*3.1. Characterization of Gum*

Table 1 showed physicochemical properties of CSG, FSG, and RSG. CSG consisted of 73.59% carbohydrate, 9.45% protein, 1.01% fat, 9.60% moisture, 6.26% ash (% *w*/*w*). FSG contained 78.56% carbohydrate, 11.38% protein, 2.16% fat, 9.08% moisture, 7.89% ash (% *w*/*w*) while RSG consist of 60.48% carbohydrate, 21.00% protein, 1.94% fat, 9.95% moisture, 6.63% ash (% *w*/*w*).


**Table 1.** Physicochemical properties of gum.

CSG: chia seed byproduct gum, FSG: flaxseed byproduct gum, RSG: rocket seed byproduct gum. The different lowercase letter in the same line indicates statistical significance (*p* < 0.05).

The protein content of gums is a very important parameter affecting the emulsification and foaming ability of gums. The protein content of the obtained gums was found to be higher than other natural and commercial gums [16,31]. RSG is rich in galactose and mannose, while FSG and CSG are rich in xylose and glucose. It can be said that RSG has a galactomannan structure as in many gums. The ratio of mannose to galactose was found to be 1.77 in RSG. The mannose to galactose ratio strongly affected the technological properties of gums such as their cold-water solubility, thickening, gelling, and crystalizing properties. The mannose galactose ratio was lower than guar gum (2:1) and LBG (4:1), and higher than fenugreek gum (1:1) [32,33]. In a similar study, xylose and glucose were reported to be higher than mannose and galactose from studies on the sugar profile of mucilage and gums obtained from flaxseed and chia seeds [34–37].

The FTIR spectrum of CSG, FSG, and RSG is illustrated in Figure 1. The results revealed that all gum samples showed a similar FTIR spectrum with some minor differences. This difference might be due to their protein content and different sugar and organic acid composition. Characteristic bands varying between 3500–3100 cm<sup>−</sup><sup>1</sup> are attributed to the hydroxyl (-OH) stretch that forms the gross structure of carbohydrates [38]. The bands between 3000–2800 cm<sup>−</sup><sup>1</sup> represent -C-H stretching of the aromatic rings and the methyl group (CH3) [38]. The bands at 1654 cm<sup>−</sup><sup>1</sup> and 1618 cm<sup>−</sup><sup>1</sup> for chia seed and its mucilage are assigned to a mannose ring [39].The bands at around 1597 cm<sup>−</sup><sup>1</sup> and 1422 cm<sup>−</sup><sup>1</sup> are due to the carboxyl groups of uronic acid residues in the gum polysaccharide or the presence of protein in the gum samples [40]. This result is compatible with the protein content of the gums. The wavenumber between 950 cm<sup>−</sup><sup>1</sup> and 1200 cm<sup>−</sup><sup>1</sup> is generally considered the fingerprint region of polysaccharides where the main chemical groups in polysaccharides are identified. The band at around 1030 cm<sup>−</sup><sup>1</sup> is assigned to C-O-C

stretching of 1→4 glycosidic bonds [41]. Also, the strong absorption at 1014 cm<sup>−</sup><sup>1</sup> shows the stretching vibration of the C–N [42]. The band at 864 cm<sup>−</sup><sup>1</sup> is assigned to the β-anomeric C-H deformation and glycosidic linkages of glucopyranose and xylopyranose units [38]. The FTIR spectrum obtained is very similar to many mucilage and gums studied in the literature. Hadad and Goli [43] observed the FTIR spectrum of flaxseed mucilage gave the absorption peaks at 3321, 2922, 1612, 1410, and 1050 cm<sup>−</sup>1. Darwish and El-Sohaimy [44] reported the absorption peaks of chia seed mucilage at 1739, 1539, 1444, 1419, 1157, 1058, and 618 cm<sup>−</sup>1.

**Figure 1.** FTIR spectra of the FSG (Flaxseed byproduct gum), CSG (Chia seed byproduct gum), and RSG (Rocket seed byproduct gum) in the spectral region between 400 and 4000 cm<sup>−</sup>1.

### *3.2. Flow Behavior Rheological Properties of the CSG, FSG, and RSG Solutions*

Figure 2 exhibits the flow properties of CSG (1.0, 1.5, and 2.0 %, *w*/*w*), FSG (1.0, 1.5, and 2.0 %, *w*/*w*), and RSG (1.0, 1.5, 2.0, 3.0, and 5.0 %, *w*/*w*) solutions with different concentrations over the range of shear rate from 0.01 to 100 s<sup>−</sup><sup>1</sup> at 25 ◦C. The decrease in viscosity by an increase in shear rate indicated a non-Newtonian shear-thinning (pseudoplastic) flow behavior for CSG, FSG, and RSG solutions at all concentrations. The decrease in the viscosity values of the samples due to the increasing shear rate can be explained by the breaking of the weak bonds between the molecules in the product as a result of the applied force and the weakening of the interaction between the components [45,46]. As predicted, the constant shear viscosity increased with the increase of gum concentrations. The most used hydrocolloids in the food industry, such as locust bean gum [47] and xanthan gum [48], showed shear-thinning rheological behavior. Similar shear-thinning flow behavior of gum dispersions was previously reported by Sanchez et al. [49], Marcotte et al. [50], Yamazaki et al. [51], Razavi et al. [52], and Chaharlang and Samavati [53]. CSG and FSG dispersions showed high viscosity and pronounced shear-thinning behavior at low concentrations (1–2%); however, more RSG exhibited weak pseudo-plasticity at lower concentrations. This might be explained by the varied origins of these gums. The gums with high molecular weight and strong intermolecular interactions have high viscosity solutions [54]. The orientation effect is another explanation for the shear thinning behavior. As the shear rate increases, the randomly distributed polymer molecules become more and more aligned in the flow direction, resulting in reduced contact between neighboring polymer chains [55].

**Figure 2.** Steady shear rheological properties of the FSG (flaxseed byproduct gum), CSG (chia seed byproduct gum), and RSG (rocket seed byproduct gum) solutions with different concentrations ((**a**) CSG (1–2%), (**b**) FSG (1–2%), (**c**) RSG (1–5%)).

Shear-thinning gums are commonly used to enhance the texture and rheological properties of food products. The high-shear processing operations, such as pumping and filling cause a reduction in the apparent viscosity of the solution. However, the high apparent viscosity produces a pleasant tongue feel during consumption [56].

The power-law model parameters (the consistency index (K) and the flow behavior index (n)) are shown in Table 2. The power-law model was successfully applied for the modeling of flow behavior properties of CSG, FSG, and RSG solutions (The coefficients of determination: R<sup>2</sup> > 0.96). Many previous investigations have shown that the power-law model was the suitable model for describing the flow behavior of gum solutions [47,50,56,57].


**Table 2.** Steady shear power-law parameters of gum solutions.

CSG: chia seed byproduct gum, FSG: flaxseed byproduct gum, RSG: rocket seed byproduct gum. A different uppercase letter in the same column indicates statistical significance (*p* < 0.05).

The K values were found as 0.209–49.028 Pa·<sup>s</sup>n. The increase of gum concentrations increased K values for all types of gum solutions. At the same concentration, CSG had the highest K values, followed by FSG and RSG. The n values of CSG, FSG, and RSG solutions at all concentrations were less than 1, indicating that all gums showed a non-Newtonian shear-thinning behavior (Table 2). All the gum solutions had strong shear-thinning behavior with *n* values as low as 0.143–0.460, indicating a significant deviation from Newtonian behavior, and they, like many other shear-thinning hydrocolloids, have a high viscosity and pleasant mouthfeel at low shear rates. CSG, FSG, and RSG samples exhibited shearthinning behavior like locust bean gum [47], monoi gum [57], guar gum [58], and xanthan gum [48], which was explained to be due to weak bonds formed as a result of shearing [59]. When the n number is smaller than 0.6, it has been observed that non-Newtonian behavior becomes relevant [60]. The increase of gum concentrations caused decreasing n values. These results demonstrated that different concentrations of CSG, FSG, and RSG solutions affected the steady shear properties of CSG, FSG, and RSG solutions.

Figure 3 shows the viscosity of CSG, FSG, and RSG solutions with different concentrations over the range of shear rate from 0.01 to 100 s<sup>−</sup>1. As seen in Figure 2, the viscosity of the CSG, FSG, and RSG samples decreased with an increase in the shear rate at all concentrations due to the pseudoplastic behavior of gum solutions. The increase in shear rate led to a breakdown of molecular bonds, and therefore molecules became regular and internal friction decreased. As a result, the viscosity of CSG, FSG, and RSG solutions decreased. As the gum became entangled in the solution, the viscosity of the gum solutions increased with gum concentration, as can be seen in Figure 3. The higher viscosity value in CSG-2 (a solution containing 2% chia gum) compared to other gum solutions was associated with the strong interactions in hydrogen bonds [61].

**Figure 3.** The viscosity of CSG: chia seed byproduct gum, FSG: flaxseed byproduct gum, RSG: rocket seed byproduct gum solutions with different concentrations ((**a**) CSG (1–2%), (**b**) FSG (1–2%), (**c**) RSG (1–5%)).


CSG, FSG, and RSG solutions were sheared at a constant shear rate of 0.5 s<sup>−</sup><sup>1</sup> at 25 ◦C in the shear decay test. At 25 ◦C, Figure 4 depicts the change in shear stress of CSG, FSG, and RSG solutions as a function of time. Following that, the data were fitted to two different models: the Weltmann [62] model and the second-order structural model [63].

The computed parameters and their related determination coefficients are shown in Table 3. Both models could accurately reflect the time-dependency of shear stress values at all gum concentration levels with good R<sup>2</sup> values.

**Figure 4.** Shear stress vs. time at a constant shear rate (0.5 s<sup>−</sup>1) for CSG: chia seed byproduct gum, FSG: flaxseed byproduct gum, RSG: rocket seed byproduct gum solutions with different concentrations ((**a**) CSG (1–2%), (**b**) FSG (1–2%), (**c**) RSG (1–5%)).

**Table 3.** Weltman and second-order structural kinetic model parameters defining the time-dependent flow behavior of gum solutions at 25 ◦C.


CSG: chia seed byproduct gum, FSG: flaxseed byproduct gum, RSG: rocket seed byproduct gum; constant shear rate (0.5 s<sup>−</sup>1). A different uppercase letter in the same column indicates statistical significance (*p* < 0.05).

The second-order structural model provides information on the change in timedependent flow characteristics caused by shearing, as well as the rate of breakdown, based on the sample's structured and nonstructured state. The rate constant (k) represents the rate of structural breakdown (thixotropy degree), whereas the initial-to-equilibrium viscosity ratio (*η*0/*ηe*) offers a relative assessment of structural breakdown quantity [26]. The parameters of the second-order structural model are shown in Table 3. Gum type also affected the magnitudes of k values and *η*0/*ηe* values. As can be expected, *η*0 and *ηe* values of gum solutions were increased with the increase of gum concentrations. Moreover, the k values and *η*0/*ηe* ratios of gum solutions were increased with the increase of gum concentrations. The highest k and *η*0/*ηe* values belong to CSG solutions, indicating that CSG solutions showed a faster rate of thixotropic breakdown and the extent of thixotropy.

The Weltman model predicted well the relationship between the shear stress and shearing time of gum solutions, and its parameters (A and B) were utilized to examine the effect of temperature on stress decay behavior (Table 3). Parameter A represents the shear stress threshold for structural breakdown, while the time coefficient-B represents the amount of structural breakdown caused by applied shear [64]. Negative B values indicate how soon the apparent viscosity achieves equilibrium [60]. Lower B values imply that the structure of a product is less affected by stirring. Therefore, RSG and FSG were affected less than CSG by stirring due to their lower B values. The Weltman model's coefficients were affected by the gum concentrations and applied constant shear rate [65].

### 3.3.2. Three Interval Thixotropic Time Test (3-ITT)

Figure 5 showed the structural recovery of CSG, FSG, and RSG solutions by 3-ITT, which simulates the sudden and nonlinear deformation of gum solutions. The structural recovery tendency of CSG, FSG, and RSG solutions increased with the increase of gum concentrations. The lowest concentrations of gum solutions caused the lowest structural recovery. These results showed that the structural breakdown observed in the second time interval due to high sudden shear force could be easily recovered as the gum concentration increased [66].

**Figure 5.** 3-ITT rheological properties of CSG: chia seed byproduct gum, FSG: flaxseed byproduct gum, RSG: rocket seed byproduct gum solutions with different concentrations ((**a**) CSG (1–2%), (**b**) FSG (1–2%), (**c**) RSG (1–5%)).

Table 4 indicates the structural deformation and recovery ratio determined by fitting 3-ITT rheological data using a second-order structural model. The thixotropic constant (k), initial storage modulus ( *G*0), equilibrium storage modulus ( *Ge*), and the ratio of *Ge* and *G*0 (*Ge*/*G*0) were calculated by the second-order structural kinetic model. The *Ge*/*G*0 value represents the recovery percentage; the larger it is numerically, the faster it can be evaluated to tend to recover. *Ge*/*G*0 values were between 1.124 and 1.750. CSG had the highest *Ge*, *G*0, and *Ge*/*G*0 values, indicating that CSG solutions were the higher recoverable character. As seen in Table 4, the k value indicates the thixotropic rate of samples, and a higher k indicates a higher recovery rate. For each type of gum, the higher gum content showed a higher k value. Samples containing the highest gum concentration showed the highest k and *Ge*/*G*0, indicating that the sample showed the highest thixotropic behavior and viscoelastic solid character. Also, FSG-2 had the highest k value.


**Table 4.** Second-order structural kinetic model parameters for 3-ITT.

CSG: chia seed byproduct gum, FSG: flaxseed byproduct gum, RSG: rocket seed byproduct gum. % D: % Deformation and % R: %Recovery. A different uppercase letter in the same column indicates statistical significance.

### *3.4. Viscoelastic Behavior of the CSG, FSG, and RSG Solutions*

A frequency sweep test was utilized for the determining viscoelastic behavior of gum solutions. Figure 6 indicated the dynamic viscoelastic characteristics of CSG, FSG, and RSG solutions with different concentrations. As seen, the changes in storage (G) and loss (G) values for gum solutions were demonstrated as a function of angular frequency (*ω*) at 25 ◦C. The structure of the gum solutions may be shown in dynamic mechanical spectra, which reveal the frequency dependence of storage modulus G and loss modulus G. There were no cross points between G and G values, revealing that G values were greater than G across the entire frequency range studied. As a result, gum solutions had typical gel-like behavior within the experimental frequency range at 25 ◦C. This viscoelastic behavior was in good agreemen<sup>t</sup> with that reported by Chaisawang and Suphantharika [67] and KUTLU et al. [68].

**Figure 6.** Viscoelastic behavior of the (**a**): CSG: chia seed byproduct gum (1–2%), (**b**): FSG: flaxseed byproduct gum (1–2%), (**c**): RSG: rocket seed byproduct gum (1–5%) solutions with different concentrations.

Non-linear regression was used to analyze experimental G and G values vs. *ω*, and the computed magnitudes of slopes (n and n), intercept (K and K), and coefficient of determination (R2) values are shown in Table 5. K values were determined to be higher than K values, indicating that gum solutions exhibited liquid-like characteristics. Similar results were reported in previous studies on different gum solutions [66–68] and different food products [69,70]. All of the solutions exhibited gel-like behavior due to the positive slopes (n and n > 0). The n value may be used to determine the strength and type of the gel; n = 0 indicates a covalent gel, while n > 0 indicates a physical gel. Low n values (around zero) indicate that G does not vary with frequency, but n values close to 1 indicate that the system acts like a viscous gel.



CSG: chia seed byproduct gum (1–2%), FSG: flaxseed byproduct gum (1–2%), RSG: rocket seed byproduct gum (1–5%); K and K: consistency coefficient (Pa·<sup>s</sup>n); n and n: flow behavior index values; R2: determination of coefficient. A different uppercase letter in the same column indicates statistical significance.

### *3.5. Rheological Properties, Zeta Potential, and Particle Size and Oxidative Stability of Low-Fat Vegan Mayonnaise Samples with Different Types of Gum*
