Enhancing the Quality of Jerusalem Artichoke Chips: The Role of Pretreatment Optimization in Combined Vacuum Freezing and Hot Air Drying

doi:10.21203/rs.3.rs-5036118/v1

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Enhancing the Quality of Jerusalem Artichoke Chips: The Role of Pretreatment Optimization in Combined Vacuum Freezing and Hot Air Drying

https://doi.org/10.21203/rs.3.rs-5036118/v1

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The Jerusalem artichoke emerges as a novel non-food energy crop, with its tuber being a rich source of inulin—the most soluble dietary fiber. This study aims to investigate the impact of pretreatment on the quality of Jerusalem artichoke chips dried using a combined method of vacuum freezing and hot air drying. The evaluation criteria encompass color, hardness, rehydration ratio, and microstructure of the Jerusalem artichoke chips. Blanching duration, NaCl concentration, and maltodextrin concentration in the pretreatment phase are key research parameters. Through a single-factor analysis experiment, optimal levels for each parameter were determined, with 60s for blanching, 0.8% for NaCl concentration, and 10% for maltodextrin concentration. Meanwhile, response surface methodology (RSM) optimization identified the optimal conditions as 67s blanching time, 0.97% NaCl concentration, and 8.35% maltodextrin concentration. Under these conditions, the Jerusalem artichoke chips exhibited an L^* value of 79.82 and a rehydration ratio of 3.92. The finished product manifested a loose, porous texture, a well-defined structure, and a crisp palate. The findings from this investigation provide substantive theoretical support for diversified processing approaches for Jerusalem artichoke.

Jerusalem artichoke

Pretreatment

Vacuum freezing

Hot air drying

Response surface methodology (RSM)

The Jerusalem artichoke (Helianthus tuberosus L.), originally native to North America and later introduced to China through Europe, has emerged as a promising non-food energy crop, renowned for its remarkable adaptability and resilience to diverse environmental conditions (Lv et al., 2019; Andrea et al., 2019). A defining feature of the Jerusalem artichoke tuber is its high inulin content, which constitutes approximately 80% of its total carbohydrates (Gupta & Chaturvedi, 2020). Inulin, a fructan polysaccharide, is highly water-soluble and is widely recognized as an optimal sugar substitute, offering numerous health benefits, including regulation of gut microbiota, enhancement of immune responses, and potential anticancer properties (Wang et al., 2016; Li et al., 2015; Yu et al., 2018; Fu et al., 2018). The multifunctional properties of inulin underscore the value of Jerusalem artichoke in the development of functional foods and dietary supplements (Mendez-Yanez et al., 2022; Qin et al., 2023; Sawicka et al., 2020).

Despite the recognized benefits of Jerusalem artichoke, research has predominantly focused on its fresh and pickled forms, with limited exploration of its dried derivatives (Zhang et al., 2021). Drying techniques are critical for extending the shelf life of agricultural products and enhancing their market value by transforming them into convenient, consumer-friendly forms (Siddiqui et al., 2024). In recent years, the global market has seen a surge in the popularity of fruit and vegetable chips, driven by consumer demand for healthier snack options (Zhang et al., 2023). Within this context, Jerusalem artichoke chips present a significant market opportunity, yet the scientific investigation into optimal drying methods and quality parameters remains insufficient.

Hot air drying (HD) is the most commonly employed method for drying fruits and vegetables due to its simplicity, cost-effectiveness, and operational ease. This technique involves circulating hot air within an oven or drying chamber to rapidly reduce moisture content (Chen et al., 2018; Deng et al., 2019). However, HD has limitations, including prolonged drying times, which can result in the loss of heat-sensitive nutrients and potential degradation of sensory qualities. In contrast, freeze drying (FD) operates by first freezing the material and then subjecting it to sublimation under vacuum conditions, thereby transitioning moisture directly from solid to gas. FD preserves the natural structure and nutritional integrity of the product, resulting in superior rehydration properties and minimal volume changes, though it is associated with higher operational costs and significant capital investment (Bao, 2023; An et al., 2022). The high costs and energy demands of FD limit its widespread application in commercial operations despite its advantages.

In light of these considerations, there is a growing interest in hybrid drying methods that combine the benefits of different techniques to achieve a balance between quality and efficiency. Combining vacuum freeze drying with hot air drying has the potential to reduce drying time while maintaining or enhancing product quality (Salehi, 2023). This approach not only optimizes the drying process but also presents opportunities for improving the texture, flavor, and overall acceptability of dried products. However, the application of this combined method to Jerusalem artichoke chips has not been fully explored, presenting a novel area for research.

The pretreatment phase plays a crucial role in the drying process, significantly influencing the final product's quality. Pretreatment methods such as blanching, color preservation, and immersion in various solutions are commonly employed to enhance the processing quality of fruits and vegetables (Szadzińska et al., 2018). Blanching is particularly effective, serving multiple functions by inactivating enzymes that could cause undesirable changes during processing, enhancing natural color, modifying microstructural properties, and influencing the expansion properties of the product during drying (Varnalis et al., 2001; Bi et al., 2010). Sodium chloride (NaCl) immersion is another critical pretreatment, primarily used to improve the flavor and safety of dried products by inhibiting microbial growth and enzymatic activity, thus enhancing shelf life and overall quality (Xu et al., 2024).

Furthermore, maltodextrin immersion has been shown to preserve the natural taste of food and improve the rehydration properties of dried products. Maltodextrin, a polysaccharide, functions as a bulking agent and stabilizer, making it an essential component in the formulation of various food products (Ren et al., 2018; Diamante et al., 2012). The combined application of these pretreatment methods can yield synergistic effects, significantly improving the texture, color, and structural integrity of the final product (Su et al., 2018). Research on carrot slices demonstrated that a combined pretreatment involving specific pressures, temperatures, and CaCl₂ concentrations significantly enhanced the product's texture and microstructure (Rastogi et al., 2008). These findings indicate that the integration of multiple pretreatment techniques can produce superior results compared to individual methods, providing a comprehensive approach to improving product quality.

This research investigates the cumulative effects of three primary pretreatment techniques—blanching, NaCl immersion, and maltodextrin immersion—on the quality of Jerusalem artichoke chips. The study aims to optimize the pretreatment process for Jerusalem artichoke slices intended for drying using a combined vacuum freeze drying and hot air drying method. Key quality parameters such as color, hardness, rehydration ratio, and microstructure will be evaluated. The objective is to establish a robust theoretical foundation that will inform future production methodologies and support the broader application of advanced drying techniques in Jerusalem artichoke processing. The outcomes of this research are expected to contribute to the development of high-quality, value-added Jerusalem artichoke products that align with the growing consumer demand for healthy and convenient snacks.

2.1. Materials

The tubers of the "Lanyu 1" variety of Jerusalem artichoke were harvested in late October 2021 and stored at 2℃ in a refrigerator. These tubers were selected for their uniform size, notable hardness, and undamaged surfaces, ensuring consistency in the experiments. The sodium chloride (NaCl) used for pretreatment was sourced from a local market in Lanzhou, Gansu province, China, while maltodextrin was obtained from Shandongwang Sugar Industry Co., LTD, Zou Ping Dextrin Branch.

2.2 Combination pretreatment of Jerusalem artichoke

To achieve products of high quality, the impacts of various pretreatments (blanching time, NaCl concentration, and maltodextrin concentration) on dried Jerusalem artichoke chips were investigated. The drying and pretreatment methods were adapted from the experimental procedures described by Tarafdar et al. (2017). Jerusalem artichoke chips underwent pretreatment influenced by three primary factors: (1) The chips were blanched for 0, 30, 60, 90, 120, 150, and 180 s, with NaCl concentration maintained at 0.8% and maltodextrin concentration at 10%. (2) In the NaCl concentration test, concentrations of 0, 0.4, 0.8, 1.2, and 1.6% were employed, with a blanching time of 60 s and a maltodextrin concentration of 10%. (3) For the maltodextrin concentration test, concentrations of 0, 5, 10, 15, and 20% were used, with a blanching time of 60 s and NaCl concentration of 0.8%.

Following pretreatment, the Jerusalem artichoke chips were drained of surface water and stored at -18℃ in a refrigerator to prepare them for vacuum freeze drying. Once preconditioning was complete, the samples were immediately subjected to vacuum freeze drying until their moisture content reached approximately 40 ± 5%. The samples were then transferred to a drum wind drying oven for final hot air drying.

2.3 Experimental optimization of combined pretreatment

To optimize the combined pretreatment process, experiments were conducted using various parameters: blanching times of 30, 60, and 90 s; NaCl concentrations of 0.4, 0.8, and 1.2%; and maltodextrin concentrations of 4, 8, and 12%. The Jerusalem artichoke slices were cleaned, weighed, and immersed in the respective treatment solutions. During the immersion, the slices were continuously stirred with a glass rod to ensure uniform exposure to the solution. The subsequent drying process followed the procedure described in Section 2.2.

2.4 Determination of color

The color of the Jerusalem artichokes chips was gauged using a colorimeter (model CR-10 Plus, Konica Minolta Holding, Inc., Japan). The L^* (luminosity) value of the samples, maintained at room temperature, was evaluated. This test was replicated for five distinct samples for each type of pretreatment.

2.5 Determination of rehydration ratio

Dried Jerusalem artichoke chips were weighed and immersed in distilled water at 25℃ for 30 min. After rehydration, the samples were drained of excess water and weighed again. Five replicates were conducted for each pretreatment type. The rehydration ratio (RR) was calculated using the equation:

$$\:\text{RR}={m}_{2}/{m}_{1}$$

Where 𝑚₁ is the weight of the dried sample, and 𝑚₂ is the weight after rehydration..

2.6 Determination of the hardness

From each set of dried samples, Jerusalem artichoke chips of roughly equivalent size and shape were selected. A texture analyzer (TexturePro CT3, Brookfield, America) gauged the hardness index of these chips. The testing parameters, employing the TA43 probe, were: a trigger load of 7g, a testing speed of 0.5mm·s^− 1, and a compression distance of 2 mm. The maximum force recorded (in grams) was used as the hardness index. Higher values indicated harder products. Each pretreatment was tested with five replicates.

2.7 Microstructure of Jerusalem artichoke chips

The microstructure of the Jerusalem artichoke chips was analyzed using scanning electron microscopy (SEM, TM3030, Hitachi Co., Japan). Chips were cut into 5×5×5 mm pieces using a sharp razor blade and mounted on an aluminum stub with conductive adhesive tape. The samples were then sputter-coated with gold and examined at 200× magnification under an accelerating voltage of 5 kV.

2.8 Experimental design and data analysis

Based on literature reports and preliminary experiments, three parameters were identified as the most significant independent factors: blanching time (X₁), NaCl concentration (X₂), and maltodextrin concentration (X₃). The Response Surface Methodology (RSM) was employed to ascertain the number of runs and the levels for the experiments. The Box-Behnken Design (BBD) was utilized, encompassing three variables at three levels, resulting in 15 experimental runs, including three central points to estimate experimental error and assess lack of fit (Sumic et al., 2016).

The data were fitted to a second-order polynomial model as described by Eq. (1). Three models were developed to relate the responses (Y)—color L^*, rehydration ratio, and hardness—to the three process variables (X):

$$\:\text{Y}={a}_{0}+{\sum\:}_{i=1}^{3}{a}_{i}{X}_{i}+{\sum\:}_{i=1}^{3}{a}_{ii}{X}_{i}^{2}+{\sum\:}_{i}^{2}·{\sum\:}_{j=i+1}^{3}{a}_{ij}{X}_{i}{X}_{j}$$

Where $\:{a}_{0}$ is a constant term, while $\:{a}_{i}$, $\:{a}_{ii}$, and $\:{a}_{ij}$ are regression coefficients, and

𝑋 represents the coded independent factors.

Multiple linear regression analysis was used to derive the mathematical models for each response, incorporating linear, quadratic, and interaction terms of the independent variables. The significance of each factor was determined using Analysis of Variance (ANOVA). Model adequacy was evaluated based on the coefficient of determination (R²) and the Root Mean Square Error (RMSE), with optimal models characterized by high R² values and low RMSE.

3.1 Single-Factor Experiments for Jerusalem artichoke chips

3.1.1 Effect of blanching time on the quality of Jerusalem artichoke chips

Blanching is a critical step in food processing that significantly impacts the sensory and textural qualities of the final product. The color of food, particularly the L^* value, plays a pivotal role in consumer acceptance, as it directly influences the visual appeal of the product. The L^* value, representing lightness, was selected as the primary color metric in this study due to its critical role in determining the visual quality of Jerusalem artichoke chips, a product where lightness is a key quality attribute. This focus on L^* value is justified given the importance of visual lightness in consumer perception, as noted by Nahar et al. (2022). While the standard practice in color analysis involves measuring L^*, a^*, and b^* values to capture the full spectrum of color changes, the emphasis on L^* in this context is to prioritize the preservation of lightness during processing. The blanching process, therefore, aims to deactivate enzymes efficiently while maintaining the product's lightness and structural integrity. However, achieving the optimal balance in blanching time is crucial—excessive heat can degrade quality by causing thermal damage, while insufficient heat may fail to inactivate enzymes, leading to undesirable browning reactions, as emphasized by Arnold and Gramza-Michalowska (2022).

The results in Table 1 illustrate the effect of varying blanching times on the L^* value, rehydration ratio, and hardness of Jerusalem artichoke chips. As blanching time increased, the L^* value of the chips first rose, reaching a peak at 90 s, before descending. This pattern suggests that 90 s of blanching optimizes enzyme inactivation while minimizing thermal degradation. However, further extension of blanching time beyond 90 s led to a decrease in L^* value, possibly due to the onset of Maillard reactions or other thermal degradation processes that darken the product. This trend is consistent with observations from Taghinezhad et al. (2023), who reported similar effects of blanching time on the coloration of potato chips. The rehydration ratio, which indicates the ability of the dried chips to regain moisture, remained relatively stable across most blanching durations, with a peak at 120 s. This suggests that up to this point, the cell structure of the chips was well-maintained, allowing for efficient water uptake during rehydration. However, a significant decline in rehydration ratio was observed at 180 s, indicating that excessive blanching may lead to overprocessing, resulting in the breakdown of cell walls and impaired water absorption. Texture, as measured by hardness, showed a positive correlation with blanching time, with hardness increasing as blanching time was prolonged. This increase in hardness is likely due to moisture loss and the possible caramelization of surface sugars, which would contribute to a firmer, less pliable texture. Considering that texture is a crucial factor in consumer palatability, this trend is important for manufacturers to consider when optimizing processing conditions. In light of these findings, a blanching time of 60 s was deemed optimal for Jerusalem artichoke chips, as it provided a favorable balance between maintaining lightness, achieving adequate rehydration capacity, and ensuring acceptable hardness, all while considering production efficiency and cost-effectiveness.

Table 1

Effect of blanching time on quality of Jerusalem artichoke chips
Blanching Time (s)	L^* Value	Rehydration Ratio	Hardness (g)
0	68.24 ± 0.60c	2.96 ± 0.12ab	1516.4 ± 52.2b
30	56.36 ± 0.65d	2.78 ± 0.08ab	1544.6 ± 69.2b
60	75.34 ± 0.30ab	3.10 ± 0.05ab	1550.8 ± 32.2b
90	77.94 ± 0.45a	3.18 ± 0.02ab	1565.2 ± 41.6b
120	73.26 ± 0.56b	3.29 ± 0.18a	1577.4 ± 50.1b
150	72.64 ± 0.47b	3.00 ± 0.05ab	1890.6 ± 77.8ab
180	68.90 ± 0.33c	2.74 ± 0.04b	2290.8 ± 136.3a

3.1.2 Effect of NaCl concentration on the quality of Jerusalem artichoke chips

Sodium chloride (NaCl) is more than just a flavor enhancer in food processing; it plays a critical role in the physicochemical properties of food, particularly in the inhibition of enzymatic browning reactions. NaCl achieves this by sequestering oxygen, which is essential for the activity of polyphenol oxidase, the enzyme responsible for browning (Adiletta et al., 2016). This study examines how varying concentrations of NaCl affect the quality attributes of Jerusalem artichoke chips, focusing on their lightness (L^* value), rehydration ratio, and texture (hardness). The data in Table 2 indicates a clear trend where the L^* value, which reflects the brightness and visual appeal of the chips, increases with higher NaCl concentrations. At concentrations of 0.8%, 1.2%, and 1.6%, the L^* values reached significantly higher levels compared to the control (0% NaCl), demonstrating the efficacy of NaCl in enhancing the lightness of the chips. However, the differences among these three concentrations were not statistically significant, suggesting that beyond a certain threshold, the effect of NaCl on lightness plateaus. This observation is consistent with the findings of Roy et al. (2022), who noted that NaCl concentration could optimize the L^* value of various food products up to an optimal point, beyond which no further improvement is observed. Interestingly, the rehydration ratio and hardness of the Jerusalem artichoke chips remained largely unaffected by the different NaCl concentrations. The stability of these parameters across the NaCl gradient indicates that while NaCl influences color, it does not significantly alter the chip’s structural properties or its ability to reabsorb water after drying. This is crucial for maintaining the desired texture and mouthfeel of the final product.

Table 2

Effect of NaCl concentration on quality of Jerusalem artichoke chips
NaCl Concentration (%)	L^* Value	Rehydration Ratio	Hardness (g)
0	66.24 ± 0.98c	2.66 ± 0.03a	1548.8 ± 55.4a
0.4	73.78 ± 0.55b	2.84 ± 0.11a	1376.8 ± 47.5a
0.8	76.24 ± 0.28ab	2.80 ± 0.0.3a	1494.0 ± 63.4a
1.2	77.54 ± 0.17a	2.97 ± 0.11a	1480.8 ± 45.2a
1.6	77.72 ± 0.24a	2.77 ± 0.14a	1685.6 ± 80.6a

However, from a sensory perspective, the impact of NaCl on taste cannot be overlooked. Excessive NaCl can dominate the flavor profile, potentially rendering the product unpalatable to some consumers. Thus, while higher NaCl concentrations enhance visual appeal, they may negatively affect taste. Balancing these factors, a NaCl concentration of 0.8% was identified as optimal, providing a significant improvement in chip lightness without compromising other quality attributes or overwhelming the flavor. This concentration allows for an enhanced visual quality while maintaining the organoleptic balance that is critical for consumer acceptance of Jerusalem artichoke chips.

3.1.3 Effect of concentration of maltodextrin on quality of Jerusalem artichoke chips

Blanching at high temperatures is a widely used method to prevent enzymatic browning in food products. However, this process often compromises the structural integrity of cells, leading to undesirable textural changes. High temperatures can induce the contraction of cell walls, rupture cell membranes, and result in a softened texture, which diminishes the quality of fruits and vegetables. To mitigate these effects, maltodextrin, a hydrocolloid known for its structural enhancement properties, is employed. By penetrating vegetable tissues, maltodextrin reinforces structural rigidity during the drying process, as noted by Rojas et al. (2001). This structural reinforcement is crucial for maintaining the desired texture of dried products, especially when exposed to high temperatures during processing. The data presented in Table 3 demonstrates that increasing the concentration of maltodextrin led to an increase in the L^* value, indicating enhanced brightness of the Jerusalem artichoke chips. The L^* value peaked at a concentration of 15%, after which it exhibited a slight decline. Despite this, the differences among the higher concentrations (10%, 15%, and 20%) were not statistically significant, suggesting that maltodextrin effectively prevents browning within this range by providing a protective barrier against oxidation. This barrier helps maintain the lightness of the chips, a key attribute for consumer appeal. The ability of maltodextrin to preserve the brightness of the chips at higher concentrations underscores its role as an effective anti-browning agent.

Table 3

Effect of maltodextrin concentration on quality of Jerusalem artichoke chips
Maltodextrin Concentration (%)	L^* Value	Rehydration Ratio	Hardness (g)
0	72.24 ± 0.34b	2.52 ± 0.30a	1449.6 ± 73.34a
5	72.90 ± 0.49b	2.87 ± 0.09a	1454.4 ± 59.85a
10	76.32 ± 0.31a	2.77 ± 0.12a	1547.6 ± 28.03a
15	77.84 ± 0.22a	2.64 ± 0.14a	1774.2 ± 56.61a
20	76.48 ± 0.56a	2.29 ± 0.05a	1837.4 ± 100.64a

The rehydration ratio, a critical measure of a dried product's ability to regain moisture, showed an initial increase as maltodextrin concentration rose, peaking at 5% and 10%. This trend aligns with the findings of Marina et al. (2017), who reported superior hydration quality in yam tablets treated with a 10% maltodextrin solution. Beyond 10%, the rehydration ratio began to decline, indicating that higher concentrations might impair the product's ability to reabsorb water effectively. This decline suggests that while maltodextrin enhances structural rigidity, excessive amounts may create barriers to water absorption, which is a vital consideration for the functional quality of the dried product.

Interestingly, the hardness of the Jerusalem artichoke chips, a crucial measure of texture and consumer satisfaction, did not significantly vary with increasing maltodextrin concentration. This stability in hardness indicates that while maltodextrin can improve certain qualitative attributes such as color and rehydration capacity, it does not adversely affect the textural firmness of the chips. Maintaining the desired texture is essential for ensuring the chips meet consumer expectations. Thus, a maltodextrin concentration of 10% was identified as optimal for pretreating Jerusalem artichoke chips, balancing enhanced lightness and rehydration capacity with the preservation of texture. This balance is key to producing a high-quality final product that meets both sensory and functional criteria, ensuring consumer acceptance and satisfaction.

3.2 Effects of factors on chips quality

Multiple regression analyses were conducted to evaluate the effects of the independent variables (blanching time, NaCl concentration, and maltodextrin concentration) on the dependent variables (L^* value, rehydration ratio, and hardness) of Jerusalem artichoke chips, as detailed in Table 4. The regression coefficients for the three models and the ANOVA results are summarized in Table 5. The regression equations, expressed in terms of coded factors for the L^* value and rehydration ratio models, are given by Eqs. (2) and (3), respectively:

Table 4

Experimental design and results of response surface methodology
Number	Factors and Levels			Response
Number	X₁	X₂	X₃	R₁	R₂	R₃
1	30	0.4	8	59.7	3.47	1679
2	90	0.4	8	70.0	3.78	1030
3	30	1.2	8	66.2	2.87	1677
4	90	1.2	8	76.2	2.92	1089
5	30	0.8	4	64.1	2.99	1340
6	90	0.8	4	72.5	3.29	1136
7	30	0.8	12	62.2	3.15	1769
8	90	0.8	12	76.8	3.38	1398
9	60	0.4	4	70.2	3.54	1231
10	60	1.2	4	72.4	3.07	1334
11	60	0.4	12	71.9	3.58	1468
12	60	1.2	12	73.4	3.38	1520
13	60	0.8	8	79.4	3.80	1126
14	60	0.8	8	77.9	4.03	1356
15	60	0.8	8	78.8	4.05	1229

Table 5

Significance analysis of regression coefficients
Regression Coefficients	P value
Regression Coefficients	R₁	R₂	R₃
Model	0.0014**	0.0139*	0.0748
X₁	0.0002***	0.0995	0.0052**
X₂	0.0138*	0.0048**	0.6034
X₃	0.3003	0.2317	0.0333*
X₁₂	0.9272	0.4423	0.8305
X₁₃	0.1038	0.8312	0.5641
X₂₃.	0.8315	0.4260	0.8579
X₁₁	0.0004***	0.0027**	0.3232
X₂₂	0.0054**	0.0256*	0.4729
X₃₃	0.0155*	0.0120*	0.2283
Lack of fit	0.1370	0.4365	0.4019
R²	0.9768	0.9404	0.8747
CV/%	9.96	4.56	2.19
Level of significance * p < 0.05, p < 0.01, * p < 0.001

$$\:{R}_{1}=78.70+5.41{X}_{1}+2.05{X}_{2}-6.88{X}_{11}-3.80{X}_{22}-2.93{X}_{33}$$

$$\:{R}_{2}=3.96+0.27{X}_{2}-0.44{X}_{11}-0.25{X}_{22}-0.31{X}_{33}$$

The L^* value of Jerusalem artichoke chips was significantly influenced by all linear terms, except for the maltodextrin concentration (X₃), which did not show a significant effect (p > 0.05). This suggests that within the range of maltodextrin concentrations tested, its impact on the L^* value was minimal, possibly indicating that maltodextrin does not play a major role in preventing browning or enhancing lightness under the conditions studied. The quadratic effects of all terms, however, significantly influenced the L* value (p < 0.05), indicating that non-linear interactions between the variables are important in determining the final color of the chips.

For the rehydration ratio (R2), NaCl concentration (X2) was the only factor that had a significant linear effect (p < 0.05), while neither blanching time (X1) nor maltodextrin concentration (X3) showed significant linear impacts. This outcome implies that the ability of Jerusalem artichoke chips to rehydrate is primarily dependent on the NaCl concentration used during pretreatment. The quadratic effects of all factors were significant (p < 0.05), further underscoring the importance of considering non-linear relationships when optimizing the rehydration capacity of the chips.

The regression model for hardness (R₃) yielded a coefficient of determination (R²) of 0.8747, and the model was not statistically significant (p > 0.05), indicating a moderate fit to the experimental data and suggesting that it may not fully capture the factors influencing hardness. This incomplete capture of variability could be due to factors such as inconsistent moisture content after drying, as suggested by Salazar et al. (2018). The ANOVA results showed that blanching time (X₁) and maltodextrin concentration (X₃) significantly affected hardness, while NaCl concentration did not have a significant influence (p > 0.05).

The regression analysis reveals that while blanching time and NaCl concentration play critical roles in influencing the color and rehydration capacity of Jerusalem artichoke chips, maltodextrin concentration primarily affects texture without significantly altering the other quality attributes. The quadratic effects highlight the complex interactions between these variables, suggesting that careful optimization is required to achieve the desired balance of color, texture, and rehydration capacity in the final product. These findings emphasize the need for precise control of pretreatment conditions to optimize the quality of Jerusalem artichoke chips.

Building on the regression analysis, a detailed examination of the individual and interactive effects of blanching time, NaCl concentration, and maltodextrin concentration on the L^* value and rehydration ratio was conducted. Blanching time emerged as the most significant factor influencing the L^* value, with its linear effect being the primary determinant, followed closely by its quadratic effect. The linear and quadratic effects of NaCl concentration were also important, ranked third and fourth, respectively. The quadratic effect of maltodextrin concentration concluded this hierarchy of influence on the L^* value. For the rehydration ratio, the most influential factor was the quadratic effect of blanching time, followed by the linear effect of NaCl concentration and the quadratic effect of maltodextrin concentration. The quadratic effect of NaCl concentration was also recognized as a significant determinant. These findings suggest that heat treatment increases cell membrane permeability, which may compromise cell integrity, reduce resistance to water loss, and accelerate the drying rate. Consequently, when these dried products undergo rehydration, the increased permeability facilitates water absorption, thereby improving the rehydration ratio (Belwal et al., 2017).

3.3 Optima model fitness and model validation

The response surface methodology (RSM) provided a rigorous framework for examining the effects of blanching time, NaCl concentration, and maltodextrin concentration on the quality attributes of Jerusalem artichoke chips, specifically focusing on L* value and rehydration ratio. The 3D response surface plots, as shown in Fig. 1, were instrumental in visualizing the complex interactions between these independent variables and how they collectively influence the dependent variables.

3.3.1 Influence on L* value

The L^* value, representing the lightness of Jerusalem artichoke chips, is critically influenced by the complex interactions between blanching time, NaCl concentration, and maltodextrin concentration. The 3D response surface plots presented in Fig. 1A, 1B, and 1C provide a comprehensive visualization of these interactions. Figure 1A highlights the significant impact of the interplay between blanching time and NaCl concentration. As illustrated, longer blanching times coupled with moderate levels of NaCl concentration lead to an increase in the L^* value, suggesting a lighter and more visually appealing chip. This outcome likely results from the combined effects of blanching in breaking down cell structures, allowing NaCl to enhance color retention by stabilizing pigments and preventing enzymatic browning during subsequent drying processes. The results emphasize the necessity for precise control of these parameters to optimize the visual quality of the chips. In Fig. 1B, the interaction between blanching time and maltodextrin concentration is explored. The plot reveals that higher maltodextrin concentrations, when combined with extended blanching times, result in significantly higher L^* values. This suggests that maltodextrin not only serves as a protective agent against browning but may also enhance the Maillard reaction, contributing to a desirable lightness in the chips. The role of maltodextrin as a moisture-retaining agent could also play a part in maintaining the surface integrity of the chips, further influencing the color. Figure 1C examines the interaction between NaCl and maltodextrin concentrations, uncovering a synergistic effect where moderate levels of both variables contribute to the highest L^* values. This synergy likely arises from the dual action of NaCl in stabilizing pigments and maltodextrin in modulating the browning reactions, leading to an optimal color profile. The collective insights from these plots underscore the importance of carefully balancing these variables to achieve a product with optimal lightness and visual appeal, reinforcing the need for a well-calibrated approach to pretreatment in the production process.

3.3.2 Influence on rehydration ratio

The rehydration ratio, a critical quality parameter for dried food products, is significantly influenced by the interactions between blanching time, NaCl concentration, and maltodextrin concentration, as depicted in Fig. 1D, 1E, and 1F. Figure 1D illustrates the interaction between blanching time and NaCl concentration, revealing that moderate levels of both factors are essential for optimizing rehydration capacity. This relationship suggests that blanching, which impacts cell membrane permeability, combined with the osmotic effects of NaCl, plays a vital role in maintaining the structural integrity of the chips during drying, thereby enhancing their ability to reabsorb water upon rehydration. The balance between sufficient heat treatment to soften cell structures and an adequate salt concentration to prevent excessive degradation appears to be key in achieving desirable rehydration properties. In Fig. 1E, the interaction between blanching time and maltodextrin concentration is explored. Although both factors influence rehydration, their combined effect is less significant than their impact on L^* value. This indicates that while maltodextrin may contribute to the hygroscopic properties of the chips, its role in rehydration is more subtle. The presence of maltodextrin likely affects the moisture absorption characteristics by modifying the surface and internal matrix of the chips, which could either enhance or moderate the rehydration process depending on its concentration and the duration of heat treatment. Figure 1F further delves into the interaction between NaCl and maltodextrin concentrations, uncovering a complex relationship. The plot reveals that higher NaCl levels generally promote rehydration by facilitating water retention and penetration. However, the addition of maltodextrin appears to moderate this effect, possibly due to its ability to form a protective barrier around the chip matrix, which helps retain moisture without compromising structural integrity during rehydration. This balancing act suggests that maltodextrin acts as a stabilizer, ensuring that the chips can absorb water efficiently while maintaining their texture and form. The combined insights from these response surfaces underscore the importance of carefully optimizing the levels of blanching time, NaCl, and maltodextrin to achieve a product with superior rehydration characteristics, highlighting the intricate balance required between these variables to produce high-quality Jerusalem artichoke chips.

3.3.3 Optimization and validation

The desirability function approach, detailed in the methodology section, was used to identify the optimal processing conditions for the drying pretreatment of Jerusalem artichoke chips. The optimal conditions—blanching time of 67 s, NaCl concentration of 0.97%, and maltodextrin concentration of 8.35%—were determined to balance the desired L^* value, rehydration ratio, and hardness. The response surface methodology predicted an L^* value of 79.048, a rehydration ratio of 3.972, and a hardness of 1228.035g under these conditions.

Validation experiments conducted under these optimized parameters yielded an L* value of 79.82, a rehydration ratio of 3.92, and a hardness of 1241g, closely matching the predicted values. This close alignment between predicted and observed results confirms the robustness of the model and underscores the efficacy of RSM in optimizing the quality attributes of Jerusalem artichoke chips.

3.4 Effects of pretreatment on the microstructure of Jerusalem artichoke chips

The microstructural analysis of Jerusalem artichoke chips, as shown in Fig. 2, reveals the significant impact of different pretreatment and drying methods on the structural characteristics of the final product.

Figu. 2A presents the microstructure of Jerusalem artichoke chips processed through freeze-drying (FAD). The chips exhibit a highly porous structure with noticeable surface cracks. The formation of these pores is a direct consequence of the vacuum freeze-drying process, where ice within the plant cells sublimates directly from solid to gas, leaving voids that contribute to the overall porosity of the product. This porous structure is advantageous in terms of rehydration capacity and enhances the chip’s utility as a dietary fiber. However, the accompanying surface cracks indicate a compromise in structural integrity, which can negatively affect the mechanical strength and visual appeal of the chips. These structural deficiencies underscore the need for carefully controlled processing conditions during freeze-drying to balance the benefits of porosity with the preservation of product integrity.

Figure 2B illustrates the microstructure of Jerusalem artichoke chips that have undergone an optimized pretreatment process before drying. This pretreatment, which includes but is not limited to the application of maltodextrin, plays a crucial role in reinforcing the chip structure. The figure reveals a more cohesive and less fragmented microstructure compared to the chips that underwent freeze-drying alone. The pretreatment process helps to stabilize the cellular structure during drying, preventing excessive collapse and reducing the occurrence of surface cracks. Among the components of the pretreatment, maltodextrin stands out for its ability to act as a structural proppant. It provides additional support to the cell walls, helping to preserve the integrity of the chip’s porous matrix while mitigating the formation of cracks. This dual role of the pretreatment—stabilizing the overall structure and enhancing the effects of maltodextrin—demonstrates the importance of a well-designed pretreatment process in producing high-quality dried products.

The comparative micrographs highlight the critical role that pretreatment plays in determining the final quality of Jerusalem artichoke chips. By combining general structural stabilization with the specific benefits of maltodextrin, the pretreatment process ensures that the chips maintain both functional properties, such as rehydration capacity, and desirable physical qualities, such as structural integrity and aesthetic appeal. This approach not only enhances the chips' suitability for various food applications but also improves their potential marketability by addressing key quality concerns.

This study explored the effects of blanching duration, NaCl concentration, and maltodextrin concentration on the pretreatment of Jerusalem artichoke chips within the FAD process, leading to significant improvements in color and rehydration properties. Blanching time was a critical factor influencing color, rehydration, and hardness, while NaCl concentration notably enhanced color, and maltodextrin played a key role in color quality, though their impact on rehydration rate and hardness was minimal. The Response Surface Methodology (RSM) effectively optimized the pretreatment parameters, identifying the ideal conditions as 67 s blanching time, 0.97% NaCl concentration, and 8.35% maltodextrin concentration, which yielded an L value of 79.048, a rehydration ratio of 3.972, and hardness of 1228.035g, resulting in Jerusalem artichoke chips with enhanced color, superior rehydration, and desirable firmness.

Conflicts of Interest:

The authors declare no conflict of interest.References

Funding:

This research was funded by the Gansu Academy of Agricultural Sciences Scientific Research Conditions Construction and Achievement Transformation Project (2022GAAS50), and the Science & Technology Project of the Gansu Agricultural and Rural Affairs Department (GNKJ-2020-4).

Author Contribution

Y. M. : investigation, data curation, writing original draft preparation, and visualization. W. G.: conceptualization, supervision, original draft, validation, software, and visualization, reviewing and editing. S. L.: investigation, data curation, and visualization. C. Z.: conceptualization, supervision, investigation, validation, visualization.

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Level of significance * p < 0.05, ** p < 0.01, *** p < 0.001

No competing interests reported.

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Enhancing the Quality of Jerusalem Artichoke Chips: The Role of Pretreatment Optimization in Combined Vacuum Freezing and Hot Air Drying

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Abstract

Figures

1. Introduction

2. Materials and methods

2.1. Materials

2.2 Combination pretreatment of Jerusalem artichoke

2.3 Experimental optimization of combined pretreatment

2.4 Determination of color

2.5 Determination of rehydration ratio

2.6 Determination of the hardness

2.7 Microstructure of Jerusalem artichoke chips

2.8 Experimental design and data analysis

3 Results and discussion

3.1 Single-Factor Experiments for Jerusalem artichoke chips

3.1.1 Effect of blanching time on the quality of Jerusalem artichoke chips

3.1.2 Effect of NaCl concentration on the quality of Jerusalem artichoke chips

3.1.3 Effect of concentration of maltodextrin on quality of Jerusalem artichoke chips

3.2 Effects of factors on chips quality

3.3 Optima model fitness and model validation

3.3.1 Influence on L* value

3.3.2 Influence on rehydration ratio

3.3.3 Optimization and validation

3.4 Effects of pretreatment on the microstructure of Jerusalem artichoke chips

4. Conclusions

Declarations

Conflicts of Interest:

Funding:

Author Contribution

References

Additional Declarations

Status:

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