Fresh-cut eggplant anti-browning and fresh-keeping method based on composite plant extract synergistic heat treatment

Abstract

The invention discloses a fresh-cut eggplant anti-browning and fresh-keeping method based on composite plant extract synergistic heat treatment, and the method comprises the following steps: S1, preparing a composite plant extract comprising the following components: a green tea extract, a rosemary extract, a licorice extract, trehalose, chitosan oligosaccharide, curcumin microcapsules, soybean lecithin, Tween, and the balance of pure water; s2, the fresh-cut eggplants are soaked in a composite plant extracting solution, gradient heat treatment is carried out, and the gradient heat treatment comprises the following three stages of a heat activation permeation stage, a cooling stabilization stage and a cold shock fixation stage; and S3, slightly draining the treated fresh-cut eggplants, and packaging with a preservative film. Through the synergistic effect of various plant extracts and an elaborately-designed gradient heat treatment process, effective inhibition of browning of the fresh-cut eggplants is achieved, the fresh-keeping period is remarkably prolonged, good quality can be kept for 10 days or above under the condition of 4 + / -1 DEG C, and the fresh-cut eggplant fresh-keeping method has a good application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of vegetable preservation, and in particular to a method for preventing fresh-cut eggplants from browning and preserving them based on composite plant extract synergistic heat treatment. Background Art

[0002] As people's demand for food safety and healthy consumption continues to increase, fresh-cut fruits and vegetables are gradually favored by the market because of their convenience, freshness and rich nutrition. However, during the processing of fresh-cut fruits and vegetables, due to cell damage, a series of biochemical reactions are prone to occur, resulting in a rapid decline in the quality of fruits and vegetables, among which the browning phenomenon is particularly prominent. Taking eggplant as an example, the tissue exposed after cutting contains polyphenols and a variety of enzymes, especially polyphenol oxidase (PPO), which catalyzes phenolic substances to generate quinone compounds under the action of oxygen, and then undergoes polymerization to form dark black-brown substances. This browning caused by enzymatic reactions not only seriously affects the appearance, taste and nutritional content of eggplant, but also shortens its shelf life, thereby restricting the application of fresh-cut eggplant in food processing and sales.

[0003] Traditionally, methods to prevent browning of fresh-cut fruits and vegetables mainly include chemical inhibitors, low-temperature storage, antioxidant treatment, and heat treatment. However, chemical inhibitors often have residual risks, which may cause food safety issues; low-temperature storage is limited by energy consumption and logistics costs; the use of a single antioxidant has limited effect and is difficult to meet the market demand for high-quality, natural, and pollution-free preservation technology. Although heat treatment can effectively inhibit the activity of enzymes, it is easy to have a negative impact on the texture and flavor of fruits and vegetables if the processing parameters are not properly controlled. Therefore, there is an urgent need for a new green, efficient, and harmless preservation method that can comprehensively utilize multiple mechanisms to inhibit enzymatic browning and extend the shelf life. Summary of the invention

[0004] Based on the problems existing in the background technology, the present invention provides a method for preventing browning and preserving fresh-cut eggplants based on synergistic heat treatment with a composite plant extract, which combines the composite plant extract with gradient heat treatment technology to achieve the purpose of effectively preventing browning and extending the shelf life through a synergistic effect.

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

[0006] A method for preventing browning and preserving fresh-cut eggplant based on composite plant extract synergistic heat treatment, comprising the following steps:

[0007] S1. Prepare a composite plant extract, comprising the following components by weight percentage: green tea extract 0.5-0.8%, rosemary extract 0.25-0.35%, licorice extract 0.15-0.3%, trehalose 0.35-0.5%, chitosan oligosaccharide 0.35-0.5%, curcumin microcapsule 0.1-0.2%, soy lecithin 0.2-0.35%, Tween 20 0.1-0.15%, and the balance is pure water;

[0008] S2. The fresh-cut eggplants are immersed in the composite plant extract and subjected to a gradient heat treatment, wherein the gradient heat treatment includes the following three stages: a heat activation penetration stage, a cooling stabilization stage, and a cold shock fixation stage;

[0009] S3. Lightly drain the processed fresh-cut eggplants and wrap them with plastic wrap.

[0010] Furthermore, in step S1, the EGCG content in the green tea extract is ≥80%.

[0011] In the composite plant extract of the present invention, a multi-level anti-browning system is formed by using a variety of plant extract ingredients. The EGCG (epigallocatechin gallate) content in green tea extract is as high as more than 80%, which can inhibit the activity of polyphenol oxidase (PPO) through multiple mechanisms: on the one hand, it binds to the enzyme active center as a competitive inhibitor, and on the other hand, it can bind to the copper ion of the enzyme to inactivate it. Phenolic compounds such as rosmarinic acid and carnosic acid in rosemary extract mainly block the propagation of browning reaction by scavenging free radicals. Glycyrrhizic acid and licorice chalcone in licorice extract not only have antioxidant effects, but also can form complexes with polyphenol compounds in eggplant to reduce the probability of oxidation. The synergistic effect of these three plant extracts is reflected in: green tea extract directly inhibits PPO activity, rosemary extract scavenges oxygen free radicals, and licorice extract protects the substrate from oxidation. The three together form a complete anti-browning system that can block browning reactions at the enzyme, free radical and substrate levels. This multiple protection mechanism is more effective than the application of a single ingredient, and can significantly extend the appearance retention time of fresh-cut eggplant, allowing the product to maintain its natural color for a long time without causing adverse browning.

[0012] Furthermore, the specific preparation method of the curcumin microcapsules in step S1 is: adding 10-15 parts of inulin, 15-18 parts of β-cyclodextrin and 5-10 parts of pectin by weight to 100 parts of pure water, stirring to dissolve, and standing overnight to obtain a completely hydrated wall material solution; adding 0.5-2 parts of curcumin powder to 30 parts of anhydrous ethanol and 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 curcumin emulsion; sending the curcumin emulsion to a spray dryer for spray drying, and then cooling to room temperature to obtain curcumin microcapsules.

[0013] Curcumin is a powerful antioxidant, but its poor water solubility and low stability limit its direct application. The microcapsule technology used in the present invention solves this problem through the composite encapsulation of β-cyclodextrin, inulin and pectin. The hydrophobicity inside and hydrophilicity outside of β-cyclodextrin can form an inclusion complex with curcumin to improve its solubility; inulin has good film-forming properties and can delay the release of curcumin; pectin provides an additional protective layer to enhance the stability of the microcapsule. This microcapsule system not only protects curcumin from environmental factors (such as light, heat, and oxygen), but also achieves a sustained release effect of curcumin, making its antioxidant effect last longer.

[0014] Furthermore, the specific preparation method of the composite plant extract in step S1 is: add soybean lecithin and Tween 20 to pure water and emulsify in a 45-50°C water bath for 3-5 minutes, add curcumin microcapsules, homogenize at 8000-10000rpm for 2-3 minutes, add trehalose and chitosan oligosaccharides and stir to dissolve, add green tea extract, rosemary extract and licorice extract in turn and stir to dissolve, and finally use citric acid-sodium citrate buffer to adjust the pH of the system to 5.2-5.5.

[0015] In the present invention, trehalose, as a non-reducing disaccharide, can stabilize proteins and membrane structures by forming hydrogen bonds, protecting cells from dehydration and oxidative damage. In fresh-cut eggplants, trehalose can reduce water loss caused by cutting and maintain tissue turgor and texture. Chitosan oligosaccharides have good film-forming properties and antibacterial activity, and can form a protective film on the surface of eggplants to reduce water evaporation and microbial contamination. The synergistic effect of these two components establishes an effective structural protection system, which not only reduces tissue dehydration and softening, but also provides additional microbial safety protection. In practical applications, this means that fresh-cut eggplants can maintain a crisp and tender taste for a long time, avoiding the common tissue softening or water loss problems in traditional preservation methods. In addition, the antibacterial effect of chitosan oligosaccharides can also reduce microbial growth, extend the shelf life of products, and reduce food safety risks.

[0016] Adjusting the pH of the composite plant extract to a weakly acidic environment of 5.2-5.5 is a key step. The optimum pH of the PPO enzyme is usually between 6-7, and its activity decreases significantly when the pH is below 5.5. Controlling the pH at 5.2-5.5 by a citric acid-sodium citrate buffer system can effectively inhibit PPO activity without producing a noticeable sour taste.

[0017] Furthermore, in step S2, the thickness of the fresh-cut eggplant slices is 4-6 mm.

[0018] Furthermore, the treatment temperature of the heat activated infiltration stage in step S2 is 40-42° C., and the treatment time is 60-90 s.

[0019] Furthermore, in step S2, the temperature reduction and stabilization stage is to reduce the temperature of the system to 30-33° C., and the processing time is 120-180 seconds.

[0020] Furthermore, in step S2, the cold shock fixation stage is to reduce the temperature of the system to 4°C, the total cooling time from 30-33°C to 4°C is 8-10min, and the 4°C holding time is 60-90s.

[0021] Gradient heat treatment is the core innovation of this program, and its working principle is based on the effect of temperature on cell membrane structure and permeability.

[0022] In the heat-activated penetration stage, moderate heat treatment increases the fluidity of the cell membrane, creating an "open window" to promote the penetration of active ingredients. This temperature increases membrane permeability, allowing the active ingredients in the compound plant extract to penetrate deeper into the eggplant tissue. At this stage, antioxidant ingredients such as EGCG in green tea extract and rosmarinic acid in rosemary extract can more effectively pass through the cell membrane with increased permeability and enter the cell to contact target enzymes such as polyphenol oxidase.

[0023] The temperature range of the cooling and stabilization stage is the optimal temperature window for the binding of various inhibitors to PPO. Too high a temperature may cause the enzyme and inhibitor molecules to move too fast, which is not conducive to the formation of a stable complex; while too low a temperature may slow down the binding kinetics. 30-33°C provides an ideal kinetic environment, promoting the effective collision and stable binding of inhibitors such as EGCG with PPO molecules. At this temperature, the cell membrane begins to reorganize, but still maintains a certain degree of permeability, forming a semi-open state, which allows the inhibitor to fully bind to the enzyme, and begins to limit the leakage of cell contents to prevent tissue texture deterioration. At this stage, the complex formed by catechins in green tea extract and PPO tends to be stable, and the complex formed by the components in licorice extract and phenolic substrates is also more solid, laying the foundation for the subsequent cold shock fixation stage.

[0024] The cold shock fixation stage further reduces the enzyme activity and fixes the treatment effect. Low temperature will significantly reduce molecular thermal motion, making the formed PPO-inhibitor complex more stable and reducing the possibility of dissociation. This "locking" effect enables the inhibitory effect to be maintained for a long time and is not easy to lose even during subsequent storage. The low temperature of 4°C allows the cell membrane to re-form a denser structure, significantly reducing the permeability, and the active substances are not easy to lose. At the same time, it also prevents possible harmful substances in the external environment from entering the cells. The present invention adopts slow cooling rather than rapid cooling to avoid damage to the cell membrane due to rapid temperature changes. At this stage, the protective effect of trehalose and chitosan oligosaccharides in the complex extract is also enhanced. The protective network they form is more stable at low temperatures, further protecting the cell structure and function.

[0025] Furthermore, the packaged fresh-cut eggplants are stored at a low temperature, with the storage temperature being 4±1°C.

[0026] Furthermore, the browning prevention and fresh-keeping method can inhibit corrosion, prevent the fresh-cut eggplant from browning and extend the shelf life of the fresh-cut eggplant.

[0027] Beneficial effects of the present invention:

[0028] The green tea extract, rosemary extract, licorice extract and curcumin microcapsules used in the composite plant extract of the present invention establish a multiple protective barrier, which can not only effectively inhibit the activity of polyphenol oxidase, but also scavenge free radicals, thereby blocking the browning reaction chain from the source. The synergistic effect of these natural antioxidants is better than the application of a single ingredient, providing a more lasting anti-browning effect. Secondly, the gradient heat treatment process used in the present invention cleverly utilizes the regulatory effect of temperature changes on cell membrane permeability. The heat-activated permeation stage improves the permeation efficiency of the active ingredients, while the subsequent cooling stabilization and cold shock fixation process help lock these active substances to form long-term protection. The whole set of processes uses natural extracts to replace traditional chemical anti-browning agents, which meets the current food industry's demand for green and safe additives. It can not only effectively extend the shelf life of fresh-cut eggplants, but also maintain the natural flavor and texture characteristics of the product. At the same time, the setting of low-temperature storage conditions further consolidates the treatment effect, so that the entire preservation system forms a complete solution for synergistic enhancement, and provides a technical path with application prospects in the field of fresh-cut fruit and vegetable processing. DETAILED DESCRIPTION

[0029] 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.

[0030] In the examples and comparative examples of the present application, the EGCG content in the green tea extract is 80%.

[0031] In the embodiments and comparative examples of the present invention, the preparation method of curcumin microcapsules is specifically 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 curcumin powder 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 curcumin emulsion; the curcumin emulsion is sent to a spray dryer for spray drying, and then cooled to room temperature to obtain curcumin microcapsules.

[0032] Example 1

[0033] A method for preventing browning and preserving fresh-cut eggplant based on composite plant extract synergistic heat treatment, comprising the following steps:

[0034] S1. Prepare a composite plant extract solution, which includes the following components by weight percentage: 0.7% green tea extract, 0.3% rosemary extract, 0.2% licorice extract, 0.4% trehalose, 0.4% chitosan oligosaccharide, 0.15% curcumin microcapsule, 0.3% soy lecithin, 0.15% Tween 20, and the balance is pure water.

[0035] The specific preparation method of the composite plant extract is as follows: add soybean lecithin and Tween 20 into pure water and emulsify in a 48°C water bath for 4 minutes, add curcumin microcapsules, homogenize at 8000rpm for 3 minutes, add trehalose and chitosan oligosaccharides and stir to dissolve, add green tea extract, rosemary extract and licorice extract in turn and stir to dissolve, and finally use citric acid-sodium citrate buffer to adjust the pH of the system to 5.3.

[0036] S2. Select fresh eggplant, wash it, drain the surface water, and cut it into 5 mm thick slices; immerse the fresh-cut eggplant in the composite plant extract and perform a gradient heat treatment, wherein the gradient heat treatment includes the following three stages:

[0037] Heat-activated infiltration stage: treatment temperature is 40°C and treatment time is 80s.

[0038] Cooling and stabilization stage: the temperature of the system is lowered to 32°C and the processing time is 150s.

[0039] Cold shock fixation stage: the temperature of the system was lowered to 4°C. The total cooling time from 32°C to 4°C was 9 min, and the 4°C holding time was 90 s.

[0040] S3. Lightly drain the processed fresh-cut eggplants, wrap them with polyethylene plastic wrap, and store the packaged fresh-cut eggplants at a low temperature of 4±1°C.

[0041] Example 2

[0042] The difference between this embodiment and embodiment 1 is that the composite plant extract solution prepared in step S1 includes the following components by weight percentage: 0.7% green tea extract, 0.35% rosemary extract, 0.25% licorice extract, 0.45% trehalose, 0.45% chitosan oligosaccharide, 0.15% curcumin microcapsule, 0.3% soy lecithin, 0.15% Tween 20, and the balance is pure water.

[0043] The specific preparation method of the composite plant extract is as follows: add soybean lecithin and Tween 20 into pure water and emulsify in a 48°C water bath for 4 minutes, add curcumin microcapsules, homogenize at 8000rpm for 3 minutes, add trehalose and chitosan oligosaccharides and stir to dissolve, add green tea extract, rosemary extract and licorice extract in turn and stir to dissolve, and finally use citric acid-sodium citrate buffer to adjust the pH of the system to 5.4.

[0044] The remaining steps are the same as in Example 1.

[0045] Comparative Example 1

[0046] In this comparative example, only the composite plant extract is used for treatment. Fresh-cut eggplants are placed in the composite plant extract and treated at room temperature for 5 minutes. The treated samples are lightly drained and packaged with polyethylene plastic wrap. The packaged fresh-cut eggplants are stored at a low temperature of 4±1°C.

[0047] Comparative Example 2

[0048] This comparative example adopts a composite plant extract and a single temperature treatment, that is, the same composite plant extract as in Example 1 is used, treated at 40°C for 3 minutes, and there is no gradient heat treatment process. The treated sample is lightly drained and packaged with polyethylene plastic wrap. The packaged fresh-cut eggplant is stored at a low temperature at a storage temperature of 4±1°C.

[0049] Comparative Example 3

[0050] This comparative example adopts a composite plant extract and a gradient temperature treatment, but the composite plant extract only contains green tea extract, and does not contain rosemary extract and licorice extract; the remaining treatment steps are the same as those in Example 1.

[0051] Comparative Example 4

[0052] This comparative example adopts a composite plant extract and a gradient temperature treatment, but the composite plant extract does not contain curcumin microcapsules, and the remaining treatment steps are the same as those in Example 1.

[0053] Test example

[0054] The fresh-cut eggplants treated in Example 1-2 and Comparative Example 1-4 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:

[0055] 1. Browning Index (BI)

[0056] 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:

[0057]

[0058] 2. Weight loss rate

[0059] The mass of fresh-cut eggplants before and after storage was measured, and the weight loss rate was calculated as follows:

[0060]

[0061] Where: m 0 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.

[0062] 3. Total colony count

[0063] 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".

[0064] 4. PPO activity

[0065] 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.

[0066] 5. POD Activity Assay

[0067] 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.

[0068] 6. Total phenol content

[0069] Weigh 2g of sample, add 20mL of 80% methanol, homogenize and extract, filter and adjust the volume to 25mL. Take 1mL of extract, add 5mL of 10% Folin-Ciocalteu reagent and 4mL of 7.5% Na 2 CO 3 The solution was mixed and placed in the dark at room temperature for 1 hour, and the absorbance at 765 nm was measured. A standard curve was prepared with gallic acid standard solution, and the total phenol content of the sample was calculated. The result was expressed in mg / 100 g.

[0070] Test results

[0071] Table 1 Effects of different treatments on the browning index of fresh-cut eggplant during storage

[0072] Group 0d 2d 4d 6d 8d 10d Example 1 15.52 18.45 22.73 26.51 30.84 35.27 Example 2 15.58 17.92 21.85 25.43 29.68 33.91 Comparative Example 1 15.87 26.31 37.52 48.94 63.87 78.24 Comparative Example 2 15.65 23.46 32.85 42.67 54.32 65.78 Comparative Example 3 15.76 20.83 29.41 37.53 45.68 53.47 Comparative Example 4 15.83 19.74 25.85 32.63 38.92 45.76

[0073] As shown in Table 1, the browning index of Example 1 and Example 2 increased slowly during storage, especially Example 2, whose browning index was only 33.91 after 10 days of storage, indicating that the appropriate increase in the concentration of rosemary extract and licorice extract in the composite plant extract further improved the effect of inhibiting browning. In contrast, the browning index of Comparative Example 1 (only treated with composite plant extract, no heat treatment) and Comparative Example 2 (single temperature treatment) rose rapidly during storage, reaching 78.24 and 65.78, respectively, showing the importance of gradient heat treatment in preventing browning of fresh-cut eggplant. Although the browning index of Comparative Example 3 (without rosemary extract and licorice extract) and Comparative Example 4 (without curcumin microcapsules) was lower than that of Comparative Examples 1 and 2, it was significantly higher than that of Examples 1 and 2, proving that the synergistic effect of the complete formula is better than that of the formula lacking key ingredients.

[0074] Table 2 Effect of different treatment methods on weight loss rate (%) of fresh-cut eggplant during storage

[0075]

[0076]

[0077] From the results in Table 2, it can be seen that the weight loss rates of the fresh-cut eggplants treated in Examples 1 and 2 during storage are significantly lower than those of the comparative examples, and the weight loss rate of Example 2 is slightly lower than that of Example 1. The results show that the composite plant extract combined with gradient heat treatment can effectively slow down the water loss of fresh-cut eggplants and maintain the texture and appearance of the product.

[0078] Table 3 Effects of different treatments on the total colony count (lg CFU / g) of fresh-cut eggplant during storage

[0079] Group 0d 2d 4d 6d 8d 10d Example 1 2.14 2.43 2.87 3.42 3.96 4.53 Example 2 2.06 2.37 2.75 3.28 3.85 4.36 Comparative Example 1 2.23 3.12 3.86 4.75 5.63 6.38 Comparative Example 2 2.18 2.85 3.54 4.36 5.17 5.84 Comparative Example 3 2.21 2.94 3.72 4.58 5.42 6.15 Comparative Example 4 2.19 2.82 3.61 4.47 5.84 5.97

[0080] From the results in Table 3, it can be seen that the total number of colonies of the fresh-cut eggplants treated in Example 1 and Example 2 during storage is significantly lower than that of the comparative examples, indicating that the composite plant extract combined with gradient heat treatment has a good inhibitory effect on microbial growth.

[0081] Table 4 Effects of different treatments on PPO activity (U / g) of fresh-cut eggplant during storage

[0082] Group 0d 2d 4d 6d 8d 10d Example 1 21.45 22.63 24.32 26.57 29.38 32.76 Example 2 19.87 20.95 22.48 24.83 27.35 30.42 Comparative Example 1 26.76 30.42 34.97 40.65 45.93 51.84 Comparative Example 2 24.89 27.46 31.79 35.92 40.87 46.29 Comparative Example 3 22.54 25.65 29.83 36.76 42.32 48.75 Comparative Example 4 22.73 26.28 28.64 35.52 40.71 46.36

[0083] PPO is one of the key enzymes that causes eggplant browning. As shown in Table 4, the PPO activity of fresh-cut eggplants treated in Example 1 and Example 2 remained at a low level throughout the storage period, and was 32.76 U / g and 30.42 U / g respectively after 10 days of storage, which was significantly lower than the treatment method in the comparative example, indicating that the green tea extract (EGCG) and licorice extract in the composite plant extract can effectively inhibit PPO activity through gradient heat treatment.

[0084] Table 5 Effects of different treatments on POD activity (U / g) of fresh-cut eggplant during storage

[0085] Group 0d 2d 4d 6d 8d 10d Example 1 14.67 15.93 17.42 19.44 22.83 25.44 Example 2 13.86 14.81 16.34 18.23 21.39 24.82 Comparative Example 1 15.62 18.21 22.37 27.12 31.54 35.72 Comparative Example 2 14.93 17.07 21.59 24.28 27.68 32.04 Comparative Example 3 14.87 17.78 22.03 25.82 29.24 33.97 Comparative Example 4 15.10 17.24 21.36 25.01 28.16 32.81

[0086] POD, like PPO, is an important enzyme that causes browning. As shown in Table 5, the POD activity in Examples 1 and 2 remained at a low level throughout the storage period, indicating that the composite plant extract formula and gradient heat treatment process in the examples have a significant inhibitory effect on POD activity and effectively slow down enzymatic browning.

[0087] Table 6 Effects of different treatments on total phenolic content (mg / 100g) of fresh-cut eggplant during storage

[0088] Group 0d 2d 4d 6d 8d 10d Example 1 73.42 71.89 69.74 67.35 64.87 62.13 Example 2 74.85 73.56 71.83 69.67 67.52 65.28 Comparative Example 1 72.36 67.43 62.57 57.42 52.18 46.75 Comparative Example 2 72.84 68.95 65.18 61.36 56.95 52.32 Comparative Example 3 72.56 68.27 63.85 59.24 54.37 49.58 Comparative Example 4 72.91 69.32 65.74 61.87 57.49 53.26

[0089] Total phenol content is one of the important indicators for evaluating the quality of fresh-cut eggplant. As shown in Table 6, during storage, the total phenol content of all samples showed a downward trend, but the total phenol content of Example 1 and Example 2 remained at a high level, which was 62.13 mg / 100 g and 65.28 mg / 100 g after 10 days of storage, respectively, retaining 84.62% and 87.21% of the initial total phenol content, respectively. This shows that the antioxidant components in the composite plant extract can effectively inhibit the oxidative degradation of polyphenol compounds through gradient heat treatment.

[0090] It can be seen from the results of Tables 1-6 that the fresh-cut eggplant anti-browning preservation method based on composite plant extract synergistic heat treatment proposed in the present invention can significantly inhibit the browning of fresh-cut eggplant, reduce the activity of PPO and POD, maintain the total phenol content, reduce the weight loss rate, and inhibit the growth of microorganisms, thereby extending the shelf life of fresh-cut eggplant. Both Example 1 and Example 2 show excellent preservation effects, among which Example 2 is slightly better than Example 1 due to the increase in the concentration of antioxidant components in the formula. The results of Comparative Examples 1-4 show that the preservation effect of the present invention cannot be achieved by simply using composite plant extract treatment (Comparative Example 1), single temperature treatment (Comparative Example 2), and composite extracts lacking key components (Comparative Examples 3 and 4). Through the synergistic effect of multiple plant extracts and a carefully designed gradient heat treatment process, the present invention achieves effective inhibition of browning of fresh-cut eggplant and significant extension of the shelf life. It can maintain good quality for more than 10 days at 4±1°C and has good application prospects.

[0091] 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 method for preventing fresh-cut eggplant from browning and preserving it based on composite plant extract synergistic heat treatment, characterized in that: The following steps are involved: S1. Prepare a composite plant extract, comprising the following components by weight percentage: green tea extract 0.5-0.8%, rosemary extract 0.25-0.35%, licorice extract 0.15-0.3%, trehalose 0.35-0.5%, chitosan oligosaccharide 0.35-0.5%, curcumin microcapsule 0.1-0.2%, soy lecithin 0.2-0.35%, Tween 20 0.1-0.15%, and the balance is pure water; S2. The fresh-cut eggplants are immersed in the composite plant extract and subjected to a gradient heat treatment, wherein the gradient heat treatment includes the following three stages: a heat activation penetration stage, a cooling stabilization stage, and a cold shock fixation stage; S3. Lightly drain the processed fresh-cut eggplants and wrap them with plastic wrap.

2. The method according to claim 1, characterized in that In step S1, the EGCG content in the green tea extract is ≥80%.

3. The method according to claim 1, characterized in that The specific preparation method of the curcumin microcapsules in step S1 is: adding 10-15 parts of inulin, 15-18 parts of β-cyclodextrin and 5-10 parts of pectin by weight to 100 parts of pure water, stirring to dissolve, and standing overnight to obtain a completely hydrated wall material solution; Add 0.5-2 parts of curcumin powder to 30 parts of anhydrous ethanol, stir and dissolve to 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 curcumin emulsion; send the curcumin emulsion to a spray dryer for spray drying, and then cool to room temperature to obtain curcumin microcapsules.

4. The method according to claim 1, characterized in that: The specific preparation method of the composite plant extract in step S1 is: add soybean lecithin and Tween 20 to pure water and emulsify in a 45-50°C water bath for 3-5 minutes, add curcumin microcapsules, homogenize at 8000-10000rpm for 2-3 minutes, add trehalose and chitosan oligosaccharides and stir to dissolve, add green tea extract, rosemary extract and licorice extract in turn and stir to dissolve, and finally use citric acid-sodium citrate buffer to adjust the pH of the system to 5.2-5.

5.

5. The method according to claim 1, characterized in that In step S2, the thickness of the fresh-cut eggplant slices is 4-6 mm.

6. The method according to claim 1, characterized in that The treatment temperature of the heat activated infiltration stage in step S2 is 40-42° C. and the treatment time is 60-90 s.

7. The method according to claim 1, characterized in that The temperature reduction and stabilization stage in step S2 is to reduce the temperature of the system to 30-33° C., and the processing time is 120-180 seconds.

8. The method according to claim 1, characterized in that The cold shock fixation stage in step S2 is to reduce the temperature of the system to 4°C. The total cooling time from 30-33°C to 4°C is 8-10 minutes, and the 4°C holding time is 60-90 seconds.

9. The method according to claim 1, characterized in that: The packaged fresh-cut eggplants are stored at a low temperature of 4±1℃.

10. The method according to claim 1, characterized in that The browning prevention and fresh-keeping method can inhibit corrosion, prevent the fresh-cut eggplant from browning and prolong the shelf life of the fresh-cut eggplant.

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