A method for drying carrot slices based on plasma technology

Abstract

The present application belongs to the technical field of fruit and vegetable drying, and particularly relates to a drying method of carrot slices based on plasma technology. The method comprises the following steps: performing plasma pretreatment on fresh carrot slices, wherein the power of the pretreatment is 300-800 W, and the processing time is 60-300 s; and then performing hot air drying on the pretreated carrot slices to obtain dried carrot slices. The fresh carrot slices are first pretreated by plasma, and then dried, the etching effect of the plasma can promote the internal moisture of the carrot slices to migrate to the surface, accelerate the evaporation of the moisture, and shorten the drying time of the carrot slices. The drying efficiency of the carrot slices is significantly improved, the energy consumption is reduced, the color, shape, rehydration capacity and sensory quality of the dried carrot slices are improved, the technical problems of low drying efficiency and product quality reduction of carrot slices in the prior art are solved, and a new technical approach is provided for high-value processing and utilization of carrot slices.

Description

Technical Field

[0001] This invention belongs to the field of fruit and vegetable drying technology, and specifically relates to a method for drying carrot slices. Background Technology

[0002] Carrots (Daucus carota L.) are a widely consumed root vegetable worldwide. They are rich in carotenoids, phenolic compounds, dietary fiber, and various vitamins and minerals, making them an important source of natural antioxidants and essential nutrients for the human body.

[0003] Fresh carrots have a high water content, making them susceptible to mechanical damage, dehydration and wilting, microbial spoilage, and nutrient degradation, resulting in a short shelf life and significant loss of commercial value. Therefore, long-term storage of carrots presents a challenge. Drying, as one of the oldest and most effective food preservation techniques, reduces the water activity of materials to inhibit biochemical reactions and microbial growth, making it a key method for achieving long-term storage, easy transportation, and intensive processing of carrots. Hot air drying, due to its low equipment cost, ease of operation, and versatility, has become the primary drying method in industrial production. However, traditional hot air drying suffers from drawbacks such as long drying time and high energy consumption. Furthermore, prolonged heat exposure can exacerbate browning, nutrient degradation, and severe tissue shrinkage in carrot slices, making it difficult to meet current consumer demands for high-quality dried products. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a drying method for carrot slices based on plasma technology. The drying method provided by this invention can shorten the drying time and improve the product quality of the dried carrot slices.

[0005] This invention provides a method for drying carrot slices based on plasma technology, comprising the following steps: Fresh carrot slices are subjected to plasma pretreatment to obtain pretreated carrot slices; the power of the plasma pretreatment is 300~800W and the treatment time is 60~300s. The pretreated carrot slices were dried with hot air to obtain dried carrot slices.

[0006] Preferably, the plasma pretreatment uses low-pressure glow discharge low-temperature plasma.

[0007] Preferably, the conditions for plasma pretreatment include: the raw material gas is N2, the velocity is 80~120 sccm, and the power is 300W.

[0008] Preferably, the plasma pretreatment time is 300s.

[0009] Preferably, the vacuum degree of the low-pressure glow discharge low-temperature plasma is ≤80Pa.

[0010] Preferably, the thickness of the fresh carrot slices is 1~10mm.

[0011] Preferably, the thickness of the fresh carrot slices is 3 mm.

[0012] Preferably, the temperature of the hot air drying is 50~70℃ and the wind speed is 0.8~1.2m / s.

[0013] Preferably, the hot air drying time is 50-75 minutes.

[0014] Preferably, the moisture content of the dried carrot slices is below 8%.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for drying carrot slices, comprising the following steps: pretreating fresh carrot slices with plasma to obtain pretreated carrot slices; the plasma pretreatment time is 60~300s; and drying the pretreated carrot slices with hot air to obtain dried carrot slices.

[0016] This invention addresses the characteristics of fresh carrot slices by subjecting them to plasma pretreatment before drying. The etching effect of plasma promotes the migration of internal moisture to the surface of the carrot slices, accelerating moisture evaporation and shortening the drying time. Simultaneously, it reduces enzyme activity, preserving the original shape and plumpness of the carrot slices during drying and minimizing shrinkage. This invention, through plasma pretreatment within a specific time range, significantly improves the drying efficiency of carrot slices, reduces energy consumption, and enhances the color, shape, rehydration ability, and sensory quality of the dried slices. It solves the technical problems of low drying efficiency and declining product quality in existing technologies, providing a new technical approach for the high-value processing and utilization of carrot slices.

[0017] Furthermore, the pretreatment time (plasma discharge time) of the present invention improves drying efficiency while reducing energy consumption, and can maximize the improvement of the color, shape, rehydration rate and sensory quality of dried carrot slices. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1A diagram of an LPGD-CP device; Figure 2 Figure 1 shows the effect of LPGD-CP pretreatment on the moisture ratio during hot air drying of carrot slices. Figure 3 Figure showing the effect of LPGD-CP pretreatment on the hot air drying rate of carrot slices; Figure 4 Figure 1 shows the effect of LPGD-CP pretreatment on the drying time of carrot slices. Figure 5 Figure 1 shows the effect of LPGD-CP pretreatment on the specific energy consumption of carrot slice drying. Figure 6 Figure showing the effect of LPGD-CP pretreatment on the effective water diffusion coefficient of carrot slices; Figure 7 Figure showing the effect of LPGD-CP pretreatment on the goodness of fit of the carrot slice drying process; Figure 8 Figure 1 shows the effect of LPGD-CP pretreatment on the appearance of dried carrot slices. Figure 9 Figure showing the effect of LPGD-CP pretreatment on the rehydration rate of dried carrot slices; Figure 10 Figure 1 shows the effect of LPGD-CP pretreatment on the rehydration kinetics of carrot slices after drying. Figure 11 Figure showing the effect of LPGD-CP pretreatment on cell morphology after rehydration of dried carrot slices; Figure 12 Figure showing the effect of LPGD-CP pretreatment on the total phenol content of dried carrot slices; Figure 13 Figure 1 shows the effect of LPGD-CP pretreatment on the total flavonoid content of dried carrot slices. Figure 14 Figure showing the effect of LPGD-CP pretreatment on the sensory evaluation results of dried carrot slices; Figure 15 Figure 1 shows the effect of LPGD-CP pretreatment on the cross-sectional wrinkles and microstructure of carrot slices. Figure 16 PCA results showing the effects of LPGD-CP pretreatment on the metabolomics of dried carrot slices; Figure 17 Image showing the strip-shaped accumulation of different compounds in metabolomics of LPGD-CP pretreated carrot slices after drying; Figure 18 A heatmap showing the metabolomics effects of LPGD-CP pretreatment on dried carrot slices. Figure 19 VIP value plot showing the effect of LPGD-CP pretreatment on metabolomics of dried carrot slices; Figure 20 A violin diagram of key metabolomics biomarkers for LPGD-CP pretreated carrot slices after drying. Detailed Implementation

[0020] This invention provides a method for drying carrot slices, comprising the following steps: Fresh carrot slices are subjected to plasma pretreatment to obtain pretreated carrot slices; the power of the plasma pretreatment is 300~800W and the treatment time is 60~300s. The pretreated carrot slices were dried with hot air to obtain dried carrot slices.

[0021] Unless otherwise specified, all materials and equipment used in this invention are commercially available products in the field.

[0022] The present invention pretreats fresh carrot slices with plasma to obtain pretreated carrot slices; the plasma pretreatment power is preferably 300~800W, more preferably 300W, and the treatment time is preferably 60~300s, more preferably 300s.

[0023] In this invention, the fresh carrot slices are preferably obtained by washing, peeling, and cutting fresh carrots. The method of washing, peeling, and cutting is not particularly important; methods commonly used by those skilled in the art can be employed. The thickness of the fresh carrot slices is preferably 1-10 mm, specifically 3 mm or 5 mm.

[0024] In this invention, the plasma pretreatment conditions include: the raw gas is preferably N2; the velocity is preferably 80-120 sccm, specifically 100 sccm; the power is preferably 300-800 W, specifically 300 W or 800 W; and the plasma pretreatment time is preferably 60-300 s, specifically 60 s or 300 s. This invention preferably uses low-pressure glow discharge low-temperature plasma (LPGD-CP) for pretreatment; in embodiments of this invention, the low-pressure glow discharge low-temperature plasma generating device (e.g., Figure 1 (As shown) Provided by Cambricon Technologies (Suzhou) Co., Ltd., the plasma is triggered when the vacuum level drops to 80 Pa. Low-temperature plasma treatment is a non-thermal physical process. The generated plasma consists of electrons, ions, free radicals, photons, ultraviolet radiation, active substances, and molecules in their ground or excited states. It can effectively improve the microstructure and hydrophilic properties of material surfaces through etching effects and the introduction of polar groups. This invention employs low-temperature plasma pretreatment, which has the advantages of short processing time, high efficiency, no pollution, and low-temperature energy saving.

[0025] After obtaining the pretreated carrot slices, the present invention performs hot air drying on the pretreated carrot slices to obtain dried carrot slices.

[0026] In this invention, the preferred temperature for hot air drying is 50~70℃, specifically 60℃; the preferred wind speed is 0.8~1.2m / s, specifically 1m / s; and the preferred time is 50~80min, specifically 56.33min, 63.67min, 69.67min, or 75min.

[0027] In this invention, the moisture content of the dried carrot slices is preferably below 8%, specifically 8% (safe moisture content).

[0028] The data from the examples show that pretreatment with low-pressure glow discharge low-temperature plasma (LPGD-CP) can promote the drying, improve the shape, and enhance the quality of carrot slices.

[0029] To further illustrate the present invention, the method for drying carrot slices provided by the present invention will be described in detail below with reference to the accompanying drawings and embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0030] Example 1: (1) Pretreatment methods The low-pressure glow discharge low-temperature plasma (LPGD-CP) generator was provided by Cambricon Technologies (Suzhou) Co., Ltd.

[0031] Fresh carrot slices, cut to 3 mm thick, were placed in a low-pressure glow discharge low-temperature plasma generator. The plasma was triggered when the vacuum level in the processing chamber dropped to 80 Pa. The feed gas was N2, flowing at a rate of 100 sccm. The processing power was set to 300 W, and the processing time was set to 60 s, denoted as CP 300W 60s.

[0032] (2) Hot air drying After pretreatment, the carrot slices were dried at a temperature of 60℃ and a wind speed of 1 m / s, and tests were conducted at different time points. The moisture content of the dried carrot slices was controlled to be below 8% to obtain dried carrot slices. Example 2:

[0033] A method for drying carrot slices based on plasma technology, which differs from Example 1 in the following ways: The processing power is 300W and the processing time is 300s, denoted as CP 300W 300s. Example 3

[0034] A method for drying carrot slices based on plasma technology, which differs from Example 1 in the following ways: The processing power is 800W and the processing time is 60s, denoted as CP 800W 60s. Example 4:

[0035] A method for drying carrot slices based on plasma technology, which differs from Example 1 in the following ways: The processing power is 800W and the processing time is 300s, denoted as CP 800W 300s.

[0036] Test method: 1. Research methods for drying kinetics (1) Methods for determining moisture content and drying rate Moisture content ratio (M) R The calculation formula is shown in equation (1), and the drying rate (D) R The calculation formula is shown in equation (2).

[0037] M R =(M t -M e ) / (M0-M e Equation (1) D R =(M t -M t+Δt Equation (2) is given by equation (2) and Δt. In the formula, M0 is the initial dry basis moisture content of the carrot slices (g / g), M t Let M be the water content (g / g) of the carrot slices at time t (s); e To balance the moisture content (g / g) of carrot slices; M t +Δt represents the dry basis moisture content (g / g) of the carrot slices at time t+Δt (s).

[0038] (2) Calculation of drying energy consumption The total energy consumption for drying carrot slices includes the energy used in the pretreatment and drying processes. Energy consumption is expressed by specific energy consumption (SEC) formula (3).

[0039] SEC=(V p I p t p +V d I d t d ) / (M0-M t Equation (3); In the formula, V p Preprocessing voltage (V); I p Pre-processing current (A), t p Preprocessing time;V d Drying voltage (V); I d The drying current is (A). t d M is the drying time; M0 is the initial dry basis moisture content of the carrot slices (g / g); M t The dry basis moisture content (g / g) of the carrot slices at time t (s) is given.

[0040] (3) Fitting the drying model and calculating the effective moisture diffusion coefficient Six commonly used drying kinetic models were used to analyze the moisture changes of carrot slices during the drying process under different pretreatment conditions. The effective moisture diffusion coefficient D during the carrot slice drying process was calculated according to Fick's second law. eff The derived formula based on Fick's second law is shown in equation (4). Fitting equation (4) yields D. eff .

[0041] M R =8 / π 2 exp(-π 2 D eff t / 4L 2 Equation (4); In the formula, L is the thickness of the carrot slice (m), and t is the drying time of the carrot slice (s).

[0042] 2. Quality testing methods (1) Total phenol content Total Phenol Content (TPC) in carrot slices was determined using the Folin-Ciocalteu method: 0.2 g of dried carrot slice powder, ground in liquid nitrogen, was added to 10 mL of 70% methanol and mixed thoroughly. The homogenate was sonicated in a 25°C water bath for 30 min, then centrifuged at 10000 r / min for 15 min at 4°C to obtain the supernatant. 0.30 mL of the crude extract was added to 1 mL of Flin-Ciocalteu reagent and 5.7 mL of distilled water and allowed to stand for 10 min. Then, 0.5 mL of 20% Na₂CO₃ solution was added to the mixture, and the volume was adjusted to 10 mL with distilled water. Finally, the mixture was incubated at 37°C for 30 min, and the absorbance was measured at 750 nm using a spectrophotometer and compared with the standard curve of gallic acid. TPC is expressed as gallic acid equivalents (mg GAE / g dry weight).

[0043] (2) Total flavonoid content The total flavonoid content (TFC) in carrot slices was determined using the NaNO2-Al(NO3)3-NaOH method: A 0.30 mg / mL rutin standard solution was prepared. 0, 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 mL of this solution were respectively added to 25 mL test tubes. 50% ethanol was added to a final volume of 6 mL, followed by 0.5 mL of 4% sodium nitrite, shaken and allowed to stand for 6 min. Then, 0.5 mL of 10% aluminum nitrate was added, shaken well and allowed to stand for 6 min. Finally, 4.0 mL of 5% sodium hydroxide was added, and the volume was brought to 10 mL with distilled water. The mixture was shaken well and allowed to stand for 10 min. The absorbance was measured at 509 nm using a spectrophotometer, and a standard curve was plotted. Sample preparation was the same as for the determination of total phenol content. Sample determination: 2 mL of appropriately diluted sample solution was pipetted into a 25 mL test tube, and the absorbance was measured according to the standard solution determination method, repeated three times. TFC is expressed as millirutin equivalents (mg RT / g dry weight).

[0044] (3) Rehydration rate First, weigh the dried carrot slices, then soak them in distilled water at 25°C. Every 5 minutes, remove the slices from the soaking water and blot dry with absorbent paper. Then weigh the rehydrated slices, and soak them again. Repeat this process until the weight of the sample remains constant. The rehydration rate is obtained by equation (5): RR=W t / W0 formula (5); In the formula, W 0 This indicates the weight (g) of the dried carrot slices before rehydration. W t The weight (g) of the sample at time t after rehydration.

[0045] (4) Color Color parameters of fresh and dried carrot slices ( L*, a*, b* The colorimeter was measured using a handheld colorimeter (3 NH, SC-10, China). Calibration was performed using a white reference plate before testing. The sample was placed on a white surface for testing to ensure the colorimeter covered the entire optical path. Color parameter tests were repeated 9 times. Sample color is expressed as the total color difference ( ). ΔE ), saturation ( C* ) represents, and is calculated according to the following formula: ΔE =[(L * -L0 * ) 2 +(a * -a0 * ) 2 +(b * -b0 * ) 2 ]1 / 2 Equation (6); C * =(a 2 +b 2 ) 1 / 2 Equation (7); In the formula ΔE Total color difference; C* Saturation; L * 、a * 、b * These represent the brightness, red-green saturation, and yellow-blue saturation values ​​of the dried sample, respectively; L0 * a0 * b0 * These are the color parameter values ​​for fresh samples.

[0046] (5) Texture The hardness, resilience, cohesion, and elasticity of dried carrot slices were tested using a texture analyzer (TA.XT Plus). The parameters were as follows: probe P / 5, pre-test rate 1.0 mm / s, mid-test rate 2.0 mm / s, post-test rate 1.0 mm / s, strain 30%, trigger value / sensor: automatic 5.0 g.

[0047] (2) Sensory evaluation Sensory evaluation was conducted by 15 professionally trained personnel, using a total score of 100 points. The specific percentages allocated to different sensory characteristics were as follows: appearance (20%), color (20%), dryness (10%), aroma (20%), mouthfeel (10%), and taste (20%). The final score for each sense was the average of all evaluators' scores. The sensory characteristics and total scores were then converted to a 5-point scale.

[0048] 4. Microstructure The surface morphology of carrot slices was observed using a field emission scanning electron microscope (SEM). The microstructure of the carrot slices after pretreatment and after rehydration was observed under reflected light using an optical microscope (ECLIPSE Ci-L).

[0049] 5. LC-MS non-targeted metabolomics analysis Carrot slice powder (0.5 g) was placed in a 2 mL centrifuge tube, and 1 mL of pre-cooled methanol / water (4:1, v / v) extraction solvent was added. The mixture was vortexed for 30 s and then allowed to stand at -20°C for 1 h. Subsequently, it was centrifuged at 4°C and 12000 rpm for 15 min. The supernatant was filtered through a 0.22 μm organic filter membrane and transferred to a sample vial for analysis. Quality control samples (QC) were used to assess instrument stability and data quality. Chromatographic separation was performed using an ultra-high performance liquid chromatography (UHPLC) system (Thermo Fisher Vanquish UHPLC). The column was a Waters ACQUITY UPLC HSS T3 (2.1 mm × 100 mm, 1.8 μm), the column temperature was set to 40°C, the injection volume was 2 μL, and the flow rate was 0.3 mL / min. In positive ion mode, mobile phase A was an aqueous solution containing 0.1% formic acid, and mobile phase B was acetonitrile containing 0.1% formic acid. In negative ion mode, mobile phase A was a 5mM ammonium acetate aqueous solution, and mobile phase B was acetonitrile. The gradient elution program was as follows: 0-1 min, 5% B; 1-8 min, 5%-95% B; 8-13 min, 95% B; 13-13.1 min, 95%-5% B; 13.1-16 min, 5% B. Detection was performed using a Thermo Fisher Q Exactive HF-X high-resolution mass spectrometer equipped with a heated electrospray ionization (HESI) source. The spray voltage was 3.5 kV in positive ion mode and -3.2 kV in negative ion mode. The sheath gas flow rate was 40 arb, the auxiliary gas flow rate was 10 arb, the capillary temperature was 320°C, and the auxiliary gas heating temperature was 350°C. Full MS / dd-MS2 acquisition mode was used, with a primary mass spectrometry scan range of m / z 70-1050 and a resolution of 120,000 FWHM, and a secondary mass spectrometry resolution of 30,000 FWHM. Collision energies were set using NCE steps (20, 40, 60 eV). Raw data files (.RAW) were processed using Compound Discoverer 3.3 software for peak extraction, peak alignment, and metabolite identification. Metabolite identification was based on the mzCloud, mzVault, and ChemSpider databases, and matched using precise mass numbers, retention times, and secondary fragment spectra.

[0050] Results and Analysis: 1. The effect of low-temperature plasma pretreatment on drying kinetics (1) Effects of low-temperature plasma pretreatment on drying rate, time and energy consumption of carrot slices The change in moisture ratio of carrot slices with drying time under different low-temperature plasma pretreatment conditions is as follows: Figure 2As shown in the figure, it can be seen that the moisture content of the carrot slices decreases continuously with the extension of drying time. Overall, the rate of decrease in moisture content of each pretreated group is significantly faster than that of the untreated group. P <0.05 indicates that low-temperature plasma pretreatment can effectively accelerate the drying process of carrot slices. Among them, the moisture content decreased most rapidly in the CP 800W 300s group, followed by the CP 300W 300s and CP 800W 60s groups. Although the CP 300W 60s group was better than the untreated group, its drying speed was slightly slower than the other pretreated groups. This trend is shown in the graph of drying rate versus moisture content (…). Figure 3 This is also confirmed in the previous study, which showed that increasing the pretreatment power and time both contribute to improving the drying rate, especially in the high-speed drying stage at the beginning. Because the etching effect of low-temperature plasma disrupts the cell structure of carrot slices, it creates more pores and channels for water migration within the tissue, reducing the mass transfer resistance to water diffusion and thus promoting the migration of internal water to the surface and accelerating evaporation. Higher power and longer processing times result in more thorough cell etching and smoother mass transfer channels, leading to faster water migration and evaporation rates. In contrast, the etching effect of CP 300W 60s is limited, and the improvement in drying rate is relatively weak.

[0051] Corresponding drying time data ( Figure 4 The drying times for each group were as follows: 123.33 min (untreated group), 75.00 min (CP 300W 600s), 69.67 min (CP 300W 300s), 63.67 min (CP 800W 60s), and 56.33 min (CP 800W 300s). Compared to the untreated group, the drying times of the low-temperature plasma pretreatment groups were shortened by 39.2%, 43.5%, 48.4%, and 54.3%, respectively, indicating that low-temperature plasma pretreatment can significantly shorten the drying time of carrot slices.

[0052] Specific energy consumption is an important indicator for evaluating the economic efficiency and sustainability of drying processes. Figure 5The specific energy consumption of the untreated group was 94.87 kW·h / kg H2O. The energy consumption of the low-temperature plasma (CP) pretreatment groups was significantly lower than that of the untreated group, indicating that low-temperature plasma pretreatment can effectively reduce the specific energy consumption of drying. Since the pretreatment time is shorter than the drying process, the energy consumed during pretreatment accounts for only a small portion of the total energy consumption. Therefore, this decrease is attributed to the significant reduction in drying time caused by CP pretreatment. Compared to the untreated group, the specific energy consumption of the pretreated groups decreased by 38.7%, 41.1%, 47.1%, and 47.8%, respectively. This shows that increasing the processing power has a more significant effect on reducing energy consumption, while extending the processing time at high power has a relatively gradual and insignificant effect on further improving energy consumption. Therefore, higher power is not necessarily better.

[0053] Unless otherwise specified, the dried carrot slices used in subsequent tests were dried for 123.33 min (CK) without pretreatment, 75 min (CP 300W 60s) with LPGD-CP-300W-60s, 69.67 min (CP 300W 300s) with LPGD-CP-300W-300s, 63.67 min (CP 800W 60s) with LPGD-CP-800W-60s, and 56.33 min (CP 800W 300s) with LPGD-CP-800W-300s.

[0054] 2. Effect of low-temperature plasma pretreatment on the effective moisture diffusion coefficient (D) of carrots eff The influence of model fitting (1) Effect of low-temperature plasma pretreatment on the effective diffusion coefficient (D) of moisture in carrot slices eff The impact of Effective water diffusion coefficient (D) eff Dm is a key parameter characterizing the ability of moisture to migrate within a material; its changes directly reflect the promoting effect of pretreatment on moisture transport during drying. This study calculated Dm... eff Values ​​such as Figure 6 As shown, the Deff of the untreated group was 1.32 × 10⁻⁶. -9 m 2 / s, D of each preprocessing group eff All significantly improved ( P <0.05). The Deff of the CP 300W 60s, CP 300W 300s, CP 800W 60s, and CP 800W 300s groups were 2.20×10⁻⁶. -9 2.73×10 -9 2.97×10 -9 and 4.33×10 -9 m 2The drying rates were 67.1%, 107.2%, 125.8%, and 228.5% higher than the control group, respectively. The trend of these changes was consistent with the drying rate results, further verifying the enhancing effect of low-temperature plasma pretreatment on the drying process of carrot slices.

[0055] (2) Effect of low-temperature plasma pretreatment on the fitting of the carrot drying model Drying kinetic models are valuable tools for estimating drying endpoints, energy consumption, and selecting optimal drying conditions. This study selected six common thin-layer drying models to fit the experimental data. The fitting results (Table 1) show that all models can describe the drying process well (R0). 2 >0.8882). Among them, the Midilli model has R under all treatment conditions. 2 The maximum value indicates the highest fitting accuracy. Figure 7 The predicted moisture content (Pred.MR) and experimental moisture content (Ep.MR) for different drying models are compared, reflecting the contrast between experimental and predicted values ​​from the drying kinetics model. The scatter plot of the Midilli model's predicted and experimental values ​​is evenly distributed around the straight line y=x, further confirming its reliability. Therefore, the Midilli model can be considered the optimal model for expressing the hot air drying kinetics of carrot slices pretreated with low-temperature plasma.

[0056] Table 1. Fitting results of different drying models

[0057] 3. The impact of low-temperature plasma pretreatment on product quality and chemical properties (1) Effects of low-temperature plasma pretreatment on the color and appearance of carrots Color is one of the key indicators for evaluating the quality of dried carrot slices, directly affecting their commercial value and consumer acceptance. This study measured L... ∗ (Brightness), a ∗ (Red-green saturation), b ∗ (Yellow-blue) value, and calculate the total color difference ( ΔE ) and saturation ( C ∗ The effect of low-temperature plasma pretreatment on the color of dried carrot slices was systematically evaluated, and the results are shown in Table 2. Regarding color parameters, compared to the untreated group, the brightness of all groups after CP pretreatment was significantly reduced, while the red-green and yellow-blue values ​​were significantly increased; however, there were no significant differences between the treatment groups. P <0.05). And the total color difference of the pre-processed group... ΔE Small, saturation C* High, this can be seen from the actual picture of dried carrot slices ( Figure 8It can be seen that the pretreated groups all exhibit a brighter red color closer to that of fresh carrots, i.e., a higher saturation. This is because the shortened drying time directly reduces the duration of material exposure to hot air, thereby greatly reducing the degradation of pigments such as carotenoids due to thermal and photo-oxidation. Simultaneously, the shorter drying time also limits the process of non-enzymatic browning, such as the Maillard reaction. On the other hand, CP can also affect the color quality of the product by inactivating polyphenol oxidase and peroxidase to inhibit enzymatic browning. Due to the inactivation of oxidases such as peroxidase and polyphenol oxidase on the grape surface, the raisins after plasma pretreatment have a brighter appearance. Furthermore, physical images show that, compared to the untreated group, all low-temperature plasma pretreated groups of dried carrot slices exhibited better surface smoothness and integrity in macroscopic morphology, with reduced shrinkage. This may be because the porous channels formed by low-temperature plasma etching reduce stress concentration during the drying process, thereby inhibiting tissue shrinkage.

[0058] Table 2. Color parameters of dried carrot slices with different pretreatments. ΔE and C* value

[0059] (2) Effect of low-temperature plasma on the texture of dried carrot slices Texture is one of the core indicators of the sensory quality of dried carrot slices, directly affecting the consumer's eating experience. The effects of different pretreatment conditions on the textural properties of carrot slices are shown in Table 3. Compared with the untreated group, the hardness of carrot slices in all CP pretreatment groups was significantly increased (…). P <0.05). This may be because the active particles generated by CP can induce the oxidation of free thiol groups in the polypeptide chains of carrot slices to form disulfide bonds, making the sample surface structure more compact and thus significantly improving hardness. On the other hand, the etching effect of CP forms microporous channels on the surface and inside of the carrot slices, accelerating the evaporation of water during the drying process. Compared with the untreated group, the pretreated group showed faster water migration, more uniform tissue shrinkage, and a more compact structure, reducing the generation of loose voids. The structure after drying has stronger support, and the hardness increases accordingly. The improved resilience is related to the enhanced elastic deformation ability of the cell structure after CP treatment, while the decrease in cohesion and elasticity is because the high-power treatment disrupts some of the fibrous connections of the cell wall, weakening the binding force of the internal structure.

[0060] Table 3. Texture properties of dried carrot slices with different pretreatments

[0061] (2) Effect of low-temperature plasma on the rehydration rate of dried carrot slices Rehydration rate (RR) is one of the core indicators of the quality of dried carrot slices, directly reflecting the ability of the dried product to restore its morphology after rehydration. This study measured the rehydration rate of dried carrot slices after different low-temperature plasma pretreatments, and the results are as follows: Figure 9 As shown, the rehydration rate of all samples pretreated with low-temperature plasma was significantly higher than that of the untreated group (as shown). P <0.05 indicates that CP treatment significantly improved the rehydration ability of dried carrot slices and accelerated the rehydration process. The CP 300W 300s group had the highest rehydration rate, increasing by 39.9% compared to the control group; the CP 300W 60s, CP 800W 60s, and CP 800W 300s groups also showed increases of 27.3%, 31.5%, and 28.6%, respectively. From the rehydration kinetic curves (…),… Figure 10 From the perspective of [data / analysis], all samples exhibited a typical two-stage characteristic: a rapid water absorption period (0-20 min) and a slow equilibrium period, consistent with the diffusion law of porous materials. Furthermore, the pretreated group showed a significantly faster initial water absorption rate. This beneficial effect may be attributed to the etching effect of CP, which erodes the cuticle layer of the carrot surface, forming a microporous structure and increasing the specific surface area, thus facilitating faster and more efficient water absorption during rehydration. In addition, CP treatment enhances surface hydrophilicity by introducing polar functional groups, further increasing the affinity of the carrot surface for water molecules.

[0062] The visual and microscopic characteristics of the rehydration process further confirmed this difference: physical observation showed that the control group sank directly to the bottom during rehydration, while all CP pretreatment groups remained in a stable suspended state; combined with optical micrographs after rehydration ( Figure 11 As can be seen, the control group had dense tissue with no obvious air bubbles, while the CP pretreated group had varying numbers of air bubbles, and the number of air bubbles was positively correlated with the rehydration rate. The essence of this phenomenon is that CP pretreatment creates a microporous structure on the surface and inside of the carrot slices through etching. During rehydration, the micropores act as channels for rapid water penetration and also retain some air to form air bubbles, reducing the sample density and causing it to suspend. In contrast, the control group suffered severe tissue collapse and had a dense structure during drying. After rehydration, the water filled the gaps without leaving any pores, resulting in a higher density and sinking to the bottom, which corresponds to its lowest rehydration rate. The difference in rehydration rate among the different CP treatment groups is related to the influence of treatment conditions on the structure: the CP 300W 300s group had the highest rehydration rate because the pretreatment under these conditions created sufficient microporous channels without excessively damaging the structural integrity. The higher power treatment group had a slightly lower rehydration rate, possibly due to the increased treatment intensity causing slight fusion or collapse of some microporous structures in the later stages of drying, but its structure was still significantly better than the control group.

[0063] (3) Effects of low-temperature plasma on the nutritional properties of dried carrot slices Phenolic and flavonoid compounds are important bioactive substances in fruits and vegetables, and their retention rate is a key indicator for evaluating the impact of drying processes on the nutritional quality of products. This study determined the total phenolic content (TPC) and total flavonoid content (TFC) of dried carrot slices after different low-temperature plasma pretreatments. The results are as follows: Figure 12 As shown. Regarding total phenol content, all pretreated groups were significantly higher than the untreated group ( P <0.05). The total phenol content (TPC) of the control group was 119.12 g GAE / g dry weight, while that of the CP group increased to 164.52, 149.87, 139.13, and 150.36 g GAE / g dry weight, respectively. This indicates that appropriate low-temperature plasma pretreatment can effectively promote or retain phenolic substances in carrots. CP pretreatment increased the total phenol content by shortening the drying time and promoting phenolic release: the control group had a longer drying time, and the carrot slices were exposed to a high-temperature environment for a long time, making phenolic substances prone to oxidative degradation; while CP pretreatment accelerated the drying rate and reduced the exposure time of phenols under high-temperature and oxygen-rich conditions, thus effectively retaining the total phenols. Polyphenolic compounds are usually stored in specific cell compartments, such as vacuoles or cell walls. The etching effect of CP disrupted the cell wall structure of the carrot slices, promoted the release of intracellular phenolic substances, and further improved the extractability of total phenols.

[0064] The trends differ in terms of total flavonoid content. Figure 13 The results showed that the TFC in the untreated group was 5.17 mg RT / g dry weight, while the TFC in all pretreated groups decreased, ranging from 3.94 to 4.19 mg RT / g dry weight. Among them, CP 800W60s had a relatively lower TFC, but it was not significantly different from the other treatment groups. P <0.05). The decrease in total flavonoid content is mainly attributed to the destruction of flavonoid structure by active particles generated during CP treatment: high-energy electrons, reactive oxygen species, ozone, and other active substances generated during CP attack the aromatic ring structure of total flavonoids, initiating modification reactions such as hydroxylation and aliphaticization, leading to the degradation of flavonoid compounds. The difference in total flavonoid content among different CP treatment groups is also related to the treatment conditions: the CP 800W 60s group had the lowest total flavonoid content because the concentration of active particles was higher under high power, resulting in more significant destruction of the flavonoid structure; while the CP 800W 300s group had slightly higher total flavonoid content, possibly because the longer treatment time further damaged the cell wall, promoted the release of some flavonoids, and alleviated the degradation effect to some extent, but overall it was still lower than the control group.

[0065] (4) Effects of low-temperature plasma on the sensory evaluation of dried carrot slices Overall sensory evaluation results ( Figure 14The results showed that low-temperature plasma pretreatment significantly improved the overall edible quality of dried carrot slices. Among them, the CP 300W 300s group performed best, achieving the highest scores in color brightness, shape uniformity, crispness, and flavor acceptability, with a significantly higher overall sensory score than other groups. This confirms that appropriate low-temperature plasma pretreatment can simultaneously optimize the sensory quality of the product while achieving efficient drying.

[0066] 3. Effects of low-temperature plasma pretreatment on the microstructure of carrot slices The microstructure is the core structural basis for the drying characteristics and rehydration performance of dried carrot slices, and its morphological features are related to the aforementioned physicochemical indicators such as drying rate and rehydration rate at the mechanism level. Combined with the cross-sectional wrinkle diagram ( Figure 15 The observations in (A) show that the surface of the untreated carrot slices was relatively smooth, while the surfaces of all the low-temperature plasma pretreated groups were rough and uneven. This rough surface can increase the heat exchange efficiency during the drying process. (SEM images) Figure 15 B. Figure 15 C) Further structural differences were revealed at the micrometer scale. The control group samples showed severe cell collapse, with sparse and blocked pores, forming a dense network structure that severely hindered water migration. After low-temperature plasma pretreatment, the microstructure of the samples underwent significant changes: intercellular connections became looser, and micropores and cracks appeared in the cell walls due to etching, forming more and more unobstructed microchannels.

[0067] CP treatment disrupts the integrity of epidermal cell walls, likely due to the interaction of reactive oxygen species (ROS) and reactive nitrogen species (RNS) with the surface, leading to the oxidative degradation of key cell wall components such as cellulose, hemicellulose, and pectin. Furthermore, the etching effect of CP treatment creates surface pores and cracks, further altering the epidermal microstructure. It is precisely the etching effect of CP pretreatment that forms a "microporous" and "channel network" structure, significantly reducing the resistance to internal moisture diffusion and providing a direct physical pathway for efficient moisture migration during drying and rapid moisture penetration during rehydration. The CP 300W300s group exhibits a uniform micropore distribution and moderate pore size. This structure provides ample moisture migration channels during drying without excessively damaging the tissue's integrity, perfectly reflecting its synergistic optimization of drying and rehydration rates. The optimal microstructure of the CP 300W 300s group also supports its comprehensive advantages in drying, rehydration, and sensory quality.

[0068] 4. Low-temperature plasma pretreatment for LC-MS non-targeted metabolomics analysis of carrot slices To systematically reveal the intrinsic regulatory mechanism of low-temperature plasma pretreatment on carrot slice quality at the metabolite level, this study used LC-MS non-targeted metabolomics technology to analyze the metabolic profiles of samples from different treatment groups. PCA results ( Figure 16 The results showed that the first two principal components explained 68.5% of the total variance, with PC1 explaining 59.5% and PC2 explaining 9.0%. The control group and each CP pretreatment group showed significant separation in the PCA score plot, indicating significant differences in the metabolome among these groups of dried carrot slices.

[0069] To investigate the compositional characteristics of metabolic changes, this study further analyzed the relative contents of major metabolites such as terpenes, phenolic acids, and amino acids. Figure 17 Overall, most functional categories showed a consistent enrichment trend in the CP 300W 300s group, with terpenes, carbohydrates, amino acids, phenolic acids, vitamins, and flavonoids increasing by 21.26%, 9.10%, 24.37%, 20.25%, 27.63%, and 30.56%, respectively. In contrast, the high-power treatment group generally showed a decrease in these contents. This trend is reflected in the metabolite heatmap (…). Figure 18 Further evidence was obtained from the study: a clear gradient in metabolite abundance was observed among the treatment groups. The CP300W 300s group had the highest overall metabolite abundance, showing widespread upregulation of metabolites, followed by the CP 300W 60s group; the CK group was in the middle; while the overall metabolite abundance was relatively low in the CP 800W 60s and CP 800W 300s groups, especially the CP 800W 300s group. This suggests that the CP pretreatment of CP 300W 300s may have induced a more active metabolic response, while high-power treatment may have easily triggered the degradation of some substances. The core reason is that the medium-power, long-term treatment of the CP 300W 300s group not only destroys the cell wall structure through etching, releasing bound terpenes, amino acids and other metabolites into free states, but also activates secondary metabolic pathways with appropriate reactive oxygen species as signaling molecules, promoting the synthesis of functional substances. In contrast, the high-power group, due to the excessively high concentration of reactive particles, not only causes the oxidative degradation of heat-sensitive flavonoids and other substances, but also leads to excessive cell damage and inactivation of metabolic enzymes, ultimately reducing the content of most metabolites.

[0070] To further screen key metabolites with differential expression between groups, this study used variable importance projection (VIP) values ​​> 1.0 and significant differences between groups. P The standard for filtering is <0.05). For example... Figure 19As shown, Dimethyl adipate, N-(3-Indolylacetyl)-L-alanine, Madlongiside C, Westernamide, and Thalicarpine have the highest VIP values, making them the most critical markers for distinguishing between groups. Notably, the metabolites ranking high in VIP values ​​include several substances closely related to carrot quality and physiological functions, such as L-Dopa, involved in plant hormone signaling; beta-Carotene and beta-Cryptoxanthin, key pigments and antioxidants; and L-Proline, related to flavor and osmotic regulation. Changes in these key metabolites suggest that CP pretreatment may regulate secondary metabolic pathways through active particles, affecting the synthesis and transformation of phytochemicals, thus supporting its comprehensive advantages in drying efficiency, color, nutrition, and sensory quality at the molecular level. (Violin diagram of key biomarkers is shown.) Figure 20 Further analysis revealed that α-carotene and β-carotene, as characteristic carotenoids of carrots, possess both antioxidant and visual health-protecting physiological activities, and are also the core material basis for color saturation. Vitamin A, as a metabolite of both, also undertakes antioxidant and nutritional supply functions. In the violin diagram, all three showed the highest mean and concentrated distribution in the CP 300W 300s group, which directly corresponds to the uniform and full color and optimal nutritional quality of the CP 300W 300s group. Caffeic acid, as a representative substance of phenolic acids, not only has strong antioxidant and anti-inflammatory activities, but also participates in the formation of flavor substances. Its distribution shows a special pattern—the CP 800W 60s group has the highest content, while the CK group has the lowest. This difference suggests that different CP treatment parameters may have different effects on specific phenolic acid metabolic pathways, and high-power short-time treatment may be more conducive to the accumulation or conversion of caffeic acid or its precursors. Overall, CP pretreatment significantly altered the metabolomic profile of carrot slices, with CP 300W 300s pretreatment showing the most balanced and prominent performance in promoting the accumulation of most beneficial metabolites.

[0071] In summary, based on a comprehensive analysis of drying kinetics, physicochemical properties, microstructure, and molecular metabolism, CP 300W 300s (i.e., plasma pretreatment power of 300W and treatment time of 300s) can significantly improve drying efficiency while maximizing the rehydration properties, sensory scores, and nutrient retention of the dried products, making it the optimal pretreatment process condition.

[0072] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, not all embodiments. People can obtain other embodiments based on the present invention without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for drying carrot slices based on plasma technology, characterized in that, Includes the following steps: Fresh carrot slices are subjected to plasma pretreatment to obtain pretreated carrot slices; the power of the plasma pretreatment is 300~800W and the treatment time is 60~300s. The pretreated carrot slices are then dried with hot air to obtain dried carrot slices.

2. The drying method according to claim 1, characterized in that, The plasma pretreatment uses low-pressure glow discharge low-temperature plasma.

3. The drying method according to claim 1 or 2, characterized in that, The conditions for plasma pretreatment include: the raw material gas is N2, the velocity is 80~120 sccm, and the power is 300W.

4. The drying method according to claim 1 or 2, characterized in that, The plasma pretreatment time is 300s.

5. The drying method according to claim 2, characterized in that, The vacuum degree of the low-pressure glow discharge low-temperature plasma is ≤80Pa.

6. The drying method according to claim 1, characterized in that, The thickness of the fresh carrot slices is 1~10mm.

7. The drying method according to claim 6, characterized in that, The thickness of the fresh carrot slices is 3mm.

8. The drying method according to claim 1, characterized in that, The temperature of the hot air drying is 50~70℃, and the wind speed is 0.8~1.2m / s.

9. The drying method according to claim 8, characterized in that, The hot air drying time is 50-130 minutes.

10. The drying method according to claim 1, characterized in that, The moisture content of the dried carrot slices is below 8%.

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