Rheological, functional properties, and stability of peach puree added with normal and high amylose retrograded starches

ABSTRACT

Texture-modified foods have become a growing trend in the market and retrograded starch can enhance the rheological properties of foods. This study assessed the effect of adding 10% (w/w) of normal (RNS) or high amylose (RHS) retrograded starches on the physicochemical and rheological properties of commercial peach puree stored at 4°C. The resistant starch content (RS), syneresis, and rheological behavior were evaluated during 14-day storage. Control puree exhibited high syneresis (60%), low consistency (6 Pa·sⁿ), and decreasing viscosity during storage. These characteristics improved after adding retrograded starches. Samples with RNS exhibited higher viscosity, lower syneresis, lower RS (2%), and poor stability; meanwhile, the systems with RHS exhibited greater stability maintaining their viscosity, syneresis, and RS (10%) relatively constant during storage. Therefore, RHS can be recommended to enhance and maintain the physicochemical, nutraceutical, and rheological properties of a food matrix like peach puree during storage.

KEYWORDS:

• Retrograded starches
• puree systems
• resistant starch
• rheological properties
• stability

1. Introduction

In recent years, there has been a growing trend among consumers to adopt a healthier lifestyle, with a focus on consuming appropriate food products that play a crucial role. Consuming fruits and vegetables is essential for preventing and treating chronic diseases because they are rich in vitamins, dietary fiber, and polyphenols (Mazzoni et al., 2021). One of the most common ways to consume fruits and vegetables is in the form of purees which are concentrated dispersions that contain sugars, organic acids, pectic substances, and water. They are obtained through thermal (cooking) and mechanical (grinding) treatment of fruits or vegetables (Espinosa-Muñoz et al., 2013).

Scientific research has focused on studying the effect of structural properties on the sensory perception of apple puree (Espinosa-Muñoz et al., 2012), as well as the rheological properties of apple (Espinosa-Muñoz et al., 2013) and tart cherry purees (Lukhmana et al., 2018). The impact of different polysaccharides on the texture and syneresis of purees has been studied. For instance, Sharma et al. (2017) examined the effect of pectin on the consistency and syneresis of carrot puree, while Cepeda and Collado (2014) investigated the impact of dietary fibers on the rheology of pimiento puree. Additionally, Dankar et al. (2018) explored the influence of agar, alginate, lecithin, and glycerol on the rheological properties of potato puree. However, the impact of incorporating various molecules as food additives in purees remains unexplored, encompassing structural, technological, and/or sensory aspects.

Starch is a suitable biopolymer for several industrial applications. In the food industry, it is widely used as a gelling agent, thickener, emulsion stabilizer, and fat replacer to modify food properties (Liu et al., 2022). It is well known that starches in their native form generally have poor thermal properties and low shear resistance; therefore, their use in industrial applications is limited. For this reason, starch modification is necessary, and for industrial food applications, physical modifications are preferred (Chiu & Solarek, 2009). Autoclaving is a relatively simple physical method to improve the functionality of native starch. Autoclaved starch is obtained through the thermal treatment of native granules at >100°C in excess of water. This leads to the loss of granular order and allows the reconfiguration of the starch molecular components during cooling and storage. Autoclaving can improve the thermal stability of starch and increase its resistance to enzymatic digestion (Soler et al., 2020). In this context, starch is classified into three major fractions according to its digestion rate: rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS). Slowly digestible starch (SDS) and resistant starch (RS) are commonly used as additives or raw materials in food processing because of their low digestion rate and resulting low glycemic index (Fan et al., 2023).

After the starch is gelatinized, it undergoes a retrogradation process that depends on several factors including temperature, amylose content, moisture, and time. This process provides different characteristics to the starch (Matignon & Tecante, 2017). The physicochemical properties of starch depend on both the botanical source and any modifications it undergoes during processing. Similarly, the amylose content is a crucial factor that drives the overall properties of starch and its dynamic during retrogradation. In this context, several studies have shown a positive correlation between the amylose content and the content of resistant starch (RS), while the amylopectin has been associated with the SDS fraction (D. Li et al., 2020; X. Li et al., 2014; Lin et al., 2017; Xu et al., 2020). Retrograded starches have demonstrated desirable physicochemical properties, including thermal stability, low water absorption, and improved sensory characteristics such as appearance and organoleptic properties. Moreover, retrograded starches have been identified as poorly digestible starches and completely or partially fermented by the gut microbiota, thereby enhancing intestinal health (Chang et al., 2021). Therefore, retrograded starches in food systems may enhance their rheological, textural, and physicochemical properties while providing beneficial health effects to consumers.

Due to their availability and low cost, starch-based thickeners are commonly used in prepared foods and purees intended for people with swallowing difficulties, such as dysphagia or gastroesophageal reflux. Starch-based thickening agents, including chemically or physically modified corn, rice, potato, and tapioca starches, are usually added to purees to enhance their physicochemical properties (González-Bermúdez et al., 2015; Yang et al., 2022). However, concerns about the possible adverse effects of chemical treatments on the health have prompted a reconsideration of their use in the food industry (Rostamabadi et al., 2022). On the other hand, physical treatments allow producing clean label starches (Kim & Baik, 2022) by modifying amylose and amylopectin packing structure through the reorganization of molecular chains (Rostamabadi et al., 2022). In that sense, the autoclaving treatment and the subsequent retrogradation treatment allow obtaining a clean label modified starch, since no chemical agents are used in this process.

Moreover, there exists an underserved segment of the global population that suffers from chronic illnesses or physiological dysfunctions that impede their capacity to chew and swallow food, such as dysphagia. It is widely known that a significant portion of the population – approximately one out of every 17 people – will experience some form of dysphagia during their lifetime. Specific segments of the global population are more susceptible to developing this condition, including elders (11–33%), individuals hospitalized with pneumonia (approximately 75%), and those experiencing a stroke (acute phase, 37–78%) (Clavé & Shaker, 2015). It is well-known that approximately 80% of individuals with Parkinson’s, Alzheimer’s, dementia, multiple sclerosis, and amyotrophic lateral sclerosis will experience some level of dysphagia as their disease progresses (Belliappa, 2021; Clavé & Shaker, 2015). A recent paper found that among the main reasons for buying purees are the following: “looks healthy,” “can be easily eaten,” “has good combination of ingredients,” and “contains natural ingredients” (Carrillo et al., 2024). Therefore, it is important to enhance the texture of food by incorporating ingredients to provide food systems that preserve nutritional value without compromising taste or texture.

This study evaluated the effect of supplementing retrograded normal and high amylose starches on the physicochemical characteristics, resistant starch content, and rheological properties of peach puree. The stability of these properties was evaluated during a 14-day storage period.

2. Materials and methods

2.1. Materials

In this study, two types of corn starch, normal and high amylose (Hylon VII), were procured from National Starch and Chemical S.A. de C.V. (Toluca, Mexico). The technical sheet indicated that the amylose content of the normal and high amylose corn starches was 27% and 70%, respectively. A commercially available peach puree (Gerber® brand) was purchased in a local supermarket in Querétaro, Mexico. The label of the puree declared only peach puree prepared from concentrate and vitamin C as ingredients.

2.2. Sample preparation

2.2.1. Retrograded starches preparation

The retrograded starches were obtained following the method described by Dominguez-Ayala et al. (2023). Briefly, Normal (NS) and high amylose (HS) corn starches dispersions (5% solids, w/v) were placed into an autoclavable Pyrex® bottle and pregelatinized at 60°C for 15 min, using constant stirring. This step was carried out to induce dispersion, slight disorganization, and swelling of the granules, as previously reported (Supare & Mahanwar, 2022). Then, the pregelatinized dispersions were heated to 120°C in an autoclave (LS-B75L, NANBEI, China), holding them at such temperature for 30 min. The autoclaved starch dispersions were dried in an Excalibur dehydrator at 40°C for 24 h, obtaining the retrograded starches (RNS and RHS).

2.2.2. Starch addition-thermic treatment

Retrograded starches (RNS and RHS) were mixed with peach puree (Gerber® brand) at 10% (w/w) under constant stirring at 25°C for 1 min. Then, 15 g of the mixture was placed in polyethylene bags, which were hermetically sealed and heated in water at 72°C for 3 min before storage at 4°C.

2.3. Resistant starch determination

The resistant starch (RS) content of the puree mixed with starch was measured using the “Rapid K-RAPRS” resistant starch assay kit from Megazyme International Ireland Ltd. (Wicklow, Ireland) following the instructions provided. Measurements were performed in duplicate.

2.4. Syneresis determination

Syneresis expresses the water-holding capacity of a material, and it was directly calculated by centrifugation according to Downey (2003), using a Rotofix 32 centrifuge (A Hettich, Tuttlingen-Germany) at 4000 rpm for 20 min. The syneresis percentage was calculated using Equation (1)(1) $\mathit{Syneresis}\left(\mathrm{\%}\right)=\left(\frac{\mathit{supernatant}\left(\mathit{g}\right)}{\mathit{Sample}\left(\mathit{g}\right)}\right)\ast 100$(1) (Rojas-Torres et al., 2021). Measurements were performed in duplicate.

(1) $\mathit{Syneresis}\left(\mathrm{\%}\right)=\left(\frac{\mathit{supernatant}\left(\mathit{g}\right)}{\mathit{Sample}\left(\mathit{g}\right)}\right)\ast 100$(1)

2.5. Rheological measurements

2.5.1. Flow curves determination

For rheological characterization, flow curves, and dynamic tests were performed in duplicate for all samples using a rheometer (Anton Paar, Physica MCR 101). The sample was placed between two 50-mm diameter parallel plates (upper plate sandblasted), using a gap of 1 mm between plates. Two measurement cycles were run at 25°C; the first cycle was from 0.01 to 300 s⁻¹, and the second up-down was from 300 to 0.01 s⁻¹. The Ostwald-de Waele equation (Equation (2))(2) $\mathit{\eta }=\mathit{K}{\left(\gamma \right)}^{\mathit{n}-1}$(2) was used to calculate the flow curves.

(2) $\mathit{\eta }=\mathit{K}{\left(\gamma \right)}^{\mathit{n}-1}$(2)

Where $\mathit{\eta }$ is the viscosity (Pa·s), K is the consistency index (Pa·sⁿ), $\mathit{\gamma }$ is the shear velocity (s⁻¹), and n is the flow behavior index (dimensionless). All determinations were carried out in triplicate.

2.5.2. Oscillatory determination

The oscillatory tests were performed in duplicate to determine the viscoelastic properties of the samples. The linear viscoelastic region (LVR) was defined using oscillation strain sweeps at 25°C, selecting a 0.1% strain value to run the frequency sweeps, which were carried out from 0.3 to 10 Hz. For each run, the storage (G’) and loss (G”) moduli, and loss angle tangent (Tan δ) were calculated.

2.5.3. Creep-recovery test

In the creep-recovery test, a constant stress of 5 Pa was applied for 100 s, and the recovery was measured for 100 s, in duplicate. The Burger model (Equation (3)(3) $\mathit{J}=J_0+J_1\left(1-exp\left(\frac{-\mathit{t}}{{\mathit{\lambda }}_{\mathit{ret}}}\right)\right)+\frac{t}{{\mu }_0}$(3) ) was used to fit the data and calculate the limiting viscosity at zero shear rate (µ_o, Pa·s), instantaneous compliance (J_o, Pa⁻¹), retarded compliance (J₁, Pa⁻¹), and relaxation time (λ_ret, s) (Jiménez-Avalos et al., 2005; Steffe, 1996).

(3) $\mathit{J}=J_0+J_1\left(1-exp\left(\frac{-\mathit{t}}{{\mathit{\lambda }}_{\mathit{ret}}}\right)\right)+\frac{t}{{\mu }_0}$(3)

The compliance during the recovery test was described using the model reported by Dolz et al. (2008) (Equation (4)(4) $\mathit{J}=J_{\mathrm{\infty }}+J_{\mathrm{kv}}\ast e^{\left(-B\ast t^C\right)}$(4) ).

(4) $\mathit{J}=J_{\mathrm{\infty }}+J_{\mathrm{kv}}\ast e^{\left(-B\ast t^C\right)}$(4)

Where B and C are parameters defining the recovery speed of the system. For t → 0 (defined as the beginning of the compliance) J = (J_∞ + J_KV) meanwhile for t → ∞, J = J_∞. Equation (5)(5) $\mathit{R}\left(\mathrm{\%}\right)=\left[\frac{\left({\mathit{J}}_{\mathit{MAX}}-J_{\mathrm{\infty }}\right)}{J_{\mathit{MAX}}}\right]\times 100$(5) was used to calculate the recovery.

(5) $\mathit{R}\left(\mathrm{\%}\right)=\left[\frac{\left({\mathit{J}}_{\mathit{MAX}}-J_{\mathrm{\infty }}\right)}{J_{\mathit{MAX}}}\right]\times 100$(5)

Where J_MAX is the maximum J value at the end of the creep test (Dolz et al., 2008). The parameters in the equations were calculated by non-linear regression using the solver add-in in MS Excel.

2.6. Statistical analysis

Statistical analysis was carried out through analysis of variance (ANOVA) using the software Statistica v7.0 (Statsoft) and means comparison test by using LSD test (p <.05). Finally, a principal component analysis (PCA) was conducted to identify the relationship between the studied variables.

3. Results and discussion

3.1. Resistant starch content

The resistant starch content of purees with and without adding retrograded normal and high amylose starches during 14 days of cold storage is presented in Figure 1. It is important to mention that the Megazyme kit used in this study, lacks the capability to differentiate between specific RS1, RS2, RS3, RS4, or RS5 types as it quantifies only the total amount (McCleary et al., 2002). Therefore, the control puree may contain RS, as fruits inherently contain it. The results indicate that the inclusion of retrograded starch from two sources, namely high amylose (P+RHS) and normal (P+RNS), at a concentration of 10%, had a significant effect (p < .05) on the resistant starch content of the puree at 0, 7, and 14 days of cold storage. In this context, the puree (control) exhibited the least resistant starch content (RS) with values of 0.37 ± 0.08, 0.29 ± 0.09, and 0.20 ± 0.09 g/100 g for storage periods of 0, 7, and 14 days, respectively. The addition of P+RNS to the puree resulted in a notable increase in the resistant starch content, ranging from 2.12 to 2.53 g/100 g. On the other hand, the puree supplemented with P+RHS exhibited a significant rise in the RS content, reaching from 10.70 to 12.08 g/100 g. The observed variation in resistant starch content can be attributed to the physicochemical properties of the different starch sources utilized in this study. In this context, it has been reported that normal corn starch (27% amylose) has a resistant starch content of 2.05 g/100 g (Morales-Sánchez et al., 2021). Conversely, high amylose corn starch has been found to possess a significantly higher RS content ranging from 30 to 40 g/100 g (Ozturk et al., 2011; Soler et al., 2020). The incorporation of resistant starch results in favorable characteristics of thickeners. Specifically, it has been added to enhance the viscosity of the fluid and promote the stability of the thickener over an extended period. Additionally, it has been demonstrated that resistant starch can improve the taste and consistency of thickened food products (Giura et al., 2021). Furthermore, the presence of resistant starch in food products offers two significant benefits. Firstly, it helps to lower the glycemic index of the food, making it a healthier option for individuals with diabetes or those looking to manage their blood sugar levels. Secondly, it provides an opportunity to leverage the health benefits and positive impact on gut microbiota associated with resistant starch.

Figure 1. Resistant starch content for peach puree added with RNS and RHS at 10% during 14 days of storage at 4°C. Data is expressed as the mean ± SD of at least three independent experiments. Different capital letters indicate statistical differences (p <.05) between storage time in the same treatment. Meanwhile, the different lowercase letter means statistical differences (p <.05) among samples at the same storage time. RS: resistant starch.

On the other hand, a trend was observed to reduce the RS content in samples as the storage time increased, obtaining the lowest values at 14 days of cold storage. Such a reduction in RS content over time could have resulted from the interaction of the starch components (amorphous and crystalline regions) with water. In that sense, the amorphous regions interact better with water resulting in a swollen and slightly looser structure (Lu et al., 2019). As a result, the crystalline regions are affected, fragmenting the ordered regions of the starch and, thus, decreasing the content of resistant starch.

Despite the reduction, RS content in P+RNS and P+RHS was higher than that in the puree control. This result is particularly interesting from a nutritional viewpoint, as it has been suggested that consuming resistant starch-rich foods has several beneficial effects, including reducing constipation, aiding weight loss, playing a role in controlling blood pressure, and potentially helping to reduce the risk of colon cancer (Bojarczuk et al., 2022). Due to its low digestibility rates, RS reduces blood sugar levels and could play an important role in maintaining glycemia stability and significantly reducing postprandial glucose levels (Fan et al., 2023). Therefore, P+RHS formulation may be considered an important source of resistant starch.

3.2. Syneresis determination

Figure 2 shows the syneresis behavior for puree added with RNS and RHS at 10% and stored for 14 days at 4°C. As for the control, the syneresis behavior was relatively constant throughout storage, with an average of 68.8%. However, this syneresis value was very high, indicating a significant loss of the moisture retained in the puree and a possible alteration of its textural and sensory characteristics over time.

Figure 2. Syneresis behavior for peach puree added with RNS and RHS at 10% and stored for 14 days at 4°C. Different capital letters indicate statistical differences (p < .05) between storage time in the same treatment. Meanwhile, the different lowercase letter means statistical differences (p < .05) among samples at the same storage time.

On the other hand, purees added with retrograded starch tended to show lower syneresis values than the control. In P+RNS, at day 0 the syneresis was lower (0.37%) than that of the control, with the highest value being observed on day 7 (10.15%), although it decreased significantly on day 14 (1.79%). Meanwhile, P+RHS had a percentage of syneresis at day 0 of 34.13%, this value decreased to 23.20% at day 14. These results suggest that adding retrograded starches to the commercial puree significantly affects syneresis. However, the type of retrograded starch used, and storage time are also important factors. The syneresis observed in P+RNS on day seven can be attributed to the gelation structure of the retrograded starch, which traps and retains water, which tended to stabilize during storage. The behavior of P+RHS could be due to its high capacity for gel formation and retrogradation, which results in a decrease in syneresis as storage time increases. In particular, the retrogradation process is a dynamic process of continuous reorganization (Lu et al., 2019), which means that over time, new interactions and bonds will continue to be produced in the matrix, facilitating water retention. Therefore, this structural rearrangement could be related to the observed slight reduction in RS content (Figure 1).

Overall, the commercial puree had a high percentage of syneresis, which could increase the difficulty of swallowing and the possible aspiration of liquids in people with swallowing problems (i.e. dysphagia) (Dhillon et al., 2022). However, purees added with retrograded starch, especially P+RHS, had a lower percentage of syneresis than the commercial puree, which could improve swallowing ability and decrease the risk of complications in patients with this type of condition. Therefore, adding retrograded starch to purees, especially high amylose starch (P+RHS), may improve texture, consistency, and intestinal health in patients with dysphagia. However, further research is needed to confirm these applications and to establish specific recommendations for patients with dysphagia.

3.3. Rheological measurements

3.3.1. Flow curves

Figure 3 shows the behavior of flow parameters K and n for purees supplemented with retrograded starches. The control puree displayed the lowest values for both parameters, with a n value ranging between 0.142 and 0.172 for storage periods of 0 and 14 days, respectively. Meanwhile, K values decreased over time from 8.54 (7 days) to 6.8 Pa·sⁿ after 14 days of storage. These results suggest that the consistency of the puree system decreases as the storage time elapses, which is consistent with the poor stability and higher syneresis percentages observed in Figure 2.

Figure 3. Consistency index (K) and flow behavior index (n) for peach puree added with RNS and RHS at 10% and storage for 14 days at 4°C.

On the other hand, purees supplemented with retrograded starch exhibited significantly higher n and K values than the control, indicating more consistent flow behavior and increased viscosity. This phenomenon is likely due to the formation of a gelatinous starch structure in the puree, which helps maintain its viscosity and consistency. This behavior was consistent with the low levels of syneresis observed in Figure 2. The interaction between the starch macromolecules and the puree matrix contributes to the stable structure, resulting in a denser matrix and a higher viscosity. The behavior of n and K was affected by the amylose content. Specifically, P+RNS exhibited the highest consistency values (K), starting at 224 Pa·sⁿ on day 0 and decreasing to 103 Pa·sⁿ on day 14. As a result, the obtained matrix was highly viscous but unstable over time, causing the consistency of the system to decrease by up to 50% as storage time increased. On the other hand, P+RHS displayed relatively constant n and K values throughout the storage period. The consistency index values (K) were between 29 and 43 Pa·sⁿ, indicating a less viscous system than that obtained with P+RNS but with greater stability over time. This suggests that a higher amount of amylose in the starch may contribute to the formation of more stable structures, preserving the consistency of the puree over time. This characteristic is desirable, as it ensures that the textural quality of the puree is maintained in the P+RHS system for the entire evaluation period (14 days), which could have positive implications for the product’s shelf life.

Additionally, the viscosity achieved in the P+RHS system, the low levels of syneresis, and the high content of resistant starch make this food suitable for people with swallowing difficulties. The above behavior could be partly explained by the resistant starch, which has been associated with a positive effect on the rheological characteristics of thickeners. It can increase the viscosity of the fluid, improve the stability of the thickener over time, and reduce the prevalence of material that remains in the pharynx after swallowing. Additionally, resistant starch can improve the shear-thinning behavior of the thickener, making it easier to swallow (Giura et al., 2021).

Overall, the high content of resistant starch in P+RHS systems has a nutraceutical potential and can improve their rheological attributes, making them a suitable option for people with swallowing difficulties.

3.3.2. Oscillatory test

Figure 4 shows the dynamic moduli G’ and G” evaluated across a frequency range of 0.3 to 10 Hz in the peach puree systems. Meanwhile, Table 1 shows the values of G’, G”, loss factor (Tan δ), and ɳ* at a fixed frequency of 2 Hz. The moduli displayed a frequency dependence, which was more noticeable in the control puree. The viscoelastic moduli G’ and G” measure the resistance of the material to deformation in different directions. Specifically, G’ measures the resistance to deformation in the direction of stress. In contrast, G” measures the resistance relative to deformation. When a force is applied to a viscoelastic material, the modulus G’ reflects its ability to recover its original shape (elastic response). Meanwhile, the modulus G” reflects the ability to dissipate energy through deformation (viscous response) (Grillet et al., 2012; Xie et al., 2012).

Figure 4. Dynamic moduli as a function of frequency sweep (0.3–10 Hz) for peach puree without and with the addition of 10% of RNS and RHS after 7 and 14 days storage at 4°C (Gʹ -close symbols; Gʹʹ -open symbol).

Table 1. Rheological parameters of peach puree with and without the addition of 10% of RNS and RHS after storage for 14 days at 4°C obtained by dynamic viscoelastic measurement at a fixed frequency of 2 Hz.

Sample	Storage (Day)	G´	G´´	Tan δ	ɳ*
		(Pa)	(Pa)		(Pa·s)
Puree	0	117.0 ± 4.7^Aa	26.0 ± 3.9^Aa	0.218 ± 0.031^Ab	11.2 ± 0.6^Aa
	7	153.5 ± 11.5^Ba	32.6 ± 1.4^Aa	0.212 ± 0.006^Ac	13.7 ± 1.1^Ba
	14	190.0 ± 1.0^Ca	39.2 ± 10.1^Aa	0.206 ± 0.052^Aa	16.2 ± 0.4^Ca
P + RNS	0	2329.9 ± 172.1^Ab	298.1 ± 14.6^Ab	0.144 ± 0.004^Aa	187.7 ± 13.7^Ab
	7	4063.3 ± 499.0^Bc	619.7 ± 44.9^Bc	0.153 ± 0.008^ABa	328.0 ± 39.9^Bc
	14	5796.7 ± 144.3^Cc	941.3 ± 24.0^Cc	0.162 ± 0.002^Ca	468.3 ± 11.5^Cc
P + RHS	0	2706.2 ± 481.7^Ab	379.9 ± 63.1^Ab	0.170 ± 0.010^Aab	216.6 ± 38.1^Ab
	7	2994.1 ± 524.7^Ab	428.2 ± 73.1^Ab	0.180 ± 0.005^Ab	240.2 ± 41.2^Ab
	14	3282.2 ± 593.2^Ab	476.5 ± 77.0^Ab	0.190 ± 0.016^Aa	263.8 ± 47.6^Ab

Data represents the mean of three independent experiments. Different capital letters indicate statistical differences (p < .05) between storage time in the same treatment. Meanwhile, the different lowercase letter means statistical differences (p < .05) among samples at the same storage time.

Results showed a significant increase in G’ values in the peach puree added with retrograded starch compared to the control (Table 1), indicating a higher stiffness and structural stability. Moreover, the control puree and puree added with RNS were dependent on storage time, tending to increase the moduli values as storage time increased. These results suggest that the control puree and puree added with RNS have a more elastic behavior, becoming more stable with time than those added with RHS. Such behavior was evidenced in P+RHS, where no difference was found in storage time and overlapping G’ and G” moduli was observed (Figure 4). The findings suggest that retrograded starches may enhance the structural stability of purees, which could be advantageous for individuals with dysphagia. Although P+RNS showed low syneresis values and its physicochemical and rheological properties were also adequate, the attributes such as the consistency index (K) exhibited significant changes over the storage period. In contrast, P+RHS showed no significant changes after 14 days of storage making it desirable for a product intended for people with swallowing disorders. The firmer and more stable structure of purees fortified with retrograded starch may prevent syneresis, which can occur during mastication and swallowing negatively affecting the sensory perception.

Studies have shown that gum-based formulations have higher G’ values than starch-based formulations, indicating that they are more elastic (Giura et al., 2021). Additionally, an increase in G’ values has been associated with a decrease in the risk of aspiration in dysphagic patients (Sukkar et al., 2018). Resistant starch has been found to have a positive effect on the G’ and G” values of thickener agents. It can increase the G’ value, which is a measure of the elasticity of the thickener, and decrease the G” value, which is a measure of the viscosity of the thickener. Additionally, resistant starch can improve the shear-thinning behavior of the thickener, making it easier to swallow (Giura et al., 2021).

3.3.3. Creep-recovery test

Figure 5 shows the results of the creep-recovery test conducted on peach purees added with and without retrograded starch. The results indicate that the control puree exhibited the highest strain values, gradually decreasing during storage. The P+RNS samples also showed a decrease in strain values over time, although at a lower extent than the control puree. However, the ability of the material to deform declined sharply in the initial seven days of storage and remained low between days 7 and 14. This behavior suggests that the material was more unstable during the first seven days and gradually becomes more homogenized and stable over time.

Figure 5. Creep-recovery curves for peach puree without and added with 10% of RNS and RHS after 14 days storage at 4°C.

In contrast, the P+RHS samples exhibited an increased deformation capacity as storage time increased, suggesting that this material is stable and can undergo some degree of deformation. Despite this, the strain values were quite similar, indicating the material’s stability. Notably, the control puree had the highest strain values (7 to 22%), indicating that the material is more prone to deformation under constant stress. In contrast, the P+RNS samples exhibited low strain values (ranging from 0.1 to 0.4%), suggesting a more rigid matrix less prone to deformation. Finally, the P+RHS samples exhibited a strain value ranging from 0.5 to 2% indicating that the matrix retains its elastic properties and is not highly prone to deformation while maintaining a certain stiffness level.

Figure 6 shows the parameter obtained from adjusting the creep-recovery data to the Burger equation based on the mechanical model of Maxwell. The instantaneous compliance (J₀), in which the bonds between different structural units are elastically stretched, is shown in Figure 6(a). The compliance is related to the corresponding modulus J₀ = 1/G₀, where G₀ is the instantaneous elastic modulus (Rao, 2014). Because of the inertial effects, the initial elastic deformation of peach puree decreased as the retrograded starch was added. This behavior indicates that the retrograded starch affected the internal structure in the puree, especially when RNS was added. Samples with RHS were slightly more stable, and a less elastic behavior was observed (Dogan et al., 2013; Monticeli et al., 2019), indicating a more solid-like material (Rayment et al., 1998), as observed in creep-recovery plots. The control sample showed the highest J₀ value, and it was deformed easily at the same stress applied. A similar trend was observed by Dolz et al. (2008) for emulsions added with modified starch. Adding RNS resulted in a reinforced and less deformable structure, increasing the rigidity of the peach puree. Also, this behavior has been related to moisture content (Wang et al., 2021). The syneresis results show that puree samples containing retrograded starch were more stable to water absorption, especially when RNS was added.

Figure 6. Parameters obtained from fitting the creep-recovery data to the Burger equation. a) instantaneous compliance (J₀); b) retarded compliance (J₁); c) zero shear viscosity (µ₀); d) relaxation time (λ_rel); e) recovery (%).

On the other hand, J₁ indicates the region where the bonds break and reform, although they do not break and reform at the same rate (Rao, 2014). The delayed elastic strain shows the beginning of the viscoelastic stage (Monticeli et al., 2019). The addition of retrograded starch in both cases decreased the J₁ values (Figure 6(b)), indicating higher resistance to deformation. The lowest values of J₁ were observed in puree added with RNS during all the storage time. RHS decreased the values, not at the same level as RNS, and those increased slightly during the storage time, showing a substantial decrease compared to the control sample. The decrease in creep compliance parameters below the control values indicates that the material reached more solid-like properties. Also, the shear strain becomes constant with time at constant stress showing a Hookean response (Rayment et al., 1998).

The zero-shear viscosity (µ₀) can be used to extend the low shear rate region of the apparent viscosity, and this zone is used to characterize the structure in polysaccharide systems (Rao, 2014). When stress is removed, there is a retarded elastic recovery because the bonds between structural units are broken, and part of the structure is not recovered. In this study, adding RNS resulted in a firmer and harder gel structure of the puree, as suggested by the µ₀ values (Figure 6(c)). On the other hand, adding RHS allows obtaining a more stable matrix, and the change in the zero-shear viscosity was not highly noticeable; however, the values are higher than the control. The structural organization of retrograded starch when constant stress is applied implies more resistance to deformation, as reflected particularly by the high viscosity values observed in puree added with RHS. Similar results were reported by Rayment et al. (1998) for guar galactomannan gels; however, Witczak et al. (2020) reported the opposite behavior.

Relaxation time (λ_rel, Figure 6(d)) is unique to each material, and it is associated with retarded elasticity. The relaxation time would be zero in Hookean solids, and the maximum strain is obtained immediately when the stress is applied (Hernandez-Perez et al., 2021). Spongy materials are more elastic than bulky ones, and the stress release is faster in the former than in the latter. This trend was observed in the peach puree samples after adding retrograded starch. Spongy samples recover the initial shape, whereas the bulky materials show a permanent deformation. This behavior was observed in puree added with RNS, depending on the storage time, probably because a lower amount of water was lost from the matrix pores (Del Nobile et al., 2007). The recovery rate of the remaining structure was similar to P+RHS. The interactions occurring among all components in the puree resulted in a homogenized structure promoted by the full incorporation of retrograded starch in the system. No structural rupture is inferred as a high percentage of recovery was observed in the creep-recovery plots. Values of λ_ret of puree added with RNS or HRS changed compared to the control, the retrograded starch reinforces the puree network and increases slightly the relaxation time of the system as mentioned by Rayment et al. (1998). In this study, adding retrograded starch decreased the viscous properties as a function of the starch type. As mentioned before, changing the type of retrograded starch allows obtaining different properties of this product to meet different preferences of the consumers, being possible to modify the peach puree. Witczak et al. (2020) reported a different behavior when adding inulin to yogurt, probably because starch and inulin interact differently with the biopolymers in the yogurt.

Finally, the recovery percentage increased after adding retrograded starches to the puree systems (Figure 6(e)). In that sense, the control sample showed the lowest recovery rate at 49.30%, but it tended to increase to 53.46% over time during storage. Meanwhile, adding puree with NRS increased its recovery compared to the control system, ranging from 56.28 to 69.48. Higher recovery values were observed regarding P+RHS, starting at 63.18 (day 0) and increasing to 68–69 after 7–14 days of storage. The results suggest that the control puree exhibited a lower ability to regain its initial structure after a deformation cycle. In the case of peach purees mixed with retrograded starches, the NRS system showed instability, which was found to be dependent on the length of storage time. In contrast, the P+RHS exhibited high stability and no time dependence, maintaining its recovery capacity throughout the storage time. The deformation properties demonstrated that P+RNS produced a less deformable matrix, whereas P+RHS produced a less cohesive matrix even more stable than the control puree, which could facilitate the swallowing process.

As mentioned earlier, the presence of resistant starch in P+RHS systems could contribute to this phenomenon. Resistant starch has been associated with enhanced structural stability and a firmer texture (Giura et al., 2021).

3.4. Principal component analysis (PCA)

A principal component analysis was conducted to comprehend the relationship between the different variables. The analysis revealed that the first two components accounted for 89% of the variability in the data. The first principal component (PC1) explained 74.89% of the data variation and was mainly influenced by λ_ret, which had a positive effect, while J_o, J₁, and syneresis had a negative impact. The second principal component (PC2), on the other hand, explains 14.43% of the remaining variation and is positively affected by the content of resistant starch (RS) and recovery (%) but negatively influenced by K and µ₀.

On the other hand, Figure 7(b) shows that the data is distributed into three main groups: puree control (red circle), P+RNS (green circle), and P+RHS (blue circle). The control puree samples had the highest values of Tan δ, syneresis, and J_o, indicating a matrix that was not very stable with low water retention over time. The opposite behavior was observed in the green group (P+RNS). Systems with more consistent and highly viscous matrices predominated, making them highly susceptible to deformation. The system was unstable during the first seven days of storage. However, from day 7 to day 14, it stabilized, and there were no significant differences between the samples at the two-time points.

Figure 7. Principal component analysis (PCA): a) contribution of each variable on each of the components of the PC analysis, the bold letter indicates stronger influence (either negative or positive). b) scatter plot of the data for the first and second components, grouped by treatment: puree (red), P+RNS (green), and P+RHS (blue). c) loading plot for the first and second components.

The P+RHS samples (blue circle) exhibited qualities that fell between the red and green groups. This means their properties remained stable over time and showed no significant differences. Additionally, these systems have a great ability to recover after deformation. They also contained the highest resistant starch values, giving them a nutritional and functional advantage over the control peach puree and the one added with RNS.

4. Conclusions

Including retrograded starch in puree systems significantly enhances their physicochemical, rheological, and nutraceutical (resistant starch) properties. Different characteristics are obtained depending on the type of starch used. When retrograded normal starch (P+RNS) is added to peach puree, high viscosity purees with a higher consistency and lower syneresis are produced. This effect becomes more pronounced over time. As a result, this retrograded starch may be useful to enhance sensory properties, such as creaminess and texture, in food products. However, it may compromise the stability of the food over time.

On the other hand, the puree systems added with retrograded high amylose starch (P+RHS) exhibited intermediate viscosity and consistency characteristics. However, they were distinguished by their superior recovery capacity after deformation (69%) and their high content of resistant starch (10%), which remained constant even after 14 days of storage. RHS possesses certain characteristics that make it an effective additive for improving the food matrix, enhancing stability, and improving sensory characteristics. Furthermore, the significant amount of resistant starch in the system facilitates its interaction with water, thereby decreasing syneresis and minimizing the likelihood of aspiration in individuals with swallowing problems. Considering the beneficial effects of resistant starch, RHS can be considered a promising functional ingredient for developing nutritious food products. However, more detailed, and specific studies are needed to evaluate these characteristics.

Acknowledgments

The authors are grateful for support from SIP-IPN, COFAA-IPN, and EDI-IPN. Dominguez-Ayala acknowledges the scholarship from the Consejo Nacional de Humanidades Ciencias y Tecnologías (CONAHCYT).

Disclosure statement

No potential conflict of interest was reported by the author(s).