Optimization of Low-Temperature Plasma Inhibition of Potato Germination Using Response Surface Methodology

Abstract

In order to solve the problems of tuber infection and nutrient loss caused by potato germination during storage, this paper conducted a systematic study using low-temperature plasma jet technology to inhibit potato germination and determine its optimal treatment conditions. This study focused on optimizing the plasma treatment parameters, including voltage, gas flow rate, and treatment time, to effectively control potato germination, reduce weight loss during storage, and determine the quality indexes such as hardness, crispness, and antioxidant enzyme activity of potatoes in storage. The study showed that the optimal conditions for plasma treatment of potatoes were voltage 18.05 kV, treatment time 20.21 s, and gas flow rate 12.79 L/min. Under these conditions, the germination rate of potatoes was significantly reduced to 31.42%, and the weight loss rate was reduced to 2.15%. For the convenience of operation, the parameters of the validation experiment were determined as a treatment voltage of 18 kV, treatment time of 20 s, and gas flow rate of 13 L/min. The resultant potato germination rate was 31.26%, and the weight loss rate was 2.29%. Compared with the blank control group, the plasma-treated group significantly increased the activities of potato antioxidant enzymes (CAT, SOD, etc.). After 16 days of storage, SOD (superoxide dismutase) activity and CAT (catalase) activity of the plasma-treated group increased by 52.63% and 29.27%, respectively, compared with the control; POD (peroxidase) and PPO (polyphenol oxidase) activities of the treated group increased by 8.69% and 18.58%, respectively, compared with the control. Compared with the blank control, the plasma treatment group increased the hardness and brittleness of potatoes. Specifically, the hardness of the treated group increased by 6.06% compared with the control, and the brittleness of the treated group decreased by only 24% within 16 days, compared with a 37.19% decrease in the control. In addition, plasma treatment also reduced the accumulation of reduced sugar and dry matter consumption, thus maintaining the storage quality of potatoes, in which reducing sugar in the treated group was reduced by 32.56% compared with the control group, and dry matter in the treated group was increased by 7.66% compared with the control group. Therefore, the reasonable use of plasma treatment can effectively inhibit and slow down the sprouting process of potatoes, which lays a foundation for revealing the mechanism of plasma technology in inhibiting potato sprouting and improving its quality.

1. Introduction

Potatoes are a key staple crop worldwide, widely grown in various climatic conditions, and a significant food source in human diets [1]. As an important storage vegetable, potato sprouting poses a substantial challenge to its storage quality and economic value [2]. Sprouting results in nutrient loss in potatoes and enhances the accumulation of harmful substances like solanine, affecting their safety and sensory properties [3]. Moreover, sprouting degrades the potatoes’ appearance, further diminishing their market value [4]. Therefore, researching and effectively controlling sprouting in potatoes is crucial for extending their storage period and enhancing their economic benefits.

Currently, the primary strategies for inhibiting sprouting in potatoes involve using chemical sprout inhibitors and low-temperature storage [5]. While chemical inhibitors effectively prevent sprouting, their application may contribute to environmental pollution and pose potential food safety risks [6]. Although low-temperature storage effectively suppresses sprouting, it may promote undesirable glycation, adversely affecting processed potatoes’ color and facilitating the formation of carcinogenic compounds, such as acrylamide [7]. Consequently, addressing the storage challenges associated with potatoes is paramount, necessitating the urgent exploration of alternative, more effective approaches.

Cold plasma technology is a commonly used non-thermal method in food processing that helps preserve the nutritional content, sensory characteristics, and safety of food [4]. This technique exposes food to ionized gases produced by electrical or radiofrequency discharges. A range of charged particles, neutral and excited atoms, are generated throughout the process. These include nitric oxide, peroxynitrite, singlet oxygen, and superoxide anions [8]. Reactive oxygen species (ROS) and reactive nitrogen species (RNS), generated by plasma, trigger oxidative stress within plant cells, thereby initiating their protective responses.

Limited research exists on the inhibition of potato sprouting by low-temperature plasma, with most studies focusing on promoting seed germination and pathogen removal. Bhawana Adhikari treated tomato seeds with plasma and found that it could trigger tomato seed coat regulation and improve germination efficiency [9]. Janne Santos de Morais used plasma treatment on edible red mini roses and found that it could improve the quality of mini roses and enhance phenolic compounds and specific volatile compounds [10]. Yang et al. conducted a study to examine how varying treatment durations affect potato germination. When the plasma treatment time was 40 s, the plasma treatment caused irreversible damage [11]. Current research on the use of low-temperature plasma for inhibiting potatoes does not specify detailed treatment parameters. Thus, the specific parameters of the plasma jet suppression potato still need to be defined.

This study evaluated the effects of various plasma treatment parameters on inhibiting potato sprouting and identified the optimal conditions to prevent sprout growth. Single-factor experiments were conducted to determine the suitable ranges for plasma treatment parameters such as voltage, gas flow rate, and treatment time. The Box–Behnken response surface method was employed to optimize these parameters for maximum efficacy in inhibiting sprouting. In addition, the study aimed to evaluate changes in catalase (CAT) and superoxide dismutase (SOD), in addition to other quality parameters, to elucidate the role of plasma treatment in suppressing sprouting and improving potato quality.

2. Materials and Methods

2.1. Plant Material

The potatoes used in this study were of the Hesin No. 3 variety (Favorita × K9304). The selection criteria included uniform size and shape, absence of deformities, yellowing disease, pest infestation, and physical damage. The harvested potatoes were delivered to the laboratory via SF Express 0 °C to 2 °C within 24 h. Store it in an incubator (8 ± 2 °C with 90% relative humidity in the dark) during the storage phase before the start of the experiment. After the start of the experiment, it was stored in an incubator (23 ± 2 °C with 90% relative humidity).

2.2. Experimental Setup

In the experimental setup, illustrated in Figure 1, argon (Ar) was utilized to generate the plasma. The setup includes a plasma reaction system, a power supply, and an oscilloscope. The plasma reaction system consists of a high-voltage electrode, a low-voltage (ground) electrode, and a quartz tube. Plasma is obtained through the gap between the high-voltage electrode and the ground electrode within the quartz tube, which has an inner diameter of 5 mm. Inside the quartz tube, a copper column has the high-voltage electrode mounted on it, and the end of the quartz tube is wrapped with the ground electrode. An alternating high-voltage power source is connected to both electrodes, with a 1 to 10 kHz frequency and the discharge current varying from 0 to 3 A.

2.3. A One-Factor Experiment

Building on preliminary experiments, single-factor variable tests were performed to evaluate the effects of treatment voltage (9, 12, 15, 18, 21, 24, and 27 kV), treatment time (10, 15, 20, 25, 30, and 35 s), and gas flow rate (9, 10, 11, 12, 13, and 14 L/min) on potato sprouting rate and weight loss. The experimental design is presented in

Table 1. Design of Single-Factor Experiment.

	Treatment Voltage (kV)	Treatment Time (s)	Gas Flow Rate (L/min)
Treatment voltage (kV)	9, 12, 15, 18, 21, 24, 27	20	10
Treatment time (s)	15	10, 15, 20, 25, 30, 35, 40	10
Gas flow rate (L/min)	20	20	9, 10, 11, 12, 13, 14

.

2.4. Optimization of Parameters for Inhibiting Potato Sprouting

Building on the results of the aforementioned single-factor experiments, optimal ranges for plasma treatment time, voltage, and gas flow rate were selected. Optimization was utilized using a Box–Behnken response surface design. Sprout rate and weight loss rate were used as the evaluation indicators. Design-Expert 12.0 software was used for the analysis.

2.5. Germination Rate

Sprouting of potatoes was defined as a bud ≥ 2 mm [12]. The germination percentage was calculated according to (1).

$$GR={\displaystyle \frac{N_d}{N}}\times 100\%$$

(1)

where N_d represents the number of sprouted eyes, and N is the total number of sprouted eyes.

2.6. Weight Loss Rate

$$Weightloss\left(\%\right)={\displaystyle \frac{\left(W_0-W_d\right)}{W_0}}\times 100\%$$

(2)

where W₀ represents the initial weight of the potato at the start of treatment and W_d is the weight of the potato on day d of treatment.

2.7. Control Experiment Design

Uniformly sized and shaped potatoes were divided into 3 groups (1 group untreated + 2 groups treated with optimal plasma parameters) of 60 potatoes per experiment. Each experiment was repeated three times, and stored in an incubator set at 23 ± 2 °C with 90% relative humidity for up to 16 days after treatment [13]. The incubator is a dark environment. Samples were taken every four days to measure the indicators, and all experiments were performed in triplicate.

2.8. The Determination of Potato Texture

This measurement method was slightly altered based on the method suggested by Blenkinsop et al. [14]. A point was taken from the inner cortex of the potato chip, and three points were evenly sampled from the outer cortex and vascular bundle ring for texture analysis. The texture index value of the chip was calculated as the average of the values obtained from the four locations. Seven chips were measured for each treatment. Testing parameters: test mode: full texture profile analysis (TPA); probe: P5; pre-test speed: 2.00 mm/s; test speed: 2.00 mm/s; post-test speed: 200.00 mm/s; strain apply: 50%; the time interval between tests: 5 s.

2.9. Reducing Sugar Content

Determining the amount of reducing sugars followed the method outlined by Singh et al. [15]. Potato tissue (2 g) was combined with 25 mL of distilled water and incubated at 50 °C for 20 min. After incubation, the sample was centrifuged at 10,000× g for 10 min, and 0.5 mL of the resulting supernatant was collected. Next, 0.5 mL of DNS solution and 4 mL of distilled water were introduced into the mixture. It was then incubated for 5 min, and the absorbance was measured at 540 nm using a UV spectrophotometer. The reduced sugar concentration was then determined and expressed in grams per kilogram (g kg⁻¹).

2.10. Dry Matter Determination

Following the method of Li et al. [16], the aluminum box that was dried to a constant weight is first weighed, denoted as M₁. Then, 2–3 g of peeled potato flesh is placed into the aluminum box, and the total mass of the aluminum box and sample is recorded as M₂. The box with the sample is placed into an oven at 105 °C for blanching for 10 min, followed by drying at 75 °C until a constant weight is reached. After removing the box, it is placed in a desiccator containing drying agents to cool. Finally, the mass of the box and the sample are measured and recorded as M₃.

$$W={\displaystyle \frac{M_3-M_1}{M_2-M_1}}\times 100\%$$

(3)

2.11. Activities of Catalase (CAT) and Superoxide Dismutase (SOD) Enzymes

For the measurement of CAT and SOD activities, one gram of potato tissue was mixed with 5 mL of cold phosphate buffer, and the mixture was homogenized. Afterward, the homogenate was centrifuged at 12,000× g for 15 min at 4 °C. For further enzyme activity measurements, the resultant supernatant was collected.

CAT activity was measured using the hydrogen peroxide method outlined by Chen et al. [17]. The reaction mixture consisted of 2.8 mL of 20 mmol L⁻¹ H₂O₂ with 200 μL of enzyme extract. An equivalent volume of distilled water was used for the blank control instead of the enzyme extract. The data were expressed as U kg⁻¹, and absorbance was measured at 240 nm.

The nitroblue tetrazolium (NBT) photoreduction method was employed to measure SOD activity [18].

The reaction mixture, totaling 3 mL, was prepared by combining 1 mL of 50 mmol L⁻¹ phosphate buffer (pH 7.8), 0.4 mL of methionine aqueous solution (130 mmol L⁻¹), 0.2 mL of NBT aqueous solution (750 μmol L⁻¹), and 0.4 mL of riboflavin aqueous solution (0.1 mmol L⁻¹). In addition, 0.4 mL of EDTA-Na₂ aqueous solution was mixed with 0.6 mL of enzyme extract. The mixture was exposed to light at 4000 Lux for 1 h. The amount of NBT photochemical reduction inhibition (50%) was used to calculate the SOD activity, which was then reported as U kg⁻¹. Absorbance was measured at 560 nm.

2.12. Peroxidase (POD) Activity

A modified version of the Shi et al. [19] method was used to measure POD activity. To prepare the crude enzyme extract, 1.0 g of frozen potato powder and 0.12 g of PVPP were mixed with 5.0 mL of PBS (0.1 mmol L⁻¹, pH 6.8). The mixture was combined and then centrifuged at 4 °C for 15 min at 11,140× g. The recovered supernatant was utilized as the crude enzyme solution.

Solution A was prepared by combining 50 mL of PBS, 28 μL of guaiacol, and 19 μL of 30% H₂O₂. 2.5 mL of Solution A was combined with 0.5 mL of PBS and 0.5 mL of the enzyme extract for the reaction. For the control, 1 mL of PBS was combined with 2.5 mL of the reaction solution.

Absorbance was recorded at 470 nm every 30 s over a 3 min period, with three measurements taken for each sample. POD activity was determined and reported as U kg⁻¹.

2.13. Polyphenol Oxidase (PPO) Activity

PPO activity was evaluated following the method described by Xing et al. [20]. Three grams of potato powder were combined with 5 mL of extraction buffer, and the resulting mixture was ground into a homogenate while kept in an ice bath. This homogenate was centrifuged at 12,000× g for 30 min at 4 °C. After centrifugation, the supernatant was stored at 4 °C for subsequent use. For activity measurement, 0.1 mL of the enzyme extract was combined with 4.0 mL of 50 mmol/L acetate-sodium acetate buffer (pH 5.5) and 1.0 mL of 50 mmol/L catechol solution. The mixture was transferred to a cuvette, and the reaction was initiated immediately. The wavelength at which absorbance was measured was 420 nm. The absorbance at 15 s was recorded as the initial value, and subsequent measurements were taken every minute, recording at least 6 data points. PPO activity was computed based on the absorbance change of 0.01 per minute per gram of sample.

2.14. Statistical Analysis

All experiments in triplicate, and the data were statistically evaluated using Design-Expert 12.0 and Origin 2021 software. A p-value of less than 0.05 is considered statistically significant.

3. Results and Discussion

3.1. One-Factor Experiment

3.1.1. Impact of Varying Treatment Voltage on the Germination Process of Potatoes

Bulleted lists look like this:

As depicted in Figure 2a, with increasing voltage, the sprouting rate of potatoes gradually decreases. The change in sprouting rate is particularly pronounced when the voltage is in the range of 15–21 kV. Studies have shown that, under constant gas flow conditions, increasing plasma voltage enhances the generation of reactive species, which is associated with the plasma’s electron density and excitation conditions [21]. However, the selected voltage range was between 9 and 24 kV for economic feasibility.

3.1.2. The Impact of Treatment Time on the Sprouting of Potatoes

As shown in Figure 2b, with the treatment duration increased, the sprouting rate of the potatoes progressively decreased. The sprouting rate slightly rises as the treatment time increases to 30 s. The sprouting rate slightly increases between 30 and 35 s, and at 40 s, it reaches its minimum. Studies have demonstrated that prolonged exposure to plasma jets may damage the cell membrane, disrupting the exchange of substances between the cell’s interior and exterior. Such effects may compromise the cell’s integrity and function, possibly causing rupture or death [22]. To avoid membrane rupture and excessive oxidative stress caused by prolonged plasma treatment, the treatment time was limited to 10–30 s to prevent over-treatment.

3.1.3. The Impact of Gas Flow Rate on the Sprouting of Potatoes

Figure 2c illustrates that with an increased gas flow rate, the sprouting rate first declines and then peaks at 13 L/min. The gas flow rate plays a crucial role in plasma discharge, significantly influencing the stability of the discharge and the generation of reactive species. Research indicates that as the gas flow rate increases, the plasma jet’s length and distribution also expand correspondingly. However, excessively high gas flow rates may induce instability in the plasma jet. Conversely, lower flow rates result in a higher concentration of reactive species, as the plasma has a longer residence time in the target area, thus facilitating the generation of additional reactive species [23]. Therefore, the selected gas flow rate range in this experiment was between 9 and 13 L/min.

3.2. Response Surface Experimental Design and Result Analysis

Response Surface Methodology (RSM) was employed to examine the impact of plasma treatment voltage (A), treatment time (B), and working gas flow rate (C) on potato sprouting and weight loss rates.

Analysis of variance (ANOVA) and statistical significance were employed to assess the impact of each factor and their interactions on potatoes’ sprouting rate and weight loss rate. This analysis provides insights into the ideal conditions for plasma treatment, considering both the effectiveness of sprouting inhibition and the minimization of weight loss. The response surface experimental design and results are shown in

Table 2. Response Surface Experimental Design.

Experiment Number	Treatment Voltage (kV)	Gas Flow Rate (L/min)	Treatment Time (s)	Germination Rate (%)	Weight Loss Rate (%)
1	12	10	20	73.4	3.05
2	24	10	20	39.8	3.09
3	12	14	20	57.5	2.3
4	24	14	20	34.8	3.06
5	12	12	10	72.5	2.14
6	24	12	10	45.8	2.48
7	12	12	30	59.45	2.52
8	24	12	30	36.8	3.04
9	18	10	10	55.9	2.69
10	18	14	10	52.2	2.05
11	18	10	30	50.9	2.83
12	18	14	30	38.9	2.1
13	18	12	20	36.5	2.36
14	18	12	20	33.4	2.1
15	18	12	20	30.9	2.11
16	18	12	20	32.4	2.13
17	18	12	20	30.01	2.01

.

As shown in

Table 3. ANOVA for the regression model assessing the sprouting rate.

Source	Sum of Squares	Degree of Freedom	F-Value	p-Value
Model	3106.56	9	65.92	<0.0001
A- Treatment Voltage	1395.24	1	266.45	<0.0001
B- Gas Flow Rate	167.45	1	31.98	0.0008
C- Treatment Time	203.52	1	38.87	0.0004
AB	29.70	1	5.67	0.0488
AC	4.10	1	0.7831	0.4056
BC	17.22	1	3.29	0.1126
A2	551.79	1	105.38	<0.0001
B2	223.47	1	42.68	0.0003
C2	383.83	1	73.30	<0.0001
Residual	36.65	7
Lack of Fit	11.18	3	0.5848	0.6561
Pure Error	25.48	4
Cor total	3143.21	16

and

Table 4. ANOVA for the Regression Model of Weight Loss Rate.

Source	Sum of Squares	Degree of Freedom	F-Value	p-Value
Model	2.45	9	10.46	0.0027
A- Treatment Voltage	0.3445	1	13.24	0.0083
B- Gas Flow Rate	0.5778	1	22.20	0.0022
C- Treatment Time	0.1596	1	6.13	0.0424
AB	0.1296	1	4.98	0.0608
AC	0.0081	1	0.3113	0.5943
BC	0.0020	1	0.0778	0.7883
A2	0.7794	1	29.95	0.0009
B2	0.3859	1	14.83	0.0063
C2	0.0031	1	0.1202	0.7391
Residual	0.1822	7
Lack of Fit	0.1143	3	2.24	0.2254
Pure Error	0.0679	4
Cor total	2.63	16

, the p-values for the quadratic regression models of the sprouting rate and weight loss rate are below 0.01, indicating a highly significant fit of the models to the actual data. The p-values of the residuals exceed 0.05, suggesting their insignificance, which further supports the quadratic regression models’ reasonableness and ability to fit the actual data adequately. After performing quadratic regression analysis on the experimental data and removing the insignificant terms, the quadratic regression equations for the sprouting rate and weight loss rate are as follows:

$$\begin{array}{c}{X}_1=32.64-13.21\mathrm{A}-4.58\mathrm{B}-5.04\mathrm{C}+2.73\mathrm{AB}+1.01\mathrm{AC}-2.08\mathrm{BC}+11.45{\mathrm{A}}^2\hfill \\ +7.29{\mathrm{B}}^2+9.55{\mathrm{C}}^2\hfill \end{array}$$

(4)

$$\begin{array}{c}{X}_1=32.64-13.21A-4.58B-5.04C+2.73\mathit{AB}+1.01\mathit{AC}-2.08\mathit{BC}\\ +11.45A^2++0.3027B^2-0.0272C^2\end{array}$$

(5)

where X₁ represents the germination rate, X₂ denotes the weight loss rate, A, B, and C refer to the treatment voltage, gas flow rate, and treatment time, respectively.

As shown in Table 3, the effects of A, B, C, A², B², and C² on the sprouting rate model are highly significant (p < 0.01), whereas the effects of AB and BC are moderately significant (p < 0.05). The effects of A, B, and BC are moderately significant (p < 0.05). Other factors do not significantly impact the model. The experimental factors’ primary and secondary influences on potatoes’ sprouting rate are as follows: treatment voltage > treatment time > gas flow rate.

As shown in Table 4, the effects of A, B, C, AB, A², and B² on the model are highly significant (p < 0.01), while the BC effect shows moderate significance (p < 0.05). The primary and secondary influences of treatment voltage, treatment time, and gas flow rate on the weight loss rate are as follows: treatment voltage > treatment time > gas flow rate.

3.3. Analysis of Model Interactions

Response surface analysis was performed on the significant interaction effects of the experimental factors to investigate the impact of interaction terms on the two experimental outcomes.

Figure 3 illustrates the influence of the interaction levels of various factors on potato germination rate. The potato germination rate varies with changes in the factors. Among them, the interaction between treatment voltage (A) and gas flow rate (B) is the most significant, followed by the interactions between gas flow rate (B) and treatment time (C) and between voltage (A) and treatment time (C). Therefore, it can be concluded that, within a specific range, appropriately increasing treatment voltage and gas flow rate helps to reduce the potato germination rate.

Figure 4 shows the impact of the interaction levels of various factors on potato germination rats. As shown in Figure 4a, it can be observed that the potato weight loss rate initially decreases and then increases with increasing treatment voltage and gas flow rate. As depicted in Figure 4b, the potato weight loss rate increases with increasing treatment time and initially decreases before increasing with the rise in treatment voltage. As depicted in Figure 4c, the potato weight loss rate increases with increasing treatment time and initially decreases before increasing with the gas flow rate. Among them, the interaction between treatment voltage (A) and gas flow rate (B) is the most significant, followed by the interactions between treatment voltage (A) and, treatment time (C) and gas flow rate (B). Therefore, it can be concluded that, within a certain range, appropriately increasing treatment voltage and gas flow rate contributes to a reduction in the potato weight loss rate.

3.4. Parameter Optimization and Verification Experiment

The multi-objective parameter optimization module in Design-Expert software was employed to optimize the above indicators, yielding the optimal parameter combination: the treatment voltage is 18.05 kV, the treatment time is 20.21 s, and the gas flow rate is 12.79 L/min. The resulting potato germination rate was 31.76%, and the weight loss rate was 2.09%. For the convenience of operation, the parameters of the validation experiment were determined as a treatment voltage of 18 kV, treatment time of 20 s, and gas flow rate of 13 L/min. The resultant potato germination rate was 31.26%, and the weight loss rate was 2.29%. Five repeated trials were conducted under this experimental parameter combination, and the average value of the experimental validation results was calculated. The experimental results showed that the potato germination rate was 31.42%, and the weight loss rate was 2.15%. The experimental validation results were consistent with the optimization results, with the relative errors between the experimental and optimized values being less than 5%. The small relative error suggests that the model was highly accurate.

3.5. The Impact of Plasma Treatment on the Hardness and Brittleness

Hardness and brittleness are critical factors in assessing the texture of potatoes [24]. The softening of potatoes during storage directly affects their quality, subsequently influencing attributes such as taste and appearance. The impact of plasma treatment on potato hardness is depicted in Figure 5a. Potato hardness exhibits a general decreasing trend throughout the storage period, with significant differences observed during the later stages. There was no significant difference in hardness between the control and treated groups from the very beginning to the fourth day. From the fourth to the sixteenth day, the trend of decreasing hardness became slower in the treated group compared to the control group. On the sixteenth day, the hardness of the treated group increased by 6.06% compared with that of the control group, likely due to water consumption during potato sprouting, which causes a breakdown of cell structure and a subsequent decrease in hardness [25].

Brittleness changes are shown in Figure 5b. Both the control and treatment groups showed a decreasing trend, but throughout the period, the control group was much lower than the treatment group. The brittleness of treated potato slices decreased by only 24% over 16 days, compared to a 37.19% reduction in the control. This indicates that the optimal plasma treatment better preserves the brittleness of the potatoes.

3.6. The Effect of Plasma Treatment on the Dry Matter Content of the Potato

Figure 5b illustrates that, on days 0 to 8, there was a decreasing trend in both the control and treated groups. On days 8 to 12, there was an upward trend in both the control and treated groups. After 12 days, a decreasing trend was observed. In the treatment group, the dry matter content decreased initially, which may be due to the conversion of reducing sugars to starch during storage, resulting in an increase in starch content and affecting the dry matter content [26]. The small increase in dry matter content in the control and treatment groups may be due to the continuous respiration and other physiological and biochemical reactions of the potato during storage, leading to water loss and the consequent relative increase in dry matter content [26]. In the later storage stages, dry matter increased by 7.66% over the control group.

3.7. The Impact of Plasma Treatment on Reducing Sugars

Reducing sugars is widely involved in the metabolic processes of plants, animals, and microorganisms, playing an essential role in regulating plant growth, storage, and processing [27]. Reducing sugars directly influences plants’ sweetness and flavor and significantly impacts their nutritional value, processing quality, and consumer acceptability [28]. Additionally, excessively reducing sugar content can participate in the Maillard reaction, resulting in changes in the flavor and color of food. The Maillard reaction produces a variety of compounds, some of which can enhance food quality, while others may lead to food deterioration if uncontrolled. Reduced sugar content decreased with increasing storage time in the treatment and control groups. After 16 d of storage, reducing sugars decreased by 32.56% compared to the control. The reason may be that the appropriate plasma treatment affected the decomposition of potato starch and reduced the accumulation of reducing sugars.

3.8. The Impact of Plasma Treatment on the Activity of SOD and CAT

SOD, a metal-based antioxidant enzyme, plays a vital role in regulating the equilibrium of reactive oxygen species (ROS) within the organism [29]. It is crucial for maintaining the equilibrium between oxidation and antioxidant processes. As shown in Figure 6a, both control and plasma-treated groups showed a steady increase in SOD activity with increasing storage time. After 16 days of storage, SOD activity was significantly enhanced in the treated group compared to the control group. After 16 d of storage, the SOD activity in the plasma-treated group increased by 52.63%, which significantly exceeded the level observed in the control group, which could be attributed to the promoting effect of plasma treatment. This result aligns with previous studies, which found that higher SOD activity decreased the germination rate of rice seeds, emphasizing the critical role of SOD activity in delaying seed germination [30].

CAT activity showed a similar pattern. During the storage period, CAT activity showed a continuous increase in both plasma-treated and control groups. After 16 days of storage, CAT activity was significantly enhanced in the treated group compared to the control group. CAT is a crucial enzyme in plants that catalyzes the breakdown of hydrogen peroxide, aiding in eliminating excess free radicals in the body [31]. The treatment group showed a rapid increase in CAT activity during the first 8 days, followed by a decline later in the storage period. This may be due to the temporary accumulation of hydrogen peroxide [32]. Plasma treatment can enhance the activity of antioxidant enzymes.

3.9. Effect of Plasma Treatment on POD Activity

As shown in Figure 6c, the POD activities of both control and plasma-treated groups increased at the initial stage and then showed a decreasing trend, however, the POD activity of the plasma-treated group was higher than that of the control group throughout the process. After 16 d of potato storage, the POD activity of the treated group increased by 8.69% compared with the control group. POD enzyme utilizes hydrogen peroxide as a substrate to oxidize phenolic compounds, and effectively scavenges hydrogen peroxide during the storage process [33]. The increase of POD and other antioxidant enzyme activities can reduce the level of reactive oxygen species (ROS) and inhibit the sprouting of potato tubers, thus prolonging dormancy. The increase in the activities of POD and other antioxidant enzymes can decrease the level of reactive oxygen species (ROS), and inhibit the sprouting of potato tubers, thereby prolonging the dormancy period [34]. The POD activities of the treatment group increased by 8.69%, compared with the control group.

3.10. The Impact of Plasma Treatment on PPO Activity

PPO mainly catalyzes the enzymatic conversion of phenolic compounds and plays a crucial role in the growth and storage of potatoes, affecting their color, flavor, and overall quality [35]. From Figure 6d, PPO activity in both the treatment and control groups initially increased, then decreased. At certain time intervals, the treatment group displayed a marked increase in PPO activity compared to the control group (p < 0.05). Research by Hazal et al. [36] indicates that potatoes contain various phenolic compounds, such as caffeic acid and catechins, which may promote sprouting by regulating the synthesis of plant hormones such as auxins and gibberellins. The PPO activities of the treatment group increased by 18.58%, repectively, compared with the control group. Plasma treatment may alter the composition or concentration of phenolic compounds, thereby modulating the levels of phenolics that affect germination.

4. Discussion

The application of low-temperature plasma technology in potato storage has significant practical and theoretical significance [37]. With the prominence of the sprouting problem during potato storage, the use of low-temperature plasma technology can not only effectively inhibit sprouting, but also improve the quality of potatose and extend its storage period. In practical application, low-temperature plasma technology by adjusting the processing parameters, such as voltage, airflow rate, and processing time, the application of this technology not only reduces the germ infection and nutrient loss caused by sprouting, but also effectively prolongs the freshness period of potato and ensures its quality [38]. In addition, low-temperature plasma has a positive effect on the antioxidant capacity of potatoes. By increasing the activity of antioxidant enzymes (e.g., SOD and CAT), plasma treatment significantly enhanced the antioxidant capacity of potato [39]. This enhanced antioxidant capacity helps to inhibit quality degradation, such as browning and nutrient loss, triggered by oxidative reactions during storage [11]. The low-temperature plasma technology also improved the texture of the potato. This effect suggests that low-temperature plasma can effectively delay the degradation of potato texture and maintain its good taste and appearance. In addition, the plasma treatment reduced the accumulation of sugar and the consumption of dry matter, which in turn maintained the nutrient content of the potato and further improved its storage quality [40].

In terms of theoretical significance, the low-temperature plasma technology provides new ideas for in-depth study of the effects of plasma on plant physiology and metabolic processes [41]. This technology provides important theoretical support for the investigation of the inhibition mechanism of potato germination and the storage and preservation of other agricultural products. With the continuous development of technology, low-temperature plasma technology is expected to be widely used in agricultural storage, food processing, and other fields to promote the progress of green and environmentally friendly storage technology [42].

Although low-temperature plasma technology has shown excellent results in potato storage, it still faces the problems of high equipment cost and technical standardization. The future needs to further optimize the treatment process and study its long-term effect, in order to promote the application of this technology on a larger scale [43]. Overall, low-temperature plasma technology provides an effective solution for potato storage and brings an innovative breakthrough in preservation technology for the food industry [44].

5. Conclusions

In this study, we used a low-temperature plasma jet to inhibit potato germination and determined the suitable conditions for low-temperature plasma to inhibit potato germination. The main conclusions are as follows: (1) The effects of plasma treatment parameters on potato germination and weight loss content were: treatment voltage > treatment time > gas flow rate. In the plasma treatment of potatoes, the optimal treatment conditions were voltage 18.05 kV, treatment time 20.21 s, and gas flow rate 12.79 L/min. The germination rate of the treated potato was significantly reduced to 31.42%, the weight loss rate was reduced to 2.15%, and the potato was still able to maintain its normal physiological activity under these conditions. (2) Compared with the blank control group, the overall trend of SOD, CAT, POD, and PPO enzyme activities in the plasma-treated group was significantly higher than that of the control group after 16 d of storage, in which the SOD and CAT activities of the treated group increased by 52.63% and 29.27%, respectively, compared with the control; and the POD and PPO activities of the treated group increased by 8.69% and 18.58%, respectively, compared with the control group. (3) The plasma treatment group increased the hardness and brittleness of potatoes, and reduced the accumulation of sugars and dry matter consumption, thus maintaining the storage quality of potatoes. The hardness of the treated group increased by 6.06% compared with that of the control group; the brittleness of potatoes in the treated group decreased by only 24% within 16 d, while that of the control group decreased by 37.19%. Reducing sugars decreased by 32.56% compared to the control; dry matter increased by 7.66% compared to the control.