ve lez-Ruiz, hysteresis loop areas than CSG (Morell, Ramírez-Lo & Fiszman, 2015; Viturawong, Achayuthakan, & Suphantharika, 2008). As shown in Table 5, sample E exhibited the lowest hysteresis loop area among the purified gums. This result was consistent with its higher modulus (related to the higher viscoelastic property), higher yield stress and also apparent viscosity. In addition, sample E had higher molecular weight compared to samples I and EI due to the degradation of chain length in the presence of isopropanol (Razmkhah et al., 2016); which might affect the interactions of polymer chains. DSR values for the purified samples showed no significant difference. This difference between the

Fig. 6. Results of the in-shear structural recovery test for crude and purified cress seed gums (CSG, crude cress seed gum; E, CSG purified by ethanol; I, CSG purified by isopropanol; EI, CSG purified by ethanol-isopropanol).

results of the structural recovery and hysteresis loop tests could be explained by the simultaneously changes of shear rate and time in the loop test, which makes the test less suitable to investigate the effect of time (Wang et al., 2010). Sikora et al. (2015) also observed no quantitative relation between DSR values and areas of the hysteresis loops for potato starch pastes. With respect to different structural and physicochemical properties of the samples (Razmkhah et al., 2016), different thixotropy behavior was expected. Karazhiyan et al. (2009) reported that Lepidium sativum seed extract had thixotropic behavior, Naji, Razavi, and Karazhiyan (2012b) and Naji and Razavi (2014)also indicated that cress seed gum exhibited thixotropic behavior under different thermal treatments and refrigeration conditions. 3.7. Intrinsic viscosity As demonstrated in Figs. 7 and 8, very good linear extrapolations observed for both Huggins and Kraemer plots, which indicate the efficiency of these relations to determine the intrinsic viscosity of the samples. The master curve (plot of log (hsp) against log C[h]) was used to determine the critical concentration (coil overlap parameter) and the dilute Newtonian domain (Fig. 9) (Launay, Cuvelier, & Martinez-Reyes, 1997; Morris, Cutler, Ross-Murphy, Rees, & Price, 1981). The master curve slope of the crude and purified gums were in

9 CSG (up) CSG (down) E (up) E (down) EI (up) EI (down) I (up) I (down)

8

Shear stress (Pa)

7

6 5 4 3 2 1 0

1

10

100

Shear rate (s-1) Fig. 5. Hysteresis loop of the flow curves for crude and purified cress seed gums (CSG, crude cress seed gum; E, CSG purified by ethanol; I, CSG purified by isopropanol; EI, CSG purified by ethanol-isopropanol).

Fig. 7. A typical dual Huggins (filled symbols) and Kraemer (blank symbols) plots of crude cress seed gum (CSG, circle symbols) and CSG purified by ethanol-isopropanol (EI, square symbols) in deionized water (25 C).

366

S. Razmkhah et al. / Food Hydrocolloids 61 (2016) 358e368

Fig. 8. A typical dual Huggins (filled symbols) and Kraemer (blank symbols) plots of cress seed gum purified by ethanol (E, circle symbols) and cress seed gum purified by isopropanol (I, square symbols) in deionized water (25 C).

Fig. 9. Log (specific viscosity) as a function of log (concentration  intrinsic viscosity) for crude and purified cress seed gums in deionized water at 25  C (CSG, crude cress seed gum; E, CSG purified by ethanol; I, CSG purified by isopropanol; EI, CSG purified by ethanol-isopropanol).

the range of 1.131e1.274, which shows all solutions were in the dilute domain. Morris et al. (1981) reported that this slope was close to 1.4 for several food gums in a dilute domain. The molecular entanglement occurs when dimensionless concentration or Berry number (C[h]) becomes more than one, and semi-dilute regime exists in the range of 1.0e10.0 (Graessley, 1974). As shown in Table 6, the C[h] value was in the range of 0.154e0.832, indicating no coil overlap occurred. The slope of power-law model (Eq. (11)) or exponent b value greater than unity is related to random coil conformation in a dilute regime, whereas less value is associated with rod-like conformation (Lapasin &Pricl, 1995; Morris et al., 1981). The b value for CSG and the purified gums were in the range of 1.133e1.252 (Table 6), which revealed random coil

conformation of them, meaning that no change occurred in molecular conformation of CSG after purification. Behrouzian et al. (2014) reported the b value of 1.08 for cress seed gum, and Karazhiyan et al. (2009) suggested that the macromolecular component in L. sativum extract had a semi-rigid chain conformation with intermediate flexibility between random coil and rigid rod. The exponent b values of the samples were very similar to that reported by Higiro, Herald, and Alavi, (2006) for LBG in the dilute regime (1.234). The Huggins constant (KH) is related to polymerepolymer interactions, and reveals the general conformation of a polymer (Cunha et al., 2007; Qian, Cui, Wu, & Goff, 2012). It is approximately 0.3e0.4 for flexible macromolecules with extended shapes in good solvents, and values higher than 1.0 are attributed to intermolecular associations (Goh, Matia-Merino, Pinder, Saavedra, & Singh, 2011; Khounvilay & Sittikijyothin, 2012). The value of KH was higher (1.373) for CSG and there was no significant difference among the purified gums (0.927e0.998) (Table 6), implying that the purified gums had higher chain flexibility. KH values of galactomannans from non-traditional sources were determined around 1.10e1.33 (Cerqueira et al., 2009).Gaisford, Harding, Mitchellt, and Bradley (1986) found KH value of 1.04 for guar gum. The instinct viscosity [h] of CSG was 0.726 dL g1 and it increased significantly after purification (1.592e1.659 dL g1), which could be related to elimination of impurities, enzymes and protein fraction. Youssef et al. (2009) also indicated that the intrinsic viscosity increased when the protein level was decreased. Intrinsic viscosity is influenced directly by molecular weight and conformation of the macromolecule (Qian, Cui, Wang, Wang, & Zhou, 2011). In general, intrinsic viscosity of the purified samples increased along the series of I, EI and E, molecular weight increased and protein content decreased significantly along the same series (Razmkhah et al., 2016). Lower intrinsic viscosity with higher molecular weight of CSG could be attributed to more compact conformation of it in comparison with the purified gums. The KH values also revealed more compact conformation of CSG (KH ¼ 1.373), as lower value of KH is expected for more extended biopolymer (Table 6). Brummer, Cui, and Wang (2003) showed that guar gum had higher intrinsic viscosity than fenugreek gum despite the fact that its molecular weight was smaller. Also, the fraction of basil seed gum with the highest molecular weight exhibited the lowest intrinsic viscosity value (Naji-Tabasi, Razavi, Mohebbi, & Malaekeh-Nikouei, 2016). The intrinsic viscosity values of the crude and purified samples were in good agreement with the results of dynamic and steady shear measurements. 4. Conclusion The strain sweep and frequency sweep measurements of the crude and purified gums indicated weak gel-like behavior, and all the samples exhibited shear thinning behavior in steady shear measurements. The purified samples had stronger and more elastic network structure than the crude gum due to elimination of impurities and protein fraction after purification. The gel network got

Table 6 Intrinsic viscosity parameters of crude and purified cress seed gums in deionized water at 25 C.

[h] dL gr1 KH C[h] b

CSG

E

EI

I

0.726 ± 0.018 d 1.373 ± 0.164 a 0.154e0.369 1.252 ± 0.019 a

1.659 ± 0.004 a 0.947 ± 0.012 b 0.414e0.832 1.165 ± 0.001 c

1.621 ± 0.000 b 0.927 ± 0.021 b 0.304e0.610 1.133 ± 0.002 d

1.592 ± 0.003 c 0.998 ± 0.051 b 0.397e0.797 1.184 ± 0.010 b

CSG, crude cress seed gum; E, CSG purified by ethanol; I, CSG purified by isopropanol; EI, CSG purified by ethanol-isopropanol. a Different letters indicate significant differences between samples at p < 0.05 by LSD test.

S. Razmkhah et al. / Food Hydrocolloids 61 (2016) 358e368

stronger along the series of I, EI and E, apparent viscosity and intrinsic viscosity also increased along the same series. Lower intrinsic viscosity of CSG was attributed to its more compact conformation in comparison with the purified gums. Microstructure of CSG was more sensitive to the temperature, and the purified gums showed stronger thixotropic properties due to their more structured systems. Therefore, the crude and purified cress seed gums can be used in a variety of applications as stabilizers, thickeners and gelling agents depending on their rheological behavior. References Abbastabar, B., Azizi, M. H., Adnani, A., & Abbasi, S. (2015). Determining and modeling rheological characteristics of quince seed gum. Food Hydrocolloids, 43, 259e264. Achayuthakan, P., & Suphantharika, M. (2008). Pasting and rheological properties of waxy corn starch as affected by guar gum and xanthan gum. Carbohydrate Polymers, 71, 9e17. Alves, V. D., Freitas, F., Costa, N., Carvalheira, M., Oliveira, R., Gonçalves, M. P., et al. (2010). Effect of temperature on the dynamic and steady-shear rheology of a new microbial extracellular polysaccharide produced from glycerol byproduct. Carbohydrate Polymers, 79, 981e988. Amid, B. T., & Mirhosseini, H. (2012). Influence of different purification and drying methods on rheological properties and viscoelastic behaviour of durian seed gum. Carbohydrate Polymers, 90, 452e461. Anvari, M., Tabarsa, M., Cao, R., You, S., Joyner, H. S., Behnam, S., et al. (2016). Compositional characterization and rheological properties of an anionic gum from Alyssum homolocarpum seeds. Food Hydrocolloids, 52, 766e773. Balaghi, S., Mohammadifar, M. A., Zargaraan, A., AhmadiGavlighi, H., & Mohammadi, M. (2011). Compositional analysis and rheological characterization of gum tragacanth exudates from six species of Iranian Astragalus. Food Hydrocolloids, 25, 1775e1784. Behrouzian, F., Razavi, S. M. A., & Karazhiyan, H. (2013). The effect of pH, salts and sugars on the rheological properties of cress seed (Lepidium sativum) gum. International Journal of Food Science and Technology, 48, 2506e2513. Behrouzian, F., Razavi, S. M. A., & Karazhiyan, H. (2014). Intrinsic viscosity of cress (Lepidium sativum) seed gum: effect of salts and sugars. Food Hydrocolloids, 25, 100e105. Bot, A., Smorenburg, H. E., Vreeker, R., P^ aques, M., & Clark, A. H. (2001). Melting behaviour of schizophyllan extracellular polysaccharide gels in the temperature range between 5 and 20 C. Carbohydrate Polymers, 45, 363e372. Bouzouita, N., Khaldi, A., Zgoulli, S., Chebil, L., Chekki, R., Chaabouni, M. M., et al. (2007). The analysis of crude and purified locust bean gum: a comparison of samples from different carob tree populations in Tunisia. Food Chemistry, 101, 1508e1515. Brummer, Y., Cui, S. W., & Wang, Q. (2003). Extraction, purification and physicochemical characterization of fenugreek gum. Food Hydrocolloids, 17, 229e236. Cerqueira, M. A., Pinheiro, A. C., Souza, B. W. S., Lima, A. M. P., Ribeiro, C., Miranda, C., et al. (2009). Extraction, purification and characterization of galactomannans from non-traditional sources. Carbohydrate Polymers, 75, ,408e414. Chandra, M. V., & Shamasundar, B. A. (2015). Rheological properties of gelatin prepared from the swim bladders of freshwater fish Catlacatla. Food Hydrocolloids, 48, 47e54. Chronakis, I. S., & Kasapis, S. (1995). Food applications of biopolymer-theory and practice. Developments in Food Science, 37, 75e109. Clark, A. H., & Ross-Murphy, S. B. (1987). Structural and mechanical properties of biopolymer gels. Advances in Polymer Science, 83, 57e192. Cox, W. P., & Merz, E. H. (1958). Correlation of dynamic and steady flow viscosities. Journal of Polymer Science, 28, 619e622. Cui, S. W. (2005). Food carbohydrates: Chemistry, physical properties, and applications. Boca Raton, FL: CRC Press, Taylor & Francis Group. Cunha, P. L. R., Paula, R. C. M., & Feitosa, J. P. A. (2007). Purification of guar gum for biological applications. International Journal of Biological Macromolecules, 41, 324e331. Da Silva, J. L. A. L., & Rao, M. A. (1992). Viscoelastic properties of food hydrocolloid dispersions. In M. A. Rao, & J. F. Steffe (Eds.), Viscoelastic properties of food (pp. 285e315). New York: Elsevier Applied Science. Dakia, P. A., Blecker, C., Robert, C., Wathelet, B., & Paquot, M. (2008). Composition and physicochemical properties of locust bean gum extracted from whole seeds by acid or water dehulling pre-treatment. Food Hydrocolloids, 22, 807e818. Fadavi, G., Mohammadifar, M. A., Zargarran, A., Mortazavian, A. M., & Komeili, R. (2014). .Composition and physicochemical properties of Zedo gum exudates from Amygdalusscoparia. Carbohydrate Polymers, 101, 1074e1080. Fang, Y., Takemasa, M., Katsuta, K., & Nishinari, K. (2004). Rheology of schizophyllan solutions in isotropic and anisotropic phase regions. Journal of Rheology (1978present), 48, 1147e1166. Gaisford, S. E., Harding, S. E., Mitchellt, J. R., & Bradley, T. D. (1986). A comparison between the hot and cold water soluble fractions of two locust bean gum samples. Carbohydrate Polymers, 6, 423e442. Goh, K. K. T., Matia-Merino, L., Pinder, D. N., Saavedra, C., & Singh, H. (2011). Molecular characteristics of a novel water-soluble polysaccharide from the New

367

Zealand black tree fern (Cyatheamedullaris). Food Hydrocolloids, 25, 286e292. Graessley, W. W. (1974). The entanglement concept in polymer rheology. In Advances in polymer science, 16Berlin: Springer-Verlag, 1e179. Higiro, J., Herald, T. J., & Alavi, S. (2006). Rheological study of xanthan and locust bean gum interaction in dilute solution. Food Research International, 39, 165e175. Higiro, J., Herald, T., Alavi, S., & Bean, S. (2007). Rheological study of xanthan and locust bean gum interaction in dilute solution: effect of salt. Food Research International, 40, 435e447. Huggins, M. L. (1942). The viscosity of dilute solutions of long-chain molecules. IV. Dependence on concentration. Journal of the American Chemical Society, 64, 2716e2718. Karazhiyan, H., Razavi, S. M. A., & Phillips, G. O. (2011). Extraction optimization of a hydrocolloid extract from cress seed (Lepidium sativum) using response surface methodology. Food Hydrocolloids, 25, 915e920. Karazhiyan, H., Razavi, S. M. A., Phillips, G. O., Fang, Y., Al-Assaf, S., & Nishinari, K. (2011). Physicochemical aspects of hydrocolloid extract from the seeds of Lepidium sativum. International Journal of Food Science and Technology, 46, 1066e1072. Karazhiyan, H., Razavi, S. M. A., Phillips, G. O., Fang, Y., Al-Assaf, S., Nishinari, K., et al. (2009). Rheological properties of Lepidium sativum seed extract as a function of concentration, temperature and time. Food Hydrocolloids, 23, 2062e2068. Khodaei, D., Razavi, S. M. A., & Khodaparast, M. H. H. (2014). Functional properties of Balangu seed gum over multiple freezeethaw cycles. Food Research International, 66, 58e68. Khondkar, D., Tester, R. F., Hudson, N., Karkalas, J., & Morrow, J. (2007). Rheological behaviour of uncross-linked and cross-linked gelatinised waxy maize starch with pectin gels. Food Hydrocolloids, 21, 1296e1301. Khounvilay, K., & Sittikijyothin, W. (2012). Rheological behaviour of tamarind seed gum in aqueous solutions. Food Hydrocolloids, 26, 334e338. €k, M. S. (2007). A comparative study on the compositions of crude and refined Ko locust bean gum: in relation to rheological properties. Carbohydrate Polymers, 70, 68e76. Koocheki, A., Taherian, A. R., & Bostan, A. (2013). Studies on the steady shear flow behavior and functional properties of Lepidium perfoliatum seed gum. Food Research International, 50, 446e456. Kraemer, E. O. (1938). Molecular weights of cellulose and cellulose derivatives. Industrial and Engineering Chemistry, 30, 1200e1203. Kurt, A., & Kahyaoglu, T. (2015). Rheological properties and structural characterization of salep improved by ethanol treatment. Carbohydrate Polymers, 133, 654e661. Lai, L., Tung, J., & Lin, P. (2000). Solution properties of hsian-tsao (MesonaprocumbensHemsl) leaf gum. Food Hydrocolloids, 14, ,287e294. Lapasin, R., & Pricl, S. (1995). Rheology of polysaccharide systems. Springer. Launay, B., Cuvelier, G., & Martinez-Reyes, S. (1997). Viscosity of locust bean, guar and xanthan gum solutions in the Newtonian domain: a critical examination of the log (hsp)0elog C[h]0 master curves. Carbohydrate Polymers, 34, 385e395. Lin, S. Y., Amidon, G. L., Weiner, N. D., & Goldberg, A. H. (1993). Viscoelasticity of cellulose polymers and mucociliary transport on frog palates. International Journal of Pharmaceutics, 95, 57e65. Lubambo, A. F., de Freitas, R. A., Sierakowski, M., Lucyszyn, N., Sassaki, G. L., Serafim, B. M., et al. (2013). Electrospinning of commercial guar-gum: effects of purification and filtration. Carbohydrate Polymers, 93, 484e491. Lv, C., Wang, Y., Wang, L., Li, D., & Adhikari, B. (2013). Optimization of production yield and functional properties of pectin extracted from sugar beet pulp. Carbohydrate Polymers, 95, 233e240. Ma, J., Lin, Y., Chen, X., Zhao, B., & Zhang, J. (2014). Flow behavior, thixotropy and dynamical viscoelasticity of sodium alginate aqueous solutions. Food Hydrocolloids, 38, 119e128. Mandala, I., Savvas, T., & Kostaropoulos, A. (2004). Xanthan and locust bean gum influence on the rheology and structure of a white model-sauce. Journal of Food Engineering, 64, 335e342. Mewis, J., & Wagner, N. J. (2009). Thixotropy. Advances in Colloid and Interface Science, 147, 214e227. Mezger, T. G. (2006). The rheology handbook: For users of rotational and oscillatory rheometers (2nd ed., pp. 114e141). Hannover: Vincentz Network. Miyoshi, E., & Nishinari, K. (1999). Non-Newtonian flow behaviour of gellan gum aqueous solutions. Colloid and Polymer Science, 277, 727e734. pez, C., Ve lez-Ruiz, J. F., & Fiszman, S. (2015). Relating HPMC Morell, P., Ramírez-Lo concentration to elicited expected satiation in milk-based desserts. Food Hydrocolloids, 45, 158e167. Morris, E. R., Cutler, A., Ross-Murphy, S., Rees, D., & Price, J. (1981). Concentration and shear rate dependence of viscosity in random coil polysaccharide solutions. Carbohydrate Polymers, 1, 5e21. Naji-Tabasi, S., & Razavi, S. M. A. (2016). New studies on basil (Ocimum bacilicum L.) seed gum: Part III e steady and dynamic shear rheology. Food Hydrocolloids. http://dx.doi.org/10.1016/j.foodhyd.2015.12.020. article in press. Naji-Tabasi, S., Razavi, S. M. A., Mohebbi, M., & Malaekeh-Nikouei, B. (2016). New studies on basil (Ocimum bacilicum L.) seed gum: Part I e fractionation, physicochemical and surface activity characterization. Food Hydrocolloids, 52, 350e358. Naji, S., & Razavi, S. M. A. (2014). Functional and textural characteristics of cress seed (Lepidiumsativum) gum and xanthan gum: effect of refrigeration condition. Food Bioscience, 5, 1e8. Naji, S., Razavi, S. M. A., & Karazhiyan, H. (2012b). Effect of thermal treatments on

368

S. Razmkhah et al. / Food Hydrocolloids 61 (2016) 358e368

functional properties of cress seed (Lepidium sativum) and xanthan gums: a comparative study. Food Hydrocolloids, 28, 75e81. Naji, S., Razavi, S. M. A., & Karazhiyan, H. (2013). Effect of freezing on functional and textural attributes of cress seed gum and xanthan gum. Food and Bioprocess Technology, 6, 1302e1311. Naji, S., Razavi, S. M. A., Karazhiyan, H., & Koocheki, A. (2012a). Influence of thermal treatments on textural characteristics of cress seed (Lepidium sativum) gum gel. Electronic Journal of Environmental, Agricultural and Food Chemistry, 11, 222e237. € Ozkan, N., Xin, H., & Chen, X. D. (2002). Application of a depth sensing indentation hardness test to evaluate the mechanical properties of food materials. Journal of Food Sciences, 67(5), 1814e1820. Qian, H. F., Cui, S. W., Wang, Q., Wang, C., & Zhou, H. M. (2011). Fractionation and physicochemical characterization of peach gum polysaccharides. Food Hydrocolloids, 25, 1285e1290. Qian, K., Cui, S., Wu, Y., & Goff, H. (2012). Flaxseed gum from flaxseed hulls: extraction, fractionation, and characterization. Food Hydrocolloids, 28, 275e283. Rao, M. A. (1999). Rheology of fluid and semisolid foods; principles and applications. USA: Aspen Publishers, Inc. Razavi, S. M. A., Bostan, A., Niknia, S., & Razmkhah, S. (2011). Functional properties of hydrocolloid extracted from selected domestic Iranian seeds (in Persian language). Journal of Food Research, 21(3), 380e389. Razavi, S. M. A., Cui, S. W., & Ding, H. (2016). Structural and physicochemical characteristics of a novel water-soluble gum from Lallemantia royleana seed. International Journal of Biological Macromolecules, 83, 142e151. Razavi, S. M. A., Cui, S. W., Guo, Q., & Ding, H. (2014). Some physicochemical properties of sage (Salvia macrosiphon) seed gum. Food Hydrocolloids, 35, 453e462. Razavi, S. M. A., Farhoosh, R., & Bostan, A. (2007). Functional properties of hydrocolloid extract of some domestic Iranian seeds. Research project No.1475, Unpublished report. Iran: Ferdowsi University of Mashhad. Razavi, S. M. A., Mortazavi, S. A., Matia-Merino, L., Hosseini-Parvar, S. H., Motamedzadegan, A., & Khanipour, E. (2009). Optimization study of gum extraction from Basil seeds (Ocimum basilicum L.) using response surface methodology. International Journal of Food Science and Technology, 44, 1755e1762. Razmkhah, S., Mohammadifar, M. A., Razavi, S. M. A., & Ale, M. T. (2016). Purification of cress seed (Lepidium sativum) gum: physicochemical characterization and functional properties. Carbohydrate Polymers, 141, 166e174. n, F., Mun ~ oz, J., Ramírez, P., Gal Rinco an, H., & Alfaro, M. C. (2014). Physicochemical and rheological characterization of Prosopisjuliflora seed gum aqueous dispersions. Food Hydrocolloids, 35, 348e357. Shatwell, K. P., Sutherland, I. W., Ross-Murphy, S. B., & Dea, I. C. M. (1991). Influence of the acetyl substituent on the interaction of xanthan with plant

polysaccharides e I.Xanthan-Locust bean gum systems. Carbohydrate Polymers, 14, 29e51. Sikora, M., Adamczyk, G., Krystyjan, M., Dobosz, A., Tomasik, P., Berski, W., et al. (2015). Thixotropic properties of normal potato starch depending on the degree of the granules pasting. Carbohydrate Polymers, 121, 254e264. da Silva, J. A. L., & Gonçalves, M. P. (1990). Studies on a purification method for locust bean gum by precipitation with isopropanol. Food Hydrocolloids, 4, 277e287. ^mara, P. B. S., Gul~ Souza, C. J. F., Ramos, A. V., Ca ao, E. S., Campos, M. F., & GarciaRojas, E. E. (2015). Polymeric complexes obtained from the interaction of bovine serum albumin and k-carrageenan. Food Hydrocolloids, 45, 286e290. Steffe, J. F. (1996). Rheological methods in food process engineering. East Lansing, MI, USA: Freeman Press. Sun, F., Huang, Q., & Wu, J. (2014). Rheological behaviors of an exopolysaccharide from fermentation medium of a Cordycepssinensis fungus (Cs-HK1). Carbohydrate Polymers, 114, 506e513. €ndar, H., Fujita, D., Saluri, K., Truus, K., et al. (2015). Tuvikene, R., Robal, M., Ma Funorans from Gloiopeltis species. Part II. Rheology and thermal properties. Food Hydrocolloids, 43, 649e657. Viturawong, Y., Achayuthakan, P., & Suphantharika, M. (2008). Gelatinization and rheological properties of rice starch/xanthan mixtures: effects of molecular weight of xanthan and different salts. Food Chemistry, 111, 106e114. € Wang, B., Li, D., Wang, L.-J., & Ozkan, N. (2010). Anti-thixotropic properties of waxy maize starch dispersions with different pasting conditions. Carbohydrate Polymers, 79, 1130e1139. € Wang, B., Wang, L.-J., Li, D., Ozkan, N., Li, S.-J., & Mao, Z.-H. (2009). Rheological properties of waxy maize starch and xanthan gum mixtures in the presence of sucrose. Carbohydrate Polymers, 77, 472e481. Wei, Y., Lin, Y., Xie, R., Xu, Y., Yao, J., & Zhang, J. (2015). The flow behavior, thixotropy and dynamical viscoelasticity of fenugreek gum. Journal of Food Engineering, 166, 21e28. Wu, Y., Ding, W., Jia, L., & He, Q. (2015). .The rheological properties of tara gum (Caesalpiniaspinosa). Food Chemistry, 168, 366e371. Xiu, A., Zhou, M., Zhu, B., Wang, S., & Zhang, J. (2011). Rheological properties of Salecan as a new source of thickening agent. Food Hydrocolloids, 25, 1719e1725. Xu, L., Gong, H., Dong, M., & Li, Y. (2015). Rheological properties and thickening mechanism of aqueous diutan gum solution: effects of temperature and salts. Carbohydrate Polymers, 132, 620e629. Yousefi, A. R., & Razavi, S. M. A. (2015). Dynamic rheological properties of wheat starch gels as affected by chemical modification and concentration. Starch, 67, 7e8, 567e576. Youssef, M. K., Wang, Q., Cui, S. W., & Barbut, S. (2009). Purification and partial physicochemical characteristics of protein free fenugreek gums. Food Hydrocolloids, 23, 2049e2053.