Fragrant pomelo peel essential oil compound preservative capable of improving storage quality of prunus salicina

Abstract

The invention discloses a fragrant pomelo peel essential oil compound preservative capable of improving the storage quality of prunus salicina, and belongs to the technical field of fruit preservation. The preservative is prepared from the following components in percentage by mass: 0.1 to 1.0 percent of fragrant pomelo peel essential oil, 0.5 to 2.0 percent of chitosan, 0.3 to 1.5 percent of modified white carbon black, 0.05 to 0.2 percent of antioxidant, 0.2 to 1.0 percent of glycerol, 0.1 to 0.5 percent of film-forming agent and the balance of deionized water. The modified white carbon black is prepared by step-by-step modification of a silane coupling agent, guar gum hydroxypropyl trimethyl ammonium chloride and sodium lignin sulfonate, can efficiently adsorb and slowly release essential oil, and enhances the compatibility with chitosan and the mechanical properties of a film layer. According to the preservative disclosed by the invention, a composite coating film is formed by dip-coating, so that water loss, browning and microbial decay after the prunus salicina is picked can be remarkably inhibited, the shelf life of the prunus salicina is prolonged to 12-15 days at normal temperature, and the preservative is suitable for large-scale storage and preservation of the prunus salicina.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of fruit preservation, and particularly relates to a compound preservative of citrus grandis peel essential oil for improving the storage quality of hollow plums. BACKGROUND

[0002] Hollow plum is a small deciduous fruit tree of Rosaceae, mainly distributed in Yanhe Tujia Autonomous County, Tongren City, Guizhou Province. Relying on the unique mountain climate, soil fertility and ecological environment, it has formed a unique flavor with crisp and tender flesh, sweet juice and rich fruit aroma. It is rich in vitamin C, dietary fiber, minerals and various bioactive substances, and has both edible and nutritional values. It is deeply favored by domestic and foreign consumers. In 2006, it was listed as a national geographical indication protection product and became one of the local characteristic agricultural pillar industries, driving the regional economic development and farmers' income increase. In recent years, the planting scale of hollow plum in Yanhe has been continuously expanding, and the annual output has broken through ten thousand tons. However, the postharvest storage and preservation problem has always been the core bottleneck restricting the high-quality development of the industry.

[0003] Hollow plum is a typical fruit of respiratory climacteric type. The postharvest respiratory metabolism is vigorous, and the enzyme activity in the flesh cells is easy to be unbalanced. At the same time, its fruit skin is thin, and the flesh moisture content is high (about 85%-90%), and the physiological characteristics are relatively fragile. In addition, its mature period is concentrated in July-August, which is the high-temperature and high-humidity rainy season in Tongren. The diurnal temperature difference is small, and the fruit is easy to quickly enter the aging period after being picked. The quality deterioration phenomena such as fruit skin browning, flesh softening, flavor fading, and nutrient loss occur. It is also easily infected by pathogenic microorganisms such as penicillium, green mold, and anthracnose, leading to rot and deterioration. The commodity value decreases greatly within 3-5 days, and the loss rate can reach 25%-30% in severe cases, which greatly affects the market circulation range and industrial economic benefits of hollow plum.

[0004] At present, postharvest preservation of hollow plum mainly relies on low-temperature storage and controlled atmosphere storage technology. Although these technologies can delay fruit deterioration to a certain extent, they require high equipment and need to be equipped with professional cold storage, air conditioning unit and other facilities. The initial investment is high, and the energy consumption is large during operation, which is not suitable for small-scale planting households and large-scale application in remote areas. Therefore, chemical preservatives are still widely used in the industry for preservation. Common chemical agents include sodium benzoate, potassium sorbate, and sulfite. Although these agents can quickly inhibit the growth of microorganisms and prolong the storage period, they have significant residual risks. Long-term intake can cause potential harm to human liver, kidney and other organs, and may also damage the ecological environment of soil and water, which is contrary to the current trend of green food consumption. With increasing social concern about food safety, consumers' demand for high-quality, residue-free fruits continues to rise. Therefore, it is an urgent need to develop new, safe, efficient and low-cost biological preservatives to solve the storage problems of hollow plum and promote the sustainable development of the industry.

[0005] Citrus essential oils, as natural plant extracts, are mainly derived from the peels of citrus fruits. They are rich in volatile active substances such as limonene, linalool, and geraniol, possessing advantages such as broad-spectrum antibacterial properties, antioxidant activity, and high safety. They can effectively replace chemical antioxidants and preservatives, showing broad application prospects in the field of fruit preservation. However, the deep processing of citrus fruits is weak, with sales primarily focused on fresh fruit. The comprehensive utilization rate of by-products such as peels and pomace is insufficient, and large quantities of essential oil-rich peel resources are carelessly discarded or incinerated, not only wasting high-value resources but also easily causing environmental pollution problems. Currently, research on using grapefruit peel essential oil as the core active ingredient to construct a compound biological preservation system for the storage of hollow plums is still lacking.

[0006] Chitosan, as a natural polysaccharide, possesses excellent biocompatibility, film-forming properties, and antibacterial activity, making it an ideal substrate for constructing fruit coating preservation systems. The resulting film forms a physical barrier on the fruit surface, reducing water evaporation and gas exchange, and inhibiting pathogenic microbial infection. However, chitosan's molecular structure is rich in hydroxyl and amino groups, exhibiting strong hydrophilicity, making it difficult to effectively anchor hydrophobic active ingredients such as pomelo peel essential oils. Direct compounding easily leads to problems like oil-water separation and system instability. Furthermore, pure chitosan films have poor mechanical properties, are prone to cracking and detachment, and have limited adsorption and slow-release capabilities for essential oils, resulting in rapid essential oil volatilization and a short preservation period, failing to meet the practical needs of large-scale storage of hollow plums. Therefore, it is urgent to construct a pomelo peel essential oil compound preservation system that combines stability, long-lasting effect, and practicality through scientific component compounding and modification optimization, overcoming many shortcomings of existing preservation technologies, and achieving improved storage quality of hollow plums and high-value utilization of pomelo peel resources. Summary of the Invention

[0007] In view of the above situation and to overcome the defects of the prior art, the present invention uses natural pomelo peel essential oil as the core antibacterial and antioxidant active ingredient, combined with the film-forming and preservation advantages of modified fumed silica and chitosan, and constructs a synergistic effect with functional components such as antioxidants and film-forming agents, to provide a pomelo peel essential oil compound preservative that improves the storage quality of hollow plums.

[0008] To achieve the above objectives, the following technical solution is adopted: This invention provides a pomelo peel essential oil compound preservative to improve the storage quality of hollow plums. The compound preservative is composed of the following components by mass fraction: pomelo peel essential oil 0.1~1.0%, chitosan 0.5~2.0%, modified silica 0.3~1.5%, antioxidant 0.05~0.2%, glycerin 0.2~1.0%, film-forming agent 0.1~0.5%, and the balance being deionized water.

[0009] Furthermore, the compound preservative is prepared through the following steps:

[0010] (1) Fresh pomelo peel is sliced, vacuum dried, and extracted by enzyme treatment and steam distillation to obtain pomelo peel essential oil; modified silica is added to deionized water to prepare modified silica dispersion, ultrasonically dispersed, pomelo peel essential oil is added to it, and stirred for 1-3 hours to obtain essential oil-modified silica complex dispersion.

[0011] (2) Add chitosan to acetic acid solution, stir to dissolve, add glycerol, continue stirring for 15-20 min to obtain chitosan-glycerol mixed solution, slowly add essential oil-modified silica complex dispersion to chitosan-glycerol mixed solution, add antioxidant and film-forming agent after the addition is complete, continue stirring for 30-45 min, then ultrasonically emulsify to form a uniform emulsion;

[0012] (3) Adjust the pH of the emulsion to 6.5-7.5 with 1-2 mol / L sodium hydroxide solution, let it stand to remove bubbles, sterilize it in a water bath, and then cool it to room temperature to obtain the compound preservative.

[0013] Furthermore, the modified silica is prepared by the following steps:

[0014] S1. Add food-grade silica to an ethanol-water mixed solvent to prepare a silica dispersion. Disperse the dispersion by ultrasonication for 20-30 min. Add sodium N-(trimethoxysilylpropyl)ethylenediaminetriacetate. Adjust the pH of the system to 4-6 with acetic acid solution. Stir the mixture at 50-70℃ and 300-500 r / min for 3-6 h. Set aside for later use.

[0015] S2. Add guar gum hydroxypropyltrimethylammonium chloride, stir at 60~80℃ for 2~4 hours, and set aside.

[0016] S3. Add sodium lignosulfonate, adjust the pH of the system to 7-8 with sodium hydroxide solution, stir at a constant temperature of 50-70℃ for 1-3 hours, after the reaction is completed, filter and collect the solid product, wash with deionized water, dry in a vacuum drying oven, cool and crush, and pass through a 200-mesh sieve to obtain the modified silica.

[0017] Further, in step (1), the enzyme treatment uses cellulase, the amount of enzyme added is 0.1~0.3% of the weight of pomelo peel, the enzymatic hydrolysis temperature is 45~55℃, the enzymatic hydrolysis time is 1~2h, the enzymatic hydrolysis pH is 4.5~5.5; the ultrasonic dispersion time is 20~25min.

[0018] Further, in step (2), the volume fraction of the acetic acid solution is 1.5~3%, the stirring and dissolving temperature of chitosan is 45~55℃, the stirring time is 40~50min; the ultrasonic emulsification power is 250~350W, and the emulsification time is 20~30min.

[0019] Furthermore, in step (3), the water bath sterilization temperature is 60~80℃ and the sterilization time is 12~18min; the static degassing temperature is 28~32℃ and the degassing time is 25~35min.

[0020] Further, in step S1, the volume ratio of the ethanol-water mixed solvent is 7:3 to 9:1, the solid-liquid ratio of the silica dispersion is 1:10 to 1:30 (g / mL), the amount of N-(trimethoxysilylpropyl)ethylenediamine triacetic acid sodium salt added is 8 to 12% of the mass of food-grade silica, and the volume fraction of the acetic acid solution is 1 to 2%.

[0021] Furthermore, in step S2, the amount of guar gum hydroxypropyltrimethylammonium chloride added is 4-6% of the mass of food-grade precipitated silica.

[0022] Furthermore, in step S3, the amount of sodium lignosulfonate added is 3-5% of the mass of food-grade silica, and the concentration of sodium hydroxide solution is 1-2 mol / L.

[0023] Furthermore, the antioxidant is selected from one of tea polyphenols, vitamin C, and phytic acid.

[0024] Furthermore, the film-forming agent is selected from one of sodium carboxymethyl cellulose, sodium alginate, and xanthan gum.

[0025] Furthermore, the compound preservative is applied through the following steps: the hollow plum fruits are washed and dried until the surface is free of moisture, then soaked in the prepared preservative solution for 3 minutes, taken out and air-dried naturally, and then packed into 0.07mm thick polyethylene bags. After sealing each bag, they are stored in a cold storage at 1°C.

[0026] The beneficial effects of this invention are:

[0027] This invention, through the synergistic effect of its components, retains the film-forming and preservation properties of chitosan and the natural antibacterial properties of pomelo peel oil. Furthermore, by modifying and optimizing the precipitated silica, it compensates for the deficiencies of each individual component, ultimately achieving a comprehensive improvement in the storage quality of hollow plums. This effectively reduces problems such as fruit weight loss, browning, and rot, while preserving the original flavor and nutritional components of the fruit. At the same time, it avoids the residual risks of chemical preservatives, combining safety and practicality, and is suitable for large-scale storage and preservation applications of hollow plums.

[0028] By condensing a silane coupling agent with the silanol groups on the surface of silica, a stable grafting of the silane coupling agent onto the silica surface is achieved. The grafted coupling agent can then bind with active components such as limonene and linalool in pomelo peel essential oil through hydrogen bonding and electrostatic interactions, enhancing the adsorption capacity and stability of the modified silica for essential oils and reducing volatilization losses during storage. Guar gum hydroxypropyltrimethylammonium chloride, with its quaternary ammonium salt structure and multiple hydroxyl groups, can undergo esterification with the carboxyl groups introduced onto the silica surface via the silane coupling agent, achieving a binding of the quaternary ammonium salt structure and hydroxyl groups on the silica surface. The quaternary ammonium salt structure possesses broad-spectrum antibacterial activity, which can synergistically enhance the preservative effect of pomelo peel essential oil. The antibacterial ability of the modified silica inhibits the growth of mold and bacteria during the storage of hollow plums, reducing the fruit rot rate. The hydroxyl groups can form hydrogen bonds with the hydroxyl groups in chitosan molecules, significantly improving the flexibility and extensibility of the chitosan film. The hydroxyl groups can enhance the hydrophilicity of the modified silica and improve its compatibility with chitosan aqueous solution, making the compound system form a uniform and stable emulsion. The large number of hydroxyl and sulfonic acid groups contained in sodium lignosulfonate molecules can combine with the active groups on the surface of silica, enriching the polar groups on the surface of silica and improving its compatibility with chitosan and deionized water. The sulfonic acid groups can enhance the surface charge density of the modified silica, improve the colloidal stability of the dispersion, and prevent the modified silica from settling in the system.

[0029] This invention solves the problem of poor compatibility between silica and chitosan. It also enables the slow release of pomelo peel essential oil through its own adsorption and slow release characteristics, extending the active period of the essential oil and thus significantly improving the shelf life of hollow plums. Under normal temperature storage conditions, the shelf life is extended to 12-15 days. At the same time, the compound preservative significantly improves the mechanical strength of the coating, enhances the adhesion of the film to the fruit surface, reduces the loss of preservative during fruit transportation and storage, and ensures a continuous and stable preservation effect. Attached Figure Description

[0030] Figure 1 This is a flowchart illustrating the preparation process of the compound preservative in this invention;

[0031] Figure 2 This is a flowchart illustrating the preparation process of modified silica in this invention.

[0032] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. Detailed Implementation

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to this invention. The preferred embodiments and materials described herein are for illustrative purposes only and do not limit the scope of this application.

[0035] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the experimental materials used in the following examples are all purchased from commercial channels.

[0036] Example 1: A pomelo peel essential oil compound preservative to improve the storage quality of hollow plums

[0037] The compound preservative is composed of the following components by mass fraction: 0.1% pomelo peel essential oil, 0.5% chitosan, 0.3% modified silica, 0.05% antioxidant, 0.2% glycerin, 0.1% film-forming agent, and the balance being deionized water; the antioxidant is tea polyphenol; and the film-forming agent is sodium carboxymethyl cellulose.

[0038] The compound preservative is prepared through the following steps:

[0039] (1) Fresh pomelo peel is sliced, vacuum dried, and extracted by enzyme treatment and steam distillation to obtain pomelo peel essential oil; modified silica is added to deionized water to prepare modified silica dispersion, ultrasonically dispersed, pomelo peel essential oil is added to it, and stirred for 1 hour to obtain essential oil-modified silica complex dispersion.

[0040] (2) Add chitosan to acetic acid solution, stir to dissolve, add glycerol, continue stirring for 15 min to obtain chitosan-glycerol mixed solution, slowly add essential oil-modified silica complex dispersion to chitosan-glycerol mixed solution, add antioxidant and film-forming agent after the addition is completed, continue stirring for 30 min, then ultrasonically emulsify to form a uniform emulsion;

[0041] (3) Adjust the pH of the emulsion to 6.5 with 1 mol / L sodium hydroxide solution, let it stand to remove bubbles, sterilize it in a water bath, and then cool it to room temperature to obtain the compound preservative.

[0042] In step (1), cellulase was used for enzyme treatment. The amount of enzyme added was 0.1% of the weight of the grapefruit peel. The enzymatic hydrolysis temperature was 45℃, the enzymatic hydrolysis time was 1h, and the enzymatic hydrolysis pH was 4.5. The ultrasonic dispersion time was 20min.

[0043] In step (2), the volume fraction of the acetic acid solution is 1.5%, the stirring and dissolution temperature of chitosan is 45℃, and the stirring time is 40min; the ultrasonic emulsification power is 250W, and the emulsification time is 20min.

[0044] In step (3), the water bath sterilization temperature is 60℃ and the sterilization time is 12min; the static degassing temperature is 28℃ and the degassing time is 25min.

[0045] The modified silica is prepared by the following steps:

[0046] S1. Add food-grade silica to an ethanol-water mixed solvent to prepare a silica dispersion. Disperse the dispersion by ultrasonication for 20 min. Add sodium N-(trimethoxysilylpropyl)ethylenediaminetriacetate. Adjust the pH of the system to 4 with acetic acid solution. Stir the system at 50℃ and 300 r / min for 3 h. Set aside for later use.

[0047] S2. Add guar gum hydroxypropyltrimethylammonium chloride, stir at 60℃ for 2 hours, and set aside.

[0048] S3. Add sodium lignosulfonate, adjust the pH of the system to 7 with sodium hydroxide solution, stir at 50°C for 1 hour, after the reaction is complete, filter and collect the solid product, wash with deionized water, dry in a vacuum drying oven, cool and pulverize, and pass through a 200-mesh sieve to obtain the modified silica.

[0049] In step S1, the volume ratio of ethanol-water mixed solvent is 7:3, the solid-liquid ratio of silica dispersion is 1:10 (g / mL), the amount of N-(trimethoxysilylpropyl)ethylenediamine triacetic acid sodium salt added is 8% of the mass of food-grade silica, and the volume fraction of acetic acid solution is 1%.

[0050] In step S2, the amount of guar gum hydroxypropyltrimethylammonium chloride added is 4% of the mass of food-grade precipitated silica.

[0051] In step S3, the amount of sodium lignosulfonate added is 3% of the mass of food-grade silica, and the concentration of sodium hydroxide solution is 1 mol / L.

[0052] Example 2: A pomelo peel essential oil compound preservative to improve the storage quality of hollow plums

[0053] The compound preservative is composed of the following components by mass fraction: 1.0% grapefruit peel essential oil, 2.0% chitosan, 1.5% modified silica, 0.2% antioxidant, 1.0% glycerin, 0.5% film-forming agent, and the balance being deionized water; the antioxidant is vitamin C; and the film-forming agent is sodium alginate.

[0054] The compound preservative is prepared through the following steps:

[0055] (1) Fresh pomelo peel is sliced, vacuum dried, and extracted by enzyme treatment and steam distillation to obtain pomelo peel essential oil; modified silica is added to deionized water to prepare modified silica dispersion, ultrasonically dispersed, pomelo peel essential oil is added to it, and stirred for 3 hours to obtain essential oil-modified silica complex dispersion.

[0056] (2) Add chitosan to acetic acid solution, stir to dissolve, add glycerol, continue stirring for 20 min to obtain chitosan-glycerol mixed solution, slowly add essential oil-modified silica complex dispersion to chitosan-glycerol mixed solution, add antioxidant and film-forming agent after the addition is completed, continue stirring for 45 min, then ultrasonically emulsify to form uniform emulsion;

[0057] (3) Adjust the pH of the emulsion to 7.5 with 2 mol / L sodium hydroxide solution, let it stand to remove bubbles, sterilize it in a water bath, and then cool it to room temperature to obtain the compound preservative.

[0058] In step (1), cellulase was used for enzyme treatment. The amount of enzyme added was 0.3% of the weight of the grapefruit peel. The enzymatic hydrolysis temperature was 55℃, the enzymatic hydrolysis time was 2h, and the enzymatic hydrolysis pH was 5.5. The ultrasonic dispersion time was 25min.

[0059] In step (2), the volume fraction of the acetic acid solution is 3%, the stirring and dissolution temperature of chitosan is 55℃, and the stirring time is 50min; the ultrasonic emulsification power is 350W, and the emulsification time is 30min.

[0060] In step (3), the water bath sterilization temperature is 80℃ and the sterilization time is 18min; the static degassing temperature is 32℃ and the degassing time is 35min.

[0061] The modified silica is prepared by the following steps:

[0062] S1. Add food-grade silica to an ethanol-water mixed solvent to prepare a silica dispersion. Disperse the dispersion by ultrasonication for 30 min. Add sodium N-(trimethoxysilylpropyl)ethylenediaminetriacetate. Adjust the pH of the system to 6 with acetic acid solution. Stir the system at 70℃ and 500 r / min for 6 h. Set aside for later use.

[0063] S2. Add guar gum hydroxypropyltrimethylammonium chloride, stir at 80℃ for 4 hours, and set aside.

[0064] S3. Add sodium lignosulfonate, adjust the pH of the system to 8 with sodium hydroxide solution, stir at 70°C for 3 hours, after the reaction is complete, filter and collect the solid product, wash with deionized water, dry in a vacuum drying oven, cool and pulverize, and pass through a 200-mesh sieve to obtain the modified silica.

[0065] In step S1, the volume ratio of ethanol-water mixed solvent is 9:1, the solid-liquid ratio of silica dispersion is 1:30 (g / mL), the amount of N-(trimethoxysilylpropyl)ethylenediamine triacetic acid sodium salt added is 12% of the mass of food-grade silica, and the volume fraction of acetic acid solution is 2%.

[0066] In step S2, the amount of guar gum hydroxypropyltrimethylammonium chloride added is 6% of the mass of food-grade precipitated silica.

[0067] In step S3, the amount of sodium lignosulfonate added is 5% of the mass of food-grade silica, and the concentration of sodium hydroxide solution is 2 mol / L.

[0068] Example 3: A pomelo peel essential oil compound preservative to improve the storage quality of hollow plums

[0069] The compound preservative is composed of the following components by mass fraction: 0.5% grapefruit peel essential oil, 1.2% chitosan, 0.9% modified silica, 0.12% antioxidant, 0.6% glycerin, 0.3% film-forming agent, and the balance being deionized water; the antioxidant is phytic acid; and the film-forming agent is xanthan gum.

[0070] The compound preservative is prepared through the following steps:

[0071] (1) Fresh pomelo peel was sliced, vacuum dried, and extracted by enzyme treatment and steam distillation to obtain pomelo peel essential oil; modified silica was added to deionized water to prepare modified silica dispersion, ultrasonically dispersed, pomelo peel essential oil was added to it, and stirred for 2 hours to obtain essential oil-modified silica complex dispersion.

[0072] (2) Add chitosan to acetic acid solution, stir to dissolve, add glycerol, continue stirring for 18 min to obtain chitosan-glycerol mixed solution, slowly add essential oil-modified silica complex dispersion to chitosan-glycerol mixed solution, add antioxidant and film-forming agent after the addition is completed, continue stirring for 38 min, then ultrasonically emulsify to form uniform emulsion;

[0073] (3) Adjust the pH of the emulsion to 7.0 with 1.5 mol / L sodium hydroxide solution, let it stand to remove bubbles, sterilize it in a water bath, and then cool it to room temperature to obtain the compound preservative.

[0074] In step (1), the enzyme treatment uses cellulase, the amount of enzyme added is 0.2% of the weight of pomelo peel, the enzymatic hydrolysis temperature is 50℃, the enzymatic hydrolysis time is 1.5h, the enzymatic hydrolysis pH is 5.0, and the ultrasonic dispersion time is 22min.

[0075] In step (2), the volume fraction of the acetic acid solution is 2.2%, the stirring and dissolution temperature of chitosan is 50℃, and the stirring time is 45min; the ultrasonic emulsification power is 300W, and the emulsification time is 25min.

[0076] In step (3), the water bath sterilization temperature is 70℃ and the sterilization time is 15min; the static degassing temperature is 30℃ and the degassing time is 30min.

[0077] The modified silica is prepared by the following steps:

[0078] S1. Add food-grade silica to an ethanol-water mixed solvent to prepare a silica dispersion. Disperse the dispersion by sonication for 25 min. Add sodium N-(trimethoxysilylpropyl)ethylenediaminetriacetate. Adjust the pH of the system to 5 with acetic acid solution. Stir the mixture at 60℃ and 400 r / min for 4.5 h. Set aside for later use.

[0079] S2. Add guar gum hydroxypropyltrimethylammonium chloride, stir at 70℃ for 3 hours, and set aside.

[0080] S3. Add sodium lignosulfonate, adjust the pH of the system to 7.5 with sodium hydroxide solution, stir at 60℃ for 2 hours, after the reaction is complete, filter and collect the solid product, wash with deionized water, dry in a vacuum drying oven, cool and pulverize, and pass through a 200-mesh sieve to obtain the modified silica.

[0081] In step S1, the volume ratio of the ethanol-water mixed solvent is 8:2, the solid-liquid ratio of the silica dispersion is 1:20 (g / mL), the amount of N-(trimethoxysilylpropyl)ethylenediamine triacetic acid sodium salt added is 10% of the mass of food-grade silica, and the volume fraction of the acetic acid solution is 1.5%.

[0082] In step S2, the amount of guar gum hydroxypropyltrimethylammonium chloride added is 5% of the mass of food-grade precipitated silica.

[0083] In step S3, the amount of sodium lignosulfonate added is 4% of the mass of food-grade silica, and the concentration of sodium hydroxide solution is 1.5 mol / L.

[0084] Comparative Example 1: In this comparative example, except that the modified silica was replaced with an equal mass of ordinary silica, the other components and preparation steps were the same as in Example 3.

[0085] Comparative Example 2: Except for the absence of pomelo peel essential oil, the other components and preparation steps of this comparative example are the same as those of Example 3.

[0086] Results Analysis

[0087] After washing and drying the hollow plums until the surface was free of moisture, they were soaked in the prepared preservation solution for 3 minutes in each of the examples and comparative examples. After being taken out and air-dried, they were packed into 0.07mm thick polyethylene bags, with 15 fruits per bag, 3 replicates, 150 bags per group, for a total of 300 bags in two groups. After sealing, they were stored in cold storage at room temperature (25℃) and 1℃ respectively. Samples were taken from the room temperature treatment group on the 8th day and from the cold storage treatment group on the 21st day to measure physiological indicators. For each treatment, 3 bags with a total of 45 fruits were cut and sampled, for a total of 5 samplings.

[0088] The indicators were measured using the following methods:

[0089] Physical and appearance indicators: Weight loss rate: determined by weighing method; Hardness: determined by GY-1 fruit hardness tester; Relative electrical conductivity (pulp): determined by electrical conductivity meter; Rot rate (%) = number of rotten fruits / number of observed fruits × 100; Rot index (%) = ∑ (rot grade × number of fruits of that grade) / (highest rot grade × total number of fruits) × 100; Browning index = Σ (browning grade × number of fruits of that grade) / (highest grade × total number of fruits) × 100;

[0090] Nutritional and flavor indicators: Soluble solids: determined by APAL-1 saccharimeter; Titratable acid: determined by titration; Malondialdehyde content: determined by thiobarbituric acid colorimetric method; Total anthocyanin content: determined by spectrophotometry.

[0091] Physiological and antioxidant indicators: Peroxidase (POD) activity: determined by guaiacol method; Ascorbate peroxidase (APX) activity: determined by ultraviolet spectrophotometry; Superoxide dismutase (SOD) activity: determined by pyrogallol autoxidation method; Glutathione: determined by 2-nitrobenzoic acid colorimetric method; Ascorbic acid (VC): determined by 2,6-dichlorophenolindophenol titration method; Respiration intensity: 15 fruits were randomly selected, weighed, and placed in a fruit and vegetable respiration analyzer for measurement.

[0092] The comparison of quality indicators of each treatment group on day 8 of storage at room temperature (25℃) and the comparison of key indicators and shelf life of each treatment group on day 21 of storage at low temperature (1℃) are shown in Table 1 and Table 2, respectively.

[0093] Table 1 Comparison of quality indicators among treatment groups after 8 days of storage at room temperature (25℃)

[0094] Detection index Blank control group Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Weight loss rate (%) 12.5 6.5 6.0 5.8 8.3 7.1 Hardness (kg / cm2) 2.1 4.3 4.5 4.7 3.8 4.0 Relative conductivity (%) 65.4 38.5 36.8 35.6 45.2 42.8 Rot rate (%) 85.3 22.5 20.1 18.7 32.5 48.6 Browning index 0.78 0.28 0.25 0.22 0.41 0.35 Soluble solids (°Brix) 8.2 11.2 11.4 11.6 10.5 10.8 Titration acid (%) 0.35 0.65 0.67 0.69 0.58 0.61 VC content (mg / 100g) 2.1 7.0 7.3 7.5 5.8 6.2 Respiratory intensity (mg CO2 / kg-h) 125.6 76.8 74.5 72.3 89.4 85.1 Malondialdehyde content (nmol / g) 12.8 5.6 5.3 5.1 7.2 6.8 SOD activity (U / g) 85 185 192 198 156 162

[0095] Table 2 Comparison of key indicators and shelf life of each treatment group on day 21 of low-temperature (1℃) storage.

[0096] Detection index Blank control group Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Rot rate (%) 45.6 12.8 11.5 10.2 18.9 25.7 Browning index 0.52 0.18 0.16 0.15 0.25 0.21 VC retention rate (%) 41.5 79.5 81.0 82.7 68.3 71.5 Hardness retention rate (%) 55.2 86.5 87.8 88.9 78.6 80.1 Normal temperature shelf life (days) 4 12 12 15 9 8 Chilled storage period (days) 14 30 32 35 28 24

[0097] Analysis of Tables 1 and 2 shows that each embodiment of the present invention performs better in all key indicators, effectively inhibiting weight loss, decay and browning, better maintaining hardness, nutrients and flavor substances, while significantly inhibiting respiration intensity, reducing membrane lipid peroxidation, and maintaining high levels of endogenous antioxidant enzyme activity and antioxidant substances.

[0098] All indicators were inferior to the example, but superior to the blank group. This indicates that ordinary silica has a certain physical adsorption and barrier effect, but due to the lack of surface modification, its compatibility with chitosan, anchoring and sustained-release ability of essential oils are insufficient, resulting in a decrease in the stability and long-term effectiveness of the preservation system, and a weakening of antibacterial and antioxidant effects.

[0099] Comparative Example 2 was significantly worse than all the examples and Comparative Example 1 in inhibiting rot rate, highlighting the core antibacterial effect of pomelo essential oil. It was close to or slightly better than Comparative Example 1 in maintaining firmness and reducing electrical conductivity, indicating that the chitosan membrane's basic barrier function was effective, but it lacked the synergistic antibacterial and antioxidant effects of the essential oil, making the fruit more susceptible to microbial attack and rot.

[0100] In terms of long-term cold storage effect, under the 1℃ cold storage condition, the rate of quality deterioration of each treatment group was slowed down, but the example still showed better long-term preservation effect, with a lower rot rate and better preservation of nutrients and texture on the 21st day.

[0101] The embodiments of this invention extend the shelf life of hollow plums at room temperature from 4 days in the control group to 12-15 days, achieving the effect described in the invention's objective. The commercial storage period under refrigeration conditions is also significantly extended. This demonstrates the crucial role of modified silica in constructing a stable and long-lasting preservation system. By improving compatibility and enhancing essential oil loading and slow release, it results in more sustained antibacterial and antioxidant activity. Grapefruit peel essential oil is an indispensable active core, and its antibacterial and antioxidant capabilities are the direct cause of reduced spoilage rate and delayed aging.

[0102] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

[0103] The present invention and its embodiments have been described above. This description is not restrictive, and the embodiments shown are only one of the embodiments of the present invention. The actual application is not limited to this. In conclusion, if those skilled in the art are inspired by this description and design similar methods and embodiments without departing from the spirit of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A pomelo peel essential oil compound preservative for improving the storage quality of hollow plums, characterized in that: The compound preservative is composed of the following components by mass fraction: 0.1-1.0% pomelo peel essential oil, 0.5-2.0% chitosan, 0.3-1.5% modified silica, 0.05-0.2% antioxidant, 0.2-1.0% glycerin, 0.1-0.5% film-forming agent, and the balance being deionized water; The compound preservative is prepared through the following steps: (1) Fresh pomelo peel is sliced, vacuum dried, and extracted by enzyme treatment and steam distillation to obtain pomelo peel essential oil; modified silica is added to deionized water to prepare modified silica dispersion, ultrasonically dispersed, pomelo peel essential oil is added to it, and stirred for 1-3 hours to obtain essential oil-modified silica complex dispersion. (2) Add chitosan to acetic acid solution, stir to dissolve, add glycerol, continue stirring for 15-20 min to obtain chitosan-glycerol mixed solution, slowly add essential oil-modified silica complex dispersion to chitosan-glycerol mixed solution, add antioxidant and film-forming agent after the addition is complete, continue stirring for 30-45 min, then ultrasonically emulsify to form a uniform emulsion; (3) Adjust the pH of the emulsion to 6.5-7.5 with 1-2 mol / L sodium hydroxide solution, let it stand to remove bubbles, sterilize it in a water bath, and then cool it to room temperature to obtain the compound preservative.

2. The pomelo peel essential oil compound preservative for improving the storage quality of hollow plums according to claim 1, characterized in that: The modified silica is prepared by the following steps: S1. Add food-grade silica to an ethanol-water mixed solvent to prepare a silica dispersion. Disperse the dispersion by ultrasonication for 20-30 min. Add sodium N-(trimethoxysilylpropyl)ethylenediaminetriacetate. Adjust the pH of the system to 4-6 with acetic acid solution. Stir the mixture at 50-70℃ and 300-500 r / min for 3-6 h. Set aside for later use. S2. Add guar gum hydroxypropyltrimethylammonium chloride, stir at 60~80℃ for 2~4 hours, and set aside; S3. Add sodium lignosulfonate, adjust the pH of the system to 7-8 with sodium hydroxide solution, stir at a constant temperature of 50-70℃ for 1-3 hours, after the reaction is completed, filter and collect the solid product, wash with deionized water, dry in a vacuum drying oven, cool and crush, and pass through a 200-mesh sieve to obtain the modified silica.

3. The pomelo peel essential oil compound preservative for improving the storage quality of hollow plums according to claim 1, characterized in that: In step (1), cellulase is used for enzyme treatment. The amount of enzyme added is 0.1-0.3% of the weight of pomelo peel. The enzymatic hydrolysis temperature is 45-55℃, the enzymatic hydrolysis time is 1-2h, and the enzymatic hydrolysis pH is 4.5-5.

5. The ultrasonic dispersion time is 20-25min.

4. The pomelo peel essential oil compound preservative for improving the storage quality of hollow plums according to claim 1, characterized in that: In step (2), the volume fraction of the acetic acid solution is 1.5-3%, the stirring and dissolving temperature of chitosan is 45-55℃, and the stirring time is 40-50 min; the ultrasonic emulsification power is 250-350W, and the emulsification time is 20-30 min.

5. The pomelo peel essential oil compound preservative for improving the storage quality of hollow plums according to claim 1, characterized in that: In step (3), the water bath sterilization temperature is 60~80℃ and the sterilization time is 12~18min; the static degassing temperature is 28~32℃ and the degassing time is 25~35min.

6. The pomelo peel essential oil compound preservative for improving the storage quality of hollow plums according to claim 2, characterized in that: In step S1, the volume ratio of the ethanol-water mixed solvent is 7:3 to 9:1, the solid-liquid ratio of the silica dispersion is 1:10 to 1:30 (g / mL), the amount of N-(trimethoxysilylpropyl)ethylenediamine triacetic acid sodium salt added is 8 to 12% of the mass of food-grade silica, and the volume fraction of the acetic acid solution is 1 to 2%.

7. The pomelo peel essential oil compound preservative for improving the storage quality of hollow plums according to claim 2, characterized in that: In step S2, the amount of guar gum hydroxypropyltrimethylammonium chloride added is 4-6% of the mass of food-grade precipitated silica.

8. The pomelo peel essential oil compound preservative for improving the storage quality of hollow plums according to claim 2, characterized in that: In step S3, the amount of sodium lignosulfonate added is 3-5% of the mass of food-grade silica, and the concentration of sodium hydroxide solution is 1-2 mol / L.

9. The pomelo peel essential oil compound preservative for improving the storage quality of hollow plums according to claim 1, characterized in that: The antioxidant is selected from one of tea polyphenols, vitamin C, and phytic acid.

10. The pomelo peel essential oil compound preservative for improving the storage quality of hollow plums according to claim 1, characterized in that: The film-forming agent is selected from one of sodium carboxymethyl cellulose, sodium alginate, and xanthan gum.

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