Rheological characterization of fenugreek gum and comparison with other galactomannans

Rheological characterization of fenugreek gum and comparison with other galactomannans

Accepted Manuscript Rheological characterization of fenugreek gum and comparison with other galactomannans Pravin Vasant Gadkari, Sylvana Tu, Khorame...

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Accepted Manuscript Rheological characterization of fenugreek gum and comparison with other galactomannans

Pravin Vasant Gadkari, Sylvana Tu, Khorametha Chiyarda, Martin J.T. Reaney, Supratim Ghosh PII: DOI: Reference:

S0141-8130(18)31840-3 doi:10.1016/j.ijbiomac.2018.07.108 BIOMAC 10152

To appear in:

International Journal of Biological Macromolecules

Received date: Revised date: Accepted date:

18 April 2018 13 July 2018 17 July 2018

Please cite this article as: Pravin Vasant Gadkari, Sylvana Tu, Khorametha Chiyarda, Martin J.T. Reaney, Supratim Ghosh , Rheological characterization of fenugreek gum and comparison with other galactomannans. Biomac (2018), doi:10.1016/ j.ijbiomac.2018.07.108

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ACCEPTED MANUSCRIPT

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Rheological characterization of fenugreek gum and comparison with other galactomannans

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and Supratim Ghosh1*

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Pravin Vasant Gadkari1, Sylvana Tu1, Khorametha Chiyarda1, Martin J.T. Reaney 2,3

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Department of Food and Bioproduct Science, 2

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Department of Plant Sciences,

College of Agriculture and Bioresources,

Guangdong Saskatchewan Oilseed Joint Laboratory, Department of Food Science and

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Engineering, Jinan University, 601 Huangpu Avenue West, Guangzhou, Guangdong

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510632, China

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University of Saskatchewan, Saskatoon, SK S7N 5A8, Canada

*Corresponding author. Tel: +1 (306) 966-2555; Fax: +1 (306) 966-8898. E-mail address: [email protected]

ACCEPTED MANUSCRIPT Abstract Fenugreek gum (FG), guar gum (GG), and locust bean gum (LBG) dispersions were studied for their flow behavior, intrinsic viscosity, viscoelasticity and the effect of environmental stress on their physicochemical properties. Shear thinning behaviour was

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observed in all three gum dispersions prepared at concentrations greater than 0.25

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wt%. The impact of the change in concentration (0.125 to 2 wt%) on dispersion flow

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behavior and consistency coefficient were determined using power law model. Both GG and LBG dispersions have a higher intrinsic viscosities (16.93 ± 0.02 dL/g and 15.20 ±

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0.02 dL/g) compared to FG (13.46 ± 0.02 dL/g), but FG has higher average viscosity

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molecular weight (3.10 ± 0.01) compared to GG and LBG. This could impart higher apparent viscosity to FG dispersions compared to GG and LBG. All gum dispersions

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above 0.1 wt% concentration showed entanglement among the polymer chains.

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Variation in pH (3 - 7) did not significantly affect viscosity of the dispersions while it was significantly decreased with the addition of NaCl. The FG had superior gelling properties

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compared to GG, and LBG at 1 wt% concentration which could have potential

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application in certain food and non-food products.

Keywords: Fenugreek gum (FG); galactomannans; intrinsic viscosity, zero-shear viscosity, viscoelasticity; environmental stress

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ACCEPTED MANUSCRIPT 1. Introduction Recently, studies have expanded our understanding of naturally derived gums or exudates and their potential for industrial application in food, cosmetics, and pharmaceuticals [1]. In response to the introduction of a wide range of applications for

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natural gums in consumer goods, demand and increased prices have prompted

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researchers to seek new sources of gums. Fenugreek (FG), locust bean (LBG) and

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guar gum (GG) are naturally derived galactomannan hydrocolloids with characteristic differences in the ratios of galactose (G) and mannose (M) subunits [2]. Although LBG

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and GG are widely used in foods as thickeners and stabilizers, FG is comparatively

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primitive, and more research regarding rheological and physicochemical properties is needed to assist in developing a wide-spread application in food and non-food systems.

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The galactomannans are seed endosperm polysaccharides of plants belonging to the

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Leguminosae family [3]. Their structure consists of linear chains of (1→4) linked β-dmannose residues (M), where some of the M residues carry a single residue of α-d-

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galactose attached by a (1→6) glycosidic bond. The major difference between

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galactomannan structures from these gums is the mannose to galactose (M:G) ratio (Fig.1). Typically the M:G ratio for FG is about 1:1, and GG is about 2:1, while for locust

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bean gum (LBG) the ratio is about 4:1 [1, 4]. All these galactomannan gums possess high water binding capacity which can generate highly viscous dispersions making them effective thickeners and stabilizers. Recently, FG has received particular interest due to its functional properties (viscosity, emulsification, gelation, foam formation, and stability) and the ability to develop weak gels at about 1 wt% concentrations [5]. One of the most expected features of

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ACCEPTED MANUSCRIPT biopolymers is their effectiveness in providing highly viscous dispersions at a lower concentration [6]. Therefore, it would be important to know how FG behaves at various dispersion concentrations and how its structure and functionality is related. To establish the utility of any polymer it is important to determine intrinsic

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viscosity, average viscosity molecular weight, and zero shear viscosity which can

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provide essential information regarding fundamental molecular properties [7]. Intrinsic

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viscosity is a measure of the contribution of a single polymer molecule to its dispersion viscosity. It can be determined using several methods such as multiple light scattering,

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size exclusion chromatography, and rheology [6]. For example, intrinsic viscosity can be

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determined from the slope of a Huggin’s and Kraemer’s curve [3]. One can also calculate the molecular weight and the hydrodynamic volume of a biopolymer using the

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Flory-Fox equation where intrinsic viscosity is inversely proportional to molecular weight

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and directly proportional to polymer hydrodynamic volume [8]. The zero-shear-rate viscosity, which describes undisturbed polymer dispersion viscosity, can be determined

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using empirical relations as proposed by Morris (1990). From the concentration

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dependency of zero-shear-rate viscosity, one can relate the shear thinning behavior of the dispersions of entangled polysaccharides [3]. Shear-induced flow behavior of gum

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dispersions are generally estimated using linear (Newtonian or Bingham), power law (Ostwald-de-Waele), power law with a yield stress (Herschel-Bulkley) or Casson models. Most of the galactomannans above 0.25 wt% dispersion concentration shows non-Newtonian behavior hence the power law is the most widely employed model to describe flow properties in theoretical analyses as well as in practical engineering applications [9].

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ACCEPTED MANUSCRIPT Food is a complex material that contains acids, bases, and salts and undergoes various heating and cooling cycles during and after processing, all of which may significantly influence gum rheological behavior. For example, it was shown that the presence of more than 1% salt in water could slow xanthan gum hydration time. Thus it

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was recommended the gum is hydrated in the absence of excess salt [10]. Therefore, it

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is important to understand the effects of such changes in environmental conditions on

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the rheological behaviour of the gum dispersions. In the present study, rheological properties (viscosity, viscoelasticity, intrinsic viscosity and entanglement behaviour) of

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underutilized FG dispersions at different concentrations were investigated and

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compared with LBG and GG. Gum dispersions were further subjected to various environmental stresses such as variation in pH and NaCl concentration to evaluate their

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effects on dispersion rheology. To our knowledge no report so far provided such

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detailed discussion on rheological behaviour of FG in comparison with GG and LBG. FG is relatively uncommon compared to GG and LBG, and a fundamental understanding of

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FG dispersion molecular interactions leading to improved rheological behaviour is

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important for developing food and non-food applications.

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2. Materials and Method 2.1. Materials

The FG was donated by Emerald Seed Product Ltd., Avonlea, SK, Canada. The GG was purchased from Bulk Barn store as a local supplier of Duinkerken Foods Inc., Canada. The LBG was donated by CP Kelco, Atlanta, GA, USA. Hydrochloric acid

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ACCEPTED MANUSCRIPT (HCl), sodium hydroxide (NaOH) and sodium chloride (NaCl) were procured from Fisher Scientific, Nepean, ON, Canada.

2.2. Sample preparation

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Gum dispersions of various concentrations (0.125 to 2 wt.%) were prepared by

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dispersing the FG, GG, and LBG powders in deionized water. In some cases, the 0.5

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wt% gum dispersions were prepared with the presence of NaCl (0, 0.1, 0.5, and 1 M) and the pH was adjusted 3, 5 and 7 by using 0.1 M HCl and 1 M NaOH solutions.

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Dispersions were hydrated for about 24 h with a constant stirring at ~400 rpm on a

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magnetic stirrer (Model: 986906, Digital Multistir 5, VWR International, Edmonton, AB,

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Canada) at 25 ± 1°C before performing any analysis.

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2.3. Determination of polysaccharide content The total polysaccharide content of FG, GG, and LBG powders were determined using

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modified phenol-sulphuric acid method [11]. Initially, 50 mg of gum powders were

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dispersed in 100 ml of distilled water in boiling water bath for 2 hr. The mixture was then centrifuged at 3000 g for 10 min. The supernatant, after centrifugation, was used for

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further analysis of polysaccharide content. Three different standard curves were prepared by mixing pure galactose and mannose to represent FG (M:G 1:1), GG (M:G 2:1), and LBG (M:G 4:1). The standard calibration curves were obtained within the concentration range of 0 to 40 µg/ ml maintaining a r2 > 0.99. To determine the polysaccharide content, 400 µl of sample was mixed with 400 µl of 5 % phenol solution and 2 ml of concentrated sulphuric acid. The mixture was then allowed to incubate at 25

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ACCEPTED MANUSCRIPT °C for 30 min so that the sulpuhric acid could break down the polysaccharide and phenol could react to develop a yellow-gold colour [11]. The absorbance of the mixture was measured using a UV-visible spectrophotometer (Model: DU 530, Beckman Life sciences, Mississauga, ON) at 490 nm. The total polysaccharide content of each gum

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was determined from the respective standard curve. All samples were analysed in

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triplicates and the % total polysaccharide content was expressed with their means and

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standard deviations.

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2.4. Rheological measurements

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The viscosity and viscoelasticity of the gum dispersions were determined using an AR G2 rheometer (TA Instrument, Montréal, QC, Canada) equipped with Peltier

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temperature controller (Smart SwapTM, TGA Heat Exchanger, TA Instrument, Montréal,

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QC, Canada) for maintaining a temperature of 25 ± 0.2 °C. Appropriate amounts of gum dispersion were transferred by pipette to the rheometer stationary plate. The rotational

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or oscillatory shear/strain was applied to the sample using a 40 mm diameter and 2°

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acrylic cone geometry. The gap between the rotational and stationary plate was set to 1000 µm. During each measurement, samples were equilibrated for 120 sec. Gum

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dispersion apparent viscosities were measured as a function of shear rate ranging from 0.01 to 1000 s-1. The rheometer was operated in the oscillatory mode to determine dispersion viscoelastic behavior, where the storage (G′) and loss (G″) moduli were measured as a function of strain (0.01–1000%) at a constant frequency (6.28 rad/s).

2.5. Rheological model fitting

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ACCEPTED MANUSCRIPT Various mathematical models were employed to analyze gum dispersion rheological behavior at various concentrations [12]. 2.5.1 Power-law model Logarithmic plots of shear stress (σ) versus shear rate (𝛾) were modeled using the

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power law given in Eq. 1 to calculate the consistency coefficient (K) and the flow

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behavior index (n): 𝜎 = 𝐾. 𝛾 𝑛

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(1)

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2.5.2 Hershel-Bulkley model

The Hershel-Bulkley model is a modification of the power law model with an additional

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yield stress term added to Eq. 1. The consistency coefficient (K), flow behavior index

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(n), and the yield stress (σ0 ) for the gum dispersions were found by fitting the experimental data using Eq. 2,

σ − σ0 = K. γn

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(2)

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Model fitting was carried out using Microsoft Excel 2013 Solver function targeting the minimization of a standard error giving the best fit [13]. The suitability of the model was

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determined by calculating the standard error (SE) and the correlation coefficient (r2) [14]. SE can be calculated using Eq. 3: 𝟎.𝟓 ∑[𝐗 𝐦 −𝐗 𝐜 ]𝟐 ) 𝐧−𝟐

(

𝐒𝐄 = (

𝐑𝐚𝐧𝐠𝐞

) × 𝟏𝟎𝟎𝟎

(3)

where Xm is the measured value, Xc is the calculated value, n is the number of data points and range is the maximum value of Xm minus the minimum value. 8

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2.6. Intrinsic viscosity and average viscosity molecular weight The intrinsic viscosity of all gum dispersions was determined at diluted gum concentrations ranging from 0.1 to 0.25 wt%. For the determination of intrinsic viscosity,

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gum dispersion apparent viscosity (η) were converted to relative viscosity (ηrel) and

(4)

ηs η−η𝑠

(5)

ηs

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ηsp =

η

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ηrel =

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specific viscosity (ηsp) using Eq. 4 and Eq. 5:

where ηs is the solvent or deionized water viscosity. Intrinsic viscosity ([η]) is obtained

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by extrapolation of ln ηrel /c to zero concentration according to the Kraemer empirical

𝐥𝐧 𝛈𝐫𝐞𝐥

= [𝛈] + 𝐤[𝛈]𝟐 𝐜

(6)

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𝐜

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equation (Eq. 6) as follows [6]:

Where k and c are the Kraemer constant and solute concentration, respectively. Once

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the intrinsic viscosity was known, the viscosity average molecular weight (Mv), was

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calculated using modified Mark-Houwink relationship (Eq. 7) given by Gaisford and coworkers [15]. For the calculation of Mv, the mannose to galactose ratio (M:G) for FG,

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GG, and LBG was considered to be 1:1, 2:1, and 4:1, respectively.

where 𝐗 =

𝟏 𝐌 𝐆

[( )+𝟏 ]

[η] = 11.55 × 10−6 [(1 − X)Mv ]0.98

and

𝐌 𝐆

(7)

is the mannose to galactose ratio of the galactomannans.

2.7. Determination of zero-shear viscosity Stiffness or shear-thinning behaviour of a biopolymer is directly proportional to zeroshear-rate viscosity (ηo). From the ηo vs. concentration curve, biopolymer molecular 9

ACCEPTED MANUSCRIPT entanglement can be detected from the deviation in the linear progression of ηo with respect to increase in concentration. Biopolymer entanglement concentration in the dispersion can be seen as the beginning of intermolecular interaction and is an important parameter for selection of a biopolymer as a food ingredient. Hence to

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determine biopolymer entanglement concentration, values of ηo were determined using

η0 0.76 ⁄ γ 1 + (γ )

(8)

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η=

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the Morris equation [16]:

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1⁄ 2

Where η is the viscosity at any shear rate (𝛾), ηo is the maximum “zero-shear” viscosity

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in the Newtonian plateau region of the viscosity vs. shear rate graph, and γ 1⁄ is the 2

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shear rate at which η is reduced to ηo/2. The y-axis intercept of η against ηγ0.76 produces a straight line which intercepts the y axis at ηo. Finally, the entanglement

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behaviour of each biopolymer in aqueous dispersion was obtained by plotting ηo against

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concentration.

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2.8. Zeta potential analysis

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Zeta potential of the gum dispersions was determined using a Zetasizer Nano-ZS90 (Malvern Instruments, Westborough, MA, USA) according to Liu et al. (2016) [17]. Prior to analysis, the samples were diluted 200 times with deionized water and then mixed uniformly. All analyses were conducted in duplicates and values were expressed as their mean and standard deviation.

2.9. Statistical analysis 10

ACCEPTED MANUSCRIPT All experiments were carried out at least in duplicates and values were presented as mean ± standard deviation. A paired sample t-test

was performed at the P < 0.05

significance level using SPSS® software (V20, IBM, USA).

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3. Results and discussion

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3.1. Polysaccharide content of the gums

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The total polysaccharide content (wet basis) in terms of galactomannan equivalent for FG, GG, and LBG powders were 72.99 ± 2.07, 81.15 ± 1.73, and 86.34 ± 0.76 wt%,

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respectively. Jiang and coworkers also reported 73.6 wt% galactomannan from

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fenugreek seed gum in their studies [18]. The moisture content of the gum powders (wet basis) were 3.40 ± 0.17, 3.08 ± 0.01, 3.05 ± 0.09 wt% for FG, GG, and LBG,

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respectively. The rest of the material in the gum powder could be from protein, lipid and

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ash content.

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3.2. Rheological behavior of galactomannans

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Knowledge of the flow behaviour of FG is important in order to evaluate its ability to modulate the spreadability and firmness of food products. Flow curves of viscosities

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versus shear rate were obtained for dispersions of each galactomannan (FG, GG, and LBG) in water at a concentration of 0.125, 0.25, 0.50, 1, and 2 wt% (Fig. 2). As galactomannan concentration increased, the viscosity of the dispersion also increased possibly due to an increase in gum water binding capacity, which reduced the availability of free water and restricted dispersion flow at higher concentrations (Fig. 2). The FG dispersion appeared to be less viscous compared to GG (at similar

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ACCEPTED MANUSCRIPT concentrations) (Fig. 2 a and b). In dilute dispersions (0.125 wt%), the viscosity of all gums was independent of shear rate hence they followed near Newtonian flow behaviour. Shear thinning behavior due to increased molecular entanglement and reduced intermolecular space [3] was evident in the dispersions of 0.25 wt % or more.

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Brummer and coworker also reported similar shear rate dependent behvaiour for FG [2].

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At very low shear rates (less than 0.1 s-1) a Newtonian plateau was observed for all gum

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dispersion, except GG at 2 wt%, where the shear rate was too low to induce any disentanglement. At higher shear rates, the rate of forced disentanglements became

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greater than the rate at which new entanglements formed and the randomely oriented

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polymer chains aligned in the direction of flow which results in the lesser interactions with the adjacent polymer chains. This increased polymer freedom of movement,

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thereby reducing dispersion viscosity [4, 5, 19].

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From all flow curves, different pseudoplastic behaviour was observed due to the variation in intrinsic viscosity and gum molecular weight [7]. To better compare gum

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dispersion rheological behaviour, the power law (Eq. 1) and Herschel-Bulkley models

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(Eq. 2) were applied to the experimental data. The Herschel-Bulkley model is a modification of power law model with an additional yield stress term in Eq. 1. The values

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of yield stress obtained with the application of Herschel-Bulkley model were negligible, and there was no significant difference in the parameters predicted by either model. Hence, only the power model prediction is reported. Table 1 gives the values of consistency coefficient (K) and the flow behaviour index (n) calculated from the power model fitted to the experimental data. The coefficient of determination (R2) and standard error (SE) were also reported in Table 1. From Table 1, it can be observed that all the

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ACCEPTED MANUSCRIPT gum dispersions possess shear thinning behavior as n < 1. The power law model regressed well and gave the best fit to the experimental data with an R2 ranging from 0.92 to 0.99 and SE ranging from 1.19 to 109.82. The criterion for modeling experimental data was minimization in SE and R2 values close to unity. For GG,

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significantly higher SE values at concentrations above 1 wt% are due to larger

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behaviour (lower values of n) compare to FG and LBG.

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deviations from the experimental data, which could be due to its higher shear thinning

To investigate power law model parameter variation with concentration and type of

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gum, flow behaviour indices (n) and consistency coefficients (K) were plotted against

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gum concentration (Fig. 3). As gum concentration increased, n decreased, while K increased. At a low gum concentration (less than 1 wt%) n ranges from 0.9 to 0.5, while

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at higher concentration (⩾ 1 wt%), it decreased into the range of 0.3 to 0.2. The value of

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n represents the extent of shear thinning flow behaviour of gum dispersion as it deviates from 1. It is an indication of an increase in gum dispersion pseudoplastic behavior at

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higher concentrations. The values of n for FG and LBG were significantly higher than

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GG at all concentrations. Opposite to the n, the values of K increased with an increase in gum concentration. K is a measure of dispersion viscosity taking into account its

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deviation from Newtonian flow behaviour. Values of K remain less than or close to 1 until 0.5 wt% gum concentration, thereafter, K increased with concentration for 1 and 2 wt% due to biopolymer entanglement and water binding capacity. Values of K for GG and LBG dispersions were significantly higher than for FG dispersions at concentrations 1 wt% and above. This could be attributed to solubility and variation in galactomannan G:M ratio. As the M:G ratios increases from 1:1 to 4:1 for FG, GG and LBG, solubility,

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ACCEPTED MANUSCRIPT and viscosity of galactomannans increased for GG and LBG (⩾ 1 wt%) (Fig. 3). The decrease in consistency coefficients from LBG to FG could be also correlated to total polysaccharide content of the gums as LBG > GG > FG. The results of the power law model analysis are in good agreement with those reported by other researchers, where

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values of n were reported to decrease from 0.67 to 0.27 with an increase in FG

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concentration from 0.5 to 2 wt% [20]. Similarly, Wu et al. also observed that n values

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decreased from 0.6 to 0.2 with increasing concentration from 0.5 to 2 wt% for GG and LBG [1].

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3.3. Intrinsic viscosity and concentration dependence of zero shear viscosity

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Each polymer molecules in the aqueous dispersion contribute to viscosity. The intrinsic viscosity provides a rough estimate of polymer molecular conformation and its

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interactions with the aqueous phase. It is also useful to calculate the polymer theoretical

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molecular weight using the Mark-Houwink relationship (Eq. 7). In the present study, a typical Kraemer’s plot provides galactomannan intrinsic viscosity (Fig. 4). Kraemer's

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model (Eq. 6) fits well with the experimental values with R2 > 0.94. The intrinsic viscosity

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of FG, GG, and LBG dispersions was calculated from the y-intercept of Fig. 4 and reported in Table 2. The intrinsic viscosities of FG, GG, and LBG dispersions are 13.46

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± 0.02, 16.94 ± 0.16, and 15.21 ± 0.02 dL/g, respectively. The GG dispersion showed the highest intrinsic viscosity followed by LBG and FG . The FG and GG have higher Dgalactose content compared to LBG. Hence, they swell and dissolve rapidly in cold water providing a higher viscosity in aqueous dispersion [21]. Polymer intrinsic viscosity directly correlates with both hydrodynamic volume and entanglement behaviour. According to the Flory–Fox equation, the relationship between

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ACCEPTED MANUSCRIPT intrinsic viscosity, molecular weight, and radius of gyration of a dispersed polymer can be estimated as: [η] = ϕ(R2 )3/2 ∕ Mw

(9)

where R is the gyration radius, Mw is the galactomannan molecular weight, and ϕ is a

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proportionality constant [8]. From Eq. 9, we know that the gyration radius and

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hydrodynamic volume are proportional to the product of intrinsic viscosity and the

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galactomannan molecular weight. Therefore, increasing the hydrodynamic volume will

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increase dispersion viscosity.

Wu and coworkers determined the intrinsic viscosity of FG (15.10 ± 0.14 dL/g), GG

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(15.80 ± 0.28 dL/g), LBG (14.20 ± 0.28 dL/g), the order of which are in good agreement with the present report [1]. Goycoolea et al. (1995) reported intrinsic viscosities for

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galactomannans, such as GG and LBG at neutral and alkaline pH values [19]. For GG,

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intrinsic viscosities did not change significantly (12.5 to 11.9 dL/g) when dispersion pH increased from neutral to alkaline (1M NaOH). However, for LBG, a similar change in

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pH led to a decrease in intrinsic viscosities from 12.1 to 5.2 dL/g. It was proposed that

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the decrease in intrinsic viscosity for LBG could be due to the dissociation of molecular entanglement at high pH-induced electrostatic repulsion. For GG, the presence of

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longer unsubstituted segments on the molecular chain led to less molecular entanglement and, hence, less change in intrinsic viscosity. In the present study, the intrinsic viscosity of LBG at neutral pH was 15.21 dL/ g which is slightly greater than those reported by Goycoolea et al. and Wu et al. [1, 19]. Higher polysaccharide or galactomannan content tend to increase intrinsic viscosity compared to the gums which contains comparitively lesser amount of polysaccharide [22].

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ACCEPTED MANUSCRIPT The average viscosity molecular weight was determined using polymer intrinsic viscosity (Eq. 7, modified Mark–Houwink relationship) as proposed by Wu and coworkers [1]. The average viscosity molecular weight of FG was significantly higher (p < 0.05) than GG and LBG (Table 2). Wu et al. (2009) determined the average viscosity

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molecular weight (Mv, ×106) for FG (3.23 ± 0.03), GG (2.91 ± 0.05), LBG (2.08 ± 0.04)

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and the order of the values were in good agreement with the present report. As seen in

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Eq. 7, galactomannan molecular weight is dependent on intrinsic viscosity and M:G ratio. Hence, FG showed higher molecular weight than GG and LBG which could be

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due to its lower M/G ratio of 1.

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Figure 5 shows the concentration dependence of zero shear viscosities for the galactomannan dispersions, calculated using Eq. 8. The plots (Eq. 8) of concentration

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dependence of zero shear viscosities for the galactomannan dispersions showed a

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remarkable increase in the slope at around 0.1 wt% concentration (Figure 4). When polymer molecules interact the slope of the line rapidly changes and the intercept of the

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two slopes is known as onset of rise in viscosity at a specific critical concentration (C*)

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[23]. Similar increase in zero shear viscosity was also observed for FG, GG, and LBG by other researchers [3, 7]. This was attributed to the transition of galactomannans from

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a dilute dispersion, where the individual polymers are present in isolated form, to the concentrated dispersion where the hydrodynamic volume of the chains exceeds the actual dispersion volume [24]. Generally, the polysaccharide molecules which have stiff conformation tend to show higher zero shear viscosity and possess strong shear thinning properties. This is attributed to quick alignment of the stiff polymer molecules in the direction of flow as shear rate increases leading to a decrease in physical

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ACCEPTED MANUSCRIPT interactions between the adjacent polymer chains [25]. Hence, as GG showed significantly higher zero shear rate viscosity compared to FG and LBG at concentration ⩾ 1 wt%, it has more shear thinning behaviour. Also, from Table 1 and Figure 3, it was clearly seen that value of n determined using power law model for GG were significantly

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less than for FG and LBG indicating its higher shear thinning behaviour. Due to the high

Viscoelastic properties of the galactomannans

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3.4.

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consistency during in-mouth food processing [26].

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shear thinning behaviour of GG dispersions can be pumped easily and provide a thinner

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Dynamic viscoelastic propertise of FG, GG and LBG dispersions was studied in the concentration range 0.125 to 2 wt%. However, data for only 1 and 2 wt% were reported

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for comparison, as no gelation was observed in the lower concentration range.

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Viscoelastic behaviour of the gum dispersions could be used to differentiate between weak and strong gels, it also provides information on the structural strength of the gum

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dispersions. Fig. 6 shows the strain dependency of G′ and G′′ at a constant angular

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frequncy of 1 Hz, and at 25°C. When controlled strain is applied on the gum dispersions, a linear viscoelastic region (LVR) appeared in the low-strain regime (below

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10% strain) where both moduli remain unchanged (Fig. 6). In the LVR, G′ and G′′ remain unchanged even if the applied strain increased, which indicates formation of strong intermolecular junction zones among the biopolymer moelcules. Stronger gels may remain in the LVR over a greater strain range compared to weaker gels [27]. At 1 wt% concentration, FG (Fig. 6a) showed G′ > G″ in the low-strain regime indicating the formation of weak gels, whereas for GG and LBG (Fig. 6c, e) a liquid-like

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ACCEPTED MANUSCRIPT behaviour (G′ < G″ in the low-strain regime) was observed. The 2 wt% concentration of FG and GG dispersion showed strong elastic nature as in both cases the G′ is significantly greater than G″ within the LVR (Fig. 6b, d). But in case of 2 wt% LBG, G’ and G” are almost equal within the LVR, indicating liquid-like behaviour (Fig. 6f). The

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increase in G′ with increase in gum concentration could be explained by the formation of

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more intermolecular junction zones formed by non-covalent interactions which further

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led to the formation of stronger three dimension network [28]. For all dispersions, beyond the LVR, a sharp drop in the moduli is observed which led to a crossover

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between G′ and G″ known as gel breakdown point [29]. Hence, a permanent

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deformation in gel structure occurs leading to liquid-like flow behaviour. Wei and coworker [5] also observed similar results, they analyzed FG dispersions (0.05 to 2

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wt%) for their viscoelasticity through frequency sweep (0.05 - 500 rad s−1) and found

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that G′ > G″ within the experimental range. The authors concluded that FG possess gellike behaviour above 0.05 wt % concentration [5].

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The comparision of the viscoelastic behaviour among the gum dispersions were

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done by replotting the plateau of G′ and G′′ at 0.1% strain (within the LVR) from Fig. 6 into Fig. 7. For 1 wt% FG dispersion, G′ was significantly higher than G″ indicating a gel-

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like behaviour (Fig. 7a). However, as the moduli values and the difference between G′ and G″ were rather low, this dispersion is a weak gel. For dispersion concentration of 2 wt% (Fig. 7b), there was a significant increase in both G′ and G″ compared to 1 wt% dispersions. Nevertheless, gel-like behaviour (G′ > G″) was only observed for FG, GG while for LBG the values of G′ and G″ remain similar. The non-gel-like behaviour of 2 wt% LBG was similar to results reported by Wu and coworkers for frequency sweep

18

ACCEPTED MANUSCRIPT studies [1]. The branched structure of galacturonic acid in LBG is much lower compared to FG and GG, hence lesser association of polymer chain with the water molecules is expected leading to the formation of a weaker structure [29, 30].

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3.5. Effect of change in pH and ionic strength on the viscosity of galactomannan

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dispersions

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The effect of salt (NaCl) concentration (0, 0.1, 0.5, and 1 M) on the galactomannan viscosity at 0.5 % wt concentration was recorded as a function of shear

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rate at three different pH values (3, 5, and 7). The apparent viscosity at 0.1 s-1 shear

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rate was plotted to compare among the gum dispersions (Fig. 8). At a constant salt concentration, no significant effect of pH on the viscosity was observed (p > 0.05),

M

except, LBG dispersions at 0.1 M salt. However, changing salt concentration had a

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significant impact on the galactomannan dispersion viscosity. At all pH values, FG and GG dispersions with salt exhibited significantly lower viscosity than when no salt was

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added. With an increase in salt concentration to 0.1 M viscosity decreased (p < 0.05),

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except for FG at pH 5. However, with a further increase in salt concentration no further change in viscosity was observed (p > 0.05) (Fig. 8a, b). At 1 M salt, the viscosity of FG

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significantly decreased (p < 0.05) when pH was increased from 3 to 5 (Fig. 8a). For LBG, the viscosity increased with an increase in salt concentration from zero to 0.1 M, thereafter a significant decrease in viscosity was observed at 0.5 M, which did not change at 1 M salt. Changes in galactomannan dispersion viscosity in the presence of salt could be due to the changes in molecular conformation. Similar behavior was observed in cress

19

ACCEPTED MANUSCRIPT seed gum and basil seed gum, when dispersions were subjected to increased salt conditions (0 to 1 wt%), and it was proposed that the apparent viscosity decreased due to an increase in the degree of polysaccharide structural compactness [6, 31]. Charge screening effects of salt could lead to a more compact conformation which can, in turn,

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reduce polymer hydrodynamic volume, and thereby reduce viscosity [32]. To test this

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hypothesis, the impact of salt (0.5 M) on the surface charge of gum dispersions was

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determined and presented in Fig. 9. The FG and GG dispersions without salt showed a change in zeta potential from 1.98 ± 0.37 mV at pH 3 to -14.86 ± 0.98 mv at pH 7 for FG

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and 2.20 ± 0.25 mV at pH 3 to -7.30 ± 0.92 mv at pH 7 for GG. This increase in the

AN

magnitude of surface charge with increased pH can be attributed to an increase in ionization of galactomannan hydroxyl groups [33]. Presence of protein, which is

M

chemically bound to the gum samples, could also be responsible for observed changes

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in surface charge as a function of pH [21]. A crossover of charge from positive to negative can also be seen at a pH of 3.61 for FG and 3.78 for GG and, which indicates

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the pKa values of the galactomannans. These values are also similar to literature

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reports [34]. The increase in surface charge with pH led to increased inter-polymer repulsion which caused structural collapse and reduction in molecular stiffness. The

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largest change in surface charge was observed for FG (Fig. 9a), which also exhibited a decrease in apparent viscosity (p < 0.05) with increased pH without the presence of salt (Fig. 8a). However, for GG, this phenomenon was not significant (p > 0.05), which could be attributed to a lesser drop in surface charge with an increase in pH (Fig. 9b) and no significant change in viscosity without salt (Fig. 8b). For LBG, no significant change in surface charge was also observed with increase in pH (p > 0.05), and the values remain

20

ACCEPTED MANUSCRIPT negative at between -4 to -6 mV throughout the pH range studied (Fig. 9c). This could be due to lack of ionization of hydroxyl groups in galactomannans with an increase in pH, and thus there was no significant change in viscosity of the LBG dispersion without salt (Fig. 8c).

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As salt concentration increased from 0 to 0.5 M, there was a decrease in the

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magnitude of the zeta potential of FG, GG, and LBG dispersions (Fig. 9). The decrease

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was much larger for FG at pH 7, where the zeta potential dropped from -14.86 ± 0.98 to -2.42 ± 3.55 mV upon addition of salt (Fig. 9a). For GG, a drop of zeta potential at pH 7

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was from -7.30 ± 0.91 to -3.10 ± 1.16 mV. At pH 3, the addition of salt not only

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decreased the magnitude of surface charge but also changed polarity from slightly negative to positive. For LBG, no significant change in surface charge upon addition of

M

0.5 M salt was also observed (p>0.05). A drop in surface charge for all gum dispersions

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due to the addition of salt indicates a collapse of gum molecular conformation due to charge screening effect which also decreased their viscosity (Fig. 8) [35]. Picone and

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Cunha stated that an increase in pH (3.5 to 7) of gellan gum dispersions led to a

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decrease in junction zone formation at pH of 7 due to greater electrostatic repulsion between gellan molecules, which in turn reduced viscosity [36]. Hosseini and co-

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workers also studied the impact of variation in pH and salt on bitter almond gum and found that increased NaCl or CaCl2 concentration (0 to 500 mM or 5 to 100 mM, respectively) led to decreased dispersion viscosity [37].

4. Conclusions

21

ACCEPTED MANUSCRIPT The rheological properties of FG, GG, and LBG dispersions were studied with concentrations varying from 0.125 to 2 wt%. Due to higher water binding capacities, gum dispersion viscosity increased with increasing concentration. The power law model provided a superior fit (e.g., higher correlation coefficient and minimum standard error)

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to the viscosity data than Herschel-Bulkley model. The power law model fit showed GG

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had lower flow behaviour index compared to LBG and FG dispersions, indicating higher

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shear thinning behaviour. The intrinsic viscosity of GG dispersions was greater than both FG and LBG dispersions, indicating larger molecular conformations. The average

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viscosity molecular weight (Mv, ×106) of FG, GG, and LBG was 3.10 ± 0.01, 2.93 ± 0.02

AN

and 2.19 ± 0.01, respectively. From zero shear viscosity vs. concentration plot, it can be concluded that the gum dispersions above 0.1 wt% concentration showed entanglement

M

among the polymer chains. A significant impact of pH and salt concentration on

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galactomannan dispersion viscosity and surface charge was observed. With the increase in dispersion pH without any salt, the apparent viscosity did not change

PT

significantly for GG and LBG, while surface charge increased. For FG, with the largest

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increase in surface charge, the apparent viscosity decreased with increase in pH. The apparent viscosities of FG, GG and LBG dispersions decreased with the addition of salt

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due to charge screening effects. The viscoelastic studies showed that only FG could form a weak gel at lower concentration (1 wt%). Due to higher surface charge and superior gelling ability at lower concentration compared to the other galactomannans (GG and LBG), FG could be a better alternative in many food and related applications.

Acknowledgment

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ACCEPTED MANUSCRIPT Financial support for this work is provided by Agriculture Development Fund (Project# 20140276), of the Saskatchewan Ministry of Agriculture, Saskatchewan, Canada. The authors would like to thank Dr. Yongfeng Ai and Tommy Z. Yuan for their valuable suggestions and help in determination of total polysaccharide content of the

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gums.

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References

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[1] Y. Wu, W. Cui, N. Eskin, H. Goff, An investigation of four commercial galactomannans on their emulsion and rheological properties, Food Res. Int. 42

AN

(2009) 1141-1146.

M

[2] Y. Brummer, W. Cui, Q. Wang, Extraction, purification and physicochemical characterization of fenugreek gum, Food Hydrocoll. 17 (2003) 229-236.

ED

[3] J.P. Doyle, G. Lyons, E.R. Morris, New proposals on “hyperentanglement” of

PT

galactomannans: Solution viscosity of fenugreek gum under neutral and alkaline conditions, Food Hydrocoll. 23 (2009) 1501-1510.

CE

[4] S. Gillet, M. Aguedo, R. Petrut, G. Olive, P. Anastas, C. Blecker, A. Richel, Structure

AC

impact of two galactomannan fractions on their viscosity properties in dilute solution, unperturbed state and gel state, Int. J. Biol. Macromol. 96 (2017) 550-559. [5] Y. Wei, Y. Lin, R. Xie, Y. Xu, J. Yao, J. Zhang, The flow behavior, thixotropy and dynamical viscoelasticity of fenugreek gum, J. Food Eng. 166 (2015) 21-28. [6] F. Behrouzian, S.M. Razavi, H. Karazhiyan, Intrinsic viscosity of cress (Lepidium sativum) seed gum: effect of salts and sugars, Food Hydrocoll. 35 (2014) 100-105.

23

ACCEPTED MANUSCRIPT [7] J. Doublier, B. Launay, Rheology of galactomannan solutions: comparative study of guar gum and locust bean gum, J. Text. Stud. 12 (1981) 151-172. [8] P. Flory, in: P. Flory (Ed.), Principles of polymer chemistry, Cornell University Press, New York, 1953, pp. 266 - 346.

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[9] M. Marcotte, A.R.T. Hoshahili, H. Ramaswamy, Rheological properties of selected

IP

hydrocolloids as a function of concentration and temperature, Food Res. Int. 34

CR

(2001) 695-703.

[10] G. Sworn, Xanthan gum, In: G.O. Phillips and P.A. Williams (Eds.),Handbook of

US

Hydrocolloids, Woodhead Publishing Limited, Cambridge, 2009, pp. 186 - 202.

AN

[11] M. Dubois, K.A. Gilles, J.K. Hamilton, P.t. Rebers, F. Smith, Colorimetric method for determination of sugars and related substances, Anal. Chem. 28 (1956) 350-356.

M

[12] G. Li, F. Zhu, Rheological properties in relation to molecular structure of quinoa

ED

starch, Int. J. Biol. Macromol. 114 (2018). 767 - 775. [13] G. Mullineux, Non-linear least squares fitting of coefficients in the Herschel–Bulkley

PT

model, Appl. Math. Model. 32 (2008) 2538-2551.

CE

[14] J. Ahmed, H. Ramaswamy, K. Sashidhar, Rheological characteristics of tamarind

231.

AC

(Tamarindus indica L.) juice concentrates. LWT-Food Sci. Technol. 40 (2007) 225-

[15] S. Gaisford, S. Harding, J. Mitchell, T. Bradley, A comparison between the hot and cold water soluble fractions of two locust bean gum samples, Carbohydr. Polym. 6 (1986) 423-442. [16] E.R. Morris, Shear-thinning of ‘random coil’polysaccharides: Characterisation by two parameters from a simple linear plot, Carbohydr. Polym. 13 (1990) 85-96.

24

ACCEPTED MANUSCRIPT [17] J. Liu, Y.Y. Shim, J. Shen, Y. Wang, S. Ghosh, M.J. Reaney, Variation of composition and functional properties of gum from six Canadian flaxseed (Linum usitatissimum L.) cultivars, Int. J. Food Sci. Technol. 51 (2016) 2313-2326. [18] J. Jiang, L. Zhu, W. Zhang, R. Sun, Characterization of galactomannan gum from

T

fenugreek (Trigonella foenum-graecum) seeds and its rheological properties, Int. J.

IP

Polym. Mater. 56 (2007) 1145-1154.

CR

[19] F. Goycoolea, E. Morris, M. Gidley, Viscosity of galactomannans at alkaline and neutral pH: evidence of ‘hyperentanglement’in solution, Carbohydr. Polym. 27 (1995)

US

69-71.

AN

[20] Y.H. Chang, S.W. Cui, Steady and dynamic shear rheological properties of extrusion modified fenugreek gum solutions, Food Sci. Biotechnol. 20 (2011) 1663-

M

1668.

ED

[21] N. Garti, Z. Madar, A. Aserin, B. Sternheim, Fenugreek galactomannans as food emulsifiers, LWT-Food Sci. Technol. 30 (1997) 305-311.

PT

[22] C. Andrade, E. Azero, L. Luciano, M. Gonçalves, Solution properties of the

CE

galactomannans extracted from the seeds of Caesalpinia pulcherrima and Cassia

185.

AC

javanica: comparison with locust bean gum, Int. J. Biol. Macromol. 26 (1999) 181-

[23] E. Morris, A. Cutler, S. Ross-Murphy, D. Rees, J. Price, Concentration and shear rate dependence of viscosity in random coil polysaccharide solutions, Carbohydr. Polym. 1 (1981) 5-21.

25

ACCEPTED MANUSCRIPT [24] G. Robinson, S.B. Ross-Murphy, E.R. Morris, Viscosity-molecular weight relationships, intrinsic chain flexibility, and dynamic solution properties of guar galactomannan, Carbohydr. Res. 107 (1982) 17-32. [25] B. Vardhanabhuti, S. Ikeda, Isolation and characterization of hydrocolloids from

T

monoi (Cissampelos pareira) leaves, Food Hydrocoll. 20 (2006) 885-891.

IP

[26] S. Hosseini-Parvar, L. Matia-Merino, K. Goh, S.M.A. Razavi, S.A. Mortazavi,

CR

Steady shear flow behavior of gum extracted from Ocimum basilicum L. seed: effect of concentration and temperature, J. Food Eng. 101 (2010) 236-243.

US

[27] R. Ali, S.M.A. Razavi, Dynamic viscoelastic study on the gelation of basil seed gum,

AN

Int. J. Food Sci. Technol. 48 (2013) 556-563.

[28] Y. Wu, R. Guo, N. Cao, X. Sun, Z. Sui, Q. Guo, A systematic rheological study of

M

polysaccharide from Sophora alopecuroides L. seed, Carbohydr. Polym. 180 (2018)

ED

63-71.

[29] J.L. Doublier, C. Castelain, J. Lefebvre. Viscoelastic propertise of mixed

PT

polysaccharides systems, in: F. Meuser, D.J. Manners, W. Seibel (Eds.), Plant

- 85.

CE

Polymeric Carbohydrates, The Royal Society of Chemistry, Cambridge, 1993, pp. 76

AC

[30] L.M. Nwokocha, P.A. Williams, M.P. Yadav, Physicochemical characterisation of the galactomannan from Delonix regia seed, Food Hydrocoll. 78 (2017) 132 - 139. [31] F. Salehi, M. Kashaninejad, Static rheological study of ocimum basilicum seed gum, Int. J. Food Eng. 11 (2015) 97-103.

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ACCEPTED MANUSCRIPT [32] H. Khouryieh, T. Herald, F. Aramouni, S. Alavi, Intrinsic viscosity and viscoelastic properties of xanthan/guar mixtures in dilute solutions: Effect of salt concentration on the polymer interactions, Food Res. Int. 40 (2007) 883-893. [33] A. Farahnaky, N. Darabzadeh, M. Majzoobi, G. Mesbahi, Physicochemical

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properties of crude and purified locust bean gums extracted from Iranian carob

IP

seeds, J. Agric. Sci. Technol. 16 (2014) 125-136.

CRC press, Boca Raton, 2007, pp. 111-112.

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[34] S. Damodaran, K.L. Parkin, O.R. Fennema, Fennema's Food Chemistry, 4th ed.,

US

[35] S. Carrington, J. Odell, L. Fisher, J. Mitchell, L. Hartley, Polyelectrolyte behaviour of

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dilute xanthan solutions: Salt effects on extensional rheology, Polymer. 37 (1996) 2871-2875.

M

[36] C.S.F. Picone, R.L. Cunha, Influence of pH on formation and properties of gellan

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gels, Carbohydr. Polym. 84 (2011) 662-668. [37] E. Hosseini, H.R. Mozafari, M. Hojjatoleslamy, E. Rousta, Influence of temperature,

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(2017) 437-443.

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pH and salts on rheological properties of bitter almond gum, Food Sci. Technol. 37

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ACCEPTED MANUSCRIPT List of figures Fig. 1. Proposed structures of galactomannans from different gums, a) fenugreek gum; b) guar gum; c) locust bean gum containing different galactose (G) and mannose (M) ratios. Fig. 2. Shear rate dependence of viscosity (Pa.s) for aqueous dispersion of (a) FG, (b)

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GG, and (c) LBG at different concentrations varying from 0.125 to 2 wt%. Missing

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values at low shear rates for 0.125 wt% dispersions were beyond the instrument limit.

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Fig. 3. Concentration dependency of (a) flow behaviour index (n), and (b) consistency coefficient (K)

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Fig. 4. Kraemer’s plot for determination of intrinsic viscosities of (a) FG, (b) GG and (c)

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LBG.

Fig. 5. Concentration-dependence of zero-shear viscosity (ηo) for FG, GG, and LBG

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Fig. 6. Strain dependent storage (G′) and loss moduli (G″) for 1 wt% (a, c, e) and 2 wt%

frequency of 6.28 rad/s.

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(b, d, f) concentration of dispersions of FG (a, b), GG (c, d) and LBG (e, f) at a constant

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Fig. 7. Storage modulus (G′) and loss modulus (G″) at 0.1 % strain from strain sweep analysis for different gum concentrations (a) 1 % wt; (b) 2 %wt.

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Fig. 8. Effect of variation in NaCl concentration and pH on apparent viscosities of 0.5 wt % (a) FG, (b) GG, and (c) LBG dispersions at a shear rate of 0.1 s-1.

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Fig. 9. Effect of NaCl (0.5 M concentration) and pH (x-axis) on the surface charge of 0.5 wt% (a) FG, (b) GG, (c) LBG dispersions.

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ACCEPTED MANUSCRIPT List of Tables Table 1 Power law model fitting parameters for FG, GG, and LBG dispersions at various gum concentrations and at a constant temperature (25 ± 1ºC). Table 2

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M

AN

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Intrinsic viscosity and average viscosity molecular weight of Galactomannans.

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ACCEPTED MANUSCRIPT Table 1 Power law model fitting parameters for FG, GG, and LBG dispersions at various gum concentrations and at a constant temperature (25 ± 1 ºC)

0.99

3.25

0.5

0.41

0.53

0.99

8.89

1

4.53

0.36

0.99

21.03

2

36.35

0.25

0.98

45.60

0.125

0.02

0.85

0.99

1.19

0.25

0.13

0.62

0.99

5.29

0.5

1.73

0.39

0.99

22.11

1

9.71

0.27

0.98

44.73

2

96.62

0.18

0.92

109.82

0.125

0.004

0.95

0.99

1.20

0.25

0.03

0.81

0.99

4.60

0.5

0.43

0.59

0.99

14.47

1

22.31

0.33

0.98

42.86

2

0.26

0.96

77.74

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0.72

90.08

AC

CE

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LBG

0.05

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GG

0.25

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law

M

Power

Type of Conc., Consistency Flow behaviour R2 Standard Gum wt. % coefficient (K) Index (n) Error (SE) 0.125 0.01 0.90 0.99 3.71 FG

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Model

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ACCEPTED MANUSCRIPT Table 2 Intrinsic viscosity and average viscosity molecular weight of Galactomannans. The values were expressed as mean ± standard deviation FG

GG

LBG

13.46 ± 0.02

16.94 ± 0.16

15.21 ± 0.02

Mv (× 106)

3.10 ± 0.01

2.93 ± 0.02

2.19 ± 0.01

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M

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Samples Intrinsic viscosity (dL/g)

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ACCEPTED MANUSCRIPT Highlights 

Among the three galactomannans, GG showed higher shear thinning than both FG and LBG



Intrinsic viscosity and average viscosity molecular weight were greater for FG

All gum dispersions above 0.1 wt% concentration showed entangled polymer

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and GG than LBG

FG dispersion above 1 wt% concentration has a unique weak gel formation

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behaviour

property

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M

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The apparent viscosity of all gum dispersions decreased with added salt

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32

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9