Plant composite preservative for prolonging shelf life of psidium guajava

Abstract

This invention discloses a plant-based compound preservative for extending the shelf life of guava, belonging to the field of fruit preservation technology. The plant-based compound preservative of this invention comprises the following components in parts by weight: 6-8 parts tea extract, 4-6 parts citrus peel extract, 8-10 parts konjac extract, 3-4 parts peach bark extract, 5-8 parts aloe vera extract, and 2-4 parts sunflower extract. This plant-based compound preservative can inhibit guava metabolism, significantly reduce respiration intensity, and delay fruit ripening; it can improve the antioxidant capacity and free radical scavenging ability of guava, slowing down the darkening of color, softening of texture, and nutrient loss caused by oxidation; it can form a protective film on the surface of guava, reducing moisture loss; and it can inhibit pathogens, reducing the rot rate of guava.

Description

Technical Field

[0001] This invention relates to the field of fruit preservation technology, and in particular to a plant-based compound preservative for extending the shelf life of guava. Background Technology

[0002] Guava ( Psidium guajava Guava, belonging to the Myrtaceae family and the genus Pyruvices, is native to tropical South America. It is an evergreen small tree or shrub, commonly known as guava, chicken droppings fruit, guava, and red heart fruit. Guava is sweet, refreshing, juicy, fragrant, and has a unique flavor. It contains a wealth of nutrients beneficial to the human body, making it popular with consumers. It also has certain edible and medicinal value, and its nutritional quality is significantly affected by the season; generally, guava is more nutritious and delicious in autumn and winter than in spring and summer. Guava is very nutritious, considered one of the fruits with the highest lycopene and vitamin C content. Its vitamin C content (50-300mg / 100g fresh weight) is 3-6 times that of oranges. It also contains abundant pectin, riboflavin, dietary fiber, minerals, essential amino acids, and various types of carotenoids, making it highly favored by consumers. However, guava is fragile, has a high metabolic rate, and is not easy to preserve. Combined with external mechanical damage, moisture loss, and unsuitable environmental factors, its shelf life is generally short. Therefore, researching methods for preserving guava, extending its shelf life, and thus improving its economic benefits has become a technical challenge that urgently needs to be addressed by those skilled in the art. Summary of the Invention

[0003] The purpose of this invention is to provide a plant-based compound preservative for extending the shelf life of guava, thereby solving the problems existing in the prior art.

[0004] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of the present invention is a plant-based compound preservative for extending the shelf life of guava, comprising the following components in parts by weight: 6-8 parts of tea extract, 4-6 parts of citrus peel extract, 8-10 parts of konjac extract, 3-4 parts of peach bark extract, 5-8 parts of aloe vera extract, and 2-4 parts of sunflower extract.

[0005] Furthermore, the method for preparing the tea extract includes the following steps: After the tea leaves are crushed, water and compound enzymes are added for enzymatic hydrolysis. After the enzymes are inactivated, the enzymatic hydrolysate is obtained. The enzymatic hydrolysate was mixed with water and then subjected to ultrasonic treatment. After centrifugation, the precipitate was collected to obtain the tea extract.

[0006] Furthermore, the complex enzyme comprises cellulase and pectinase in a mass ratio of 1:2; The amount of the compound enzyme used is 0.5-0.8% of the tea mass; The ultrasonic treatment has a power of 200~300W, a temperature of 40~45℃, and a time of 30~40min.

[0007] Furthermore, the enzymatic hydrolysis is performed at a temperature of 45-55°C for a time of 25-35 minutes. The cellulase has an enzyme activity of 100,000 U / g; the pectinase has an enzyme activity of 30,000 U / g.

[0008] Furthermore, the preparation method of the citrus peel extract includes the following steps: The citrus peel is crushed and added to water, then ball-milled and filtered to obtain residue and first filtrate. The filter residue was added to an ethanol solution, ultrasonicated, and then filtered to obtain the second filtrate. The first and second filtrates were mixed, concentrated, and dried to obtain the citrus peel extract.

[0009] Furthermore, the ratio of citrus peel to water is 1g:10~15mL; The ball milling time is 2-3 hours; The concentration of the ethanol solution is 60-70 vol.%. The ratio of the filter residue to the ethanol solution is 1g:10~12mL; The ultrasonic treatment has a power of 200~300W, a temperature of 40~45℃, and a time of 15~20min.

[0010] Furthermore, the preparation method of the konjac extract includes the following steps: After homogenizing the konjac slurry, water was added, and the mixture was extracted by ultrasound and filtered. The residue was then vacuum dried, washed with ethanol, air-dried, and ground to obtain the konjac extract.

[0011] Furthermore, the ratio of konjac to water is 1g:8~10mL; The ultrasonic extraction was performed at a power of 150-250W, a temperature of 25-35℃, and a time of 30-40 minutes.

[0012] Furthermore, the preparation method of the peach bark extract includes the following steps: The peach bark was crushed and mixed with an ethanol solution. After extraction at room temperature, the extract was concentrated and extracted with ethyl acetate. After removing the solvent, the peach bark extract was obtained.

[0013] Furthermore, the ratio of peach bark to ethanol solution is 1g:10~12mL; The concentration of the ethanol solution is 75-85 vol.%. The extraction temperature is 20~25℃, and the time is 18~24h; The concentration is to concentrate to 1 / 5 of the volume of the extract; The extraction with ethyl acetate is performed 2 to 3 times.

[0014] Furthermore, the method for preparing the aloe vera extract includes the following steps: Fresh aloe vera is pressed to obtain aloe vera juice; The aloe vera juice was heated to remove the surface ash, cooled to room temperature, concentrated, and dried to obtain the aloe vera extract.

[0015] Furthermore, the heating temperature is 105~115℃, and the heating time is 15~25min.

[0016] Furthermore, the method for preparing the sunflower extract includes the following steps: The sunflower head was crushed and mixed with an ethanol solution. After heating and extraction, the extract was collected, and the solvent was removed to obtain the sunflower extract.

[0017] Furthermore, the concentration of the ethanol solution is 90-95 vol.%. The ratio of sunflower head to ethanol solution is 1g:12~15mL; The heating extraction temperature is 70~80℃, and the time is 2~3h.

[0018] The tea extract of this invention contains a large amount of tea polyphenols, which have strong antioxidant capacity. They can inhibit the activity of ACC synthase (ACS) and ACC oxidase (ACO), reduce ethylene production, and simultaneously reduce the respiration rate of fruits, delay the activity of pectinase and cellulase, and reduce fruit softening. Furthermore, tea polyphenols have significant antibacterial effects, effectively inhibiting pathological water loss caused by harmful microorganisms damaging fruits.

[0019] Citrus peel extract contains substances such as lemon polyphenols and flavonoids, which have a significant ability to scavenge free radicals and can slow down the darkening of color, softening of texture, and loss of nutrients in fruits caused by oxidation. At the same time, citrus peel extract is rich in pectin, a natural polysaccharide that can form a gel-like film on the surface of fruits, which can lock in water, isolate air, and block pollutants.

[0020] Konjac extract contains a large amount of glucomannan, which can physically block gas exchange, significantly reduce respiration intensity, and delay fruit ripening.

[0021] Peach bark extract has strong hydrophilicity and forms a soft film, which can prevent the peel from drying and cracking and reduce fruit weight loss.

[0022] Aloe extract contains aloe polysaccharides, which have excellent film-forming properties. They can form a thin, breathable protective film on the fruit surface, reducing transpiration water loss, delaying shrinkage, and maintaining fruit firmness and freshness. They can also scavenge reactive oxygen species such as superoxide anions and hydroxyl radicals, reduce membrane lipid peroxidation, protect cell membrane integrity, and reduce browning and aging. Furthermore, they can inhibit pathogens and reduce rot, exhibiting inhibitory effects on common postharvest pathogenic fungi such as anthracnose, Botrytis cinerea, Penicillium, and Mucor, thus reducing the fruit rot rate.

[0023] Sunflower extract contains a large amount of diterpenoids, which can effectively inhibit fungi that cause fruits and vegetables to rot, indirectly helping to maintain the integrity of fruits and vegetables, thereby reducing water loss.

[0024] The second technical solution of the present invention: a method for preparing the above-mentioned plant compound preservative, comprising the following steps: The plant-based compound preservative was obtained by mixing tea extract, citrus peel extract, konjac extract, peach bark extract, aloe vera extract, and sunflower extract evenly.

[0025] The third technical solution of the present invention: the application of the above-mentioned plant compound preservative in extending the shelf life of guava.

[0026] The present invention discloses the following technical effects: The plant-based compound preservative of this invention can inhibit the metabolism of guava, significantly reduce respiration intensity, and delay fruit ripening; it can improve the antioxidant capacity and free radical scavenging ability of guava, and slow down the darkening of color, softening of texture and loss of nutrients caused by oxidation; it can form a protective film on the surface of guava to reduce moisture loss; and it can inhibit pathogens and reduce the rot rate of guava.

[0027] The plant-based compound preservative of this invention contains tea extract, citrus peel extract, konjac extract, peach bark extract, aloe vera extract, and sunflower extract, which work synergistically to significantly improve the preservation effect of guava and thus extend its shelf life.

[0028] Using the plant-based compound preservative of this invention will not affect the flavor of guava fruit. Detailed Implementation

[0029] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0030] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0031] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0032] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0033] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0034] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0035] Guava fruits have thin, delicate skins, making them highly susceptible to bruising, softening, yellowing, and rotting after harvest. This severely impacts the fruit's edible quality and commercial value, posing significant challenges to its storage, transportation, and long-distance distribution. Therefore, it is necessary to research methods for controlling post-harvest quality deterioration in guava fruits, reducing post-harvest losses, maintaining good edible quality, and enhancing their commercial value.

[0036] I. Current Status of Postharvest Physiological Research on Guava Fruit 1. Respiration and ethylene release Respiration is a crucial indicator of postharvest fruit life activity. It involves the slow breakdown of complex organic matter in fruit tissues into simpler organic compounds under the action of enzymes, releasing energy in the process. While respiration maintains normal postharvest fruit metabolism and reduces the accumulation of harmful intermediate products, it also leads to depletion of the fruit's nutrient matrix, resulting in decreased fruit quality, tissue aging, weight loss, water loss, and senescence. Ethylene, a senescence-promoting plant hormone, promotes and increases the respiration intensity of postharvest fruits and vegetables, accelerating the release of ethylene and postharvest ripening and senescence. It also promotes chlorophyll degradation and softening of the fruit, leading to a decline in postharvest quality and a shortened shelf life. Studies by Singh et al. found that guava fruits exhibited a significant respiratory peak on the 4th day after harvest (stored at 25℃), which was observed with 300 nL·L⁻¹. -1 1-MCP treatment for 24 hours, 600 nL·L -1 Treatment with 1-MCP for 6 or 12 hours delayed the onset of the respiratory peak in guava fruits, with the peak occurring only on the 8th day. The peak value was significantly lower than that of untreated guava fruits. Untreated guava fruits reached their peak ethylene release on the 5th day post-harvest, while those treated with 300 nL·L⁻¹... -1 1-MCP treatment for 24 hours, 300 nL·L -1 After 1-MCP treatment for 12 or 24 hours, the peak ethylene release was delayed by 3 days, and the peak value was significantly lower than that of untreated guava fruit. Studies by Bassetto et al. also showed that guava fruit exhibited a respiratory peak on the 5th day post-harvest (stored at 25°C), with a peak CO2 concentration of 148.9 mg·kg⁻¹. -1 ·h -1 After 900 nL·L -1 The respiration rate of guava treated with 1-MCP was only 85.3 mg·kg⁻¹ during the later stages of storage. -1 ·h -1 .

[0037] 2. Fruit firmness Firmness is an important indicator of fruit quality, and softening is the most significant sign of ripening and softening. Freshly harvested guava fruits have a firmer core than flesh, making them more difficult to eat. As the fruit ripens after harvest, the core firmness decreases rapidly, becoming soft and delicate with a pleasant aroma. On the day of harvest, the average firmness of guava fruit is 8 kg / cm². 2 After one day of storage (25℃), its hardness decreased to 2.8 kg / cm². 2 The hardness decreased by approximately 65%, but from day 1 to day 3, the hardness only decreased by 0.8 kg / cm². 2 The reduction was approximately 10%, and the hardness decreased by 1.13 kg / cm² from day 3 to day 5. 2Subsequently, from day 5 to day 9, the rate of decrease in hardness slowed down, with a total reduction of 0.4 kg / cm². 2 Therefore, the hardness of guava fruit decreases most rapidly in the early stages of ripening. Bassetto et al. reported that the hardness of guava pulp was 132.5 N at harvest, but only 16.2–22.3 N in the later stages of storage (5 days after storage at 25°C). Bashir's research also showed that the hardness of guava fruit began to decrease sharply after 4 days of storage at room temperature (22±1°C, 90–95% RH) after harvest.

[0038] 3. Softening related enzymes Fruit softening is caused by the degradation of cell wall substances such as pectin methyl esterase (PME), polygalacturonase (PG), cellulase, and β-galactosidase by major cell wall degrading enzymes, leading to changes in the ultrastructure of the cell wall (reduced intercellular connections, loosened cell structure, cell dissociation, etc.). However, these cell wall degrading enzymes play different roles in the degradation of cell wall substances and the destruction of cell wall structure. PME's main function is to remove the methoxy group from the uronic acid residues in pectin, catalyzing the conversion of pectin methyl esterase to pectic acid, which facilitates the degradation of polygalacturonic acid by PG, resulting in fruit softening. PG is one of the main cell wall hydrolytic enzymes; its main function is to hydrolyze the 1,4-2-D-galactosidic bonds of pectic acid in the fruit cell wall, causing cell wall disintegration and resulting in fruit softening. Cellulase is widely present in mature fruits. Its main function is to hydrolyze the β-1,4 glycosidic bonds of cellulose in the fruit cell wall, breaking it down into glucose, thus degrading the cell wall skeleton material cellulose and softening the fruit.

[0039] 4. Nutritional components Guava fruit has thick, fine-textured flesh, high sugar content, and a suitable acidity, possessing a unique sweetness and aroma. Studies by Chen Weihui et al. have shown that during post-harvest storage of *Guava 'New Century'*, the soluble solids content of the fruit increases, with vitamin C and organic acids increasing rapidly in the early stages, while the latter decreases likely due to further ripening and dehydration. Liu Shenghui et al. reported that the vitamin C content varies in different parts of the *Guava 'New Century'* flesh, with the highest content near the peel, followed by the core, and the lowest in the middle. Li Shengfeng et al. reported that the soluble sugars in guava fruit flesh are mainly fructose, glucose, and sucrose, while the organic acids are mainly citric acid (accounting for over 50% of the total acid) and succinic acid, with slight differences in the proportions among different varieties. Studies by Bashir et al. have shown that during postharvest storage, the soluble solids and total soluble sugars of guava increase as its hardness decreases; reducing sugars and titratable acids show an increasing trend before the guava respiratory climacteric and then decrease after the climacteric; the total protein content gradually increases before full ripening and decreases after full ripening.

[0040] 5. Fruity aroma The aroma components of guava fruit are mainly terpenes, esters, alcohols, and aldehydes. As guava fruit matures, the content of terpenes and alcohols decreases, while the content of esters and aldehydes increases, with esters being the dominant component in fully ripe fruit. Studies by Flavio et al. have shown that esters are the main aroma components of ripe guava fruit, with cis-3-vinyl acetate and trans-3-vinyl acetate being the main components, containing 21.78% and 17.80%, respectively. Studies by Chen Xinjun et al. have also found that the aroma components of guava fruit are mainly esters and sesquiterpene hydrocarbons. The main ester component in the aroma of unripe guava fruit is ethyl acetate, while the main ester components in the aroma of ripe fruit are hexyl acetate and ethyl hexanoate. The sesquiterpene hydrocarbons in the aroma of unripe guava fruit are mainly β-caryophyllene and geraniol.

[0041] 6. Fruit peel pigments Fruit color is an important attribute of fruit sensory quality. The pigments in guava fruit peel mainly consist of chlorophyll, carotenoids, and flavonoids. When unripe, guava peel is greenish-yellow, gradually turning yellowish-green or yellow as it ripens. Studies by Li et al. have shown that guava fruit color is primarily determined by chlorophyll and carotenoids; fruit bagging significantly reduces the total chlorophyll content, but has little impact on its degradation. The chlorophyll content of guava peel is high in different seasons, but varies, being relatively higher in summer (512 mg / 100g) and relatively lower in winter (432 mg / 100g). Studies by Chen Weihui et al. have shown that after 15 days of storage at room temperature, the chlorophyll content of guava fruit decreased from 488.27 mg / 100g at harvest to 282.75 mg / 100g.

[0042] 7. Postharvest diseases of fruit Guava fruits are highly susceptible to water loss after harvest, severely impacting their post-harvest commercial value. After 5 days at room temperature, post-harvest guava fruits exhibit a weight loss rate of 9.8%. The peel first shrivels from dehydration, followed by a separation between the placenta and the inner pericarp, causing the fruit to soften rapidly, rot, and lose its commercial value. However, after individual guava fruits are bagged and stored in controlled atmosphere (8-10℃) for 20 days, the weight loss rate is only 0.5%, effectively reducing weight loss, extending post-harvest storage life, and increasing commercial value. Furthermore, polyethylene film or low-density polyethylene bags effectively control the natural water loss of guava fruits.

[0043] Guava is a chilling-sensitive fruit. Although low temperatures can effectively extend its shelf life, chilling injury will occur at a critical temperature (around 5℃), rendering the fruit unmarketable. The main symptoms of chilling injury in guava include browning and discoloration of the peel, surface depressions, and in severe cases, waterlogging of the core. Ye Siwei's research shows that 'Pearl' guava fruit showed chilling injury symptoms after 4 days of storage at 0℃, but only after 22 days of storage at 5℃. Furthermore, the severity of chilling injury worsened after 3 days of rewarming at 20℃, suggesting that the critical temperature for chilling injury in 'Pearl' guava is approximately 5℃. Pre-storage heat treatment or salicylic acid treatment cannot effectively control chilling injury in 'Pearl' guava fruit at 0℃. Fumigation with 100 mg / L methyl jasmonate (MeJA) for 16 hours can effectively alleviate the occurrence of chilling injury symptoms after 14 days of rewarming at 0℃. Soaking with MeJA does not reduce chilling injury.

[0044] Fungal infection is the main cause of post-harvest rot in guava fruit. Currently, the main diseases affecting guava fruit both domestically and internationally are anthracnose, which occurs widely during the fruit ripening period. The main symptoms are circular or nearly circular lesions with a sunken center, water-soaked appearance, and brown to dark brown color, with a diameter of 3-30 cm. Scorched rot begins to damage the fruit in the later stages of ripening, with a higher incidence in large-fruited guavas. It generally starts from both ends of the fruit, with lesions initially appearing as light brown, round spots, later turning dark brown to black. The peel wrinkles, and eventually the entire fruit turns black and rots, with small black granules covering the lesions. When the diseased fruit is cut open, the flesh is brown to black. The main symptoms of purple rot are that the skin of the affected fruit turns brown to brownish-brown. In severe cases, the entire fruit becomes brown and soft, with many small black granules growing on the surface. The flesh is purplish-blue, eventually turning brown. Brown rot often enters from the fruit stem. Initially, round, yellowish-brown, water-soaked patches appear on the affected area, followed by fruit rotting. Small milky white to light brown spots appear on the affected area, and the flesh of the diseased fruit is brown. The main symptoms of fruit rot are sunken brown spots with small black spots growing on them. The flesh under the peel of the diseased area is gray. Pre-harvest bagging of guava fruits can reduce the occurrence of fungal diseases during post-harvest storage. At the same time, yeast and Bacillus subtilis can also effectively control the occurrence of post-harvest scorch rot in guava fruits.

[0045] Currently, methods to improve the shelf life of guava are mainly divided into five categories: pre-harvest management, physical, chemical, biological, and integrated preservation. Each method has its effectiveness but also significant drawbacks. Pre-harvest methods, such as nitrogen and potassium control, pre-harvest water control, fruit bagging, and harvesting at 7-8 maturity, enhance the fruit's inherent storage resistance. However, this method is time-consuming, slow to show results, difficult to control maturity, and cannot address post-harvest aging and disease problems. Physical preservation is the mainstream method, including low-temperature refrigeration, controlled atmosphere storage, heat treatment, irradiation, and packaging preservation. Low-temperature refrigeration easily leads to chilling injury in guava and has high cold chain costs; controlled atmosphere storage equipment is expensive, and excessive CO2 can cause off-flavors and browning; heat treatment is cumbersome and easily burns the fruit peel; irradiation is costly and has low consumer acceptance; packaging preservation is prone to condensation, mold growth, or CO2 damage. Chemical preservation is fast-acting and low-cost, commonly using fungicides and ethylene inhibitors, but it carries risks of pesticide residues, resistance, and compliance issues, and may also affect fruit flavor and chilling injury tolerance. Biological preservation methods, such as antagonizing microorganisms and using natural extracts, are green and safe, but their effects are unstable, slow to take effect, and costly. Some extracts can also mask the aroma of the fruit, limiting their commercial application. It is clear that current methods all have limitations and cannot simultaneously extend the shelf life of guava while minimizing the impact on fruit quality.

[0046] In the following examples, "parts" refers to "parts by weight".

[0047] Example 1 A plant-based compound preservative for extending the shelf life of guava: (1) Preparation of tea extract: Fresh green tea leaves (Longjing 43) were dried at 60℃ and then pulverized to 100 mesh to obtain tea powder. After mixing tea powder and water at a ratio of 1g:10mL, add 0.6% of the tea powder mass of compound enzyme (compound enzyme consists of cellulase and pectinase in a mass ratio of 1:2, with cellulase having an enzyme activity of 100,000 U / g and pectinase having an enzyme activity of 30,000 U / g). Enzymatically hydrolyze at 50℃ for 35min, then heat to 90℃ to inactivate the enzyme. Filter through 8 layers of gauze to obtain the enzymatic hydrolysate. The enzymatic hydrolysate and water were mixed in a 1:1 volume ratio and ultrasonically treated for 35 minutes at a power of 250W and a temperature of 40℃. After centrifugation, the precipitate was collected, dried at 60℃, and ground to 200 mesh to obtain the tea extract.

[0048] (2) Preparation of citrus peel extract: After the citrus peel is naturally dried (with a moisture content of about 10%), it is pulverized to 50 mesh to obtain citrus peel powder. Citrus peel powder and water were mixed at a ratio of 1g:12mL. Grinding balls (made of zirconium oxide, with a diameter of 2mm, and the amount was 3 times the mass of citrus peel powder) were added. After grinding for 3 hours, the mixture was filtered through 8 layers of gauze to obtain the filter residue and the first filtrate. The filter residue and a 70 vol.% ethanol aqueous solution were mixed at a ratio of 1 g: 10 mL, and ultrasonically treated for 20 min at a power of 300 W and a temperature of 45 °C. The mixture was then filtered through 8 layers of gauze to obtain the second filtrate. The first and second filtrates were mixed, concentrated, and dried (at 50°C) to obtain the citrus peel extract.

[0049] (3) Preparation of konjac extract: Fresh konjac is washed and homogenized to obtain konjac homogenate; Konjac homogenate and water were mixed at a ratio of 1g:10mL and ultrasonically treated for 40min at 200W and 30℃. After filtration through 8 layers of gauze, the residue was vacuum dried (40℃ and -0.08MPa). Finally, it was washed with anhydrous ethanol, air-dried, and ground to 200 mesh to obtain konjac extract.

[0050] (4) Preparation of peach bark extract: The peach bark is dried (at 50°C) and then pulverized to 100 mesh to obtain peach bark powder. Peach bark powder and an 80 vol.% ethanol aqueous solution were mixed at a ratio of 1 g: 11 mL, and the mixture was extracted at room temperature (20~25℃) for 24 h. The extract was then filtered through 8 layers of gauze to obtain the extract. The extract was concentrated to 1 / 5 of its original volume to obtain a concentrated solution. The concentrate was extracted three times with an equal volume of ethyl acetate. The ethyl acetate extracts were then mixed and removed by rotary evaporation to obtain peach bark extract.

[0051] (5) Preparation of aloe vera extract: Fresh aloe vera is sliced, wrapped in four layers of gauze, and then pressed for 30 hours to obtain aloe vera juice. The aloe vera juice was heated to 105°C and held for 15 minutes. The surface ash was removed, and the mixture was cooled to room temperature. It was then concentrated and dried (at 80°C) to obtain the aloe vera extract.

[0052] (6) Preparation of sunflower extract: After the sunflower heads are naturally dried (with a moisture content of about 10%), they are pulverized to 100 mesh to obtain sunflower head powder. Sunflower disc powder and 95 vol.% ethanol aqueous solution were mixed at a ratio of 1 g: 12 mL, heated to 80 °C for 2 h, and the extract was obtained by filtration through 8 layers of gauze. After removing the ethanol from the extract by rotary evaporation, the extract was dried (at a temperature of 60°C) to obtain sunflower extract.

[0053] (7) Preparation of plant compound preservative: Eight parts of tea extract, five parts of citrus peel extract, ten parts of konjac extract, three parts of peach bark extract, six parts of aloe vera extract, and three parts of sunflower extract were mixed evenly to obtain a plant-based compound preservative.

[0054] Example 2 A plant-based compound preservative for extending the shelf life of guava: (1) Preparation of tea extract: Fresh green tea leaves (Longjing 43) were dried at 60℃ and then pulverized to 100 mesh to obtain tea powder. After mixing tea powder and water at a ratio of 1g:10mL, add 0.5% of the tea powder mass of compound enzyme (compound enzyme consists of cellulase and pectinase in a mass ratio of 1:2, with cellulase having an enzyme activity of 100,000 U / g and pectinase having an enzyme activity of 30,000 U / g). Enzymatically hydrolyze at 55℃ for 25min, then heat to 90℃ to inactivate the enzyme. Filter through 8 layers of gauze to obtain the enzymatic hydrolysate. The enzymatic hydrolysate and water were mixed in a 1:1 volume ratio and ultrasonically treated for 40 minutes at a power of 300W and a temperature of 40℃. After centrifugation, the precipitate was collected, dried at 60℃, and ground to 200 mesh to obtain the tea extract.

[0055] (2) Preparation of citrus peel extract: After the citrus peel is naturally dried (with a moisture content of about 10%), it is pulverized to 50 mesh to obtain citrus peel powder. Citrus peel powder and water were mixed at a ratio of 1g:10mL. Grinding balls (made of zirconium oxide, 2mm in diameter, and 3 times the mass of citrus peel powder) were added and ground for 2 hours. The mixture was then filtered through 8 layers of gauze to obtain the residue and the first filtrate. The filter residue and a 65 vol.% ethanol aqueous solution were mixed at a ratio of 1 g: 12 mL, and ultrasonically treated for 15 min at a power of 250 W and a temperature of 40 °C. The mixture was then filtered through 8 layers of gauze to obtain the second filtrate. The first and second filtrates were mixed, concentrated, and dried (at 50°C) to obtain the citrus peel extract.

[0056] (3) Preparation of konjac extract: Fresh konjac is washed and homogenized to obtain konjac homogenate; Konjac homogenate and water were mixed at a ratio of 1g:8mL and ultrasonically treated for 30min at a power of 250W and a temperature of 25℃. After filtration through 8 layers of gauze, the residue was vacuum dried (temperature of 40℃ and pressure of -0.08MPa). Finally, it was washed with anhydrous ethanol, air-dried, and ground to 200 mesh to obtain konjac extract.

[0057] (4) Preparation of peach bark extract: The peach bark is dried (at 50°C) and then pulverized to 100 mesh to obtain peach bark powder. Peach bark powder and 85 vol.% ethanol aqueous solution were mixed at a ratio of 1 g: 10 mL, and extracted at room temperature (20~25℃) for 18 h. The extract was then filtered through 8 layers of gauze to obtain the extract. The extract was concentrated to 1 / 5 of its original volume to obtain a concentrated solution. The concentrate was extracted twice with an equal volume of ethyl acetate. The ethyl acetate extracts were then mixed and removed by rotary evaporation to obtain peach bark extract.

[0058] (5) Preparation of aloe vera extract: Fresh aloe vera is sliced, wrapped in four layers of gauze, and then pressed for 30 hours to obtain aloe vera juice. The aloe vera juice was heated to 115°C and held for 20 minutes. The surface ash was removed, and the mixture was cooled to room temperature. It was then concentrated and dried (at 80°C) to obtain the aloe vera extract.

[0059] (6) Preparation of sunflower extract: After the sunflower heads are naturally dried (with a moisture content of about 10%), they are pulverized to 100 mesh to obtain sunflower head powder. Sunflower disc powder and 90 vol.% ethanol aqueous solution were mixed at a ratio of 1 g: 15 mL, heated to 70 °C for 3 h, and the extract was obtained by filtration through 8 layers of gauze. After removing the ethanol from the extract by rotary evaporation, the extract was dried (at a temperature of 60°C) to obtain sunflower extract.

[0060] (7) Preparation of plant compound preservative: A plant-based compound preservative was obtained by mixing 6 parts of tea extract, 6 parts of citrus peel extract, 9 parts of konjac extract, 4 parts of peach bark extract, 8 parts of aloe vera extract, and 2 parts of sunflower extract evenly.

[0061] Comparative Example 1 Same as Example 1, except that the plant-based compound preservative for extending the shelf life of guava does not contain tea extract or citrus peel extract.

[0062] Comparative Example 2 Same as Example 1, except that the plant-based compound preservative for extending the shelf life of guava does not contain konjac extract or peach bark extract.

[0063] Comparative Example 3 Same as Example 1, except that the plant-based compound preservative used to extend the shelf life of guava does not contain sunflower extract.

[0064] Comparative Example 4 Same as Example 1, except that the citrus peel extract in the plant compound preservative used to extend the shelf life of guava is replaced with an equal number of parts by weight of grape skin extract. The preparation method of grape skin extract is as follows: After naturally drying the grape skins (with a moisture content of about 10%), grind them to 50 mesh to obtain grape skin powder. Grape skin powder and water were mixed at a ratio of 1g:12mL. Grinding balls (made of zirconium oxide, 2mm in diameter, and 3 times the mass of grape skin powder) were added and ground for 3 hours. The mixture was then filtered through 8 layers of gauze to obtain the filter residue and the first filtrate. The filter residue and a 70 vol.% ethanol aqueous solution were mixed at a ratio of 1 g: 10 mL, and ultrasonically treated for 20 min at a power of 300 W and a temperature of 45 °C. The mixture was then filtered through 8 layers of gauze to obtain the second filtrate. The first and second filtrates were mixed, concentrated, and dried (at 50°C) to obtain the grape skin extract.

[0065] Comparative Example 5 Same as Example 1, except that the preparation method of the peach bark extract is as follows: The peach bark is dried (at 50°C) and then pulverized to 100 mesh to obtain peach bark powder. Peach bark powder and an 80 vol.% ethanol aqueous solution were mixed at a ratio of 1 g: 11 mL, and the mixture was extracted at room temperature (20~25℃) for 24 h. The extract was then filtered through 8 layers of gauze to obtain the extract. The extract was concentrated and then dried (at 50°C) to obtain peach bark extract.

[0066] Comparative Example 6 Same as Example 1, except that the preparation method of the plant compound preservative is as follows: Mix 3 parts tea extract, 10 parts citrus peel extract, 5 parts konjac extract, 6 parts peach bark extract, 2 parts aloe vera extract, and 8 parts sunflower extract evenly to obtain a plant-based compound preservative.

[0067] Example 1 The tested variety was *Prunus cerasifera*, with autumn flowers and spring fruits, collected from Guangxi. Uniformly sized, green-ripe guava fruits were harvested in the early morning and transported back to the laboratory within 2 hours of harvesting. Care was taken during harvesting and transportation to avoid mechanical damage. The plant-based compound preservative prepared in the examples or comparative examples was weighed and prepared into a 5 wt.% solution. Sodium alginate was then added to achieve a sodium alginate concentration of 0.8 wt.% in the preservative solution. The preservative solution was obtained by mixing and dissolving the alginate. Guava fruits were immersed in the preservative solution for 2 minutes, then removed, air-dried, and stored at 20°C and 85% relative humidity. Each treatment consisted of 100 guava fruits, with guava fruits not treated with the preservative solution serving as a control. The weight loss and decay rates of the guava were measured and calculated at 5, 10, and 20 days of storage. The results are shown in Tables 1 and 2.

[0068] Weight loss rate = (weight loss / original weight) × 100% Rot rate = (Number of rotten items / Total number of items) × 100%.

[0069] Table 1. Weight loss rate of guava Table 2. Guava Rot Rate Sensory evaluation of guava fruit was conducted based on its texture and flavor, and the results are shown in Table 3.

[0070] Table 3 Sensory evaluation results The volatile components and contents of guava fruits harvested in the early morning during the green-ripe stage and of uniform size, as well as guava fruits stored for 20 days, were determined by headspace solid-phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS). The results are shown in Table 4.

[0071] Table 4. Volatile components and their contents in guava fruit. The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A plant-based compound preservative for extending the shelf life of guava, characterized in that, It includes the following components in parts by weight: 6-8 parts tea extract, 4-6 parts citrus peel extract, 8-10 parts konjac extract, 3-4 parts peach bark extract, 5-8 parts aloe vera extract, and 2-4 parts sunflower extract.

2. The plant compound preservative according to claim 1, characterized in that, The method for preparing the tea extract includes the following steps: After the tea leaves are crushed, water and compound enzymes are added for enzymatic hydrolysis. After the enzymes are inactivated, the enzymatic hydrolysate is obtained. The enzymatic hydrolysate was mixed with water and then subjected to ultrasonic treatment. After centrifugation, the precipitate was collected to obtain the tea extract.

3. The plant compound preservative according to claim 2, characterized in that, The complex enzyme comprises cellulase and pectinase in a mass ratio of 1:2; And / or, the amount of the compound enzyme used is 0.5-0.8% of the tea mass; And / or, the ultrasonic treatment has a power of 200~300W, a temperature of 40~45℃, and a time of 30~40min.

4. The plant compound preservative according to claim 1, characterized in that, The method for preparing the citrus peel extract includes the following steps: The citrus peel is crushed and added to water, then ball-milled and filtered to obtain the residue and the first filtrate. The filter residue was added to an ethanol solution, ultrasonicated, and then filtered to obtain the second filtrate. The first and second filtrates were mixed, concentrated, and dried to obtain the citrus peel extract.

5. The plant compound preservative according to claim 1, characterized in that, The preparation method of the konjac extract includes the following steps: After homogenizing the konjac slurry, water was added, and the mixture was extracted by ultrasound and filtered. The residue was then vacuum dried, washed with ethanol, air-dried, and ground to obtain the konjac extract.

6. The plant compound preservative according to claim 1, characterized in that, The method for preparing the peach bark extract includes the following steps: The peach bark was crushed and mixed with an ethanol solution. After extraction at room temperature, the extract was concentrated and extracted with ethyl acetate. After removing the solvent, the peach bark extract was obtained.

7. The plant compound preservative according to claim 1, characterized in that, The preparation method of the aloe vera extract includes the following steps: Fresh aloe vera is pressed to obtain aloe vera juice; The aloe vera juice was heated to remove the surface ash, cooled to room temperature, concentrated, and dried to obtain the aloe vera extract.

8. The plant compound preservative according to claim 1, characterized in that, The method for preparing the sunflower extract includes the following steps: The sunflower head was crushed and mixed with an ethanol solution. After heating and extraction, the extract was collected, and the solvent was removed to obtain the sunflower extract.

9. A method for preparing the plant composite preservative according to any one of claims 1 to 8, characterized in that, Includes the following steps: The plant-based compound preservative was obtained by mixing tea extract, citrus peel extract, konjac extract, peach bark extract, aloe vera extract, and sunflower extract evenly.

10. The application of the plant-based compound preservative according to any one of claims 1 to 8 in extending the shelf life of guava.

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