Fresh-keeping method and device for refrigerated shelf of picked blueberries

Abstract

The invention discloses a fresh-keeping method and a fresh-keeping device for a refrigeration shelf after picking of blueberries, belongs to the technical field of postharvest treatment of fruits and vegetables, takes natural metabolism regulation and control and cell stable quality regulation as core innovation points, breaks through the limitation that traditional controlled atmosphere fresh-keeping needs to depend on external energy and single nutrient enrichment, and improves the fresh-keeping effect of the blueberries. And organic unification of environmental control and physiological regulation is realized. The method is simple and convenient to operate, remarkable in effect, low in cost and high in safety, is not only suitable for preservation of picked blueberries, but also can be popularized to storage and transportation links of other perishable berries such as strawberries, blackberries and raspberries, provides an efficient, green and sustainable technical path for preservation of picked fruits and vegetables, and has important industrial popularization value and social application significance.

Description

Technical Field

[0001] This invention belongs to the field of postharvest processing technology of fruits and vegetables, and in particular relates to a method and apparatus for the preservation of blueberries in a cold storage shelf after harvest. Background Technology

[0002] Blueberries (Vaccinium spp.), a type of small berry with high nutritional value, are popular among consumers due to their delicate skin, unique flavor, and rich content of anthocyanins and polyphenols. Their cultivation and market scale have expanded rapidly in recent years. However, blueberries have thin skins, crisp flesh, high water content, and vigorous respiration metabolism, making them highly susceptible to dehydration, softening, rotting, and flavor degradation after harvest. They are typical fruits with low storability. Under normal temperature conditions, their shelf life is typically less than three days, and even under refrigeration (0-4℃), it rarely exceeds two weeks. This characteristic makes blueberries highly susceptible to quality deterioration during long-distance transportation, cross-regional sales, and supply to high-end markets, severely limiting their commercialization and industrial chain extension. Therefore, developing an efficient, safe, economical, and environmentally adaptable post-harvest preservation technology system for blueberries has become an important research direction in the field of fruit and vegetable post-harvest processing.

[0003] Currently, research on post-harvest preservation of blueberries both domestically and internationally mainly focuses on several technical approaches, including refrigeration, controlled atmosphere storage, physical sterilization, and nutrient fortification. Low-temperature refrigeration, by reducing respiration and microbial reproduction rates, slows fruit senescence and is the most commonly used method. However, this method is highly dependent on cold chain equipment, consumes a lot of energy, and is prone to condensation and microbial reactivation due to temperature fluctuations, affecting preservation stability. Controlled atmosphere storage technology, by regulating the O2 and CO2 ratio in the storage environment to inhibit respiration and ripening processes, can significantly extend refrigerated shelf life. However, the system is expensive, complex to operate, and requires strict sealing, making it unsuitable for initial processing at the production site or decentralized sales scenarios. Ozone sterilization, as a green and residue-free physical preservation method, can effectively kill common pathogens such as gray mold and anthracnose and degrade ethylene gas, inhibiting ripening reactions. However, ozone has strong oxidizing properties; if the concentration or time is not properly controlled, it can easily cause oxidation, softening, or even browning of the fruit peel, leading to a decline in marketability. Furthermore, while methods using natural plant extracts, essential oils, or chitosan coatings possess certain antibacterial and antioxidant effects, their widespread application is limited by issues such as uneven coating, flavor interference, and short-lasting effects. On the other hand, to enhance the stability of fruit tissue structure and anti-aging capabilities, the academic community widely employs calcium salts and polyamine nutrients. Calcium ions can cross-link with pectin to form an "egg-box structure," increasing the mechanical strength of cell walls. Polyamines, such as putrescine and spermidine, can inhibit the activity of cell wall degrading enzymes, delay softening, and promote the activation of antioxidant enzyme systems. However, these chemical or nutritional preservation methods mostly act on the interior of the fruit and lack the ability to directly kill already attached microorganisms, failing to achieve comprehensive preservation independently and often requiring the use of other technologies. Although some studies have attempted to use polyamine-calcium composite solutions to balance cell stabilization and nutritional fortification, problems such as insufficient external environmental control and incomplete pathogen control remain unresolved.

[0004] In recent years, bio-fermentation gas production regulation technology has attracted attention as a natural and low-energy-consumption atmosphere control method. By introducing controllable food-grade microorganisms (such as yeast and lactic acid bacteria) and carbon source substrates, carbon dioxide can be generated and oxygen consumed in a closed environment, thereby creating a low-oxygen, high-CO2 microclimate and achieving passive regulation similar to a controlled atmosphere environment. This technology requires no external gas or energy source, has a simple structure, and is particularly suitable for small- to medium-scale operations and mobile transportation scenarios. However, currently, such technologies mostly focus on regulating the composition of ambient gases and lack synergistic design with the fruit's endogenous defense system, resulting in limited anti-aging and disease-resistant effects on high-respiration-rate fruits such as blueberries. At the same time, traditional chemical controlled atmosphere agents or ethylene inhibitors pose a risk of residue, while natural molecules such as melatonin can delay fruit senescence by inducing the activity of antioxidant enzymes (SOD, CAT) and scavenging free radicals, but their exogenous application effect is easily affected by fluctuations in humidity, temperature, and oxygen concentration, resulting in insufficient duration of action and difficulty in maintaining stable effects during actual storage and transportation.

[0005] In summary, existing post-harvest preservation technologies for blueberries generally suffer from the following problems: First, most solutions rely on a single preservation mechanism, making it difficult to simultaneously address the triple requirements of sterilization, quality stabilization, and anti-aging. Second, there is a disconnect between external environmental control and internal metabolic defense, resulting in short-lived preservation effects and low synergistic efficiency. Third, traditional cold chain and controlled atmosphere systems are highly dependent on equipment and consume a lot of energy, making them unsuitable for decentralized, small-scale production and the trend towards low-carbon practices. Fourth, some technologies suffer from unstable effects, high costs, or flavor interference, limiting their industrial-scale promotion. Therefore, existing post-harvest preservation systems for blueberries cannot yet achieve a comprehensive protection effect that is low-energy, residue-free, environmentally friendly, and stable over the long term. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a method and apparatus for post-harvest cold storage preservation of blueberries. This invention proposes a post-harvest preservation method for blueberries that combines a bio-fermentation gas module with a polyamine-calcium ion composite preservative solution. By organically combining a controllable bio-fermentation gas module with a fruit cell stabilization system, a dual preservation mechanism of "external gas regulation - internal tissue enhancement" is constructed. This method utilizes the continuous release of carbon dioxide and reduction of oxygen concentration during the bio-fermentation process to create a mild and stable micro-modified atmosphere to inhibit respiration and disease. Simultaneously, the polyamine-calcium ion composite preservative solution acts on the cell wall structure and antioxidant metabolic pathways, enhancing the stability and anti-aging properties of the fruit tissue. This achieves synergistic control and quality maintenance of post-harvest blueberry preservation without the need for complex equipment or energy, overcoming the limitations of existing technologies such as environmental regulation and fruit defense against cracking, short preservation periods, and high costs.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a post-harvest cold storage shelf preservation device for blueberries, including an encapsulation structure and a bio-fermentation gas module. The bio-fermentation gas module is disposed inside the encapsulation structure and has a double-chamber structure, with the two chambers separated by a breathable membrane. The outer wall of the bio-fermentation gas module is provided with a press-activated area that can break the breathable membrane.

[0009] Furthermore, the packaging structure is selected from high-barrier plastic packaging bags or high-barrier plastic food storage containers; the bio-fermentation gas module is made of a breathable material, which is selected from non-woven fabric, microporous membrane material or cellulose-based breathable membrane.

[0010] Furthermore, the high-barrier plastic packaging bag is made of a multi-layer co-extruded or composite film, the film comprising an outer polyolefin layer, a middle barrier layer and an inner food contact layer, wherein the outer polyolefin layer is selected from polyethylene (PE) or polypropylene (PP), the middle barrier layer is selected from ethylene-vinyl alcohol copolymer (EVOH), polyamide (PA) or polyvinylidene chloride (PVDC), and the inner food contact layer is selected from PE or PP.

[0011] The high-barrier plastic food storage container is made of one or more of the following materials: polyamide / polyethylene (PA / PE), polyamide / ethylene-vinyl alcohol copolymer / polyethylene (PA / EVOH / PE), and polyethylene terephthalate (PET).

[0012] The breathable material used in this invention has good gas permeability, which can achieve gas exchange while keeping the gas-producing microbial agent and carbon source nutrient substrate stored independently. It can also withstand the mechanical breakage of the activated structure under pressure, with no powder leakage, and can be used to construct a dual-chamber fermentation module.

[0013] Secondly, the present invention provides a method for post-harvest cold storage shelf preservation of blueberries, comprising the following steps: placing a carbon source nutrient matrix and a gas-producing microbial agent in the two cavities of the above-mentioned double-cavity packaging structure respectively; soaking or pre-cooling blueberries in a polyamine-calcium ion composite preservative solution; drying and placing them in the above-mentioned packaging structure; breaking the permeable membrane through the pressing activation area to allow the carbon source nutrient matrix and the gas-producing microbial agent to come into contact and undergo a micro-fermentation reaction; closing the packaging structure; and storing the post-harvest cold storage shelf preservation device of blueberries at 10±2℃.

[0014] This invention proposes a comprehensive post-harvest cold storage shelf preservation method for blueberries based on the synergistic effect of an "external gas regulation-internal quality stabilization and protection" dual mechanism. Through the combined action of a bio-fermentation gas module and a polyamine-calcium ion composite preservative solution, the method achieves microenvironmental regulation and cell structure stabilization of blueberries throughout the entire post-harvest storage and transportation process, thereby extending the storage period, reducing the spoilage rate, and maintaining fruit firmness and nutritional quality. This method is characterized by its green and safe approach, low energy consumption, and residue-free production, making it particularly suitable for applications such as initial processing at the production site, cold chain logistics, and long-distance transportation.

[0015] Furthermore, the gas-producing microbial agent is selected from dry yeast and / or lactic acid bacteria; the carbon source nutrient matrix includes glucose and / or sucrose.

[0016] Furthermore, when the gas-producing microbial agent is dry yeast, the viable count of the dry yeast is 1.0 × 10⁻⁶. 8 ~1.0×10 10 CFU / g, preferably, the viable count of the dry yeast is 5.0 × 10⁻⁶. 8 ~5.0×109 CFU / g, wherein the mass ratio of the dry yeast to the carbon source nutrient matrix is ​​1:(20-40); preferably, the mass ratio of the dry yeast to the carbon source nutrient matrix is ​​1:(25-35).

[0017] When the gas-producing microbial agent is lactic acid bacteria, the viable count of the lactic acid bacteria is 1.0 × 10⁻⁶. 8 ~1.0×10 10 CFU / g, preferably, the viable count of the lactic acid bacteria is 5.0 × 10⁻⁶. 8 ~5.0×10 9 CFU / g; the mass ratio of the lactic acid bacteria to the carbon source nutrient substrate is 1:(20-50), preferably, the mass ratio of the lactic acid bacteria to the carbon source nutrient substrate is 1:(25-40).

[0018] The gas release rate of the bio-fermentation gas module provided by this invention can be adjusted by the carbon source nutrient substrate quality, the proportion of microbial agents, or the ambient temperature to match the gas control requirements of storage containers of different capacities.

[0019] Furthermore, the polyamine-calcium ion composite preservative liquid includes polyamine compounds, soluble calcium salts, and antioxidant stabilizers.

[0020] Furthermore, the polyamine-calcium ion composite preservative solution also includes a trace amount of buffer.

[0021] Furthermore, the polyamine compound is selected from putrescine or spermidine; the soluble calcium salt is selected from calcium chloride or calcium lactate; and the antioxidant stabilizer is selected from ascorbic acid or citric acid to enhance the ability to fight free radicals and retain vitamin C.

[0022] Furthermore, the concentration of the polyamine compound in the polyamine-calcium ion composite preservative solution is 0.5-2 mmol / L; the concentration of the soluble calcium salt is 0.5-3 wt.%; and the concentration of the antioxidant stabilizer is 0.05 wt.%.

[0023] Furthermore, the soaking time is 1-2 minutes.

[0024] The polyamine-calcium ion composite preservative solution is evenly applied to the surface of blueberries and partially penetrates the peel through soaking or low-pressure spraying. Polyamine compounds inhibit cell wall degrading enzyme activity and promote antioxidant enzyme expression, thus slowing down cell membrane lipid peroxidation and tissue softening. Calcium ions cross-link with pectin to form an "oval box structure," enhancing cell wall rigidity and membrane system stability. The synergistic effect of these two components significantly improves the compressive and crack resistance of fruit tissues, slows down softening and water loss rates, and provides a favorable physiological basis for subsequent storage.

[0025] After pre-cooling, the blueberries are air-dried for 5-10 minutes to remove surface moisture. They are then placed in a sealed storage container equipped with a bio-fermentation gas module. This module consists of food-grade gas-producing microbial agents (such as active dry yeast or lactic acid bacteria) and a carbon source nutrient substrate (such as glucose powder or sucrose powder), separated and encapsulated. The permeable membrane is broken by pressing the activation zone, allowing the gas-producing microbial agents to contact the carbon source nutrient substrate and initiate the fermentation reaction. The microorganisms slowly release carbon dioxide (CO2) and consume oxygen (O2) within the container, creating a micro-controlled atmosphere with an O2 concentration of approximately 5-10% and a CO2 concentration of approximately 10-20% within the first 24 hours of storage. This atmosphere effectively reduces the blueberry respiration rate and ethylene synthesis level, inhibits pathogen reproduction, and delays fruit ripening, while avoiding the dependence on external gas and electricity found in traditional controlled atmosphere systems. The bio-fermentation gas module can be placed inside the encapsulation structure (packaging box or modified atmosphere bag) in an independent small package structure, or it can be designed as an attached structure to adapt to different packaging specifications. The fermentation process is stable and controllable, and the CO2 release rate can be adjusted by the amount of bacteria and the proportion of substrate.

[0026] During the refrigerated shelf stage (8~12℃), the bio-fermentation gas module continuously maintains a dynamic balance environment of low oxygen and high carbon dioxide, externally regulating the metabolic activities of blueberries. Simultaneously, the previous polyamine-calcium ion compound preservative treatment has established a stable anti-aging and disease-resistant system within the fruit. This dual mechanism works synergistically on both the internal and external levels of the fruit: external atmospheric regulation achieves respiration inhibition and microbial control, while the internal cellular homeostasis system maintains tissue structure and antioxidant capacity, thus forming a comprehensive preservation effect of "external softness and internal stability." Experiments show that blueberries treated with this method can be stably stored on refrigerated shelves for 20 days at 10±2℃, with a rot rate of less than 30%, a fruit firmness reduction rate slowed by more than 20%, and anthocyanin and vitamin C retention rates significantly higher than the untreated control group, maintaining good color and flavor during the refrigerated shelf life.

[0027] Compared with the prior art, the present invention has the following advantages and technical effects:

[0028] In long-term refrigerated shelf testing, blueberries treated with the post-harvest refrigerated shelf preservation method provided by this invention exhibited excellent overall preservation effects. Fruit treated with this method could be stably stored for 20 days at 10±2℃, with a rot rate remaining below 30%. The rate of decline in fruit firmness was significantly slowed, and the retention rates of anthocyanins and vitamin C were 52.68% and 27.93% higher, respectively, than the untreated group. Soluble solids and antioxidant enzyme activity remained at high levels. Fruits stored at room temperature for 24 hours after refrigeration still retained good color, flavor, and texture elasticity, indicating that this invention effectively maintains the commercial appearance and edible quality of blueberries while extending their refrigerated shelf life. This demonstrates that this invention not only achieves microbial inhibition and respiration retardation but also significantly improves the stability of the cell membrane system and nutrient retention capacity, resulting in a synergistic enhancement in structure, metabolism, and flavor.

[0029] This invention offers significant advantages in terms of low cost and wide applicability in economic applications. The bio-fermentation gas module consists of gas-producing microbial agents and a carbon source nutrient matrix, using inexpensive materials and simple operation. The polyamine compounds and calcium salts are both edible-grade raw materials, readily available and safe. The entire preservation process does not rely on complex equipment or high-energy-consuming systems, and can be flexibly deployed at the production site sorting line, cold chain connection links, and export packaging stage, with a single processing cost as low as 0.05-0.1 yuan per kilogram of fruit. This preservation method is compatible with existing refrigeration or controlled atmosphere systems and can also operate independently under conditions of no electricity or limited resources, providing an economical and practical solution for small and medium-sized fruit farmers and processing enterprises.

[0030] In terms of safety and environmental friendliness, the materials and processes used in this invention are all green and harmless systems. The microorganisms used in the bio-fermentation gas module are food-grade microorganisms, and the fermentation products are only carbon dioxide and trace amounts of water, without producing any toxic or irritating substances; polyamine compounds and calcium ions are natural plant metabolic components, harmless to the human body, and will not cause chemical residue pollution. The entire process complies with green agriculture and pollution-free fruit standards, and is characterized by being biodegradable, low-carbon, and sustainable, meeting the requirements of the high-end fruit market and export inspection.

[0031] In summary, this invention, with its core innovations in natural metabolic regulation and cellular homeostasis, overcomes the limitations of traditional controlled atmosphere storage, which relies on external energy and single-nutrient fortification, achieving an organic unity of environmental control and physiological regulation. This method is simple to operate, highly effective, low-cost, and safe. It is not only suitable for post-harvest preservation of blueberries but can also be extended to the storage and transportation of other perishable berries such as strawberries, blackberries, and raspberries. It provides an efficient, green, and sustainable technical path for post-harvest preservation of fruits and vegetables, possessing significant industrialization value and social application significance. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 The blueberry post-harvest cold storage shelf preservation device provided by the present invention includes 1 as an encapsulation structure, 2 as a bio-fermentation gas module, 3 as a breathable membrane, and 4 as a press-activated area.

[0034] Figure 2 This invention provides a schematic diagram of a post-harvest cold storage shelf preservation method for blueberries.

[0035] Figure 3 The graphs show the gas concentration changes during storage in Examples 2 and Comparative Examples 1-3.

[0036] Figure 4 This is a comparison chart of the hardness of Example 2, Comparative Example 1, Comparative Example 2 and Comparative Example 3 within the refrigerated shelf time;

[0037] Figure 5 The blueberry pulp cell structure in Example 2;

[0038] Figure 6 The cell structure of blueberry pulp in Comparative Example 3. Detailed Implementation

[0039] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0040] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0041] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0042] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0043] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0044] This invention provides a post-harvest cold storage shelf preservation device for blueberries, such as... Figure 1 As shown, the device includes an encapsulation structure 1 and a bio-fermentation gas module 2. The bio-fermentation gas module 2 is disposed inside the encapsulation structure 1 and has a dual-chamber structure, with the two chambers separated by a breathable membrane 3. The outer wall of the bio-fermentation gas module 2 is provided with a press-activated area 4 that can break the breathable membrane. The lower part of the press-activated area 4 is a pointed structure. When pressed forcefully, the pointed structure punctures the breathable membrane 3, allowing the carbon source nutrient substrate and the gas-producing microbial agent in the two chambers to come into contact.

[0045] In a preferred embodiment, the packaging structure is selected from a high-barrier plastic packaging bag or a high-barrier plastic food storage box; the bio-fermentation gas module is made of a breathable material, which is selected from non-woven fabric, microporous membrane material or cellulose-based breathable membrane.

[0046] The high-barrier plastic used in this invention is a multilayer composite material with low oxygen and water vapor permeability. The encapsulation structure employed in this invention exhibits excellent gas and moisture barrier properties, with an oxygen barrier resistance (OTR) of 0.3–35 cm⁻¹ at 10°C and 0.1 MPa. 3 ·m -2 24h -1 More preferably 0.3~8cm 3 ·m -2 24h -1 Its moisture permeability (WVTR) is 0.3~12 g·m³ at 10℃ and 90%RH. -2 24h -1More preferably, it is 0.3~6 g·m -2 24h -1 .

[0047] This invention also provides a method for preserving blueberries in a post-harvest cold storage shelf, comprising the following steps: placing a carbon source nutrient matrix and a gas-producing microbial agent into the two cavities of the double-cavity packaging structure of the blueberry post-harvest cold storage shelf preservation device; immersing pre-cooled blueberries in a polyamine-calcium ion composite preservative solution; drying and then placing them in the encapsulation structure of the blueberry post-harvest cold storage shelf preservation device; breaking the permeable membrane through the pressing activation area to allow the carbon source nutrient matrix and microbial agent to come into contact and begin a micro-fermentation reaction; closing the encapsulation structure; and storing the blueberry post-harvest cold storage shelf preservation device at 10±2℃.

[0048] The post-harvest cold storage shelf preservation method for blueberries proposed in this invention, which combines a bio-fermentation gas module with a polyamine-calcium ion composite preservative liquid, demonstrates significant comprehensive advantages in terms of technical principles, preservation effects, economic applicability, and safety and environmental protection. It can effectively overcome the problems of fragmented mechanisms, equipment dependence, unstable effects, and chemical residues in existing blueberry preservation technologies, and establish a green, low-energy, and efficient post-harvest quality maintenance system.

[0049] This invention achieves synergistic preservation through a dual mechanism of "external atmosphere regulation" and "internal tissue stabilization." The bio-fermentation gas module, within a sealed storage environment, relies on food-grade microbial metabolism to release carbon dioxide and simultaneously consume oxygen, creating a low-oxygen, high-carbon dioxide microclimate. This effectively inhibits blueberry respiration rates, delays ethylene synthesis and fruit ripening, and suppresses major pathogens such as gray mold and anthracnose. This process requires no external energy or gas source; the gas release is mild and the concentration is stable, maintaining a suitable gas ratio throughout the entire storage and transportation cycle, thus achieving natural external regulation of fruit metabolism and microbial growth. Simultaneously, after treatment with a polyamine-calcium ion composite preservative solution before storage, the cell structure of the blueberries is strengthened and stabilized. Polyamine molecules can inhibit the activity of cell wall degrading enzymes, promote the expression of antioxidant enzymes such as SOD and CAT, and reduce cell membrane lipid peroxidation levels; calcium ions cross-link with pectin to form a stable "egg box structure," enhancing cell wall toughness and membrane system stability. The synergistic effect of these two mechanisms maintains the fruit's firmness and integrity during storage, reducing water loss and softening, and establishing an internal physiological barrier against aging and disease. Through the coupling of external micro-atmosphere control and internal quality stabilization mechanisms, this invention achieves bidirectional preservation from the environmental to the cellular level, significantly improving the fruit's storability and flavor stability.

[0050] In a preferred embodiment, the gas-producing microbial agent is selected from one or more of dry yeast or lactic acid bacteria; the carbon source nutrient matrix includes one or more of glucose or sucrose.

[0051] In a preferred embodiment, when the gas-producing microbial agent is dry yeast, the viable count of the dry yeast is 1.0 × 10⁻⁶. 8 ~1.0×10 10 CFU / g, preferably, the viable count of the dry yeast is 5.0 × 10⁻⁶. 8 ~5.0×10 9 CFU / g, exemplarily, the viable count of the dry yeast is 1.0 × 10⁻⁶. 10 CFU / g, the mass ratio of the dry yeast to the carbon source nutrient substrate is 1:(20-40); preferably, the mass ratio of the dry yeast to the carbon source nutrient substrate is 1:(25-35), and exemplaryly, the mass ratio of the dry yeast to the carbon source nutrient substrate is 1:25; when the gas-producing microbial agent is lactic acid bacteria, the viable count of the lactic acid bacteria is 1.0×10⁻⁶. 8 ~1.0×10 10 CFU / g, preferably, the viable count of the lactic acid bacteria is 5.0 × 10⁻⁶. 8 ~5.0×10 9 CFU / g; the mass ratio of the lactic acid bacteria to the carbon source nutrient substrate is 1:(20-50), preferably, the mass ratio of the lactic acid bacteria to the carbon source nutrient substrate is 1:(25-40).

[0052] In a preferred embodiment, the polyamine-calcium ion composite preservative liquid includes a polyamine compound, a soluble calcium salt, and an antioxidant stabilizer.

[0053] In a preferred embodiment, the polyamine compound is selected from putrescine or spermidine; the soluble calcium salt is selected from calcium chloride or calcium lactate; and the antioxidant stabilizer is selected from ascorbic acid or citric acid.

[0054] In a preferred embodiment, the concentration of the polyamine compound in the polyamine-calcium ion composite preservative solution is 0.5-2 mmol / L; the concentration of the soluble calcium salt is 0.5-3 wt.%; and the concentration of the antioxidant stabilizer is 0.05 wt.%.

[0055] In a preferred embodiment, the soaking time is 1-2 minutes.

[0056] Figure 2 This invention provides a schematic flowchart of a post-harvest cold storage shelf preservation method for blueberries. The method includes: blueberry pre-cooling treatment → treatment with a polyamine-calcium ion composite preservative solution → natural air drying → loading into a packaging structure with a bio-fermentation gas module → pressing the activation zone to initiate micro-fermentation → sealed storage → cold storage shelf preservation at 10±2℃. Figure 2 As shown, the post-harvest cold storage shelf preservation method for blueberries of the present invention specifically includes the following steps:

[0057] S1. Pre-cooling treatment

[0058] After harvesting, select blueberries, removing those with mechanical damage or disease spots. Pre-cool the qualified berries at 10℃ for 2 hours to rapidly lower the fruit temperature.

[0059] S2. Polyamine-Calcium Ion Composite Preservative Treatment

[0060] Soak the pre-cooled blueberries in a polyamine-calcium ion composite preservative solution for 1-2 minutes to allow the preservative ingredients to adhere evenly to the surface of the fruit peel and partially penetrate the intercellular spaces.

[0061] S3. Air dry

[0062] After soaking, place the blueberries on a clean work surface and let them air dry for 5-10 minutes to remove free water from the surface of the fruit, so as to avoid local water accumulation during the subsequent packaging process.

[0063] S4. Loading into the packaging structure

[0064] The air-dried blueberries are packed into a high-barrier encapsulation structure, which contains a pre-installed bio-fermentation gas module.

[0065] S5. Activate the bio-fermentation gas module

[0066] By pressing the activation area to break the permeable membrane inside the module, the carbon source nutrient substrate comes into contact with the gas-producing microbial agent and starts a micro-fermentation reaction, slowly releasing CO2 and consuming O2.

[0067] S6. Sealed and refrigerated shelf storage

[0068] The packaging structure is quickly sealed and stored at 10±2℃. The quality of the blueberries is maintained through the synergistic effect of the external micro-atmosphere environment and the internal stable structure.

[0069] The combined application of the bio-fermentation gas module and polyamine-calcium ion composite preservative solution provided by this invention can be extended to other berries, including strawberries, blackberries, and raspberries, achieving similar preservation effects using the same treatment parameters. The post-harvest cold storage shelf preservation method for blueberries provided by this invention is both green and safe, and highly operable. The microorganisms used in the bio-fermentation gas module are all food-grade active microorganisms, and the fermentation gas is non-toxic and residue-free. The polyamines and calcium ions in the polyamine-calcium ion composite preservative solution are natural nutrients, safe and harmless to the human body. The entire preservation process requires no external energy or chemical preservatives, resulting in low costs and suitability for small and medium-sized fruit growers, cooperatives, and the commercial processing of exported fruits. Compared to existing technologies, this invention overcomes the limitations of traditional controlled atmosphere storage, which relies on complex equipment and single nutrient fortification. By combining external atmosphere control with internal physiological regulation, it constructs a comprehensive post-harvest blueberry preservation system of "low-oxygen quality stabilization and anti-aging synergy," achieving a green, efficient, and sustainable fruit quality maintenance model.

[0070] Using the "rabbiteye" blueberry as a representative variety, and combined with experimental verification data, this invention further explains the post-harvest cold storage shelf preservation method and device for blueberries.

[0071] Example 1: A post-harvest cold storage shelf for blueberries

[0072] The blueberry post-harvest cold storage shelf preservation device provided in this embodiment includes a packaging structure 1 (a high-barrier plastic preservation box, made of PET / PA / PE multi-layer co-extruded composite material, with an oxygen barrier rate (OTR) of 20~40 cm under 10℃ and 0.1MPa conditions). 3 ·m -2 24h -1 The water permeability (WVTR) at 10°C and 90% RH is 2–5 g·m³. -2 24h -1 The biological fermentation gas module 2 has a dual-chamber structure, with the two chambers separated by a breathable membrane 3. One chamber contains a carbon source nutrient substrate (5g glucose powder), and the other chamber contains a gas-producing microbial agent (0.2g active dry yeast powder, with a viable count of 1×10⁻⁶). 10 The outer wall of the bio-fermentation gas module (CFU / g) is equipped with a press-activated area 4 that can break the breathable membrane. When in use, fermentation is activated by mechanically pressing or manually squeezing the breathable membrane, releasing CO2 and absorbing O2 to generate a micro-modified atmosphere.

[0073] Example 2: A method for post-harvest cold storage shelf preservation of blueberries

[0074] S1. Within 2 hours after blueberry harvest, place the fruit on a clean operating table for screening, remove mechanically damaged and diseased fruit, and select fruit with uniform shape and intact skin for use. In order to inhibit early respiration and microbial reproduction, the selected fruit is first pre-cooled (10℃, 2h) to make the fruit temperature drop rapidly and slow down the metabolic rate.

[0075] S2. Preparation of polyamine-calcium ion composite preservative solution: Add calcium chloride to the putrescine aqueous solution and stir until completely dissolved. Slowly add food-grade citric acid solution to adjust the pH of the system to 6.0±0.2. Then add the antioxidant auxiliary ascorbic acid and mix well to obtain the polyamine-calcium ion composite preservative solution, wherein the concentration of putrescine is 1.0 mmol / L, the concentration of calcium chloride is 1.5 wt.%, and the concentration of ascorbic acid is 0.05 wt.%.

[0076] S3. Immerse the pre-cooled blueberries from S1 in the polyamine-calcium ion composite preservative solution prepared in S2 for 2 minutes to ensure that the preservative ingredients are evenly attached and partially penetrate the skin. Then remove them and air dry them naturally for 10 minutes (until no visible water droplets are visible on the surface) to ensure that there are no obvious water droplets left on the surface, so as to avoid microbial growth caused by local water accumulation.

[0077] S4. Place the air-dried blueberries from S3 into the high-barrier plastic storage container from Example 1. Before use, gently press the outer shell of the bio-fermentation gas module to rupture the breathable membrane. The dry yeast powder and glucose powder will immediately begin a micro-fermentation reaction upon contact. The bio-fermentation gas module is placed in a 1L high-barrier plastic storage container and sealed together with the blueberries. Within 24 hours, the CO2 concentration inside the container gradually rises to 15%, and the O2 concentration drops to about 8%, forming a stable low-oxygen, high-carbon dioxide atmosphere. This gas environment can effectively inhibit the respiration intensity of blueberries, reduce ethylene production, and reduce pathogen activity. A non-powered micro-controlled atmosphere system is constructed from the outside. The blueberries are stored at 10±2℃ for 20 days, during which the fermentation module maintains gas balance for about 1 day.

[0078] It should be noted that the present invention does not limit the order of S1 and S2.

[0079] Comparative Example 1

[0080] Same as Example 2, except that after removing the bio-fermentation gas module in Example 1, the blueberries dried in S3 in Example 2 are placed into the high-barrier plastic preservation box in Example 1 and stored at 10±2℃ for 20 days.

[0081] Comparative Example 2

[0082] Same as Example 2, except that the pre-cooled blueberries were not immersed in the polyamine-calcium ion composite preservative solution.

[0083] Comparative Example 3

[0084] No further treatment was applied to the blueberries that underwent the pre-cooling treatment in Example 2 (S1).

[0085] Figure 3 The graph shows the gas concentration change curves during the storage process of Example 2 (bio-fermentation gas module + polyamine-calcium ions), Comparative Example 1 (polyamine-calcium ions), Comparative Example 2 (bio-fermentation gas module), and Comparative Example 3 (CK).

[0086] Figure 5 This is a diagram of the blueberry pulp cell structure in Example 2. Figure 6 This is a diagram of the blueberry pulp cell structure in Comparative Example 3, showing the structure through comparison. Figure 5 and Figure 6It can be seen that the blueberry pulp cells in Example 2 have clear outlines, maintain high cell wall integrity, have tight intercellular connections, relatively small intercellular spaces, and no obvious cell membrane rupture; the pectin structure in the pulp tissue is still relatively dense, and the texture between cells is uniform. In contrast, the blueberry tissue in Comparative Example 3 shows significant structural deterioration: cells collapse and shrink significantly, cell walls are discontinuous or even broken, some cell contents are lost, intercellular spaces are significantly enlarged, and the pectin matrix shows dissolution and cavitation. These phenomena indicate that in Comparative Example 3, the activity of cell wall degrading enzymes is enhanced and the membrane lipid peroxidation reaction is intensified during storage, leading to rapid destruction of cell structure. In contrast, Example 2, due to treatment with a polyamine-calcium ion composite preservative solution before storage and being stored in a micro-controlled atmosphere, has its cell wall degradation process inhibited, and its cell membrane stability is higher, thus significantly delaying the tissue softening and aging process.

[0087] Effect test

[0088] The decay rate, respiration rate, firmness, soluble solids content, anthocyanin content, vitamin C content, and polyphenol content of blueberries in Example 2 and Comparative Examples 1-3 were examined at 0, 5, 10, 15, and 20 days, respectively. During the testing, the parallel sample size for each group was 300g, and three replicates were performed for each indicator. The decay rate was determined by visually counting the number of fruits showing soft rot, mold, or obvious decay. The decay rate was calculated as: (Number of rotten fruits / Total number of fruits) × 100%. The respiration rate was determined by weighing approximately 200g of blueberries and placing them in a sealed container. The container was equilibrated at 25°C for 1 hour, and the CO2 concentration was measured using a portable residual oxygen meter. The respiration rate was calculated based on the sample mass, expressed in mg·kg⁻¹. - ¹·h - ¹. Methods for determining firmness: A texture analyzer was used. The probe was pressed into the fruit at the equatorial region at a rate of 2 mm / s, and the maximum breaking force was recorded in N. 15 fruits were measured per group, and the average value was taken. Methods for determining soluble solids content: Fruit juice was dropped onto the detection surface of a handheld digital refractometer, and the reading was taken directly. 15 fruits were measured per group, and the unit was %. Methods for determining anthocyanin content: The pH differential method was used. The absorbance at 520 nm and 700 nm was measured in buffer systems with pH 1.0 and pH 4.5, respectively. The anthocyanin content was calculated based on the difference, and the unit was g·kg⁻¹. - ¹. Determination of Vitamin C content: The 2,6-dichlorophenolindophenol titration method was used for quantitative analysis of the fruit juice extract, and the results were converted to g·kg⁻¹. - ¹; Determination of polyphenol content: The Folin-Ciocalteu colorimetric method was used to measure the absorbance at 760 nm. The total polyphenol content was calculated using gallic acid as a standard, and the unit is g·kg. - ¹, The test results are shown in Table 1-7.

[0089] Table 1 Results of the decay rate test

[0090]

[0091] Table 2 Results of respiratory intensity test

[0092]

[0093] Table 3 Hardness test results

[0094]

[0095] Table 4 Results of soluble solids content test

[0096]

[0097] Table 5. Results of anthocyanin content test

[0098]

[0099] Table 6. Results of Vitamin C Content Test

[0100]

[0101] Table 7. Results of Polyphenol Content Test

[0102]

[0103] As shown in Tables 1-7, Example 2 and Comparative Example 3 exhibited significant differences during the 20-day storage period. The decay rate of Example 2 was less than 30%, while that of Comparative Example 3 exceeded 60% after 20 days. The fruit firmness of Example 2 decreased by only 34% after 20 days, and the anthocyanin retention rate was 80.2% and the vitamin C retention rate was 65.7%, both significantly better than those of Comparative Example 3. Furthermore, the blueberry fruit decay rate, respiration rate, firmness, soluble solids content, anthocyanin content, vitamin C content, and polyphenol content of Example 2 were all superior to those of Comparative Example 1 and Comparative Example 2.

[0104] Figure 4 The image shows a comparison of the hardness of Example 2 and Comparative Examples 1-3 within the refrigerated shelf time. Example 2 is a treatment with a bio-fermentation gas module and polyamine-calcium ions, Comparative Example 1 is a treatment with polyamine-calcium ions, Comparative Example 2 is a treatment with a bio-fermentation gas module, and Comparative Example 3 is a control.

[0105] Sensory evaluation test

[0106] After storage at 10±2℃ for 20 days, the blueberries from Examples 2 and Comparative Examples 1-3 underwent the following sensory evaluation: Sensory evaluation was conducted based on six indicators: color, bloom integrity, firmness, texture, flavor, off-putting odor, and overall marketability. Each indicator was scored out of 10 points, for a total of 60 points. The evaluation panel consisted of 10 trained evaluators, using anonymously coded samples, and the evaluation was conducted under natural sunlight conditions. The evaluation criteria are as follows:

[0107] (1) Color (10 points)

[0108] A uniform, bright blue-purple color scores 9-10 points; a slightly darker color with some fruit showing discoloration scores 6-8 points; and fruit showing signs of dehydration, shriveling, or browning scores 0-5 points.

[0109] (2) Integrity of fruit powder (10 points)

[0110] Fruit powder intact and not falling off: 9-10 points; fruit powder slightly falling off: 6-8 points; fruit powder mostly falling off: 0-5 points.

[0111] (3) Hardness and texture (10 points)

[0112] Firm and elastic flesh scores 9-10 points; slightly soft flesh but still elastic scores 6-8 points; visibly softened or rotten flesh scores 0-5 points.

[0113] (4) Flavor (10 points)

[0114] A rich fruity aroma and a balanced sweet and sour taste score 9-10; a slightly bland flavor or a slight fermented taste score 6-8; a deteriorated flavor or an off-flavor score 0-5.

[0115] (5) Rotten smell (10 points)

[0116] No putrid smell scores 9-10; slight odor scores 6-8; obvious putrid sour smell scores 0-5.

[0117] (6) Overall product quality (10 points)

[0118] A score of 9-10 is given for a complete appearance and good shelf appeal; a score of 6-8 is given for a general appearance with a few wrinkles or fruit powder falling off; and a score of 0-5 is given for a severely deteriorated appearance or one that is not commercially viable.

[0119] The evaluation results show that:

[0120] The sample from Example 2 performed best in color, bloom integrity, firmness, and flavor, with a total score of 52–55. The fruit retained its bright blue-purple color, with intact bloom, good elasticity of the flesh, no off-odors or rotten smells, and good marketability after 24 hours on the shelf.

[0121] Comparative Example 1 scored 44–48 points, showing slight bloom shedding, a more significant decrease in firmness than Example 2, and a slight sour taste in some fruits, but the overall marketability was still acceptable.

[0122] Comparative Example 2 scored 42–46 points, with good color but noticeable bloom shedding, slightly soft flesh, and a slight decrease in flavor.

[0123] Comparative sample 3 scored 30–35 points, exhibiting characteristics such as significant bloom shedding, noticeably softened flesh, and a rotten, sour taste in some fruits, indicating poor overall marketability.

[0124] The sensory evaluation results were consistent with the physicochemical indicators such as rot rate, firmness, and anthocyanin content, further proving that the present invention can effectively maintain the appearance, flavor, and commercial quality of blueberries during refrigerated shelf life.

[0125] The blueberry preservation process of this invention (excluding the conventional pre-cooling step) can be completed in a short time. From the end of fruit pre-cooling to the completion of preservation liquid treatment, air drying, packaging, and activation of the bio-fermentation gas module, the entire operation takes approximately 10-15 minutes. It requires no complex equipment or external energy input, making it suitable for rapid deployment in production sorting centers and cold chain transportation nodes. The module structure can also be flexibly adjusted according to packaging specifications; for example, when using 0.5 L small packages, the carbon source and bacterial count in the fermentation module can be halved proportionally.

[0126] Cost calculation per processing session:

[0127] The calculation is based on the following: The cost estimation of this invention is based on the single-use consumption of the preservative liquid raw material, the bio-fermentation gas module, and the high-barrier packaging material. The polyamine-calcium ion composite preservative liquid used in this invention has a low concentration, with approximately 5-10 mL of soaking or spraying solution per kilogram of blueberries, resulting in a cost of only 0.008-0.03 yuan / kg. The bio-fermentation gas module consists of dry yeast, a carbon source nutrient matrix, and a breathable membrane material; the cost of a single module is approximately 0.03-0.06 yuan, applicable to 0.5-2 kg of blueberries, resulting in a cost of 0.02-0.05 yuan / kg. The cost difference between the high-barrier packaging material used and ordinary PE bags is approximately 0.02-0.03 yuan / kg. Therefore, the overall single-use cost of this invention is 0.05-0.1 yuan / kg of blueberries, significantly lower than the processing costs of traditional modified atmosphere systems, ozone sterilization, and nutrient fortification technologies, demonstrating outstanding economic efficiency and suitability for large-scale routine promotion.

[0128] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A post-harvest cold storage shelf preservation device for blueberries, characterized in that, It includes an encapsulation structure and a bio-fermentation gas module. The bio-fermentation gas module is disposed inside the encapsulation structure and has a dual-chamber structure, with the two chambers separated by a breathable membrane. The outer wall of the bio-fermentation gas module is provided with a press-activated area that can break the breathable membrane.

2. The blueberry post-harvest cold storage shelf preservation device according to claim 1, characterized in that, The packaging structure is selected from high-barrier plastic packaging bags or high-barrier plastic food storage boxes; the bio-fermentation gas module is made of breathable material, which is selected from non-woven fabric, microporous membrane material or cellulose-based breathable membrane.

3. A method for post-harvest cold storage preservation of blueberries, characterized in that, Includes the following steps: The carbon source nutrient matrix and the gas-producing microbial agent are respectively placed in the two cavities of the double-cavity packaging structure of the blueberry post-harvest cold storage shelf preservation device according to claim 1 or 2. After the blueberries have been soaked in polyamine-calcium ion composite preservation liquid or pre-cooled by low-pressure spraying, they are dried and placed in the packaging structure of the blueberry post-harvest cold storage shelf preservation device according to claim 1 or 2. The breathable membrane is broken by pressing the activation area, so that the carbon source nutrient matrix and the gas-producing microbial agent come into contact and carry out a micro-fermentation reaction. The packaging structure is then closed, and the blueberry post-harvest cold storage shelf preservation device is placed at 10±2℃ for storage.

4. The method for post-harvest cold storage preservation of blueberries according to claim 3, characterized in that, The gas-producing microbial agent is selected from dry yeast or lactic acid bacteria; the carbon source nutrient substrate includes one or more of glucose or sucrose.

5. The method for post-harvest cold storage preservation of blueberries according to claim 4, characterized in that, When the gas-producing microbial agent is dry yeast, the viable count of the dry yeast is 1.0 × 10⁻⁶. 8 ~1.0×10 10 CFU / g, wherein the mass ratio of the dry yeast to the carbon source nutrient substrate is 1:(20-40). When the gas-producing microbial agent is lactic acid bacteria, the viable count of the lactic acid bacteria is 1.0 × 10⁻⁶. 8 ~1.0×10 10 CFU / g, wherein the mass ratio of the lactic acid bacteria to the carbon source nutrient substrate is 1:(20-50).

6. The method for preserving blueberries in a post-harvest cold storage shelf according to claim 3, characterized in that, The polyamine-calcium ion composite preservative solution includes polyamine compounds, soluble calcium salts, and antioxidant stabilizers.

7. The method for post-harvest cold storage preservation of blueberries according to claim 6, characterized in that, The polyamine compound is selected from putrescine or spermidine; the soluble calcium salt is selected from calcium chloride or calcium lactate; and the antioxidant stabilizer is selected from ascorbic acid or citric acid.

8. The method for post-harvest cold storage preservation of blueberries according to claim 6, characterized in that, The concentration of polyamine compounds in the polyamine-calcium ion composite preservative solution is 0.5-2 mmol / L; the concentration of soluble calcium salt is 0.5-3 wt.%; and the concentration of antioxidant stabilizer is 0.05-0.1 wt.%.

9. The method for post-harvest cold storage preservation of blueberries according to claim 3, characterized in that, The soaking time is 1-2 minutes.

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