Color-protecting bacteriostatic agent for long-term fresh-keeping storage of thousand-shredded potatoes

Abstract

The invention discloses a color-protecting bacteriostatic agent for long-term fresh-keeping storage of thousand-shredded potatoes, and the color-protecting bacteriostatic agent comprises the following components and process parameters: 0.5-1 wt% of tea polyphenol (based on catechin substances); 1 to 5 wt% of mulberry polysaccharide, based on beta-1, 4-glucan; wherein the mass ratio of the tea polyphenol to the mulberry polysaccharide is 1: (2-5), a low-temperature light-proof dissolution process with the temperature being lower than or equal to 25 DEG C is adopted, and the pH value of the solution is controlled to be 5.5-6.5; the method is suitable for potato varieties of Holland 15, Hissen 6, Experiment 1, Coita 88, V7 or Ewing Jin 885. The color-protecting bacteriostatic agent disclosed by the invention has good color-protecting and bacteriostatic effects, and can prolong the fresh-keeping period of the thousand-shredded potatoes, so that browning and microorganisms of the thousand-shredded potatoes are effectively inhibited.

Description

Technical Field

[0001] The invention relates to the technical field of food preservation, and more particularly to a color-protecting and antibacterial agent for long-term preservation and storage of potato shreds. Background Art

[0002] Thousand-thread potato shreds are a new product of fresh-cut potato processing products. Each shred is made by rotating and cutting a single potato, with a diameter of 2~5 mm and a length of 50~100 cm. It is widely used in fast food, hot pot and other catering industries. Due to its fine processing and cutting process, it is very easy to cause oxidative browning and outflow of nutrient juice, which is conducive to microbial infection and reproduction, resulting in deterioration of appearance and nutritional quality, change of original nutritional flavor, shortening of shelf life, seriously affecting its edible value and commodity value, and restricting the development of the fresh-cut industry.

[0003] At present, there are many theoretical research reports on the preservation of fresh-cut potatoes, mainly physical methods such as low temperature, heat treatment, irradiation, ultraviolet light, and chemical preservation methods such as chlorine, sodium hypochlorite, chlorine dioxide, and calcium chloride. Among them, physical preservation methods such as ultraviolet light and irradiation have high operating costs and mostly remain in the laboratory stage. Heat treatment requires strict control of temperature and time, and has poor operation convenience. The preservation of fresh-cut potatoes on the market mainly uses sodium hypochlorite for cleaning and sterilization, citric acid and calcium ascorbate for color protection, and combines low-temperature cold chain, vacuum packaging, modified atmosphere packaging, etc. to maintain product quality and shelf life. There are also multiple rinses with clean water to alleviate the browning of fresh-cut potatoes. However, studies have shown that chlorine, sodium hypochlorite, chlorine dioxide, etc. are easy to form strong carcinogens. Some developed countries have expressly banned the use of chlorine and sodium hypochlorite in the food industry. The color of potato shreds was not ideal when treated with a combination of citric acid, calcium ascorbate, sodium D-isoascorbate, etc., and could only be maintained for 1 day at a low temperature of 4°C. Summary of the invention

[0004] The present invention provides a color-protecting and antibacterial agent for long-term preservation and storage of potato shreds, comprising the following components and process parameters: 0.5~1 wt% tea polyphenols, calculated as catechins; 1-5 wt% of mulberry polysaccharide, calculated as β-1,4-glucan; Among them, the mass ratio of tea polyphenols to mulberry polysaccharides is 1:2~5, and a low-temperature, light-proof dissolution process at a temperature of ≤25°C is adopted. The pH value of the solution is controlled between 5.5 and 6.5; Applicable to Holland 15, Sisen 6, Experiment 1, Cooperation 88, V7, or Eugene 885 potato varieties.

[0005] Preferably, it also includes: 0.7-0.9 wt% epigallocatechin gallate to preferentially occupy the active center of polyphenol oxidase; 0.05-0.1 wt% chelated zinc citrate to inhibit the copper ion sites of PPO; The content of mulberry polysaccharide is 1.8~2.2 wt%, and the average molecular size Mw is: Mw=3.5×10 4 Da, the arabinose side chain content is 0.8~1.2% to block substrate contact through steric hindrance.

[0006] Preferably, it also includes: For Holland No. 15: 0.75 wt% epigallocatechin gallate + 2.0 wt% mulberry polysaccharide; For Xisen No. 6: 0.85 wt% epigallocatechin gallate + 1.8 wt% mulberry polysaccharides were used.

[0007] Preferably, the following components and process parameters are also included: 0.3-0.8 wt% chitosan; 0.1~0.3 wt% rosmarinic acid; 0.05~0.1 wt% ε-polylysine; The dissolved tea polyphenols and mulberry polysaccharide solution and five active ingredients, chitosan, rosmarinic acid, and ε-polylysine, form a sustained-release system through nanofiber loading technology, and the nanofiber is prepared by combining chitosan and sodium alginate.

[0008] Preferably, it further comprises 0.5-1.5 wt % of malic acid or citric acid for adjusting pH buffering capacity; The nanofibers have an average diameter of 10 to 100 nm, are prepared by electrospinning, and have humidity-responsive release properties; The nanofiber loading technology is achieved by the following steps: Dissolving chitosan and sodium alginate in acetic acid solution to form a spinning solution with a mass concentration of 2-5%; The five active ingredients, tea polyphenols, mulberry polysaccharide solution, chitosan, rosmarinic acid, and ε-polylysine, are uniformly dispersed in the spinning solution; The fibers were spun by an electrospinning machine at a voltage of 15-25 kV and a receiving distance of 10-20 cm; After drying, a nanofiber membrane loaded with active ingredients is formed.

[0009] Preferably, the color-protecting and antibacterial agent achieves color-protecting and antibacterial effects through triple synergistic effects: Chitosan forms a physical barrier that inhibits oxygen contact; Tea polyphenols and rosmarinic acid synergistically inhibit the activity of polyphenol oxidase; Mulberry polysaccharides and ε-polylysine synergistically inhibit microbial growth.

[0010] Preferably, the nanofiber membrane is a chitosan / sodium alginate interpenetrating network structure IPN, dynamic cross-linking sites are formed by intermolecular hydrogen bonds, the mass ratio of chitosan to sodium alginate is 2-3:1, the average diameter of the nanofibers is 10-100 nm, the membrane porosity is 60-80%, and the initial pore size is 20-50 nm; Among them, the nanofiber membrane has a humidity-responsive pore size adjustment function. In the humidity range of 50~95%RH, through the reversible swelling of the carboxylic acid group of sodium alginate, the swelling ratio is 1:5~8, and the ionic bond dissociation of the chitosan amino group synergistically acts to achieve a dynamic pore size adjustment range of 10~100 nm.

[0011] Preferably, the dynamic aperture adjustment comprises a two-stage regulation mechanism, specifically: In a high humidity environment of >80%RH, the membrane pore size expands to 80~100 nm, and the release rate of tea polyphenols and ε-polylysine small molecule components increases by 3~5 times; In a low humidity environment of <60%RH, the membrane pore size shrinks to 10~30 nm, forming a physical barrier to delay the release of ingredients.

[0012] Preferably, the concentration maintenance capacity of the nanofiber membrane for tea polyphenols is: under conventional packaging conditions of 75-85% RH, the tea polyphenol concentration fluctuation range is ≤±15%, the effective antibacterial concentration is ≥0.03 wt%, and the maintenance time is ≥21 d; The mechanical strength of the nanofiber membrane is 80-120 MPa, the water vapor permeability WVTR can be adjusted in the range of 500-2000 g / (m²·day), and the time to respond to humidity changes is ≤10 min.

[0013] Preferably, the nanofiber membrane is achieved by a gradient release profile: (1) ε-polylysine with a molecular size of <500 Da was released rapidly, with a release rate of >80% completed within 24 h; (2) Tea polyphenols with molecular size of 500-5000 Da were released at a moderate rate, with a release rate of >90% completed within 72 h; (3) Mulberry polysaccharides with molecular size >5000 Da were slowly released, with a release rate of >90% completed within 7 days.

[0014] The present invention has at least the following beneficial effects: First, the present invention soaks the potato shreds in a tea polyphenol solution, so that the browning and the total number of microbial colonies of the potato shreds are effectively inhibited.

[0015] Second, by soaking different varieties of potato shreds in tea polyphenol solution, the shelf life of V7 and Eugene 885 is significantly extended from 2 to 3 days to more than 21 days compared with those not soaked in tea polyphenol.

[0016] Third, the present invention uses tea polyphenols to protect color, which is natural, safe, pollution-free and degradable, and can replace chemical preservatives in production, and is easily accepted by consumers.

[0017] Fourth, the present invention obtains a color-protecting and antibacterial agent by physically mixing tea polyphenols and mulberry polysaccharides. Mulberry polysaccharides and tea polyphenols work synergistically to significantly extend the shelf life of Holland 15 and Xisen No. 6 potato shreds.

[0018] Fifth, the present invention forms a sustained-release system with multiple components of the color-protecting and antibacterial agent through loading technology, thereby effectively inhibiting enzyme activity. Compared with the tea polyphenols and mulberry polysaccharide formula of Example 4, it has obvious advantages in inhibiting the activity of polyphenol oxidase in potato shreds, maintaining the color of potato shreds, and delaying browning.

[0019] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a graph showing the juice yield of different potato varieties in the present invention; Figure 2 It is a browning index diagram of the shredded potato products processed from different varieties of potatoes in the present invention; Figure 3 This is a sensory score diagram of the shredded potato products processed from different varieties of potatoes in the present invention; Figure 4 A fresh-keeping period diagram of the thousand-thread potato shreds product processed from different varieties of potatoes in the present invention; Figure 5 The sensory quality photos of untreated potato shreds of different varieties of potatoes in the present invention after being left exposed at room temperature for 2 hours; Figure 6 The sensory quality photos of potato shreds of different varieties treated with 0.5 wt% tea polyphenols in the present invention after being sealed and stored at low temperature for 15 days; Figure 7 The sensory quality photos of the potato shreds products of different varieties of potatoes treated with 0.5wt% tea polyphenols in the present invention after being sealed and stored at low temperature for 27 days; in, Figure 6 and Figure 7 The potatoes A to F correspond to variety 1 (Holland 15), variety 2 (Hissen 6), variety 3 (Experimental 1), variety 4 (Cooperation 88), variety 5 (Eugene 885), and variety 6 (V7). DETAILED DESCRIPTION

[0021] The present invention is further described in detail below in conjunction with embodiments so that those skilled in the art can implement the invention with reference to the description.

[0022] It should be noted that the experimental methods described in the following embodiments are conventional methods unless otherwise specified, and the reagents and materials can be obtained from commercial channels unless otherwise specified.

[0023] According to production experience, after slicing potatoes, potatoes with lower juice yield are more suitable for processing shredded potato. In order to screen out potato varieties that can be used to process shredded potato, the present invention investigates the juice yield of potato slices of multiple varieties (Holland 15, Xisen No. 6, Experimental No. 1, Cooperation 88, Eugene 885, V7, etc.), and the specific operation is as follows: After slicing potatoes of multiple varieties, potato slices of different varieties were obtained. Three slices of potato slices of each variety were randomly selected, and the surface juice was absorbed with absorbent filter paper. The mass before and after the absorbent filter paper was absorbed and the surface area of ​​the potato slice section were recorded. The juice yield of the potato sections of different varieties was calculated according to the following formula, and the average value was taken: Juice yield (mg / cm 2 ) = (m1-m0) / A×100% Where: m0 is the initial mass of the absorbent filter paper (g), m1 is the mass of the absorbent filter paper after absorbing the juice (g), A is the surface area of ​​the potato slice (cm 2 ).

[0024] Screening found that 6 varieties of potato slices had low juice yields, all less than 15%, and could be used to process shredded potato. Figure 1 As shown, variety 1 is Holland 15, variety 2 is Xisen 6, variety 3 is Experimental 1, variety 4 is Cooperation 88, variety 5 is Eugene 885, and variety 6 is V7. Among them, the juice yield of potato slices of variety 5 (Eugene 885) and variety 6 (V7) is lower. The specific juice yield results of potato slices of each variety are shown in Tables 1 and Figure 1 As shown: Table 1 Juice yield of potato slices of various varieties <Tea polyphenols concentration screening> The long-term fresh-keeping storage method of thousand-thread potato shreds comprises the following steps: Step 1: Wash V7 potatoes, immerse them in running water, peel them, and cut them into potato shreds; Step 2: Soak the potato strips in the tea polyphenol solution for 5 minutes; The concentrations of tea polyphenols solutions were 0.125 wt%, 0.25 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, and 2 wt%, respectively; Step 3: Drain the water, seal the fresh-cut PET boxes, and store at 4°C.

[0025] The shredded potato products soaked in tea polyphenols of various concentrations were observed and scored for sensory quality. The sensory quality scores of the shredded potato products soaked in 0.5-1wt% tea polyphenols were all higher than 80 points after storage for 14 days, which was the best. The sensory quality of the shredded potato products soaked in 2 wt% tea polyphenols was second best, while the sensory quality scores of the shredded potato products soaked in 0.125 wt%, 0.25 wt% and 1.5wt% tea polyphenols were significantly lower than 80 points, which showed that they lost their commercial quality.

[0026] Based on the above experimental results, from the perspective of enterprise production costs, the preferred tea polyphenol concentration is 0.5 wt%.

[0027] <Example 1> The long-term fresh-keeping storage method of thousand-thread potato shreds comprises the following steps: Step 1: After washing, immersing V7 potatoes in running water, peeling, and cutting into potato shreds; Step 2: Soak the potato shreds in a 0.5 wt% tea polyphenols solution for 5 min.

[0028] Step 3: Drain the water, seal the fresh-cut PET boxes, and store at 4°C.

[0029] <Blank Group> The long-term fresh-keeping storage method of thousand-thread potato shreds comprises the following steps: Step 1: After washing, immersing V7 potatoes in running water, peeling, and cutting into potato shreds; Step 2: Soak the potato strips in clean water for 5 minutes; Step 3: Drain the water, seal the fresh-cut PET boxes, and store at 4°C.

[0030] <Control group 1> The long-term fresh-keeping storage method of thousand-thread potato shreds comprises the following steps: Step 1: After washing, immersing V7 potatoes in running water, peeling, and cutting into potato shreds; Step 2: Soak the potato strips in 0.2 wt% citric acid for 5 min; Step 3: Drain the water, seal the fresh-cut PET boxes, and store at 4°C.

[0031] <Control group 2> The long-term fresh-keeping storage method of thousand-thread potato shreds comprises the following steps: Step 1: After washing, immersing V7 potatoes in running water, peeling, and cutting into potato shreds; Step 2: 100 mg·L of potato shreds -1 Sodium hypochlorite solution was used to immerse the samples for 5 min, and then 30 mg·L -1 Soak in sodium hypochlorite solution for 5 min; Step 3: Drain the water, seal the fresh-cut PET boxes, and store at 4°C.

[0032] <Control group 3> The long-term fresh-keeping storage method of thousand-thread potato shreds comprises the following steps: Step 1: After washing, immersing V7 potatoes in running water, peeling, and cutting into potato shreds; Step 2: 100 mg·L of potato shreds -1 Sodium hypochlorite solution was used to immerse the samples for 5 min, and then 30 mg·L -1 Soak in sodium hypochlorite solution for 5 min, then soak in 0.2 wt% citric acid solution for 5 min; Step 3: Drain the water, seal the fresh-cut PET boxes, and store at 4°C.

[0033] <Browning Index Test> 1.1. Determination basis According to the degree of browning of the potato shreds, the browning of the potato shreds is divided into 5 levels, specifically: Level 0: no browning; Level 1: Discoloration spots appear, slight discoloration; Level 2: The color turns pink or gray, and the browning area is 20%~35%; Level 3: The color changes to reddish brown or dark gray, and the browning area is no more than 50%; Level 4: The color changes to black or dark brown and the area is greater than 50%.

[0034] When all the potato shreds show level 1 browning or 50% of them show level 2 browning, that is, the browning index is greater than 25%, they are no longer accepted by consumers.

[0035] 1.2 Determination method For Example 1, the blank group and the control groups 1 to 3, 3 boxes were respectively drawn from each group each time, and the browning level and the number of shredded potato roots corresponding to each level were recorded to calculate the browning index, wherein the browning index = Σ (browning level × the number of shredded potato roots corresponding to the level) / (highest level × the total number of shredded potato roots) × 100%, and the maximum number of days when the browning index of each group of shredded potato products was ≤ 25% (accepted by consumers) was counted, as shown in Table 2 below: Table 2 Maximum number of days when the browning index of each group of potato shreds products is ≤25% According to the data in Table 2, the maximum number of days when the browning index of the shredded potato product obtained in Example 1 is ≤25% is significantly longer than that of the blank group and the control group 1-3, indicating that the shredded potato soaked in the color-protecting and antibacterial agent of tea polyphenols can significantly slow down the browning of the shredded potato, and the browning effect is better than that of citric acid, sodium hypochlorite and the combination of citric acid and sodium hypochlorite, and the shredded potato is still accepted by consumers after being stored at low temperature for 27 days. The reason is that tea polyphenols contain catechins, anthocyanins, flavonols and phenolic acids, among which catechins have antioxidant properties and can effectively control the oxidative browning of the shredded potato.

[0036] <Bacterial inhibition test> Microbial control of fresh-cut fruit and vegetable products is very important. Generally, the total colony count and the MPN value of Escherichia coli are mainly investigated. Within 0 to 14 days of sealed storage at 4°C, the shredded potato products of Example 1, the blank group, and the control groups 1 to 3 were extracted, and the MPN value and the total colony count of Escherichia coli were detected with reference to GB4789.2-2016 and GB4789.3-2016 standards. The results are shown in Tables 3 and 4 below: Table 3 MPN values ​​of Escherichia coli in each group of shredded potato products ( / g) Table 4 Total colony counts of potato shreds in each group (CFU / g) According to the data in Table 3, no Escherichia coli was detected in Example 1, which had an antibacterial effect, and was comparable to the inhibitory effects of Control Group 1, Control Group 2 and Control Group 3 on Escherichia coli. However, the tea polyphenols used in Example 1 were plant extracts, which were safe and did not pose a risk of carcinogenesis. According to the data in Table 4, in terms of the total colony count, the total colony count of Example 1 with a storage period of ≥8 d is smaller than that of the control group 1-3 with a corresponding number of days, indicating that tea polyphenols can effectively inhibit the reproduction and growth of colonies on the potato shreds product, and when the storage period is ≥8 d, the antibacterial effect of tea polyphenols is better than that of citric acid, sodium hypochlorite and the combination of citric acid and sodium hypochlorite.

[0037] <Example 2> The long-term fresh-keeping storage method of thousand-thread potato shreds comprises the following steps: Step 1: After washing the potatoes, immerse them in running water to peel them and cut them into potato shreds; Among them, the potato varieties are variety 1 (Holland 15), variety 2 (Sisen 6), variety 3 (Experimental 1), variety 4 (Cooperation 88), and variety 5 (Eugene 885); Step 2: soak the potato strips in a 0.5 wt% tea polyphenol solution for 5 min; Step 3: Drain the water, seal the fresh-cut PET boxes, and store at 4°C.

[0038] <Testing of shredded potato products processed from different potato varieties> For the potato shreds of Example 1 and Example 2, 3 boxes were taken from each group each time, and the browning index, sensory quality and shelf life were measured accordingly. The results are as follows: Figures 2~4 As shown, Figures 2~4 Variety 6 in the embodiment is variety V7 in Example 1; 2.1 Browning index of shredded potato products processed from different potato varieties The browning index test results of the shredded potato products processed from different potato varieties are the same as the above-mentioned “browning index test” method. Figure 2 As shown, from Figure 2 It can be seen that during the sealed storage process, the browning index of the potato shreds of variety 5 (Eugene 885) and variety 6 (V7) soaked in tea polyphenols is the smallest. The browning index of the potato shreds of each variety during storage is shown in Table 5 below: Table 5 Browning index of various varieties of shredded potato products during storage (%) 2.2 Sensory quality of shredded potato products made from different potato varieties The sensory quality of shredded potato is scored on a 100-point scale, and the scoring criteria are as follows: 90-100 points: fresh, good, shiny, no browning, firm and crispy, with a unique potato fragrance; 80-89 points: fresh, good quality, slightly pink or gray in some parts, lighter in color, firm and crisp, with a lighter fragrance. 70-79 points: Fair, the browning or graying becomes darker and larger, the texture is relatively hard and medium crisp, the unique fragrance of potatoes disappears, and it is no longer commercially available; 60-69 points: wilting, shrinking, serious browning or graying, further enlargement of the area, decreased hardness and brittleness, no odor; <60 points: Severe water loss and shrinkage, severe browning and blackening, softened texture, poor brittleness, peculiar smell, and inedible.

[0039] Among them, 80 points is the consumption rejection point. If the score is lower than this, it means that the product value is lost.

[0040] Sensory quality scores of potato shreds made from different potato varieties Figure 3 As shown, from Figure 3 It can be seen that during the sealed storage process, the sensory quality scores of the shredded potato products of varieties 5 (Eugene 885) and 6 (V7) soaked in tea polyphenols were better than those of varieties 1 to 4. The sensory quality scores of the shredded potato products of each variety during storage are shown in Table 6 below: Table 6 Sensory quality scores of various varieties of shredded potato products during storage 2.3 Shelf life of shredded potato products made from different potato varieties Determination of the shelf life: The shelf life limit is a sensory quality score of 80 points.

[0041] The shelf life of shredded potato products processed from different potato varieties is as follows Figure 4 As shown, from Figure 4 It can be seen that the shelf life of shredded potato products of variety 5 (Eugene 885) and variety 6 (V7) is 21 days and 27 days respectively. Compared with the shelf life (2-3 days) of shredded potato products of variety 5 (Eugene 885) and variety 6 (V7) not soaked in tea polyphenols, the shelf life of shredded potato products of variety 5 (Eugene 885) and variety 6 (V7) soaked in tea polyphenols can be significantly extended. The specific shelf life of shredded potato products of each variety is shown in Table 7 below: Table 7 Shelf life of various varieties of shredded potato products From the test results of the shelf life, it can be seen that the commodity quality of the potato shreds of variety 5 (Eugene 885) and variety 6 (V7) soaked in tea polyphenols is significantly improved during the shelf life, and the shelf life is extended from the original 2-3 days to more than 21 days.

[0042] like Figure 5 As shown, the potato in a is variety 6 (V7), the potato in b is variety 2 (Xisen No. 6), the potato in c is variety 1 (Holland 15), the potato in d is variety 4 (Cooperation 88), the potato in e is variety 3 (Experiment No. 1), and the potato in f is variety 5 (Eugene 885). In order to more intuitively observe the sensory quality of the thousand-thread potato shreds, the thousand-thread potato shreds were left open at room temperature for 2 h, and photographed and preserved. It was observed that the sensory quality of variety 1 (Holland 15) was the worst, and the sensory quality of varieties 5 (Eugene 885) and variety 6 (V7) was the best. like Figure 6 As shown, in order to observe the sensory quality of shredded potato more intuitively, the shredded potato products of the tea polyphenols treatment group were photographed and stored at low temperature for 15 days. It was observed that the sensory quality of variety 1 (Holland 15) was the worst, while variety 5 (Eugene 885) and variety 6 (V7) had the best sensory quality. like Figure 7 As shown, in order to observe the sensory quality of shredded potato more intuitively, the shredded potato products of the tea polyphenols treatment group were stored in a sealed state at low temperature for 27 days and photographed. It was observed that variety 1 (Holland 15) had the worst sensory quality, while varieties 5 (Eugene 885) and 6 (V7) had the best sensory quality.

[0043] <Example 3> The long-term fresh-keeping storage method of thousand-thread potato shreds comprises the following steps: Step 1: After washing the potatoes, immerse them in running water to peel them and cut them into potato shreds; Among them, the potato varieties are variety 1 (Holland 15), variety 2 (Hissen 6), variety 3 (Experimental 1), variety 4 (Cooperation 88), variety 5 (Eugene 885), and variety 6 (V7); Step 2: Soak the potato strips in a color-protecting and antibacterial agent for 5 minutes; Step 3: Drain the water, seal the fresh-cut PET boxes, and store at 4°C.

[0044] The preparation method of the color-protecting and antibacterial agent comprises the following steps: 5 g of tea polyphenols and 10 g of mulberry polysaccharides, measured by mass, were mixed, water was added to make up to 1000 g, and the mixture was stirred and dissolved under shade to obtain the color-protecting and antibacterial agent.

[0045] <Control group 4> The long-term fresh-keeping storage method of thousand-thread potato shreds comprises the following steps: Step 1: After washing the potatoes, immerse them in running water to peel them and cut them into potato shreds; Among them, the potato varieties are variety 1 (Holland 15), variety 2 (Hissen 6), variety 3 (Experimental 1), variety 4 (Cooperation 88), variety 5 (Eugene 885), and variety 6 (V7); Step 2, soaking the potato shreds in a 1 wt% mulberry polysaccharide solution for 5 min; Step 3: Drain the water, seal the fresh-cut PET boxes, and store at 4°C.

[0046] <Shelf life of shredded potato products made from different potato varieties processed using different methods> The same determination method as the above "Determination of the shelf life" was used to determine the shelf life of multiple varieties of shredded potato obtained by the tea polyphenol-mulberry polysaccharide treatment of Example 3 and the mulberry polysaccharide treatment of Control 4, and the shelf life of multiple varieties of shredded potato treated with tea polyphenols in Example 2 and Example 1 was compared accordingly. The results are shown in Table 8 below: Table 8 Shelf life of shredded potato products in different treatment groups (d) variety Tea polyphenols treatment group Tea polyphenols-mulberry polysaccharide treatment group Mulberry polysaccharide treatment group Variety 1 1 6 2 Variety 2 6 10 3 Variety 3 12 13 3 Variety 4 6 8 4 Variety 5 21 22 4 Variety 6 27 28 5 According to the data in Table 8, the shredded potato products of varieties 1 and 2 processed in Example 3 have a significantly prolonged shelf life compared with the shredded potato products of the corresponding varieties processed in Example 2, indicating that soaking in the color-protecting and antibacterial agent compounded with mulberry polysaccharides and tea polyphenols is significantly better than soaking in tea polyphenol solution alone for prolonging the shelf life of shredded potato products of varieties 1 and 2. The reason for this is that under the physical mixture of tea polyphenols and mulberry polysaccharides, mulberry polysaccharides and tea polyphenols work synergistically to prolong the shelf life of shredded potato products of Holland 15 and Xisen No. 6.

[0047] <Example 4> The long-term fresh-keeping storage method of thousand-thread potato shreds comprises the following steps: Step 1: After washing the potatoes, immerse them in running water to peel them and cut them into potato shreds; Among them, the potato varieties are variety 1 (Holland 15), variety 2 (Hissen 6), variety 3 (Experimental 1), variety 4 (Cooperation 88), variety 5 (Eugene 885), and variety 6 (V7); Step 2: Soak the potato strips in a color-protecting and antibacterial agent for 5 minutes; Step 3: Drain the water, seal the fresh-cut PET boxes, and store at 4°C.

[0048] The preparation method of the color-protecting and antibacterial agent comprises the following steps: 5 g of tea polyphenols and 20 g of mulberry polysaccharides, measured by mass, were mixed, water was added to make up to 1000 g, and the mixture was stirred and dissolved under shade to obtain the color-protecting and antibacterial agent.

[0049] <Example 5> Preparation of color-protecting and antibacterial agent: Tea polyphenols (calculated as catechins) and mulberry polysaccharides of different masses (calculated as β-1,4-glucan, with an average molecular size of Mw = 3.5×10 4 Da, arabinose side chain content of 1.0%, blocking substrate contact by steric hindrance) was dissolved in an appropriate amount of water using a 20°C low-temperature, light-protected dissolution process, and the pH value of the solution was adjusted to 6.0 to obtain multiple solutions; Epigallocatechin gallate (to preferentially occupy the active center of polyphenol oxidase), chelated zinc citrate (to inhibit the copper ion site of PPO), chitosan, rosmarinic acid, and ε-polylysine are added to multiple solutions and stirred evenly, and then a sustained-release system is formed by nanofiber loading technology. The nanofiber is prepared by compounding chitosan and sodium alginate. The specific steps are as follows: Dissolve chitosan and sodium alginate in an acetic acid solution at a mass ratio of 2.5:1 to form a spinning solution with a mass concentration of 3%; The five active ingredients are uniformly dispersed in the spinning solution; The fibers were spun by an electrospinning machine at a voltage of 20 kV and a receiving distance of 15 cm; After drying, a nanofiber membrane loaded with active ingredients is formed. The average diameter of the nanofibers is 50 nm. The nanofiber membrane is a chitosan / sodium alginate interpenetrating network structure IPN. Dynamic cross-linking sites are formed by intermolecular hydrogen bonds. The membrane porosity is 70% and the initial pore size is 35 nm. Malic acid was added to the system to adjust the pH buffering capacity; Color-protecting and antibacterial agent A and color-protecting and antibacterial agent B were obtained respectively, wherein the concentration of tea polyphenols in color-protecting and antibacterial agent A and color-protecting and antibacterial agent B was 0.5 wt%, the concentration of chitosan was 0.8 wt%, the concentration of rosmarinic acid was 0.3 wt%, the concentration of ε-polylysine was 0.1 wt%, the concentration of epigallocatechin gallate in color-protecting and antibacterial agent A was 0.75 wt%, and the concentration of mulberry polysaccharide was 2.0 wt%, and the concentration of epigallocatechin gallate in color-protecting and antibacterial agent B was 0.85 wt%, and the concentration of mulberry polysaccharide was 1.8 wt%.

[0050] The potato shreds prepared from potato varieties Holland No. 15 and Xisen No. 6 were soaked and other operations were performed using the method of Example 1 to obtain different potato shreds products (Group A and Group B). The potato shreds prepared from Holland No. 15 and Xisen No. 6 in Example 4 were stored at 4°C and 75% RH. The L value, a value, and b value of the potato shreds products were determined using a colorimeter at 0 d, 7 d, 14 d, 21 d, and 28 d of storage, and the polyphenol oxidase activity of the potato shreds products was determined using spectrophotometry. The results are shown in Tables 9 and 10 below: Table 9 L value, a value, and b value of potato shreds products in different treatment groups at different times According to the data in Table 9, in Example 5, group A (0.75 wt% epigallocatechin gallate + 2.0 wt% mulberry polysaccharide) and group B (0.85 wt% epigallocatechin gallate + 1.8 wt% mulberry polysaccharide) is significantly better than Example 4 in inhibiting color change, indicating that the potato shreds products of Group A and Group B can better maintain brightness and color stability, and effectively delay the darkening of color and browning; in Group A, the color stability of Holland No. 15 is better than that of Xisen No. 6, and its L value, a value and b value change range are smaller, while in Group B, Xisen No. 6 has better color retention effect, indicating that different color protection and antibacterial agent formulas have different color retention effects on different varieties of potatoes; in summary, the color protection and antibacterial agents A and B play a key role in protecting the color of fresh-cut potatoes through the synergistic effect of multiple ingredients to form a sustained-release system. Compared with the color protection and antibacterial agent of Example 4 (tea polyphenols + mulberry polysaccharide), the formulas of Group A and Group B show significant advantages in maintaining the color of potato shreds, and can more effectively delay the color deterioration of potato shreds during storage.

[0051] Table 10 Polyphenol oxidase activity of potato shreds in different treatment groups at different times According to the data in Table 10, the inhibitory effect of Group A and Group B on the activity of polyphenol oxidase was significantly stronger than that in Example 4, indicating that the components such as epigallocatechin gallate and chelated zinc citrate in Group A and Group B effectively inhibited the activity of PPO and slowed down the browning reaction; the initial polyphenol oxidase activity of different varieties was different, with the initial activity of Holland No. 15 being 120 U / g and that of Heeson No. 6 being 200 U / g. U / g, under the same treatment, group A and group B have similar inhibition trends on enzyme activities of different varieties, and both can better control the rate of enzyme activity decline. In group A, the rate of enzyme activity decline of Holland No. 15 is faster than that of Xisen No. 6, while in group B, on the contrary, the decline of enzyme activity of Xisen No. 6 is more obvious, which further reflects the difference in the inhibition of enzyme activity of different varieties of potatoes by different formulas; in summary, the sustained-release system formed by the nanofiber loading technology of multiple ingredients in color-protecting and antibacterial agents A and B can accurately act on the active center and copper ion site of polyphenol oxidase, thereby effectively inhibiting enzyme activity. Compared with the single tea polyphenol and mulberry polysaccharide formula in Example 3, group A and group B have obvious advantages in inhibiting the activity of polyphenol oxidase of fresh-cut potatoes and delaying browning, which proves the effectiveness of the formula and the sustained-release system.

[0052] According to another embodiment of the present invention, the preparation and application of the color-protecting and antibacterial agent of Dutch No. 15 potato shreds are as follows: Weigh 0.75 g of epigallocatechin gallate (EGCG) and 2.0 g of mulberry polysaccharide, and prepare a total of 100 g of solution using deionized water as solvent; The weighed EGCG and mulberry polysaccharide were added to deionized water in sequence and stirred in a 45°C constant temperature water bath until completely dissolved; Adjust the solution pH to 4.0-4.5 (using food grade citric acid); Potato shreds processing: Dutch No. 15 potatoes were selected, washed, peeled, and cut into thin strips with a cross-section of 1.5 × 1.5 mm; Immerse the cut potato strips in the color-protecting and antibacterial agent solution at a solid-liquid ratio of 1:3 (w / w) at 10-15°C for 20 min. After draining, vacuum pack and store in a cold storage at 4±1℃.

[0053] Effect verification: The control group (untreated group) showed obvious browning (ΔE>5) after storage for 72 h, and the total number of colonies exceeded 10 4 CFU / g; after storage for 21 days, the color of the treated group in this example was stable (ΔE<2), the total colony count remained ≤10² CFU / g, and the texture crispness retention rate was >85%.

[0054] According to another embodiment of the present invention, the preparation and application of the color-protecting and antibacterial agent of Xisen No. 6 potato shreds are as follows: Weigh 0.85 g of epigallocatechin gallate (EGCG) and 1.8 g of mulberry polysaccharide, and prepare a solution according to the same process as in Example 1.

[0055] According to the characteristics of polyphenol oxidase in Xisen No. 6, the soaking temperature was raised to 18-20℃ and the soaking time was shortened to 15min. Before packaging, a centrifugal dehydration process (800 rpm, 2 min) was added to reduce the surface water activity.

[0056] HPLC detection showed that mulberry polysaccharide could delay the degradation rate of EGCG, and the effective ingredient retention rate reached 92.3% after 21 days; Compared with the single use of EGCG or mulberry polysaccharide, the antibacterial efficiency of the complex increased by 2.1~3.8 times (Staphylococcus aureus inhibition experimental data).

[0057] Industry application description: This solution is particularly suitable for pre-prepared food processing scenarios in central kitchens. The processed potato shreds are directly used as ready-to-use fresh-cut clean vegetables for cold chain distribution. The shelf life is 2 to 3 times longer than that of traditional treatment solutions using commonly used preservatives such as citric acid, calcium ascorbate, and sodium D-isoascorbate.

[0058] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and the embodiments shown and described herein.

Claims

1. A color-protecting and antibacterial agent for long-term preservation and storage of potato shreds, characterized in that: Contains the following components and process parameters: 0.5~1 wt% tea polyphenols, calculated as catechins; 1-5 wt% of mulberry polysaccharide, calculated as β-1,4-glucan; The mass ratio of tea polyphenols to mulberry polysaccharides is 1:2~5, and a low-temperature, light-proof dissolution process at a temperature of ≤25°C is used. The pH value of the solution is controlled between 5.5 and 6.5; Applicable to Holland 15, Sisen 6, Experiment 1, Cooperation 88, V7, or Eugene 885 potato varieties.

2. The color-protecting and antibacterial agent for long-term preservation and storage of potato shreds according to claim 1, characterized in that: Also includes: 0.7-0.9 wt% epigallocatechin gallate to preferentially occupy the active center of polyphenol oxidase; 0.05-0.1 wt% chelated zinc citrate to inhibit the copper ion sites of PPO; The content of mulberry polysaccharide is 1.8~2.2 wt%, and the average molecular size Mw is: Mw=3.5×10 4 Da, the arabinose side chain content is 0.8~1.2% to block substrate contact through steric hindrance.

3. The color-protecting and antibacterial agent for long-term preservation and storage of potato shreds according to claim 2, characterized in that: Also includes: For Holland No. 15 with PPO activity of 85~120U / g: 0.75 wt% epigallocatechin gallate + 2.0wt% mulberry polysaccharide; For Xisen No. 6 with PPO activity of 150~200U / g: 0.85 wt% epigallocatechin gallate + 1.8wt% mulberry polysaccharide are used.

4. The color-protecting and antibacterial agent for long-term preservation and storage of potato shreds according to claim 1, characterized in that: It also includes the following components and process parameters: 0.3-0.8 wt% chitosan; 0.1~0.3 wt% rosmarinic acid; 0.05~0.1 wt% ε-polylysine; The dissolved tea polyphenols and mulberry polysaccharide solution and five active ingredients, chitosan, rosmarinic acid, and ε-polylysine, form a sustained-release system through nanofiber loading technology, and the nanofiber is prepared by combining chitosan and sodium alginate.

5. The color-protecting and antibacterial agent for long-term preservation and storage of potato shreds according to claim 4, characterized in that: It also contains 0.5-1.5 wt% of malic acid or citric acid to adjust the pH buffering capacity; The nanofibers have an average diameter of 10 to 100 nm, are prepared by electrospinning, and have humidity-responsive release properties; The nanofiber loading technology is achieved by the following steps: Dissolving chitosan and sodium alginate in acetic acid solution to form a spinning solution with a mass concentration of 2-5%; The five active ingredients, tea polyphenols, mulberry polysaccharide solution, chitosan, rosmarinic acid, and ε-polylysine, are uniformly dispersed in the spinning solution; The fibers were spun by an electrospinning machine at a voltage of 15-25 kV and a receiving distance of 10-20 cm; After drying, a nanofiber membrane loaded with active ingredients is formed.

6. The color-protecting and antibacterial agent for long-term preservation and storage of potato shreds according to claim 5, characterized in that: The color protection and antibacterial agent achieves color protection and antibacterial through triple synergistic action: Chitosan forms a physical barrier that inhibits oxygen contact; Tea polyphenols and rosmarinic acid synergistically inhibit the activity of polyphenol oxidase; Mulberry polysaccharides and ε-polylysine synergistically inhibit microbial growth.

7. The color-protecting and antibacterial agent for long-term preservation and storage of potato shreds according to claim 5, characterized in that: The nanofiber membrane is a chitosan / sodium alginate interpenetrating network structure IPN, dynamic cross-linking sites are formed by intermolecular hydrogen bonds, the mass ratio of chitosan to sodium alginate is 2-3:1, the average diameter of the nanofibers is 10-100 nm, the membrane porosity is 60-80%, and the initial pore size is 20-50 nm; Among them, the nanofiber membrane has a humidity-responsive pore size adjustment function. In the humidity range of 50~95%RH, through the reversible swelling of the carboxylic acid group of sodium alginate, the swelling ratio is 1:5~8, and the ionic bond dissociation of the chitosan amino group synergistically acts to achieve a dynamic pore size adjustment range of 10~100 nm.

8. The color-protecting and antibacterial agent for long-term preservation and storage of potato shreds according to claim 7, characterized in that: The dynamic aperture adjustment includes a two-stage control mechanism, specifically: In a high humidity environment of >80%RH, the membrane pore size expands to 80~100 nm, and the release rate of tea polyphenols and ε-polylysine small molecule components increases by 3~5 times; In a low humidity environment of <60%RH, the membrane pore size shrinks to 10~30 nm, forming a physical barrier to delay the release of ingredients.

9. The color-protecting and antibacterial agent for long-term preservation and storage of potato shreds according to claim 8, characterized in that: The concentration maintenance capacity of the nanofiber membrane for tea polyphenols is: under the conventional packaging conditions of 75-85% RH, the concentration fluctuation range of tea polyphenols is ≤±15%, the effective antibacterial concentration is ≥0.03 wt%, and the maintenance time is ≥21 d; The mechanical strength of the nanofiber membrane is 80-120 MPa, the water vapor permeability WVTR can be adjusted in the range of 500-2000 g / (m²·day), and the time to respond to humidity changes is ≤10 min.

10. The color-protecting and antibacterial agent for long-term preservation and storage of potato shreds according to claim 9, characterized in that: The nanofiber membrane is achieved through a gradient release profile: (1) ε-polylysine with a molecular size of <500 Da was released rapidly, with a release rate of >80% completed within 24 h; (2) Tea polyphenols with molecular size of 500-5000 Da were released at a moderate rate, with a release rate of >90% completed within 72 h; (3) Mulberry polysaccharides with molecular size >5000 Da were slowly released, with a release rate of >90% completed within 7 days.

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