Freeze-drying treatment method for fresh rose flowers

Abstract

The invention discloses a treatment method for freeze-drying fresh rose flowers, and belongs to the technical field of color protection of the rose flowers, the method comprises the following steps: (1) pretreatment: soaking the fresh rose flowers in a color fixative for color protection treatment; (2) pre-freezing: pre-freezing the roses subjected to color protection treatment; (3) vacuum hot air drying: performing vacuum hot air drying on the pre-frozen roses; and (4) baking: baking the roses subjected to vacuum hot air drying for aroma enhancement, and taking out the roses after baking for aroma enhancement to obtain the freeze-dried fresh roses. The prepared freeze-dried fresh rose flowers can retain the shape and color of the fresh rose flowers and are not prone to browning after being stored for a long time.

Description

TECHNICAL FIELD

[0001] The present application relates to the freeze-drying technology field of rose flowers, and in particular to a processing method for freeze-drying fresh rose flowers. BACKGROUND

[0002] Rose tea is a scented tea made from rose flowers as the main raw material. It not only has a unique aroma and taste, but also contains rich nutrients including vitamins, anthocyanins, and flavonoids. These nutrients have many benefits for human health, such as beautifying, antioxidant, and promoting digestion. Currently, rose tea is mainly consumed by brewing with dried rose flowers.

[0003] In existing rose flower drying technologies, microwave drying and freeze vacuum drying are commonly used. However, these traditional drying methods can cause significant changes in the color of rose flowers, shrinkage of the shape, and astringency, resulting in poor taste. To improve the product quality of freeze-dried rose flowers, some new technologies have emerged, such as freeze vacuum-hot air combined technology, which integrates freeze vacuum drying with hot air drying. Compared to previous technologies, this method can better maintain the shape before drying, preserve the original flavor and nutrients of roses, and improve the internal quality. However, the color change problem of rose flowers still needs to be addressed. This is because rose flowers contain phenolic substances and polyphenol oxidase. During the drying process, the cell structure is destroyed, and polyphenol oxidase is activated, catalyzing the oxidation of phenolic substances into quinones. Quinones further polymerize to form brown polymers, causing the color of rose flowers to darken and brown.

[0004] Therefore, to address the above problems, the present application provides a unique freeze-drying processing method for fresh rose flowers, which improves the freeze vacuum-hot air combined technology to solve the problems of browning and shrinkage after drying rose flowers. SUMMARY

[0005] In view of the above, the purpose of the present application is to provide a processing method for freeze-drying fresh rose flowers to solve the problems of color change and shape shrinkage of fresh rose flowers.

[0006] The present application solves the above technical problems through the following technical means:

[0007] (1) Pretreatment: Soak the fresh rose flowers in a color protection agent for color protection treatment;

[0008] (2) Pre-freezing: Spray vitamin C solution on the color-protected fresh rose flowers after pre-freezing;

[0009] (3) Vacuum hot air drying: Vacuum hot air dry the pre-frozen fresh rose flowers;

[0010] (4) baking: baking the vacuum hot air dried rose flower to extract fragrance, and taking out the rose flower after the baking to obtain the rose flower freeze-dried flower.

[0011] Further, the soaking time in the step (1) is 20 min.

[0012] Further, the pre-freezing in the step (2) is specifically operated as follows: pre-freezing for 1 h at a temperature of-15 to-10 DEG C, pre-freezing for 40 min at a temperature of-25 to-20 DEG C, and pre-freezing for 20 min at a temperature of-35 to-30 DEG C, and spraying a vitamin C solution with a concentration of 1 wt% after the pre-freezing.

[0013] Further, the vacuum hot air drying in the step (3) is specifically operated as follows: opening the vacuum pump switch, controlling the vacuum degree to be 0.09 to 0.1 Mpa, drying for 2 h at 30 to 35 DEG C, drying for 3 h at 38 to 40 DEG C, and drying for 5 h at 42 to 45 DEG C.

[0014] Further, the moisture of the rose flower after the vacuum hot air drying in the step (3) is 15% to 18%.

[0015] Further, the baking in the step (4) is specifically operated as follows: baking the vacuum hot air dried rose flower by using a baking machine at 95 to 100 DEG C for 10 to 15 min.

[0016] Further, the moisture of the rose flower freeze-dried flower after the baking in the step (4) is less than or equal to 7%.

[0017] The pre-freezing can form ice crystal skeleton in the rose flower, which is beneficial to subsequent sublimation into gaseous state, so that the appearance of the rose flower is less affected, and the shape of the rose flower freeze-dried flower can be protected to the greatest extent, the solute damage zone can be quickly crossed, and more nutrient components can be reserved.

[0018] Further, the color protection agent in the step (1) comprises the following raw materials: glutathione, polyethylene glycol, trehalose, arabic gum, and sodium chloride.

[0019] Further, the ratio of each raw material of the color protection agent is as follows:

[0020] The weight ratio of the glutathione, polyethylene glycol, trehalose, arabic gum, and sodium chloride is 6:(1.2-1.4):(1.2-1.5):(0.5-0.8):0.05.

[0021] Further, the color protection agent preparation method is as follows:

[0022] Polyethylene glycol is dissolved in a PBS solution containing 10wt% ethanol to prepare a polyethylene glycol solution with a concentration of 2mg / ml, then glutathione is added, the pH is adjusted to 6.8-7, and the reaction is stirred at room temperature for 2-3h, then centrifugal filtration and drying are performed to obtain a glutathione mixed powder;

[0023] Trehalose is added to water to prepare a 50wt% trehalose solution, then sodium chloride and arabic gum are added and uniformly mixed, and then the glutathione mixed powder is added and uniformly stirred again to obtain the color protection agent.

[0024] Further, the color protection treatment of step (1) needs to be diluted by mixing the color protection agent with water at a weight ratio of 1:2.

[0025] The color and luster of rose fresh flowers are prone to change during the freeze-drying process, which is only because the polyphenols contained in the rose fresh flowers cause browning of the rose flowers under the action of polyphenol oxidase. Therefore, the color protection effect of freeze-drying of rose fresh flowers is achieved by inhibiting the enzyme with glutathione.

[0026] Spraying vitamin C after step-by-step freeze-drying can prevent discoloration of rose petals and oxidation of glutathione, but its shelf life is short and it is prone to inactivation and degradation in the later stage of hot air drying, so glutathione is further used to synergistically protect the color. Glutathione is prone to oxidation to form oxidized glutathione at high temperatures, thereby losing the ability to inhibit polyphenol oxidase. In the present application, the temperature during drying and baking of rose flowers is high, which can inactivate glutathione, thereby reducing the effect of the color protection agent. Therefore, the present application uses polyethylene glycol and glutathione to form a complex, improves the heat resistance and stability of glutathione, prevents the decomposition of glutathione during drying or baking, and uses trehalose and arabic gum to form a gel to protect the glutathione-polyethylene glycol mixture. The gel forms a glassy barrier to isolate oxygen during high-temperature processes, further preventing oxidation of glutathione and contact of rose petals with oxygen, so that glutathione remains active during baking, while preventing discoloration of rose flowers. Rose petals have a certain hydrophobic effect and trehalose is prone to crystallization at low temperatures during freeze-drying, so adding arabic gum can enhance the viscosity and stability of the trehalose solution, inhibit crystallization and make it more evenly distributed on the rose petals.

[0027] Beneficial effects:

[0028] The improved freezing-vacuum and hot air combined technology is adopted to treat rose fresh flowers, and a color protection agent is used to treat the flowers, and the inhibitory effect of glutathione on polyphenol oxidase is used to prevent the browning of rose flowers, so that the rose fresh flowers can be freeze-dried without color change and shape shrinkage, and the color and shape of the product can be kept unchanged for a long time. Meanwhile, the freeze-dried tea soup of the rose fresh flowers treated by the method has clear color and mellow taste. The color protection agent added is prepared from non-toxic and harmless products, and the glutathione raw material is a good health product with the functions of improving human immunity, protecting liver and resisting aging. Therefore, the rose fresh flower freeze-dried product treated by the method has higher quality and is more popular among the public. DETAILED DESCRIPTION

[0029] The application will be described in detail below in combination with specific examples.

[0030] Example 1

[0031] In this example, the color protection agent is prepared first, and the specific preparation process is as follows:

[0032] 1.2g of polyethylene glycol (PEG400) is dissolved in a PBS (pH=7.4) solution containing 10wt% ethanol to prepare a polyethylene glycol solution with a concentration of 2mg / ml, then 6g of glutathione is added, the pH is adjusted to 7, and the reaction is stirred at room temperature for 2h, followed by centrifugal filtration and drying to obtain a glutathione mixed powder;

[0033] After 1.2g of trehalose is dissolved in water to prepare a 50wt% trehalose solution, 0.05g of sodium chloride and 0.5g of gum arabic are added and uniformly mixed, and then the glutathione mixed powder is added, and the mixture is stirred again to obtain the color protection agent. The color protection agent is mixed with water in a weight ratio of 1:2 and then diluted for use.

[0034] The steps of the rose fresh flower freeze-drying treatment method are as follows:

[0035] (1) Pretreatment: the rose fresh flowers are placed in the diluted color protection agent for color protection treatment, the rose fresh flowers are fully contacted with the diluted color protection agent, that is, the diluted color protection agent is just enough to cover the rose fresh flowers, and the rose fresh flowers are soaked at room temperature for 20min, then taken out and naturally dried for use;

[0036] (2) Pre-freezing: the rose fresh flowers treated by color protection and dried are placed in a pre-freezing box, pre-frozen at-15℃ for 1h, then cooled to-25℃ for secondary pre-freezing for 40min, and finally cooled to-35℃ for tertiary freezing for 20min, then taken out, sprayed with 1wt% vitamin C solution, and uniformly sprayed for the next step.

[0037] (3) Vacuum hot air drying: the pre-frozen rose flowers were put into the vacuum machine, the vacuum pump switch was turned on, the vacuum degree was controlled at 0.09 Mpa, first dried at 30℃ for 2h, then the temperature was raised to 38℃, dried for 3h, finally the temperature was raised to 42℃, dried for 5h, until the moisture of the rose flowers was reduced to about 15%, the machine was stopped and the rose flowers were taken out;

[0038] (4) Baking: the rose flowers dried by vacuum hot air were baked to enhance the fragrance, the baking machine was set at 95℃, the rose flowers were baked for 10min, until the moisture of the rose flowers was reduced to about 6%, the rose flowers were taken out, and the rose flower freeze-dried flowers were obtained.

[0039] Example 2:

[0040] In this example, the color protection agent was prepared first, and the specific preparation process was as follows:

[0041] 1.3g polyethylene glycol (PEG400) was dissolved in a PBS (pH = 7.4) solution containing 10wt% ethanol to prepare a polyethylene glycol solution with a concentration of 2mg / ml, then 6g glutathione was added, the pH was adjusted to 6.8, and the mixture was stirred at room temperature for 2h, then centrifuged and filtered, and dried to obtain a glutathione mixed powder;

[0042] 1.3g trehalose was dissolved in water to prepare a 50wt% trehalose solution, then 0.05g sodium chloride and 0.6g gum arabic were added and mixed uniformly, then the glutathione mixed powder was added, and the mixture was stirred again to obtain the color protection agent. The color protection agent was mixed with water at a weight ratio of 1:2 and then diluted for use.

[0043] The steps of the rose flower freeze-drying method are as follows:

[0044] (1) Pretreatment: the rose flowers were put into the diluted color protection agent for color protection treatment, the rose flowers were fully contacted with the color protection agent, i.e. the diluted color protection agent was just enough to cover the rose flowers, and the rose flowers were soaked at room temperature for 20min, then taken out and naturally dried for use;

[0045] (2) Pre-freezing: the rose flowers dried after color protection treatment were put into a pre-freezing box, first pre-frozen at -12℃ for 1h, then pre-frozen at -22℃ for 40min, and finally pre-frozen at -32℃ for 20min. After the third freezing for 20min, the rose flowers were taken out, sprayed with a 1wt% vitamin C solution, and then uniformly sprayed for the next step.

[0046] (3) Vacuum hot air drying: the pre-frozen rose flowers were put into the vacuum machine, the vacuum pump switch was turned on, the vacuum degree was controlled at 0.09 Mpa, first dried at 32℃ for 2h, then the temperature was raised to 39℃, dried for 3h, finally the temperature was raised to 43℃, dried for 5h, until the moisture of the rose flowers was reduced to about 16%, the machine was stopped and the rose flowers were taken out;

[0047] (4) Baking: the vacuum hot air dried rose flower was baked to enhance the fragrance, the baking machine was set at 98℃ and baked for 10 min, until the moisture of the freeze-dried rose flower was reduced to about 6%, and then the freeze-dried rose flower was taken out, to obtain the freeze-dried rose flower.

[0048] Example 3:

[0049] In this example, the color protection agent was first prepared, and the specific preparation process was as follows:

[0050] 1.4 g of polyethylene glycol (PEG400) was dissolved in a PBS (pH = 7.4) solution containing 10 wt% ethanol to prepare a polyethylene glycol solution with a concentration of 2 mg / ml, then 6 g of glutathione was added, the pH was adjusted to 7, and the reaction was stirred at room temperature for 2 h, then centrifugal filtration was performed, and after drying, a glutathione mixed powder was obtained;

[0051] 1.5 g of trehalose was dissolved in water to prepare a 50 wt% trehalose solution, then 0.05 g of sodium chloride and 0.8 g of gum arabic were added and mixed uniformly, and then the glutathione mixed powder was added, and after stirring uniformly again, the color protection agent was obtained, which was mixed with water in a weight ratio of 1:2 and then diluted for use.

[0052] The freeze-drying process of the rose flower was as follows:

[0053] (1) Pretreatment: the rose flower was placed in the diluted color protection agent for color protection treatment, the rose flower was fully contacted with the diluted color protection agent, that is, the diluted color protection agent was just enough to cover the rose flower, and then the rose flower was soaked at room temperature for 20 min, and then taken out and naturally dried for use;

[0054] (2) Pre-freezing: the rose flower after color protection treatment and drying was placed in a pre-freezing box, pre-frozen at -10℃ for 1 h, then cooled to -20℃ for secondary pre-freezing, the secondary pre-freezing time was 40 min, finally cooled to -30℃ for third pre-freezing, the third pre-freezing time was 20 min, then sprayed with a 1 wt% vitamin C solution, and then uniformly sprayed for the next step;

[0055] (3) Vacuum hot air drying: the pre-frozen rose flower was placed in a vacuum machine, the vacuum pump switch was turned on, and the vacuum degree was controlled at 0.09 Mpa. First dried at 35℃ for 2 h, then increased to 40℃ for 3 h, and finally increased to 45℃ for 5 h, until the moisture of the rose flower was reduced to about 17%, and then the machine was stopped and the rose flower was taken out;

[0056] (4) Baking: the vacuum hot air dried rose flower was baked to enhance the fragrance, the baking machine was set at 100℃ and baked for 10 min, until the moisture of the freeze-dried rose flower was reduced to about 6%, and then the freeze-dried rose flower was taken out, to obtain the freeze-dried rose flower.

[0057] Comparative Example 1:

[0058] The comparative example is compared with Example 1, and the only difference from Example 1 is that no glutathione is added in the process of preparing the color protection agent, and the specific preparation process is as follows:

[0059] 1.2 g of polyethylene glycol (PEG400) is dissolved in water to prepare a polyethylene glycol solution with a concentration of 2 mg / ml;

[0060] After 1.2 g of trehalose is dissolved in water to prepare a 50 wt% trehalose solution, 0.05 g of sodium chloride and 0.5 g of gum arabic are uniformly mixed, and then the polyethylene glycol solution is added. After stirring uniformly again, the color protection agent is obtained. The color protection agent is mixed with water in a weight ratio of 1:2 and then diluted for use.

[0061] The freeze-drying treatment method steps of the rose fresh flowers are the same as those of Example 1.

[0062] Comparative Example 2:

[0063] The comparative example is compared with Example 1, and the only difference from Example 1 is that no polyethylene glycol is added in the process of preparing the color protection agent, and the specific preparation process is as follows:

[0064] After 1.2 g of trehalose is dissolved in water to prepare a 50 wt% trehalose solution, 0.05 g of sodium chloride and 0.5 g of gum arabic are uniformly mixed, and then 6 g of glutathione is added. After stirring uniformly again, the color protection agent is obtained. The color protection agent is mixed with water in a weight ratio of 1:2 and then diluted for use.

[0065] The freeze-drying treatment method steps of the rose fresh flowers are the same as those of Example 1.

[0066] Comparative Example 3:

[0067] The comparative example is compared with Example 1, and the only difference from Example 1 is that no trehalose is added in the process of preparing the color protection agent, and the specific preparation process is as follows:

[0068] 1.2 g of polyethylene glycol (PEG400) is dissolved in a PBS (pH = 7.4) solution containing 10 wt% ethanol to prepare a polyethylene glycol solution with a concentration of 2 mg / ml, and then 6 g of glutathione is added. The pH is adjusted to 7, and the reaction is stirred at room temperature for 2 h, followed by centrifugal filtration and drying to obtain a glutathione mixed powder;

[0069] 0.05 g of sodium chloride and 0.5 g of gum arabic are uniformly mixed to prepare a 50 wt% mixed solution, and then the glutathione mixed powder is added. After stirring uniformly again, the color protection agent is obtained. The color protection agent is mixed with water in a weight ratio of 1:2 and then diluted for use.

[0070] The freeze-drying treatment method steps of the rose fresh flowers are the same as those of Example 1.

[0071] Comparative Example 4:

[0072] This comparative example is contrasted with Example 1, and the only difference from Example 1 is that no raw material sodium chloride is added in the process of preparing the color protection agent, and the specific preparation process is as follows:

[0073] 1.2 g of polyethylene glycol (PEG400) is dissolved in a PBS (pH = 7.4) solution containing 10 wt% ethanol to prepare a polyethylene glycol solution with a concentration of 2 mg / ml, then 6 g of glutathione is added, the pH is adjusted to 7, and the reaction is stirred at room temperature for 2 h, then centrifugal filtration is performed, and after drying, a glutathione mixed powder is obtained;

[0074] 1.2 g of trehalose is dissolved in water to prepare a 50 wt% trehalose solution, then 0.05 g of sodium chloride is added and mixed uniformly, then the glutathione mixed powder is added, and after stirring uniformly again, a color protection agent is obtained. The color protection agent is mixed with water in a weight ratio of 1:2 and then diluted for use.

[0075] The freeze-drying treatment method steps of the fresh rose flowers are the same as those of Example 1.

[0076] Comparative Example 5:

[0077] This comparative example is contrasted with Example 1, and the only difference from Example 1 is that no raw material sodium chloride is added in the process of preparing the color protection agent, and the specific preparation process is as follows:

[0078] 1.2 g of polyethylene glycol (PEG400) is dissolved in a PBS (pH = 7.4) solution containing 10 wt% ethanol to prepare a polyethylene glycol solution with a concentration of 2 mg / ml, then 6 g of glutathione is added, the pH is adjusted to 7, and the reaction is stirred at room temperature for 2 h, then centrifugal filtration is performed, and after drying, a glutathione mixed powder is obtained;

[0079] 1.2 g of trehalose is dissolved in water to prepare a 50 wt% trehalose solution, then 0.5 g of gum arabic is added and mixed uniformly, then the glutathione mixed powder is added, and after stirring uniformly again, a color protection agent is obtained. The color protection agent is mixed with water in a weight ratio of 1:2 and then diluted for use.

[0080] The freeze-drying treatment method steps of the fresh rose flowers are the same as those of Example 1.

[0081] Comparative Example 6:

[0082] This comparative example is contrasted with Example 1, and the only difference from Example 1 is that no color protection agent is added in the pretreatment step, and water is directly used for soaking, and the specific steps are as follows:

[0083] (1) Pretreatment: Put the fresh rose flowers into clean water for color protection treatment. The fresh rose flowers are fully contacted with the clean water, that is, the clean water covers the fresh rose flowers. Soak for 20 minutes at room temperature, take out, and naturally dry for later use;

[0084] (2) Pre-freezing: Put the dried fresh rose flowers after color protection treatment into a pre-freezing box. First, pre-freeze at -15°C for 1 hour, then reduce the temperature to -25°C for secondary pre-freezing for 40 minutes, and finally reduce the temperature to -35°C for tertiary freezing for 20 minutes. Then spray 1 wt% vitamin C solution evenly, and proceed to the next step.

[0085] (3) Vacuum hot air drying: Put the pre-frozen rose flowers into a vacuum machine. Turn on the vacuum pump switch and control the vacuum degree at 0.09 Mpa. First, dry at 30°C for 2 hours, then increase the temperature to 38°C and dry for 3 hours, and finally increase the temperature to 42°C and dry for 5 hours, until the moisture content of the rose flowers is about 15%, and then stop and take out.

[0086] (4) Baking: Bake the dried rose flowers to enhance the aroma. Bake in a baking machine at 95°C for 10 minutes until the moisture content of the freeze-dried rose flowers is about 6%, and then take out to obtain freeze-dried rose flowers.

[0087] Comparative Example 7:

[0088] This comparative example is compared with Example 1, and the only difference from Example 1 is that the pretreatment step directly uses a vitamin C aqueous solution for soaking. The specific steps are as follows:

[0089] (1) Pretreatment: Put the fresh rose flowers into 1 wt% vitamin C solution for color protection treatment. The fresh rose flowers are fully contacted with the vitamin C solution, that is, the vitamin C solution covers the fresh rose flowers. Soak for 20 minutes at room temperature, take out, and naturally dry for later use;

[0090] (2) Pre-freezing: Put the dried fresh rose flowers after color protection treatment into a pre-freezing box. First, pre-freeze at -15°C for 1 hour, then reduce the temperature to -25°C for secondary pre-freezing for 40 minutes, and finally reduce the temperature to -35°C for tertiary freezing for 20 minutes. Then proceed to the next step.

[0091] (3) Vacuum hot air drying: Put the pre-frozen rose flowers into a vacuum machine. Turn on the vacuum pump switch and control the vacuum degree at 0.09 Mpa. First, dry at 30°C for 2 hours, then increase the temperature to 38°C and dry for 3 hours, and finally increase the temperature to 42°C and dry for 5 hours, until the moisture content of the rose flowers is about 15%, and then stop and take out.

[0092] (4) Baking: the vacuum hot air dried rose flowers were baked to enhance the fragrance, the baking machine was set at 95℃ and baked for 10 min, until the moisture of the freeze-dried rose flowers was reduced to 6%, and then the rose flowers were taken out, to obtain freeze-dried rose flowers.

[0093] Comparative Example 8:

[0094] This comparative example is compared with Example 1, and the only difference from Example 1 is that the multi-step pre-freezing is not used in the pre-freezing step, and the one-step pre-freezing is directly used, and the same color protection agent as that of Example 1 is used.

[0095] (1) Pretreatment: the rose flowers were placed in the color protection agent prepared in Example 1 for color protection treatment, the rose flowers were fully contacted with the color protection agent, that is, the diluted color protection agent was just enough to cover the rose flowers, and then the rose flowers were soaked at room temperature for 20 min, and then taken out and naturally dried for later use;

[0096] (2) Pre-freezing: the rose flowers treated by color protection were directly pre-frozen in a pre-freezing box. After pre-freezing at -35℃ for 1 h, the rose flowers were taken out, sprayed with a vitamin C solution with a concentration of 1 wt%, and then uniformly sprayed, and then the next step was performed;

[0097] (3) Vacuum hot air drying: the pre-frozen rose flowers were placed in a vacuum machine, the vacuum pump switch was turned on, and the vacuum degree was controlled at 0.09 Mpa. After drying at 30℃ for 2 h, the temperature was increased to 38℃, and then dried for 3 h. Finally, the temperature was increased to 42℃, and then dried for 5 h, until the moisture of the rose flowers was reduced to about 15%, and then the machine was stopped and the rose flowers were taken out;

[0098] (4) Baking: the vacuum hot air dried rose flowers were baked to enhance the fragrance, the baking machine was set at 95℃ and baked for 10 min, until the moisture of the freeze-dried rose flowers was reduced to about 6%, and then the rose flowers were taken out, to obtain freeze-dried rose flowers.

[0099] Comparative Example 9:

[0100] This comparative example is compared with the freeze-drying process prepared in Example 1, and the only difference from Example 1 is that the multi-step drying is not used in the vacuum hot air drying step, and the one-step drying is directly used, and the same color protection agent as that of Example 1 is used.

[0101] (1) Pretreatment: the rose flowers were placed in the color protection agent prepared in Example 1 for color protection treatment, the rose flowers were fully contacted with the color protection agent, that is, the diluted color protection agent was just enough to cover the rose flowers, and then the rose flowers were soaked at room temperature for 20 min, and then taken out and naturally dried for later use;

[0102] (2) Pre-freezing: the dried rose flowers after color protection treatment were put into a pre-freezing box, pre-frozen at -15°C for 1 h, then cooled to -25°C for secondary pre-freezing for 40 min, and finally cooled to -35°C for tertiary freezing for 20 min, then taken out, sprayed with 1 wt% vitamin C solution, and evenly sprayed for the next step;

[0103] (3) Vacuum hot air drying: the pre-frozen rose flowers were put into a vacuum machine, the vacuum pump switch was turned on, the vacuum degree was controlled at 0.09 Mpa, and dried at 42°C for 8 h until the moisture content of the rose flowers was about 15%, then taken out;

[0104] (4) Baking: the rose flowers dried by vacuum hot air were baked to enhance the aroma, the baking machine was baked at 95°C for 10 min until the moisture content of the rose flowers was reduced to 6%, then taken out to obtain rose flower freeze-dried flowers.

[0105] Experiment:

[0106] The rose flower freeze-dried flowers obtained in Example 1 and Comparative Examples 1-9 were subjected to sensory evaluation and color difference determination.

[0107] 1. The sensory quality of the rose flower freeze-dried flowers obtained in Example 1 and Comparative Examples 1-9 is shown in Table 2, wherein the evaluation criteria are shown in Table 1:

[0108] Table 1

[0109]

[0110] Table 2

[0111]

[0112] 2. The color difference value ΔE of the rose flower freeze-dried flowers obtained in Example 1 and Comparative Examples 1-9 was determined. The color difference was measured using the CIB color system. The L, a, b values of each group of rose flowers were measured before drying using a full-automatic color difference meter, then the freeze-dried L1, a1, b1 values of the dried rose flowers were measured, and the color difference values ΔL, Δa, Δb were calculated. The L2, a2, b2 values of the rose flower freeze-dried flowers were measured again after storage for 180 days, and the color difference values ΔL', Δa', Δb' were calculated. The results are shown in Table 3:

[0113] Table 3

[0114] Experimental item Color difference value ΔE Color difference value ΔE' Example 1 0.4 0.8 Comparative Example 1 4.7 5.9 Comparative Example 2 4.5 5.6 Comparative Example 3 2.9 3.8 Comparative Example 4 2.9 3.8 Comparative Example 5 2.8 3.6 Comparative Example 6 6.8 8.1 Comparative Example 7 5.4 6.7 Comparative Example 8 0.5 1 Comparative Example 9 0.5 0.9

[0115] From the analysis of Table 1 and Table 2, it can be seen that:

[0116] 1. The comparison between Example 1 and Comparative Examples 1-7 is in terms of color preservatives. The freeze-dried fresh rose flowers of Example 1 are purplish red, uniform, bright and shiny, and have a full flower shape, a smooth and stretched petal surface, a strong floral fragrance, and good quality. The color difference value is only 0.4. The freeze-dried fresh rose flowers prepared in Comparative Examples 1-7 have poor color, especially Comparative Example 6 (blank control), which is the worst. The color is yellowish, the browning is more serious, the gloss is poor, and the floral fragrance is not obvious. The color difference value reaches 6.8, indicating that the color difference of the fresh rose flowers before and after freeze-drying changes greatly, seriously affecting the quality. The comparison between Example 1 and Comparative Examples 8-9 is the comparison of the pre-freezing and vacuum hot air drying processes. The freeze-dried fresh rose flowers of Comparative Example 1 have a full flower shape, a smooth and non-wrinkled petal surface, and a strong floral fragrance, and good quality. The freeze-dried fresh rose flowers of Comparative Examples 8-9 have obvious changes in flower shape, severe wrinkling of the petal surface, and a weak floral fragrance, which affects the quality of the rose flowers. It can be seen from this that the freeze-dried rose prepared by the method disclosed in Example 1 has little color difference and a complete shape without shrinkage.

[0117] 2. In a comparison of Example 1 and Comparative Examples 1-7 regarding the color preservative, the color difference value of the freeze-dried fresh rose flowers prepared in Example 1 after 180 days of storage was only 0.8, while the color difference values ​​of the freeze-dried fresh rose flowers prepared in Comparative Examples 1-7 changed significantly after 180 days of storage, with the color difference value of Comparative Example 6 showing the largest change. This indicates that the freeze-dried fresh rose flowers prepared using the color preservative in Example 1 can be stored for long periods of time without discoloration.

[0118] 3. In the color preservative preparation of Comparative Example 1, glutathione was not added. The roses prepared were light yellow with a slight browning, and the color difference value reached 4.7, indicating that the color difference of the rose flowers before and after freeze-drying changed significantly. This is because glutathione can inhibit polyphenol oxidase, thereby protecting the color of the freeze-dried flowers.

[0119] 4. In Comparative Example 2, the color preservative was prepared without the addition of polyethylene glycol. The freeze-dried fresh rose flowers obtained were slightly yellowish and slightly browned, and the color difference value reached 4.5, indicating that the color difference of the fresh rose flowers before and after freeze-drying changed significantly. This is because glutathione is easily oxidized at high temperatures, and the hot air drying and baking processes both cause excessively high temperatures for glutathione, resulting in oxidation of glutathione and loss of its function in protecting the color of the flowers. Therefore, the use of polyethylene glycol to convert glutathione into a more stable structure can enable glutathione to remain active during the hot air drying and baking processes.

[0120] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for freeze-drying fresh rose flowers, characterized in that: The method comprises the following steps: (1) Pretreatment: soaking fresh rose flowers in a color-protecting agent for color-protection treatment; (2) Pre-freezing: Pre-freeze the rose flowers after color protection treatment and then spray them with vitamin C solution; (3) Vacuum hot air drying: the pre-frozen rose flowers are vacuum hot air dried; (4) Baking: Baking the fresh rose flowers after vacuum hot air drying to enhance the fragrance, and taking them out after baking to obtain freeze-dried rose flowers.

2. The method for freeze-drying fresh rose flowers according to claim 1, wherein: In the color protection treatment of step (1), the color protection agent and water need to be mixed in a weight ratio of 1:2 and then diluted for use; the soaking time is 20 minutes.

3. The method for freeze-drying fresh rose flowers according to claim 2, wherein: The specific operation of pre-freezing in step (2) is: pre-freezing at a temperature of -15 to -10°C for 1 hour, then pre-freezing for a second time at a temperature of -25 to -20°C for 40 minutes, and finally pre-freezing for a third time at a temperature of -35 to -30°C for 20 minutes. After the pre-freezing is completed, spraying a vitamin C solution with a concentration of 1 wt%.

4. The method for freeze-drying fresh rose flowers according to claim 3, wherein: The vacuum degree of the vacuum hot air drying in step (3) is 0.09-0.1 MPa, and the drying operation is first drying at 30-35°C for 2 hours, then drying at 38-40°C for 3 hours, and finally drying at 42-45°C for 5 hours.

5. The method for freeze-drying fresh rose flowers according to claim 4, wherein: After the vacuum hot air drying in step (3) is completed, the moisture content of the roses is 15% to 18%.

6. The method for freeze-drying fresh rose flowers according to claim 5, wherein: The specific operation of baking in step (4) is: baking the roses after vacuum hot air drying in a baking machine at 95-100° C. for 10-15 minutes.

7. The method for freeze-drying fresh rose flowers according to claim 6, wherein: After the baking step (4), the moisture content of the fresh rose freeze-dried flowers is ≤7%.

8. The method for freeze-drying fresh rose flowers according to claim 7, wherein: The color preservative in step (1) comprises the following raw materials: glutathione, polyethylene glycol, trehalose, gum arabic, and sodium chloride.

9. The method for freeze-drying fresh rose flowers according to claim 8, wherein: The ratio of each raw material of the color retaining agent is as follows: The weight ratio of glutathione, polyethylene glycol, trehalose, gum arabic and sodium chloride is 6: (1.2-1.4): (1.2-1.5): (0.5-0.8): 0.

05.

10. A method for freeze-drying fresh rose flowers according to any one of claims 1 to 9, characterized in that: Described color retaining agent preparation method is as follows: Dissolve polyethylene glycol in a PBS solution containing 10 wt% ethanol to prepare a polyethylene glycol solution with a concentration of 2 mg / ml, then add glutathione, adjust the pH to 6.8-7, stir at room temperature for 2-3 hours, centrifuge, filter, and dry to obtain a glutathione mixed powder; Trehalose is added with water to prepare a 50 wt% trehalose solution, sodium chloride and gum arabic are added and mixed evenly, and then glutathione mixed powder is added and stirred evenly again to obtain a color protecting agent.

Images