A preparation method of butterfly pea flower anthocyanin colorant for flour-based foods

Abstract

The invention discloses a preparation method of a butterfly pea anthocyanidin colorant for flour-based foods, including S1: butterfly pea flower drying, crushing, and sieving; S2: butterfly pea flower powder is mixed with an ethanol aqueous solution, ultrasonic-assisted extraction is adopted, and the filtrate is collected by filtration; S3: after adding metal ions to the filtrate, vacuum rotary evaporation is concentrated to obtain a concentrated solution; S4: β-cyclodextrin is dissolved in water, the concentrated solution is added to the β-cyclodextrin aqueous solution, ultrasonicated, and prepared into anthocyanidin colorant through low-temperature spray drying. After adding an appropriate amount of metal ions to the butterfly pea anthocyanidin of the present invention, it is concentrated, and then β-cyclodextrin and anthocyanidin concentrated solution are used to embed an embedded material with "hydrophilic outer wall and hydrophobic inner cavity". The prepared anthocyanidin colorant can be mixed with flour for use, and has a good coloring effect, especially can improve the stability of the color of steamed buns, solves the technical problem that only anthocyanidin is added in the traditional steamed bun process, and anthocyanidin is unstable and the color of steamed buns is not good.

Description

Technical Field

[0001] The present invention relates to the technical field of food, and in particular to a method for preparing a butterfly pea flower anthocyanin colorant for flour-based foods. Background Art

[0002] Butterfly pea (Clitopea) belongs to the genus Clitoria in the family Leguminosae. Its numerous blue flowers have been the subject of numerous studies on the extraction of anthocyanins from butterfly pea flowers. Anthocyanins, a flavonoid in the phenolic family, possess numerous health benefits, including antioxidant, anti-cancer, anti-inflammatory, anti-aging, anti-obesity, improved brain function, and vision protection. Therefore, they hold broad application prospects in the food, pharmaceutical, and cosmetic sectors. However, anthocyanins are inherently unstable and easily affected by environmental factors, such as light, temperature, pH, metal ions, and oxidants, resulting in limited application.

[0003] Currently, in the application of butterfly pea anthocyanidins, when used in the production of bread, the anthocyanidins can maintain a good color. However, when used in the production of steamed buns, the anthocyanidins fade seriously. Therefore, in the production of pasta, how to improve its stability to ensure the color of the product is particularly important. Summary of the Invention

[0004] The invention overcomes the technical problem in the prior art that, when butterfly pea anthocyanin is used as a colorant in the production of steamed buns and other pasta, the anthocyanin is unstable and the product fades seriously, and provides a method for preparing a butterfly pea anthocyanin colorant for flour-based foods.

[0005] A method for preparing a butterfly pea flower anthocyanin colorant for flour-based foods, comprising the following steps:

[0006] S1: drying freshly picked butterfly pea flowers in a 40-50° C. forced air drying oven for 15-20 h, crushing and sieving;

[0007] S2: According to the material-liquid ratio of 1g:85-130ml, the butterfly pea flower powder was mixed with 50-80w% ethanol aqueous solution, and ultrasonic-assisted extraction was performed at 50-60°C for 10-40min. The mixture was filtered through a double-layer filter cloth and vacuum filtered to obtain the butterfly pea anthocyanin extract;

[0008] S3: adding one or both of 0.01-0.05 wt % zinc citrate and 1-3 wt % sodium chloride to the extract, and concentrating the extract by rotary evaporation under reduced pressure until the volume of the extract is reduced by more than half to obtain a concentrated solution;

[0009] S4: dissolving β-cyclodextrin in water at a ratio of 1 g: 5-8 ml, adding the concentrated solution to the β-cyclodextrin aqueous solution at a mass ratio of 1:1-10, ultrasonically treating the solution and spray drying the solution at low temperature to prepare an anthocyanin colorant.

[0010] Furthermore, in S3, the temperature of the vacuum rotary evaporation and concentration is 40-60° C., and the pressure of the vacuum rotary evaporation and concentration is 7-8 kPa.

[0011] Furthermore, in S2, the power of the ultrasonic extraction is 600-700W;

[0012] Furthermore, in S4, the ultrasonic treatment has an ultrasonic power of 200-300 W, an ultrasonic time of 5-15 min, and an ultrasonic temperature of 50-60°C.

[0013] Furthermore, in S4, the inlet air temperature of the low-temperature spray drying is 50-60°C, the outlet air temperature is 10°C lower than the inlet air temperature, the feed flow rate is 30-35 r / min, and the fan frequency is 80-100 Hz.

[0014] The present invention also aims to protect the anthocyanin colorant prepared by the above-mentioned preparation method of butterfly pea flower anthocyanin colorant for flour-based foods.

[0015] Furthermore, the flour-based foods include but are not limited to bread, buns, dumplings, and wontons.

[0016] The present invention also aims to protect a method for applying the butterfly pea flower anthocyanin colorant, which comprises adding the anthocyanin colorant to flour in an amount of 4-5wt% and mixing the colorant.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] When the inventor carried out applied research on butterfly pea anthocyanidin, it was found that anthocyanidin was used for the making of bread, and color was purple-blue, and color was bright. When butterfly pea anthocyanidin was applied to the making of steamed buns, anthocyanidin loss was serious, and steamed buns were seriously faded. Therefore, the inventor studied this phenomenon, and believed that steamed buns and bread were equally flour fermented products. The difference was that the heating mode was different. Bread was prepared through baking, and steamed buns were obtained through steaming. The moisture content of steamed buns was much higher than that of bread. Therefore, the inventor believed that under high temperature conditions, moisture content was one of the factors affecting the stability of anthocyanidin. For this reason, the inventor carried out many-sided stability study on anthocyanidin, and found that different metal ions had varying degrees of influence on butterfly pea anthocyanidin, and high concentrations of zinc ions and sodium ions not only had color enhancement effects, but also could improve the stability of anthocyanidin. Although zinc is a food nutrient fortifier, there are certain limit standards for zinc when added to food as a food nutrient fortifier. Therefore, the stability problem of butterfly pea anthocyanin cannot be solved by adding high concentrations of zinc. Although there is no specific limit requirement for sodium ions, when adding too much sodium ions to yeast-fermented pasta such as bread and buns, it will affect the fermentation of yeast. Therefore, the addition of zinc ions and sodium ions should not be excessive. In this regard, the inventors added an appropriate amount of zinc citrate and sodium chloride to the butterfly pea anthocyanin obtained by low-temperature alcohol extraction and concentrated it, and then used β-cyclodextrin and anthocyanin concentrate to embed it to form an embedding material with "hydrophilic outer wall and hydrophobic inner cavity". On the one hand, β-cyclodextrin can not only isolate anthocyanin from water, but also reduce the effect of moisture on anthocyanin when applied to flour products, especially when steaming buns. At the same time, β-cyclodextrin can wrap anthocyanin and zinc and sodium metal ions, ensuring that anthocyanin is in a high concentration of zinc and sodium environment, and effectively avoiding the dispersion of zinc, sodium ions and anthocyanin when mixed with flour, resulting in low concentrations of zinc and sodium ions and the inability to increase color and improve the stability of anthocyanin. At the same time, β-cyclodextrin can wrap anthocyanin in a dark environment, which can avoid the influence of light on anthocyanin and further improve the stability of anthocyanin. The anthocyanin colorant prepared by the invention can be mixed with flour for use, has good coloring effect, and can especially improve the color stability of steamed buns, thereby solving the technical problem that in the traditional steamed bun making process, only anthocyanin is added, but the anthocyanin is unstable and the color of the steamed buns is poor. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a comparison chart of the effects of different metal ions on the stability of butterfly pea anthocyanin;

[0020] Figure 2 This is a comparison chart of the effects of different light conditions on the stability of butterfly pea anthocyanins;

[0021] Figure 3 This is a comparison chart of the effects of different pH values on the stability of butterfly pea anthocyanin; DETAILED DESCRIPTION

[0022] The present invention will be further described below in conjunction with examples and tests.

[0023] Example 1

[0024] A method for preparing a butterfly pea flower anthocyanin colorant for flour-based foods, comprising the following steps:

[0025] S1: freshly picked butterfly pea flowers were placed in a 50°C forced air drying oven and dried for 15 h, crushed and sieved before use;

[0026] S2: According to the material-liquid ratio of 1g:130ml, butterfly pea flower powder was mixed with 50w% ethanol aqueous solution, and ultrasonic-assisted extraction was performed at 60°C for 10min. The mixture was filtered through a double-layer filter cloth and vacuum-filtered to obtain butterfly pea anthocyanin extract; the power of the ultrasonic extraction was 700W;

[0027] S3: adding 0.01 wt% zinc citrate and 1 wt% sodium chloride to the extract, and concentrating the extract by vacuum rotary evaporation until the volume of the extract is reduced by half to obtain a concentrated solution; the vacuum rotary evaporation temperature and the vacuum rotary evaporation pressure are 40° C. and 8 kPa, respectively;

[0028] S4: β-cyclodextrin is dissolved in water at a ratio of 1 g:5 ml, the concentrate is added to the β-cyclodextrin aqueous solution at a mass ratio of 1:10, and ultrasonic treatment is performed with an ultrasonic power of 200 W and an ultrasonic temperature of 60°C for 5 minutes, followed by low-temperature spray drying to prepare an anthocyanin colorant; the inlet air temperature of the low-temperature spray drying is 60°C, the outlet air temperature is 10°C lower than the inlet air temperature, the feed flow rate is 30 r / min, and the fan frequency is 100 Hz.

[0029] Example 2

[0030] S1: freshly picked butterfly pea flowers were placed in a 40° C. forced air drying oven and dried for 20 h. After crushing and screening, they were sealed in a glass container and stored in the dark for 45 days to proceed to the following S2 step;

[0031] S2: According to the material-liquid ratio of 1g:85ml, butterfly pea flower powder was mixed with 80w% ethanol aqueous solution, and ultrasonic-assisted extraction was performed at 50°C for 40min. The mixture was filtered through a double-layer filter cloth and vacuum-filtered to obtain butterfly pea anthocyanin extract; the power of the ultrasonic extraction was 600W;

[0032] S3: After adding 0.05 wt % zinc citrate to the extract, vacuum rotary evaporation was performed until the volume of the extract was reduced by two-thirds to obtain a concentrated solution; the vacuum rotary evaporation temperature was 60° C. and the vacuum rotary evaporation pressure was 7 kPa;

[0033] S4: β-cyclodextrin is dissolved in water at a ratio of 1 g:8 ml, the concentrate is added to the β-cyclodextrin aqueous solution at a mass ratio of 1:1 between the β-cyclodextrin aqueous solution and the concentrate, and an anthocyanin colorant is prepared by ultrasonic treatment at an ultrasonic power of 300 W and an ultrasonic temperature of 50°C for 15 minutes, followed by low-temperature spray drying; the inlet air temperature of the low-temperature spray drying is 50°C, the outlet air temperature is 10°C lower than the inlet air temperature, the feed flow rate is 35 r / min, and the fan frequency is 80 Hz.

[0034] Example 3

[0035] S1: freshly picked butterfly pea flowers are placed in a 45° C. air drying oven and dried for 18 h, crushed and sieved, and then used; the butterfly pea flowers are directly subjected to the preparation processes of S1-S3 after being crushed and sieved, or the preparation processes of S1-S3 are carried out within 45 days after being sealed and stored in a non-metallic container away from light;

[0036] S2: According to the material-liquid ratio of 1g:100ml, butterfly pea flower powder was mixed with 60w% ethanol aqueous solution, and ultrasonic-assisted extraction was performed at 55°C for 20min. The mixture was filtered through a double-layer filter cloth and vacuum-filtered to obtain butterfly pea anthocyanin extract; the power of the ultrasonic extraction was 650W;

[0037] S3: After adding 3 wt % sodium chloride to the extract, vacuum rotary evaporation and concentration were carried out until the volume of the extract was reduced by three-fifths to a concentrated solution; the vacuum rotary evaporation and concentration temperature was 50° C., and the vacuum rotary evaporation and concentration pressure was 8 kPa;

[0038] S4: Dissolve β-cyclodextrin in water at a ratio of 1 g:6 ml, add the concentrated solution to the β-cyclodextrin aqueous solution at a mass ratio of 1:8, and perform ultrasonic treatment at an ultrasonic power of 280 W and an ultrasonic temperature of 55° C. for 10 minutes, followed by low-temperature spray drying to prepare an anthocyanin colorant; the low-temperature spray drying has an inlet air temperature of 55° C., an outlet air temperature 10° C. lower than the inlet air temperature, a feed flow rate of 32 r / min, and a fan frequency of 90 Hz.

[0039] Example 4

[0040] The application of the anthocyanin colorant prepared in Example 1 is applied in the production of bread in this example. The method for making bread is as follows: 280g high-gluten flour, 3g high-activity Angel yeast, 40g white sugar, 15g anthocyanin colorant prepared in Example 1, 2g edible salt, and 20g milk powder are added to a bowl and mixed evenly. An egg is added and 110g water is added. After kneading into a smooth dough by hand, 20g softened butter is added. The dough is kneaded, rubbed, thrown, and stretched until it can be kneaded. After expanding into a film state, transfer it to a container and ferment it to 2.5 times its original size. Knead the dough evenly to release the air and divide it into three equal parts. Cover with plastic wrap and relax for 20 minutes. Take a dough, knead it evenly and roll it into a long tongue shape with a length of about 30 cm. Gently roll it up from one end until it is completely rolled up, and place the edges underneath. Roll out the remaining dough, roll it up and place it in a toast box. Ferment it again until the toast box is 80% to 90% full. Preheat the oven to 200 degrees, place the toast box in the lower layer of the oven, and bake for 40 minutes to get toast.

[0041] Example 5

[0042] The application of the anthocyanin colorant prepared in Example 2 is applied in the production of steamed buns in this example. The production method of the steamed buns is as follows: 30 g of the anthocyanin colorant prepared in Example 2 is added to 500 g of all-purpose flour and stirred evenly. First, 5 g of highly active Angel Yeast and a spoonful of white sugar are dissolved in 250 g of 38°C warm water to form yeast water. The yeast water is poured into the stirred all-purpose flour in batches and kneaded until the dough is smooth and does not stick to the hands or the bowl. After fermentation to 1.5-2 times its size, the dough is taken out and continued to be kneaded to exhaust. After exhaustion, it is divided into equal amounts of 50 g small doughs, rolled into thin skins, and then filled with fillings. The dough is placed in a steamer and then placed in a pot filled with water without turning on the fire for secondary fermentation for 15 minutes. After the steamed buns become larger, they are steamed in cold water for 15 minutes on the fire. After turning off the fire, the steamed buns are obtained by simmering for 3 minutes.

[0043] Example 6

[0044] The anthocyanin colorant prepared in Example 3 is used in the production of steamed buns. The production method of the steamed buns is as follows: 30 g of the anthocyanin colorant prepared in Example 3 is added to 500 g of all-purpose flour and stirred evenly. First, 5 g of highly active Angel Yeast and 40 g of white sugar are dissolved in 250 g of 38°C warm water to form yeast water. The yeast water is poured into the stirred all-purpose flour in batches and kneaded until the dough is smooth and does not stick to the hands or the bowl. Then, the dough is kneaded outward into long round strips, cut into uniform small pieces with a knife, and gently shaped into square pieces with both hands. The pieces are placed in a steamer and then placed in a pot filled with water and fermented without turning on the heat for 40 minutes. The pieces are then steamed with cold water on a heat for 15 minutes. After turning off the heat, the steamed buns are obtained by simmering for 3 minutes.

[0045] Control group 1

[0046] The filtrate obtained in S2 of Example 1 was used as a colorant to make bread. The production method was as follows: 280 g of high-gluten flour, 3 g of highly active Angel yeast, 40 g of sugar, 2 g of table salt, and 20 g of milk powder were added to a bowl and mixed evenly. An egg was added, and 110 g of water and 15 ml of the filtrate obtained in S2 of Example 1 were added. The dough was kneaded into a smooth dough by hand, and then toast was prepared according to the production method of Example 4.

[0047] Control group 2

[0048] Control group 2 was used for the preparation of steamed buns. The anthocyanin used in control group 2 was the concentrated solution prepared by S3 in Example 1.

[0049] The method for making the steamed buns is as follows: first, dissolve 5g of highly active Angel Yeast and a spoonful of white sugar in 250g of 38°C warm water to make yeast water; then, pour the yeast water into the stirred all-purpose flour in batches; and then add 20ml of the concentrate prepared in S3 of Example 1. The mixture is stirred and kneaded until the dough is smooth and does not stick to the hands or the bowl. After fermentation to 1.5-2 times its original size, the dough is removed and further kneaded to release the air. After release, the dough is divided into equal portions of 50g small doughs, rolled into thin wrappers, and then filled with fillings. The dough is placed in a steamer and then placed in a pot of water without turning on the heat for a secondary fermentation of 15 minutes. After the buns have grown in size, they are steamed in cold water for 15 minutes, then turned off the heat and simmered for 3 minutes to obtain the steamed buns.

[0050] Control group 3

[0051] Control group 3 is a method for making steamed buns. The method of this control group is basically the same as that of Example 5, except that the anthocyanin used in control group 3 is prepared by the following method:

[0052] S1: removing the stamens, calyx and pedicel of butterfly pea flowers, drying the flowers, crushing them and sieving them;

[0053] S2: According to the material-liquid ratio of 1g:100ml, butterfly pea flower powder was mixed with 60w% ethanol aqueous solution, and ultrasonic-assisted extraction was performed at 55°C for 20min. The mixture was filtered through a double-layer filter cloth and vacuum-filtered to obtain butterfly pea anthocyanin extract; the power of the ultrasonic extraction was 650W;

[0054] S3: Concentrating the filtrate by vacuum rotary evaporation until the volume of the filtrate is reduced by half to obtain a concentrated solution; the vacuum rotary evaporation concentration temperature is 60° C. and the vacuum rotary evaporation concentration pressure is 8 kPa;

[0055] S4: dissolving β-cyclodextrin in water at a ratio of 1 g:8 ml, adding the concentrated solution to the β-cyclodextrin aqueous solution at a mass ratio of 1:10, using an ultrasonic power of 200-300 W, at an ultrasonic temperature of 60° C., ultrasonic treatment for 15 minutes, and then low-temperature spray drying to prepare an anthocyanin colorant; the conditions for low-temperature spray drying are: an inlet air temperature of 60° C., an outlet air temperature 10° C. lower than the inlet air temperature, a feed flow rate of 35 r / min, and a fan frequency of 100 Hz.

[0056] Control group 4

[0057] Control group 4 is for making steamed buns, and its preparation method is basically the same as that of Example 5, except that chitosan is used in place of β-cyclodextrin in Example 5.

[0058] Control group 5

[0059] Control group 5 is for making steamed buns, and its preparation method is basically the same as that of Example 5, except that control group 5 uses gum arabic and whey protein isolate with a mass ratio of 3:1 instead of β-cyclodextrin in Example 5.

[0060] (1) In order to explore the reasons why butterfly pea anthocyanidins fade when used in the production of steamed buns and to find a method to improve the stability of anthocyanidins, the inventors conducted the following experimental studies:

[0061] Materials: The butterfly pea flowers were picked from the flower garden of the Guangxi Subtropical Crops Research Institute from August to September 2022. They were double-petal butterfly pea flowers with good growth and shape.

[0062] method:

[0063] Extraction of butterfly pea anthocyanins: Place the butterfly pea flowers in a 50℃ forced air drying oven and dry them for 16 hours, crush and sieve them, seal them and store them in a desiccator away from light, add 50% ethanol according to a material-liquid ratio of 1:100, place them in 50℃ for ultrasonic extraction for 30 minutes, the ultrasonic power is 600W, filter them with double-layer filter cloth, and vacuum filter them to obtain the butterfly pea anthocyanin extract for later use.

[0064] Experimental Design 1: Prepare 0.1 mol / L Mg 2+ 、Cu 2+ 、Zn 2+ , Ca 2+ 、Al 3+ 、Na +、 、Fe 2+ 、Fe 3+ The solutions were added to butterfly pea anthocyanin extract respectively, placed in the dark at room temperature (22° C.) for 24 h, and UV-visible absorption spectrum scanning was performed in the range of 400-700 nm.

[0065] The results can be found in Figure 1 Since the 2-phenylbenzopyran cation structure of anthocyanidin has high reactivity due to the lack of electrons, and multiple hydroxyl groups are connected to the parent nucleus, it is unstable. The specific manifestation of the change in stability is the change in its color. Figure 1 It can be seen that at a concentration of 0.1 mol / L, Mg 2+ , Ca 2+ 、Na + 、Zn 2+ and Fe 2+ The trend of the effect on the absorbance of butterfly pea anthocyanin was similar to that of the control, indicating that Mg 2+ , Ca 2+ 、Na + 、Zn 2+ and Fe 2+ It can complex with butterfly pea anthocyanin molecules to increase its stability; and Fe 3+ 、Al 3+ and Cu 2+ The effect on the absorbance of butterfly pea anthocyanin was significantly different from that of the control, and the original blue butterfly pea anthocyanin solution was added with Fe 3+ Then it turns reddish brown and adds Al 3+ Then it turns purple-red and Cu is added 2+ Then it turns blue-green, indicating that butterfly pea anthocyanin is in Fe 3+ 、Al 3+ and Cu 2+ It is unstable under certain conditions, so during the processing and packaging of butterfly pea anthocyanin, it should be avoided from contact with iron, aluminum and copper products. When using butterfly pea anthocyanin, it can be used in combination with magnesium ions, sodium ions, calcium ions and zinc ions.

[0066] Experimental Design 2: Based on the results of Experimental Design 1, 0.25 mol / L, 0.5 mol / L, 0.75 mol / L, 0.1 mol / L and 1.25 mol / L of Zn were prepared. 2+ and Na + The solution was added to butterfly pea anthocyanin extract, and anthocyanin solution without metal ions was used as control. The solution was placed in the dark at room temperature (22 ° C) for 24 h at λmax and λ 700nm The absorbance values were measured at different locations to compare the effects of different metal ions on butterfly pea anthocyanins (expressed by △A, △A=A λmax -A λ700nm ).

[0067] The results are shown in Table 1 below.

[0068] Table 1

[0069]

[0070]

[0071] As shown in Table 1, after adding metal ions to the butterfly pea anthocyanin solution, the △A of the anthocyanin solution showed an upward trend with the increase of sodium ion and zinc ion concentrations, and the higher the concentration, the more obvious the increase. When the concentration exceeded 0.1 mol / L, the △A value was greater than that of the control, indicating that sodium ions and zinc ions can improve the stability of anthocyanins at a certain concentration.

[0072] Experimental Design 3:

[0073] After diluting butterfly pea anthocyanin extract 20 times, it was placed in three different lighting environments: dark environment, indoor natural light (200 lux) and 15000 lux light for 12 hours and dark for 12 hours, and stored for 45 days. The absorbance was measured at a certain wavelength and recorded as A0; samples were taken for monitoring at regular intervals, and the absorbance was measured and recorded as A1. There were 3 replicates in each group, and the preservation rate was calculated.

[0074] Retention rate (%) = ΔA1 / ΔA0 × 100 (1)

[0075] In the formula: ΔA=A 620nm -A 700nm

[0076] The results can be found in Figure 2 ,Depend on Figure 2 It can be seen that the stability of butterfly pea anthocyanins decreases with the extension of storage time. Different lighting conditions have different effects on the stability of butterfly pea anthocyanins. The effect of placing it in a dark environment for 45 days is small. The preservation rate is still above 90% at the 10th day, and the preservation rate is 88.45% at the 45th day. This shows that butterfly pea anthocyanins degrade relatively slowly in a dark environment and can be used as a long-term storage method. The effect of placing it in indoor natural light (April-May, 200 lux) for 30 days is small (the preservation rate is above 86%), but the preservation rate is 66.75% at the 45th day, indicating that butterfly pea anthocyanins can be stored for a period of time under indoor natural light. The treatment of 15000 lux light for 12 hours and dark for 12 hours has a greater effect on butterfly pea anthocyanins, accelerating the degradation rate. The preservation rate is 74.07% at the 10th day, and the retention rate is only 43.07% at the 45th day. Therefore, light has a great influence on butterfly pea anthocyanins and they should be kept away from light during storage. Therefore, the present invention adopts beta-cyclodextrin to embed anthocyanidin, can be wrapped in a dark environment by anthocyanidin, therefore can improve the stability of anthocyanidin.Based on this experiment, it can also be seen that in the preparation of butterfly pea anthocyanidin powder, fresh butterfly pea flower and dried powder should preferably be adopted to seal and keep in dark for 45 days after sieving.

[0077] Experimental Design 4:

[0078] The pH value of the butterfly pea anthocyanin extract was adjusted to 1.0, 3.0, 5.0, 7.0, 9.0, 11.0 and 13.0 using 1 mol / L HCl solution and 1 mol / L NaOH solution, and the volume was fixed to 50 ml with deionized water. Each treatment was repeated 3 times. After storing in the dark for 3 h, the UV-visible absorption spectrum was scanned in the range of 400-700 nm.

[0079] Its Figure 3 As shown. Figure 3 It can be seen that when the pH value is 1, the butterfly pea anthocyanin has a maximum absorption peak at 546nm. When the pH value is 3, the color of the solution changes from red to purple, and the absorption peak shows a significant color shift, splitting into two peaks at 568nm and 619nm, and a shoulder peak at 532nm. At pH values of 5 and 7, the solution is blue, and the absorption peaks at 573nm and 619nm increase slightly with increasing pH. At pH 9, another color shift occurs, with a maximum absorption peak at 623nm, and the solution is green. At pH values of 11 and 13, the absorption spectrum characteristics are significantly different from those at other pH values. The absorbance between 400nm and 450nm gradually decreases with increasing wavelength, and the solution also changes from dark green to yellow. For a substance to produce pure blue, the absorbance should be relatively high at a wavelength of around 580-620nm. From the absorption spectrum, butterfly pea anthocyanin has a high absorbance in the range of 580-620nm at pH values of 5 and 7, and the corresponding solution color is blue. At a pH of 9, the absorption peak at 573nm disappears, and the absorption peak near 620nm and the absorbance near 400-450nm make the solution green (green can be obtained by adding yellow to blue). Therefore, pH-dependent structural transformation may lead to color change, and butterfly pea anthocyanin appears blue-green in the range of pH 5-7. Scanning diagrams of different pH values show that butterfly pea anthocyanin is more stable in the range of acidic and neutral (pH 3.0-9.0), and the pH value of flour after yeast fermentation can meet the range of 3-9. Therefore, the stability of anthocyanin is high.

[0080] (2) In order to verify the stabilizing effect of anthocyanin colorants of the present invention when applied to bread and buns, the inventors referred to the evaluation method of "Food Sensory Evaluation" and had 10 trained tasters conduct sensory evaluations on the exterior and interior (observation of the cross-section after cutting) of the foods of Examples 4 to 6 and Control Groups 1 to 5 according to the standards in Table 2 below. The average score was taken. The results are shown in Table 3 below:

[0081] Table 2

[0082]

[0083]

[0084] Table 3

[0085] Experimental group external internal Example 4 18.3 18.6 Example 5 17.4 17.6 Example 6 17.0 17.9 Control group 1 16.1 16.5 Control group 2 7.4 7.1 Control group 3 12.3 13.2 Control group 4 8.2 8.6 Control group 5 9.3 9.6

[0086] As shown in Tables 2 and 3, the butterfly pea anthocyanidin colorant prepared by the present invention has a good color effect on bread, steamed buns and dumplings. As shown in Example 4 compared with Control Group 1, when making bread, the preparation process of anthocyanidin has little effect on the stability of butterfly pea flower, and the color is also good. As shown in Example 5 compared with Control Group 2, the butterfly pea anthocyanidin without protective treatment has poor stability and will seriously lose color when making dumplings. As shown in Example 5 compared with Control Group 3, the butterfly pea anthocyanidin with only beta-cyclodextrin protective treatment has better stability, but will also lose some color, so the color score is not high, and will seriously lose color when making dumplings. As shown in Example 5 compared with Control Group 4 and Control Group 5, other embedding materials do not have the good protection effect of beta-cyclodextrin.

[0087] The above description shows that the butterfly pea anthocyanidin of the present invention is added with an appropriate amount of metal ions and then concentrated, and then β-cyclodextrin and anthocyanidin concentrate are used to embed to form an embedding material with "hydrophilic outer wall and hydrophobic inner cavity". The prepared anthocyanidin colorant can be mixed with flour as a food colorant and has a good coloring effect, especially can improve the stability of steamed buns, and solves the technical problem that only anthocyanidin is added in the traditional steamed bun process, and the anthocyanidin is unstable and the steamed buns have poor color.

[0088] The above description is a detailed description of the preferred embodiments of the present invention, but the embodiments are not intended to limit the scope of the patent application of the present invention. Any equivalent changes or modifications completed under the technical spirit suggested by the present invention should fall within the patent scope covered by the present invention.

Claims

1. A method for preparing butterfly pea flower anthocyanin colorant for steamed buns or steamed bread, characterized in that: The method comprises the following steps: S1: freshly picked butterfly pea flowers were placed in a 40-50°C forced air drying oven and dried for 15-20 hours, then crushed and sieved; S2: According to the material-liquid ratio of 1g:85-130ml, butterfly pea flower powder was mixed with 50-80wt% ethanol aqueous solution, and ultrasonic-assisted extraction was performed at 50-60°C for 10-40min. The mixture was filtered through a double-layer filter cloth and vacuum filtered to obtain butterfly pea anthocyanin extract; S3: adding 0.01-0.05 wt % zinc citrate and 1-3 wt % sodium chloride to the extract, and concentrating the extract by rotary evaporation under reduced pressure until the volume of the extract is reduced by more than half to obtain a concentrated solution; S4: dissolving β-cyclodextrin in water at a ratio of 1 g: 5-8 ml, adding the concentrated solution to the β-cyclodextrin aqueous solution at a mass ratio of 1:1-10, ultrasonically treating the solution and spray drying the solution at low temperature to prepare an anthocyanin colorant.

2. The method for preparing a butterfly pea flower anthocyanin colorant for steamed buns or steamed bread according to claim 1, wherein In S3, the temperature of the vacuum rotary evaporation and concentration is 40-60°C, and the pressure of the vacuum rotary evaporation and concentration is 7-8 kPa.

3. The method for preparing a butterfly pea flower anthocyanin colorant for steamed buns or steamed bread according to claim 1, wherein In S2, the power of the ultrasonic extraction is 600-700W.

4. The method for preparing a butterfly pea flower anthocyanin colorant for steamed buns or steamed bread according to claim 1, wherein In S4, the ultrasonic treatment has an ultrasonic power of 200-300 W, an ultrasonic time of 5-15 min, and an ultrasonic temperature of 50-60°C.

5. The method for preparing a butterfly pea flower anthocyanin colorant for steamed buns or steamed bread according to claim 1, wherein In S4, the inlet air temperature of the low-temperature spray drying is 50-60°C, the outlet air temperature is 10°C lower than the inlet air temperature, the feed flow rate is 30-35 r / min, and the fan frequency is 80-100 Hz.

6. An anthocyanin colorant prepared by the method for preparing a butterfly pea flower anthocyanin colorant for steamed buns or steamed bread according to any one of claims 1 to 5.

7. A method for using the anthocyanidin colorant according to claim 6, characterized in that: The method comprises adding the mixture in an amount of 4-5 wt % to flour for mixing.

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