Preparation method of green plum juice

Abstract

The invention discloses a preparation method of green plum juice, which comprises the following steps: pretreatment: picking fruits, standing at a ventilated and shady place for one night, removing pedicels on the fruits, cleaning the fruits, and drying the cleaned fruits to obtain green plum juice; the green plum juice is prepared by the following steps: cleaning green plum fruits, spreading the fruits in a clean, shady, cool and ventilated place for airing, freezing at low temperature: freezing the treated fruits at low temperature, and canning: canning the treated fruits and isomaltooligosacharide, so as to obtain the green plum juice after one week. The green plums are treated by a pre-freezing method of freezing at-20 DEG C for 24 hours, the green plum juice is prepared by weighing the IMO, the green plum fruits and the IMO according to the proportion of 1: 1 (w / w), and the green plum juice can be drunk after being sealed and soaked for one week, so that the production efficiency of the green plum juice is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of making prunus mume syrup, and particularly relates to a preparation method of prunus mume syrup. Background Art

[0002] Prunus mume Sieb. et Zucc. is a perennial woody plant belonging to the genus Prunus of the Rosaceae family. Its fruits are rich in nutrients and aromatic substances, and have health care effects such as appetizing the spleen, relieving cough and pain, nourishing the lungs, relieving fatigue and irritability, detoxifying, inhibiting bacteria, purifying blood, and antioxidant, and have significant nutritional and medicinal values.

[0003] Prunus mume syrup is an extract obtained by sugaring prunus mume fruits, which can reduce the acidity of the fruits, has a suitable sweet and sour taste, retains most of the natural components, and is convenient for long-term storage. However, there is a lack of research on the main nutritional components and flavor analysis of prunus mume syrup at home and abroad. The changes in the nutrients of prunus mume and the aroma components of prunus mume fruits are important indicators for evaluating the quality of prunus mume products, and both have important guiding significance for the comprehensive development of prunus mume resources, processing quality control, and product quality detection.

[0004] The traditional method for making prunus mume syrup requires at least three months of soaking time, uses white granulated sugar or rock sugar as the main raw materials, and these sugars are all disaccharides. Although sugar is an important part of the human energy source, excessive intake may lead to health problems such as decreased immunity and weight gain. Therefore, in order to reduce the health risks caused by excessive sugar intake, it is urgent to develop a sugar substitute to replace traditional sugars.

[0005] Isomalto-oligosaccharides (IMO), as a new type of functional sugar substitute, has a sweetness only half that of sucrose, and has a low glycemic index (GI) and calories, which helps to control weight and prevent related diseases. IMO has high stability, excellent heat and acid resistance, and high solubility, can be added to drinks such as milk for combined drinking, and can also be added to foods such as cakes for use. At the same time, IMO has the characteristics of inhibiting the growth of harmful bacteria, promoting the health of intestinal flora, enhancing immunity, and promoting nutrient absorption.

[0006] By using isomaltooligosaccharide (IMO) to replace traditional white granulated sugar, this patent can significantly reduce the GI value of greengage dew, allowing diabetic patients and those with sugar intolerance to consume it with confidence. In addition, IMO also has the property of inhibiting the growth of harmful bacteria, solving the problems of easy mildew and serious loss during the traditional production process of greengage dew. The freezing method is currently widely used in experiments on animals, plants, microorganisms, and pathological medicine. By destroying cell structures, it can promote the exudation of intracellular fluid. Through the pretreatment of greengages using the freezing method, this patent not only effectively shortens the production cycle but also improves production efficiency, meeting the requirements of industrialized and large-scale production.

[0007] Therefore, by treating greengages with the freezing method and using IMO to replace white granulated sugar, this patent not only optimizes the production process of greengage dew, improves the healthiness and market competitiveness of the product, but also solves multiple problems in the traditional production method, having significant technical advantages and market prospects.

[0008] And the production process of greengage dew is also recorded in the prior art. Specifically, first, pretreatment is carried out on the large, undamaged greengage fruits purchased. The surface of each fruit is washed with running tap water; then it is washed with distilled water, and the washed fruits are dried at room temperature. There are two impregnation methods. One is to directly impregnate the whole fruit, and the other is to cut the fruit with a sterile knife and manually remove the fruit core, and use the pitted pulp to impregnate the greengage dew.

[0009] Then the fruits and sugar are bottled to make greengage dew. In a 2L glass jar that has been surface-sterilized, a total of 600g of whole greengage fruits or pitted pulp is added, and 400g of refined sugar is added to each jar. When bottling, 1 - 2 cm of refined sugar is spread at both the bottom and top of the bottle, and the fruits and sugar are alternately filled into the jar. Each glass jar is partially sealed with a clean cotton cloth, covered with a plastic lid, and first stored at room temperature for 2 days. After 2 days, 200g of refined sugar is added to each glass jar in a 1:1 (w / w) ratio with the fruits or pitted pulp, and the prepared glass jars are naturally fermented in the dark at room temperature for 3 months.

[0010] Currently, the production efficiency of greengage dew products is extremely low. The impregnation time for preparing greengage dew by traditional methods requires at least three months, and sometimes even as long as half a year or one and a half years. The traditional production method of greengage dew has significantly increased the production time and labor cost of the product, which is also the most critical problem for the current difficulty in large-scale production of greengage dew products, but there is no relevant technology to solve this problem.

[0011] Traditional greengage dew is made with a large amount of granulated sugar, which does not meet the requirements of modern nutrition and the pursuit of a healthy diet by contemporary people. Currently, the number of patients with various chronic diseases including diabetes caused by excessive sugar intake has been increasing year by year, seriously threatening national health. In actual production, using granulated sugar or rock sugar to make greengage dew is prone to generating a large number of miscellaneous bacteria, prone to mildew, and the loss is very serious.

[0012] This patent proposes a solution to the problems existing in the actual production of greengage dew, and invents a set of efficient, complete, specific, low-cost and easily replicable production technologies. Summary of the Invention

[0013] The purpose of the present invention is to provide a preparation method of greengage dew to solve the problems of low efficiency, long time consumption in the traditional production method of greengage dew, the sugar used not meeting the health needs of consumers, and being prone to mildew in actual production.

[0014] To achieve the above object, the present invention provides the following technical solution: A preparation method of greengage dew, comprising the following steps:

[0015] S1: Pretreatment: Select large fruits at seven - maturity (fruit diameter: 25 - 40 cm, single fruit weight: 18 - 25 g) with smooth and undamaged appearance and fewer fruit spots on a sunny day. After the fresh fruits are picked, they are placed in a ventilated and shady place and left to stand overnight, then the fruit stalks on the fruits are removed, and then the fruits are washed and spread out flat to dry in a clean, shady and ventilated place. It should be noted that if the plum fruits are directly placed on a non - breathable plane such as a plastic sheet, they need to be dried in the shade for another 3 - 4 hours, that is, after the water on the upper surface of the fruits is dried, turn them over to ensure that the surface of the fruits is completely dry.

[0016] S2: Low - temperature freezing: Put the processed plum fruits into a clean sealed bag and freeze them in a low - temperature refrigerator at - 20 °C for 24 h for pretreatment.

[0017] S3: Making and canning: Disinfection of glass jars: Put the glass jars into clean water, heat them to 100 °C, boil for 10 - 15 min, then pour out the water, put them into a drying oven and dry for 3 h for standby.

[0018] Before making greengage dew, the operator should wear a mask and sterile nitrile gloves. Weigh the greengage fruits and isomaltooligosaccharide according to the ratio of 1:1 (w / w) (if the volume of the bottle increases, the mass of the fruit and sugar increases in equal proportion). First, spread a layer of sugar at the bottom, then a layer of fruits, and then layer by layer of sugar and fruits until it is full, and the top layer is capped with sugar. The sugar needs to cover the fruits to achieve the effect of isolating air and reducing the mildew rate. Finally, cover it with a sealed lid and store it in a shady and ventilated place. It can be drunk after one week.

[0019] Technical effects and advantages of the present invention: In this application, the pretreatment freezing method at -20°C for 24 hours is used to process greengage plums. Combining with IMO, greengage plum fruits and IMO are weighed in a ratio of 1:1 (w / w) to make greengage plum dew. After sealing and impregnating for one week, it can be consumed, greatly improving the production efficiency of greengage plum dew;

[0020] As an oligosaccharide, IMO has a protective effect and can reduce the degradation of heat-sensitive and oxidation-sensitive components (such as VC) in the syrup. Pretreating the plum fruits by freezing can greatly shorten the impregnation and liquid extraction time. Freezing pretreatment can accelerate the loss of water and inclusions by destroying the cell structure of the plum fruits, shortening the impregnation time. Due to its smaller molecule size and high solubility, IMO is easier to dissolve and melts faster than granulated sugar. Description of the Drawings

[0021] Figure 1 This is the greengage plum fruit of the present invention;

[0022] Figure 2 This is the total acid content of the greengage plum dew of the present invention;

[0023] Figure 3 This is the soluble solid content of the present invention;

[0024] Figure 4 This is the change situation of impregnated greengage plum dew under different treatments of the present invention,

[0025] The order of greengage plum dew from left to right is WF, WR, IF, IR. WF: White Sugar with Freezing Method; WR: White Sugar at Room Temperature; IF: IMO with Freezing Method; IR: IMO at Room Temperature;

[0026] Figure 5 This is the antioxidant activity of impregnated greengage plum dew under different treatments of the present invention;

[0027] Figure 6 This is the types of aroma compounds of fresh fruits and impregnated greengage plum dew under different treatments of the present invention;

[0028] Figure 7 This is the sensory evaluation radar chart of impregnated greengage plum dew under different treatments of the present invention;

[0029] Figure 8 This is the nitrite content of impregnated greengage plum dew under different treatments of the present invention. Detailed Embodiments

[0030] The following further describes the specific embodiments of the present invention in conjunction with the accompanying drawings. It should be noted here that the description of these embodiments is for helping to understand the present invention, but does not constitute a limitation to the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0031] Example 1:

[0032] (1) Fruit treatment

[0033] First is fruit treatment. Select a sunny day for fruit picking. Choose large fruits at seven - maturity with smooth and undamaged appearance and fewer fruit spots (fruit diameter: 25 - 40 cm, single - fruit weight: 18 - 25 g). This is to avoid reducing the probability of mold in the plum dew during later impregnation. After fresh fruits are picked, place them in a ventilated and cool place and let them stand overnight. In this way, the fruit stalks will become slightly loose, which is beneficial for removing the fruit stalks in the next step. The next day, use toothpicks to remove the fruit stalks on the fruits, then wash the fruits, and lay them flat in a clean, cool and ventilated place to dry. It should be noted that if the plum fruits are directly placed on a non - breathable plane such as a plastic sheet on the lower surface of the fruits, they need to be dried in the shade for another 3 - 4 hours, that is, turn the fruits over after the water on the upper surface of the fruits is dried to ensure that the surface of the fruits is completely dry and then they can be reserved for use. This is also to reduce the probability of mold in the impregnated plum dew. If mechanical treatment is used for fruit treatment here, it can save labor costs, improve production efficiency, and the actual operation steps are simple and highly feasible.

[0034] (2) Low - temperature freezing

[0035] After the fruit is treated, a low - temperature pretreatment is required to achieve the purpose of efficiently and quickly impregnating juice. Put the treated plum fruits into a clean and sealed bag and freeze them in a - 20°C low - temperature refrigerator for 24 h. This operation step is simple. If large - scale production is carried out, they can be directly placed in a - 20°C low - temperature cold storage for low - temperature treatment and reserved for use.

[0036] (3) Preparation for bottling

[0037] While the fruits are being put into the refrigerator for low - temperature pretreatment, it is necessary to prepare clean and sterile sealable glass bottles in advance, which can reduce the mold rate of the impregnated plum dew. The specific steps are as follows: First, put the glass jars into water and heat them to 100°C, boil for 10 - 15 min, pour out the water, and then put them into a drying oven to dry for 3 h and reserve for use. After the plum fruits are frozen at low temperature for 24 h, the formal production of plum dew can begin. This step will be more convenient and faster when carried out by mechanical operation in the factory.

[0038] Before making the greengage dew, the operator is required to wear a mask and sterile nitrile gloves to minimize operations that may cause the greengage dew to mold later. The greengage fruits and IMO are weighed in a mass ratio of 1:1 to make the greengage dew. First, a layer of sugar is spread at the bottom, then a layer of fruits, and then layer by layer of sugar and fruits until it is full, and the top layer is capped with sugar. The sugar needs to cover the fruits to achieve the effect of isolating air and reduce the mold rate. Finally, cover it with a sealed lid, label the glass bottle with the name and date, and store it in a ventilated and cool place. This step of bottling, if operated manually, has simple steps and is easy to operate. It can also be produced mechanically, which is more cost-effective, has higher efficiency, and greatly reduces the mold rate.

[0039] Since after the treatment by the freezing method combined with IMO, the greengage dew will not produce too many bubbles, the producer can directly immerse the greengage dew in the commercial glass bottle. After disinfecting in the autoclave according to the food production standard, it can be directly packaged and sold to consumers. Or after the immersion is completed, the drink can be pasteurized, and then sub-packed, packed, and sold in plastic bottles. This not only meets the national food production standard but also does not affect the efficacy and nutritional value of the inactivated drink.

[0040] Prepared according to the above method, denoted as IF.

[0041] Example 2:

[0042] The preparation process is the same as that of Example 1, except that only IMO is replaced with white granulated sugar, and the prepared product is denoted as WF.

[0043] Example 3:

[0044] The preparation process is the same as that of Example 2, except that freezing is replaced with room temperature, and the prepared product is denoted as WR.

[0045] Example 4:

[0046] The preparation process is the same as that of Example 1, except that only freezing is replaced with room temperature, and the prepared product is denoted as IR.

[0047] Perform physical and chemical index tests on the greengage dew prepared in Examples 1, 2, 3, and 4 above:

[0048] 1. General physical and chemical properties

[0049] Combined Figure 2 And Table 1, the total acid content of the greengage dew of IF7d is the highest, which is 7.55 mg / L, Figure 3Among them, the soluble solids content of the IMO impregnation group was lower than that of the white granulated sugar group, and the IF7d content was the lowest, at 36.27%, lower than IR7d (47.6%), and only higher than that of fresh fruits. After impregnation for 90 days, the soluble solids content of the white granulated sugar group was the highest, with WF90d being 61.8% and WR90d reaching 62.3%. In addition, after impregnation for 90 days, the soluble solids content of the frozen-pretreated greengage dew group increased significantly, and IF90d (51.3%) even exceeded IR90d (46.5%).

[0050] Table 1 General physicochemical properties of fresh fruits and greengage dews impregnated with different sugars at 7 days and 90 days

[0051]

[0052] 2. Apparent and color change characteristics

[0053] The color of greengage dews with different sugars and different pretreatments changed significantly with the increase of impregnation time ( Figure 4 ), and it can be clearly seen that the greengage dews impregnated with IMO were clearer and more translucent than those impregnated with white granulated sugar.

[0054] 3. IMO + freezing pretreatment method improves the juice yield

[0055] The traditional production method has low production efficiency, resulting in greengage dew being produced only in small workshops and being difficult to achieve large-scale production and enter the market. In this invention, the greengage is treated by a freezing method with a pretreatment of freezing at -20°C for 24 hours, combined with IMO. Greengage dew is made with greengage fruits and IMO in a mass ratio of 1:1, and it can be drunk after sealing and impregnation for one week, greatly improving the juice extraction efficiency of greengage dew. Among them, the juice extraction rates of IF7d and IR7d are both very high, being 92.35% and 96.25% respectively. However, when impregnated for 7 days, the juice extraction volume of IF7d (495.3 mL) is more than that of IR7d (488.7 mL).

[0056] Table 2 Juice extraction rate and juice extraction volume of greengage dews impregnated for 7 days with different treatments

[0057]

[0058] 4. Freezing method + IMO increases the nutrients in greengage dew

[0059] (4.1) Organic acids

[0060] The organic acid content in the plum dew is very rich. The main organic acids are citric acid, malic acid, and succinic acid. Moreover, the organic acid content in the plum dew impregnated with IMO is higher than that with white granulated sugar. Among them, the IR has the highest nutrient content. In IR90d, the citric acid content is 11365.35 ug / mL, the malic acid content is 11864.23 ug / mL, and the succinic acid content is 8614.37 ug / mL. IF90d ranks second, with the citric acid content being 8745.55 ug / mL, the malic acid content being 10796.56 ug / mL, and the succinic acid content being 8111.97 ug / mL.

[0061] (4.2) Other Nutrients

[0062] IMO can better extract nutrients such as flavonoids, phenylpropanoids, and VC in plums during the impregnation process, while their contents in the white granulated sugar group are extremely low or even absent. Among them, the contents of flavonoids (counted by rutin content), phenylpropanoids (counted by chlorogenic acid content), and VC in IF90d are all the highest, being 1.23 ug / mL, 45.85 ug / mL, and 27.66 ug / mL respectively. IR90d ranks second, being 0.93 ug / mL, 44.48 ug / mL, and 25.42 ug / mL respectively.

[0063] (4.3) Total Sugar, Reducing Sugar

[0064] The WR90d has the highest total sugar content and reducing sugar content, being 399.81 ug / mL and 44.42 ug / mL respectively. WF90d ranks second, being 347.83 ug / mL and 38.65 ug / mL respectively. And with the increase of the impregnation time, the total sugar and reducing sugar contents in the plum dew also increase significantly. In short, the shorter the impregnation time, the less the total sugar and reducing sugar contents.

[0065] (4.4) IMO Impregnation of Plum Dew Improves Amino Acid Content and Antioxidant Activity

[0066] The amino acid content of IF7d is the highest, being 82.06 umol / mL, showing a highly significant difference from other treatments.

[0067] The experimental results show that through the comprehensive determination of ABTS radical scavenging activity, hydroxyl radical (·OH) scavenging activity, and DPPH scavenging activity, it can be seen that the comprehensive antioxidant ability of IF7d is the strongest ( Figure 5 ).

[0068] Therefore, it is imperative to introduce safe and healthy isomaltooligosaccharide to replace traditional white granulated sugar and improve the beneficial effects of the product, which fully conforms to the trend of modern people pursuing health preservation. It can greatly improve the economic benefits of the product, promote the development of the industrial economy, and improve the per capita health level of society.

[0069] 5. Aroma Compounds of Plum Dew by Freezing Method + IMO Impregnation

[0070] (5.1) Changes in Aroma Substances of Plum Dew by Freezing Method + IMO Impregnation

[0071] To compare the changes in volatile compounds of plum dew impregnated by different methods over the impregnation time, all aromas were further analyzed.

[0072] The experimental results showed that after 90 days of impregnation, the total content of aroma substances in IF increased, rising from 578.18 mg / L at IF7d to 1181.40 mg / L, and the ethanol content increased less. New alcohols, esters, and aldehydes were produced, such as Furfural, which has an almond aroma and can bring a strong sweet aroma to foods like baked sweet potatoes and is mostly used in winemaking. While other treatments had more aroma types, most had pungent odors such as 1-Butanol, 3-methyl-. In short, IF90d increased the types and content of aromatic substances, while IR had excessive fermentation, producing too much ethanol and unpleasant odors, and the plum dew impregnated with white granulated sugar had a large number of new pungent volatiles.

[0073] (5.2) IF7d Has Less Ethanol Content and More Aroma Substances

[0074] Aroma is one of the most important sensory characteristics of fruit quality. To understand the aromatic flavor characteristics of plum fruits and plum dew impregnated by different treatments, this study used headspace solid-phase microextraction-gas chromatography-mass spectrometry (GC-MS) to detect the aroma composition. A total of 121 different volatile compounds ( Figure 6 ) were detected in fresh fruits and 8 different treatments of plum dew, including 48 esters, 25 alcohols, 12 aldehydes, 11 ketones, 8 acids, 3 phenols, 5 olefins, 4 alkanes, 1 yne hydrocarbon, 1 heterocyclic compound, and 3 unclassified compounds.

[0075] Through experiments, it was found that although the total volatile compound contents of WF90d and WR7d were extremely high, reaching 9194.28 mg / L and 7168.24 mg / L respectively, the highest content in both was ethanol, reaching 1590.97 mg / L and 2465.48 mg / L in WF90d and WR7d respectively, which are not pleasant aromatic compounds and are slightly pungent. While the volatile substances in IF7d and IR7d were extremely low, the ethanol content in them was the lowest among all treatments, 112.22 mg / L and 41.24 mg / L respectively, and IF7d had more pleasant aromatic substances, such as ethyl acetate (with a fruit aroma) and phenethyl alcohol (with an aroma similar to rose, honey, and banana) having higher contents compared to IR7d.

[0076] In summary, IF7d contains fewer pungent aroma compounds, and has a relatively larger variety and higher content of pleasant aromatic substances.

[0077] (5.3) Sensory evaluation

[0078] Figure 7 The sensory evaluation results of the greengage dew samples with 8 different treatments by 117 persons are shown. In terms of color, the evaluation of IF90d is the highest, reaching 9.5 points. There is no obvious change in the color before and after IR7d, which is relatively stable. However, for the greengage dew impregnated with granulated sugar, the color value drops significantly with time increasing, showing poor stability. In terms of aroma, the overall evaluation of the greengage dew impregnated for 7 days is significantly higher than that for 90 days. In terms of the clarity of the liquid, IF90d received unanimous praise with a full score of 10 points, while the greengage dew impregnated with granulated sugar for 90 days has the lowest evaluation and the most turbid liquid. In terms of the taste acidity, the score of IF is the highest, and that of IR7d ranks second. From the overall evaluation, the greengage dew impregnated for 7 days is superior to the greengage dew impregnated for a long time, which may be due to internal fermentation caused by too long impregnation time, resulting in changes.

[0079] Therefore, impregnating greengage with IMO combined with freeze pretreatment for 7 days can optimize the color and clarity of greengage dew, and retain more aroma and better taste.

[0080] 6. Food safety assessment

[0081] (6.1) Nitrous acid content

[0082] According to the provisions of the "National Food Safety Standard Drinking Water" (GB 5749-2022), the content standard of nitrite (calculated as nitrite ion) in drinking water is 2173.44 μmol / mL. The highest nitrite content in the greengage dew with other different treatments is WF90d, only 141.84 μmol / mL, which is extremely significantly lower than this standard and fully meets the food safety requirements ( Figure 8 ).

[0083] (6.2) Detection of microbial content

[0084] According to the provisions in the standard (GB / T 22474-2008), the total number of colonies shall not exceed 10 5 CFU / mL (colony forming unit), the number of Escherichia coli shall not exceed 100 CFU / mL, and the number of molds shall not exceed 150 CFU / mL. The requirement for the number of yeasts is not clearly specified in the national standard, but too many yeasts may affect the taste and texture of the jam. In this study, all treatments meet the requirements of international food safety standards, within the safe edible range, and the pathogenic bacteria Escherichia coli and molds are not found in all treatments.

[0085] This technology uses a freezing method with a pretreatment of freezing at -20°C for 24 hours to process greengage plums. In combination with IMO, greengage plum fruits and IMO are weighed according to a ratio of 1:1 (w / w) to make greengage plum dew. After sealing and soaking for one week, it can be consumed, greatly improving the production efficiency of greengage plum dew. In addition, this study discussed the effect of the combined treatment of IMO and freezing pretreatment on the quality of the soaked greengage plum dew.

[0086] The results showed that among the greengage plum dews treated differently, the total acid content of IF7d was the highest, reaching 7.55 mg / L. And soaking greengage plum dew with IMO can precipitate and completely retain a large amount of the main organic acids. In IF90d, the citric acid content was 8745.55 μg / mL, the malic acid content was 10796.56 μg / mL, and the succinic acid was 8111.97 μg / mL. In addition, the combination of IMO and the freezing method can also precipitate a large amount of flavonoids, phenylpropanoids and Vc. Among them, the contents of flavonoids, phenylpropanoids and VC in IF90d were the highest, being 1.23 μg / mL, 45.85 μg / mL and 27.66 μg / mL respectively. This may be because IMO has strong permeability and a low osmotic pressure, and can more effectively penetrate into greengage plum cells, promoting the release of water-soluble nutrients (such as vitamins, minerals and organic acids), while avoiding excessive leaching of the internal water of greengage plums, so that some nutrients are retained inside the greengage plum fruits. And, as an oligosaccharide, IMO has a protective effect and can reduce the degradation of heat-sensitive and oxidation-sensitive components (such as VC) in the syrup. Pretreating the plum fruits by freezing can greatly shorten the soaking and liquid extraction time. This may be because freezing pretreatment can accelerate the loss of water and inclusions by destroying the cell structure of the plum fruits, shortening the soaking time. IMO is easier to dissolve and has a faster melting speed than granulated sugar due to its smaller molecules and high solubility.

[0087] In addition, the best soaking time for greengage plum dew is 7 days. Otherwise, it will increase the total sugar, reducing sugar content and the content of yeasts, affecting the flavor and taste. The total sugar and reducing sugar in IF7d were 107.51 μg / mL and 11.95 μg / mL respectively. However, after soaking for 90 days, the total sugar and reducing sugar in IF90d were 253.22 μg / mL and 28.14 μg / mL respectively. The combination of IMO and freezing pretreatment for soaking greengage plum dew can significantly improve the liquid extraction efficiency. The liquid extraction rate of IF7d was 92.35%, and the liquid extraction volume was 495.3 mL. From the perspective of antioxidant capacity, the amino acid content in IF7d was the highest, being 82.06 μmol / mL, showing a highly significant difference from other treatments. And through comprehensive ABTS radical scavenging activity, hydroxyl radical (·OH) scavenging activity and DPPH scavenging activity, it can be seen that the comprehensive antioxidant capacity of IF7d is the strongest.

[0088] In terms of aroma, the ethanol content in IF7d is extremely low, only 112.22 mg / L, increasing the variety and content of pleasant aromatic compounds, such as ethyl acetate (66.6 mg / L) with a rich fruity aroma and phenethyl alcohol (54.04 mg / L) with aromas similar to rose, honey, and banana. In terms of sensory evaluation, the scores for color and clarity are the highest, 9.5 points and 10 points respectively, maintaining more aroma and a better taste, with an overall good score, showing excellent application prospects. Finally, all the prepared Prunus mume extracts with different treatments passed the food safety detection standards. The WF90d with the highest nitrite content was also extremely significantly lower than the standard of 2173.44 μmol / mL required in the "National Food Safety Standard - Drinking Water"; the total number of colonies, the number of Escherichia coli, the number of molds, and the number of yeasts all met the requirements of international food safety standards, within the safe and edible range, and the pathogenic bacteria Escherichia coli and molds were not found in all treatments.

[0089] In conclusion, the combination of freeze pretreatment and IMO impregnation for Prunus mume extract can significantly improve the production efficiency, nutrient retention, and antioxidant capacity of Prunus mume extract, while ensuring its food safety, showing good application prospects.

[0090] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing green plum juice, characterized in that: The following steps are involved: S1: Pre-treatment: After the fruits are picked, they are placed in a ventilated and cool place for one night, the fruit stems are removed, the fruits are washed, and laid flat in a clean, cool and ventilated place to dry; S2: Low temperature freezing: freezing the processed fruits at low temperature; S3: Canning: The processed fruits and isomaltooligosaccharide are put into cans, and green plum juice is obtained after one week.

2. The method for preparing green plum juice according to claim 1, characterized in that: In step S1, after drying, turn it over and dry it for another 3-4 hours.

3. The method for preparing green plum juice according to claim 1, characterized in that: In step S1, the fruit is green plum fruit.

4. The method for preparing green plum juice according to claim 1, characterized in that: In step S2, the processed fruits are placed in sealed bags and processed at -20°C for 24 hours.

5. The method for preparing green plum juice according to claim 1, characterized in that: In step S3, the fruit and isomaltooligosaccharide are added into the tank at a mass ratio of 1:

1.

6. The method for preparing green plum juice according to claim 1, characterized in that: In step S3, the jars are first sterilized by placing the glass jars in clean water, heating them to 100°C, boiling them for 10-15 minutes, then pouring out the water, placing them in a drying oven and drying them for 3 hours for later use.

7. The method for preparing green plum juice according to claim 1, characterized in that: In step S3, a layer of isomaltooligosaccharide is first spread on the bottom of the jar, and then a layer of fruit is spread, and then a layer of isomaltooligosaccharide and a layer of fruit are spread to the mouth of the jar.

8. The method for preparing green plum juice according to claim 7, characterized in that: In step S3, the canned product is sealed and then stored in a cool and ventilated place.

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