Production method of fresh-locked Chinese wolfberry rich in high-value active ingredients and fresh-locked Chinese wolfberry

Abstract

The invention belongs to the technical field of Chinese wolfberry processing, and particularly relates to a production method of fresh-locked Chinese wolfberry rich in high-value active ingredients and the fresh-locked Chinese wolfberry. According to the method, the Chinese wolfberry fruits are pretreated before vacuum drying, namely preheating is carried out, high-temperature treatment on the fresh Chinese wolfberry fruits is rapidly realized, and the influence of stress reaction and long-time heating in later drying on functional active ingredients of the Chinese wolfberry fruits is prevented by combining medium and short infrared waves and a short-time high-temperature process. The sensory quality (such as color value and meat texture) of the Chinese wolfberry is kept at a higher level, the functional active ingredients of the Chinese wolfberry are protected, and the loss of nutritional ingredients is reduced. And the fresh-locked Chinese wolfberry fruits prepared by the process disclosed by the invention are stable in quality and have good reproducibility.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of wolfberry processing, and particularly relates to a method for producing fresh-keeping wolfberry rich in high-value active ingredients and fresh-keeping wolfberry. BACKGROUND

[0002] Wolfberry has the effects of nourishing liver and kidney and benefiting essence and eyesight. In the traditional dry processing method of wolfberry, fresh wolfberry fruits without stalks are used as raw materials, washed, treated with sodium bicarbonate to remove wax, and then dried by natural air-drying or hot air drying.

[0003] Wolfberry is a precious medicine and food, and its value lies in its specific active ingredients. Modern research shows that wolfberry polysaccharide is the most important high-value active ingredient in wolfberry, which is a protein-containing complex polysaccharide composed of a polysaccharide side chain of six monosaccharides and a protein main chain of various amino acids. Its biological activity depends on its protein part. During the drying process of fresh wolfberry, long-term heating may affect the molecular structure and molecular weight of the protein, and thus affect the quantitative detection results and biological activity of wolfberry polysaccharide. In addition, fresh wolfberry is still a living body that maintains physiological respiration and has cell biological activity. After being separated from the tree, it may produce a stress response due to the influence of physiological environmental factors such as water and temperature during the long drying process. The endogenous protease and glycosidase may affect the molecular structure and molecular composition of the glycoprotein of wolfberry polysaccharide, and thus affect the quantitative detection results and biological activity of wolfberry polysaccharide.

[0004] Fresh-keeping wolfberry is a new product category that has led the wolfberry industry in the past decade. Fresh-keeping wolfberry uses vacuum drying technology (including pulse drying between vacuum and normal pressure and vacuum drying). Compared with conventional wolfberry (natural air-drying or hot air drying), this technology does not use any additives, does not need to be immersed in alkali to remove wax, and completely retains the natural wax protective layer of the surface layer of fresh wolfberry fruits. In terms of sensory evaluation (brighter red color and more natural taste) and drying efficiency, it has a greater improvement than conventional wolfberry (hot air drying).

[0005] However, the existing production-type equipment for vacuum drying of fresh-keeping wolfberry has problems in vacuum extraction and process, which can easily cause an uncontrollable pressure difference between the inside and outside of the fresh wolfberry, resulting in compression of the pulp and peel inside the wolfberry, and thus causing the dried wolfberry to have an empty shell and an undesirable taste of the peel.

[0006] For example, the Chinese patent application No. 201911390223.2 discloses a drying device and method for vacuum pulse cold-dried wolfberry. The wolfberry is dried by vacuum pulse drying and vacuum cold drying. The color of the vacuum-dried fresh-keeping wolfberry is better than that of conventionally dried wolfberry, and the shape is more plump. However, it is prone to produce bubble fruits, empty shells, and the protection rate of the active ingredients of wolfberry, especially wolfberry polysaccharide, is still low. SUMMARY

[0007] Therefore, the application provides a method for producing fresh-keeping wolfberry rich in high-value active ingredients and the fresh-keeping wolfberry to solve the technical problems of low protection rate of active ingredients and low quality of the fresh-keeping wolfberry in the prior art.

[0008] The technical solution of the application to solve the above technical problems is as follows: The method for producing fresh-keeping wolfberry rich in high-value active ingredients comprises the following steps: short-time preheating pretreatment of wolfberry, low-temperature vacuum equal-difference pulse drying, and vacuum constant-difference drying. The fresh wolfberry is placed in a drying chamber, and the fresh wolfberry is preheated under infrared wavelength of 0.78-4.0 μm, preheating temperature of 75-85℃, and preheating time of 30-300s. The wolfberry is rapidly cooled to 40-50℃ after preheating.

[0009] Preferably, in the production method, the temperature rising time of the short-time preheating is 1-10s.

[0010] Preferably, in the production method, the rapid cooling is specifically as follows: the cold trap refrigerant temperature is set to 0- -30℃, the cold trap valve is opened, and the wolfberry is cooled.

[0011] Preferably, in the production method, the vacuum equal-difference pulse drying comprises the following steps: T1. The absolute vacuum degree is set to 0.095-0.065 bar, the temperature is set to 0-40℃, the drying time is set to 10-20 minutes, and the cold trap refrigerant temperature is set to 0- -15℃. T2. The absolute vacuum degree is set to 0.080-0.050 bar, the temperature is set to 0-40℃, the drying time is set to 3-6 minutes, and the cold trap refrigerant temperature is set to 0- -15℃. The steps T1 and T2 are cycled, the cycle number is 1-32, the absolute vacuum degree in the step T1 is reduced by 0.002 bar each cycle, the absolute vacuum degree in the step T2 is reduced by 0.015 bar than that in the step T1, and the absolute vacuum degree in the vacuum equal-difference pulse drying stage is greater than or equal to 0.016 bar.

[0012] Preferably, in the production method, the vacuum constant-difference drying is as follows: the absolute vacuum degree is reduced by 50-500 pa each time, the temperature is set to 40-65℃, the time is set to 20-40 minutes, the cold trap refrigerant temperature is set to 0- -30℃, until the drying is completed, and the absolute vacuum degree in the vacuum constant-difference drying stage is greater than or equal to 200 pa.

[0013] Preferably, the production method, the vacuum constant difference drying is that the vacuum degree is set to be reduced by 200 pa each time, the temperature is 55 DEG C, the time is 30 minutes, the cold trap refrigerant temperature is -15 DEG C, and the absolute vacuum degree of the vacuum constant difference drying stage is greater than or equal to 200 pa.

[0014] Preferably, the production method further comprises cooling the vacuum dried wolfberry dried fruit to room temperature to obtain the fresh-keeping wolfberry finished product.

[0015] A fresh-keeping wolfberry rich in high-value active ingredients is prepared by the production method of the fresh-keeping wolfberry rich in high-value active ingredients.

[0016] Compared with the prior art, the application has at least the following advantages: The application discloses a fresh-keeping wolfberry production method and a fresh-keeping wolfberry rich in high-value active ingredients. Before vacuum drying, the wolfberry is pretreated, that is, preheated, so that the fresh wolfberry is rapidly treated at high temperature, combined with medium and short infrared waves, and the high-temperature process is short, and then the temperature is reduced from high to low, so that the environment is greatly changed, which may promote the synthesis or transformation of some effective components in the wolfberry. At the same time, the short-time high temperature rapidly inactivates the fresh wolfberry, prevents drying stress reaction, protects the active components of the wolfberry, prevents the influence of long-time heating in the later drying process on the active components of the wolfberry, maintains the original sensory quality of the fresh wolfberry, reduces the loss of nutritional components, and achieves a better drying effect.

[0017] The vacuum drying process of the application adopts vacuum equidifference pulsation: linear stable differential pressure type (rapid small-amplitude pressure reduction-air mixing mode) for a certain time, and the "systolic pressure and diastolic pressure" formed by the pulsation is stable and constant, and the vacuum degree is reduced with the moisture content, so that the natural property of the fruit peel is protected, and the fruit shape is prevented from being wrinkled and bubble fruit caused by excessive pressure difference stretching effect. In the middle and later stages of drying, vacuum constant difference is adopted, which is beneficial to maintaining the stability of the fruit shape and rapid water loss. The vacuum drying process of the application is beneficial to adapt to the characteristics of the wolfberry water loss process in different stages, the rapid change of the vacuum degree in the air mixing stage is beneficial to the formation of water channels, improves the water loss rate, and the linear small-amplitude change of the vacuum degree maintains the limited wrinkling of the wolfberry and avoids the empty shell. Low-temperature drying, the fusion of two heat sources and two drying methods ensures high activity of nutritional components, secondly, shortens the drying time, improves the drying efficiency, also plays a role in protecting the effective components and reducing the loss, and the nutritional components and activity are higher than those of the existing fresh-keeping wolfberry.

[0018] The fresh-locked goji berries prepared according to the method described in this application, compared with goji berries dried by ordinary hot air, show an average increase of 14.5 in color value (46.4% increase); an average increase of 18.5 mg / 100g in vitamin C (86.9% increase); an average increase of 1.6 mg / g in lycopene (84.7% increase); an average increase of 1.3g / 100g in polysaccharides (39.5% increase); an average increase of 21.6g / 100g in reducing sugars (49.0% increase); an average increase of 4.5 mg / g in total flavonoids (90.4% increase); and an average increase of 6.2% in DPPH scavenging rate (19.1% increase). Compared to directly vacuum-dried goji berries, the average color value increased by 11.0, a rate of 31.9%; the average lycopene content increased by 0.8 mg / g, a rate of 30.0%; the average polysaccharide content increased by 1.2 g / 100g, a rate of 36.2%; the average reducing sugar content increased by 20.8 g / 100g, a rate of 46.3%; the average total flavonoid content increased by 3.6 mg / g, a rate of 62.6%; and the average DPPH scavenging rate increased by 7.7%, a rate of 24.6%. This not only maintains the sensory quality of goji berries (e.g., color value, fleshy texture) at a high level but also protects the active ingredients and reduces the loss of nutrients. Furthermore, the fresh-locked goji berries prepared using this method meet the relevant national standards for ready-to-eat goji berries in terms of food safety indicators (total bacterial count, coliform bacteria, and mold). The fresh-locked goji berries prepared using this process also exhibit stable quality and good reproducibility. Attached Figure Description

[0019] Figure 1 This is a curve showing the test results of samples from embodiments of this application. Detailed Implementation

[0020] It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of this invention can be combined with each other. The technical solutions of this invention will be further described below in conjunction with the embodiments of this invention, and this invention is not limited to the specific implementation methods described below.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0022] In one specific embodiment of this application, a method for producing fresh-locking goji berries rich in high-value active ingredients involves first performing a short-term preheating pretreatment on the goji berries, then performing low-temperature vacuum differential pulse drying, and finally performing vacuum constant-difference drying. The short-term preheating pretreatment includes: placing the fresh goji berries in a drying chamber and preheating them at an infrared wavelength of 0.78~4.0μm at a temperature of 75℃~85℃ for 30s~300s; after preheating, rapidly cooling the goji berries to 40℃~50℃. Further, the preheating time is 1s~10s. Rapid cooling can be achieved through a plate system, vacuuming, or a cold trap. The cold trap primarily functions by rapidly absorbing water vapor, increasing the evaporation rate and thus lowering the temperature. In this application, cold trap cooling is preferred. Therefore, the rapid cooling specifically involves setting the cold trap refrigerant temperature to 0℃~-30℃ to cool the goji berries.

[0023] This method involves pre-treating the goji berries before vacuum drying, essentially preheating them to achieve rapid high-temperature treatment. Combined with short- and medium-infrared waves, this short-duration high-temperature process prevents stress reactions and protects the active ingredients of the goji berries. Simultaneously, the short-duration high temperature rapidly deactivates the active ingredients in the fresh goji berries, preventing the impact of prolonged heating during the later drying process on the active components, maintaining the original sensory quality of the fresh goji berries, minimizing nutrient loss, and achieving superior drying results. Furthermore, the short-duration high temperature dissolves the surface wax structure, facilitating the expansion of the goji berry's micropores, thereby promoting effective moisture migration, effectively shortening the drying time, reducing unfavorable oxidation reactions during drying, and protecting the goji berry polysaccharides and other effective substances from damage and alteration. Experiments showed that the fresh-locked wolfberries prepared using this method had an average increase of 14.5 in color value (46.4%) compared to the control group of wolfberries dried by ordinary hot air; an average increase of 18.5 mg / 100g in vitamin C (86.9%); an average increase of 1.6 mg / g in lycopene (84.7%); an average increase of 1.3g / 100g in polysaccharides (39.5%); an average increase of 21.6g / 100g in reducing sugars (49.0%); an average increase of 4.5 mg / g in total flavonoids (90.4%); and an average increase of 6.2% in DPPH scavenging rate (19.1%).

[0024] In one specific embodiment of this application, the vacuum drying is performed by first subjecting the wolfberries to vacuum differential pulse drying, and then to vacuum constant differential drying.

[0025] Furthermore, the vacuum differential pulse drying includes the following steps: T1. Set absolute vacuum degree to 0.095~0.065 bar, temperature to 0~40℃, drying time to 10~20 minutes, and cold trap refrigerant temperature to 0℃~-15℃; T2. Set absolute vacuum degree to 0.080~0.050 bar, temperature to 0~40℃, drying time to 3~6 minutes, and cold trap refrigerant temperature to 0℃~-15℃; The process involves repeating steps T1 and T2 as described above, with the number of cycles ranging from 1 to 32. In each cycle, the absolute vacuum level in step T1 decreases by 0.002 bar, and the absolute vacuum level in step T2 decreases by 0.015 bar compared to the absolute vacuum level in T1. Furthermore, the absolute vacuum level in the vacuum differential pulsating drying stage is ≥0.016 bar.

[0026] Specifically, after performing step T1, step T2 is performed, thus completing one cycle, which is repeated 1 to 32 times. After each execution of step T1, the vacuum level is reduced by 0.002 bar before the next execution of T1. Within the same cycle, the absolute vacuum level in step T2 is 0.015 bar lower than the absolute vacuum level in T1, and at the end of the last cycle, the absolute vacuum level of this vacuum differential pulsating drying stage is ≥0.016 bar.

[0027] In one specific embodiment of this application, the vacuum constant difference drying is performed by setting the absolute vacuum to decrease by 50~500 Pa each time, the temperature to be 40℃~65℃, the time to be 20~40 minutes, and the cold trap refrigerant temperature to be 0℃~-30℃ until the drying is completed, and the absolute vacuum degree of the vacuum constant difference drying stage is ≥200 Pa.

[0028] Preferably, the vacuum constant difference drying is performed by reducing the absolute vacuum by 200 Pa each time, setting the temperature to 55°C, the time to 30 minutes, and keeping the cold trap refrigerant temperature at -15°C until the drying is complete.

[0029] It is worth noting that the absolute vacuum level mentioned above refers to the vacuum level during goji berry drying, and the temperature refers to the controlled temperature at the center of the goji berry interior, which is regulated by a vacuum system and a temperature control system.

[0030] This process employs a linear, stable differential pressure method (rapid, small-amplitude pressure reduction followed by gas injection) maintained for a certain period, evacuating to a near-absolute vacuum pressure (with relatively linear pressure changes), and continuing this process in the middle and later stages (only gas injection is stopped). This approach leverages the advantages of different material characteristics at different stages. The rapid change in vacuum during the initial gas injection promotes the formation of moisture channels, increasing water loss, while the linear, small-amplitude vacuum changes maintain limited shrinkage of the goji berries, preventing empty shells. Low-temperature drying, combining two heat sources and two drying methods, ensures high activity of nutrients. Furthermore, it shortens drying time and improves drying efficiency, also protecting the active ingredients and reducing losses. The resulting nutrient content and activity are higher than existing methods for preserving fresh goji berries.

[0031] Furthermore, it also includes cooling the vacuum-dried goji berries to room temperature to obtain fresh-locked goji berry products.

[0032] In another specific embodiment of this application, a fresh-locked goji berry rich in high-value active ingredients is produced using the production method of fresh-locked goji berries rich in high-value active ingredients as described above.

[0033] The drying of fresh goji berries is mainly achieved through vacuum drying equipment. For example, the vacuum pulsed cold drying goji berry drying device described in application number 201911390223.2 is used to dry fresh goji berries. The vacuum drying equipment in this application mainly includes: a drying body, a vacuum system and temperature control system, and a cold trap refrigerant temperature control system. The dryer consists of two parts: a drying chamber at the front and a refrigeration chamber at the rear, separated by an isolation plate. The refrigeration chamber contains at least one cold trap, which is a stainless steel coil filled with silicone oil or compressor refrigerant, connected to a heat exchanger or compressor refrigeration system via piping. The drying chamber comprises n relatively independent drying compartments, each with a drying area ≤1 / 5 of the total drying chamber area, and each drying compartment having a drying area ≥40 square meters. Each drying compartment has an independent evacuation pipe and automatic control valve connected to the evacuation unit, as well as an independent connecting pipe and automatic control valve to the cold traps. It also has an independent venting pipe (for gas mixing) and automatic control valve. Each independent drying compartment contains several trays, with a medium- or short-wave infrared device installed below each tray. Trays containing fresh goji berries can be directly placed on the trays within the corresponding independent drying compartments. The circulating medium providing heat energy within the trays of the drying chamber is purified water or silicone oil. The trays are made of perforated stainless steel or aluminum alloy with a mesh size of 30-100. Several trays are combined to form a cart, and the cart is matched with an independent drying chamber in the drying chamber.

[0034] This equipment divides the drying chamber into several independent drying chambers, each connected to a vacuum system and a cold trap system. This avoids the problem of existing equipment using a single drying chamber with a single evacuation port and cold trap port, which can easily create a pressure difference between the inside and outside of the goji berries during periods of high evaporation (especially in the initial drying stage and when the quantity of goji berries is large). It solves the problem of pressure differences and evaporation rate variations between different areas. Due to the directional flow inertia of the evaporating airflow, a positive pressure difference exists between the inside and outside of the goji berries in the drying chamber, and due to differences in distance from the evacuation port and cold trap port. This causes the central pulp to be pressed against the peel, resulting in a peely texture, hollow centers, and uncontrollable processing issues. Thus, it solves the problems of existing goji berry drying equipment, providing strong controllability of process conditions, reducing the likelihood of hollow shells, improving pulp texture, increasing marketability, and enhancing drying efficiency.

[0035] The drying chamber of the equipment is divided into n relatively independent drying rooms. Each drying room has an independent evacuation pipe and automatic control valve connected to the evacuation unit, as well as an independent pipe and control valve connected to the cold trap. In this way, the equipment utilizes a complementary combination of mid- and short-wave infrared heating and plate heating. Rapid temperature control and adjustment are achieved using mid- and short-wave infrared technology, while temperature maintenance is achieved using the plate system. This allows for precise control of the drying process, producing high-quality, fresh-locking goji berries.

[0036] Vacuum system: consists of several vacuum pumps and Roots pumps.

[0037] Gas mixing system: A dried and filtered gas source (with air or inert gas).

[0038] The automatic control system enables coordinated control of the internal temperature of the goji berries with the temperature of the heat transfer medium and the heat exchange system within the drying chamber. It also links humidity monitoring within the drying chamber with the switching on and off of the cold trap, thereby controlling vacuum and humidity. Furthermore, it accurately collects drying condition data, adjusts key parameters in real time, and automatically determines the drying end point based on humidity changes.

[0039] In the specific production process, before preheating the fresh goji berries, they need to be cleaned, for example: ① Cold chain preservation: The fresh goji berries are moderately ripe and have been kept in a cold chain from harvesting from the tree until drying. The cold chain preservation temperature is 10℃~15℃. ② Cleaning and selection: The cold-chain preserved goji berries are put into a washing, selection and grading integrated machine. The fresh goji berries are washed twice with bubbling water (first tap water + second purified water) and selected and graded (in purified water), and the surface water is drained. Thorough cleaning and water selection without damage are performed, and berries of the same size and quality are dried in the same batch. ③ Quantitative loading: The cleaned goji berries of the same grade and quality are quantitatively and evenly spread (preferably in a single layer) into the trays. The trays are placed on the racks of the material cart and sent into the drying chamber in sequence. The partition plates are closed one by one to form an independent drying chamber. After the entire drying chamber is filled with fresh goji berries, the drying chamber door is closed.

[0040] Pretreatment: Place the quantitatively packaged fresh goji berries to be dried in the drying chamber; open all air inlet valves, close the gas mixing valve, and keep the evacuation valve and cold trap valve closed; start the plate circulation system and set the plate temperature to 75℃~85℃; turn on the medium-short wave infrared device, setting the infrared wavelength to 0.78~4.0μm, the preheating time to 30s~300s, and ensuring the center temperature of the fresh goji berries is the same as the plate temperature. Set the cold trap refrigerant temperature to 0℃~-30℃, and after preheating, rapidly cool the goji berries to 40℃~50℃.

[0041] Vacuum differential pulse drying: T1. Turn off the medium and short wave infrared device, close the air inlet valve, close the gas mixing valve, open the evacuation valve, open the cold trap valve, turn on the vacuum system and set the absolute vacuum degree to 0.095~0.065 bar, set the center temperature of the wolfberry and the plate temperature to 0~40℃, the drying time to 10~20 minutes, and the cold trap refrigerant temperature to 0℃~-15℃.

[0042] T2. After completing the previous step, open the gas mixing valve and set the absolute vacuum level and holding time to be achieved. Set the absolute vacuum level to 0.080~0.050 bar, the center temperature of the goji berries and the temperature of the plate to 0~40℃, the drying time to 3~6 minutes, and the refrigerant temperature of the cold trap to 0℃~-15℃. The cycle is performed according to T1 and T2 as described above. The vacuum degree is set such that the absolute vacuum degree of T1 decreases by 0.002 bar per cycle. After gas injection, the absolute vacuum degree of T2 decreases by 0.015 bar per cycle compared to T1. The number of cycles is 1 to 32. The absolute vacuum degree of the vacuum differential pulsating drying stage is ≥0.016 bar.

[0043] Vacuum constant difference drying: After completing the previous step, cancel the gas mixing operation, set the vacuum level to decrease by 50~500pa each time, the temperature to 40℃~65℃, the time to 20~40 minutes, and the cold trap refrigerant temperature to 0℃~-30℃ until drying is completed, and the absolute vacuum level of the vacuum constant difference drying stage is ≥200pa.

[0044] After drying, the drying trays are removed from the drying chamber, and the dried goji berries are cooled to room temperature in a clean environment to obtain the finished product of fresh-locked goji berries.

[0045] It is worth noting that the process temperature and process time involved in the above embodiments are all temperatures or times used in the experiment. Any reasonable adjustments made by those skilled in the art based on the process temperature and process time provided by the present invention, within the error range, should be included within the protection scope of the present invention.

[0046] The technical solution and effects of the present invention will be further illustrated below through specific embodiments.

[0047] Since polysaccharides and lycopene (zeaxanthin dipalmitate) in wolfberry usually exist in mixed form, different drying methods have a significant impact on their chemical composition and activity. Modern research shows that the immunomodulatory, neuroprotective, blood sugar regulating, and liver function improving biological activities of wolfberry polysaccharides are all related to their antioxidant activity. Therefore, this invention, using the same batch of fresh wolfberry obtained according to the scheme of this application as raw material, conducted research on different drying processes, and determined the color value Lab,a, fleshy texture, vitamin C, lycopene, wolfberry polysaccharides, reducing sugar, sucrose, and total flavonoids of the dried wolfberry. Furthermore, the simple, easy-to-perform, and reproducible in vitro antioxidant activity DPPH scavenging rate (%) was used for comparative verification and screening of pretreatment temperatures.

[0048] 1. Experimental instruments, materials and methods 1.1 Experimental materials: Fresh wolfberries of Ningqi No. 7 produced in 2025.

[0049] 1.2 Experimental Apparatus Rotary evaporator RE-52AA, variety analysis scanner AP-Z-01, ultraviolet spectrophotometer UV-1780, high performance liquid chromatograph 1260, analytical balance, centrifuge TD-5A, plant pulverizer DFY-200A, electric thermostatic drying oven GZX-9240MBE 1.3 Experimental Methods: The determination of Lycium barbarum polysaccharides was carried out in accordance with GB 18672-2014 Lycium barbarum, Appendix. The determination of reducing sugars was carried out according to GB 5009.7-2016, by direct titration. The determination of sucrose shall be carried out in accordance with GB 5009.8-2016; Vitamin C was determined according to GB5009.86-2016; The determination of lycopene was carried out in accordance with the standard "T / NXFSA 004S—2020 Determination of Lycopene by High Performance Liquid Chromatography". Methods for determining total flavonoids and antioxidant activity (DPPH free radical scavenging ability) of wolfberry: Sample pretreatment: The dried goji berries were pulverized using a micro plant sample pulverizer and passed through a 40-mesh sieve to obtain goji berry powder, which was then set aside for later use.

[0050] Preparation of the test solution: Weigh 0.05 kg of wolfberry powder and place it in a standard reflux apparatus. Add 0.5 L of petroleum ether and reflux at 60 °C for defatting three times, 1 hour each time. Filter out the solvent, air-dry the residue, add 0.5 L of 80% ethanol, and reflux at 60 °C for 1 hour each time, recovering the ethanol. Then extract with water at 70 °C three times, 2 hours each time, with a solid-liquid ratio of 1:10. Combine the water extract filtrates and concentrate them. Precipitate with 4 times the volume of 95% ethanol, let stand overnight, and centrifuge to obtain the precipitate for reconstitution with water of different concentrations.

[0051] Determination of DPPH free radical scavenging ability: Weigh 4 mg of DPPH into a 250 mL volumetric flask, dissolve it in a very small amount of ethanol, and then add 50% ethanol to the mark. Take 2 mL of a sample solution with a mass concentration of 1.5 mg / mL, add 2 mL of DPPH solution, react at room temperature for 30 min, and measure the absorbance at a wavelength of 525 nm, which is Ai. Calculate the DPPH free radical scavenging rate using the following formula.

[0052] Clearance rate = {1 - (Ai - Aj)} / Ac × 100% In the formula, Ac: DPPH solution without sample; Aj: blank absorbance; Ai: absorbance of sample solution.

[0053] Determination of total flavonoids: Preparation of reference solution: Accurately weigh 10.0 mg of rutin reference standard, place it in a 5 mL volumetric flask, add an appropriate amount of 80% ethanol to dissolve it, and dilute to the mark to obtain a 2.000 mg / mL rutin reference solution.

[0054] Standard curve construction: The NaNO2-Al(NO3)3-NaOH colorimetric method was used, and the absorbance was measured at 510 nm using a UV spectrophotometer. Plotting absorbance as the ordinate (Y) and rutin concentration as the abscissa (X), the regression equation for the standard curve was calculated as Y = 3.79X + 0.045, R² = 0.9974, showing good linearity within the concentration range of 0–0.2000 mg / mL.

[0055] Determination method: Accurately measure 2.0 mL of the test solution and determine the absorbance according to the method for plotting the rutin standard curve.

[0056] Determination of food safety indicators: Refer to GB 14884 National Food Safety Standard for Candied Fruit.

[0057] 2. Comparative Example 1 Cleaned, drained, and sorted fresh goji berries were quantitatively packed into trays and placed in a hot air constant temperature drying oven. The drying temperature was set as follows: first, the temperature was raised to 40℃ and dried for 10 hours, and then the temperature was raised to 65℃ and dried for 18 hours to obtain the dried goji berry product, which was marked as CK1.

[0058] 3. Comparative Example 2 Cleaned, drained, and sorted fresh goji berries are quantitatively packaged into trays and placed in the drying room; Vacuum differential pulse drying: T1. Turn off the medium and short wave infrared device, close the air inlet valve, close the gas mixing valve, open the evacuation valve, open the cold trap valve, turn on the vacuum system and set the absolute vacuum degree to 0.085 bar, set the center temperature of the wolfberry and the plate temperature to 40℃, the drying time to 15 minutes, and the cold trap refrigerant temperature to -8℃.

[0059] T2. After completing the previous step, open the gas mixing valve, set the desired absolute vacuum level and holding time. Set the absolute vacuum level to 0.070 bar, the center temperature of the goji berries and the plate temperature to 40°C, the drying time to 5 minutes, and the cold trap refrigerant temperature to -8°C. The cycle is performed according to T1 and T2 as described above. The vacuum degree is set such that the absolute vacuum degree of T1 decreases by 0.002 bar per cycle. After gas injection, the absolute vacuum degree of T2 decreases by 0.015 bar per cycle compared to T1. The cycle is repeated 27 times. During the vacuum differential pulsating drying stage, the absolute vacuum degree is ≥0.016 bar.

[0060] Vacuum constant difference drying: After completing the previous step, cancel the gas mixing operation, set the vacuum level to decrease by 100 Pa each time, the temperature to 55℃, the time to 30 minutes, and the cold trap refrigerant temperature to -15℃, until the drying is completed and the absolute vacuum level during the constant vacuum drying stage is ≥200 Pa.

[0061] After drying, the drying trays are removed from the drying chamber, and the dried goji berries are cooled to room temperature in a clean environment to obtain the fresh-locked goji berry product, which is labeled CK2.

[0062] 4. Example 1 Cleaned, drained, and sorted fresh goji berries are quantitatively packaged into trays and placed in the drying room; Pretreatment: Open all air inlet valves, close the mixing valve and evacuation valve, and keep the cold trap valve closed; start the plate circulation system and set the plate temperature (see Table 1 for pretreatment); turn on the medium-short wave infrared device, set the infrared wavelength to 3.0 μm, the preheating time to 8 s, the preheating time to 200 s, and the preheating temperature (center temperature of fresh goji berries) as shown in Table 1. Set the cold trap refrigerant temperature to -8℃, and after preheating, rapidly cool the goji berries to 45℃.

[0063] The other steps were the same as those for the comparative example. The obtained fresh-locked wolfberry samples were labeled as Sample 1 to Sample 6.

[0064] Table 1 Process data for each group

[0065] Table 2. Detection results of each group of samples

[0066] Note: The color value is detected by the Lab color analyzer. A positive value of 'a' represents red, and a negative value represents green. The higher the 'a' value, the brighter the red color of the goji berries, and vice versa. It is the core parameter for judging the color.

[0067] As shown in the table above, in Comparative Example 1 (CK1 group), which was dried using ordinary hot air, the sensory quality and active ingredients of the goji berries were both low. In Comparative Example 2 (CK2 group), which was dried directly using vacuum, although the color value and vitamin C content of the goji berries remained at a high level, the removal rates of lycopene, polysaccharides, reducing sugars, total flavonoids, and DPPH were significantly lower than those of the samples in Experimental Example 1, and the total bacterial count, Escherichia coli, and mold did not meet the national standards. In Experimental Example 1, samples 1 to 6 underwent a short-term preheating pretreatment before vacuum drying, which significantly improved the active ingredients of the goji berries. In particular, samples 3 to 5, compared with CK1, showed an average increase of 14.5 in color value (46.4%), an average increase of 18.5 mg / 100g in vitamin C (86.9%), an average increase of 1.6 mg / g in lycopene (84.7%), an average increase of 1.3 g / 100g in polysaccharides (39.5%), an average increase of 21.6 g / 100g in reducing sugars (49.0%), an average increase of 4.5 mg / g in total flavonoids (90.4%), and an average increase of 6.2% in DPPH scavenging rate (19.1%).

[0068] Compared to the CK2 group, in Experiment 1, samples 3 to 5 showed an average increase of 11.0 in color value (31.9%), an average increase of 0.8 mg / g in lycopene (30.0%), an average increase of 1.2 g / 100g in polysaccharides (36.2%), an average increase of 20.8 g / 100g in reducing sugars (46.3%), an average increase of 3.6 mg / g in total flavonoids (62.6%), and an average increase of 7.7% in DPPH scavenging rate (24.6%). In other words, pre-treatment (preheating) before vacuum drying of goji berries, involving rapid, short-duration high-temperature treatment combined with short- and medium-infrared waves, not only maintains the sensory quality of goji berries (e.g., color value, fleshy texture) at a high level but also protects the active ingredients and reduces nutrient loss.

[0069] In Experiment 1, the short-term preheating temperatures of Samples 1 and 2 were relatively low compared to the other groups, and the protective effect on the active ingredients in wolfberry was not maximized. The short-term preheating temperature of Sample 6 was 88℃, and the protective effect on the active ingredients of wolfberry was lower than that of Samples 3 to 5. Therefore, the optimal temperature for short-term preheating is 75℃~85℃.

[0070] 5. Example 2 Five parallel experimental cases were set up under the same process conditions as sample 4 in Example 1 above. The resulting fresh-locked wolfberries were labeled as samples 7 to 11, and their test results are shown in Table 3.

[0071] Table 3. Detection results of each group of samples in Example 2

[0072] Please refer to the table above. The test results of the above groups of samples are not significantly different from those of the sample in Example 1, indicating that the fresh-locked wolfberries prepared by this process have stable quality and good reproducibility.

[0073] The above embodiments merely illustrate several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for producing fresh-keeping wolfberry rich in high-value active ingredients, characterized in that, the method comprises the following steps: first, preheating the wolfberry for a short time, then low-temperature vacuum differential pulse drying, and finally vacuum constant difference drying; wherein the preheating for a short time comprises: placing the fresh wolfberry in a drying chamber, preheating the fresh wolfberry under an infrared wavelength of 0.78-4.0 μm, a preheating temperature of 75-85 °C, and a preheating time of 30-300 s; and then rapidly cooling the wolfberry to 40-50 °C after preheating; the preheating time is 1-10 s; the rapid cooling is performed by setting the cold trap refrigerant temperature to 0-30 °C and opening the cold trap valve to cool the wolfberry; the vacuum differential pulse drying comprises the following steps: T1. setting an absolute vacuum degree of 0.095-0.065 bar, a temperature of 0-40 °C, a drying time of 10-20 minutes, and a cold trap refrigerant temperature of 0-15 °C; T2. setting an absolute vacuum degree of 0.080-0.050 bar, a temperature of 0-40 °C, a drying time of 3-6 minutes, and a cold trap refrigerant temperature of 0-15 °C; wherein, the steps T1 and T2 are cycled for 1-32 times, the absolute vacuum degree is reduced by 0.002 bar in each cycle of the step T1, the absolute vacuum degree is reduced by 0.015 bar than that in the step T1 in each cycle of the step T2, and the absolute vacuum degree in the vacuum differential pulse drying stage is greater than or equal to 0.016 bar; the vacuum constant difference drying is performed by setting the vacuum degree to be reduced by 50-500 pa each time, a temperature of 40-65 °C, a time of 20-40 minutes, and a cold trap refrigerant temperature of 0-30 °C until the drying is completed, and the absolute vacuum degree in the vacuum constant difference drying stage is greater than or equal to 200 pa; the vacuum constant difference drying is performed by setting the vacuum degree to be reduced by 200 pa each time, a temperature of 55 °C, a time of 30 minutes, and a cold trap refrigerant temperature of -15 °C until the drying is completed, and the absolute vacuum degree in the vacuum constant difference drying stage is greater than or equal to 200 pa; and the method further comprises cooling the dried wolfberry fruit to room temperature to obtain the fresh-keeping wolfberry product. The fresh-keeping wolfberry rich in high-value active ingredients is produced by the method according to any one of claims 1-7. ​ ​ ​ 2. The production method according to claim 1, wherein ​ 3. The production method according to claim 1, wherein ​ 4. The production method according to claim 1, wherein ​ ​ ​ ​ 5. The production method according to claim 1, wherein ​ 6. The production method according to claim 5, wherein ​ 7. The production method according to claim 1, wherein ​ 8. A fresh-keeping Chinese wolfberry fruit enriched with high-value active ingredients, characterized in that, ​

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