A multi-fruit adaptive postharvest freshness intelligent indication label with a multi-stage response gradient and a preparation method and application thereof

Abstract

The present application belongs to the technical field of food intelligent packaging and fruit and vegetable fresh-keeping logistics, and particularly relates to a multi-fruit adaptive postharvest freshness intelligent indication label with a multi-stage response gradient and a preparation method and application thereof. The present application selects natural high-molecular starch as a basic film-forming base, introduces a paper-based material to construct a composite network to overcome the mechanical and moisture-proof defects of single starch film, uses the complementary properties of the chemical synthesis indicator methyl red and bromothymol blue within the pH response range to prepare a mixed indicator MRB with multi-stage color change ability for CO2, and precisely controls the crosslinking strength of Ca 2+ by changing the initial pH environment of the film-forming system to successfully construct a sensing label array with a multi-stage response gradient, thereby realizing the differential and precise monitoring of the freshness of fruits of respiratory climacteric and non-respiratory climacteric types under different storage and transportation conditions.

Description

Technical Field

[0001] This invention belongs to the field of intelligent food packaging and fruit and vegetable preservation logistics technology, specifically involving a multi-level response gradient multi-fruit adaptable intelligent post-harvest freshness indicator label and its preparation method and application. Background Technology

[0002] Traditional methods for detecting fruit freshness (such as computer vision, hyperspectral imaging, near-infrared spectroscopy, and electronic noses) rely heavily on expensive, large-scale analytical instruments, making them difficult to implement in retail and home storage scenarios. Emerging visual smart labeling addresses these shortcomings. However, currently available or research-based smart labels often suffer from the following drawbacks:

[0003] Matrix performance defects: Because single starch-based films are not thermoplastic, they have problems such as high brittleness, poor mechanical properties, excessive hydrophilicity and hygroscopicity leading to easy curling and poor barrier properties, which limits their application scenarios.

[0004] Limited application scope: Current domestic and international research focuses mainly on monitoring animal-derived foods such as livestock, poultry and aquatic products, and is poorly adapted to the complex respiratory dynamics of fruits and vegetables after harvest.

[0005] Lack of response gradient: Traditional label monitoring has a narrow range and fixed sensitivity, and cannot simultaneously cover diverse consumption scenarios such as high metabolism at room temperature and low metabolism in cold chain, making it difficult to achieve accurate full-time capture of the starting point of fruit freshness, quality inflection point and edibility limit. Summary of the Invention

[0006] To address the above problems, this invention provides a multi-fruit-adaptive smart label for postharvest freshness with a multi-level response gradient, comprising a carrier matrix, a mixed indicator, a crosslinking agent, a plasticizer, and a buffer conditioner;

[0007] The carrier matrix is ​​a composite material of starch and paper-based materials;

[0008] The mixed indicator is a mixed solution of methyl red and bromothymol blue;

[0009] The crosslinking agent is a multivalent metal salt crosslinking agent;

[0010] The buffer conditioner is an alkaline pH adjuster.

[0011] Furthermore, the paper-based material is medium-speed filter paper.

[0012] Furthermore, the buffer conditioner is a sodium hydroxide solution, and the multivalent metal salt crosslinking agent is calcium chloride.

[0013] Furthermore, the mass ratio of methyl red to bromothymol blue is 1:1, and the total mass concentration of the mixed indicator solution is 5 g / L to 15 g / L.

[0014] Furthermore, the labels form an array of labels with different color change response gradients by adjusting the amount of calcium chloride added and the initial pH value of the film-forming gelatinization solution.

[0015] This invention also provides a method for preparing the above-mentioned multi-fruit-adaptive smart postharvest freshness indicator label with a multi-level response gradient, comprising the following steps:

[0016] Step 1: Mix methyl red and bromothymol blue in a certain proportion and dissolve them in pure water to prepare a mixed indicator solution;

[0017] Step 2: Disperse starch in purified water, add glycerin, heat to gelatinize, cool, add the mixed indicator solution, stir evenly to obtain film-forming gelatinized liquid;

[0018] Step 3: Add calcium chloride and sodium hydroxide solution to the film-forming gelatinized solution to adjust the crosslinking strength and initial pH value. After degassing, an indicator starch gelatinized solution with a specific response gradient is obtained.

[0019] Step 4: After immersing the paper base material in pure starch pretreatment solution, lay it flat, coat the indicator starch gelatinization solution with the paper base material in a semi-dry state, dry and shape it to obtain the smart indicator label.

[0020] Furthermore, in step one, the mass ratio of methyl red to bromothymol blue is 1:1, and the total mass concentration of the mixed indicator solution is 5 g / L to 15 g / L.

[0021] Furthermore, in step three, the amount of calcium chloride added is 0–3.0 w / v%, the concentration of sodium hydroxide solution is 1 mol / L, and the initial pH value of the film-forming gelatinization solution is controlled within the range of 7.5–12.5.

[0022] Furthermore, in step four, the pH value of the pure starch pretreatment solution is 7.0–9.0, the concentration is 2%–5%, the wet film coating thickness is 2.0 mm–3.5 mm, the drying temperature is 35℃–50℃, and the drying time is 4–8 hours.

[0023] This invention also provides the application of the above-mentioned multi-fruit-adaptive intelligent postharvest freshness indicator tag with multi-level response gradient in the monitoring of postharvest freshness of climacteric and non-climacteric fruits.

[0024] The present invention has the following beneficial effects:

[0025] 1. Significantly improved mechanical and moisture-proof properties: This invention overcomes the inherent weaknesses of single-starch matrix films, such as easy moisture absorption, curling, and brittle breakage. This is achieved by introducing a paper-based porous cellulose network and combining it with Ca... 2+Ion crosslinking, while maintaining the green, pollution-free, and biodegradable characteristics of the entire packaging material, significantly increases the physical dimensions of the label and improves its tensile strength; and Ca 2+ The coordination hydrogen bonds formed with starch hydroxyl groups significantly increase the water contact angle of the label surface to over 90°, resulting in excellent moisture resistance.

[0026] 2. A multi-level color change response gradient system was successfully constructed: This invention expands the color change kinetic range by controlling the micro-environment of inorganic crosslinking degree and initial pH. The high color change threshold group can withstand the slow release of low concentrations of CO2 or the basal release of fruits with high respiration intensity in long-term cold chain without premature false alarms; the low threshold high-sensitivity crosslinking group can quickly respond to acidic gas color changes and is perfectly suited for fresh-cut products with extremely short turnover periods.

[0027] 3. High color saturation and extremely stable product storage: Compared to single-component films, the starch-paper-based composite structure produces more vibrant colors with higher color saturation, making it easier for consumers to visually observe. After 42 days of storage in a light-proof, sealed environment, the label's color variation is minimal, demonstrating extremely high stability for commercial shelf placement. Attached Figure Description

[0028] 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.

[0029] Figure 1 An example diagram of the application of the intelligent freshness indicator label of the present invention in fruit packaging boxes (arrays from left to right are: S-8, P-8, SPCa1-8, SPCa2-8, SP-10, SP-12).

[0030] Figure 2 The present invention relates to a visual gradient color change trajectory response map of the freshness intelligent indicator label under four different storage and transportation conditions (whole peaches at room temperature, whole peaches at 10℃ with high humidity cold chain, fresh-cut peaches at 10℃, and strawberries at room temperature) as the number of storage days increases. Detailed Implementation

[0031] Various exemplary embodiments of the present invention are now described in detail. Unless otherwise specified, the methods used in the embodiments are conventional methods, and the reagents used are commercially available reagents or reagents prepared using conventional methods. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics, and embodiments of the present invention.

[0032] 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. Any stated value or intermediate value within a stated range, as well as each smaller range between 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.

[0033] 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.

[0034] 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 readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0035] 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.

[0036] Example 1: Accurate monitoring of whole peach freshness on shelves at room temperature (20℃) throughout the entire process

[0037] Postharvest physiological data support the following: Postharvest whole peaches exhibit typical respiratory climacteric characteristics during their shelf life at room temperature. Days 0-2 are the pre-climacteric phase, with stable respiratory metabolism; from days 2-4, due to postharvest stress and ripening, endogenous ethylene and respiration intensity increase sharply, entering the respiratory climacteric phase, with ethylene synthesis reaching its peak on day 4. At this time, the fruit flavor (lactone aroma compounds) reaches its highest edible quality; after day 4, the fruit firmness rapidly decreases from the initial 10.8 N to 2.6 N, and the texture softens; brown spots appear on the surface on day 8, and severe deterioration occurs on day 10.

[0038] Implementation of visual color-changing application for tag arrays:

[0039] Fresh Start (Day 0-2): The CO2 percentage inside the packaging box is extremely low, and the label array maintains its initial dark green color, indicating that the product is fresh.

[0040] Quality Inflection Point / Optimal Consumption Period (Day 4): As the whole peach enters the peak of its respiratory climacteric phase, CO2 accumulates linearly, leading to environmental acidification. At this time, low-threshold, highly sensitive labels respond first, rapidly changing color from green to orange-yellow, perfectly capturing the physiological point at which the peach reaches its optimal edible quality.

[0041] Edible Limit / Deterioration Warning Point (Days 6-10): As the storage period extends, peach senescence enters the late stage of rapid change, with a large accumulation of acidic metabolites, represented by hexanoic acid. At this time, the conventional high-sensitivity label on the far left turns completely red, providing a direct and precise visual warning in yellow and red for the peach's inedibility and overripe state.

[0042] Example 2: Monitoring the long shelf life of whole peaches in a low-temperature cold chain (10℃)

[0043] Physiological data supporting cold chain peach production show that at 10℃, the kinetic characteristics of various physiological indicators of peach fruit are significantly different from those under normal temperature conditions. Transmembrane transpiration and metabolic consumption are inhibited, and the decay rate is significantly slowed down. Fruit firmness decreases gradually in a stepwise manner, only dropping to around 5N by the 12th day, and only showing slight browning or sunken patches on the surface by the 20th day. The peak ethylene production period is significantly prolonged.

[0044] Implementation of visual color-changing label array application: Due to the extremely slow accumulation of CO2 within packaging under cold chain conditions, the color-changing speed of conventional low-threshold labels is significantly suppressed, with a color change similar to the orange-yellow of the room-temperature group on day 4 only appearing on day 12. Even at the extreme over-ripeness stage on day 20, the high-threshold enhanced label (SP-12) remains greenish / yellow, not reaching the extreme deep red. This demonstrates that the label array of this invention can objectively and effectively match and delay color-changing nodes in the cold chain logistics chain, avoiding the frequent premature false alarms caused by the high sensitivity of traditional labels.

[0045] Example 3: Early warning system for fresh-cut, short-shelf-life peach products in low-temperature cold chain (10℃)

[0046] Physiological data supporting fresh-cut peaches show that mechanical damage during processing causes a strong respiratory burst in the peach flesh, resulting in an exponential increase in weight loss (>2.0% by day 5). Firmness drops sharply from an initial 11N to around 3.4N by day 5 (a decrease of 69%). A non-pathological ethylene transition point occurs on day 4, and mold growth begins on day 5, resulting in an extremely short shelf life.

[0047] Implementation of visual color-changing label array application: Due to the high concentration of CO2 generated in a very short time by mechanical slicing, this labeling system is used when the label contains Ca... 2+The highly sensitive ion-based label exhibits extremely rapid color development, with the orange-red color change exceeding that of the whole cold-chain peaches on day 8 by day 3. It preemptively enters the red danger warning zone three days before the tissue structure completely collapses and mold develops, achieving highly sensitive and proactive control over the safety of short-shelf-life fresh-cut fruits and vegetables.

[0048] Example 4: Monitoring postharvest freshness of non-climacteric strawberries at room temperature (20℃)

[0049] Postharvest physiological data supporting the findings indicate that strawberries are non-climacteric fruits, exhibiting a stable respiration rate without a peak after harvest. However, they experience significant water loss and shriveling at room temperature, with a weight loss rate reaching 16% by day 5, and a continuous decline in firmness. Ascorbic acid (AsA) levels begin to decline after day 4, particularly the AsA / DHA ratio, which reflects cellular homeostasis, experiencing a sharp drop after day 3, indicating a physiological decline in tissue antioxidant regeneration efficiency. Esters / alcohols, which originally dominated fruit and floral aromas, disappear by days 4-5, while degraded fatty acids, characterized by hexanoic acid, accumulate in large quantities, resulting in off-flavors. CO2 levels within the packaging show a stable and continuous increase with storage days.

[0050] Implementation of Visualized Color-Changing Label Array Application: A multi-level response label array was applied inside strawberry boxes. Due to the continuous and stable respiration of non-catatonic fruits, the CO2 content within the packaging steadily increased. The high-sensitivity group in the label array gradually changed color from green to yellowish-green / pale orange within 1-3 days (the prime period when strawberries have a strong antioxidant system). In this scenario, the buffered label with a high color-changing threshold remained almost constantly green throughout its entire lifespan (within 5 days) as the initial alkaline environment was not completely neutralized. Thus, by differentiating between the "changes" and "unchanged" states of the array, precise labeling of the physiological milestones in the shelf life of non-catatonic fruits was achieved.

[0051] Table 1 Different formulations of pH-sensitive smart packaging labels

[0052]

[0053] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A multi-level response gradient, multi-fruit adaptable intelligent post-harvest freshness indicator label, characterized in that, Includes carrier matrix, mixed indicator, crosslinking agent, plasticizer, and buffer conditioner; The carrier matrix is ​​a composite material of starch and paper-based materials; The mixed indicator is a mixed solution of methyl red and bromothymol blue; The crosslinking agent is a multivalent metal salt crosslinking agent; The buffer conditioner is an alkaline pH adjuster.

2. The multi-level response gradient, multi-fruit adaptable post-harvest freshness intelligent indicator label according to claim 1, is characterized in that, The paper base material is medium-speed filter paper.

3. The multi-level response gradient, multi-fruit adaptive postharvest freshness intelligent indicator label according to claim 1, is characterized in that, The mass ratio of methyl red to bromothymol blue is 1:1, and the total mass concentration of the mixed indicator solution is 5 g / L to 15 g / L.

4. The multi-level response gradient, multi-fruit adaptive post-harvest freshness intelligent indicator label according to claim 1, is characterized in that, The smart indicator tag is a tag array, which includes several tag units with different calcium chloride contents and / or different initial pH values.

5. The multi-level response gradient, multi-fruit adaptive post-harvest freshness intelligent indicator label according to claim 1, characterized in that, The buffer conditioner is a sodium hydroxide solution, and the multivalent metal salt crosslinking agent is calcium chloride.

6. A method for preparing a multi-fruit-adaptive postharvest freshness intelligent indicator label with a multi-level response gradient as described in any one of claims 1 to 5, characterized in that, Includes the following steps: Step 1: Mix methyl red and bromothymol blue in a certain proportion and dissolve them in pure water to prepare a mixed indicator solution; Step 2: Disperse starch in purified water, add glycerin, heat to gelatinize, cool, add the mixed indicator solution, stir evenly to obtain film-forming gelatinized liquid; Step 3: Add calcium chloride and sodium hydroxide solution to the film-forming gelatinized solution to adjust the crosslinking strength and initial pH value. After degassing, an indicator starch gelatinized solution with a specific response gradient is obtained. Step 4: After immersing the paper base material in pure starch pretreatment solution, lay it flat, coat the indicator starch gelatinization solution with the paper base material in a semi-dry state, dry and shape it to obtain the smart indicator label.

7. The preparation method according to claim 6, characterized in that, In step one, the mass ratio of methyl red to bromothymol blue is 1:1, and the total mass concentration of the mixed indicator solution is 5 g / L to 15 g / L.

8. The preparation method according to claim 6, characterized in that, In step three, the amount of calcium chloride added is 0–3.0 w / v%, the concentration of sodium hydroxide solution is 1 mol / L, and the initial pH value of the film-forming gelatinization solution is controlled within the range of 7.5–12.

5.

9. The preparation method according to claim 6, characterized in that, In step four, the pH value of the pure starch pretreatment solution is 7.0-9.0, the concentration is 2%-5%, the wet film coating thickness is 2.0 mm-3.5 mm, the drying temperature is 35℃-50℃, and the drying time is 4-8 hours.

10. The application of a multi-fruit-adaptive smart postharvest freshness indicator tag with a multi-level response gradient as described in any one of claims 1 to 5, or a multi-fruit-adaptive smart postharvest freshness indicator tag with a multi-level response gradient prepared according to any one of claims 6 to 9, in monitoring the postharvest freshness of climacteric and / or non-climacteric fruits.

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