Preparation method of malus ionensis flavor syrup based on low-temperature solid-state fermentation technology

Abstract

The application discloses a preparation method of a roxburgh rose flavor syrup based on low-temperature solid fermentation technology, and particularly relates to the field of roxburgh rose flavor syrup, which comprises the following steps: removing seeds and cutting a roxburgh rose fruit into pieces to obtain roxburgh rose fruit pieces; weighing the roxburgh rose fruit pieces and special crystal sugar according to a mass ratio of 50:50 to obtain weighed raw materials; mixing the weighed raw materials to obtain a mixture; performing solid extraction on the mixture under a low-temperature condition by using a microbial low-oxygen environment, and stirring the mixture at preset time intervals during the fermentation process; detecting the content of vitamin C, tannin, flavone, SOD and total phenol in real time during the fermentation process to form monitoring data; and terminating the fermentation when the monitoring data indicates that the sugar content reaches and stably maintains at 58±2 Brix; and through the solid fermentation under the low-temperature condition and the combination of real-time monitoring and process control, the active ingredients of the roxburgh rose are maximally reserved in a mild environment, and the balanced release of flavor substances and the consistency between product batches are realized.

Description

Technical Field

[0001] This invention relates to the field of prickly pear flavored syrup technology, and more specifically, to a method for preparing prickly pear flavored syrup based on low-temperature solid-state fermentation technology. Background Technology

[0002] In existing fruit syrup processing, common high-temperature boiling or liquid fermentation processes can quickly produce syrup, but they cause a large amount of active substances in prickly pear, such as vitamin C, SOD, and flavonoids, to degrade, resulting in a significant decrease in nutritional value and a tendency for the product to have a monotonous flavor. Commercially available syrups also rely heavily on artificial flavorings, lacking natural properties and failing to meet health needs. Furthermore, the lack of dynamic monitoring of nutritional and flavor components during fermentation makes it difficult to guarantee the stability and consistency between batches of the product.

[0003] It is evident that although prickly pear is rich in various functional components, current technology cannot effectively preserve and utilize its active substances, ultimately creating a contradiction between nutritional degradation and flavor. Therefore, the problem with existing technologies is: how to maintain the integrity of the active ingredients of prickly pear during processing and obtain a syrup product that has both flavor and nutrition and is stable and consistent. Summary of the Invention

[0004] To overcome the aforementioned deficiencies of the prior art, embodiments of the present invention provide a method for preparing prickly pear flavored syrup based on low-temperature solid-state fermentation technology. By carrying out solid-state fermentation under low-temperature conditions and combining it with real-time monitoring and process control, the active ingredients of prickly pear are preserved to the maximum extent in a mild environment, while achieving balanced release of flavor substances and consistency between product batches, thereby solving the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing prickly pear flavored syrup based on low-temperature solid-state fermentation technology, comprising: S1. Raw material weighing: Remove seeds and thorns from fresh prickly pears and cut them into pieces to obtain prickly pear pieces; S2. Culture medium preparation: Special crystalline sugars are used as the basic culture medium. The special crystalline sugars need to be pre-treated, such as crushing or grinding them into particles of appropriate size, so as to facilitate the utilization of microorganisms and the extraction process. As needed, an appropriate amount of water or other solvents can be added to dissolve or partially dissolve the sugars to form a solid matrix suitable for extraction. Microorganisms or proteases can be added to the culture medium as extraction factors. The selection of proteases should be based on their ability to maintain activity at low temperatures and effectively promote the generation of the target product. S3. Mixing: Mix the prickly pear with special crystalline sugar to obtain a mixture; Place the inoculated culture medium and mixture in a sealed extraction container; adjust the oxygen concentration in the container to a low level by filling with nitrogen or other inert gas; set the extraction temperature to 0-4 degrees Celsius and maintain it constant; S4. Low-temperature solid-state fermentation and process monitoring: The mixture is subjected to solid-state fermentation under low-temperature conditions, and the mixture is stirred at preset time intervals during the fermentation process; during the fermentation process, samples are taken in real time to detect the content of vitamin C, tannins, flavonoids, SOD and total phenols to form monitoring data; when the monitoring data indicates that the sugar content reaches 58±2 Brix, the fermentation is terminated. S5. Filtration: The fermentation product is subjected to solid-liquid separation and filtration to obtain a clear syrup; S6. Syrup filling: The clarified syrup is filled to obtain filled syrup; S7, HPP sterilization: The filling syrup is sterilized by high-pressure treatment to obtain sterilized syrup; S8. Refrigeration: The sterilized syrup is refrigerated to obtain prickly pear flavored syrup.

[0006] In a preferred embodiment, in S1, the special crystalline sugar includes granular crystalline sugar obtained by sieving, wherein the particle size of the granular crystalline sugar includes 4 mesh, 8 mesh or 20 mesh, which is used to regulate the dissolution rate of the sugar and the penetration efficiency in the prickly pear fruit pieces. In S1, the mass ratio of the prickly pear fruit chunks to the special crystalline sugar includes 0.5:1, 1:1, or 2:1, in order to control the balance between the sweetness and yield of the obtained prickly pear flavored syrup.

[0007] In a preferred embodiment, in S1, the pretreatment method of the fresh prickly pear fruit includes two options: deseeding or not deseeding, so as to obtain differentiated effects in terms of nutrient retention rate and syrup yield of prickly pear flavored syrup according to different treatment methods.

[0008] In a preferred embodiment, in step S3, the fermentation time of the low-temperature solid-state fermentation includes 4 weeks, 5 weeks, 8 weeks or 13 weeks, so as to achieve differentiated retention effects of vitamin C, flavonoids, tannins, SOD and total phenols at different time points. In step S3, the real-time detection results of the monitoring data are stored in an existing database, and the contents of vitamin C, tannins, flavonoids, SOD and total phenols are determined based on the monitoring trends in the database to determine the point at which fermentation ends.

[0009] In a preferred embodiment, in step S6, the pressure range of the high-pressure sterilization is 300-600 MPa, and the duration of the high-pressure sterilization is 1-10 minutes, so as to maintain the stability of the nutrients while meeting the microbiological safety requirements.

[0010] In a preferred embodiment, in step S7, the refrigeration temperature range is 0-4°C, which is used to slow down the degradation rate of vitamin C and SOD in the prickly pear flavored syrup.

[0011] In a preferred embodiment, in S3, the mixture is layered and stacked in a fermentation vessel before entering solid-state fermentation. The layered stacking includes a first layer of prickly pear fruit pieces, a carrier layer, and a second layer of prickly pear fruit pieces, wherein: The carrier layer is made of plant fiber material, which includes at least one of corn cob particles, rice husk particles or coconut shell fiber. The thickness of the carrier layer is 20% to 60% of the average thickness of adjacent prickly pear fruit block layers, which is used to form a stable porosity gradient in the direction of gravity penetration. The carrier layer is pre-humidified and steam sterilized before being stacked, and pre-humidified until there is no visible water on the surface. After the layered stacking is completed, directional compaction is carried out in the fermentation container. The compaction pressure increases layer by layer along the direction of gravity, so that a continuous capillary channel network is formed between the carrier layer and the adjacent prickly pear fruit block layer.

[0012] In a preferred embodiment, the carrier layer is pre-inoculated with accompanying microorganisms before stacking. The accompanying microorganisms are immobilized with food-grade polysaccharide gel and then formed into micromicelle particles by spray encapsulation, which are uniformly dispersed in the carrier layer. In S3, the carrier layer of the fermentation vessel is provided with sidewall microporous aeration components and bottom microporous membrane aeration components at corresponding positions to form a micro-oxygen environment within the carrier layer. When the ethanol production rate or lactic acid accumulation rate monitored in the process reaches a preset threshold, the aeration intensity and aeration cycle of the aeration components are adjusted to maintain the stable colonization of the accompanying microorganisms within the carrier layer and to limit their disorderly expansion into the prickly pear fruit block layer.

[0013] In a preferred embodiment, the partition reconstruction operation is performed in S3, including: In the first stage of fermentation, the first prickly pear fruit block layer and the second prickly pear fruit block layer are swapped in position, while the carrier layer remains in place, so as to achieve interlayer matrix renewal without damaging the capillary channel network of the carrier layer. In the second stage of fermentation, based on the combined determination results of acidity, reducing sugar content and aromatic precursor ratio obtained from stratified sampling, the porosity of the aeration component is adjusted in different zones, and the carrier layer is supplemented with immobilized accompanying micromicelle particles or partially replaced. Before fermentation is terminated, the prickly pear fruit block layer and the carrier layer after partition reconstruction are subjected to solid compaction and resetting to maintain the continuity of the interlayer capillary channels. The sugar content and target nutritional indicators of the stratified samples reach a preset threshold as the termination condition. Together with the condition that the sugar content is stably maintained at 58±2Brix, they constitute the joint judgment rule for fermentation termination.

[0014] The technical effects and advantages of this invention are as follows: 1. This method uses low-temperature solid-state fermentation combined with real-time monitoring to avoid the large-scale degradation of active ingredients such as vitamin C and SOD in prickly pear caused by traditional high-temperature boiling or liquid fermentation. This solves the core problems of existing technologies, such as difficulty in preserving nutrients, monotonous flavor, and insufficient batch stability. 2. Dynamic monitoring and database linkage are used during the fermentation process to enable real-time monitoring of the changes in sugar content, acidity and functional components. Fermentation is terminated when the sugar content reaches and is stably maintained at 58±2 Brix, thereby ensuring the stability and consistency of the product in terms of nutrition and flavor. 3. By introducing special crystalline sugars and limiting their particle size, the penetration efficiency and dissolution rate are controlled by using different particle sizes of 4 mesh, 8 mesh or 20 mesh, which promotes the uniform exudation of flavor substances and nutrients in prickly pear fruit pieces, thereby improving the syrup yield and composition balance. 4. By setting up layered stacking and carrier layer structures in the process, and forming a capillary channel network through directional compaction, the gas and nutrient transfer conditions in the solid-state fermentation system are improved, local metabolic imbalances are reduced, thereby enhancing the stability and controllability of microecological succession. 5. By using parameters ranging from 300 to 600 MPa and 1 to 10 minutes during the high-pressure sterilization stage, the potential bacteria such as yeast and lactic acid bacteria are effectively inactivated, while the nutritional and active substances in the prickly pear syrup are well preserved, thus forming a product that combines safety and functionality. By controlling the temperature range of 0 to 4°C during the refrigerated storage stage, the degradation rate of vitamin C and SOD is slowed down, so that the nutrition and flavor of the syrup remain stable during the storage period, solving the problem of rapid decay of active substances in traditional syrups during storage. Attached Figure Description

[0015] Figure 1 This is a graph showing the vitamin C content of the prickly pear flavored syrup during refrigeration, as presented in this invention.

[0016] Figure 2 This is a graph showing the total acidity of the prickly pear flavored syrup during refrigeration, as presented in this invention.

[0017] Figure 3 This is a graph showing the tannin detection during the refrigeration period of the prickly pear frozen fruit flavored syrup of the present invention.

[0018] Figure 4This is a flavonoid detection chart of the prickly pear flavored syrup of the present invention during refrigeration.

[0019] Figure 5 This is a graph showing the SOD (superoxide dismutase) detection during the refrigeration period of the prickly pear flavored syrup of the present invention.

[0020] Figure 6 This is a graph showing the total phenol content of the prickly pear frozen fruit flavored syrup during refrigeration, as presented in this invention.

[0021] Figure 7 The production process of prickly pear fresh fruit flavored syrup of the present invention is as follows. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Refer to the instruction manual appendix Figure 1-7 An embodiment of the present invention provides a method for preparing prickly pear flavored syrup based on low-temperature solid-state fermentation technology, comprising: S1. Raw material weighing: Remove seeds and thorns from fresh prickly pears and cut them into pieces to obtain prickly pear pieces; S2. Culture medium preparation: Special crystalline sugars are used as the basic culture medium. The special crystalline sugars need to be pre-treated, such as crushing or grinding them into particles of appropriate size, so as to facilitate the utilization of microorganisms and the extraction process. As needed, an appropriate amount of water or other solvents can be added to dissolve or partially dissolve the sugars to form a solid matrix suitable for extraction. Microorganisms or proteases can be added to the culture medium as extraction factors. The selection of proteases should be based on their ability to maintain activity at low temperatures and effectively promote the generation of the target product. S3. Mixing: Mix the prickly pear with special crystalline sugar to obtain a mixture; Place the inoculated culture medium and mixture in a sealed extraction container; adjust the oxygen concentration in the container to a low level, which can be achieved by filling with nitrogen or other inert gas; set the extraction temperature to 0-4 degrees Celsius and maintain it constant; S4. Low-temperature solid-state fermentation and process monitoring: The mixture is subjected to solid-state fermentation under low-temperature conditions, and the mixture is stirred at preset time intervals during the fermentation process; during the fermentation process, samples are taken in real time to detect the content of vitamin C, tannins, flavonoids, SOD and total phenols to form monitoring data; when the monitoring data indicates that the sugar content reaches ±2Brix, the fermentation is terminated. S5. Filtration: The fermentation product is subjected to solid-liquid separation and filtration to obtain a clear syrup; S6. Syrup filling: The clarified syrup is filled to obtain filled syrup; S7, HPP sterilization: The filling syrup is sterilized by high-pressure treatment to obtain sterilized syrup; S8. Refrigeration: The sterilized syrup is refrigerated to obtain prickly pear flavored syrup.

[0024] In S1, the special crystalline sugar includes granular crystalline sugar obtained by sieving, and the particle size of the granular crystalline sugar includes 4 mesh, 8 mesh or 20 mesh, which is used to control the dissolution rate of the sugar and the penetration efficiency in the prickly pear fruit pieces. In S1, the mass ratio of the prickly pear fruit chunks to the special crystalline sugar includes 0.5:1, 1:1, or 2:1, in order to control the balance between the sweetness and yield of the obtained prickly pear flavored syrup.

[0025] In S1, the pretreatment method of the fresh prickly pear fruit includes two options: deseeding or not deseeding, so as to obtain the differentiated effects of prickly pear flavored syrup in terms of nutrient retention rate and syrup yield according to different treatment methods.

[0026] In step S3, the fermentation time of the low-temperature solid-state fermentation includes 4 weeks, 5 weeks, 8 weeks or 13 weeks, so as to achieve differentiated retention effects of vitamin C, flavonoids, tannins, SOD and total phenols at different time points. In step S3, the real-time detection results of the monitoring data are stored in an existing database, and the contents of vitamin C, tannins, flavonoids, SOD and total phenols are determined based on the monitoring trends in the database to determine the point at which fermentation ends.

[0027] In step S6, the pressure range of the high-pressure sterilization is 300-600 MPa, and the duration of the high-pressure sterilization is 1-10 minutes, so as to maintain the stability of the nutrients while meeting the microbiological safety requirements.

[0028] In step S7, the refrigerated storage temperature range is 0-4℃, which is used to slow down the degradation rate of vitamin C and SOD in the prickly pear flavored syrup.

[0029] In S3, the mixture is layered and stacked in a fermentation vessel before entering solid-state fermentation. The layered stacking includes a first layer of prickly pear fruit pieces, a carrier layer, and a second layer of prickly pear fruit pieces, wherein: The carrier layer is made of plant fiber material, which includes at least one of corn cob particles, rice husk particles or coconut shell fiber. The thickness of the carrier layer is 20% to 60% of the average thickness of adjacent prickly pear fruit block layers, which is used to form a stable porosity gradient in the direction of gravity penetration. The carrier layer is pre-humidified and steam sterilized before being stacked, and pre-humidified until there is no visible water on the surface. After the layered stacking is completed, directional compaction is carried out in the fermentation container. The compaction pressure increases layer by layer along the direction of gravity, so that a continuous capillary channel network is formed between the carrier layer and the adjacent prickly pear fruit block layer. It should be noted that: in step S3, the mixture is layered and stacked before entering solid-state fermentation in order to establish a spatial structure with functional differences inside the fermentation vessel. The first and second prickly pear fruit block layers provide the main fermentable substrate, while the carrier layer, composed of corn cob particles, rice husk particles, or coconut shell fibers, has a thickness controlled at 20% to 60% of the average thickness of adjacent prickly pear fruit block layers. This is used to form a stable porosity gradient in the direction of gravity permeability, thereby improving the permeability and air permeability of the substrate. Before stacking, the carrier layer is pre-humidified and sterilized by hot steam to ensure that it has suitable moisture conditions without introducing contaminating bacteria. After the layered stacking is completed, directional compaction is performed layer by layer along the direction of gravity to form a continuous capillary channel network between the carrier layer and the adjacent prickly pear fruit block layers. This enables the uniform transfer of nutrients, metabolites, and water during solid-state fermentation, ensuring stable succession of the microecology and improving the controllability and stability of the fermentation system.

[0030] Before being stacked, the carrier layer is pre-inoculated with accompanying microorganisms. These accompanying microorganisms are immobilized with food-grade polysaccharide gel and then formed into micromicelle particles by spray encapsulation, which are uniformly dispersed in the carrier layer. In S3, the carrier layer of the fermentation vessel is provided with sidewall microporous aeration components and bottom microporous membrane aeration components at corresponding positions to form a micro-oxygen environment within the carrier layer. When the ethanol production rate or lactic acid accumulation rate monitored in the process reaches a preset threshold, the aeration intensity and aeration cycle of the aeration components are adjusted to maintain the stable colonization of the accompanying microorganisms within the carrier layer and to limit their disorderly expansion into the prickly pear fruit block layer. It should be noted that in step S3, the carrier layer is pre-inoculated with accompanying microorganisms before stacking, and immobilized with food-grade polysaccharide gel to form spray-embedded micromicelle particles that are uniformly dispersed. This is to ensure that the accompanying microorganisms obtain a stable initial attachment environment within the carrier layer, preventing excessive drift during the early stages of fermentation. During fermentation, the sidewall microporous aeration components and bottom microporous membrane aeration components positioned at corresponding locations on the carrier layer can establish a controlled micro-oxygen environment locally within the layer. This provides the oxygen required for the metabolism of the accompanying microorganisms while preventing the overall mixture from entering a state of total oxygen, which could lead to metabolic imbalance. When the ethanol production rate or lactic acid accumulation rate reaches a preset threshold, the disorderly expansion of the accompanying microorganisms can be promptly suppressed by adjusting the aeration intensity and aeration cycle, ensuring their stable colonization within the carrier layer. This maintains the dynamic balance between the accompanying microorganisms and the core functional microorganisms in the fermentation system, thereby ensuring the continuous and controllable release of flavor substances and nutrients.

[0031] Performing partition reconstruction operations in S3 includes: In the first stage of fermentation, the first prickly pear fruit block layer and the second prickly pear fruit block layer are swapped in position, while the carrier layer remains in place, so as to achieve interlayer matrix renewal without damaging the capillary channel network of the carrier layer. In the second stage of fermentation, based on the combined determination results of acidity, reducing sugar content and aromatic precursor ratio obtained from stratified sampling, the porosity of the aeration component is adjusted in different zones, and the carrier layer is supplemented with immobilized accompanying micromicelle particles or partially replaced. Before fermentation is terminated, the prickly pear fruit block layer and the carrier layer after partition reconstruction are solid-state compacted and reset to maintain the continuity of the interlayer capillary channels. The sugar content and target nutrient index of the stratified samples reach a preset threshold as the termination condition. Together with the condition that the sugar content is stably maintained at 58±2Brix, they constitute the joint judgment rule for fermentation termination. It should be noted that the partitioned reconstruction operation in step S3 is because, during solid-state fermentation, the first and second prickly pear fruit block layers may experience uneven distribution of substrate nutrients and local accumulation of metabolites due to long-term accumulation. By exchanging positions in the first stage of fermentation while keeping the carrier layer in its original position, the interlayer substrate can be renewed and balanced without damaging the capillary channel network of the carrier layer. In the second stage of fermentation, by sampling and detecting acidity, reducing sugar content, and the ratio of aromatic precursor substances in layers, the porosity of the ventilation components is adjusted in zones based on the detection results. The carrier layer is supplemented or partially replaced with immobilized micromicelle particles of the accompanying microbial community, which can maintain the stable colonization and continuous release of functions of the accompanying microbial community. Before the fermentation is terminated, the prickly pear fruit block layer and the carrier layer after partitioned reconstruction are solid-state compacted and reset to ensure the continuity of the interlayer capillary channels. The combined determination of sugar content and target nutrient indicators is used as the fermentation termination condition, thereby achieving dynamic equilibrium and controllable termination of the fermentation process, ensuring that this method can be stably implemented in practical applications.

[0032] This solution also includes the following embodiments: The operation steps include: pretreatment of prickly pear fruit (removing seeds and cutting into pieces) → weighing of raw materials (50% prickly pear fruit, 50% special crystalline sugar) → mixing → low-temperature solid-state fermentation (stirring and shaking regularly, and monitoring the content of vitamin C, tannins, flavonoids, SOD and total phenols in real time) → solid-liquid separation → syrup filtration → HPP sterilization. Key parameter optimizations include: (1) Effect of sugar particle size (4 mesh, 8 mesh, 20 mesh) on sugar penetration efficiency; (2) The effect of sugar dosage (0.5:1, 1:1, 2:1) on the sweetness and yield of prickly pear flavored syrup; (3) The dynamic relationship between fermentation time and the formation of flavor substances and changes in nutrient content.

[0033] The innovations include: (1) Process innovation: Low-temperature solid-state fermentation was applied to prickly pear syrup for the first time. Combined with sugar particle size control, the syrup yield and the retention rate of nutrients (Vc, tannins, flavonoids, SOD, total phenols) were improved. (2) Product innovation: Develop natural prickly pear flavored syrup, which is different from artificial flavored products and has the potential to claim functions such as supplementing vitamin C, anti-oxidation and anti-inflammatory. (3) Monitoring innovation: Establish a dynamic database of flavor substances and nutrients to achieve intelligent quality control of the production process.

[0034] Results analysis: The results analysis only involved sensory evaluation and dynamic monitoring of nutritional components (Vc, tannins, flavonoids, SOD, and total phenols) in the two groups of prickly pear flavored syrup: seeded and seedless. The basic indicators include: (1) Dissolution time of special crystalline sugars: The special crystalline sugars in experimental groups ① and ② were completely dissolved in the fourth week of refrigerated storage; (2) Syrup precipitation: The syrup precipitation in experimental groups ① and ② reached the maximum in the fourth week and did not increase in the later period; the analysis showed that the syrup precipitation was related to the dissolution time of the special crystalline sugar. After the sugar was completely dissolved, the syrup precipitation was not related to the storage time. (3) Sugar content: In the third week, the sugar content of experimental groups ① and ② reached 58±2Brix and remained stable at 58±2Brix in the later period, with no change in sugar content.

[0035] Sensory evaluation: (1) Aroma: During the experiment, experimental groups ① and ② had no odor and emitted the aroma of prickly pear fruit; (2) Taste: Full sugar flavor → sugar flavor accompanied by fresh prickly pear flavor → sugar flavor, fresh prickly pear flavor, astringent flavor → sugar flavor, fresh prickly pear flavor, sour flavor; There was no significant difference in taste between experimental groups ① (seeds removed) and ② (seeds not removed); Table 1. Changes in the taste of prickly pear flavored syrup during refrigeration. Physicochemical properties during refrigeration: Samples of prickly pear flavored syrup (with and without seeds) were taken at three time periods (week 4, week 5, week 8, and week 13) during low-temperature storage for dynamic monitoring of physicochemical indicators (vitamin C, total acid, tannins, flavonoids, SOD, and total phenols). Specific analytical results are as follows: Figure 1-6 As shown in Table 2, the optimal storage period for each indicator is summarized in the table.

[0036] Table 2. Physicochemical properties of prickly pear flavored syrup; Optimal refrigeration period. (1) Vc index: such as Figure 1 As shown, during the 13-week refrigeration period, the vitamin C content of both the seeded and unseeded prickly pear flavored syrup showed a decreasing-increasing-decreasing trend. Specifically, by week 8 of refrigeration, the vitamin C content of both the seeded and unseeded versions reached its maximum, with the seeded version having a higher vitamin C content than the unseeded version. By week 13, the vitamin C content of both versions had decreased to its minimum. In conclusion, eight weeks is the optimal refrigeration period for prickly pear syrup to achieve the highest vitamin C content; excessively long refrigeration periods can actually decrease the vitamin C content. (2) Total acidity index: such as Figure 2As shown, during the 13-week refrigeration period, the total acid of the seedless version of the prickly pear flavored syrup continuously decreased, while the total acid of the unremoved version first increased, then decreased, and then increased again. By the 8th week of refrigeration, the total acid of both the seedless and unremoved versions reached their lowest values, with the unremoved version having the lowest total acid content. In conclusion, 8 weeks is the optimal refrigeration period for the prickly pear syrup to have the lowest total acid content. Excessive refrigeration can actually increase the total acid content of the unremoved version. Combined with taste analysis, it was found that the longer the refrigeration period, the more volatile aromatic compounds in the prickly pear volatilize and permeate into the special crystalline sugar solution, resulting in a more pronounced sour taste of the prickly pear fruit in the syrup and promoting an increase in total acid content. (3) Tannin index: such as Figure 3 As shown, the tannin content of prickly pear flavored syrup continued to increase during the 13-week refrigeration period. In the fourth week, the tannin content of the seedless version was lower than that of the seedless version. The lower the tannin content, the lower the astringency and the better the taste of the prickly pear flavored syrup. Combined with the taste analysis, experimental groups ① and ② in the fourth week both had obvious sugary taste and fresh prickly pear fruit flavor. In conclusion, four weeks is the optimal refrigeration period for prickly pear syrup with the lowest tannin content. (4) Flavonoid indicators: such as Figure 4 As shown, during the 13-week refrigeration period, the flavonoid content of experimental group ① (seedless version) and experimental group ② (without seed) showed a trend of first increasing-decreasing-increasing; in the 5th week, the flavonoid content of the without seed version was greater than that of the seedless version. The higher the flavonoid content, the higher the nutritional content of the prickly pear flavored syrup. In conclusion, 5 weeks is the optimal refrigeration period for prickly pear syrup to have the highest flavonoid content. (5) SOD detection: such as Figure 5 As shown, the flavonoid content in experimental group ① (seedless version) changed from decreasing to increasing, while the flavonoid content in experimental group ② (without seeds) changed from increasing to decreasing. In week 13, the SOD activity of the seedless version reached its maximum value. The higher the SOD activity, the stronger the antioxidant effect. In summary, week 13 is the optimal refrigeration period for prickly pear syrup to have the highest SOD activity. The effects of sterilization process on physicochemical, microbiological, and sensory properties: Microbiological and physicochemical indicators of prickly pear flavored syrup were tested before and after sterilization. The results are shown in Tables 3-4. The results of microbiological index testing are shown in Table 3: After sterilization, the prickly pear flavored syrup passed the tests for mold, yeast, total bacterial count, and coliform bacteria.

[0037] Table 3. Results of Microbiological Indicators Detection for Prickly Pear Frozen Fruit Flavor Syrup As shown in Table 4, the physicochemical data results show that experimental group ① (after deseeding and sterilization) can increase the content of vitamin C, flavonoids, total phenols, total acid, and tannins, while only the SOD content decreases. This indicates that sterilization not only ensures product quality but also increases its nutritional value. However, the increase in total acid and tannins indicates that the sour and astringent taste of prickly pear in the syrup of experimental group ① is more pronounced after sterilization. Experimental group ② (without seeds, after sterilization) can increase the content of flavonoids and SOD, while the content of vitamin C, total acid, tannins and total phenols decreases, indicating that sterilization has a significant impact on the nutritional value of the unseeded prickly pear flavored syrup. Comparing the physicochemical data of experimental group ① and experimental group ② after sterilization, it was found that only the flavonoid content of experimental group ② was higher than that of experimental group ①, while the contents of other components such as vitamin C, total acid, tannin, SOD and total phenol were lower than those of experimental group ①. In conclusion, the nutritional value of experimental group ① (seedless) is better. Table 4. Test results of physicochemical properties of prickly pear frozen fruit flavored syrup The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing prickly pear flavored syrup based on low-temperature solid-state fermentation technology, characterized in that, include: S1. Raw material weighing: Remove seeds and thorns from fresh prickly pears and cut them into pieces to obtain prickly pear pieces; S2. Culture medium preparation: Special crystalline sugars are used as the basal culture medium; Specialty crystalline sugars require pretreatment, such as crushing or grinding them into particles of appropriate size to facilitate microbial utilization and the extraction process; if necessary, appropriate amounts of water or other solvents can be added to dissolve or partially dissolve the sugar, forming a solid matrix suitable for extraction. Microorganisms or proteases can be added to the culture medium as extraction factors. The selection of proteases should be based on their ability to maintain activity at low temperatures and effectively promote the generation of the target product. S3. Mixing: Mix the prickly pear with special crystalline sugar to obtain a mixture; Place the inoculated culture medium and mixture in a sealed extraction container; adjust the oxygen concentration in the container to a low level by filling with nitrogen or other inert gas; set the extraction temperature to 0-4 degrees Celsius and maintain it constant; S4. Low-temperature solid-state fermentation and process monitoring: The mixture is subjected to solid-state fermentation under low-temperature conditions, and the mixture is stirred at preset time intervals during the fermentation process; during the fermentation process, samples are taken in real time to detect the content of vitamin C, tannins, flavonoids, SOD and total phenols to form monitoring data; when the monitoring data indicates that the sugar content reaches ±2Brix, the fermentation is terminated. S5. Filtration: The fermentation product is subjected to solid-liquid separation and filtration to obtain a clear syrup; S6. Syrup filling: The clarified syrup is filled to obtain filled syrup; S7, HPP sterilization: The filling syrup is sterilized by high-pressure treatment to obtain sterilized syrup; S8. Refrigeration: The sterilized syrup is refrigerated to obtain prickly pear flavored syrup.

2. The method for preparing prickly pear flavored syrup based on low-temperature solid-state fermentation technology according to claim 1, characterized in that: In S1, the special crystalline sugar includes granular crystalline sugar obtained by sieving, and the particle size of the granular crystalline sugar includes 4 mesh, 8 mesh or 20 mesh, which is used to control the dissolution rate of the sugar and the penetration efficiency in the prickly pear fruit pieces. In S1, the mass ratio of the prickly pear fruit chunks to the special crystalline sugar includes 0.5:1, 1:1, or 2:

1.

3. The method for preparing prickly pear flavored syrup based on low-temperature solid-state fermentation technology according to claim 2, characterized in that: In S1, the pretreatment method of the fresh prickly pear fruit includes two options: deseeding or not deseeding, so as to obtain the differentiated effects of prickly pear flavored syrup in terms of nutrient retention rate and syrup yield according to different treatment methods.

4. The method for preparing prickly pear flavored syrup based on low-temperature solid-state fermentation technology according to claim 1, characterized in that: In step S3, the fermentation time of the low-temperature solid-state fermentation includes 4 weeks, 5 weeks, 8 weeks or 13 weeks, so as to achieve differentiated retention effects of vitamin C, flavonoids, tannins, SOD and total phenols at different time points. In step S3, the real-time detection results of the monitoring data are stored in an existing database, and the contents of vitamin C, tannins, flavonoids, SOD and total phenols are determined based on the monitoring trends in the database to determine the point at which fermentation ends.

5. The method for preparing prickly pear flavored syrup based on low-temperature solid-state fermentation technology according to claim 1, characterized in that: In step S6, the pressure range of the high-pressure sterilization is 300-600 MPa, and the duration of the high-pressure sterilization is 1-10 minutes.

6. The method for preparing prickly pear flavored syrup based on low-temperature solid-state fermentation technology according to claim 1, characterized in that: In step S7, the refrigerated storage temperature range is 0-4℃, which is used to slow down the degradation rate of vitamin C and SOD in the prickly pear flavored syrup.

7. The method for preparing prickly pear flavored syrup based on low-temperature solid-state fermentation technology according to claim 1, characterized in that: In S3, the mixture is layered and stacked in a fermentation vessel before entering solid-state fermentation. The layered stacking includes a first layer of prickly pear fruit pieces, a carrier layer, and a second layer of prickly pear fruit pieces, wherein: The carrier layer is made of plant fiber material, which includes at least one of corn cob particles, rice husk particles or coconut shell fiber. The thickness of the carrier layer is 20% to 60% of the average thickness of adjacent prickly pear fruit block layers, which is used to form a stable porosity gradient in the direction of gravity penetration. The carrier layer is pre-humidified and steam sterilized before being stacked, and pre-humidified until there is no visible water on the surface. After the layered stacking is completed, directional compaction is carried out in the fermentation container. The compaction pressure increases layer by layer along the direction of gravity, so that a continuous channel network is formed between the carrier layer and the adjacent prickly pear fruit block layer.

8. The method for preparing prickly pear flavored syrup based on low-temperature solid-state fermentation technology according to claim 7, characterized in that: Before being stacked, the carrier layer is pre-inoculated with accompanying microorganisms. These microorganisms are immobilized with food-grade polysaccharide gel and then formed into micromicelle particles by spray encapsulation, which are uniformly dispersed in the carrier layer. In S3, the carrier layer of the fermentation vessel is provided with sidewall ventilation components and bottom ventilation components at corresponding positions to create an oxygen environment within the carrier layer. When the ethanol production rate or lactic acid accumulation rate monitored in the process reaches a preset threshold, the ventilation intensity and ventilation cycle of the ventilation components are adjusted to maintain the colonization of the accompanying microorganisms within the carrier layer and to limit their disorderly expansion into the prickly pear fruit block layer.

9. The method for preparing prickly pear flavored syrup based on low-temperature solid-state fermentation technology according to claim 8, characterized in that: Performing partition reconstruction operations in S3 includes: In the first stage of fermentation, the first prickly pear fruit block layer and the second prickly pear fruit block layer are swapped in position, while the carrier layer remains in place, so as to achieve interlayer matrix renewal without damaging the channel network of the carrier layer. In the second stage of fermentation, based on the combined determination results of acidity, reducing sugar content and aromatic precursor ratio obtained from stratified sampling, the porosity of the aeration component is adjusted in different zones, and the carrier layer is supplemented with immobilized accompanying micromicelle particles or partially replaced. Before fermentation is terminated, the prickly pear fruit block layer and the carrier layer after partition reconstruction are solid-state compacted and reset to maintain the continuity of the interlayer channels. The sugar content and target nutritional index of the stratified samples reach a preset threshold as the termination condition. Together with the condition in claim 1 that the sugar content is stably maintained at 58±2Brix, they constitute the joint determination rule for fermentation termination.

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