Freeze-dried strawberry mixed color preservative and preparation method thereof

Abstract

The present invention discloses a mixed color preservative for freeze-dried strawberries and a preparation method thereof, wherein the mixed color preservative comprises a composite penetrant composed of sodium alginate and calcium lactate and a mixed solution composed of orientin solution. The method comprises the following steps: (1) preparing 1.2% sodium alginate solution and 3.0% calcium lactate solution, and then mixing equal volumes of a composite penetrant composed of 1.5% calcium lactate and 0.6% sodium alginate. (2) preparing a 0.04 mg / ml orientin solution of Dr. Louis tea phenol extract. (3) mixing equal volumes of the above (1) and (2) to prepare a mixed color preservative. The mixed color preservative in the present invention can better protect strawberry pigments and antioxidants, thereby improving their color stability. Compared with other color preservatives, the mixed color preservative of the present invention introduces the concept of mixed color preservative treatment and proves its effectiveness in protecting the color of freeze-dried strawberries. It is crucial for maintaining the quality of freeze-dried strawberry products during storage and sales, and is also of great significance to the sustainable development of the freeze-dried strawberry industry.

Description

Technical Field

[0001] The invention relates to a mixed color preservative for freeze-dried strawberries, in particular to a preparation method and application of a mixed color preservative composed of orientin, a unique tea phenol substance of Dr. Louis tea. Background Art

[0002] Strawberries are a berry fruit with a short harvest period, concentrated production, and difficulty preserving. To extend their shelf life, freeze-drying is often used to produce freeze-dried strawberry products. However, the freeze-drying process can lead to color loss due to significant water loss and anthocyanin decomposition. Furthermore, the product shrinks and collapses, causing capillary closure and structural changes, ultimately reducing the quality of the freeze-dried product.

[0003] Currently, relatively little research has been conducted on the color protection of strawberries. Previous studies have primarily focused on the use of single colorants, with limited research on complex colorants. Strawberries contain anthocyanins, a class of water-soluble natural pigments widely found in plants. Factors that influence anthocyanin stability include pH, temperature, oxygen concentration, ascorbic acid, sulfur dioxide, metal ions, and sugars. Temperature fluctuations and autolysis of anthocyanins during the freeze-drying process are the primary causes of discoloration and whitening in strawberries. Anthocyanins are naturally sensitive to light, temperature, oxygen, and the presence of acids and bases in the surrounding matrix. To enhance the color stability of anthocyanins in strawberries, one of the best approaches is to form molecular complexes between anthocyanins, known as co-pigmentation. Orientin, found in rooibos tea, has been identified as an effective co-pigment of pelargonidin, exhibiting a stronger co-pigmentation than its sugar polysaccharide, luteolin. Orientin also exhibits the most pronounced color shift in heat-treated solutions. This ingredient is derived from natural plant extracts and does not contain any chemically synthesized substances, making it harmless to human health. Adding this color preservative during processing not only preserves the color of freeze-dried strawberries but also enhances the product's antioxidant capacity, improving its quality and market competitiveness. The flavonoid-rich portion of rooibos tea phenol extract, consisting of luteolin, apigenin, and quercetin glycosides, is believed to be a color enhancer and stabilizer for strawberry products. It can covalently bind to the aromatic chromophores of anthocyanins, improving the product's color stability.

[0004] It can be seen that Rooibos tea phenol extract can be used in the development of mixed color preservatives. There are few studies in the existing literature on the effect of orientin from Rooibos tea phenol extract on the color of freeze-dried strawberries. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing a novel color preservative for food, in particular a color preservative for freeze-dried strawberries.

[0006] The technical problem to be solved by the present invention is to prepare a freeze-dried strawberry mixed color preservative, which is characterized by comprising a mixed solution consisting of a composite penetrant composed of sodium alginate and calcium lactate and an orientin solution.

[0007] The technical solutions adopted to achieve the purpose of the present invention are as follows:

[0008] Appropriate amounts of calcium lactate and sodium alginate are dissolved to form a solution, which is then mixed in proportion to obtain a composite solution of the required concentration (1.5% calcium lactate and 0.6% sodium alginate), which is then mixed with orientin solution in a 1:1 (V / V) ratio to obtain a mixed color preservative.

[0009] The preparation method of the mixed color retaining agent comprises the following steps:

[0010] (1) Dissolve 7.5g of calcium lactate and 3.0g of sodium alginate in 250ml of water by heating to obtain a solution containing 1.2% sodium alginate and 3.0% calcium lactate. Mix the two solutions in a 1:1 (V / V) ratio and heat with stirring until a composite osmotic agent containing 1.5% calcium lactate and 0.6% sodium alginate is obtained.

[0011] (2) Add 20 mg of orientin (a unique tea phenol in Dr. Louis Tea) to 500 mL of distilled water, slowly add a small amount of food-grade ethanol, and stir with a magnetic stirrer for 1 hour or until the solid powder is dissolved, to obtain a 0.04 mg / mL orientin solution. The orientin solution is mixed with the composite penetrant (1.5% calcium lactate and 0.6% sodium alginate) obtained in step (1) at a ratio of 1:1 (V / V) to prepare a mixed color preservative.

[0012] Preferably, sodium alginate solid with high viscosity should not be selected in step (1) of the present invention, as it forms an extremely viscous liquid with the aqueous solution, which has a negative impact on subsequent mixing.

[0013] Furthermore, in step (1) of the present invention, the composite osmotic agent needs to be appropriately heated to 50°C, and then the prepared sodium alginate solution is slowly added to the calcium lactate solution and stirred rapidly. Sodium alginate is a marine polysaccharide, and its aqueous solution has a high viscosity and quickly forms a gel when it encounters calcium ions.

[0014] Furthermore, orientin dissolution requires the addition of a small amount of food-grade ethanol. Orientin is a luteolin derivative with a chemical structure consisting of a ketone group, two ether groups, and a phenyl group. It is soluble in organic solvents but insoluble in water. To prepare the orientin solution, food-grade ethanol is slowly added dropwise until the orientin is completely dissolved, followed by dilution with a large amount of water. This produces an orientin solution while significantly minimizing the effects of ethanol.

[0015] Beneficial effects of the present invention:

[0016] This invention relates to a mixed color preservative for freeze-dried strawberries, designed to address the problem of traditional freeze-dried strawberries fading during processing. This mixed color preservative, formulated with a combination of multiple natural plant extracts and rich in antioxidants such as anthocyanins and carotenoids, effectively preserves the color and nutritional content of strawberries.

[0017] The present invention has the following beneficial effects: 1. It significantly improves the color stability of freeze-dried strawberry products, extending their shelf life. 2. It preserves the original flavor and natural color of strawberries, enhancing the product's visual appeal. 3. The mixed color preservative ingredients are natural and harmless to human health, meeting consumer demand for green food. 4. Through a scientifically formulated formulation, it enhances the antioxidant capacity of strawberry products and slows down their quality degradation. The freeze-dried strawberry mixed color preservative of the present invention has broad application prospects in the fields of food processing and nutrition and health care. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The specific implementation manner and beneficial effects of the present invention will be further described in detail below with reference to the accompanying drawings.

[0019] Figure 1 Anthocyanin content in freeze-dried strawberries treated with a water control, a composite osmotic agent, an orientin solution, and a mixed color-protecting agent. (Note: CK - water control; CP - composite osmotic agent containing 1.5% calcium lactate and 0.6% sodium alginate; OS - 0.04 mg / ml orientin solution; MCF - a mixed color-protecting agent consisting of a 1:1 (v / v) mixture of a 0.04 mg / ml orientin solution and a composite osmotic agent containing 1.5% calcium lactate and 0.6% sodium alginate. Different lowercase letters indicate significant differences among treatments as determined by the LSD test, P < 0.05; same as in the following figures).

[0020] Figure 2 Total acid content of freeze-dried strawberries treated with water control, composite osmotic agent, orientin solution and mixed color preservatives.

[0021] Figure 3 Vitamin C content of freeze-dried strawberries treated with water control, composite osmotic agent, orientin solution and mixed color preservatives.

[0022] Figure 4 L, a, and b values ​​of freeze-dried strawberries treated with water control, composite osmotic agent, orientin solution, and mixed color preservative. DETAILED DESCRIPTION

[0023] Example 1

[0024] This embodiment provides an implementation process of mixing freeze-dried strawberries with a color preservative. The specific technical steps are as follows:

[0025] (1) Weigh 3.0 g of sodium alginate into a 250 ml conical flask and dissolve it in 250 ml of distilled water. Then heat the mixed solution and stir it on a magnetic stirrer for about an hour until the sodium alginate is completely dissolved. Finally, let the solution stand at room temperature overnight to ensure that the sodium alginate is evenly dissolved.

[0026] (2) Weigh 7.5 g of calcium lactate into a 250 ml conical flask and dissolve it in 250 ml of distilled water. Then heat the mixed solution and stir it on a magnetic stirrer for 1 h until the mixture is completely dissolved. Finally, let the above solution stand overnight to ensure that the mixture is evenly dissolved.

[0027] (3) Add 20 mg of orientin (a unique tea phenol in Dr. Louis tea) to 500 mL of distilled water, and slowly add a small amount of food-grade ethanol. Then stir with a magnetic stirrer for 1 h or until the solid powder is dissolved, and finally obtain a 0.04 mg / ml orientin solution.

[0028] (4) The synthesis process of the mixed color preservative is as follows: the calcium lactate solution prepared in step (2) is slowly mixed with the sodium alginate solution in step (1) at a ratio of 1:1 (V / V), stirring while adding until a composite penetrant is formed. The resulting composite penetrant is then mixed with the orientin solution prepared in step (3) at a ratio of 1:1 (V / V) to prepare a mixed color preservative.

[0029] Example 2 Experimental results of freeze-dried strawberry mixed color preservative prepared in Example 1

[0030] The relevant experiments of this embodiment were conducted based on the freeze-dried strawberry mixed color preservative in Example 1, specifically:

[0031] 1. Sensory evaluation, the specific experimental process and experimental conclusions are as follows:

[0032] Four groups of freeze-dried strawberry slices (300 slices each) prepared in 1.5 were randomly selected and plated. Twenty undergraduate students majoring in Food Science and Engineering from the Hyde College of Ocean University of China were invited to form a freeze-dried strawberry sensory evaluation panel. The panel conducted sensory tests in 20 separate laboratory rooms (or compartments) and evaluated and scored the appearance, color, taste, and tissue integrity of the freeze-dried strawberries (see Table 1).

[0033] Table 1 Sensory scoring criteria for freeze-dried strawberries

[0034]

[0035] The sensory evaluation of freeze-dried strawberries was based primarily on appearance, color, flavor, and tissue integrity. The results are shown in Table 2. One-way analysis of variance showed that the different treatments significantly affected the appearance, color, flavor, and tissue integrity of the freeze-dried strawberries, as well as their total scores (P < 0.001). The order of the four sensory evaluation indicators and their total scores was: mixed color preservative > orientin solution > composite penetrant > water control (Table 2).

[0036] Sensory evaluation scores for appearance and flavor of freeze-dried strawberries treated with the mixed color-protecting agent were significantly higher than those of the water control, compound osmotic agent, and orientin solution. Appearance scores increased by 16.80%-25.00%, and flavor scores increased by 8.86%-10.88% (P < 0.05; Table 2). Furthermore, sensory evaluation scores for appearance and flavor of freeze-dried strawberries treated with the water control, compound osmotic agent, and orientin solution showed no significant differences (P > 0.05; Table 2). Furthermore, tissue integrity scores of freeze-dried strawberries treated with the mixed color-protecting agent were significantly higher than those of the water control, compound osmotic agent, and orientin solution, increasing by 17.19%-77.17% (P < 0.05; Table 2). There was no significant difference in tissue integrity between the compound osmotic agent and orientin solution treatments (P > 0.05), but both treatments were significantly higher than the water control, increasing by 41.73% and 51.18%, respectively (P < 0.05; Table 2).

[0037] The total sensory and color scores of freeze-dried strawberries treated with the mixed color-protecting agent were significantly higher than those treated with the water control, the composite osmotic agent, and the orientin solution. The color score increased by 13.71%-54.95%, and the total sensory score increased by 13.48%-30.45% (P < 0.05; Table 2). The total sensory and color scores of freeze-dried strawberries treated with the orientin solution were significantly higher than those of the water control and the composite osmotic agent. The color score increased by 36.26% and 19.23%, and the total sensory score increased by 14.95% and 6.50%, respectively (P < 0.05; Table 2). Furthermore, the total sensory and color scores of freeze-dried strawberries treated with the composite osmotic agent were significantly higher than those of the water control, increasing by 14.29% and 6.50%, respectively (P < 0.05; Table 2).

[0038] Table 2 Sensory scores of freeze-dried strawberries treated with water control, composite osmotic agent, orientin solution, and mixed color preservatives and one-way ANOVA between treatments (F / P values)

[0039]

[0040] Note: The measured index data in the table are mean ± standard error; ***Indicates one-way analysis of variance, P<0.001; the indicators in the same row marked with different lowercase letters have significant differences among the treatments after LSD test (P<0.05).

[0041] 2. Nutritional composition determination

[0042] 1. Anthocyanin content of freeze-dried strawberries

[0043] The higher the anthocyanin content, the brighter the red color of the strawberry. One-way ANOVA showed that the anthocyanin content of freeze-dried strawberries differed significantly between the different treatments (F = 42.37, P < 0.001; Table 3). Compared with the water control, the anthocyanin content of freeze-dried strawberries treated with the composite osmotic agent, orientin solution, and mixed color preservatives increased; among them, the anthocyanin content of freeze-dried strawberries treated with orientin solution and mixed color preservatives increased significantly by 14.85% and 71.88% (P < 0.05; Figure 1 ), and the anthocyanin content of freeze-dried strawberries treated with the mixed color-protecting agent was significantly higher than that of freeze-dried strawberries treated with the composite osmotic agent and orientin solution, which increased significantly by 68.31% and 49.66%, respectively (P<0,05; Figure 1 ). It can be seen that the anthocyanin content in freeze-dried strawberries treated with composite penetrant, orientin solution and mixed color preservatives increased, among which the freeze-dried strawberries treated with mixed color preservatives had the best color preservative effect.

[0044]

[0045] 2. Total acid content of freeze-dried strawberries. The specific experimental process and experimental conclusions are as follows:

[0046] Total acid represents the number of hydrogen ions that can ultimately be released. The higher the total acid content, the higher the acidity. Anthocyanins are water-soluble pigments that change color according to the acidity of the cell fluid. Therefore, the higher the total acid content, the more obvious the red color of the sample. One-way analysis of variance showed that the total acid content of freeze-dried strawberries differed significantly between the different treatments (F = 4.50, P = 0.040; Table 3). The total acid content of freeze-dried strawberries treated with the mixed color preservative was significantly higher than that of freeze-dried strawberries treated with the water control, the composite osmotic agent, and the orientin solution, with significant increases of 30.59%, 32.81%, and 18.26%, respectively (P < 0.05;

[0047] Figure 2 ).

[0048] 3. Vitamin C content of freeze-dried strawberries. The specific experimental process and experimental conclusions are as follows:

[0049] One-way ANOVA showed that the vitamin C content of freeze-dried strawberries differed significantly among the different treatments (F = 18.56, P < 0.001; Table 3). Compared with the water control, the vitamin C content of freeze-dried strawberries treated with the composite osmotic agent, orientin solution, and mixed color preservatives increased; among them, the vitamin C content of freeze-dried strawberries treated with orientin solution and mixed color preservatives increased significantly by 17.21% and 31.56% (P < 0.05; Table 3). Figure 3 ), and the vitamin C content of freeze-dried strawberries treated with mixed color preservatives was significantly higher than that treated with composite osmotic agents and orientin solution, which increased significantly by 26.45% and 12.24%, respectively (P<0,05; Figure 3 ). It can be seen that the loss of vitamin C content in freeze-dried strawberries treated with composite osmotic agent, orientin solution and mixed color preservative is the least, among which the freeze-dried strawberries treated with mixed color preservative have the best treatment effect.

[0050] 3. Determination of L, a, and b values. The specific experimental process and experimental conclusions are as follows:

[0051] One-way ANOVA showed that the L value (F = 11.56, P = 0.0028), a value (F = 17.58, P < 0.001) and b value (F = 33.68, P < 0.001) of freeze-dried strawberries were significantly different among the different treatments (Table 3). Compared with the water control, the L, a and b values ​​of freeze-dried strawberries treated with the composite osmotic agent, orientin solution and mixed color preservative were all improved ( Figure 4 Among them, the L value of freeze-dried strawberries treated with mixed color-protecting agents was significantly higher than that of the water control, composite osmotic agent and orientin solution treatments, which increased significantly by 18.63%, 14.68% and 12.88% respectively (P<0.05; Figure 4 A); the a and b values ​​of freeze-dried strawberries treated with orientin solution and mixed color preservatives were significantly higher than those treated with water and composite osmotic agents, and the a and b values ​​of freeze-dried strawberries treated with mixed color preservatives were significantly higher than those treated with orientin solution (P<0.05; Figure 4 B and Figure 4 C). It can be seen that the orientin solution and the mixed color-protecting agent treatment have a good color-protecting effect on freeze-dried strawberries, and the mixed color-protecting agent treatment has the best color-protecting effect on freeze-dried strawberries, which can effectively enhance the redness and brightness of freeze-dried strawberries.

[0052] This invention introduces the concept of mixed color preservative treatment and demonstrates the effectiveness of the mixed color preservative (made by mixing equal volumes of a 0.04 mg / ml orientin solution with a composite osmotic agent containing 1.5% calcium lactate and 0.6% sodium alginate) in preserving the color of freeze-dried strawberries. Compared to the effectiveness of a single color preservative in maintaining strawberry color, the mixed color preservative treatment significantly improves the color preservation of freeze-dried strawberries. Before freeze-drying, the mixed color preservative treatment can better protect strawberry pigments and antioxidants, thereby improving the color stability of the strawberries. This is crucial for maintaining the quality of freeze-dried strawberry products during storage and sales, and is also of great significance to the sustainable development of the freeze-dried strawberry industry.

Claims

1. Application of a composite penetrant and orientin in the preparation of a mixed food color preservative, characterized in that: The food comprises freeze-dried food, wherein the freeze-dried food is freeze-dried strawberries, and the composite osmotic agent comprises sodium alginate and calcium lactate; The preparation method of the food mixed color retaining agent comprises the following steps: (1) 7.5 g of calcium lactate and 3.0 g of sodium alginate were heated and dissolved in 250 ml of water to obtain a solution containing 1.2% sodium alginate and 3.0% calcium lactate; the mixture was then mixed in a 1:1 (V / V) ratio and heated with stirring until a composite osmotic agent containing 1.5% calcium lactate and 0.6% sodium alginate was obtained; (2) Add 20 mg of orientin to 500 mL of distilled water, and slowly add a small amount of food-grade ethanol, and then stir with a magnetic stirrer for 1 hour or until the solid powder is dissolved, finally obtaining a 0.04 mg / ml orientin solution; the obtained orientin solution is mixed with the composite penetrant (1.5% calcium lactate and 0.6% sodium alginate) obtained in step (1) in a ratio of 1:1 (V / V) to prepare a mixed color color protection agent.

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