A fresh-cut lotus root multi-field synergistic sterilization and browning prevention preservation method

Abstract

This invention discloses a multi-field synergistic sterilization and anti-browning preservation method for fresh-cut lotus root, belonging to the field of fruit and vegetable preservation technology. Addressing the problems of severe enzymatic browning, chemical color-protecting agent residues, and poor single physical preservation effects in existing fresh lotus root slices, this invention's method includes: rinsing fresh lotus root slices; preparing low-temperature plasma activated water (PAW) using radio frequency plasma (discharge power 40-70W, treatment time 8-15min, pH 2.8-4.0); simultaneously applying ultrasound to the PAW for multi-field synergistic treatment (solid-liquid ratio 1:5-1:8, ultrasound power 100-400W, frequency 20-40kHz, treatment time 5-15min); and vacuum packaging followed by refrigeration at 4±1℃. This invention utilizes the simultaneous fusion of PAW and ultrasound treatment, enabling the synergistic effect of ultrasonic cavitation and chemical oxidation to significantly inhibit polyphenol oxidase activity (inhibition rate ≥60%). Combined with vacuum packaging for oxygen isolation and freshness locking, it can simultaneously maintain the color and firmness of the lotus root slices (browning degree ≤20% and firmness retention rate ≥75% after 8 days of storage). The entire process is purely physical, safe and residue-free, extending the shelf life of fresh lotus root slices at 4°C from 3-5 days to 10-14 days. The process is simple and suitable for industrial application.

Description

Technical Field

[0001] This invention belongs to the field of food processing and fruit and vegetable preservation technology, specifically relating to a physical synergistic preservation method for fresh-cut lotus root that addresses the problems of easy browning and softening by using low-temperature plasma to activate water and ultrasonic simultaneous fusion treatment combined with vacuum packaging. Background Technology

[0002] Fresh lotus root is crisp, tender, and nutritious, making it a favorite among consumers. However, after peeling and slicing, lotus root is highly susceptible to enzymatic browning, turning black and rapidly softening its brittle structure, significantly reducing its commercial value. Currently, color preservation of fresh lotus root slices mainly relies on chemical color-protecting agents such as citric acid, ascorbic acid, and sodium bisulfate. While such treatments can inhibit browning in the short term, they pose a risk of chemical residues and are inconsistent with the trend towards green and healthy consumption.

[0003] In recent years, physical preservation technologies have attracted much attention. Low-temperature plasma activated water (PAW), rich in reactive oxygen and nitrogen species, has the potential to kill bacteria and inhibit enzyme activity, and has been tested for preservation of fresh-cut lotus root. However, lotus root treated with PAW alone still suffers from decreased hardness and loss of crispness during storage, resulting in a limited shelf life. To address this, researchers have combined PAW with ultrasound technology. For example, an existing patent (CN201911079620.8) discloses a "method for cleaning and preserving fruits and vegetables based on ultrasound-assisted plasma activated water," but it mainly targets the cleaning and sterilization of whole fruits and vegetables, failing to specifically address the dual problems of browning and softening in fresh-cut lotus root, nor does it propose a targeted solution for maintaining crispness.

[0004] In summary, existing technologies lack a simple, safe, efficient, and targeted preservation method to simultaneously inhibit enzymatic browning of fresh-cut lotus root while maintaining its crispness. Currently, no literature or patent reports a dedicated technical solution that uses fresh-cut lotus root as the sole treatment target, aims to inhibit browning and maintain firmness simultaneously, employs both PAW (Proteinizing Acid Wave) and ultrasonic (Ultrasonic) physical field non-thermal technologies, and integrates vacuum packaging to form a complete freshness-locking chain. This invention addresses this technological gap. Summary of the Invention

[0005] This invention aims to overcome the technical shortcomings of existing fresh lotus root slice preservation technologies, such as severe enzymatic browning, chemical reagent residues, poor effect of single physical treatment, short shelf life, and lack of specificity. It provides a safe, residue-free, synergistic, and industrially compatible method for preventing browning in fresh lotus root slices.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for preserving fresh-cut lotus root through multi-field synergistic sterilization and anti-browning, characterized by the following steps:

[0008] (1) Fresh lotus root pretreatment: Select fresh lotus root, wash and peel it and cut it into slices with a thickness of 2-5 mm. Rinse with deionized water to remove surface impurities and starch, and drain at room temperature for later use.

[0009] (2) Preparation of low-temperature plasma activated water (PAW): Using a radio frequency plasma generator with air as the working gas, the discharge power is controlled at 40-70W and the processing time is 8-15min to prepare low-temperature plasma activated water with pH value of 2.8-4.0 and oxidation-reduction potential of 800-1200mV;

[0010] (3) Multi-field synergistic sterilization and anti-browning treatment: The pretreated fresh lotus root slices are completely immersed in the PAW prepared in step (2), and ultrasonic treatment is applied at the same time as the immersion, so that the ultrasonic treatment and PAW soaking are carried out simultaneously; the solid-liquid ratio is controlled at 1:5 to 1:8 g / mL, the ultrasonic power is 100 to 400 W, the ultrasonic frequency is 20 to 40 kHz, and the treatment is continued for 5 to 15 min;

[0011] (4) Vacuum packaging and low temperature storage: Take out the fresh lotus root slices processed in step (3), drain the water, vacuum package them, and then store them in a cold storage environment of 4±1℃.

[0012] In the above method, the simultaneous synergistic treatment of water activated by low-temperature plasma and ultrasound can reduce the activity of polyphenol oxidase and microbial load in fresh-cut lotus root, thereby improving color stability and the ability to maintain tissue firmness.

[0013] Furthermore, in step (2), the discharge power is 50W and the processing time is 10min.

[0014] Further, in step (3), the ultrasonic power is 200W, the ultrasonic frequency is 28kHz, the processing time is 8min, and the solid-liquid ratio is 1:5g / mL.

[0015] Furthermore, the ultrasonic treatment in step (3) and the PAW immersion are completed synchronously in the same treatment tank, and there are no additional dielectric barrier discharge post-treatment steps throughout the process.

[0016] Furthermore, when fresh-cut lotus root treated by any one of claims 1 to 4 is stored at 4°C for 8 days, the browning degree is ≤20% and the hardness retention rate is ≥75%.

[0017] The beneficial effects of this invention are:

[0018] Compared with the prior art, the present invention has the following significant advantages:

[0019] (1) Synergistic effect of anti-browning and crispness preservation: PAW and ultrasonic treatment simultaneously inhibited polyphenol oxidase (PPO) by more than 60%. After 8 days of storage at 4℃, the browning degree of lotus root slices was ≤20% and the hardness retention rate was ≥75%, thus solving the problems of browning and softening at the same time.

[0020] (2) Significant synergistic effect: The PPO inhibition rate of simultaneous treatment (63.2%) far exceeded that of PAW alone (28.5%), ultrasound alone (22.3%) and the sequential treatment of the two (43.3%). The effect is not a simple additive and is unpredictable.

[0021] (3) Safe, green and residue-free: The entire process is purely physical, with no chemical additives or toxic byproduct residues, and meets food safety standards;

[0022] (4) Significantly extended shelf life: at 4°C, the shelf life is extended from the traditional 3-5 days to 10-14 days, which is about twice as long as PAW alone;

[0023] (5) Strong industrial adaptability: conventional equipment, simple process (two-step method), low cost, suitable for large-scale production, and avoids thermal damage to lotus root slices caused by high voltage electric field. Attached Figure Description

[0024] Figure 1 Effects of different treatment methods on the total bacterial count during the storage period of fresh-cut lotus root

[0025] Figure 2 Effects of different treatment methods on browning degree during storage of fresh-cut lotus root

[0026] Figure 3 Effects of different treatment methods on the retention rate of firmness during storage of fresh-cut lotus root Detailed Implementation

[0027] The invention will be further illustrated below with examples, but the scope of protection of the invention is not limited thereto:

[0028] Example 1 (Synchronous Processing)

[0029] Fresh lotus roots without rot or damage were selected, washed, peeled, and cut into uniform 3 mm slices. The slices were rinsed twice with deionized water and drained. Low-temperature plasma-activated water with pH 3.2 and ORP 1050 mV was prepared using a radio frequency plasma generator with air as the working gas, a discharge power of 50 W, and a treatment time of 10 min. The lotus root slices were immersed in the PAW at a solid-liquid ratio of 1:5 g / mL, and the ultrasonic power was set to 200 W and the frequency to 28 kHz for simultaneous and continuous treatment for 8 min. The lotus root slices were then removed, drained naturally, vacuum-packed, and stored in a refrigerated environment at 4℃.

[0030] Example 2 (Synchronous Processing)

[0031] Fresh lotus roots without rot or damage were selected, washed, peeled, and cut into uniform 3 mm slices. The slices were rinsed twice with deionized water and drained. Low-temperature plasma-activated water with pH 3.4 and ORP 1089 mV was prepared using a radio frequency plasma generator with air as the working gas, a discharge power of 40 W, and a treatment time of 15 min. The lotus root slices were immersed in the PAW at a solid-liquid ratio of 1:8 g / mL, and the ultrasonic power was set to 100 W and the frequency to 20 kHz for simultaneous and continuous treatment for 15 min. The lotus root slices were then removed, drained naturally, vacuum-packed, and stored in a refrigerated environment at 4℃.

[0032] Comparative Example 1 (PAW processing alone)

[0033] PAW was prepared using the optimal parameters of Example 1. Fresh lotus root slices were soaked in PAW for 8 minutes without ultrasonic treatment. The other pretreatment and storage conditions were the same as in Example 1.

[0034] Comparative Example 2 (ultrasound treatment alone)

[0035] Fresh lotus root slices were treated for 8 minutes using the optimal ultrasonic parameters (200W, 28kHz) of Example 1, without soaking in PAW. The other pretreatment and storage conditions were the same as in Example 1.

[0036] Comparative Example 3 (PAW and ultrasound sequential processing)

[0037] Fresh lotus root from the same batch as in Example 1 was used, and the pretreatment method was the same. Lotus root slices were first soaked in PAW solution prepared according to the parameters of Example 1 for 8 minutes, then removed and placed in deionized water for treatment with the same ultrasonic parameters (200 W, 28 kHz) for 8 minutes. After treatment, the water was drained, vacuum-packed, and stored at 4°C.

[0038] Performance testing

[0039] 1) Changes in browning degree

[0040] The absorbance of the fresh lotus root slice extract was measured at a wavelength of 410 nm using spectrophotometry, and the relative browning degree of the samples was calculated. As shown in Table 1, under refrigerated storage conditions at 4℃, the browning degree of each group of lotus root slices increased with the extension of storage time. Among them, the rate of increase in browning degree of Examples 1-2 of this invention was significantly slower. On the 8th day of storage, the browning degree of Example 1 was 10.1%, and the browning degree of Example 2 was 12.1%, which was much lower than that of PAW treatment alone (29.1%) and ultrasonic treatment alone (34.8%). Compared with Comparative Example 3 (browning degree 21.5%), which was treated sequentially by PAW and ultrasonic treatment, the browning degree of synchronous treatment was reduced by nearly 44%, proving that the "synchronous" operation method has a significant advantage over the "sequential" operation method.

[0041] Table 1. Browning degree after 8 days of storage

[0042]

[0043] 2) Polyphenol oxidase (PPO) activity assay

[0044] PPO activity was determined using the catechol spectrophotometric method. The PPO activity of fresh, untreated lotus root slices (blank group) was used as a baseline (set at 186.6 U / g; the inhibition rate was calculated as: inhibition rate (%) = (blank group PPO activity − treated group PPO activity) / blank group PPO activity × 100%). Table 2 shows that the simultaneous treatment in Examples 1-2 of this invention achieved PPO inhibition rates of 64.6% and 63.2%, respectively, while the inhibition rates of the PAW treatment group and the ultrasonic treatment group alone were only 28.5% and 22.3%, respectively. If only the effects of the two technologies were simply superimposed, the expected inhibition rate would be approximately 50.8% (28.5% + 22.3%). The actual effect of this invention (63.2%) was significantly higher than the predicted value (p < 0.05), demonstrating a significant synergistic effect. Furthermore, compared to the sequentially treated Comparative Example 3 (inhibition rate 43.3%), the simultaneous treatment showed an inhibition rate nearly 20 percentage points higher, further proving that the "simultaneous" operation method is key to achieving synergistic enhancement.

[0045] Table 2. PPO activity and inhibition rate after 8 days of storage

[0046]

[0047] 3) Hardness change

[0048] The hardness of fresh-cut lotus root slices was measured using a texture analyzer. The initial hardness of the fresh lotus root slices was used as a baseline (set at 169 N), and the hardness retention rate was calculated using the formula: Hardness on day 8 of storage / Initial hardness × 100%. As shown in Table 3, on day 8 of storage, the hardness value of Example 1 reached 144.26 N, with a hardness retention rate of 85.3%; the hardness value of Example 2 reached 135.2 N, with a hardness retention rate of 80.0%. The hardness retention rates of the PAW-treated group and the ultrasonic-treated group were 64.0% and 59.5%, respectively. Compared with Comparative Example 3 (hardness retention rate 72.4%), which underwent sequential treatment, the hardness retention rate of the synchronous treatment was significantly higher, indicating that the "synchronous" operation method has a unique advantage in maintaining the crispness of the lotus root slices.

[0049] Table 3. Hardness and Hardness Retention Rate after 8 Days of Storage

[0050]

[0051] 4) Changes in total bacterial count

[0052] The total bacterial count was determined according to GB4789.2-2022. As shown in Table 4, on the 8th day of storage, the total bacterial counts of Example 1 and Example 2 were 5.33 and 5.65 lg CFU / g, respectively, both significantly lower than those of sequential treatment (6.01 lg CFU / g), PAW treatment alone (6.23 lg CFU / g), and ultrasonic treatment alone (6.87 lg CFU / g), demonstrating that the dual physical field simultaneous treatment of the present invention has a good bactericidal effect.

[0053] Table 4. Total bacterial count after 8 days of storage

[0054]

[0055] 5) Decay rate and shelf life

[0056] The rot rate was determined by manual counting (the lotus root slices were considered rotten if they showed obvious browning, softening, off-odor, or mold). As shown in Table 5, on the 8th day of storage, the rot rates of the PAW-treated group and the ultrasonic-treated group exceeded 30% and 35%, respectively, while the rot rate of the sequential treatment group was about 25%, and the rot rates of Examples 1 and 2 were both below 15%. The effective shelf life was determined by combining sensory, physicochemical, and microbiological indicators: Examples 1 and 2 could reach 12 days, the sequential treatment group was 8 days, and the PAW-treated group and the ultrasonic-treated group were only 6 days and 5 days, respectively.

[0057] Table 5. Effective shelf life of fresh-cut lotus root

[0058]

[0059] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A fresh-cut lotus root multi-field synergistic sterilization and anti-browning preservation method, characterized in that, Includes the following steps: (1) Fresh lotus root pretreatment: Select fresh lotus root, wash and peel it and cut it into slices with a thickness of 2–5 mm. Rinse with deionized water to remove surface impurities and starch, and drain at room temperature for later use. (2) Preparation of low-temperature plasma activated water (PAW): Using a radio frequency plasma generator with air as the working gas, the discharge power is controlled at 40-70 W and the processing time is 8-15 min to prepare low-temperature plasma activated water with pH value of 2.8-4.0 and oxidation-reduction potential of 800-1200mV. (3) Multi-field synergistic sterilization and anti-browning treatment: The pretreated fresh lotus root slices are completely immersed in the PAW prepared in step (2), and ultrasonic treatment is applied at the same time as the immersion, so that the ultrasonic treatment and PAW soaking are carried out simultaneously; the solid-liquid ratio is controlled at 1:5-1:8 g / mL, the ultrasonic power is 100-400 W, the ultrasonic frequency is 20-40 kHz, and the treatment is continued for 5-15 min. (4) Vacuum packaging and low temperature storage: Take out the fresh lotus root slices processed in step (3), drain the water, vacuum package them, and then store them in a cold storage environment of 4±1℃.

2. The multi-field synergistic sterilization and browning prevention fresh-cut lotus root preservation method according to claim 1, characterized in that: In step (2), the discharge power is 50 W and the processing time is 10 min.

3. The multi-field synergistic sterilization and browning prevention fresh-cut lotus root preservation method according to claim 1, characterized in that: The ultrasonic power in step (3) is 200 W, the ultrasonic frequency is 28 kHz, the processing time is 8 min, and the solid-liquid ratio is 1:5 g / mL.

4. The method for preservation of fresh-cut lotus root by multi-field synergistic sterilization and browning resistance according to claim 1, characterized in that: The ultrasonic treatment and PAW immersion in step (3) are completed synchronously in the same treatment tank, and there are no additional dielectric barrier discharge post-treatment steps throughout the process.

5. The multi-field synergistic sterilization and browning prevention fresh-cut lotus root preservation method according to any one of claims 1-4, characterized in that: When fresh lotus root slices treated by the method are stored at 4℃ for 8 days, the browning degree is ≤20% and the hardness retention rate is ≥75%.

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