Color fixative for colorful potatoes and color protection method for colorful potatoes

Abstract

The invention discloses a color fixative for colorful potatoes and a color protection method for the colorful potatoes, and belongs to the technical field of deep processing of agricultural products. The color fixative used in the invention is composed of citric acid, ascorbic acid, L-cysteine, gallic acid and water, and the mass ratio of the citric acid to the ascorbic acid to the L-cysteine to the gallic acid to the water is (0.4-0.6): (0.4-0.6): (0.2-0.3): (0.6-1): 100. The preparation method comprises the following steps: peeling fresh flower-color potatoes, dicing, soaking in a color fixative for 40 minutes, pre-drying diced potatoes, freezing and thawing, drying with hot air, crushing and sieving to obtain raw whole flour; through the color protection treatment, enzymatic browning of the flower-color potatoes can be reduced, meanwhile, the color of the potatoes is reserved, and the stability of anthocyanin is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of deep processing of agricultural products, and in particular relates to a color protecting agent for colorful potatoes and a color protecting method for colorful potatoes. Background Art

[0002] Colorful potatoes rich in anthocyanins are loved by consumers for their rich nutritional value and diverse colors. Fresh colorful potatoes have a high moisture content, which is not conducive to transportation and storage, so it is particularly important to process them. The production of whole potato flour is an extremely effective way to fully utilize potato resources and convert them into value-added on a large scale.

[0003] During the production of whole potato flour, the cells are broken after peeling and cutting, which easily leads to the contact of polyphenol oxidase (PPO) in the cells with phenolic substrates to generate quinone substances. Quinone substances will combine with amino acid groups to generate black or brown substances, thus causing enzymatic browning. In addition, for colorful potatoes, because they are rich in anthocyanins, they have a variety of colors and excellent antioxidant properties. However, during the processing and subsequent storage of colorful potatoes, temperature, light and PPO have a great impact on the stability of anthocyanins, resulting in a reduction in the nutritional value of colorful potatoes.

[0004] At present, the raw materials for preparing raw whole potato flour are mainly common varieties, such as yellow potatoes, white or red sweet potatoes, etc. The main problem of this type of potato in the flour making process is enzymatic browning caused by polyphenol oxidase, so only the problem of polyphenol oxidase activity inhibition needs to be solved. However, for colorful potatoes rich in anthocyanins, anthocyanins themselves, as a soluble phenolic compound, are easily degraded to varying degrees due to the conditions of the potatoes themselves and external conditions, which greatly affects the nutrition and color of the whole flour prepared from colorful potatoes.

[0005] At present, the main methods for color protection of potatoes in the food field are divided into two categories, namely chemical inhibition and physical inhibition. Chemical inhibition is mainly based on the inhibitory effect of color protectants on polyphenol oxidase, thereby reducing the effect of enzymatic browning. At present, most of the color protectants used are mainly compounded with antioxidants such as citric acid, sulfite and ascorbic acid. Such color protectants are prone to chemical residues, which not only harm the environment, but also pose a greater threat to human health. In order to solve the problem of chemical residue hazards, patent CN 113519802 A discloses a color protection method for the preparation process of raw potato flour, which mainly solves the enzymatic browning problem caused by polyphenol oxidase by soaking in color protection liquid and treating with liquid nitrogen. However, this method is not suitable for color protection of colorful potatoes, mainly because the color protection method does not have a protective effect on anthocyanins and is difficult to improve the color change caused by the degradation of anthocyanins. Patent CN101642237A discloses a color preservative for yam slices. During the soaking process of yam, the mucus on the surface may retain more color preservatives to achieve a more stable color protection effect. For the cut surface of colored potatoes, the color preservative can only achieve the color protection effect by soaking. Therefore, higher requirements are placed on the color preservative, and the color preservative cannot solve the problem of reduced stability of anthocyanins in colored potatoes. Physical inhibition methods mainly use freeze-thaw, blanching and temperature regeneration inhibition methods to assist chemical methods in the processing process to make the color protection effect more significant. For example, patent CN104872583A discloses a process for preparing whole potato flour by freeze drying. Freeze drying can maintain the shape and color of the sample to a great extent, but for the preparation of whole flour, the cost of preparing whole flour by freeze drying is very expensive, which is not conducive to mass production. Summary of the invention

[0006] In view of the above problems, the present invention aims to provide a color preservative for colored potatoes and a color preservative method for colored potatoes, so as to solve the problems of enzymatic browning and reduced stability of anthocyanins in the processing of colored potato whole raw flour.

[0007] To achieve the above-mentioned purpose, the present invention first provides a color preservative for colorful potatoes, which consists of citric acid, ascorbic acid, L-cysteine, gallic acid and water, wherein the mass ratio of citric acid, ascorbic acid, L-cysteine, gallic acid and water is (0.4-0.6):(0.4-0.6):(0.2-0.3):(0.6-1):100.

[0008] In one embodiment of the present invention, the color protecting agent consists of citric acid, ascorbic acid, L-cysteine, gallic acid and water, wherein the mass ratio of citric acid, ascorbic acid, L-cysteine, gallic acid and water is 0.6:0.6:0.25:1:100.

[0009] In one embodiment of the present invention, the colorful potatoes include at least one of colorful sweet potatoes, potatoes, cassava, yam, and taro.

[0010] As a component of color preservatives, citric acid can, on the one hand, lower the pH value of the color preservative solution, making the color preservative solution as a whole in an acidic environment, creating an environment that is not suitable for the activity of polyphenol oxidase, thereby reducing the occurrence of enzymatic browning; on the other hand, although citric acid does not have antioxidant properties, it can synergize with other antioxidants to enhance the antioxidant effect and jointly protect the color in food.

[0011] Ascorbic acid plays a color protection role in food mainly through reducing pigments, inhibiting oxidases, chelating metal ions, scavenging free radicals and inhibiting Maillard reactions. It also has a synergistic effect with other color protection agents.

[0012] As an amino acid, L-cysteine ​​is used as a color preservative in the food industry. Its mechanism of action mainly includes: scavenging free radicals through its reducing sulfhydryl group (-SH) to inhibit oxidation reactions; inhibiting the activity of enzymes such as polyphenol oxidase to reduce enzymatic browning; forming complexes with metal ions to reduce the catalytic effect of metal ions on oxidation reactions; directly reacting with quinone substances in the oxidation process to prevent further oxidation of pigments; in some cases, L-cysteine ​​can also prevent the formation of pigments by reacting with pigment precursors. In addition, L-cysteine ​​has potential synergistic effects with other color preservatives such as citric acid and ascorbic acid, which can improve the overall color protection effect.

[0013] Gallic acid, as a co-pigment substance, stabilizes anthocyanins through various mechanisms. Its main mode of action is to covalently link to the chromophore of anthocyanin through weak hydrophobic bonds to form a more stable complex, thereby enhancing the color of anthocyanins. In addition, gallic acid can also work in different ways, including antioxidant effects, chelating metal ions, forming hydrogen bonds and π-π interactions, and regulating pH. These mechanisms can reduce the oxidation and degradation of anthocyanins and enhance their stability and color retention in different environments.

[0014] The present invention also provides a method for protecting the color of colorful potatoes, comprising the following steps:

[0015] (1) Pretreatment: Select intact, non-moldy and colorful potatoes, wash and peel them, and cut them into 3-5 mm cubes;

[0016] (2) Color protection: soak the diced potatoes in the above-mentioned color protection agent;

[0017] (3) Pre-drying: Spread the potato cubes soaked in the color preservative on a tray for pre-drying to remove residual moisture on the surface;

[0018] (4) Freeze-thaw: Freeze the pre-dried potato cubes, and then take them out and thaw them;

[0019] (5) Drying and powdering: The thawed potato cubes in step (4) are placed in a hot air dryer for drying, and then crushed to obtain colorful potato whole flour.

[0020] In one embodiment of the present invention, the colored potatoes include at least one of colored sweet potatoes, potatoes, cassava, yam, and taro.

[0021] In one embodiment of the present invention, in step (2), the volume of the color protecting agent used during soaking is 3 to 5 times the volume of the material, and the soaking time is 30 to 50 minutes.

[0022] In one embodiment of the present invention, in step (2), the color protection agent used is composed of citric acid, ascorbic acid, L-cysteine, gallic acid and water, calculated by mass percentage, wherein the mass ratio of citric acid, ascorbic acid, L-cysteine, gallic acid and water is (0.4-0.6):(0.4-0.6):(0.2-0.3):(0.6-1):100.

[0023] In one embodiment of the present invention, in step (3), the pre-drying temperature is 30-40° C., the time is 30-50 min, and the pre-drying method is hot air drying.

[0024] In one embodiment of the present invention, in step (4), the freezing temperature is -15 to -20°C, the freezing time is 12 to 18 hours, the ambient temperature during thawing is 25 to 30°C, and the thawing time is 30 to 60 minutes.

[0025] In one embodiment of the present invention, in step (5), the drying temperature is 50-55° C., and the drying time is 2-4 hours.

[0026] In one embodiment of the present invention, in step (5), the moisture content of the potato particles after drying is 5% to 8%, and the potato particles need to be sieved through an 80-mesh sieve after being crushed.

[0027] Beneficial effects:

[0028] (1) The present invention uses citric acid, ascorbic acid, L-cysteine ​​and gallic acid as raw materials to prepare a color protection agent, and soaks the colored potatoes for color protection treatment. Under the synergistic effect of citric acid, ascorbic acid, L-cysteine ​​and gallic acid, the color protection agent of the present invention has a good color protection effect, which can not only greatly reduce the activity of polyphenol oxidase, but also has a good protective effect on anthocyanins, making anthocyanins more stable and thus stabilizing the color, thereby achieving the purpose of double color protection.

[0029] (2) The color protection agent of the present invention is highly dependent on the concentrations of citric acid, ascorbic acid, L-cysteine ​​and gallic acid. An increase or decrease in the amount of any one of the components will result in a decrease in the color protection effect.

[0030] (3) The present invention also achieves the purpose of maintaining the integrity of the cell wall through freeze-thaw treatment, providing a physical barrier for intracellular substances, reducing contact with the external environment, and alleviating anthocyanin degradation to a certain extent.

[0031] (4) Through freeze-thaw treatment, low temperature can be used to condense the water in the cells into ice crystals. Then, during the melting process, the cell walls shrink, which reduces the binding force between cells and makes it easier to disperse into fine particles, thereby reducing the cell breakage rate in the subsequent powder making process.

[0032] (5) The color preservative used in the present invention is compounded with safer and more efficient compounds, which meets the health and safety requirements of the human body and fully utilizes the nutritional value of colorful potatoes. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The following are color pictures of purple potatoes and the whole cornstarch prepared in Example 1 and Comparative Examples 1 to 9, wherein (a) is purple potato, and (b) to (k) are the whole cornstarch prepared in Example 1 and Comparative Examples 1 to 9, respectively. DETAILED DESCRIPTION

[0034] Test Method

[0035] 1. Determination of polyphenol oxidase activity

[0036] Solution preparation:

[0037] 0.2mol / LpH6.0 sodium dihydrogen phosphate-disodium hydrogen phosphate buffer: weigh 29.33g sodium dihydrogen phosphate dihydrate and 4.30g disodium hydrogen phosphate dodecahydrate, dissolve them in distilled water, make up to 1L, and measure the pH value of the buffer with a pH meter. If there is a deviation, use a small amount of sodium hydroxide and hydrochloric acid solution to adjust to an accurate pH of 6.0.

[0038] 0.118 mol / L catechol solution: weigh 1.299 g of catechol, add distilled water to dissolve, and then dilute to 100 mL.

[0039] Experimental steps:

[0040] Accurately weigh 1.5 g (accurate to 0.001 g) of sample, put it into a 50 mL conical flask, mix it evenly with 10.0 mL of sodium dihydrogen phosphate-disodium hydrogen phosphate buffer (0.2 mol / L, pH 6.0), add 2.00 mL of catechol solution (0.118 mol / L), and oxidize it in a 37 ° C constant temperature shaker for 15 min. Quickly put it into 0 ° C ice water and let it stand for 3 min to terminate the reaction. The sample solution was introduced into a 50 mL centrifuge tube and centrifuged in a refrigerated centrifuge (4 ° C, 10000 r / min) for 10 min. Filter with qualitative filter paper, pour the filtrate into a 1 cm quartz colorimetric dish, and measure its absorbance at 410 nm with a spectrophotometer, and adjust it to zero with the blank solution.

[0041] The calculation formula of polyphenol oxidase activity is: X = A / (0.001×m×t);

[0042] Wherein, X is the polyphenol oxidase activity in the sample, in U; ​​A is absorbance; 0.001 is the activity unit conversion coefficient; m is the sample mass, in grams (g); t is the reaction time, in minutes (min).

[0043] 2. Chromaticity contrast

[0044] The colorimeter was used for testing, the Lab coordinate system was selected, and the color protection effects of different examples were evaluated based on the measured parameters.

[0045] 3. Thermal acceleration test

[0046] The samples were sealed and packaged in transparent containers to ensure the uniformity of the samples. The packaged samples were placed in an oven (temperature 50℃±2℃). The experimental time was set to 8 days. The samples were tested with a colorimeter every two days. The total color difference was calculated using the data obtained from the colorimeter, and a curve was drawn to evaluate the color stability and predict the color change trend at room temperature.

[0047] Preparation of blank samples:

[0048] Wash and peel fresh purple potatoes, and then cut them into 3-5 mm cubes. Soak the cubes in distilled water at a volume ratio of 1:5 at 30°C for 40 minutes, and then dry them with hot air. The temperature of the hot air drying machine is set at 55°C for 5 hours, and the moisture content is dried to 6%. After crushing, pass through an 80-mesh sieve to obtain raw whole flour.

[0049] Example 1

[0050] A color preservative for colorful potatoes, which consists of the following components: 0.6g of citric acid, 0.6g of ascorbic acid, 0.25g of L-cysteine, 1g of gallic acid and 100g of water.

[0051] A color protection method for colorful potatoes comprises the following steps:

[0052] Wash and peel fresh purple potatoes, and then cut them into 3-5mm cubes. Soak the cubes in a color potato color preservative at a volume ratio of 1:5 at 30°C for 40 minutes. After soaking, take out the cubes and spread them on a tray. Place the tray in a 30°C hot air blower for pre-drying for 30 minutes to reduce some moisture. Freeze the processed cubes at -20°C for 12 hours. Thaw the frozen cubes at 30°C for 30 minutes and then perform hot air drying. The hot air drying machine temperature is set at 55°C for 4 hours. Dry to a moisture content of 6%, crush and pass through an 80-mesh sieve to obtain raw whole flour.

[0053] Comparative Example 1

[0054] A color preservative for colorful potatoes, which consists of the following components: 0.2g of citric acid, 0.6g of ascorbic acid, 0.25g of L-cysteine, 1g of gallic acid and 100g of water.

[0055] A color protection method for colorful potatoes comprises the following steps:

[0056] Wash and peel fresh purple potatoes, and then cut them into 3-5mm cubes. Soak the cubes in a color-preserving agent for colorful potatoes at a solid-liquid ratio of 1:5 for 40 minutes at 30°C. After soaking, place them in a hot air blower at 30°C for pre-drying for 30 minutes to reduce some of the moisture. The processed cubes are frozen at -20°C for 12 hours. The frozen cubes are thawed at 30°C for 30 minutes and then hot-dried. The hot air drying machine is set at 55°C for 4 hours until the moisture content is 6%. After crushing, pass through an 80-mesh sieve to obtain raw whole flour.

[0057] Comparative Example 2

[0058] A color preservative for colorful potatoes, which consists of the following components: 0.6g of citric acid, 0.6g of ascorbic acid, 0.25g of L-cysteine, 0.5g of gallic acid and 100g of water.

[0059] A color protection method for colorful potatoes comprises the following steps:

[0060] Wash and peel fresh purple potatoes, and then cut them into 3-5mm cubes. Soak the cubes in a color-preserving agent for colorful potatoes at a solid-liquid ratio of 1:5 for 40 minutes at 30°C. After soaking, place them in a hot air blower at 30°C for pre-drying for 30 minutes to reduce some of the moisture. The processed cubes are frozen at -20°C for 12 hours. The frozen cubes are thawed at 30°C for 30 minutes and then hot-dried. The hot air drying machine is set at 55°C for 4 hours until the moisture content is 6%. After crushing, pass through an 80-mesh sieve to obtain raw whole flour.

[0061] Comparative Example 3

[0062] The difference between Comparative Example 3 and Example 1 is that the color protection method of colored potatoes is different.

[0063] A color protection method for colorful potatoes comprises the following steps:

[0064] Wash and peel fresh purple potatoes, and then cut them into 3-5mm cubes. Soak the cubes in a color potato color preservative at a solid-liquid ratio of 1:5 for 40 minutes at 30°C. After soaking, place them in a 30°C hot air blower for pre-drying for 30 minutes to reduce some moisture. The processed cubes are frozen at -10°C for 6 hours. The frozen cubes are thawed at 30°C for 30 minutes and then hot-dried. The hot air drying machine is set at 55°C for 4 hours until the moisture content is 6%. After crushing, pass through an 80-mesh sieve to obtain raw whole flour.

[0065] Comparative Example 4

[0066] A color preservative for colorful potatoes, which consists of the following components: 0.2g of citric acid, 0.15g of ascorbic acid, 0.1g of calcium chloride and 100g of water.

[0067] A color protection method for colorful potatoes comprises the following steps:

[0068] Wash and peel fresh purple potatoes, and then cut them into 3-5mm cubes. Soak the cubes in a color-preserving agent for colorful potatoes at a solid-liquid ratio of 1:5 for 40 minutes at 30°C. After soaking, place them in a hot air blower at 30°C for pre-drying for 30 minutes to reduce some of the moisture. The processed cubes are frozen at -20°C for 12 hours. The frozen cubes are thawed at 30°C for 30 minutes and then hot-dried. The hot air drying machine is set at 55°C for 4 hours until the moisture content is 6%. After crushing, pass through an 80-mesh sieve to obtain raw whole flour.

[0069] Comparative Example 5

[0070] A color preservative for colorful potatoes, which consists of the following components: 0.15g of citric acid, 1g of ascorbic acid, 0.1g of calcium chloride and 100g of water.

[0071] A color protection method for colorful potatoes comprises the following steps:

[0072] Wash and peel fresh purple potatoes, and then cut them into 3-5mm cubes. Soak the cubes in a color-preserving agent for colorful potatoes at a solid-liquid ratio of 1:5 for 40 minutes at 30°C. After soaking, place them in a hot air blower at 30°C for pre-drying for 30 minutes to reduce some of the moisture. The processed cubes are frozen at -20°C for 12 hours. The frozen cubes are thawed at 30°C for 30 minutes and then hot-dried. The hot air drying machine is set at 55°C for 4 hours until the moisture content is 6%. After crushing, pass through an 80-mesh sieve to obtain raw whole flour.

[0073] Comparative Example 6

[0074] A color preservative for colorful potatoes, which consists of the following components: 0.6g of citric acid, 0.6g of ascorbic acid, 0.25g of L-cysteine ​​and 100g of water.

[0075] A color protection method for colorful potatoes comprises the following steps:

[0076] Wash and peel fresh purple potatoes, and then cut them into 3-5mm cubes. Soak the cubes in a color potato color preservative according to the material-liquid ratio for 40 minutes at a temperature of 30°C. After soaking, place them in a 30°C hot air blower for pre-drying for 30 minutes to reduce some moisture. The processed cubes are frozen at -20°C for 12 hours. The frozen cubes are thawed at 30°C for 30 minutes and then hot-dried. The hot air drying machine temperature is set at 55°C and the drying time is 4 hours. Dry to a moisture content of 6%, crush and pass through an 80-mesh sieve to obtain raw whole flour.

[0077] Comparative Example 7

[0078] A color preservative for colorful potatoes consists of the following components: 0.6 g of citric acid, 0.6 g of ascorbic acid, 0.25 g of L-cysteine, 1 g of phytic acid and 100 g of water.

[0079] A color protection method for colorful potatoes comprises the following steps:

[0080] Wash and peel fresh purple potatoes, and then cut them into 3-5mm cubes. Soak the cubes in a color-preserving agent for colorful potatoes at a solid-liquid ratio of 1:5 for 40 minutes at 30°C. After soaking, place them in a hot air blower at 30°C for pre-drying for 30 minutes to reduce some of the moisture. The processed cubes are frozen at -20°C for 12 hours. The frozen cubes are thawed at 30°C for 30 minutes and then hot-dried. The hot air drying machine is set at 55°C for 4 hours until the moisture content is 6%. After crushing, pass through an 80-mesh sieve to obtain raw whole flour.

[0081] Comparative Example 8

[0082] A color preservative for colorful potatoes, which consists of the following components: 0.6g of citric acid, 0.6g of ascorbic acid, 0.25g of L-cysteine, 0.13g of ferulic acid and 100g of water.

[0083] A color protection method for colorful potatoes comprises the following steps:

[0084] Wash and peel fresh purple potatoes, and then cut them into 3-5mm cubes. Soak the cubes in a color-preserving agent for colorful potatoes at a solid-liquid ratio of 1:5 for 40 minutes at 30°C. After soaking, place them in a hot air blower at 30°C for pre-drying for 30 minutes to reduce some of the moisture. The processed cubes are frozen at -20°C for 12 hours. The frozen cubes are thawed at 30°C for 30 minutes and then hot-dried. The hot air drying machine is set at 55°C for 4 hours until the moisture content is 6%. After crushing, pass through an 80-mesh sieve to obtain raw whole flour.

[0085] Comparative Example 9

[0086] The difference between Comparative Example 9 and Example 1 is that the color protection method of colored potatoes is different.

[0087] A color protection method for colorful potatoes comprises the following steps:

[0088] Wash and peel fresh purple potatoes, and then cut them into 3-5mm cubes. Soak them at 30℃ for 40min at a material-liquid ratio of 1:5. After soaking, place them in a hot air dryer for hot air drying. The temperature of the hot air dryer is set at 55℃ for 5 hours. Dry to a moisture content of 6%, crush them and pass through an 80-mesh sieve to obtain raw whole flour.

[0089] Table 1 Polyphenol oxidase activity

[0090] Serial number name Polyphenol oxidase activity (U) 1 blank 206.19 2 Example 1 14.77 3 Comparative Example 1 51.20 4 Comparative Example 2 27.41 5 Comparative Example 3 45.54 6 Comparative Example 4 39.10 7 Comparative Example 5 32.43 8 Comparative Example 6 49.69 9 Comparative Example 7 45.90 10 Comparative Example 8 20.22 11 Comparative Example 9 59.70

[0091] As can be seen from the above table, the enzyme activity of the blank sample is significantly higher than that of the remaining several examples. Compared with the blank sample, the enzyme activity of the embodiments and the comparative examples is significantly reduced, and the enzyme activity of the embodiments 1 and the comparative example 2 is the most significantly reduced. It is shown that the color retaining agent prepared by mixing citric acid, ascorbic acid and L-cysteine ​​in a certain ratio helps to inhibit the enzymatic browning caused by polyphenol oxidase, and the addition of gallic acid can further inhibit the activity of polyphenol oxidase on the one hand, and further inhibit the occurrence of browning in colorful potatoes. On the other hand, the inhibition of polyphenol oxidase activity by gallic acid depends on the concentration of gallic acid. Only when the concentration of gallic acid reaches a certain height, the activity of polyphenol oxidase will significantly decrease.

[0092] Comparative Example 1 reduces the amount of citric acid on the basis of Example 1. From the results, the reduction in the amount of citric acid will directly lead to a significant change in the activity of polyphenol oxidase. This may be because the reduction in the citric acid content causes a significant change in the pH of the color protection solution. The pH of Comparative Example 1 is more conducive to the increase in polyphenol oxidase activity. On the other hand, the reduction in the citric acid content will also lead to a decrease in its synergistic effect with other substances with antioxidant activity, further reducing the inhibitory effect on enzymatic browning of colorful potatoes.

[0093] Comparative Examples 4 and 5 use calcium chloride instead of L-cysteine, omit gallic acid, and adjust the proportion of each component. Although the color protection agent finally obtained also has a certain color protection effect, the color protection effect is poor.

[0094] Comparative Example 7 uses phytic acid to replace gallic acid, and the results show that the color protection effect of the color protection agent is poor. This may be because although phytic acid has a certain effect of inhibiting the activity of polyphenol oxidase and helps to adjust the pH of the color protection agent, these inhibitory effects on the activity of polyphenol oxidase are limited, and phytic acid does not have the effect of protecting the stability of anthocyanins, and its addition cannot further reduce the decrease in polyphenol oxidase activity caused by the instability of anthocyanins. Comparative Example 8 uses ferulic acid to replace the gallic acid of the present invention. Although ferulic acid has a good effect of protecting the stability of anthocyanins, experiments have found that the solubility of ferulic acid is low. When the addition amount of ferulic acid is 0.13g, the system has already appeared saturated. Therefore, in the color protection agent system of the present invention, the addition amount of ferulic acid is at most 0.13g, resulting in a poor color protection effect of the system.

[0095] The freeze-thaw process of the present invention also has a great influence on the color protection effect of colored potatoes. It can be seen from Example 1 and Comparative Example 9 that if the freeze-thaw process is not combined, the activity of polyphenol oxidase is very large. It can be seen from Comparative Example 3 that freeze-thaw helps to reduce the activity of polyphenol oxidase, but the low freezing temperature and short freezing time are not enough to significantly reduce the activity of polyphenol oxidase.

[0096] Table 2 Chromaticity value of raw whole flour

[0097] name L a b blank 69.37 7.25 -2.03 Example 1 61.18 15.76 -12.89 Comparative Example 1 65.26 10.96 -6.91 Comparative Example 2 70.02 8.12 -0.24 Comparative Example 3 62.82 13.66 -8.62 Comparative Example 4 74.35 1.50 10.90 Comparative Example 5 73.06 1.82 11.17 Comparative Example 6 77.09 1.44 10.90 Comparative Example 7 67.74 14.20 -5.98 Comparative Example 8 73.69 7.07 4.86 Comparative Example 9 69.64 7.71 -3.10

[0098] According to the data in the table, it can be seen that the best color protection effect is the raw whole powder prepared in Example 1. From the perspective of color difference:

[0099] The meanings of various parameters are as follows:

[0100] L: Brightness (ranging from 0 to 100, with 0 being black and 100 being white).

[0101] a: The color axis from green (-a) to red (+a).

[0102] b: The color axis from blue (-b) to yellow (+b).

[0103] As can be seen from Table 2, Example 1 has the lowest brightness, and the values ​​of the red and blue axes are more balanced. Compared with other examples, the color is closer to true purple, and as the values ​​approach the ends of the color axis, the color becomes more obvious. In the comparative examples with different formulations, Comparative Examples 1 and Comparative Examples 3 have a certain presentation of purple, but the distribution of their values ​​on the red and blue axes is quite different, and the absolute value of the a value of several samples is greater than the absolute value of the b value, which will result in the color being purple but slightly biased towards the red area, such as Figure 1 As shown. Although the b values ​​of Comparative Examples 2, 7 and 9 are negative, they are close to 0. When combined with a larger a value, they will present a light red color. Although there is some protection for anthocyanins, the color protection effect is still insufficient. In Comparative Examples 4, 5, 6 and 8, although the a value is positive, it is close to 0, and the b value is a larger positive value, which results in the color of the raw whole powder being yellow, proving that several methods lack protection and stabilization functions.

[0104] Table 3 Changes in color of whole raw pink (ΔE)

[0105]

[0106] The serial numbers in Table 3 represent the serial numbers of the 1st to 4th sampling tests, and ΔE represents the color difference between the current sampling and the previous sampling. The larger the value, the greater the color change. The color change data of the whole raw powder were obtained by performing accelerated experiments on the whole raw powder of Example 1 and Comparative Examples 1 to 9. As can be seen from Table 2, the samples with better color protection effects on the whole powder are Example 1, Comparative Example 1 and Comparative Example 3, so the color changes of these samples are mainly compared in the accelerated experiment. As can be seen from Table 3, compared with the chromaticity when the whole raw powder is prepared, the color change of the whole powder in Comparative Examples 1 and Comparative Examples 3 is very significant at the first sampling, and the stability is not good.

[0107] In summary, the present invention utilizes citric acid, ascorbic acid, L-cysteine ​​and gallic acid prepared color preservatives to soak the material for color protection treatment, and combined with the freeze-thaw process, the enzymatic browning can be effectively controlled, and the harm of color preservative residues is reduced. In addition, the method has a positive effect on the stability of anthocyanins. By adding gallic acid, on the basis of stabilizing the original color, it can also achieve a certain color enhancement effect.

[0108] The embodiments provided above are not intended to limit the scope of the present invention, and the steps described are not intended to limit the execution order thereof. Those skilled in the art may make obvious improvements to the present invention in combination with existing common knowledge, which also fall within the scope of protection defined by the claims of the present invention.

Claims

1. A color retaining agent for colorful potatoes, characterized in that: The color protecting agent is composed of citric acid, ascorbic acid, L-cysteine, gallic acid and water, wherein the mass ratio of citric acid, ascorbic acid, L-cysteine, gallic acid and water is (0.4-0.6):(0.4-0.6):(0.2-0.3):(0.6-1):

100.

2. The color protecting agent according to claim 1, characterized in that The color protecting agent consists of citric acid, ascorbic acid, L-cysteine, gallic acid and water, wherein the mass ratio of citric acid, ascorbic acid, L-cysteine, gallic acid and water is 0.6:0.6:0.25:1:

100.

3. The color protecting agent according to claim 1, characterized in that The colorful potatoes include at least one of colorful sweet potatoes, potatoes, cassava, yam and taro.

4. A method for protecting the color of colorful potatoes, characterized in that: The following steps are involved: (1) Pretreatment: Select intact, non-moldy and colorful potatoes, wash and peel them, and cut them into 3-5 mm cubes; (2) Color protection: soak the diced potatoes in the above-mentioned color protection agent; (3) Pre-drying: Spread the potato cubes soaked in the color preservative on a tray for pre-drying to remove residual moisture on the surface; (4) Freeze-thaw: Freeze the pre-dried potato cubes, and then take them out and thaw them; (5) Drying and powdering: The thawed potato cubes in step (4) are placed in a hot air dryer for drying, and then crushed to obtain colorful potato whole flour.

5. The color protection method according to claim 4, characterized in that: In step (2), the volume of the color protecting agent used during soaking is 3 to 5 times the volume of the material, and the soaking time is 30 to 50 minutes.

6. The color protection method according to claim 4, wherein in step (2), the color protection agent used is composed of citric acid, ascorbic acid, L-cysteine, gallic acid and water, by mass percentage, wherein: The mass ratio of citric acid, ascorbic acid, L-cysteine, gallic acid and water is (0.4-0.6):(0.4-0.6):(0.2-0.3):(0.6-1):

100.

7. The color protection method according to claim 4, wherein in step (3), the pre-drying temperature is 30-40°C, the time is 30-50 minutes, and the pre-drying method is hot air drying.

8. The color protection method according to claim 4, wherein in step (4), the freezing temperature is -15 to -20°C, the freezing time is 12 to 18 hours, the ambient temperature during thawing is 25 to 30°C, and the thawing time is 30 to 60 minutes.

9. The color protection method according to claim 4, wherein in step (5), the drying temperature is 50-55°C and the drying time is 2-4 hours.

10. The color protection method according to claim 4, wherein in step (5), the moisture content of the potato particles after drying is 5% to 8%, and the potato particles need to be sieved through an 80-mesh sieve after being crushed.

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