Physicochemical properties
The variations in total soluble solids (TSS), moisture content, pH, titratable acidity and vitamin C of red cherry tomato puree were presented in Table 1. The puree samples were adjusted to TSS levels of 15, 19, 23 and 27
oBrix by drying or dilution with distilled water. An inverse relationship was observed between TSS and moisture content, with TSS increasing from 15 to 27
oBrix, moisture content decreased from 74.22% to 57.1%. The pH decreased from 6.08 to 5.47 as TSS increased showing acidification during concentration. These values were slightly higher than the common pH range (4.0-4.6) reported for commercial tomato products
(Aykas et al., 2020). Titratable acidity increased steadily with higher TSS, likely due to concentration of organic acids such as citric and malic acids. Vitamin C increased from 8.5 mg (100 g)
-1 at 15
oBrix to 11 mg (100 g)
-1 at 27
oBrix, consistent with
Haseen et al. (2019) and
Koh et al. (2012), who reported that higher TSS can help protect ascorbic acid from enzymatic breakdown. This relative stability at higher concentrations also agrees with
Vigneshwaran et al. (2022), showing that although thermal processing causes some initial vitamin C loss, further concentration does not substantially increase its degradation
(Dippong et al., 2025).
Rheological properties
The shear stress and viscosity data at different temperatures and shear rate for lowest and highest concentration levels were presented in Table 2. The rheogram in Fig 2 showed the relationship between shear stress and shear rate for red cherry tomato puree at four concentrations of 15
o, 19
o, 23
o and 27
o Brix.
For all the samples, shear stress increased as shear rate increased, showing a non-Newtonian, shear-thinning (pseudoplastic) behaviour as also reported by
Stanciu (2022),
(Fadeyibi et al., 2024) for tomato sauce. Samples with higher TSS had higher shear stress at the same shear rate indicating that more soluble and structural solids increased resistance to flow and raised apparent viscosity also reported by
Evangelista et al. (2020). Among the samples the puree at 27
oBrix showed the highest shear stress of 3.708 Pa at 0.1 s
-1 while the 15
oBrix sample recorded the lowest value of 3.0008 Pa at 200 s
-1, confirming that concentration strongly affected rheological properties.
The variation of apparent viscosity with shear rate for red cherry tomato puree samples was shown in Fig 3. All samples exhibited a marked decrease in viscosity with increasing shear rate, confirming a shear-thinning (pseudoplastic) behaviour typical of fruit purees. This rheological behaviour was attributed to the breakdown of internal structure and alignment of particles under shear. Furthermore, at any given shear rate, samples with higher TSS showed significantly higher viscosity values. The puree at 27
oBrix demonstrated the highest viscosity (37.18 Pa. s) at shear rate of 0.1 s
-1, while the 15
oBrix sample had the lowest (0.02 Pa. s) at shear rate of 0.1 s
-1 indicating that increased soluble solids contribute to greater resistance to flow and structural rigidity.
Both temperature and total soluble solid (TSS) content had a significant effect on the viscosity of red cherry tomato puree, consistent with observations reported for persimmon puree (
Mazlum and Lodos, 2025) and pomelo juice concentrate
(Keshani et al., 2012). An increase in temperature enhances molecular mobility and intermolecular spacing thereby reducing flow resistance. Consequently, the viscosity of red cherry tomato puree decreased markedly with increasing temperature, as shown in Fig 4. This effect was more pronounced at higher TSS levels.
In contrast, TSS concentration exhibited a strong positive influence on viscosity which is characteristic of non-Newtonian fluids. Increasing soluble solid content alters the degree of hydration of solute molecules and promotes hydrogen bonding between hydroxyl groups, leading to reduced intermolecular spacing and increased resistance to flow. As a result, the viscosity of red cherry tomato puree increased significantly with increasing TSS.
Rheological models
One of the most widely used models for describing viscosity data is the power law model which contains only two parameters (K and n) to represent shear stress-shear rate behaviour. Due to its simplicity and ability to express rheological behaviour as a linear relationship under shear, it has been extensively applied to fluid foods. The flow behavior index reflects the deviation from Newtonian flow and quantifies the non-Newtonian nature of fluids
(Pang et al., 2020). A value of 1 indicates Newtonian behaviour, whereas values greater than 1 signify dilatant flow
(Gao et al., 2021). In this study shear stress and shear rate data were fitted to Equation 1 and the resulting parameters are presented in Table 3. The consistency index (K) increased from 0.85 at 15
oBrix to 4.8 at 27
oBrix, while the flow behavior index (n) decreased from 0.22 to 0.13, indicating shear-thinning (pseudoplastic) behaviour. The Herschel-Bulkley model, which combines power law and Bingham characteristics and is widely used for non-Newtonian fluids, was also fitted using Equation 2, with parameters reported in Table 3. The model similarly indicated pseudoplastic behaviour as reflected by flow behavior index values below 1 (0.44 to 0.82). The consistency index increased (0.03 to 0.48) with increasing concentration. Yield stress defined as the minimum shear stress required to initiate flow, is an important property of multiphase systems (
González-Montemayor et al., 2022). In this study, yield stress increased with concentration, reaching a maximum value of 5.3 Pa at 27
oBrix. The Casson model commonly applied to concentrated fruit and vegetable purées exhibiting yield stress, effectively described the non-Newtonian behaviour of the samples. Parameters (Table 3) obtained from Equation 3 showed that Casson yield stress increased with total soluble solids and was comparable to the Herschel-Bulkley yield stress values. Casson plastic viscosity decreased with increasing concentration, suggesting possible particle rearrangement or reduced inter-particle friction after yielding. Overall, regression analysis based on R
2 and RMSE indicated that all three models-Power Law, Herschel-Bulkley and Casson-provided a good fit to the experimental data, confirming consistent pseudoplastic behaviour of red cherry tomato puree across different concentrations and temperatures. Among these, the Power Law model showed the highest R
2 and the lowest RMSE, indicating superior fitting performance. However, the presence of yield stress at low shear rates suggests that models incorporating yield stress (Herschel-Bulkley and Casson) may better represent the initial flow behaviour. Similar results were obtained during measurement of rheological behaviour of yoghurt at 10-85 s
-1 shear rate using a rotational viscometer
(Karmakar et al., 2025).
Effect of temperature on apparent viscosity
The temperature dependence of the apparent viscosity of red cherry tomato puree was evaluated using the Arrhenius model (Equation 4). A linear relationship was observed between the natural logarithm of apparent viscosity (ln μ) and the reciprocal of absolute temperature (1/T), confirming the suitability of the Arrhenius equation for describing the thermal behavior of the puree. As shown in Fig 5, the apparent viscosity decreased with increasing temperature for all Brix levels, indicating a typical pseudoplastic and temperature-sensitive nature of the product which was also reported by
(Hopper et al., 2025 and
Ali et al., 2024).
The calculated slopes from the linear equations allowed for the determination of activation energy (Ea). The activation energies and the Arrhenius constants (A) determined from the curve were listed in Table 4. The increasing trend in activation energy with higher TSS levels suggests that the puree becomes more sensitive to temperature changes at higher concentrations also observed by (
Mazlum and Lodos, 2025). This behaviour could be attributed to the greater presence of soluble solids such as sugars and pectins, which form more structured networks that resist flow at lower temperatures but break down more rapidly with heat. The regression equations derived from the experimental data yielded high coefficients of determination (R
2) with the highest being 0.989 at 27
oBrix demonstrating excellent model fit. A molecule needs activation energy to move and when the temperature rises, the liquid flowed more readily because of the higher activation energy in high temperatures. Furthermore, the increased alignment of constituent molecules was linked to the decrease in viscosity with an increase in shear rate
(Haminiuk et al., 2006).
Viscoelastic behaviour
The amplitude sweep test was conducted to determine the linear viscoelastic region (LVR) of red cherry tomato puree at different TSS levels by applying oscillatory shear with increasing strain at a constant angular frequency as shown in Fig 6, 7, 8 and 9. The amplitude sweep test parameters of lowest and highest TSS levels were listed in Table 5.
The storage modulus represented elastic portion and the loss modulus characterize viscous portion. The results revealed that the storage modulus (G′) was consistently higher than the loss modulus (G″) within the LVR, indicating that the puree exhibited predominantly elastic or solid-like behavior under small deformations, aligning with finding by
Wan et al., (2025); Fadeyibi et al., (2024); Giura et al., (2022); Augusto et al., (2011). Beyond the LVR, all samples showed a gradual decrease in both G′ and G″ with increasing strain (strain-softening). At larger strains, G′ and G″ approached each other and crossed over (G′ =G″), marking the transition from solid-dominated to liquid-dominated behaviour (flow point), signifying the breakdown of the internal structure and a transition from elastic to viscous behavior. The point where G″ cross over G′ was known as the yield point or critical strain. Based on the graph, the yield point occurred at higher strain for the more concentrated Purees (23 and 27
oBrix) than for the diluted one (15
oBrix). However, no yield point was observed for 15
oBrix sample in the range of applied strain. The amplitude sweep test provided critical insights into the viscoelastic strength and deformation tolerance of tomato puree under different compositional conditions.