Treatment method for improving fresh-keeping effect of fresh-cut eggplants

Abstract

The invention discloses a treatment method for improving the fresh-keeping effect of fresh-cut eggplants, which comprises the following steps: cleaning, pre-cooling and cutting fresh eggplants to obtain fresh-cut eggplants; soaking the fresh-cut eggplants in an anti-browning soaking solution for treatment, and draining off water after the treatment is completed; spraying a film coating liquid on the surface of the drained eggplant; a calcium chloride solution is sprayed on the surfaces of the sprayed eggplants, and the eggplants are air-dried at room temperature until the surfaces do not have obvious moisture; and packaging and storing the treated eggplants. According to the comprehensive fresh-keeping method for the fresh-cut eggplants based on the double-layer coating technology, the first layer is an anti-browning soaking solution, and the problems of browning and texture softening are solved; and the second layer is functional coating spraying liquid and is used for controlling gas exchange and microorganism growth. According to the method, multiple fresh-keeping barrier technologies are effectively integrated, green and natural fresh-keeping components are completely adopted, the shelf life of the fresh-cut eggplants is remarkably prolonged through scientific formula design and a modern food processing technology, and meanwhile good sensory quality and nutritional value are kept.

Description

Technical Field

[0001] The invention relates to the technical field of vegetable preservation, and in particular to a processing method for improving the preservation effect of fresh-cut eggplants. Background Art

[0002] As a convenient and quick form of vegetable, fresh-cut eggplant has been in increasing demand in fresh supermarkets, food distribution and catering industries in recent years. However, the exposed tissue after eggplant cutting is very easy to brown, soften and be contaminated by microorganisms, which seriously limits its commodity value and shelf life. At present, the conventional shelf life of fresh-cut eggplant is usually only 2-5 days, which is far from meeting the needs of modern food circulation and consumption. The main mechanism of browning of fresh-cut eggplant is that polyphenol oxidase (PPO) catalyzes the oxidation of phenolic substances to form quinones, which further polymerize to form brown melanin. Eggplant is rich in phenolic substances such as chlorogenic acid and caffeic acid. After cutting destroys the cell structure, these phenolic substances come into contact with PPO and quickly undergo browning reaction in the presence of oxygen. Browning not only affects the appearance, but also leads to flavor changes, nutritional loss and texture deterioration.

[0003] At present, the commonly used technologies for preserving fresh-cut eggplants mainly include chemical preservative treatment, single anti-browning treatment, modified atmosphere packaging, cold chain and irradiation treatment, and single-layer coating technology. Chemical preservative treatment mainly uses chemical preservatives such as sulfites and potassium sorbate. Although the effect is obvious, consumers generally have concerns about chemical additives. Single anti-browning treatment generally uses reducing agents or acidifiers such as ascorbic acid and citric acid. These methods are simple and easy to implement, but the anti-browning effect is not sustainable enough and the effect on microbial control is limited. Modified atmosphere packaging inhibits browning and microbial growth by controlling the gas composition in the package, but the equipment investment is large and it cannot fundamentally inhibit the activity of browning enzymes. Cold chain and irradiation treatment inhibits enzyme activity and microbial growth through low temperature and irradiation, but cold chain conditions are difficult to always guarantee, and irradiation treatment has the problems of expensive equipment and low consumer acceptance. Single-layer coating technology uses coatings such as pectin and carboxymethyl cellulose to form a physical barrier, but a single coating often cannot solve multiple problems such as browning, microbial growth and texture softening at the same time. These existing technologies have obvious limitations in practical applications, and it is difficult to effectively solve the multiple problems faced by fresh-cut eggplants, such as browning, water loss, texture softening and microbial contamination. In addition, some technologies rely on chemical synthetic preservatives, which do not meet the needs of modern consumers for green and natural food. Summary of the invention

[0004] Based on the problems existing in the background technology, the present invention provides a comprehensive preservation method for fresh-cut eggplant based on double-layer coating technology. The first layer is an anti-browning soaking liquid to solve the problems of browning and texture softening; the second layer is a functional coating spray liquid to control gas exchange and microbial growth. This method effectively integrates multiple preservation barrier technologies, completely adopts green and natural preservation ingredients, and significantly extends the shelf life of fresh-cut eggplant through scientific formula design and modern food processing technology, while maintaining good sensory quality and nutritional value.

[0005] The present invention is implemented by the following technical solutions:

[0006] A processing method for improving the fresh-keeping effect of fresh-cut eggplants comprises the following steps:

[0007] S1. Wash, pre-cool and cut fresh eggplant to obtain fresh-cut eggplant;

[0008] S2. Immerse the fresh-cut eggplant in an anti-browning soaking solution and drain the water after the treatment;

[0009] S3. Spray the coating liquid on the surface of the drained eggplant;

[0010] S4. Spray the calcium chloride solution on the surface of the eggplant after spraying, and air-dry at room temperature until there is no obvious moisture on the surface;

[0011] S5. Packaging and storing the processed eggplants;

[0012] Wherein, the anti-browning soaking solution comprises ascorbic acid, citric acid, chitosan, EDTA-2Na, calcium lactate, tea polyphenols, monoglyceride and ascorbyl palmitate;

[0013] The coating liquid comprises carboxymethyl cellulose, sodium alginate, glycerol, monoglyceride, rosemary extract, ε-polylysine, clove microcapsules and nisin.

[0014] Furthermore, the mass percentages of the components in the anti-browning soaking solution are: ascorbic acid 0.8-1.2%, citric acid 0.3-0.7%, chitosan 0.6-1.0%, EDTA-2Na 0.03-0.07%, calcium lactate 0.2-0.4%, tea polyphenols 0.1-0.3%, monoglyceride 0.2-0.4%, ascorbyl palmitate 0.1-0.3%, and the balance is water.

[0015] The components in the anti-browning soaking solution interact with each other to form a multi-level, multi-mechanism browning inhibition system. Among them, ascorbic acid, as a strong reducing agent, can directly reduce quinone substances generated by polyphenol oxidase (PPO) to phenolic compounds, blocking the browning reaction chain; citric acid creates an acidic environment that is not conducive to PPO activity by lowering the pH value, and at the same time has weak metal ion chelating ability; EDTA-2Na, as a specific metal ion chelating agent, can strongly chelate the copper ions in the active center of PPO and directly inhibit enzyme activity; these three components work together to synergistically inhibit enzymatic browning reactions from three levels: pH regulation, metal ion chelation, and quinone reduction. At the same time, after dissolving under acidic conditions, chitosan can form a translucent protective film on the cut surface of eggplant, effectively blocking oxygen, and its amino group can combine with polyphenols to further reduce the substrates involved in the browning reaction; tea polyphenols not only have strong antioxidant activity, but can also combine with PPO to form an inactive complex, enhancing the enzyme inhibition effect; ascorbyl palmitate, as a fat-soluble antioxidant, can be embedded in the cell membrane structure to provide lasting protection, making up for the disadvantage of easy loss of water-soluble ascorbic acid, and forming a water-soluble / fat-soluble dual antioxidant protection network with ascorbic acid and tea polyphenols; the calcium ions of calcium lactate can combine with pectin in the cell wall to form calcium pectate, enhancing tissue hardness and slowing down softening; monoglyceride as an emulsifier ensures that ascorbyl palmitate can be evenly dispersed in the aqueous phase, thereby improving the overall anti-browning efficiency.

[0016] Furthermore, the specific preparation method of the anti-browning soaking liquid comprises the following steps:

[0017] a. Dissolve ascorbic acid, citric acid and EDTA-2Na in part of the water;

[0018] b. Dissolve chitosan in 1% acetic acid solution and stir until completely dissolved;

[0019] c. Dissolve tea polyphenols in a small amount of warm water;

[0020] d. Melt and mix ascorbyl palmitate and monoglyceride at 60-70°C, and add a small amount of warm water under high-speed stirring to form colostrum;

[0021] e. Dissolve calcium lactate in a small amount of water;

[0022] f. Mix the above solutions in order, add the remaining water at last, stir evenly, and you have the product.

[0023] Furthermore, the fresh-cut eggplant is immersed in the anti-browning soaking liquid for 3-5 minutes.

[0024] Furthermore, the mass percentage of each component in the coating liquid is: carboxymethyl cellulose 1.0-2.0%, sodium alginate 0.3-0.7%, glycerol 0.8-1.2%, monoglyceride 0.2-0.4%, rosemary extract 0.1-0.2%, ε-polylysine 0.01-0.03%, clove microcapsule 0.02-0.04%, nisin 0.03-0.07%, and the balance is water.

[0025] Furthermore, the preparation method of clove microcapsules is specifically as follows: adding 10-15 parts of inulin, 15-18 parts of β-cyclodextrin and 5-10 parts of pectin to 100 parts of pure water by weight, stirring to dissolve, and standing overnight to obtain a completely hydrated wall material solution; adding 0.5-2 parts of clove essential oil to 30 parts of anhydrous ethanol, stirring to dissolve, to obtain a core material solution; mixing the wall material solution and the core material solution, stirring evenly to obtain a mixed solution, homogenizing to obtain a clove essential oil emulsion; sending the clove essential oil emulsion to a spray dryer for spray drying, and then cooling to room temperature to obtain clove essential oil microcapsules.

[0026] The coating liquid builds an efficient physical barrier and natural antibacterial system. Among them, carboxymethyl cellulose and sodium alginate are compounded to form a composite membrane structure with superior performance: carboxymethyl cellulose provides basic film-forming properties and suitable gas permeability, while sodium alginate forms a three-dimensional network structure through subsequent calcium chloride cross-linking, which significantly enhances the mechanical strength and moisture barrier properties of the membrane; glycerol is used as a plasticizer, maintaining a ratio of about 1:2 with the total colloid (CMC + sodium alginate), ensuring the formation of a flexible and non-cracking membrane layer; monoglyceride reduces the surface tension of the solution, improves the spreadability and permeability on the hydrophobic eggplant surface, and promotes the stable dispersion of fat-soluble components in the aqueous phase. In terms of antibacterial, the present invention constructs a full-spectrum natural antibacterial defense line composed of rosemary extract, ε-polylysine, clove microcapsules and nisin: rosemary extract contains a variety of phenolic substances such as rosmarinic acid and carnosic acid, which have strong antioxidant and antibacterial activities, especially the inhibition of aerobic bacteria; ε-polylysine, as a natural polypeptide antibacterial agent, causes leakage of cell contents by destroying the bacterial cell membrane structure; eugenol in clove microcapsules has a broad-spectrum antibacterial activity, especially against molds and yeasts, and microencapsulation technology achieves a sustained release effect of active ingredients; nisin, as an antibacterial peptide produced by lactic acid bacteria fermentation, has a specific killing effect on Gram-positive bacteria. These four antibacterial ingredients cover different antibacterial spectra, and through synergistic effects, achieve broad-spectrum and efficient microbial control at a lower total concentration, and avoid sensory effects. After the coating liquid is sprayed, it is cross-linked by spraying calcium chloride solution. Sodium alginate quickly combines with calcium ions to form a gel network, which significantly improves the physical strength and stability of the membrane and optimizes the gas permeability. It controls water evaporation while allowing moderate gas exchange, avoiding the production of unpleasant flavors caused by anaerobic respiration.

[0027] Furthermore, the specific preparation method of the coating liquid comprises the following steps:

[0028] a. Slowly add carboxymethyl cellulose into a portion of 70°C hot water and stir until completely dissolved;

[0029] b. Add sodium alginate to a small amount of water and stir until completely dissolved;

[0030] c. Mix the carboxymethyl cellulose solution and the sodium alginate solution, stir evenly, and cool to 50°C;

[0031] d. adding glycerol and monoglyceride to the mixed solution;

[0032] e. Continue to cool down to below 40°C, add rosemary extract, ε-polylysine, clove microcapsules and nisin, and finally add the remaining water, stir evenly, and let it stand to exhaust.

[0033] Furthermore, in step S3, the spraying amount of the coating liquid is 2-5 mL / kg, the temperature of the coating liquid during spraying is 35-45° C., and the spraying pressure is 0.3-0.6 MPa.

[0034] Furthermore, the concentration of the calcium chloride solution in step S4 is 0.5-1.0%, and the spraying amount is 3-8 mL / m2.

[0035] Furthermore, the eggplants packaged in step S5 are stored at a low temperature, with the storage temperature being 4±1°C.

[0036] Beneficial effects of the present invention:

[0037] The present invention uses an anti-browning soaking liquid and a coating liquid to form a double-layer protection mechanism during the preservation process of fresh-cut eggplants: the first layer of anti-browning soaking treatment specifically solves the enzymatic browning problem of the eggplant section, while maintaining tissue hardness through calcium lactate; the second layer of coating treatment mainly controls water evaporation and microbial growth, and the two complement each other. During the treatment process, the anti-browning soaking treatment is first carried out to allow the antioxidant components to fully penetrate into the section tissue; then the coating treatment is carried out to form a physical barrier on the surface to lock in moisture and block external microorganisms; finally, calcium chloride cross-linking is used to strengthen the coating performance to form a stable protection. This multi-level, multi-mechanism synergistic protection system enables the present invention to significantly extend the shelf life of fresh-cut eggplants while maintaining good sensory quality and nutritional value, providing a comprehensive and efficient solution for the preservation of fresh-cut eggplants. DETAILED DESCRIPTION

[0038] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments, but the protection scope of the present invention is not limited to the following embodiments.

[0039] The preparation method of the clove microcapsules used in the embodiments and comparative examples of the present invention is as follows: 12 parts of inulin, 16 parts of β-cyclodextrin and 8 parts of pectin are added to 100 parts of pure water by weight, stirred to dissolve, and allowed to stand overnight to obtain a completely hydrated wall material solution; 1 part of clove essential oil is added to 30 parts of anhydrous ethanol, stirred to dissolve, and a core material solution is obtained; the wall material solution and the core material solution are mixed, stirred evenly to obtain a mixed solution, and homogenized to obtain a clove essential oil emulsion; the clove essential oil emulsion is sent to a spray dryer for spray drying, and then cooled to room temperature to obtain clove essential oil microcapsules.

[0040] Example 1

[0041] A processing method for improving the fresh-keeping effect of fresh-cut eggplants comprises the following steps:

[0042] Step S1: Take fresh and ripe eggplants, clean the surface dirt in running water, soak them in 0.01% sodium hypochlorite solution for 1 minute for disinfection, and then rinse them with clean water. Precool the eggplants to 10° C., and then use a sharp stainless steel knife to evenly cut the eggplants into 5 mm thick slices.

[0043] Step S2: preparing an anti-browning soaking solution; the mass percentage of each component is: ascorbic acid 1.0%, citric acid 0.5%, chitosan 0.8%, EDTA-2Na 0.05%, calcium lactate 0.3%, tea polyphenols 0.2%, monoglyceride 0.3%, ascorbyl palmitate 0.2%, and the balance is water.

[0044] The specific preparation steps are as follows: dissolving ascorbic acid, citric acid and EDTA-2Na in part of the water; dissolving chitosan in 1% acetic acid solution and stirring until completely dissolved; dissolving tea polyphenols in warm water; melting and mixing ascorbyl palmitate and monoglyceride at 65°C, and adding warm water under high-speed stirring conditions of 12000r / min to form colostrum; dissolving calcium lactate in water; mixing the above solutions in order, and finally adding the remaining water and stirring evenly to obtain the anti-browning soaking solution.

[0045] Soak the sliced ​​eggplant in the anti-browning soaking solution for 4 minutes, making sure the slices are fully submerged and gently stirring to allow for full contact with the soaking solution. When soaking is complete, remove the slices and place them on a stainless steel sieve for 2 minutes to drain any excess liquid.

[0046] Step S3: preparing a coating solution; the mass percentages of the components in the coating solution are: 1.5% carboxymethyl cellulose, 0.5% sodium alginate, 1.0% glycerol, 0.3% monoglyceride, 0.15% rosemary extract, 0.02% ε-polylysine, 0.03% clove microcapsules, 0.035% nisin, and the balance is water.

[0047] The specific preparation steps are: slowly add carboxymethyl cellulose into 70°C hot water and stir until completely dissolved; add sodium alginate into water and stir until completely dissolved; mix the carboxymethyl cellulose solution and the sodium alginate solution, stir evenly, and cool to 50°C; add glycerol and monoglyceride and continue stirring; when the temperature drops below 40°C, add rosemary extract, ε-polylysine, clove microcapsules and nisin, and finally add the remaining water, stir evenly, and let stand for 15 minutes to exhaust.

[0048] Place the drained eggplants on a stainless steel grid and spray the coating liquid evenly on the surface of the eggplants. The spraying amount is 3 mL / kg. The temperature of the coating liquid during spraying is 40° C. and the spraying pressure is 0.4 MPa.

[0049] Step S4: Prepare 0.8% calcium chloride solution, and use a fine mist sprayer to evenly spray the calcium chloride solution on the surface of the eggplant after spraying the coating liquid, with a spraying amount of 5mL / m2. After spraying, let it stand for 90 seconds to allow the sodium alginate to fully cross-link, and then place the eggplant in an environment of 22°C to air dry for 20 minutes until there is no obvious moisture on the surface.

[0050] Step S5: The processed fresh-cut eggplants are packed into microporous polypropylene packaging bags, with each bag weighing 200 g. The bags are sealed after some air is gently expelled, and then placed in a refrigerator at 4±1° C. for storage.

[0051] Example 2

[0052] The difference between Example 2 and Example 1 lies in the adjustment of the component contents of the anti-browning soaking liquid and the coating liquid.

[0053] Step S1: Same as Example 1.

[0054] Step S2: preparing an anti-browning soaking solution; the mass percentages of the components in the anti-browning soaking solution are: ascorbic acid 1.2%, citric acid 0.6%, chitosan 1.0%, EDTA-2Na 0.06%, calcium lactate 0.4%, tea polyphenols 0.3%, monoglyceride 0.4%, ascorbyl palmitate 0.3%, and the balance is water. The remaining steps are the same as in Example 1.

[0055] Step S3: preparing a coating solution; the mass percentages of the components in the coating solution are: 1.8% carboxymethyl cellulose, 0.6% sodium alginate, 1.2% glycerol, 0.3% monoglyceride, 0.2% rosemary extract, 0.03% ε-polylysine, 0.03% clove microcapsules, 0.06% nisin, and the balance is water. The remaining steps are the same as in Example 1.

[0056] Steps S4-S5: Same as in Example 1.

[0057] The remaining steps are the same as in Example 1.

[0058] Comparative Example 1

[0059] This comparative example adopts the conventional single anti-browning treatment.

[0060] Step S1: Same as Example 1.

[0061] Step S2: prepare a simple anti-browning soaking solution: an anti-browning solution of 1% ascorbic acid + 0.5% citric acid. Soak the cut eggplant slices in the solution for 4 minutes, then take them out and drain the water.

[0062] Step S3-S4: No coating treatment and calcium chloride cross-linking treatment are performed.

[0063] Step S5: directly pack the processed fresh-cut eggplants into microporous polypropylene packaging bags, 200 g per bag, gently expel some air and seal the bags, and store them in a refrigerator at 4±1°C.

[0064] Comparative Example 2

[0065] Based on Example 1, only the first layer of the comparative example is treated with anti-browning immersion.

[0066] Steps S1-S2: Same as in Example 1.

[0067] Step S3-S4: No coating treatment and calcium chloride cross-linking treatment are performed.

[0068] Step S5: Same as Example 1.

[0069] Comparative Example 3

[0070] Based on Example 1, the anti-browning soaking liquid of this comparative example does not include ascorbyl palmitate and monoglyceride.

[0071] Step S1: Same as Example 1.

[0072] Step S2: preparing an anti-browning soaking solution; the mass percentages of the components are: ascorbic acid 1.0%, citric acid 0.5%, chitosan 0.8%, EDTA-2Na 0.05%, calcium lactate 0.3%, tea polyphenols 0.2%, and the balance is water.

[0073] The specific preparation steps are: dissolving ascorbic acid, citric acid and EDTA-2Na in part of the water; dissolving chitosan in 1% acetic acid solution and stirring until completely dissolved; dissolving tea polyphenols in warm water; dissolving calcium lactate in water; mixing the above solutions in order, and finally adding the remaining water and stirring evenly to obtain the anti-browning soaking solution.

[0074] Soak the sliced ​​eggplant in the anti-browning soaking solution for 4 minutes, making sure the slices are fully submerged and gently stirring to allow for full contact with the soaking solution. When soaking is complete, remove the slices and place them on a stainless steel sieve for 2 minutes to drain any excess liquid.

[0075] Steps S3-S5: Same as Example 1.

[0076] Comparative Example 4

[0077] On the basis of Example 1, the coating liquid of this comparative example only contains rosemary extract.

[0078] Steps S1-S2: Same as in Example 1.

[0079] Step S3: preparing a coating solution; the mass percentages of the components in the coating solution are: 1.5% carboxymethyl cellulose, 0.5% sodium alginate, 1.0% glycerol, 0.3% monoglyceride, 0.15% rosemary extract, and the balance is water.

[0080] The specific preparation steps are: slowly add carboxymethyl cellulose to 70°C hot water and stir until completely dissolved; add sodium alginate to water and stir until completely dissolved; mix the carboxymethyl cellulose solution and the sodium alginate solution, stir evenly, and cool to 50°C; add glycerol and monoglyceride and continue stirring; when the temperature drops below 40°C, add rosemary extract and finally add the remaining water, stir evenly, and let stand for 15 minutes to exhaust.

[0081] Place the drained eggplants on a stainless steel grid and spray the coating liquid evenly on the surface of the eggplants. The spraying amount is 3 mL / kg. The temperature of the coating liquid during spraying is 40° C. and the spraying pressure is 0.4 MPa.

[0082] Steps S4-S5: Same as in Example 1.

[0083] Comparative Example 5

[0084] This comparative example is based on Example 1 but does not undergo calcium chloride crosslinking treatment.

[0085] Steps S1-S3: Same as in Example 1.

[0086] Step S4: Without spraying the calcium chloride solution for cross-linking treatment, the eggplants sprayed with the coating solution are directly placed in an environment of 22° C. for air drying for 20 minutes until there is no obvious moisture on the surface.

[0087] Step S5: Same as Example 1.

[0088] Test example

[0089] The fresh-cut eggplants treated in Examples 1-2 and Comparative Examples 1-5 were packaged with polyethylene cling film, and the packaged fresh-cut eggplants were placed in a vertical freezer (4° C., relative humidity 85-90%) for 10 days. Samples were sampled and tested every 2 days. The test items were as follows:

[0090] 1. Browning Index (BI)

[0091] Use a colorimeter to measure the color difference of the sample, L * The value indicates the lightness, a * Value represents green-red, b * The value represents blue-yellow, and BI is calculated as follows:

[0092]

[0093] 2. Weight loss rate

[0094] The mass of fresh-cut eggplants before and after storage was measured, and the weight loss rate was calculated as follows:

[0095]

[0096] Where: m0 is the initial mass of fresh-cut eggplant, g; m z is the mass of fresh-cut eggplant during storage (z = 2, 4, 6, 8, 10 d), g.

[0097] 3. Total colony count

[0098] The determination of the total colony count of fresh-cut eggplant during storage is based on GB 4789.2-2022 "National Food Safety Standard Food Microbiological Examination Determination of Total Colony Count".

[0099] 4. PPO activity

[0100] Weigh 5g of sample, add 15mL of pre-cooled 0.1mol / L phosphate buffer (pH 6.8, containing 1% polyvinylpyrrolidone), homogenize for 2 minutes under ice bath conditions, centrifuge at 12000rpm for 15 minutes at 4℃, and take the supernatant as the crude enzyme solution. With catechol as the substrate, measure the change in absorbance at 420nm, calculate the PPO activity, and the result is expressed as U / g fresh weight.

[0101] 5. POD Activity Assay

[0102] The same crude enzyme solution as that used for the PPO activity assay was used, with guaiacol as the substrate and H2O2 as the oxidant. The change in absorbance at 470 nm was measured and the POD activity was calculated. The results were expressed in U / g fresh weight.

[0103] 6. Total phenol content

[0104] Weigh 2g of sample, add 20mL 80% methanol, homogenize and extract, filter and dilute to 25mL. Take 1mL of extract, add 5mL 10% Folin-Ciocalteu reagent and 4mL 7.5% Na2CO3 solution, mix well and place at room temperature in the dark for 1 hour, measure the absorbance at 765nm, make a standard curve with gallic acid standard solution, calculate the total phenol content of the sample, and the result is expressed in mg / 100g.

[0105] Test results

[0106] Table 1 Effects of different treatments on the browning index of fresh-cut eggplant during storage

[0107]

[0108]

[0109] As can be seen from Table 1, the browning index of each sample during storage showed an upward trend, among which Comparative Example 1 rose the fastest, and the browning index reached 61.82 when stored for 6 days, indicating that the traditional single anti-browning treatment has limited effect on long-term inhibition of browning. The browning index of Example 1 and Example 2 rose slowly, and even after storage for 10 days, the browning index remained at a low level (30.14 and 27.39, respectively), indicating that the double-layer coating treatment of the present invention has a significant inhibitory effect on browning. The browning index of Comparative Example 3 (without ascorbyl palmitate) is significantly higher than that of Example 1, confirming the important role of fat-soluble antioxidants in long-term anti-browning.

[0110] Table 2 Effect of different treatment methods on weight loss rate (%) of fresh-cut eggplant during storage

[0111] Group 2d 4d 6d 8d 10d Example 1 0.68 1.25 1.87 2.46 3.12 Example 2 0.52 0.98 1.45 1.93 2.41 Comparative Example 1 2.35 4.78 7.26 9.58 11.42 Comparative Example 2 1.93 3.85 5.94 7.82 9.65 Comparative Example 3 0.72 1.38 2.05 2.69 3.36 Comparative Example 4 0.71 1.32 1.95 2.57 3.25 Comparative Example 5 1.38 2.74 4.15 5.42 6.75

[0112] As can be seen from Table 2, the weight loss rates of Examples 1 and 2 are significantly lower than those of the comparative examples, especially compared with Comparative Examples 1 and 2. This shows that the double-layer coating treatment can effectively reduce water evaporation, among which the weight loss rate of Example 2 is the lowest, which is only 2.41% after storage for 10 days. The weight loss rate of Comparative Example 5 (without calcium chloride crosslinking treatment) is significantly higher than that of Example 1, reaching 6.75%, which confirms the important role of calcium chloride crosslinking in enhancing the barrier properties of the coating and reducing water loss.

[0113] Table 3 Effects of different treatments on the total colony count (lg CFU / g) of fresh-cut eggplant during storage

[0114]

[0115]

[0116] As can be seen from Table 3, the total colony count of each sample increases with the storage time, but there are obvious differences in the rate of increase. The total colony count of Example 1 and Example 2 increases the slowest, and the total colony counts are 3.89lgCFU / g and 3.65lgCFU / g respectively after storage for 10d. The total colony count of Comparative Example 4 (containing only rosemary extract, without other natural antibacterial ingredients) has exceeded 5.00lgCFU / g after storage for 8d, indicating that a single antibacterial ingredient cannot provide a comprehensive microbial inhibition effect. The multiple natural antibacterial systems (rosemary extract, ε-polylysine, clove microcapsules and nisin) used in Example 1 and Example 2 show excellent synergistic antibacterial effects.

[0117] Table 4 Effects of different treatments on PPO activity (U / g) of fresh-cut eggplant during storage

[0118] Group 0d 2d 4d 6d 8d 10d Example 1 12.6 13.2 14.5 15.8 17.2 18.9 Example 2 11.8 12.3 13.4 14.5 15.7 17.2 Comparative Example 1 28.3 35.6 42.8 49.5 56.2 63.8 Comparative Example 2 12.5 14.7 17.2 19.8 22.5 25.6 Comparative Example 3 13.2 15.6 18.4 21.3 24.7 28.5 Comparative Example 4 12.8 13.9 15.3 16.8 18.5 20.3 Comparative Example 5 12.7 13.8 15.2 16.9 18.8 20.9

[0119] PPO is one of the key enzymes that causes eggplant browning. As can be seen from Table 4, the PPO activity of Examples 1 and 2 remained at a low level during the entire storage period, indicating that the anti-browning soaking solution of the present invention can effectively inhibit the activity of the PPO enzyme. The PPO activity of Comparative Example 1 was significantly higher than that of the other samples, confirming that simple ascorbic acid and citric acid treatment could not effectively inhibit the long-term activity of the PPO enzyme.

[0120] Table 5 Effects of different treatments on POD activity (U / g) of fresh-cut eggplant during storage

[0121] Group 0d 2d 4d 6d 8d 10d Example 1 12.56 13.91 15.69 17.45 19.38 21.40 Example 2 12.34 13.44 14.67 15.99 17.37 19.12 Comparative Example 1 15.81 19.8 23.61 29.02 34.71 39.94 Comparative Example 2 13.15 15.47 18.91 22.59 27.01 32.14 Comparative Example 3 12.59 14.82 17.36 20.14 23.35 26.83 Comparative Example 4 12.69 14.23 16.49 18.60 20.95 23.45 Comparative Example 5 12.63 14.47 16.63 18.94 21.46 24.09

[0122] As can be seen from Table 5, the POD activity of each sample increases with the extension of storage time, but the POD activity of Example 1 and Example 2 has the smallest growth rate. POD is one of the important indicators of oxidative metabolism of fresh-cut products. The double-layer coating treatment of the present invention can effectively regulate oxygen exchange and inhibit oxidative metabolism, so the POD activity increases relatively slowly.

[0123] Table 6 Effects of different treatments on total phenolic content (mg / 100g) of fresh-cut eggplant during storage

[0124] Group 0d 2d 4d 6d 8d 10d Example 1 77.57 75.42 73.77 71.92 70.07 68.02 Example 2 77.95 76.35 74.20 72.61 71.20 69.51 Comparative Example 1 75.76 68.75 60.46 51.83 43.63 36.01 Comparative Example 2 76.35 72.27 67.41 62.68 57.71 52.76 Comparative Example 3 77.07 73.74 70.09 66.55 62.88 59.00 Comparative Example 4 76.92 74.93 72.36 69.78 67.28 64.57 Comparative Example 5 77.62 74.45 71.65 68.71 65.58 62.61

[0125] As can be seen from Table 6, the total phenol content of each sample decreased with the extension of storage time, but the total phenol content retention rate of Example 1 and Example 2 was the highest, and 87.7% and 89.2% of the initial value were maintained after storage for 10 days, respectively. The total phenol content of Comparative Example 1 decreased most significantly, and only 47.5% of the initial value was maintained after storage for 10 days, indicating that the traditional single anti-browning treatment cannot effectively protect phenolic substances from oxidation. The good maintenance of total phenol content is positively correlated with the browning inhibition effect, which confirms the effectiveness of the multiple anti-browning mechanisms of the present invention.

[0126] Through comprehensive analysis of the indicators in Tables 1-6, it can be seen that the double-layer coating preservation method provided by the present invention has a comprehensive preservation effect on fresh-cut eggplant:

[0127] 1. Anti-browning effect: Through multiple inhibition mechanisms (enzyme activity inhibition, reduction protection, physical barrier), the occurrence of browning reaction is effectively controlled. Even after storage for 10 days, the browning index of Example 1 and Example 2 remains at a low level;

[0128] 2. Moisture retention effect: The double-layer coating structure, especially the network structure formed by the cross-linking of sodium alginate and calcium chloride, significantly reduces water evaporation and keeps the weight loss rate at a low level;

[0129] 3. Microbial control effect: Multiple natural antibacterial ingredients work synergistically to effectively inhibit the growth of microorganisms, making the total colony count far below the limit of food safety standards;

[0130] 4. Enzyme activity inhibition effect: effectively inhibits the activity of oxidases such as PPO and POD, slowing down the browning and oxidative metabolism process;

[0131] 5. Nutritional preservation effect: It protects the phenolic substances in eggplant well and reduces nutritional loss.

[0132] In summary, the double-layer coating preservation treatment method for fresh-cut eggplant provided by the present invention achieves comprehensive control of browning, water loss and microbial reproduction through scientific formula design and process optimization, significantly prolongs the shelf life of fresh-cut eggplant, and provides effective technical support for the commercial processing and sales of fresh-cut eggplant.

[0133] Finally, it should be noted that the above-mentioned embodiments only express several implementation methods of the present invention and are not intended to limit the invention. For those skilled in the art, any modification, equivalent replacement, improvement, etc. made without departing from the concept of the present invention should be included in the protection scope of the invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A processing method for improving the preservation effect of fresh-cut eggplant, characterized in that: The following steps are involved: S1. Wash, pre-cool and cut fresh eggplant to obtain fresh-cut eggplant; S2. Immerse the fresh-cut eggplant in an anti-browning soaking solution and drain the water after the treatment; S3. Spray the coating liquid on the surface of the drained eggplant; S4. Spray the calcium chloride solution on the surface of the eggplant after spraying, and air-dry at room temperature until there is no obvious moisture on the surface; S5. Packaging and storing the processed eggplants; Wherein, the anti-browning soaking solution comprises ascorbic acid, citric acid, chitosan, EDTA-2Na, calcium lactate, tea polyphenols, monoglyceride and ascorbyl palmitate; The coating liquid comprises carboxymethyl cellulose, sodium alginate, glycerol, monoglyceride, rosemary extract, ε-polylysine, clove microcapsules and nisin.

2. The processing method according to claim 1, characterized in that: The mass percentages of the components in the anti-browning soaking liquid are: ascorbic acid 0.8-1.2%, citric acid 0.3-0.7%, chitosan 0.6-1.0%, EDTA-2Na 0.03-0.07%, calcium lactate 0.2-0.4%, tea polyphenols 0.1-0.3%, monoglyceride 0.2-0.4%, ascorbyl palmitate 0.1-0.3%, and the balance is water.

3. The processing method according to claim 2, characterized in that: The specific preparation method of the anti-browning soaking liquid comprises the following steps: a. Dissolve ascorbic acid, citric acid and EDTA-2Na in part of the water; b. Dissolve chitosan in 1% acetic acid solution and stir until completely dissolved; c. Dissolve tea polyphenols in a small amount of warm water; d. Melt and mix ascorbyl palmitate and monoglyceride at 60-70°C, and add a small amount of warm water under high-speed stirring to form colostrum; e. Dissolve calcium lactate in a small amount of water; f. Mix the above solutions in order, add the remaining water at last, stir evenly, and you have the product.

4. The processing method according to claim 1, characterized in that: The fresh-cut eggplant is immersed in the anti-browning soaking liquid for 3-5 minutes.

5. The processing method according to claim 1, characterized in that: The mass percentages of the components in the coating liquid are: 1.0-2.0% carboxymethyl cellulose, 0.3-0.7% sodium alginate, 0.8-1.2% glycerol, 0.2-0.4% monoglyceride, 0.1-0.2% rosemary extract, 0.01-0.03% ε-polylysine, 0.02-0.04% clove microcapsules, 0.03-0.07% nisin, and the balance is water.

6. The processing method according to claim 5, characterized in that: The preparation method of clove microcapsules is specifically as follows: 10-15 parts of inulin, 15-18 parts of β-cyclodextrin and 5-10 parts of pectin are added to 100 parts of pure water by weight, stirred to dissolve, and allowed to stand overnight to obtain a completely hydrated wall material solution; Add 0.5-2 parts of clove essential oil to 30 parts of anhydrous ethanol, stir and dissolve, and obtain a core material solution; mix the wall material solution and the core material solution, stir evenly to obtain a mixed solution, and homogenize to obtain a clove essential oil emulsion; send the clove essential oil emulsion to a spray dryer for spray drying, and then cool to room temperature to obtain clove essential oil microcapsules.

7. The processing method according to claim 5, characterized in that: The specific preparation method of the coating liquid comprises the following steps: a. Slowly add carboxymethyl cellulose into a portion of 70°C hot water and stir until completely dissolved; b. Add sodium alginate to a small amount of water and stir until completely dissolved; c. Mix the carboxymethyl cellulose solution and the sodium alginate solution, stir evenly, and cool to 50°C; d. adding glycerol and monoglyceride to the mixed solution; e. Continue to cool down to below 40°C, add rosemary extract, ε-polylysine, clove microcapsules and nisin, and finally add the remaining water, stir evenly, and let it stand to exhaust.

8. The processing method according to claim 1, characterized in that: In step S3, the spraying amount of the coating liquid is 2-5 mL / kg, the temperature of the coating liquid during spraying is 35-45° C., and the spraying pressure is 0.3-0.6 MPa.

9. The processing method according to claim 1, characterized in that: The concentration of calcium chloride solution in step S4 is 0.5-1.0%, and the spraying amount is 3-8 mL / m 2 .

10. The processing method according to claim 1, characterized in that: In step S5, the packaged eggplants are stored at a low temperature, and the storage temperature is 4±1°C.

Images