Strawberry cv. Dandong (n = 576 fruit), were purchased from Beijing Agricultural Products Market, Beijing, China; LB Nutrient Agar, Beijing Aoboxing Biotechnology Co., Ltd., Beijing, China; Sodium Chloride (analytically pure), Phenolphthalein (98% mass fraction), Shanghai Aladdin Biochemical Science and Technology Co., Ltd., Shanghai, China; Sodium hydroxide standard solution, Shandong Keyuan Biochemistry Co., Ltd., Heze, Shandong, China; Potassium iodide (analytically pure), Tianjin Juhengda Chemical Co., Ltd., Tianjin, China; soluble starch (analytically pure), Tianjin Fuchen Chemical Reagent Co., Ltd., Tianjin, China.

The experiment employed the apparatus shown in Fig. 1. PPA was generated by an arc discharge system (Lab-V1 plasma preservation device), which ignited an air flow between two-point electrodes (spacing: 3 cm) via a 20–40 kV high-voltage electric field to form a plasma discharge. Using air as the gas source, the cold plasma device was activated to produce atmospheric pressure cold plasma (CAPP). The generated CAPP was introduced into a sealed chamber via a vacuum circulation pump (flow rate: 40 L/min), thereby producing plasma-activated gas (PPA). The discharge power was set at 220 W, with the high-voltage power supply operating at a center frequency of 50 kHz and a discharge volume of 30 dm³. Strawberries were processed in batches within the chamber for treatment durations of 15 seconds, 30 seconds, and 60 seconds. After preheating is complete, sample processing begins. Energy consumption during the experiment is the product of the equipment power and the processing time.

Uniform strawberry samples with consistent size, color, and weight, and free of mechanical damage were selected. Remove the pedicel and place the fruit in a refrigerated device (model: YC-300L) at a constant temperature of 4 °C for 4–6 hours to achieve thermal equilibrium.

Strawberries were randomly assigned to three experimental treated and one untreated experimental groups, PPA15, PPA30, PPA60 and CK, respectively (15 s PPA treatment = PPA15; 30 s PPA treatment = PPA30; 60 s PPA treatment = PPA60; untreated control = CK). Samples were packed in polypropylene trays (Model: TQBC-0775; dimensions: 222 $\times$ 132 $\times$ 40 mm; Sealed Air Co., Ltd., Shanghai, China) containing six fruit each. Each treatment group was triplicated (3 trays containing 6 six strawberries each per treatment).

Fig. 1 shows the atmospheric plasma processing equipment, comprised by a plasma generator, a conveyor belt, a laminated machine, and a heat sealer. After the air was broken down in the discharge ceramic tube, plasma active substances were generated, and used to treat the strawberries in the chamber. Each batch of strawberries (6 fruit each) was processed at a time. After processing, all samples were immediately transferred to the conveyor belt and heat sealed with food-grade polyethylene (PE) film to complete the entire sterilization and packaging process, and stored in a crisper under controlled temperature conditions (4 °C $\pm$ 2 °C). Quality assessment was carried out every 3 days throughout the storage period.

The data collected was analyzed by one-way ANOVA to determine the significant differences between treatments (SPSS 20.0, IBM, New York, USA). The least significant difference a p 0.05 was also used, and the data were expressed as mean and standard-deviation. Furthermore, plots were analyzed using Origin 2014 (OriginLab Corporation, Massachusetts, USA), with the different letters (a, b, c) within each graph representing significant differences between treatments at each storage time.

Table 2 shows quality attributes of PPA-treated and untreated strawberries.

For the weight loss of strawberries at moment zero, the treatment group showed a slight reduction of less than 0.1% compared to the control sample, indicating that the PPA had a negligible effect on this quality parameter. The results of this study are in agreement with the results of Rana et al., 2020 [22], who studied whole fresh strawberries using in-package air discharges to generate plasma, as well as Giannoglou et al., 2021 [23] who showed that plasma treatment of strawberries did not significantly change their weight loss percentage score.

The color (L* and a*) of the PPA-treated strawberries was retained, and hardness showed only minor changes, none of which were significant (p $>$ 0.05) compared to the control, as confirmed by sensory evaluation on day 0. Additionally, TSS, TA, pH, and ASA content remained stable across treatment conditions (p $>$ 0.05), indicating that PPA treatment did not affect strawberry nutrient composition. These findings align with previous studies [22], which reported no significant impact of plasma treatment on strawberry flavor or color. Furthermore, no significant difference in respiratory rate was observed between the treatment group and the control group (p $>$ 0.05), which is consistent with the findings of Zhang et al., 2023 [24] that plasma treatment initially causes only minor changes in the respiratory rate of blueberries.

It is worth noting that, compared with the control group, the total number of bacterial colonies on strawberries significantly decreased after PPA treatment (p 0.05), and the reduction in bacterial colony counts on the strawberry surface became more pronounced as treatment time increased (Fig. 2). The total number of bacterial colonies on the surface of strawberries in the control group was 2.49 log CFU/g. After PPA treatment for 15 s, 30 s, and 60 s, the total number of bacterial colonies was 2.04 log CFU/g, 1.47 log CFU/g, and 1.18 log CFU/g, respectively, representing reductions of 64.52%, 90.45%, and 95.10% compared to the untreated control. The 60 s PPA treatment demonstrated significant sterilization efficacy, achieving a reduction of 1.31 log levels.

As expected, the reactive oxygen and nitrogen species generated by surface discharge diffuse into the fruit, exerting a sterilizing effect on the strawberries and reducing the microbial content on their surfaces. The sterilization efficacy of PPA treatment increases with longer treatment times, as the active components within PPA come into more prolonged and thorough contact with the strawberry surfaces. This confirms that PPA, after diffusing to the surface of strawberries in the treatment chamber, can effectively inactivate microorganisms on the surface of strawberries [25], and its inactivation effect is proportional to the treatment time.

Moisture loss in strawberries, resulting from ripening, respiration, and transpiration processes, leads to diminished surface gloss, wilting, and shriveling. Weight loss rate serves as a critical indicator for evaluating the efficacy of postharvest preservation treatments [26]. The weight loss rate exhibited a progressive increase with prolonged storage duration (Fig. 3). One-way ANOVA revealed statistically significant differences (p 0.05) between PPA-treated groups and the control during the initial storage phase. Notably, the PPA30 treatment demonstrated exceptional efficacy, achieving a 0.93% weight loss rate by day 3 (1.68%, 1.72%, and 1.2% for CK, PPA15, and PPA60, respectively). Compared to the control group, this treatment effectively reduced the rate of weight loss. No statistically significant differences (p $>$ 0.05) were detected between treated and control groups in the later storage stages. Weight loss rate of the PPA30-treated was slightly lower but there was no significant difference compared to the PPA15 or PPA60. Compared to the control group (CK), its weight loss rate was lower. This observation can be attributed to the metabolic activity-induced wilting and water transpiration occurring predominantly in the early storage phase [4], suggesting that PPA treatment exerts inhibitory effects on strawberry metabolic processes. During the advanced storage phase, the progression of fruit decay resulted in reduced moisture loss, leading to a stabilization of weight loss rates.

Firmness represents a critical quality attribute in strawberries, serving as a key indicator of both ripeness and postharvest storage quality [27]. All treatments exhibited a biphasic firmness pattern during storage, characterized by initial increase followed by gradual decline (Fig. 4). This phenomenon may be attributed to incomplete maturity at harvest, with subsequent postharvest ripening during storage, accompanied by progressive strengthening of cell wall integrity and pectin cross-linking [28], as well as moisture loss-induced tissue densification leading to increased firmness. Prolonged storage resulted in significant softening, likely due to enzymatic degradation of cell wall components, and based on the morphological characteristics of the decayed area (such as softening of the flesh) and the extent of decay, it can be inferred that this may be related to microbial activity.

PPA-treated strawberries showed the highest stability in firmness (p 0.05). An increase in the initial firmness was observed in strawberries, regardless of the treatment (0–6 days for control, 0–15 days for PPA-treated), attributable to ongoing ripening processes and moisture loss, suggesting that PPA treatment effectively delays strawberry softening. Among treatments, PPA30 demonstrated optimal efficacy in hardness preservation, with only an 8% decrease before softening began on the fifth day (CK, PPA15, and PPA60 showed decreases of 12.16%, 23.64%, and 12.16%, respectively). During late storage, the PPA-treated group maintained superior firmness, potentially due to suppressed pectin methylesterase (PME) activity. PME, abundantly present in plant cell walls, catalyzes pectin demethylation leading to cell wall loosening and consequent firmness reduction [27]. This finding aligns with Giannoglou et al., 2021 [23], who reported that plasma treatment had a significant effect on PME activity inhibition.

The color parameters L*, a*, b*, and $\mathrm{\Delta }$E were used to evaluate color changes in stored strawberries showing a gradual decrease during storage, while the color difference value $\mathrm{\Delta }$E gradually increased (Fig. 5). The redness value a* on the surface of strawberries is crucial for market and sensory acceptance. Compared to the control, the a* value of PPA-treated samples showed a slower decrease (p 0.05). This result is consistent with the study by Hou et al., 2019 [29], which reported that plasma treatment improves the color stability of blueberry. After harvest, surface brightness L* values of strawberry changed due to physiological activities, fruit ripening, enzymatic oxidation, and anthocyanin synthesis [4]. Although the L* values of the PPA-treated strawberries were slightly higher than those of the control group, suggesting that the inhibitory effect of metabolic processes on surface reflectance is limited, this difference was not statistical significance. These results are consistent with the findings of Misra et al. (2014) [30], who showed that atmospheric cold plasma treatment had a limited effect on strawberry surface color. The b* value remained relatively stable throughout storage, while the color difference $\mathrm{\Delta }$E between treatments exhibited significant variability (p $>$ 0.05), indicating that plasma gas treatment plays a crucial role in preserving strawberry surface color.

Total soluble solids (TSS) content, a key biochemical indicator for assessing strawberry sugar content [31], exhibited a continuous decline in both control and treated fruits during storage (Fig. 6A), with no significant difference observed between treatments and control throughout. This reduction can be attributed to the combined effects of respiratory metabolism and microbial activity [25], where soluble carbohydrates are metabolized to sustain cellular functions while microbial proliferation concurrently consumes available nutrients. Notably, the PPA30 treatment demonstrated superior efficacy in TSS preservation, suggesting an optimal treatment for maintaining fruit quality within the tested concentration range. These findings corroborate previous reports on low-temperature plasma applications in strawberry preservation [25], supporting the potential of plasma-based technologies in postharvest management.

The titratable acidity (TA) content, a key biochemical indicator of sugar-acid balance and sensory quality in strawberries, exhibited a characteristic biphasic pattern during storage (Fig. 6B), with an initial decline (0–12 days) followed by a subsequent increase. This dynamic profile primarily reflects metabolic regulation, particularly through respiratory pathways [32]. The initial TA decrease corresponds to normal physiological maturation, where organic acids are preferentially metabolized as respiratory substrates. PPA treatment had limited impact on TA dynamics, with no statistically significant differences observed between the 0–12 day treatment groups and the control group (p $>$ 0.05), indicating minimal interference with primary metabolic processes. The subsequent rise in TA is closely associated with accelerated fruit senescence and microbial proliferation, where hydrolytic enzymes from spoilage microorganisms degrade fruit components and produce acidic metabolites. Notably, after 12 days, total acid accumulation in PPA-treated samples was significantly lower than in the control group (p 0.05), indicating its effective inhibition of microbial activity and maintenance of fruit quality. Among the treatments, PPA30 exhibited optimal performance by maintaining the most stable TA profile throughout storage, highlighting its superior efficacy in delaying senescence while preserving fruit biochemical composition, thereby substantiating the potential of PPA treatment as an effective postharvest intervention strategy for quality maintenance during extended storage periods.

The antioxidant properties of ASA, a water-soluble antioxidant with strong reducing properties, helps reducing oxidative damage while enhancing fruit resistance to abiotic and biotic stresses [26]. Our results showed a progressive decline in ASA content during storage across all treatments (Fig. 6C), attributable to the combined effects of exogenous oxidative stress, endogenous respiratory metabolism, and microbial growth. However, no significant differences in ASA content were observed between treated and control strawberries throughout the entire storage period (0–21 days) (p $>$ 0.05). This indicates that the PPA treatment had no significant effect on the ASA content of strawberry under the present experimental conditions, and did not significantly interfere with the ASA-related metabolic pathways or antioxidant system in strawberry, thus maintaining the relative stability of the ASA content. The observed stability implies that the applied PPA treatment preserved the suggests antioxidant capacity of strawberries without inducing substantial changes in their redox homeostasis.

The pH value can affect the balance of organic acids and sugars to maintaining the unique sweet and sour flavour of strawberries, and too high or too low of a value may lead to an imbalance in flavour, which has an important effect on storage quality of fruits and vegetables [33]. Results from our study showed constrained pH fluctuations within a relatively narrow range throughout storage (Fig. 6D), with the initial phase showing minimal divergence between treated and control fruit. However, prolonged storage resulted in systematically higher pH values in PPA-treated samples, potentially mediated through suppressed microbial proliferation and consequent reduction in acid generation on fruit surfaces, though statistical analysis indicated these differences were not significant (p $>$ 0.05). These results suggest that while PPA treatment exhibits a directional influence on pH modulation through microbial suppression, the intervention does not fundamentally alter the intrinsic acid-base equilibrium of strawberry tissues, consistent with previous findings regarding plasma-based treatments [23]. Overall, the results suggest PPA treatment primarily affects secondary microbial-mediated acid production rather than inducing substantial modifications to the primary biochemical parameters governing strawberry pH characteristics.

Postharvest respiratory metabolism in strawberries, a critical physiological process for maintaining cellular functions [30], was significantly modulated by PPA treatment as evidenced by characteristic gas composition changes showing progressive O₂ depletion and CO₂ accumulation (Fig. 7). These results were consistent with established respiratory patterns in strawberry fruit [28]. Comparative gas analysis revealed significantly higher O₂ and lower CO₂levels in PPA-treated samples compared to control (p 0.05). The PPA30 treatment exhibited optimal respiratory suppression, achieving 40% inhibition of respiratory activity. In addition, PPA treatment showed antimicrobial effect, reducing the number of microorganisms on the surface of strawberries, decreasing the respiratory metabolic activity of microorganisms, and indirectly reducing the production of O₂ and the consumption of CO₂ inside the package. Similarly, Du et al. (2024) [34] also showed that plasma treatment inhibited wolfberries respiration during storage.

Ethylene, is a phytohormone that promotes the respiration of fruits and vegetables, and accelerates ripening and senescence, affecting the quality of fruits during storage [28]. During the storage period, the ethylene content of strawberries showed an increasing trend, regardless of the treatment (Fig. 8A). The PPA15 and PPA30 treated strawberries showed significantly lower (p 0.05) ethylene content compared to the control group, with up to 15.9% of the ethylene content being inhibited from being released. The PPA60 treatment showed a higher peak of ethylene, which may be attributed to the prolonged PPA treatment, that might have triggered a stress the stress response of from strawberries and thus leading to the synthesis of a higher amount of ethylene in response to the external stimuli. PPA delays strawberry ripening by reducing ethylene production through the suppression of respiration, metabolism, and other physiological activities. However, excessively prolonged PPA treatment may negatively impact the physiological state of the fruit.

Cell membrane permeability, which serves as a critical indicator of cellular integrity and senescence progression in fruit, exhibited a characteristic increase during storage (Fig. 8B), reflecting oxidative damage [35]. The integrity of the cell wall provides a stable environment for the selective permeability of the cell membrane. Therefore, our results suggest that the integrity of the cell wall of strawberries was disrupted during storage. Statistical analysis showed significant differences (p 0.05) in membrane permeability between PPA-treated strawberries, with PPA15 and PPA30 treatments demonstrating reductions of 1.4% and 21.6%, respectively. These results that the plasma treatment plasma-induced microbial inactivation and subsequent attenuation of oxidative stress. Conversely, PPA60 treatment resulted in 10.8% higher membrane permeability than the control, revealing a dose-dependent duality of plasma effects. That is, while moderate exposure (15–30 s) seemed to preserve membrane integrity through microbial suppression, prolonged treatment (60 s) induced cellular damage through reactive oxygen and nitrogen species-mediated membrane peroxidation, consistent with previous reports of plasma-induced cellular damage at excessive exposure durations [36].

The microbial load on strawberry surfaces, is a critical food safety concern and primary contributor to postharvest decay [37]. Botrytis cinerea, also known as gray mold, one of the primary fungus causing strawberry spoilage, and responsible for most of postharvest losses. In this study, the number of colonies on the surface of strawberries showed a gradual increase during storage regardless of the treatment (Fig. 9). However, a significant growth suppressio was observed in PPA-treated fruit compared to the control (p 0.05). The microbial inhibitory effect of PPA treatment was mainly attributed to reactive oxygen and nitrogen species (ROS/RNS) in non-thermal plasma, which disrupt microbial cell membrane integrity, leading to intracellular content leakage and suppressed proliferation [11, 38].

PPA30 reduced the total colony count by 1.09 log units (91.85% lower than the control group) (Fig. 9A), with a final microbial load of 3.04 log CFU/g. This indicates effective growth inhibition, but it did not meet sterilization standards, as the reduction did not reach the 6-log threshold required for sterilization. Reactive oxygen species/reactive nitrogen species (ROS/RNS) primarily damage cell membranes rather than causing complete cell disintegration. As shown by Giannoglou et al., 2021 [23], total bacterial counts decreased by 0.6 log levels after cold plasma treatment. The mechanism of action of PPA aligns with microbial inhibition rather than sterilization, consistent with the plasma-induced cell membrane damage mechanism. Rana et al., 2020 [22] also confirming the effectiveness of PPA in controlling microbial growth.

The decay rate analysis revealed significant preservation effects of PPA treatment, with treated strawberries exhibiting delayed onset and reduced severity of decay compared to the control (Fig. 9B, Fig. 10). While decay initiated on day 15 in both control and PPA15 treated fruit, PPA30 and PPA60 treatments extended the decay-free period to day 18, demonstrating temporal extension of fruit quality (Fig. 11). Quantitative assessment showed PPA30 achieved optimal efficacy with 56.1% decay reduction, surpassing PPA15 (32.0%) and PPA60 (10.0%), revealing a non-linear relationship between treatment duration and preservation outcomes. That is, insufficient exposure (PPA15) allowed for residual microbial proliferation, while excessive exposure time (PPA60) induced cellular damage compromising fruit defense mechanisms, as evidenced by accelerated late-stage decay. These findings align with established plasma research showing positive correlation between treatment duration and antimicrobial efficacy [39], while supporting observations of potential tissue damage from prolonged PPA exposure [36]. Results from our study highlight the critical importance of optimizing treatment parameters to balance immediate antimicrobial effects with preservation of host resistance mechanisms for maximal postharvest benefit.

Sensory evaluation, as a comprehensive assessment index, integrates a variety of sensory experiences to reveal the overall quality of fruits and vegetables during handling and storage, and has great significance to the commerciality of strawberries [40]. Sensory evaluation revealed a progressive deterioration in strawberry quality during storage (Fig. 11), with PPA-treated strawberries demonstrating significantly (p 0.05) superior sensory attributes compared to untreated fruit. These results suggest that PPA treatment had a good effect on maintaining the quality characteristics of strawberries during storage. The shelf-life analysis revealed substantial extension in PPA-treated strawberries. With PPA30 treated fruit exhibiting optimal performance by doubling the storage duration (18 days) relative to the control (9 days), while PPA15 and PPA60 achieved intermediate preservation (15 and 16 days respectively). This preservation effect stems from dual mechanisms, that is, physiological regulation through suppression of respiratory metabolism and ethylene biosynthesis, coupled with antimicrobial action that collectively delay senescence and maintain organoleptic properties (Fig. 12) The non-linear response to treatment duration, characterized by maximal efficacy at intermediate exposure (PPA30), suggests an optimal balance between beneficial physiological modulation and potential oxidative stress, highlighting the importance of precise parameter optimization in plasma applications for postharvest management.