Freeze-dried broccoli processing method

Abstract

The invention relates to the technical field of food processing, in particular to a freeze-dried broccoli processing method. The invention provides a freeze-dried broccoli processing method which comprises the following steps: taking cleaned broccoli, and cutting the broccoli into small flower types which are consistent in size, shape, thickness and height; carrying out instantaneous fixation by adopting steam, immediately soaking the broccoli subjected to fixation in ice water, fishing out the broccoli, and draining water; stacking the quick-frozen broccoli and the dry ice layer by layer; and after the temperature of the broccoli is reduced to-40 DEG C to-60 DEG C, performing vacuum freeze drying until the water content is less than or equal to 3% to obtain the dehydrated broccoli. According to the method, the loss of functional components such as glucoraphanin and polyphenol is reduced; formation of ice crystals is reduced, cell damage is reduced to the maximum extent, the content of functional components is effectively maintained, the color is close to that of fresh broccoli, and rehydration performance is good; the retention rates of functional components of glucoraphanin, flavone and vitamin C in broccoli all reach 98% or above.

Description

Technical Field

[0001] This invention relates to the field of food processing technology, specifically to a method for processing freeze-dried broccoli. Background Technology

[0002] broccoli( Brassica oleracea L.var. italica Plenck (a type of broccoli) is rich in glucosinolates (mainly sulforaphane), flavonoids, phenolic substances, anthocyanins, vitamin C, carotenoids, and various vitamins and minerals, earning it the reputation of "vegetable crown." sulforaphane is a secondary metabolite found in cruciferous plants such as broccoli. Through endogenous myrosinase enzymatic hydrolysis, it can generate sulforaphane, which possesses various physiological functions including anti-cancer, anti-inflammatory, antioxidant, and chronic disease prevention. For example, sulforaphane can activate the Nrf2 signaling pathway, releasing Nrf2 into the cell nucleus. There, it binds to small tendinoplastin (maf) and recognizes the antioxidant response element (ARE), thereby initiating the expression of antioxidant enzymes and enhancing the cell's antioxidant stress resistance.

[0003] In intact broccoli tissue, sulforaphane and myrosinase reside in separate organelles, isolated from each other and not reacting. When the plant tissue ruptures due to chewing or mechanical damage, sulforaphane and myrosinase are released and undergo enzymatic hydrolysis to produce sulforaphane. Studies have shown that sulforaphane is very stable but lacks biological activity; only after being hydrolyzed by myrosinase to produce sulforaphane can it exert various biological activities. However, both sulforaphane and myrosinase are unstable and easily degraded or inactivated during blanching and storage. During blanching, temperature also leads to a significant loss of polyphenols, vitamin C, and carotene. If hot water is used for blanching, in addition to the above-mentioned components, water-soluble active substances such as sulforaphane will also be lost due to dissolution in hot water. Furthermore, during freeze-drying, if the cooling rate is not properly controlled, ice crystal formation can lead to cell rupture, also causing a significant loss of active ingredients such as sulforaphane.

[0004] According to our research group and related literature, sulforaphane can be converted into sulforaphane under the action of intestinal flora or probiotics, and the conversion ability of intestinal flora can be further enhanced after repeated induction. Therefore, even though myrosinase has lost its activity after dehydration of broccoli, as long as sulforaphane is retained, it can still generate sulforaphane in the intestine, thus exerting various beneficial properties. Therefore, how to effectively preserve active substances such as sulforaphane during freeze-drying is an important research topic and is of great significance for improving the nutritional efficacy of broccoli.

[0005] Existing technologies primarily aim to increase sulforaphane content. For example, patent CN 115500486 B discloses a method for preparing broccoli powder rich in sulforaphane and polyphenols, and its application, increasing the sulforaphane and polyphenol content in the broccoli powder by over 42% and 80%, respectively. Patent CN 103416688 B discloses a broccoli sprout powder rich in sulforaphane and its production method; in one embodiment, the sulforaphane content in freeze-dried broccoli sprout powder can reach 1478.44 μg / g. However, extensive literature from our research group and other researchers indicates that sulforaphane has poor stability, with a short half-life even under -20℃ freezing conditions. Unlike sulforaphane, sulforaphane glycosides are more stable and can be enzymatically hydrolyzed by intestinal flora to release sulforaphane, erucin, and other isothiocyanates. CN 104542910 B proposes a method for preparing dehydrated broccoli that effectively retains glucosinolates, pointing out that heat pump drying is superior to freeze drying because endogenous myrosinase is only partially inhibited during the pre-freezing process of broccoli, leading to the decomposition of some glucosinolates. Therefore, this invention completely inactivates myrosinase through pretreatment and uses rapid freezing to control ice crystal formation, thereby maintaining cell integrity and maximizing the retention of functional components such as glucosinolates, demonstrating significant innovation.

[0006] In addition, other patents have also proposed methods to improve the quality of broccoli from different perspectives. For example, CN114601132A discloses a freeze-dried ready-to-eat ultrafine powder of selenium-enriched broccoli and its processing method, which effectively protects the color and taste of broccoli through sweeteners and color-protecting agents. Patent CN 120391513A discloses a freeze-dried preserved vegetable and its preparation process, which significantly improves the retention rate of vitamin C by using a color-protecting liquid. However, there is currently no method to improve the freeze-drying process while simultaneously maintaining functional components such as glucosinolates, flavonoids, phenolic substances, and vitamin C. Summary of the Invention

[0007] In view of the problems existing in the prior art, the purpose of this invention is to design a technical solution for a freeze-dried broccoli processing method.

[0008] The present invention is specifically implemented using the following technical solutions: The first aspect of this invention provides a method for processing freeze-dried broccoli, comprising: (1) Raw material pretreatment: Take the harvested and cleaned broccoli and cut it into small flower shapes with consistent size, shape, thickness and height to ensure consistent freeze-drying and rehydration rates, effectively improving product quality; (2) Blanching: Take the broccoli from step (1) and place it in the blanching equipment. Use steam to blanch the broccoli instantly. After blanching, immediately soak the broccoli in 0°C ice water, take it out and drain the water thoroughly. (3) Quick-freezing: Take the broccoli and dry ice from step (2) and stack them layer by layer to make the temperature of the broccoli drop sharply and reduce the formation of ice crystals; (4) Vacuum freeze drying: When the temperature of the broccoli in step (3) drops to -40℃ to -60℃, put the rapidly frozen broccoli into an industrial freeze drying equipment and freeze dry it under vacuum until the moisture content is ≤3%.

[0009] Furthermore, the small flower shape described in step (1) has a size of 9-11×9-11×9-11 mm.

[0010] Furthermore, the instantaneous steam blanching in step (2) involves a steam pressure of 0.2–0.3 MPa and a processing time of 50–60 s.

[0011] Furthermore, the ice water soaking time in step (2) is 10 to 20 seconds.

[0012] Furthermore, the ratio of broccoli to dry ice in step (3) is 1:2 to 1:3 (kg / kg).

[0013] Furthermore, the vacuum freeze-drying in step (4) has a vacuum degree of 0.005-0.015 mbar, a temperature of -50℃ to -70℃, and a time of 65-75 h.

[0014] A second aspect of the present invention provides freeze-dried broccoli prepared by the above method.

[0015] The present invention has the following beneficial effects: Instantaneous blanching with steam reduces the loss of functional components such as glucosinolates and polyphenols.

[0016] Rapid freezing with dry ice reduces ice crystal formation, minimizing cell damage and effectively preserving the content of functional ingredients. At the same time, the color is close to that of fresh broccoli, and it has good rehydration properties.

[0017] By combining steam instant blanching, dry ice rapid freezing, and vacuum freeze-drying technologies, the retention rates of functional components in broccoli, such as glucosinolates, flavonoids, and vitamin C, all reach over 98%. Attached Figure Description

[0018] Figure 1 Ion chromatograms and mass spectra obtained from liquid chromatography-mass spectrometry (LC-MS). Detailed Implementation

[0019] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features can be combined with each other. Unless otherwise specified, the methods used in the embodiments of the present invention are conventional methods, and the reagents used are commercially available.

[0020] Take 1.0 g of dehydrated broccoli, extract thoroughly with 100 mL of 50% ethanol solution, filter, and determine the contents of glucosinolates, flavonoids, and vitamin C in the filtrate using the following methods. Extraction and determination methods of sulforaphane Take 1.0 g of dehydrated broccoli, extract it thoroughly with 100 mL of 50% ethanol solution, filter it, and take the filtrate for testing.

[0021] LC-MS / MS analysis conditions: BEH C18 column (100 mm × 2.1 mm × 1.7 μm), sample loading volume 2 μL, mobile phase A: 0.1% formic acid aqueous solution, mobile phase B: acetonitrile, flow rate 0.3 mL / min, cation detection mode ESI+. 0-1 min: 95% A, 1-9.1 min: 95%-5% A, 9.1-10 min: 5%-20% A, 10-11 min: 20%-95% A. The ion chromatogram and mass spectrum of the LC-MS / MS are shown below. Figure 1 As shown.

[0022] Flavonoid Extraction and Determination Methods Take 1.0 g of dehydrated broccoli, extract thoroughly with 100 mL of 50% ethanol solution, filter, and collect the filtrate. Determine the flavonoid content using the aluminum chloride method. Take 1 mL of broccoli extract into a 25 mL volumetric flask, add 8 mL of 1.5% aluminum trichloride solution and 4 mL of pH 5.5 sodium acetate solution, then dilute to volume with 50% ethanol solution. After standing for 0.5 h, measure at 415 nm using a UV spectrophotometer.

[0023] Vitamin C Extraction and Determination Methods Take 1.0 g of dehydrated broccoli and extract it thoroughly with 100 mL of 50% ethanol solution. Filter the solution and determine the vitamin C content using the 2,6-dichlorophenolindophenol titration method. Transfer 10 mL of the broccoli extract to a 50 mL Erlenmeyer flask and titrate with a standardized concentration of 2,6-dichlorophenolindophenol solution until the solution turns pink and does not fade within 15 seconds. Perform a blank experiment simultaneously and calculate the vitamin C content based on the titration amount.

[0024] Chlorophyll determination method The contents of chlorophyll a and chlorophyll b were determined by ultraviolet-visible spectrophotometry, and the total chlorophyll content was determined accordingly, expressed in mg / g.

[0025] Example 1: Content and retention rate of various functional components in dehydrated broccoli Broccoli grown locally in Linhai, Zhejiang Province, was immediately washed after harvesting and cut into small florets of uniform size, shape, and thickness (9–11 × 9–11 × 9–11 mm). Ten kg of the cut broccoli were then briefly steam-blanched at a precisely controlled pressure of 0.2 MPa for 60 seconds. Immediately after blanching, the broccoli was immersed in 0°C ice water for 10 seconds, then removed and thoroughly drained. The broccoli was then layered with 30 kg of dry ice to rapidly freeze it to -60°C, effectively reducing ice crystal formation. The rapidly frozen broccoli was then placed in an industrial freeze-drying apparatus, with the vacuum level adjusted to 0.01 mbar and the temperature set to -60°C, and freeze-dried for 70 hours. At this point, the broccoli's moisture content was approximately 3%.

[0026] Take another 10 g of fresh broccoli and determine its content of glucosinolates, flavonoids, and vitamin C, as well as the water content of the broccoli, using the methods described above. Calculate the content of each substance in the dried broccoli and calculate the retention rate of the active ingredients using the following formula:

[0027] In the formula, A1: content of functional components in fresh broccoli (on a dry basis, mg / DW g) B1: Weight of fresh broccoli (dry basis, DW g) A2: Functional component content of dehydrated broccoli (on a dry basis, mg / DW g) B2: Weight of dehydrated broccoli (dry basis, DW g) y: Functional component retention rate (%) The content and retention rate of glucosinolates, flavonoids, and vitamin C in dehydrated broccoli were analyzed using the above method, and the results are shown in Table 1.

[0028] Table 1. Content and retention rate of various functional components in dehydrated broccoli

[0029] Example 2: Comparison of hot water blanching and steam blanching Broccoli produced locally in Linhai, Zhejiang Province, was cut and divided into 6 groups, 1 kg per group. Three groups were blanched in hot water, and the other three were blanched in steam. The hot water blanching conditions were: 150 s in 97℃ hot water. The steam blanching conditions were: 0.3 MPa for 50 s. Immediately after blanching, all groups of broccoli were immersed in 0℃ ice water for 10 s, then removed and thoroughly drained. Each group of broccoli was stacked with 3 kg of dry ice to rapidly freeze to -60℃. The rapidly frozen broccoli was then placed in a vacuum freeze-drying apparatus, with the vacuum level adjusted to 0.01 mbar and the temperature set to -60℃ for 70 h. At this point, the moisture content of the broccoli was approximately 3%. 1 g of each dehydrated broccoli was taken, and its glucosinolates, flavonoids, and vitamin C were measured. The results are shown in Table 2.

[0030] Table 2. Effects of blanching method on the content of functional components in broccoli

[0031] The results show that steam rinsing is more effective than hot water rinsing.

[0032] Example 3: Comparison of dry ice quick-freezing and cold storage quick-freezing Broccoli produced locally in Linhai, Zhejiang Province, was cut and divided into 6 groups, each weighing 1 kg. Three groups were quick-frozen with dry ice, and the other three were quick-frozen by machine. The steam blanching conditions were: 0.3 MPa, processing time 50 s. Immediately after blanching, the broccoli was immersed in 0℃ ice water for 10 s, then removed and thoroughly drained. The quick-freezing process involved stacking each group of broccoli with 3 kg of dry ice to rapidly freeze them to -50℃. The machine-freezing process involved placing each group of broccoli in a cold storage room, adjusting the temperature to -40℃, and maintaining this temperature for 6 hours. The frozen broccoli was then placed in a vacuum freeze-drying apparatus, with the vacuum level adjusted to 0.01 mbar and the temperature set to -60℃, for 70 hours of vacuum freeze-drying. At this point, the broccoli's moisture content was approximately 3%. 1 g of each dehydrated broccoli was taken, and its glucosinolates, flavonoids, and vitamin C content were determined. The results are shown in Table 3.

[0033] Table 3. Effects of quick-freezing method on the content of functional components in broccoli

[0034] The results show that dry ice freezing is more effective than cold storage freezing.

[0035] Example 4: Comparison of the invented dehydration method with hot air drying Broccoli produced locally in Linhai, Zhejiang Province, was cut and divided into 6 groups, each weighing 1 kg. Three groups were dried using the process described in this invention, while the other three were dried using traditional hot air drying. The steam blanching conditions were: 0.3 MPa, processing time 50 s. Immediately after blanching, the broccoli was immersed in 0℃ ice water for 10 s, then removed and thoroughly drained. The vacuum freeze-drying group was prepared by stacking each group of broccoli with 3 kg of dry ice, rapidly freezing the broccoli to -50℃. The frozen broccoli was then placed in a vacuum freeze-drying device, with the vacuum level adjusted to 0.01 mbar and the temperature set to -60℃, for 70 hours of vacuum freeze-drying. The hot air drying group was prepared by spreading the blanched, cooled, and drained broccoli evenly on a material tray and placing it in a drying chamber equipped with a heat pump dryer. The temperature was set to 60℃, the air velocity to 1 m / s, and drying was carried out for 10 hours, ultimately yielding dehydrated broccoli. 1 g of dehydrated broccoli was taken from each group of samples, and its glucosinolates, flavonoids and vitamin C were determined. The results are shown in Table 4.

[0036] Table 4. Effects of dehydration methods on the content of functional components in broccoli

[0037] The results show that, compared with hot air drying, vacuum freezing produces similar levels of glucosinolates and flavonoids, but it is more effective in terms of vitamin C content and color difference.

Claims

1. A method for processing freeze-dried broccoli, characterized in that, include: S.1 Raw material pretreatment: Take the cleaned broccoli and cut it into small florets of uniform size, shape, thickness and height; S.2 Blanching: Place the broccoli from S.1 into the blanching equipment and steam it. Immediately after blanching, soak the broccoli in ice water, remove it and drain the water. S.3 Quick-freeze: Take the broccoli and dry ice from S.2 and stack them layer by layer; S.4 Vacuum freeze drying: After the temperature of the broccoli in S.3 drops to -40℃~-60℃, put the broccoli into an industrial freeze drying equipment and freeze dry it under vacuum until the moisture content is ≤3%.

2. The freeze-dried broccoli processing method as described in claim 1, characterized in that, The small flower shape described in step S.1 has a size of 9-11×9-11×9-11 mm.

3. The freeze-dried broccoli processing method as described in claim 1, characterized in that, The steam treatment described in step S.2 involves a steam pressure of 0.2–0.3 MPa and a treatment time of 50–60 s.

4. The freeze-dried broccoli processing method as described in claim 1, characterized in that, The ice water immersion time described in step S.2 is 10-20 seconds.

5. The freeze-dried broccoli processing method as described in claim 1, characterized in that, The mass ratio of broccoli to dry ice in step S.3 is 1:2 to 1:

3.

6. The freeze-dried broccoli processing method as described in claim 1, characterized in that, The vacuum freeze drying in step S.4 has a vacuum degree of 0.005 to 0.015 mbar, a temperature of -50℃ to -70℃, and a time of 65 to 75 h.

7. Freeze-dried broccoli prepared by the method according to any one of claims 1-6.

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