Preparation method and application of carrot powder

Abstract

The invention discloses a preparation method and application of carrot powder. The method comprises the following steps: cutting peeled fresh carrots into small blocks, blanching the carrots with boiling water, and rapidly cooling the carrots with crushed ice; immersing the treated and cooled carrot blocks into a composite protective solution containing sodium alginate, Tween and ascorbic acid, and treating by adopting a high-speed wall breaking technology; and uniformly spreading the obtained carrot slurry in a drying tray, performing multi-stage program temperature control drying by a microwave vacuum drying system, crushing by a cyclone mill, and sieving by a 40-mesh sieve to obtain the carrot powder product with bright color and rich nutrition. The carrot powder prepared by the method can effectively retain nutritional ingredients such as natural carotene, polyphenol, flavone and the like. The prepared carrot powder product can be widely applied to food systems such as noodles, steamed buns, rice cakes and glue pudding, and shows excellent color stability and nutrition retentivity in the freezing storage and hot processing processes.

Description

Technical Field

[0001] The invention relates to the technical field of food processing, in particular to a preparation method of carrot powder and application of the carrot powder in the food industry. Background Art

[0002] As an important root vegetable resource in my country, carrots are rich in bioactive ingredients such as β-carotene, dietary fiber, polyphenols, flavonoids and vitamins, and have important nutritional value and health functions. Using carrots to prepare fruit and vegetable powder can not only extend its shelf life, but also broaden its application range, which is of great significance to promoting the high-value utilization and sustainable development of my country's carrot industry. However, in the industrial production of carrot powder, there are the following technical bottlenecks: (1) Color stability problem: The natural pigments in carrots are easily degraded by factors such as heat, light, and oxygen during processing, resulting in product color deterioration; (2) Serious nutritional loss: Traditional processing methods such as hot air drying will cause a large loss of heat-sensitive components such as polyphenols and flavonoids; (3) Poor process adaptability: Although freeze-drying can better retain nutrients, it has problems such as high energy consumption and long cycle. Although microwave vacuum drying is more efficient, it is easy to cause local overheating and damage the ingredients.

[0003] Therefore, developing a method for preparing carrot powder that can simultaneously ensure stable product color, high nutrient retention rate and is suitable for industrial production has become a technical problem that needs to be urgently solved in the field. Summary of the invention

[0004] The present invention effectively solves the above technical problems by innovatively combining composite color protection technology and multi-stage microwave vacuum drying process.

[0005] The purpose of the present invention is to provide a preparation process of carrot powder, wherein the carrot powder prepared by the process retains the color, nutritional components (such as carrot powder polyphenols, flavonoids and β-carotene) and activity of carrot powder, and is applied to various scenarios, such as making noodles, steamed buns, rice cakes, glutinous rice balls, etc.

[0006] To achieve the above object, the present invention provides a method for preparing carrot powder, characterized in that the method comprises:

[0007] (1) Raw material pretreatment: Peeled fresh carrots were cut into uniform small pieces with a size of (4±1 cm)×(1±0.2 cm)×(1±0.2) cm;

[0008] (2) Blanching: Blanch carrot pieces in boiling water for 3 ± 1 min, then immediately cool with crushed ice;

[0009] (3) Wall-breaking treatment: Add the cooled carrot pieces to the composite protective liquid according to the mass-volume ratio of 200 g:40 mL. The composite protective liquid is prepared from sodium alginate, Tween, and ascorbic acid according to the mass ratio of 0.2:0.1:0.08, and perform wall-breaking treatment at 27,000 r / min for 4 - 8.0 min;

[0010] (4) Microwave vacuum drying: Spread the wall-broken carrot slurry evenly on the drying tray and perform segmented drying using a multi-stage drying process: The first stage is drying at 1000 W for 50 min; the second stage is drying at 500 W for 50 min; the third stage is standing still at 0 W for 10 min; the fourth stage is drying at 300 W for 100 min;

[0011] (5) Crushing and sieving: Crush the dried product with a cyclone sample mill and then sieve it through a 40-mesh sieve to obtain the finished carrot powder.

[0012] Furthermore, during the microwave vacuum drying process, the vacuum degree is maintained at -0.08 to -0.1 MPa.

[0013] The present invention also protects the use of the carrot powder prepared by the described preparation method for frozen cooked rice and noodle products.

[0014] Furthermore, the frozen cooked rice and noodle products refer to noodles, steamed buns, rice cakes, and glutinous rice balls. Description of the Drawings

[0015] Figure 1 Influence diagram of high-speed homogenization time on FTIR of carrot powder.

[0016] Figure 2 Influence diagram of high-speed homogenization time on the microstructure of carrot powder (A: optical microscope; B: laser confocal microscope; C: scanning electron microscope).

[0017] Figure 3 Influence diagram of different embedding conditions on the color of carrot powder.

[0018] Figure 4 Influence diagram of embedding treatment on the microstructure of carrot powder.

[0019] Figure 5 Color stability diagram of carrot powder (a: thermal color stability; b: light color stability).

[0020] Figure 6 Diagram of β-carotene content and bioavailability in carrot powder.

[0021] Figure 7 Visualization image of carrot powder in frozen cooked rice and noodle products.

[0022] Figure 8Influence diagram of the T2 relaxation time and the T2 peak area ratio of carrot powder in frozen cooked rice and noodle products (A-D and a-d represent the T2 relaxation time and the peak area ratio of noodles, steamed buns, glutinous rice balls, and rice cakes, respectively). Detailed implementation mode

[0023] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are intended to explain the present invention and should not be construed as a limitation of the present invention. For those not specified in the embodiments regarding specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in the field or according to the product specifications. For the reagents or instruments not specified for the manufacturers, they are all conventional products that can be obtained through commercial purchase.

[0024] Example 1: Influence of ultra-high-speed homogenization time on the physicochemical properties of carrot powder

[0025] This example is to explore the influence of high-speed homogenization time on the physicochemical properties and antioxidant activity of carrot powder. The physicochemical properties such as particle size distribution, color, solubility, dietary fiber composition, polyphenol content, flavonoid content, and β-carotene content of carrot powder are measured, as well as the scavenging abilities of hydroxyl (OH), 2,2'-Azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS), 1,1-diphenyl-2-phenylhydrazine (DPPH) free radicals and the Fe 3+ reducing ability. The research results will provide theoretical guidance for the production process of preparing carrot powder by high-speed homogenization and cell wall breaking treatment.

[0026] 1. Experimental raw materials:

[0027] Fresh carrots: "Seoul Six-inch" (140 ± 10 g / root), produced in Zhangzhou, Fujian, purchased from RT-Mart Supermarket in Xiamen.

[0028] 2. Experimental methods:

[0029] Raw material processing: Peeled fresh carrots were cut into 4cm×1cm×1cm blocks, blanched in boiling water for 3±1min, and quickly cooled with crushed ice. The cooled carrot blocks were added with distilled water at a material-liquid ratio of 5:1 (w / w), and homogenized with a wall-breaking food processor at 27000r / min for 0.5, 1.0, 2.0, 4.0 and 8.0min respectively. 300g of the obtained carrot pulp was evenly spread on a 30cm×20cm×10cm plate and dried in an oven at 70℃ for 4h. The dried carrots were crushed by a cyclonic sample mill (10000rpm), and the sample particles that passed through a 40-mesh screen after crushing flowed into a sample bottle through a separator and stored at -20℃ for later use.

[0030] 3. Test items

[0031] 1) Particle size determination: After the carrot powder is evenly dispersed in water, the particle size and distribution of the carrot powder are determined using a laser particle size analyzer. The medium refractive index is 1.333, and the refractive index is between 7% and 12%. The average particle size, specific surface area and particle size distribution span of the powder are calculated by the software configured by the laser particle size analyzer.

[0032] Particle size and its distribution are one of the important physical parameters of powder. The average particle size reflects the size of the particles, while the distribution span can reflect the uniformity of the particle size distribution. The effect of homogenization time on the particle size of carrot powder is shown in Table 1. As the homogenization time increases, the D50 value of carrot powder gradually decreases and the specific surface area gradually increases, indicating that high-speed homogenization destroys the fiber structure of carrots and increases the particles per unit volume. With the increase of homogenization time, the value of the powder particle size distribution span shows a trend of first decreasing and then increasing, indicating that long-term homogenization reduces the uniformity of the particle size distribution of carrot powder. The increase in the value of the particle size distribution span caused by long-term homogenization may be due to differences in the sensitivity of particles to mechanical crushing.

[0033] Table 1 Effect of high-speed homogenization time on carrot powder particle size

[0034] Homogenization time 0.5 1.0 2.0 4.0 8.0 D50 (μm) 102.34±0.90a 100.69±0.40b 81.45±1.61c 66.39±0.32d 47.33±0.44e Specific surface area 127.48±0.41e 166.12±3.14d 222.16±0.35c 378.37±3.88b 458.64±5.63a Distribution span 2.71±0.01b 2.51±0.03c 2.43±0.02d 2.23±0.03e 2.81±0.01a

[0035] 2) Color measurement: The color of carrot powder was measured using a WSC-S colorimeter. 1 g of carrot powder was weighed and spread on a sample plate, and the color parameters L* (whiteness), a* (redness) and b* (yellowness) were measured.

[0036] Color is one of the most important characteristics of fruit and vegetable powder, which will directly affect consumers' choice and acceptance. The results of this study show (Table 2) that with the increase of homogenization time, the particle size of carrot powder tends to decrease gradually, and the specific surface area increases accordingly, which promotes the increase of Maillard reaction degree during heating and drying. It is worth noting that as the homogenization time increases, the L *The value first decreases and then increases, which may be due to the synergistic effect of the Maillard reaction degree and particle size change. On the other hand, the a * and b * values of carrot powder first increase and then decrease with the prolongation of homogenization time. This phenomenon may be related to the destructive effect of homogenization on the cell wall structure. Appropriate mechanical force can promote the dissolution of β-carotene. The experimental results show that an ideal color effect can be obtained in the homogenization time range of 4 - 8 min, which provides an important reference for the optimization of the production process.

[0037] Table 2 Effect of high-speed homogenization time on the color of carrot powder

[0038]

[0039] 3) Solubility characteristics:

[0040] ① Water-holding capacity determination: Weigh 0.5 g of carrot powder and disperse it in 20 mL of distilled water. Stir for 30 min to make it fully mixed. After centrifugation (5000 r / min, 20 min), measure the mass of the precipitate and calculate the water-holding capacity according to formula (1).

[0041]

[0042] In the formula:

[0043] m1: mass of the sample, g; m2: mass of the precipitate, g.

[0044] ② Oil-holding capacity determination: Weigh 0.5 g of carrot powder and disperse it in 10 mL of soybean oil. Stir for 30 min to make it fully mixed. After centrifugation (5000 r / min, 20 min), measure the mass of the precipitate and calculate the oil-holding capacity of the sample according to formula (2).

[0045]

[0046] In the formula:

[0047] m1: mass of the sample, g; m2: mass of the precipitate, g.

[0048] ③ Solubility determination: Weigh 0.5 g of carrot powder and disperse it in 20 mL of distilled water. Keep it in a water bath at 80 °C for 30 min, cool it, and then centrifuge (5000 r / min, 20 min). Dry the obtained supernatant at 105 °C and measure the mass of the solids in the supernatant. Calculate the solubility of the sample in water according to formula (3).

[0049]

[0050] In the formula:

[0051] m1: sample mass, g; m2: mass of supernatant solids, g.

[0052] The effect of homogenization time on the water-holding capacity of carrot powder is shown in Table 3. It can be seen that with the increase of homogenization time, the water-holding capacity of carrot powder gradually decreases, probably because the homogenization shear force destroys the fiber network structure and hydrogen bonds on the fiber chain.

[0053] The homogenization time has no significant effect on the oil-holding capacity of carrot powder (Table 3). This may be because the binding ability of powder and oil is determined by various factors such as the microstructure, surface characteristics and particle hydrophobicity of the powder. With the increase of homogenization time, the solubility of carrot powder gradually increases from 17.46% to 29.07% (Table 3), which may be due to the promotion of the conversion of insoluble fiber into soluble components by homogenization.

[0054] Table 3 Effect of high-speed homogenization time on the water-holding capacity, oil-holding capacity and solubility of carrot powder

[0055]

[0056] 4) Determination of basic components: The total sugar content was determined by the phenol-sulfuric acid method; the protein content was determined by the Kjeldahl method (GB5009.5—2016); the moisture content was determined by the direct drying method (GB 5009.3—2016); the ash content was determined by the ignition method (GB5009.4—2016); the contents of total dietary fiber (TDF), insoluble dietary fiber (IDF) and soluble dietary fiber (SDF) were determined by the enzymatic gravimetric method (AOAC 991.43); the β-carotene content was determined by high performance liquid chromatography (GB5009.83—2016).

[0057] As shown in Table 4, when the homogenization time reaches 4 min or more, the total sugar content in carrot powder shows a significant increase. This may be because physical shear destroys the glycosidic bonds on the fiber chain, converting a part of dietary fiber into soluble sugar, resulting in a relative decrease in protein content. On the other hand, the homogenization time has no significant effect on the moisture content and ash content.

[0058] The effect of homogenization time on the dietary fiber content of carrot powder is shown in Table 4. As the homogenization time increases, the IDF content in carrot powder decreases from 26.26% to 13.74%, while the SDF content increases from 7.95% to 15.67%, indicating that homogenization treatment can convert IDF in carrot powder into SDF. In addition, the TDF content after homogenization shows a decreasing trend, which further indicates that physical shear force breaks the glycosidic bonds in the fiber, converting a part of dietary fiber into small molecule sugars.

[0059] Table 4 Effect of high-speed homogenization time on the basic components of carrot powder

[0060] Homogenization time (min) 0.5 1.0 2.0 4.0 8.0 Total sugar (%) <![CDATA[43.43±0.60 c > <![CDATA[42.18±0.31 c > <![CDATA[41.25±0.20 c > <![CDATA[44.86±0.70 b > <![CDATA[47.54±0.15 a > Protein (%) <![CDATA[6.62±0.19 a > <![CDATA[6.25±0.06 b > <![CDATA[5.81±0.17 c > <![CDATA[5.66±0.06 d > <![CDATA[5.64±0.06 d > Ash (%) <![CDATA[5.06±0.48 a > <![CDATA[5.10±0.20 a > <![CDATA[5.47±0.08 a > <![CDATA[5.34±0.11 a > <![CDATA[5.38±0.63 a <!-- 4 -->]]> Moisture (%) <![CDATA[4.52±0.36 a > <![CDATA[4.40±0.34 a > <![CDATA[4.51±0.41 a > <![CDATA[4.45±0.21 a > <![CDATA[4.34±0.36 a > IDF (%) <![CDATA[26.26±0.58 a > <![CDATA[25.89±0.35 b > <![CDATA[24.58±0.41 c > <![CDATA[20.86±0.39 d > <![CDATA[13.47±0.50 e > SDF (%) <![CDATA[7.95±0.19 e > <![CDATA[8.19±0.05 d > <![CDATA[9.62±0.29 c > <![CDATA[12.83±0.41 b > <![CDATA[15.67±0.26 a > TDF (%) <![CDATA[34.92±0.52 a > <![CDATA[34.27±0.33 a > <![CDATA[34.31±0.77 a > <![CDATA[33.61±0.67 a > <![CDATA[29.04±0.62 b >

[0061] 5) Extraction and determination of free phenolic compounds:

[0062] Mix 1 g of carrot powder with 50 mL of 50:50 (v / v) chilled ethanol-aqueous solution at 4 °C for 10 min, and centrifuge (4000 r / min, 10 min) to obtain the supernatant. Under the same conditions, further extract the remaining precipitate twice with 25 mL of 50:50 (v / v) chilled ethanol-aqueous solution, and combine the obtained supernatants.

[0063] Take 1 mL of the supernatant, add 1 mL of Folin-Ciocalteu reagent, 5 mL of deionized water, 3 mL of 7.5% Na2CO3, and incubate at 35 °C for 2 h. Measure the absorbance of the sample at a wavelength of 765 nm, and calculate the polyphenol content according to the gallic acid standard curve.

[0064] 6) Extraction and determination of bound phenolic compounds

[0065] After extracting free phenolic compounds, add 10 mL of 2 mol / L NaOH solution to the residue, digest at 95 °C for 30 min, stir at room temperature for 1 h, adjust the pH of the mixture to 7 with 2 mol / L HCl, and extract with hexane to remove lipids. Extract the mixture 5 times with 10 mL of ethyl acetate, combine the ethyl acetate extracts, and after vacuum rotary evaporation at 45 °C, redissolve the bound phenolic compounds in 100 mL of 50% (v / v) chilled ethanol-aqueous solution. The content of bound polyphenols is determined according to the method of Kamble et al.

[0066] As can be seen from Table 5, the β-carotene content in the carrot powder prepared by homogenization for 0.5 min was 75.51 mg / 100 g. Along with the extension of the homogenization time, the β-carotene content in the carrot powder showed a trend of first increasing and then decreasing. β-carotene exists in the chromoplasts within the cell walls of fruits and vegetables in crystalline form. Homogenization shear will break the cell walls in the Bell fruits and dissolve out the β-carotene, but β-carotene will undergo aerobic degradation during the hot air drying process. Therefore, extending the homogenization time will dissolve β-carotene out of the cells, but during drying, the β-carotene content may decrease due to oxidation. There is a relatively good effect at 4 - 8 minutes.

[0067] Bound phenols are part of the plant cell wall, while free phenols are mainly distributed in the vacuoles of plant cells. The effects of homogenization time on the polyphenol and flavonoid contents of carrot powder are shown in Table 5. When the homogenization time increased from 0.5 min to 8.0 min, the bound polyphenol content in the carrot powder increased from 4.19 mg / g to 8.08 mg / g, and the bound flavonoid content increased from 2.54 mg / g to 4.54 mg / g. This is because high-speed shear breaks the carrot cell walls, exposing the polyphenols and flavonoids bound to the cell walls. Therefore, extending the homogenization time is beneficial for the dissolution of bound polyphenols and bound flavonoids into water.

[0068] With the increase of homogenization time, the free polyphenol and free flavonoid contents of carrot powder showed a trend of first increasing and then decreasing (Table 5). Along with the extension of the homogenization time, polyphenols and flavonoids were gradually released from within the cell walls, but were also damaged by long-term high-speed shear. As a result, the contents of both free polyphenols and free flavonoids showed a trend of first increasing and then decreasing.

[0069] Table 5 Effects of high-speed homogenization time on the contents of polyphenolic compounds and β-carotene in carrot powder

[0070] Homogenization time (min) 0.5 1.0 2.0 4.0 8.0 β-Carotene (mg / 100g) <![CDATA[75.51±0.94 d > <![CDATA[79.24±0.15 b > <![CDATA[80.59±0.94 a > <![CDATA[81.58±0.96 a > <![CDATA[78.27±0.22 c > Free polyphenols (mg / g) <![CDATA[2.68±0.01 e > <![CDATA[3.99±0.06 d > <![CDATA[6.93±0.07 b > <![CDATA[7.56±0.06 a > <![CDATA[6.00±0.05 c > Bound polyphenols (mg / g) <![CDATA[4.19±0.04 e > <![CDATA[4.80±0.04 d > <![CDATA[6.50±0.06 c > <![CDATA[7.68±0.04 b > <![CDATA[8.08±0.04 a >

[0071] 7) Determination of antioxidant activity

[0072] ① Determination of OH scavenging rate

[0073] Carrot powder (1 g) was mixed with 50 mL of frozen 50% ethanol-aqueous solution (v / v) for 10 min. The resulting mixture (1 mL) was mixed with 0.3 mL of 8 mmol / L FeSO4 solution, 0.25 mL of 30% 20 mmol / L H2O2 solution and 1 mL

[0074] Mix well with 3 mmol / L salicylic acid solution, react in the dark at 37 °C for 30 min, cool with ice water, then add 0.45 mL of distilled water, shake well, after centrifugation (5000 r / min, 10 min), measure the absorbance value of the supernatant at 510 nm, and calculate the OH free radical scavenging rate of the sample according to formula (4).

[0075]

[0076] In the formula:

[0077] X: OH free radical scavenging rate, %; A S : Absorbance value of the sample;

[0078] A C : Absorbance value measured by using distilled water instead of salicylic acid;

[0079] A0: Absorbance value of distilled water replacing the sample.

[0080] ② Determination of DPPH free radical scavenging rate

[0081] Mix 1 g of carrot powder with 50 mL of frozen 50% ethanol - aqueous solution (v / v) for 10 min to obtain a mixture. Add an equal volume of 0.2 mmol / L DPPH solution to 1 mL of the mixture, mix well, react in the dark at room temperature for 30 min, after centrifugation (10000 r / min, 10 min), measure the absorbance value of the supernatant at 517 nm. Calculate the DPPH free radical scavenging rate of the sample according to formula (5).

[0082]

[0083] In the formula:

[0084] X: DPPH free radical scavenging rate, %; A S : Absorbance value of the sample;

[0085] A C : Absorbance value measured after the reaction of 50% ethanol with the sample;

[0086] A0: Absorbance value of distilled water replacing the sample.

[0087] ③ Determination of ABTS free radical scavenging rate

[0088] Preparation of ABTS radical working solution: An aqueous solution of 2 mmol / L ABTS and a solution of 2.45 mmol / L potassium persulfate were mixed at a ratio of 1:1 (v / v), placed in the dark for 12 h, and then diluted with 95% ethanol solution to make the absorbance value of the ABTS radical working solution at 734 nm be 0.9 ± 0.05. Carrot powder (1 g) was mixed with 50 mL of frozen 50% ethanol-aqueous solution (v / v) for 10 min to obtain a mixture. 1.2 mL of the working solution was mixed with 0.3 mL of the carrot mixture, and after standing for 6 min, the absorbance value at 734 nm was measured, and the ABTS radical scavenging rate was calculated according to formula (6).

[0089]

[0090] In the formula:

[0091] X: ABTS radical scavenging rate, %; A S : Absorbance value of the sample;

[0092] A C : Absorbance value measured by replacing the ABTS radical working solution with distilled water;

[0093] A0: Absorbance value of the initial concentration of the ABTS reagent.

[0094] ④ Determination of reducing power

[0095] Carrot powder (1 g) was mixed with 50 mL of frozen 50% ethanol-aqueous solution (v / v) for 10 min to obtain a mixture. 1 mL of 0.2 mol / L pH = 6.6 phosphate buffer and 1 mL of 1% potassium ferricyanide solution were added to 1 mL of the mixture, and after shaking and mixing evenly, the reaction was carried out in a water bath at 50 °C for 20 min. 1.0 mL of 10% trichloroacetic acid was added to the above mixed solution, and centrifuged at 4000 r / min for 10 min. 2 mL of the supernatant was taken, 2 mL of distilled water and 0.4 mL of 0.1% potassium ferricyanide solution were added, and after mixing evenly, it was allowed to stand at room temperature for 10 min, and the absorbance value at 700 nm was measured.

[0096] To explore the effect of homogenization time on the antioxidant activity of carrot powder, the OH, DPPH, ABTS radical scavenging rates and Fe 3+ reducing power of carrot powder were measured (Table 6). The OH, DPPH, ABTS radical scavenging rates and Fe 3+ reducing power of carrot powder prepared with a homogenization time of 4.0 min were the largest, which were 73.63%, 47.87%, 70.01% and 2.31 respectively. With the decrease or increase of the homogenization time, the radical scavenging rates of OH, ABTS, DPPH, etc. and Fe 3+The reducing ability showed a decreasing trend, indicating that long-term homogenization damaged the antioxidant components. On the other hand, the OH, ABTS, DPPH free radical scavenging rates and Fe of carrot powder 3+ The correlation coefficients between the reducing ability and the free polyphenol content exceeded 0.88 (Table 7), indicating that free polyphenols are the key components of the antioxidant activity of carrot powder.

[0097] Table 6 Effects of high-speed homogenization time on the antioxidant activity of carrot powder

[0098]

[0099] Table 7 Correlation analysis of free polyphenols in carrots and free radical scavenging rates

[0100] <![CDATA · OH clearance rate]]> <![CDATA[DPPH · Scavenging rate]]> <![CDATA[ABTS ·+ Clearance rate]]> <![CDATA[Fe 3+ Reducing ability]]> Free polyphenols <![CDATA[0.93 * > <![CDATA[0.94 * > <![CDATA[0.90 * > <![CDATA[0.88 * >

[0101] There was no significant difference between any two means in the same row with the same letter behind (p < 0.05).

[0102] 8) FTIR

[0103] Spread an appropriate amount of the sample evenly on the sample stage, and use FTIR equipped with attenuated total reflection to analyze the chemical structure of the sample. The wavelength absorption range is 4000 - 400 cm -1 , and each sample was scanned 16 times at a resolution of 4 cm -1 .

[0104] Use FTIR to explore the effect of homogenization time on the cell wall structure of carrot powder ( Figure 1 ). It can be seen that when the homogenization time was extended from 0.5 min to 8.0 min, the characteristic absorption peaks of carrot powder at 3280 cm -1 and 1254 cm -1 shifted to 3273 cm -1 and 1243 cm -1 , and the intensity of the characteristic absorption peak at 1027 cm -1 gradually decreased. This indicates that high-speed homogenization damaged the hydrogen bonds within cellulose, hemicellulose, and pectin molecules in carrots.

[0105] 9) Microstructure

[0106] ① Observation with an optical microscope

[0107] After mixing 1 g of carrot powder with 20 mL of distilled water, place a drop of the sample in the center of a glass slide, cover it with a coverslip, and observe the sample particles and cell wall morphology through an optical microscope.

[0108] ② Observation with CLSM

[0109] 0.1g carrot powder was mixed with 20ml 0.1g / 100mL Congo red solution and stained for 30min. The cell wall structure of carrot powder was observed by CLSM under a 40x objective lens. The fluorescent dye was excited by an argon 488nm laser and the fluorescence was detected in the range of 540-670nm.

[0110] ③SEM observation

[0111] The microstructure of the sample was observed using SEM. The carrot powder was placed on a sample stage and gold-plated in an ion sputtering instrument at 20 mA for 60 s, and then the morphology of the sample was observed at an accelerating voltage of 10 kV.

[0112] The results of the effect of high-speed homogenization time on the microstructure of carrot powder are shown in Figure 2 , where A: optical microscope; B: laser confocal microscope; C: scanning electron microscope. Under an optical microscope with a magnification of 10 times, the carrot powder prepared by homogenization for 0.5 min contains large particles and small particles ( Figure 2 As the homogenization time increases, the number of large particles of carrot powder gradually decreases while the number of small particles gradually increases. Under a partially magnified optical microscope, as shown by the arrow, regular cell walls can be observed and connected together. As the homogenization time increases, the cell wall fiber structure gradually becomes irregular and the cell wall edge gradually breaks. At 8.0 min of homogenization, the complete cell wall structure basically disappears.

[0113] The effect of homogenization time on the particle morphology of carrot powder suspension was investigated by CLSM. Figure 2 B). The red substance represents the cellulose in the cell wall after Congo red staining. When homogenized for 0.5 min, it was observed that the red fibers were tightly aggregated together. As the homogenization time increased, the degree of fiber aggregation gradually decreased. At 8.0 min of homogenization, the aggregated fibers disappeared, and a large number of fiber fragments and particles appeared. These phenomena indicate that extending the homogenization time will cause the cell wall cellulose to degrade.

[0114] The effect of homogenization time on the microstructure of carrot powder was observed by SEM images ( Figure 2 C). In the SEM image of carrot powder obtained by homogenization for 0.5 min, closely arranged quadrilateral or pentagonal cell wall structures can be observed at the place indicated by the arrow. These cell wall structures are composed of cellulose, lignin and pectin. As the homogenization time increases, the cell wall structure is gradually destroyed, and irregular fragmented particles appear.

[0115] Effect of the above homogenization time on the microstructure of carrot powder ( Figure 2) It is consistent with the trend of average particle size change (Table 1), indicating that prolonging the homogenization time will damage the cell wall, resulting in the exposure of the carotenoids, polyphenols and flavonoids embedded inside (Table 5), and fine-particle carrot powder can be prepared.

[0116] Example 2: Color protection experiment of carrot powder

[0117] The research in Example 1 found that homogenization can damage the carrot cell wall, release the nutrients and antioxidant components inside the cells, and improve the antioxidant activity of carrot powder. However, during processing and storage, the high specific surface area of the powder may lead to the degradation of carotenoids, resulting in visual bleaching of the powder and loss of color intensity. In addition, in addition to poor chemical stability, the high lipophilicity of carotenoids also limits their application in food, pharmaceuticals and nutraceuticals. To overcome these limitations, protecting carotenoids during the preparation of carrot powder can improve the stability of its color during processing and storage, and promote its combination with water-soluble foods.

[0118] Using carrots as raw materials, they were encapsulated with sodium alginate, Tween and ascorbic acid, and carrot powder was prepared by microwave vacuum drying. The effects of the addition amounts of sodium alginate, Tween and ascorbic acid on the color of carrot powder were explored through single-factor experiments and orthogonal experiments, and the carrot powder prepared under the optimal process conditions was characterized.

[0119] 1. Experimental raw materials: the same as in Example 1

[0120] 2. Preparation of carrot powder

[0121] After peeling fresh carrots and cutting them into pieces of 4 cm×1 cm×1 cm, they were blanched in boiling water for 3 min and quickly cooled with crushed ice. Take 200 g of the cooled carrot pieces and add them to the sodium alginate-Tween-ascorbic acid solution dissolved in 40 mL of distilled water, and homogenize with a wall-breaking blender at 27000 r / min for 8.0 min. Spread the obtained carrot pulp evenly on a plate of 30 cm×15 cm, and place it in a microwave vacuum drying oven for segmented drying (1000 W, 50 min; 500 W, 50 min; 0 W, 10 min; 300 W, 100 min), then crush it with a cyclone sample mill and collect it through a 40-mesh sieve. The collected carrot powder was stored at -20 °C for standby.

[0122] In addition, carrot powder prepared by replacing the sodium alginate-Tween-ascorbic acid solution with distilled water was used as the control group.

[0123] 3. Performance measurement:

[0124] 1) Color measurement

[0125] The color parameters such as L*, a*, and b* of the carrot powder were measured using a colorimeter. Among them, L* represents the brightness of the sample, a* represents the redness of the sample, and b* represents the yellowness of the sample. The total color difference (ΔE) reflects the overall color change of the sample, and this value is calculated according to formula (7).

[0126]

[0127] 2) Single-factor experiment

[0128] Through single-factor optimization experiments, the effects of the addition amounts of Tween, sodium alginate, and ascorbic acid (based on the weight of carrots) on ΔE of carrot powder were explored.

[0129] (1) Fix the addition amounts of sodium alginate and ascorbic acid at 0.10% and 0.06% respectively, and explore the effect of the addition amount of Tween (0.04%, 0.08%, 0.12%, 0.16%, 0.20%) on ΔE of carrot powder, and determine the appropriate range of Tween addition amount according to ΔE.

[0130] (2) Fix the addition amounts of Tween and ascorbic acid at 0.12% and 0.06% respectively, and explore the effect of the addition amount of sodium alginate (0.06%, 0.08%, 0.10%, 0.12%, 0.14%) on ΔE of carrot powder, and determine the appropriate range of sodium alginate addition amount according to ΔE.

[0131] (3) Fix the addition amounts of Tween and sodium alginate at 0.12% and 0.10% respectively, and explore the effect of the addition amount of ascorbic acid (0.02%, 0.04%, 0.06%, 0.08%, 0.10%) on ΔE of carrot powder, and determine the appropriate range of ascorbic acid addition amount according to ΔE.

[0132] Color is one of the important characteristics of dried products, which has an important impact on consumers' choices and is also a key indicator for measuring the quality changes and certain chemical reactions during food processing. Therefore, in this example, the effects of the addition amounts of Tween, sodium alginate, and ascorbic acid on ΔE of carrot powder were investigated, and the results are as Figure 3 shown, where (a) is the graph of the effect of the addition amount of Tween on the color of carrot powder, (b) is the graph of the effect of the addition amount of sodium alginate on the color of carrot powder, and (c) is the graph of the effect of the addition amount of ascorbic acid on the color of carrot powder.

[0133] As the addition amount of Tween increases, ΔE of carrot powder shows a trend of first increasing and then decreasing ( Figure 3 in (a)), indicating that excessive addition of Tween reduces the color intensity of carrot powder instead. It shows that adding an appropriate amount of Tween can protect the color of carrot powder. Therefore, the addition amounts of Tween at 0.12%, 0.16%, and 0.20% were selected as three levels in the orthogonal experiment.

[0134] With the increase of sodium alginate addition, the ΔE of carrot powder showed a trend of increasing first and then decreasing ( Figure 3 (b)). Adding 0.14% sodium alginate actually reduced the ΔE of carrot powder, probably because excessive sodium alginate reduced its ability to protect carotenoids. Therefore, the orthogonal experiment selected three levels of sodium alginate addition: 0.08%, 0.12%, and 0.14%.

[0135] With the increase of ascorbic acid addition, the ΔE of carrot powder showed a trend of increasing first and then decreasing ( Figure 3 (c)) indicates that the effect of adding excessive ascorbic acid on protecting the color of carrot powder is reduced. Therefore, the orthogonal test selected three levels of ascorbic acid addition: 0.04%, 0.06% and 0.08%.

[0136] 3) Orthogonal test

[0137] Based on the results of the single factor experiment, three more appropriate levels were selected among the addition amounts of Tween, sodium alginate and ascorbic acid. Taking the ΔE of carrot powder as an indicator, a three-factor three-level orthogonal experiment was used to optimize the preparation process of carrot powder. The experimental factors and levels are shown in Table 8.

[0138] Table 8L9(3 3 ) Orthogonal table of factors and levels in the screening test of carrot powder embedding materials

[0139]

[0140] 4)CLSM

[0141] 0.1g carrot powder was mixed with 5mL distilled water, and 20μL 1mg / mL Nile red solution was added, and the mixture was allowed to stand for 30min. The distribution of β-carotene in carrot powder was observed by CLSM under a 63x objective lens. The emission wavelength and excitation wavelength of Nile red were 605nm and 561nm, respectively.

[0142] According to the results of the single factor experiment, L9(3 3 ) orthogonal table was used to conduct a three-factor three-level orthogonal test, and the test results are shown in Table 9. It can be seen from the range R that the influence of the three factors on the color of carrot powder is ranked as ascorbic acid> sodium alginate> Tween. The best process for encapsulating and protecting the color of carrot powder is to add 0.20%, 0.10% and 0.08% of Tween, sodium alginate and ascorbic acid respectively.

[0143] Table 9 Orthogonal test results analysis table

[0144]

[0145] result:

[0146] ①. Effect of adding Tween - sodium alginate - ascorbic acid assisted microwave vacuum drying on the color of carrot powder

[0147] The results are shown in Table 10. The L*, a*, and b* values of the carrot powder prepared by freeze - drying are 75.86, 28.69, and 34.11 respectively, which are all higher than the L*, a*, and b* values (47.61, 26.14, and 25.42) of the carrot powder obtained by ultra - high - speed homogenization for 8 min in Example 1 (Table 2).

[0148] Compared with the carrot powder prepared by freeze - drying, the a* value of the carrot powder prepared by microwave vacuum drying is larger, while the L* and b* values are lower.

[0149] The color of the carrot powder was further improved by adding Tween - sodium alginate - ascorbic acid assisted microwave vacuum drying. The L* value of the prepared carrot powder is between that of the samples prepared by microwave vacuum drying and freeze - drying, and the a* and b* values have no obvious difference from those of the freeze - dried samples. This may be because after adding Tween - sodium alginate - ascorbic acid, Tween - sodium alginate covers the surface of carotenoids, increasing the L* value and decreasing the a* and b* values of the carrot powder; on the other hand, Tween - sodium alginate - ascorbic acid can reduce the degradation of carotenoids, increasing the a* and b* values of the carrot powder. Therefore, by optimizing the addition amount of Tween - sodium alginate - ascorbic acid, the color of the carrot powder prepared by microwave vacuum drying is close to that of the sample prepared by vacuum freeze - drying.

[0150] Table 10 Effect of embedding treatment on the physical properties of carrot powder

[0151] Freeze drying Microwave vacuum drying Encapsulation-assisted microwave vacuum drying L* <![CDATA[75.86±0.08 a > <![CDATA[72.44±0.14 c > <![CDATA[74.49±0.19 b > a* <![CDATA[28.69±0.09 b > <![CDATA[31.08±0.15 a > <![CDATA[29.94±0.15 b > b* <![CDATA[34.11±0.10 a > <![CDATA[33.22±0.05 b > <![CDATA[34.31±0.18 a >

[0152] ② Effect of adding Tween - sodium alginate - ascorbic acid assisted microwave vacuum drying on the microstructure of carrot powder

[0153] By observing the color of the dispersion of carrot powder in water and comparing the solubility of carotenoids in water in the carrot powder prepared by freeze - drying, microwave vacuum drying, and adding Tween - sodium alginate - Tween assisted microwave vacuum drying, the results are as Figure 4 shown, where FD, MVD, and E - MVD represent the carrot powder prepared by freeze - drying, microwave vacuum drying, and adding Tween - sodium alginate - Tween assisted microwave vacuum drying respectively. The same applies to the following figures. The colors of the dispersions of freeze - dried and microwave - vacuum - dried carrots are lighter, while the dispersion of the carrot powder prepared by embedding - assisted microwave vacuum drying shows uniform orange - yellow, indicating that adding Tween - sodium alginate - ascorbic acid increases the solubility of carotenoids in water. Therefore, the uniform orange - yellow color of the carrot powder dispersion may be due to the promotion of the solubility of carotenoids in water by adding Tween - sodium alginate - ascorbic acid.

[0154] Distribution of carotenoids in carrot powder suspension was investigated by CLSM( Figure 4 ). The red substances represent carotenoids after Nile red staining. Carotenoids in the carrot powder suspensions prepared by freeze-drying and microwave vacuum drying were dispersed and had a low content; while in the carrot powder prepared by embedding-assisted microwave vacuum drying, carotenoids could be observed to aggregate together and had a high content( Figure 4 ), which further indicated that the addition of Tween-sodium alginate-ascorbic acid improved the solubility of carotenoids in water.

[0155] 5) Color stability

[0156] The samples were sealed in transparent food packaging bags and placed in an 80 °C water bath. Color parameters were measured every 15 min to evaluate the thermal stability of the samples. The samples sealed in transparent food packaging bags were placed in a constant temperature and humidity chamber at 25 °C and stored under a fluorescent lamp at a distance of 10 cm. Color parameters were measured every 12 h to evaluate the light stability of the samples.

[0157] Results and discussion:

[0158] Effect of embedding-assisted microwave vacuum drying with Tween-sodium alginate-ascorbic acid on the color stability of carrot powder:

[0159] To explore the thermal stability of the color of carrot powder, the changes in color L*, a*, and b* of carrot powder during treatment at 80 °C for 420 min were investigated( Figure 5 ), where Figure 5 (a) is the color thermal stability graph, Figure 5 (b) is the color light stability graph. With the prolongation of time, the L* values of carrot powder prepared by freeze-drying, microwave vacuum drying, and embedding-assisted microwave vacuum drying decreased by 36.69%, 30.78%, and 28.60% respectively, which might be due to the non-enzymatic browning reaction of carrot powder under high-temperature conditions. With the prolongation of time, the a* values of freeze-drying and microwave vacuum drying gradually decreased, while the a* value of embedding-assisted microwave vacuum drying showed a trend of first increasing and then decreasing, and freeze-drying, microwave vacuum drying, and embedding-assisted microwave vacuum drying decreased by 37.61%, 35.62%, and 8.80% respectively, indicating that embedding-assisted microwave vacuum drying improved the stability of a* of carrot powder at 80 °C. The b* values of freeze-dried, microwave vacuum-dried, and embedding-assisted microwave vacuum-dried carrot powder all showed a trend of first increasing and then decreasing with time, which was attributed to non-enzymatic browning reaction and carotenoid degradation. Therefore, embedding-assisted microwave vacuum drying improved the thermal stability of the color of carrot powder, which might be because the embedding treatment prevented carotenoids from being destroyed at high temperature.

[0160] The color change of carrot powder stored under light conditions for 14 days is as shown in Figure 5 (b). In the first 4 days of storage, there was no obvious change in the color of carrot powder. After 4 days of storage, with the extension of storage time, the L* of carrot powder gradually increased while a* gradually decreased. This is because carotene in carrot powder degraded under light, reducing the red color of the powder and enhancing the white color of the fiber. When carrot powder was stored for 14 days under light conditions, the L* of carrot powder obtained by embedding-assisted microwave vacuum drying increased by 10.75%, while the a* value and b* value decreased by 29.26% and 55.33% respectively. This change is less than the increase in L* value and the decrease in a* value and b* value of carrot powder prepared by freeze-drying and microwave vacuum drying (freeze-drying L*: 21.65%, a*: 78.53%, b*: 84.74%; microwave vacuum drying L*: 18.80%, a*: 66.37%, b*: 75.63%). This indicates that embedding-assisted microwave vacuum drying improves the light stability of the color of carrot powder.

[0161] In vitro simulated digestion:

[0162] After dissolving 1.1 g of KCl, 3.1 g of NaCl, 0.2 g of CaCl2 and 0.6 g of NaHCO3 in 950 ml of distilled water, 2.36 g of pepsin was added, and the pH was adjusted to 3 with 0.1 mol / L HCl solution and made up to 1000 mL to prepare simulated gastric juice. After dissolving 0.6 g of KCl, 5.4 g of NaCl and 0.2 g of CaCl2 in 950 ml of distilled water, the pH was adjusted to 7 with 0.1 mol / L NaOH solution, 6.4 g of pancreatin, 8.45 g of trypsin and 20 g of bile salts were added, and then the pH was adjusted to 7 with 0.1 mol / L NaOH solution and made up to 1000 ml to prepare simulated intestinal juice.

[0163] The whole digestion process of the in vitro simulated digestion experiment of carrot powder was carried out in the dark. Exactly 1 g of carrot powder was weighed and added to 20 mL of simulated gastric juice, and the pH was adjusted to 3.0, and it was digested in an oscillating water bath (37 °C, 120 rpm) for 2 h. Then, the pH of the solution was adjusted to 7.0 with 0.1 mol / L NaOH, 20 mL of simulated intestinal juice was added, and it was digested in an oscillating water bath (37 °C, 120 rpm) for 2 h. The products after gastric and intestinal simulated digestion were centrifuged (4 °C, 10000×g, 20 min), and the supernatant was collected. Both the undigested centrifuged liquid and the collected supernatant were freeze-dried, and the β-carotene content of the obtained powder was determined according to GB5009.83-2016. The β-carotene bioavailability in carrot powder was calculated according to formula (8).

[0164]

[0165] Wherein:

[0166] m1: The content of β - carotene in the undigested and uncentrifuged solution (μg / g);

[0167] m2: The content of β - carotene in the supernatant after centrifugation (μg / g).

[0168] Data statistics and analysis: The same as in Example 1.

[0169] Result discussion:

[0170] Effect of adding Tween - sodium alginate - ascorbic acid on assisting microwave vacuum drying on the β - carotene and bioavailability of carrot powder:

[0171] Diagram of the content of β - carotene and bioavailability in carrot powder Figure 6 As shown, where (a) is the content of β - carotene and (b) is the bioavailability of β - carotene. Compared with freeze - drying, the content of β - carotene in the sample prepared by microwave vacuum drying is lower, while there is no significant difference between the sample prepared by adding Tween - sodium alginate - ascorbic acid to assist microwave vacuum drying and the sample prepared by freeze - drying. Encapsulation can prevent β - carotene from being oxidized. Therefore, the content of β - carotene in the carrot powder prepared by encapsulation - assisted microwave vacuum drying is the highest.

[0172] The bioavailability of β - carotene in carrot powder was characterized by in vitro simulated digestion, and the results are as Figure 6 shown in (b). The bioavailability of β - carotene in the carrot powder prepared by freeze - drying and microwave vacuum drying is 28.81% and 29.20% respectively, while the bioavailability of β - carotene in the carrot powder obtained by encapsulation - assisted microwave vacuum drying reaches 48.84%, indicating that the encapsulation treatment significantly improves the bioavailability of β - carotene. This is attributed to the fact that the encapsulation treatment with sodium alginate and Tween improves the water - solubility of β - carotene, enabling it to dissolve better in the digestive fluid.

[0173] In summary, through orthogonal experiments, it is determined that the optimal color - protection scheme is the addition amount of Tween 0.20%, the addition amount of sodium alginate 0.10%, and the addition amount of ascorbic acid 0.08%. Compared with freeze - drying and microwave vacuum drying, the carrot β - carotene prepared by encapsulation - assisted microwave vacuum drying has the highest content, the highest bioavailability, and the color is closer to that of the carrot powder prepared by freeze - drying. In addition, the color of the carrot powder prepared by encapsulation - assisted microwave vacuum drying is more stable during storage.

[0174] Example 3: Application experiment of carrot powder in frozen cooked rice and noodle products

[0175] In order to explore the color stability of carrot powder in different application scenarios and its effect on the sensory properties of the products, this example selects frozen cooked rice and flour products (noodles, steamed buns, glutinous rice balls and rice cakes) prepared without adding carrot powder as a blank group, freeze-dried carrot powder as a control group, and carrot powder obtained by Tween-sodium alginate-ascorbic acid assisted microwave vacuum drying (i.e., a scheme with 0.20% Tween addition, 0.10% sodium alginate addition and 0.08% ascorbic acid addition) as an experimental group to observe the effects of carrot powder on frozen cooked rice and flour products and their visualized images, color, visible light reflectance, texture, moisture distribution and sensory evaluation during freeze-thaw cycles, thereby providing data support for the wide application of carrot powder.

[0176] 1. Experimental materials and equipment:

[0177] Wheat flour was purchased from Yihai Kerry Food Industry Co., Ltd.; water-milled glutinous rice flour and sticky rice flour were purchased from Xinxiang Liangrun Whole Grain Food Co., Ltd.; carrot powder was prepared in the laboratory; active dry yeast was purchased from Angel Yeast Co., Ltd.

[0178] 2. Experimental methods:

[0179] 1) Preparation of carrot powder cooked rice flour products

[0180] ① Preparation of noodles

[0181] Mix wheat flour and 5% carrot powder by weight and pour into a dough mixer. Gradually add pure water during the mixing process, the mass of which is 40% of the total mass of the mixed powder, and continue mixing for 5 minutes until the surface of the dough is uniform and smooth. Then wrap the dough with plastic wrap and proof it in a proofing box at a temperature of 25°C and a relative humidity of 75% for 20 minutes. Place the proofed dough on a noodle rolling machine and roll it 6 times until a dough sheet with uniform color and uniform thickness is obtained. Use a noodle cutter to cut the dough sheet with a 2mm aperture to obtain carrot powder noodles. Put these noodles into boiling water and cook them until the optimal cooking time, then take them out and cool them for later use.

[0182] ②Preparation of steamed bread and rice cake

[0183] Mix 1000 g of wheat flour and 50 g of carrot powder evenly to obtain a flour mixture. Activate 10 g of yeast with warm water at 36 °C and slowly add it to the above flour mixture. While stirring slowly, add 400 mL of pure water to the flour and continue stirring for 15 min. Wrap the dough with plastic wrap and place it in a proofing box. Ferment at 37 °C and a relative humidity of 80% for 40 min. Knead the fermented dough to expel gas as much as possible. Divide the dough into 50 g portions and make evenly sized hemispherical steamed bun embryos. Let the steamed bun embryos proof again in a fermentation box at 37 °C and a relative humidity of 85% for 20 min. After secondary fermentation, steam heat the steamed buns for about 20 min, and then cool them at room temperature for standby. Additionally, rice flour and glutinous rice flour can be mixed evenly in a ratio of 3:2 to replace wheat flour to prepare rice cakes.

[0184] ③ Preparation of Glutinous Rice Balls

[0185] Mix the glutinous rice flour evenly with 5% of its mass of carrot powder, and then add 80% of the pure water of the mass of the mixed powder and knead evenly. Then wrap the dough with plastic wrap and proof at 25 °C and a relative humidity of 85% for 20 min. Weigh 10 g of the dough and roll it into a ball by hand. Boil the processed glutinous rice balls in boiling water for 3 min, and cool for standby.

[0186] 2) Freeze - thaw treatment of carrot - powder - containing rice and wheat flour products

[0187] Conduct freeze - thaw cycle experiments on the obtained noodles, steamed buns, rice cakes and glutinous rice balls above. Put the cooled noodles, steamed buns, rice cakes and glutinous rice balls into self - sealing bags, freeze them at - 35 °C for 2 h, and then store them in a refrigerator at - 18 °C. During the frozen storage, freeze - thaw treatment is used to simulate temperature fluctuations. The samples are frozen at - 18 °C for 24 h, and then thawed at 4 °C for 12 h, regarded as a complete freeze - thaw cycle, and repeated for 5 cycles. After the corresponding number of freeze - thaw cycles, steam heat the steamed buns and rice cakes for 15 min, while boil the noodles and glutinous rice balls in boiling water for 90 s. After cooling, dry the surface moisture with absorbent paper for measurement.

[0188] 3. Performance testing:

[0189] 1) Color measurement of frozen - cooked rice and wheat flour products

[0190] Place the noodles, steamed buns, rice cakes and glutinous rice balls that have gone through the freeze - thaw steps above on a white board, and use a colorimeter to measure their color parameters L*, a* and b*. The results are shown in Table 11.

[0191] As shown in Table 11, the addition of carrot powder has an impact on the color of noodles. Compared with the blank group, the L* of the noodles in the control group and the experimental group decreased, while a* and b* increased. This is because the carotenoids contained in the carrot powder impart an orange-yellow tone to the noodles. On the other hand, the L*, a*, and b* of the experimental group were all greater than those of the control group, because there were differences in color between the carrot powder used in the control group (L* = 72.44, a* = 31.08, b* = 33.22) and the carrot powder used in the experimental group (L* = 74.49, a* = 29.94, b* = 34.31). However, although the a* of the carrot powder in the control group was larger than that of the carrot powder in the experimental group, the experimental group could maintain a relatively stable a* value during the preparation process, indicating that the carrot powder used in the experimental group had good color stability. Consistent with the results of Example 2, the addition of Tween-sodium alginate-ascorbic acid during the preparation of carrot powder can improve the thermal stability. After 5 freeze-thaw cycles, there was no obvious change in the color of the noodles in the blank group. Under the same freeze-thaw conditions, the L*, a*, and b* of the noodles in the control group decreased by 10.20%, 14.71%, and 10.85% respectively, which were higher than the reduction rates of L*, a*, and b* of the noodles in the experimental group (6.28%, 10.13%, and 7.32%). This indicates that the carrot powder prepared by adding Tween-sodium alginate-ascorbic acid assisted microwave vacuum drying can maintain color stability during the freeze-thaw cycle of noodles.

[0192] The impact of adding carrot powder on the color of frozen cooked steamed buns is shown in Table 11. Compared with the blank group, a* and b* of the control group increased to 26.49 and 51.83, while a* and b* of the experimental group increased to 31.15 and 55.33. This color difference is mainly because after being treated with Tween-sodium alginate-ascorbic acid, the carrot powder in the experimental group can maintain color stability during the preparation of steamed buns. After 5 freeze-thaw cycles, a* and b* of the steamed buns in the control group decreased by 18.38% and 6.69% respectively, which were both higher than the reduction rates of a* and b* of the steamed buns in the experimental group (12.55% and 5.78%). This indicates that the carrot powder prepared by adding Tween-sodium alginate-ascorbic acid assisted microwave vacuum drying can maintain color stability better during the freeze-thaw cycle of steamed bun products.

[0193] The effects of adding carrot powder on the color of frozen cooked glutinous rice balls are shown in Table 11. The L*, a*, and b* values of the blank group of glutinous rice balls are 82.30, -1.04, and 10.84, respectively. Compared with the blank group, the L* value of the glutinous rice balls in the control group and the experimental group decreased, while the a* and b* values increased, indicating that the glutinous rice balls prepared with added carrot powder showed bright orange-yellow color. Compared with the color of the control group, there was no significant difference in the L* and a* values of the glutinous rice balls in the experimental group, but the b* value increased significantly. This may be because β-carotene in the carrot powder prepared with Tween-sodium alginate-ascorbic acid was more easily dissolved in the glutinous rice balls. After 5 freeze-thaw cycles, the L*, a*, and b* values of the blank group of glutinous rice balls all increased. This may be because the water in the glutinous rice balls migrated to the surface during multiple freeze-thaw cycles, resulting in an increase in light reflectance. Under the same freeze-thaw conditions, the change rates of L*, a*, and b* values of the glutinous rice balls in the control group were 1.42%, 16.04%, and -8.66%, respectively, which were all higher than the change rates of L*, a*, and b* values of the glutinous rice balls in the experimental group (-4.50%, 7.86%, and -12.17%). This indicates that the carrot powder prepared by adding Tween-sodium alginate-ascorbic acid-assisted microwave vacuum drying can reduce the color fluctuation of glutinous rice balls during the freeze-thaw cycle.

[0194] The effects of adding carrot powder on the color of frozen cooked rice cakes are shown in Table 11. The L*, a*, and b* values of the blank group of rice cakes are 74.35, -1.44, and 10.99, respectively, while the L* values of the control group and the experimental group decreased, and the a* and b* values increased, indicating that adding carrot powder imparted an orange-yellow color to the rice cakes. After 5 freeze-thaw cycles, the L*, a*, and b* values of the control group of rice cakes decreased by 8.82%, 18.46%, and 13.38%, respectively, which were all higher than the change rates of L*, a*, and b* values of the rice cakes in the experimental group (3.23%, 11.65%, and 8.28%). This indicates that the carrot powder prepared by adding Tween-sodium alginate-ascorbic acid-assisted microwave vacuum drying can maintain color stability during the freeze-thaw cycle of rice cakes.

[0195] Table 11 Effects of carrot powder on the color of frozen cooked rice and noodle products

[0196]

[0197]

[0198] The effects of carrot powder on the visual images of frozen cooked rice and noodle products are as Figure 7 shown. Among them, blank group -0, control group -0, experimental group -0, blank group -5, control group -5, experimental group -5 represent the noodles, steamed buns, glutinous rice balls, and rice cakes of the blank group frozen 0 times, the control group frozen 0 times, the experimental group frozen 0 times, the blank group frozen 5 times, the control group frozen 5 times, and the experimental group frozen 5 times, respectively. The specific analysis is as follows:

[0199] In noodles, compared with the blank group, the noodles in the control group with added carrot powder showed orange-red color, while the noodles in the experimental group showed bright orange-yellow color, indicating that the carrot powder used in the experimental group could endow the noodles with a more acceptable color closer to that of carrots. After 5 freeze-thaw cycles, the brightness of the noodles in both the control group and the experimental group decreased, but the noodles in the experimental group still showed relatively bright orange-yellow color, indicating that the carrot powder used in the experimental group could maintain good color stability during the freeze-thaw cycle.

[0200] In steamed buns, compared with the blank group, the steamed buns in the control group showed dark orange-red color, while the steamed buns in the experimental group showed bright orange-yellow color. After 5 freeze-thaw cycles, the steamed buns in the control group showed dark yellow color, while the steamed buns in the experimental group still remained orange-yellow, indicating that the added carrot powder in the experimental group could better maintain a stable color during the freeze-thaw cycle.

[0201] Generally speaking, the appearance quality of glutinous rice balls is mainly evaluated by considering their formability, color, and surface smoothness. High-quality glutinous rice balls usually show a round and plump shape, and their color is mostly white or milky white. Compared with the glutinous rice balls in the blank group, the glutinous rice balls in both the control group and the experimental group showed translucent orange-yellow color. After 5 freeze-thaw cycles, the glutinous rice balls with added carrot powder in the experimental group were significantly brighter than those in the control group, indicating that the carrot powder in the experimental group could maintain color stability during the freeze-thaw cycle of glutinous rice balls.

[0202] Compared with the rice cakes in the blank group and the control group, the rice cakes with added carrot powder in the experimental group showed bright orange-yellow color with uniform color distribution. After 5 freeze-thaw cycles, the colors of the rice cakes all changed to some extent. However, compared with the control group, the rice cakes in the experimental group were more brightly colored and translucent, indicating that the carrot powder in the experimental group could maintain color stability during the preparation of rice cakes.

[0203] 2) Texture determination of frozen cooked rice and noodle products

[0204] Place the carrot powder-containing rice and noodle products after heating and cooling treatment in the center of the test platform, and use a P / 36R probe for determination. The pre-test speed is 1.0 mm / s, the test speed is 1.0 mm / s, the post-test speed is 1.0 mm / s, the trigger force is set at 5.0 g, and the strain is 30%.

[0205] As an important index reflecting food quality, texture characteristics are of great significance in the research on food processing and utilization. Therefore, this study determined the effect of adding carrot powder on the texture of frozen cooked rice and noodle products, and the results are shown in Table 12.

[0206] The texture of noodles is one of the important qualities for consumers' acceptance of products. Among them, the hardness, elasticity, cohesiveness, and adhesiveness of noodles are closely related to their structure and water content; chewiness is the energy required to simulate the stable state of chewing the sample by teeth in terms of sensory perception, and numerically it is the product of hardness, cohesiveness, and elasticity, which is mainly related to the protein characteristics in noodles. The effects of adding carrot powder on the texture of noodles are shown in Table 12. Compared with the noodles in the blank group, the hardness and chewiness of the control group and the experimental group increased, while there was no obvious effect on elasticity, cohesiveness, and adhesiveness. This indicates that the addition of carrot powder changed the texture characteristics of noodles, probably because the dietary fiber in carrot powder swelled after absorbing water and could fill in the gluten network, increasing the internal firmness and making the extensibility worse, thus resulting in an increase in hardness. During the freeze-thaw cycle, ice crystals are easily formed, which can lead to an increase in the content of damaged starch and the rupture of the gluten network structure, making the water-holding capacity of frozen cooked noodles worse and the migration of water into the noodles weaker, and the original hardness and elasticity of the noodles are damaged. Compared with the proportions of the decrease in hardness, elasticity, adhesiveness, and chewiness of the noodles in the control group and the blank group, which are (10.05%, 17.95%, 10.9%, 26.61%) respectively, the proportions of the decrease in hardness, elasticity, adhesiveness, and chewiness of the noodles in the experimental group are all smaller (9.94%, 8.97%, 9.06%, 17.74%), indicating that the carrot powder in the experimental group can reduce the change ratio of noodles during the freeze-thaw cycle. This may be because the interaction between the carrot powder, sodium alginate, starch, and gluten in the experimental group forms a complex with a stable structure, which helps to improve the freeze-thaw stability of frozen cooked noodles and thus resist the mechanical damage caused by ice crystals to the gluten network.

[0207] The elasticity and cohesiveness of steamed buns are positively correlated with their quality, while hardness, gumminess, and chewiness show a negative correlation. Compared with the blank group of steamed buns, the hardness, elasticity, and gumminess of the control group and experimental group of steamed buns decreased, showing better chewiness. This may be because the addition of carrot powder interacted with gluten proteins to form a more stable network structure. After freeze-thaw cycles, the hardness, cohesiveness, gumminess, and chewiness of the steamed buns increased, while the elasticity decreased. This may be because during the freeze-thaw cycles, the volume of the steamed buns shrank, the porosity decreased, and the gluten network lost its supporting force, resulting in a decrease in elasticity. After 5 freeze-thaw cycles, compared with the proportional changes in hardness, elasticity, gumminess, and chewiness of the blank group and the control group of steamed buns (24.17%, -7.53%, 10.45%, 14.83.61%, 6.13% and 21.67%, -4.87%, 7.79%, 31.10%, 24.61), the proportional changes in hardness, elasticity, cohesiveness, gumminess, and chewiness of the experimental group of steamed buns were all smaller (8.23%, 7.06%, 10.39%, 21.92, 12.54%). This indicates that the carrot powder in the experimental group can reduce the proportional changes of steamed buns during freeze-thaw cycles. This may be because the carrot powder in the experimental group can modify the ice crystal morphology, making the ice crystals smaller and more evenly distributed, thus making the texture of the steamed buns soft and delicate.

[0208] Hardness is usually used as an indicator of the overall texture properties and can effectively measure the comprehensive quality of glutinous rice balls. The effects of adding carrot powder on the texture properties of glutinous rice balls are shown in Table 12. Compared with the texture properties of the blank group of glutinous rice balls, the hardness of the control group and the experimental group of glutinous rice balls increased. This may be because the dietary fiber in carrot powder has good water-holding capacity. When it is compounded with glutinous rice flour to prepare glutinous rice balls, due to the interaction between dietary fiber and water, the binding ability of rice flour and water is weakened, resulting in an increase in the hardness of glutinous rice balls and a better taste. After 5 freeze-thaw cycles, compared with the proportional changes in hardness, elasticity, cohesiveness, gumminess, and chewiness of the blank group of glutinous rice balls (-29.02%, 20.62%, 2.41%, -29.02%, -1.54%), the proportional changes in hardness, elasticity, cohesiveness, gumminess, and chewiness of the experimental group of glutinous rice balls were all smaller (-25.60%, 10.34%, 0%, -25.62%, -12.21%). This indicates that adding carrot powder in the experimental group can reduce the change range of the texture properties of glutinous rice balls during freeze-thaw cycles. This may be because the hydrophilic hydroxyl groups in dietary fiber can interact with the starch of glutinous rice flour through hydrogen bonds to form a strong gel network structure.

[0209] As can be seen from Table 12, the addition of carrot powder will change the texture properties of rice cakes. Compared with the blank group, the hardness, adhesiveness, and chewiness of the control group and the experimental group decreased, while the elasticity and cohesiveness increased. Hydrogen bond cross-links are formed between the high content of amylose in rice flour, thus forming a certain gel structure. However, the addition of carrot powder may disrupt the original starch structure of rice flour and hinder the formation of a double helix structure of starch, resulting in a decrease in hardness, adhesiveness, and chewiness. After 5 freeze-thaw cycles, compared with the proportions of changes in the hardness, elasticity, adhesiveness, and chewiness of the blank group rice cakes (13.30%, -14.13%, -2.90%, -4.92%), the proportions of changes in the hardness, elasticity, cohesiveness, adhesiveness, and chewiness of the experimental group rice cakes were all smaller (7.04%, -11.46%, 7.05%, 5.22%), indicating that the addition of carrot powder in the experimental group can reduce the degree of texture change of rice cakes during the freeze-thaw cycle.

[0210] Table 12 Influence of Carrot Powder on the Texture of Frozen Cooked Rice and Flour Products

[0211]

[0212]

[0213]

[0214] 3) Low-field nuclear magnetic resonance

[0215] Transfer 2.0 g of carrot powder rice and flour products to a glass tube for low-field nuclear magnetic resonance testing. The test conditions are: temperature 32 °C, sampling interval (TW) 600 ms, echo time (TE) 3.0 ms, number of echoes (NECH) 1300, and number of scans (NS) 2.

[0216] 1.1 Influence of Carrot Powder on the Moisture Distribution of Frozen Cooked Rice and Flour Products

[0217] Moisture distribution is one of the most important factors determining the physical and chemical properties of foods, and changes in the state of water binding will affect the quality of frozen foods. Low-field nuclear magnetic resonance is a non-destructive and non-invasive spectroscopic technique that can be used to measure the moisture content and mobility in foods. Among them, T 22 (10 - 100 ms) and T 23 (100 - 10000 ms) represent the relaxation times of quasi-bound water and free water, and A 22 and A 23 represent the proportions of quasi-bound water and free water in the sample moisture. From Figure 8 (A - D), it can be seen that there are mainly two forms of moisture, quasi-bound water and free water, in rice and flour products. From Figure 8 (a - d), it can be seen that frozen cooked rice and flour products mainly exist in the form of quasi-bound water.Figure 8 A22 and A23 in it represent quasi-bound water and free water. Blank group - 0, control group - 0, experimental group - 0, blank group - 5, control group - 5, experimental group - 5 respectively represent noodles, steamed buns, glutinous rice balls, and rice cakes of the blank group frozen 0 times, the control group frozen 0 times, the experimental group frozen 0 times, the blank group frozen 5 times, the control group frozen 5 times, and the experimental group frozen 5 times.

[0218] In noodles, compared with the blank group, the free water in the noodles of the control group and the experimental group decreased, and the weakly bound water increased, indicating that carrot powder caused part of the free water to migrate to weakly bound water. This may be because carrot powder promoted the combination of water with gluten protein and starch, restricting the mobility of water. On the other hand, it may be because carrot powder has strong hydrophilicity and water-holding capacity, changing the distribution of water in the dough and making the water in the system combine more tightly with starch and gluten. Compared with the control group, the free water in the experimental group was less, which may be because sodium alginate in the carrot powder of the experimental group promoted the formation of the noodle gluten network and enhanced the water-binding ability of the noodles. After five freeze-thaw cycles, the content of free water in the blank group increased significantly. This may be because during the frozen storage process, the growth and recrystallization of ice crystals damaged the gluten protein network structure, resulting in part of the bound water bound by components being converted into free water, and the generation of more freezable water will also generate more ice crystals, causing more serious damage to the structure of frozen cooked noodles. Under the same freeze-thaw cycle, compared with the blank group noodles, the A of the control group and the experimental group 22 was higher, while the A 23 was lower, indicating that adding carrot powder can inhibit the conversion of quasi-bound water to free water during the freeze-thaw cycle. This may be because the hydrophilic groups of carrot powder itself can inhibit the free movement of water molecules. At the same time, dietary fiber and polysaccharides in carrot powder have more hydrogen bond binding sites, which can combine with proteins, starches, etc. in the dough to form a complex system, jointly intercepting water molecules, increasing the proportion of weakly bound water, and reducing the water mobility.

[0219] In steamed buns, compared with the blank group, the A of the control group and the experimental group 23 increased, indicating that adding carrot powder increased the content of free water in the steamed buns. This may be because adding carrot powder hindered the formation of the gluten network during the fermentation process of the dough. After five freeze-thaw cycles, the weakly bound water in the blank group steamed buns decreased and the free water increased, while the bound water in the control group and the experimental group increased and the free water decreased, indicating that adding carrot powder can prevent the conversion of weakly bound water to free water during the freeze-thaw cycle of steamed buns.

[0220] In tangyuan, compared with the blank group, the free water of the tangyuan in the control group and the experimental group decreased, while the weakly bound water increased, indicating that the addition of carrot powder significantly increased the integral peak area of bound water, enhancing the water stability of tangyuan during frozen storage. This is mainly because the dietary fiber in carrot powder has strong hydrophilicity and is more likely to combine with water molecules, resulting in enhanced water retention of cooked and frozen tangyuan. After five freeze-thaw cycles, compared with the blank group, the free water in the control group and the experimental group decreased, while the weakly bound water increased, indicating that the addition of carrot powder can promote the conversion of free water to weakly bound water in tangyuan. During the frozen storage of the product, the increase in weakly bound water will promote the formation of more ice crystals, damaging the internal structure of tangyuan and reducing the edible quality of the product.

[0221] In rice cakes, compared with the control group, the addition of rice cakes had no significant effect on the water distribution of tangyuan. After five freeze-thaw cycles, compared with the blank group, the free water in the control group and the experimental group decreased, while the weakly bound water increased, indicating that the addition of carrot powder can promote the conversion of free water to weakly bound water in rice cakes.

[0222] 4) Sensory evaluation

[0223] The sensory score table of carrot powder frozen cooked rice and noodle products is shown in Table 13.

[0224] Table 13 Sensory evaluation table of carrot frozen cooked rice and noodle products

[0225]

[0226] Sensory indicators are also important criteria for evaluating food quality. They can directly reflect consumers' preferences and recognition of products, thus further improving the quality evaluation system of frozen cooked rice and noodles. The influence of adding carrot powder on the sensory score of frozen cooked rice and noodle products is shown in Table 14.

[0227] According to Table 14, compared with the blank group of noodles, the sensory scores of the noodles in the experimental group and the control group both increased. This is because the addition of carrot powder gives the noodles a bright orange-yellow color, increases their elasticity, chewiness and taste, and also has the unique flavor of carrot powder. Compared with the blank group of noodles, the orange-yellow noodles are more popular. After five freeze-thaw cycles, all sensory indicators of the noodles showed a downward trend. The total sensory score of the blank group decreased by 21.01%, while the control group and the experimental group decreased by 19.35% and 17.28% respectively, indicating that the addition of carrot powder can reduce the degree of change in sensory indicators of noodles during the freeze-thaw cycle.

[0228] The sensory evaluation of steamed buns with added carrot powder is shown in Table 14. Compared with the blank group of steamed buns, the sensory scores of the steamed buns in the experimental group and the control group both increased. This is because the addition of carrot powder is beneficial for the steamed buns to form a plump and upright shape, promotes the uniform distribution of internal pores, gives the steamed buns good elasticity, a soft texture without sticking to the teeth, has a wheat fragrance and good rehydration. After 5 freeze-thaw cycles, all sensory indicators (color, texture, taste, flavor) of the steamed buns showed a downward trend, which may be due to the weakening of the protein network structure and the degradation of carotenoids during the freeze-thaw cycle. The sensory scores of the blank group and the control group decreased by 14.61% and 15.79% respectively, while the sensory score of the experimental group decreased by 13.09%. This indicates that adding carrot powder in the experimental group can reduce the degree of change in sensory indicators of steamed buns during the freeze-thaw cycle.

[0229] The sensory evaluation of glutinous rice balls with added carrot powder is shown in Table 14. The taste of glutinous rice balls is the most important condition for evaluating the quality of glutinous rice balls, and it is closely related to the acceptability of consumers. Glutinous rice balls with a higher sensory score should have a complete structure, smooth and shiny exterior, no strange smell, and have the unique fragrance of glutinous rice, be smooth and refreshing, have a delicate taste, be elastic and not sticky to the teeth.

[134] . Compared with the blank group of glutinous rice balls, the sensory scores of the glutinous rice balls in the experimental group and the control group both increased. This is because the carrot powder gives the glutinous rice balls a translucent orange-yellow color, and the addition of carrot powder also reduces the cohesiveness of the glutinous rice balls, making them refreshing and not sticky to the teeth, thus having a better sensory experience. During the freeze-thaw cycle, the internal ice crystals of the glutinous rice balls will experience repeated freezing and thawing and recrystallization, resulting in the destruction of the internal structure of the glutinous rice balls.

[115] . After 5 freeze-thaw cycles, the sensory scores of the blank group and the control group decreased by 20.78% and 22.80% respectively, while the sensory score of the experimental group decreased by 18.05%. This indicates that the carrot powder in the experimental group can reduce the degree of change in sensory indicators of glutinous rice balls during the freeze-thaw cycle because the addition of carrot powder improves the water retention of glutinous rice balls. Adding carrot powder to glutinous rice balls can reduce the loss of moisture during processing and storage, and avoid quality problems such as dry shrinkage and cracking of glutinous rice balls.

[0230] The influence of added carrot powder on the sensory evaluation of rice cakes is shown in Table 14. Compared with the blank group, the sensory scores of the control group and the experimental group both increased. This indicates that the rice cakes prepared with 5% added carrot powder are orange-yellow in color, have a uniform color, are moderately hard and soft, are fragrant, glutinous, soft and refreshing, have a delicate texture, and have a pure and strong aroma of carrots, with an overall good flavor, meeting the taste of the general public. After 5 freeze-thaw cycles, the sensory scores of the blank group and the control group decreased by 28.99% and 23.47% respectively, while the sensory score of the experimental group decreased by 16.34%. This indicates that adding carrot powder can reduce the degree of change in sensory indicators of rice cakes during the freeze-thaw cycle.

[0231] Table 14 Influence of freeze-thaw cycle on the sensory evaluation of carrot powder frozen cooked rice and noodle products

[0232]

[0233]

[0234] In this study, wheat flour and rice flour were used as the main raw materials, and carrot powder prepared by Tween-sodium alginate-ascorbic acid assisted microwave vacuum drying was added to prepare frozen cooked rice and noodle products (noodles, steamed buns, glutinous rice balls and rice cakes). By observing the color changes of rice and noodle products during the preparation and freeze-thaw cycle, it was found that the added carrot powder in the experimental group could maintain its stable orange-yellow color. Through the texture analysis of rice and noodle products, it was concluded that adding carrot powder could reduce the texture changes of rice and noodle products during the freeze-thaw cycle. The results of moisture distribution showed that adding carrot powder could inhibit the conversion of weakly bound water to free water during the freeze-thaw cycle of rice and noodle products. Through texture analysis, it was found that adding carrot powder could effectively slow down the texture changes of rice and noodle products during the freeze-thaw cycle. Therefore, applying the carrot powder prepared by Tween-sodium alginate-ascorbic acid assisted microwave vacuum drying to frozen cooked rice and noodle products can ensure their color and color stability during the freeze-thaw cycle, improve the product quality, enhance the flavor of rice and noodle products, and provide data support for the wide application of carrot powder.

[0235] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principle and spirit of the present invention.

Claims

1. A method for preparing carrot powder, characterized in that, The method is as follows: (1) Raw material pretreatment: Cut the peeled fresh carrots into uniform small pieces with specifications of (4±1 cm)×(1±0.2 cm)×(1±0.2) cm; (2) Blanching treatment: Blanch the small carrot pieces in boiling water for 3±1 min, and then quickly cool them with crushed ice immediately; (3) Cell wall breaking treatment: Add the cooled carrot pieces to the compound protective liquid according to the mass-volume ratio of 200 g:40 mL. The compound protective liquid is prepared from sodium alginate, Tween, and ascorbic acid according to the mass ratio of 0.2:0.1:0.08, and perform cell wall breaking treatment at 27000 r / min for 4 - 8.0 min; (4) Microwave vacuum drying: Spread the carrot slurry after cell wall breaking treatment evenly on the drying tray, and perform segmented drying using a multi-stage drying process: The first stage is drying at 1000 W for 50 min; the second stage is drying at 500 W for 50 min; the third stage is standing still at 0 W for 10 min; the fourth stage is drying at 300 W for 100 min; (5) Crushing and sieving: Crush the dried product with a cyclone sample mill and sieve it through a 40-mesh sieve to obtain the finished carrot powder.

2. The preparation method according to claim 1, characterized in that, During the microwave vacuum drying process, the vacuum degree is maintained at -0.08~-0.1 MPa.

3. Use of the carrot powder prepared by the preparation method according to any one of claims 1 - 2 for frozen cooked rice and flour products.

4. The use according to claim 3, wherein The frozen cooked rice and flour products refer to noodles, steamed buns, rice cakes, and glutinous rice balls.

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