Viscoelastic Characterization of Sage Seed Gum

Abstract

Wild sage seed is a small, rounded, and mucilaginous seed, which comes from Salvia macrosiphon. The viscoelastic behavior of sage seed gum, at different concentrations (0.5–2%, w/w), was examined by measuring the transient (in-shear structural recovery and creep/recovery tests) and dynamic (stress and frequency sweeps) rheological properties. The mechanical spectra showed typical weak gel behavior at all concentrations, with storage modulus higher than loss modulus, and little variation with frequency. Both moduli greatly increased with increasing the concentration, and the concentration dependency was well described by the power-law model. The loss tangent was increased slightly with increasing the frequency in the range of 0.25–0.67, although it was not affected by an increase in gum concentration. Moreover, the complex viscosity was found to increase with the increase of sage seed gum concentration and to decrease linearly with the increase of frequency. All samples showed typical viscoelastic response to stress in creep/recovery tests, with recoverable strain increasing in direct proportion to sage seed gum concentration. Creep curves were adequately fitted with a Burger model of four parameters. The elastic and viscous contributions to the general viscoelastic behavior were analyzed through the obtained parameters. The concentration had no specific effect on the in-shear recovery properties of sage seed gum gels, and the gel structure was highly recovered after applying shear. The results of this article indicated that sage seed gum may offer an excellent alternative for commercial gums as a thickening/gelling agent.

Keywords:

• Salvia macrosiphon
• Rheology
• Oscillation
• Creep
• Hydrocolloid

INTRODUCTION

Hydrocolloids as thickener, gelling, and stabilizer agents can help to enhance the texture and taste of foods. The global hydrocolloid market was worth about $19.0 billion in 2006, growing at about 3–4% per year between 2006 and 2011, and valued at $22.5 billion by 2011.[1] Factors feeding demand include increases in processed/prepared foods and growing consumer interest in healthier and more nutritional products. The volume share of food ingredients depends on the security of their supply, quality, and price. Hydrocolloids from plants have the advantage over those from animals because of their friendly image towards consumers.[2] In the last decade, significant efforts have been dedicated to find new structure-functionality issues, in order to maximize hydrocolloids’ effectiveness and to produce novel formulations. However, there is still a place in the hydrocolloid market for new sources of plant hydrocolloids to meet the demand for ingredients with more specific functionality in food and chemical systems. Some plants, growing in different regions of Iran, have valuable polysaccharides. Seeds extract from these plants can be used as novel food hydrocolloid sources.[3] For example, the seeds of plants known as Alyssum homolocarpum (Qodume Shirazi), [4–6] Lallemantia royleana (Balangu), [7–9] Lepidium perfoliatum (Qodume Shahri),[10] Lepidium sativum (Shahi),[11,12] Ocimum basilicum L. (Reihan), [13–15] Plantago major L. (Barhang),[16,17] and Salvia macrosiphon (Marve) [18–20] have been traditionally used as herb seeds and pharmaceutical sources for hundreds of years, due to their valuable medical effects. However, these seeds are known to contain mucilage in large amounts that could be suitable for applications as stabilizing and thickening agents. [3,10] In this sense, our research works have been focused on the study of physical properties of seeds, extraction optimization, chemical analysis, functional properties, and food applications of hydrocolloid extract of these domestic seeds since four years ago.

Wild sage seed (Salvia macrosiphon) is a small rounded seed, which readily swells in water to give mucilage.[19] This mucilage can be extracted quantitatively with water by a centrifugal filtering system. Bostan et al. optimized the extraction process conditions of sage seed gum (SSG) using response surface methodology.[18] At optimum conditions, the yield, apparent viscosity (1%, 122 s⁻¹ and 25°C), and emulsion stability of SSG were determined as 10.1%, 312 mPa.s, and 403 min, respectively. The SSG powder obtained at optimum conditions contained 6.72% moisture, 0.85% lipid, 8.17% ash, 2.84% protein, 1.67% crude fiber, and 79.75% carbohydrate. There is no more information about the chemical structure of SSG because of the novelty of the subject. Razavi et al.[20] studied the steady-shear flow behavior of SSG dispersions as a function of SSG concentration (0.5–2%) and temperature (20–50°C). The results demonstrated that SSG dispersion has high zero-shear-rate-viscosity and very shear-thinning behavior at all conditions tested. In addition, it was even more pronounced than those reported for commercial hydrocolloids like xanthan, guar gum, and locust bean gum. The Heschel-Bulkley model was found to be the most suitable model to describe steady-shear flow behavior of SSG dispersions. They suggested application of this new gum as a stabilizer, thickener, binder, and gelling agent in food, cosmetics, and pharmaceutical systems. Up to now, many papers have been published on the viscoelastic characterization of different seed gums, [21–29] while no information on the sage seed extract is available. Therefore, the purpose of this study was to investigate the linear viscoelastic properties of sage seed gum, as well as their structural breakdown/recovery behavior under steady shear, as a function of gum concentration.

MATERIALS AND METHODS

Gum Extraction

Sage seed gum was extracted at optimum conditions (temperature 25°C, water to seed ratio 51:1, and pH 5.5) using the same procedure as described by Bostan et al.[18] The dispersions were dried overnight in a forced convection oven (Model 4567, Kimya Pars Com., Mashad, Iran) at 70°C, then milled and sieved using a mesh 18 sifter.

Sample Preparation

Seven concentration levels of sage seed gum in aqueous solutions (0.5, 0.75, 1, 1.25, 1.5, 1.75, and 2% w/w) were prepared by dispersing the sage gum powder in deionized distilled water at ambient temperature (25°C). Sodium azide (0.02%) was added to all dispersions as an anti-microbial preservative. The samples were stirred at 300 rpm for 24 h, and kept for 24 h at room temperature (25°C) to complete the hydration prior to the experiments. The samples were then loaded onto the rheometer to evaluate the rheological properties.

Rheological Tests

All rheological measurements were carried out using a controlled-stress/strain rheometer (Gemini 150, Bohlin Instruments Ltd., Malvern, UK) equipped with cone-plate geometry (40 mm of diameter, 4° cone angle, and 1 mm gap). The temperature was fixed, using a Peltier system, at 20°C and then each sample was equilibrated, at least for 5 min, before the rheological test. All rheological tests were performed, at least, in triplicate.

Small amplitude oscillatory shear (SAOS) measurements

First of all, stress sweep tests in oscillatory shear were conducted in the range of 0.01 to 150 Pa at 20°C, and a constant frequency of 1 Hz. These experiments were carried out in order to determine the maximum deformation attainable by all samples in the linear viscoelastic range (LVR). Frequency sweep tests were then conducted, within the LVR (maximum strain of 1%), in the range of 0.01 to 10 Hz, at a constant temperature of 20°C. The mechanical spectra obtained were characterized by the storage modulus (G′), loss modulus (G″), complex modulus (G*), complex dynamic viscosity (η*), and the loss tangent (tan δ) as a function of frequency (f, Hz).

Creep/recovery measurements

Creep/recovery tests were performed at constant shear stress (1 Pa) and temperature (20°C). The stress was applied instantly and kept for a period of 300 s. After removing stress, recovery compliance was measured also during 300 s. The creep and recovery compliances (J_C and J_R ) were the resulting strain (γ) divided by the applied stress (τ) during creep and recovery periods, respectively. In this study, based on the creep/recovery behavior observed (Fig. 1), the four-component Burger model, comprising the association in series of the Maxwell model and the Kelvin–Voigt model, was used to describe the transient data. In this model, the creep compliance, J_C , as a function of time, corresponds to the following equation:[30]

(1)

Figure 1 Compliance versus time for the Burger's model in creep/recovery test.

where J _0C is the instantaneous elastic compliance (Pa⁻¹) of the Maxwell spring and J _1C is the elastic compliance (Pa⁻¹) of Kelvin–Voigt unit. The latter represents the contributions of the retarded elastic region to the total compliance. λ _ret is the retardation time (s) of the Kelvin–Voigt component, and η₀ is the Newtonian viscosity (Pa.s) of the Maxwell dashpot. The recovery compliance, J_R , corresponds to an equation of the following type:[31]

(2)

where B and C are parameters that define the recovery speed of the system. J _∞ and J _1R are the recovery compliance of the Maxwell dashpot and Kelvin–Voigt element, respectively. When t → 0, J_R is equal to (J _∞ + J _1R ), which corresponds to the maximum deformation of the dashpots in the Burger model (Fig. 1). For t → ∞, J(t) is equal to J _∞, as it corresponds to the irreversible sliding of the Maxwell dashpot. Additionally, the deformation suffered by the Maxwell spring, or initial shear compliance J _0R , was obtained by using Eq. (3), where J _max is the maximum deformation corresponding to the compliance value for the longest time (300 s) in the creep transient analysis:

(3)

Full mechanical characterization of a system can be established by calculating the contribution of the compliances of Eqs. (1) and (2), at the maximum deformation to which the system is subjected. The percentage deformation of each element of the system can be calculated by:[31]

(4)

where J_element is the corresponding compliance: J _0C , J _1C , J _0R , J _1R , and J _∞. In this article, the percentage deformation of η₀ was also determined by the following relationship:

(5)

In addition, the final percentage recovery (R, %) of the entire system can be calculated by the following equation:

(6)

In-shear structural recovery measurements

In-shear structural recovery of the samples was determined according to the procedure of Mezger.[32] The sample was loaded onto the rheometer at 20°C, then a three-stepped shear flow test was performed as follows: (1) a constant shear rate of 1 s⁻¹ was applied for 120 s (with pre-shear at 1 s⁻¹ for 30 s), and subsequently, (2) a constant shear rate of 300 s⁻¹ was applied for 60 s, and then (3) a constant shear rate of 1 s⁻¹ was applied for 180 s. The in-shear recovery value was calculated as the ratio of average apparent viscosity (η _a3) obtained during the first 120 s of the third step to the average η _a1 value determined in the first step.

RESULTS AND DISCUSSION

SAOS Rheological Functions

Figure 2 shows the values of the linear viscoelasticity moduli, G′ and G″, as a function of shear stress obtained from stress sweep performed at a fixed frequency (1 Hz) and temperature (20°C), in a shear stress range from 0.01 to 150 Pa. As can be observed, all SSG samples show an initial linear viscoelastic region where both linear viscoelastic moduli are independent of the stress. Figure 2 also illustrates the effect of gum concentration on the extension of the linear viscoelastic regime and on the stress dependence in the nonlinear region. The SSG samples exhibited higher dependency to stress amplitude at lower concentrations; therefore, lower stress values must be attained to ensure linear viscoelastic properties. Generally, there was no abrupt change in G′ up to a stress amplitude of 0.33 Pa for 0.5% concentration. Thus, the frequency sweep tests conducted at 1% strain were well within the LVR, and the gel network was not damaged by the strain imposed during the measurements. In all cases, the storage modulus was approximately two orders of magnitude greater than the loss modulus over the entire range of stresses, indicating the presence of a gel structure.

Figure 3 (Continued).

Figure 2 Stress dependence (1 Hz, 20°C) of (a) loss modulus and (b) storage modulus for sage seed gum at different concentrations (◊, 0.5%; □, 0.75%; △, 1%; ×, 1.25%; *, 1.5%; ◯, 1.75%; +, 2%).

Figures 3a–3d shows the mechanical spectra of SSG samples as a function of frequency at 20°C and strain amplitude of 1.0%. It can be found that all the samples were characterized by a gel behavior with a slight dependency of G′ and G″ on the frequency, over the range of 10⁻² to 10 Hz, with G′ greater than G″, linear reduction in log η* with increasing log f, and Tan δ < 1. The G′ and G″ curves of all concentrations were almost parallel and a crossover between the two moduli was not observed throughout the frequency domain. The mechanical spectra of SSG at different concentrations indicate a weak gel behavior.[33] This type of behavior has been observed for some gums, such as psyllium gels,[34] waxy maize starch/xanthan mixtures,[35] Corchorus olitorius leaves’ hydrocolloid,[36] konjac gluco-mannan/xanthan solutions,[37] gellan gels,[38] and k-carrageenan/LBG gels.[39] These “gel like” properties may be attributed to tenuous association of ordered chains and it has been reported for some conventional gums like xanthan above ∼0.3 w/v.[40] On the other hand, some researchers observed a liquid-like behavior at a lower frequency (G″ > G′) and solid-like behavior at a higher frequency (G′ > G″), which is a typical behavior of concentrated polymer solutions. [21,23,24,26–29] The SSG gels exhibited very similar/higher values of both G″ and G′, compared with the other gums like guar and tragacanth,[41] fenugreek gum, guar gum, tara gum and locust bean gum,[24] Mucuna flagellipes seed gum,[23] fenugreek seed gum,[26] and lesquerella fendleri seed gum[29] reflecting pronounced elastic behavior and strong network development in sage seed gum as a new hydrocolloid.

In the present study, SSG gels exhibited lower Tan δ at low frequencies, but it increased slightly at higher frequencies, showing a higher contribution of the viscous component at higher frequencies. Tan δ is a measure of the energy loss per cycle relative to energy stored per cycle, which characterizes the sol–gel transition. The low values of tan δ (<1) show a tendency toward more solid-like behavior and it observed the loss factor values around 0.2–0.3 for amorphous polymers, and near 0.01 for glassy crystalline polymers and gels. [34,42] In this article, the loss factor of SSG gels was mean 0.25 (±0.02) at 0.01 Hz and increased to average value of 0.67 (±0.08) at 10 Hz in the concentration range of 0.5 to 2.0%.

The frequency dependencies of G′ and G″ for physical gels were approximated by a power-law model as follows:[42]

(7)

(8)

The magnitudes of slopes (n′ and n″), intercepts (k′ and k″), and R ² (determination coefficient) were summarized in Table 1. It was found that sage seed gum displayed gel-like behavior because the slopes (n′ = 0.20–0.24 and n″ = 0.37–0.41) were positive, which were much lower than those reported for a Maxwellian fluid (G′ ∞ ω² and G″ ∞ ω). There was no difference between n′ or n″ values at different concentrations, indicating no effect of concentration on the slopes’ values. The magnitudes of k′ (7.28–107.15) were much higher than those of k″ (3.42–51.66), showing the G″/G′ ratio was mean 0.47, and confirming a gel-like behavior of SSG in the concentration range of 0.5–2.0%.[43] As shown in Table 1, increase in the concentration of SSG also increased considerably the values of k′ and k″, suggesting an increase in the stiffness of continuous phase due to the thickening effect of SSG. In this article, the values of intercepts increased about twofold with an increase in SSG concentration by 0.25%.

Table 1  Frequency dependency of elastic and viscous moduli of SSG at different concentrations and constant temperature of 20°C

	Elastic modulus (G′)			Viscous modulus (G”)
Concentration (%)	n′	K′ (Pa.s)	R ^2	n″	K″ (Pa.s)	R ^2
0.5	0.20 ± 0.01	7.26 ± 0.54	0.986	0.37 ± 0.01	3.42 ± 0.24	0.965
0.75	0.22 ± 0.02	12.58 ± 1.25	0.983	0.41 ± 0.01	6.37 ± 0.60	0.987
1.0	0.22 ± 0.01	22.17 ± 1.98	0.978	0.41 ± 0.01	10.53 ± 0.68	0.981
1.25	0.22 ± 0.01	43.22 ± 0.93	0.987	0.39 ± 0.01	20.28 ± 0.51	0.991
1.5	0.22 ± 0.00	62.50 ± 9.85	0.989	0.36 ± 0.01	27.13 ± 3.20	0.994
1.75	0.22 ± 0.01	89.96 ± 5.88	0.988	0.38 ± 0.01	41.42 ± 1.68	0.994
2.0	0.24 ± 0.00	107.14 ± 2.91	0.993	0.38 ± 0.01	51.64 ± 0.69	0.996

Figure 4 shows how the dynamic rheological parameters of SSG gels vary with respect to gum concentration. In general, both storage and loss moduli increased dramatically with increasing the SSG concentration, reflecting stronger gel structure at higher concentrations, although the loss factor remained relatively unchanged. The concentration dependencies of the storage and loss moduli can be represented by the following power law relationships:

(9)

(10)

The power-law exponent value of approximately 2 is in good agreement with that reported for one-component thermo-reversible gels. [44–46] Square power-law relationship is valid only when the concentration range investigated is far greater than the critical gelling concentration.[47]

Creep/Recovery Compliance

The examination of viscoelastic properties of SSG gels was followed by shear creep/recovery experiments. The creep/recovery curves of sage seed gum as a function of concentration is shown in Fig. 5. It is observed that SSG samples showed viscoelastic behavior, and the creep/recovery compliances decreased with concentration because of solidity. There was no full recovery even after 600 s for all cases studied. In viscoelastic materials, according to Burger's model, recovery of the applied stress is partial, controlled by the more elastic or viscous character of the sample, situated at an intermediate position between solid and liquid. The greater the compliance, the easier it is to deform the sample. In this study, the strains generated in the sample containing 0.5% SSG was high; however, for the other concentrations studied, the curve of compliance versus time had the form characteristic of a predominantly elastic network, indicating a viscoelastic solid behavior of sage seed gum (Fig. 5). It means that when the stress was applied, there was a sharp and instantaneous increase in strain, followed by a slight increase over time, which can be attributed to some re-arrangement of network structure. On removal of the stress, there was also a corresponding sharp reduction in compliance, with little residual deformation at the end of the recovery period. At concentrations higher than 1.25%, the SSG gels were almost recovered to their original states, and permanent deformation was small after removal of stress, indicating an elastic gel structure (Fig. 5). The higher the recovery phase, the higher is the viscoelastic solid character of the sample. In addition, it is obvious that the systems very quickly approached the equilibrium compliance conditions.

Figure 5 Compliance versus time in “creep and recovery test” for sage seed gum at different concentrations (applied shear stress: 1 Pa; temperature: 20°C). (Color figure available online.)

The fitting of J_C = f(t), in the interval 0 ≤ t ≤ 300 s, for all the concentrations studied and based on the Burger model (Eq. 1), yielded values of r ≥ 0.983 in all cases, indicating that the Burger model of four elements was adequate to describe SSG creep behavior. Figure 6 shows an example of the experimental creep compliance data and the values predicted by the Burger model for SSG gel at 2% concentration. The values of Burger model parameters, including J _0C , J _1C , η₀, and λ _ret and the correlation coefficient obtained, are listed in Table 2.

Table 2  Creep parameters of the Burger model, obtained from the fits by Eq. (1), for sage seed gum at different concentrations (20°C).^a

Concentration (%)	J 0C (Pa^−1)	J 1C (Pa^−1)	η0 (10^−3 Pa.s)	λ ret (s)	r
0.5	0.341	0.781	0.434	13.23	0.988
0.75	0.136	0.232	2.017	6.89	0.983
1.0	0.072	0.106	4.077	7.00	0.983
1.25	0.045	0.063	6.368	7.04	0.987
1.5	0.026	0.032	12.037	7.18	0.988
1.75	0.020	0.025	12.687	7.15	0.988
2.0	0.017	0.022	15.782	7.46	0.989
^a J 0C and J 1C are the elastic compliance of Maxwell and Kelvin-Viogt springs, η0 is the viscosity of Maxwell dashpot, λ ret is the retardation time, and r is the correlation coefficient.

The instantaneous elastic compliance (J _0C ) represents the value of instantaneous shear creep compliance at initial time, and it may be related to the undisturbed hydrocolloid network structure.[37] A higher value of J _0C reflects a higher degree of non-retarded Hookean-type (elastic) deformation, representing that the network is relatively free to rearrange between cross-links.[22] In this case, J _0C decreased with concentration, indicating that the SSG becomes more rigid and has greater hardness at higher concentration.

The retarded compliance (J _1C ) represents the principal component of the viscoelastic behavior of SSG. It was observed that J _1C decreased with concentration (Table 2). The decrease of this parameter is associated with a more solid (elasticity) and less viscoelastic behavior. In all cases studied, the contribution of J _1C to the total deformation was larger than the contribution of J _0C , reinforcing the concept of a behavior closer to a viscoelastic material than to an elastic one. The sum of J _0C and J _1C is called the steady state compliance.[30] Thus, creep process of SSG gels consisted mainly of steady state compliance, which is important in view of gelation.

The Newtonian viscosity of the free dashpot (η₀) increased considerably with SSG concentration (Table 2). η₀ measures the mechanical behavior of the fluid part of the system. In fact, this parameter is associated with the breakdown of the gel network structure. It also characterizes the linear region of the viscous compliance.[30] In this study, the slope of the linear region (1/η₀) approached to zero when concentration increased from 0.5 to 2.0%. It means that the time period of creep phase was sufficient to access steady flow conditions.

The retardation time (λ _ret ) was not affected by concentration, except for increasing from 0.5 to 0.75%, which it was decreased greatly by 50% (Table 2). The retardation time is unique for each material. Generally, the higher the retardation time of a system network, the longer it takes to reach full deformation on application of shear stress.[30] This also implies that retardation times are inversely related to network viscoelasticity.

The fits of the values of recovery compliance (J_R ) as a function of time, have been made based on Eq. (2). The results obtained, together with the parameters B and C, and the correlation coefficients are presented in Table 3. For all cases analyzed, correlation coefficients were 0.999, confirming the excellent fitting quality of Eq. (2) in describing the recovery phase. J _0R and J _1R represent instantaneous elastic compliance and retarded compliance at the recovery phase, respectively. It can be seen that there was a similar trend for J _0R and J _1R with concentration, as observed for J _0C and J _1C in the creep phase (Table 2). The residual compliance at the end of the recovery period (J _∞) decreased greatly as the SSG concentration increased, showing more recovery and elasticity at higher concentrations. Furthermore, it was found that the B parameter decreased generally with an increase in SSG concentration, whereas the C parameter increased slightly when the concentration increased, indicating the speed of structural recovery of sage seed gum network increased by increasing the concentration of SSG (Table 3).

Table 3  Recovery parameters, obtained from the fits by Eqs. (2) and (3), for sage seed gum at different concentrations (20°C).^a

Concentration (%)	J 0R (Pa^−1)	J 1R (Pa^−1)	J ∞ (Pa^−1)	B (s^−c)	C	r
0.5	0.203	0.371	1.113	0.296	0.407	0.999
0.75	0.114	0.192	0.181	0.333	0.403	0.999
1.0	0.062	0.107	0.069	0.358	0.378	0.999
1.25	0.042	0.064	0.041	0.292	0.407	0.999
1.5	0.024	0.035	0.019	0.264	0.413	0.999
1.75	0.020	0.031	0.015	0.262	0.396	0.999
2.0	0.017	0.026	0.012	0.214	0.448	0.999
^a J 0R and J 1R are the recovery compliance of Maxwell and Kelvin-Viogt springs, J ∞ is the recovery compliance of Maxwell dashpot, B and C are the recovery speed of the system, and r is the correlation coefficient.

Table 4 shows J _max, J _0C *, J _1C *, J _2C *, J _0R *, J _1R *, J _∞*, and R for SSG samples. It can be seen that J _max decreased greatly with concentration, however, J _0C *, J _1C *, and J _2C * parameters were affected slightly by the concentration of SSG. It seems that when concentration is increased, the increase in interaction of molecules allows smaller deformation of the SSG network. In all cases, the retarded elastic deformation percentage, J _1C *, was greater than the instantaneous elastic deformation percentage, J _0C *, and the viscosity flow deformation percentage, J _2C *. It means that the retarded elastic deformation played the most important role in the total creep deformation, followed by the instantaneous elastic deformation and the viscosity flow deformation. In the case of recovery, we see that the percentage deformation of the elements of the recovery phase (J _0R *, J _1R *, J _∞*) are in the same proportion of the creep phase. As it can be found from Table 4, the contribution of Kelvin–Voigt element (J _1R *) was higher than the other two elements, Maxwell spring (J _0R *) and Maxwell dashpot (J _∞*), except for 0.5% concentration, in which the contribution of Maxwell dashpot (J _∞*) was considerably greater than the others. Moreover, the contribution of residual compliance at the end of the recovery period (J _∞*) decreased by about 43% as the concentration of SSG increased from 0.5 to 2%.

Table 4  Maximum compliance and creep/recovery normalized parameters for sage seed gum at different concentrations (20°C).^a

	Creep phase				Recovery phase
Concentration (%)	J max(Pa^−1)	J 0C * (%)	J 1C * (%)	J 2C *(%)	J 0R * (%)	J 1R * (%)	J ∞*(%)	R (%)
0.5	1.687	20.21	46.29	33.50	12.02	22.01	65.96	34.03
0.75	0.487	27.92	47.64	24.44	23.38	39.45	37.16	62.84
1.0	0.237	30.77	45.30	23.93	25.99	44.98	29.02	70.98
1.25	0.147	30.61	42.86	26.53	28.81	43.46	27.72	72.27
1.5	0.078	33.33	41.02	25.65	30.67	44.60	24.72	75.28
1.75	0.065	30.30	37.88	31.82	29.93	47.78	22.29	77.71
2.0	0.055	30.91	40.00	29.09	30.28	47.32	22.39	77.61
^a J max is the creep compliance at t = 300, J 0C *, J 1C *, J 2C *, J 0R *, J 1R *, and J ∞* are the percentage deformation of J 0C , J 1C , η0, J 0R , J 1R , and J ∞, respectively. R is the system recovery.

In this study, the final percentage recovery values (R, %) ranged from 34.03 to 77.71%, indicating a viscoelastic behavior of sage seed gum (Table 4). As the concentration of SSG samples increased, the value of R increased and SSG network can recover up to approximately 78% of its maximum deformation. This parameter gives clear evidence of SSG elasticity behavior with concentration. The results obtained by creep/recovery analysis were in agreement with the dynamic assay results (Figs. 3 and 4).

Table 5  In-shear recovery properties of sage seed gum as a function of concentration at 20°C.^a,b,c

Concentration (%)	η a1 (Pa.s)	η a2 (Pa.s)	η a3 (Pa.s)	Recovery (%)
0.5	2.157 ± 0.177	0.047 ± 0.026	1.275 ± 0.126	59.821 ± 9.417
0.75	3.313 ± 0.277	0.090 ± 0.024	1.833 ± 0.134	57.457 ± 7.941
1.0	5.643 ± 0.537	0.122 ± 0.022	3.216 ± 0.205	57.648 ± 7.849
1.25	8.004 ± 0.715	0.173 ± 0.034	4.703 ± 0.304	59.410 ± 8.217
1.5	8.579 ± 0.835	0.174 ± 0.020	4.272 ± 0.210	50.292 ± 5.923
1.75	15.693 ± 1.149	0.317 ± 0.041	8.891 ± 0.893	57.192 ± 8.841
2.0	15.947 ± 1.650	0.356 ± 0.022	9.677 ± 0.795	61.616 ± 10.200
^aData were the mean of 10 replications.
^bThe program in this test was: step 1, shear rate 1 s^−1 for 120 s; step 2, shear rate at 300 s^−1 for 60 s; step 3, shear rate at 1 s^−1 for 180 s.
^cη a1, η a2, and η a3 are the apparent viscosities of steps 1, 2, and 3, respectively. The recovery (%) is defined as (η a3/η a1) × 100.

In-Shear Structural Recovery

The in-shear structural recovery test was carried out in order to investigate the capability of the SSG gels to recover their original structure under low shear conditions after decomposition under high-shear conditions. [32,35] The results of in-shear recovery experiments are presented in Table 5. It can be found that increasing SSG concentration had no distinct effect on the in-shear structural recovery. In addition, the structural recovery of SSG samples were obtained relatively high (>50%) and it was mean at 57.63%, indicating rapid rearrangement of structure after the high shear step. This result is useful for practical applications, in which the resistance to high shear conditions (like pumping and mixing) and fast recovery of the initial viscosity (anti-thixotropy) are very important factors for selection of a suitable stabilizer/thickener. As expected, increase in SSG concentration increased considerably the apparent viscosity both at low and high shear rates (Table 5). For example, increasing the concentration from 0.5 to 1.0, 1.5, and 2.0% resulted in an increase of apparent viscosity of step 1 (η _a1) by 162, 298, and 639%, respectively. This result was in agreement with the steady shear results reported for SSG.[20] In addition, increase in concentration of samples by 0.25% increased the apparent viscosity (η _a ) by about 44 ± 0.01%, independent of shear rate used. It means that the viscosity decrease caused by thixotropic behavior from steps 1–3 was little.

CONCLUSION

Mechanical spectra obtained by frequency sweep tests showed that the sage seed gum at all concentrations ranging from 0.5 to 2% (w/w) exhibited weak gel behavior like some commercial gums, because G′ was larger than G″ throughout the frequency range and the loss factor was larger than 0.1. Creep tests at different concentrations allowed gaining a better understanding of viscoelastic properties of sage seed gum. The decreasing of J ₀ and J ₁, and increasing of η₀ with concentration may be explained by more stabilizing of the SSG network. A semi-empirical approach was used to obtain the contribution of each compliance parameter to the total deformation of the system. The contribution of J ₁ to the total deformation was larger than the contribution of J ₀, reinforcing the concept of a behavior closer to a viscoelastic material than to an elastic one. The in-shear recovery properties of SSG gels showed that there is no dependency to concentration and the structure can be relatively highly recovered after applying high shear conditions. The results of this article will contribute to the research of new potential of hydrocolloids, as a substitute to the conventional ones as thickening/gelling agents, and to the development of novel food formulations, addressing the demands of the modern consumer.

ACKNOWLEDGMENTS

The authors would like to thank Cristina Fuentes and Juan Andres Sandoval for their technical assistance.