Long-term stable food-grade capillary foam composition and preparation method and application of capillary foam system

Abstract

The invention provides a long-term stable food-grade capillary foam composition and a preparation method and application of a capillary foam system, and belongs to the technical field of food-grade foam. The method comprises the following steps: by taking rice protein powder as a raw material, extracting to obtain rice glutelin through the steps of alkali dissolution and acid precipitation; performing alkali heat treatment on the rice glutelin to obtain rice glutelin colloidal particles; the rice glutelin colloidal particles and water are prepared into a suspension, an oil phase is added into the suspension, and the capillary foam system is obtained after high-speed stirring, dispersing and inflating. The stable period of the capillary foam system is as long as 2 months. The raw materials are wide in source and high in safety and nutritional value, the preparation process is green and safe, the technology is simple, and the raw materials and the preparation method are both suitable for manufacturing stable foam in the field of food processing.

Description

Technical Field

[0001] The invention relates to the technical field of food-grade foams, and in particular to a preparation method and application of a food-grade capillary foam composition and a capillary foam system that are stable for a long time. Background Art

[0002] Foam is a system formed by bubbles as dispersed phases in a semi-solid or liquid continuous phase. It is a highly thermodynamically unstable system that is prone to drainage, coalescence, and coarsening. Foam is widely used in various fields in daily life, including food processing, daily chemical cleaning, pharmaceuticals, building materials, etc., and is one of the common multiphase dispersed systems. However, food foam is an extremely unstable multiphase system from a thermodynamic point of view, and it is still a huge challenge to maintain the kinetically stable state of the foam system for a long time. At present, water-based foam systems with water as the continuous phase in food usually use low molecular weight surfactants, macromolecular substances, etc. to reduce the high surface free energy of the gas-liquid interface, thereby stabilizing the foam system, but these still cannot achieve long-term stability in the liquid state, which is also a key and difficult problem in the current food foam research.

[0003] The Chinese patent application publication CN115633785A discloses a food-grade lipid Pickering fat globule-stabilized foam and a preparation method thereof: 1) mixing a high melting point lipid with water or mixing a high melting point lipid, an emulsifier and water, shearing at high speed, cooling, adding sodium caseinate, guar gum and xanthan gum, stirring and mixing to obtain a solid lipid nanoparticle dispersion; 2) mixing the solid lipid nanoparticle dispersion with vegetable oil, preliminarily shearing, high pressure homogenizing, standing at low temperature, whipping and aerating to obtain a stable food-grade foam. In this method, lipid nanoparticles are used as raw materials to prepare a food-grade foam with a stability of 40 days. CN114009741A discloses a food-grade lipid Pickering fat globule-stabilized foam and a preparation method thereof, mixing a high melting point lipid with water, then shearing at high speed, cooling, obtaining lipid Pickering particles; stirring and mixing lipid Pickering particles with sodium caseinate, guar gum and xanthan gum, and then aerating to obtain a food-grade foam. In this application, lipid Pickering particles are also used as raw materials to prepare food-grade foam with a maximum stability time of 1 month. The Chinese patent application announcement text CN103402370B discloses a particle-stabilized emulsion or foam, comprising at least two phases and a plurality of solid particles, wherein the solid particles are starch particles and the starch particles or a part thereof are located at the interface between the two phases. The foam prepared in this scheme can be stable for up to one month.

[0004] The above-mentioned prior arts all use Pickering particles to stabilize foam, but these particle-stabilized foam systems still have the following problems: (1) Strict requirements on the surface properties of particles (wettability, morphology and size, etc.). For given particles, complex modification methods are required to achieve foam stability; (2) The accumulation of particles adsorbed at the interface makes it difficult to close all the "hole" structures that allow gas molecules to diffuse, and it is still difficult to completely prevent bubble disproportionation. Its foam stability needs to be further improved. "Capillary foam" is to introduce gas into the "capillary suspension" system so that the bubbles are covered in a thin composite layer formed by the secondary liquid (oil phase) and the adsorbed particles; at the same time, the liquid bridges generated by the secondary liquid connect the particles to form a network structure that fixes the bubbles. The foam prepared in this way shows very high stability, which can solve the problems existing in the Pickering foam system.

[0005] Rice protein contains a variety of amino acids in a reasonable ratio, and has the characteristics of low allergy and low cholesterol. Therefore, it is very suitable to add rice protein to the food of infants and special groups to replace animal protein or soy protein. Rice protein can be divided into the following four types of proteins according to its solubility: water-soluble albumin, salt-soluble globulin, alcohol-soluble alcohol-soluble protein and alkali-soluble gluten, accounting for 3.8%-8.8%, 9.6%-10.8%, 2.6%-3.3%, and 66%-78% of the total protein, respectively. Among them, rice gluten is the main storage protein in rice. Due to the hydrophobic effect between protein molecules and the cross-linking of sulfhydryl or disulfide bonds between subunits, it has the characteristics of high hydrophobicity, is difficult to dissolve in water, and has poor emulsification and foaming properties, which will limit its application in the food industry. Summary of the invention

[0006] Based on the above technical problems, the present invention provides a long-term stable food-grade capillary foam composition. The foam composition is prepared using rice gluten as a raw material. The food-grade capillary foam system prepared using the foam composition has a stability period of up to two months, and the preparation method is simple, the raw materials are safe, and it is suitable for application in the food industry.

[0007] Specifically, the present invention adopts the following technical solutions to achieve the above objectives: A long-term stable food-grade capillary foam composition comprises the following components: rice gluten colloidal particles, an oil phase and water; the mass concentration of the rice gluten colloidal particles in water is 1%-5%; the mass of the oil phase accounts for 0.05%-5% of the mass of the rice gluten colloidal particle suspension.

[0008] In a preferred embodiment, the oil phase includes at least one of coconut oil, peanut oil, soybean oil, wheat germ oil, sunflower oil and olive oil.

[0009] A method for preparing a long-term stable food-grade capillary foam system comprises the following steps: S1, dissolving rice protein powder in an alkaline solution, mixing uniformly, centrifuging, adjusting the pH of the supernatant to acidic, centrifuging, and washing the precipitate with water to obtain rice gluten; S2, adding the rice gluten protein to water, mixing evenly, to obtain a mixed solution A; adjusting the pH of the mixed solution A to alkaline, heating in a water bath, and then rapidly cooling in an ice bath, ultrasonically treating, and freeze-drying to obtain rice gluten protein colloidal particles; S3, adding the rice gluten colloidal particles into water, mixing evenly, and obtaining a suspension B; adjusting the pH of the suspension B to 4.0-5.0, adding an oil phase, stirring and dispersing and foaming at a speed of 10000-16000 rpm, and obtaining a food-grade capillary foam system.

[0010] In a preferred embodiment, the alkaline solution in step S1 is a 0.09 mol / L NaOH solution, and the mass volume ratio of the rice protein powder to the alkaline solution is (1 g:4 mL) to (1 g:10 mL).

[0011] In a preferred embodiment, the pH of the supernatant in step S1 is adjusted to 4.8.

[0012] In a preferred embodiment, the mass concentration of rice gluten in the mixed solution A in step S2 is 1% to 5%.

[0013] In a further preferred embodiment, the mass concentration of rice gluten in the mixed solution A of step S2 is 2% to 4%.

[0014] In a preferred embodiment, the pH of the mixed solution A in step S2 is adjusted to 11.0-12.0.

[0015] In a preferred embodiment, the conditions for water bath heating in step S2 are: preheating in a 50-70° C. water bath for 10-30 minutes, and continuing heating in a 80-90° C. water bath for 10-20 minutes.

[0016] In a preferred embodiment, the mass concentration of the rice gluten colloidal particles in the suspension B in step S3 is 1% to 5%.

[0017] In a further preferred embodiment, the mass concentration of the rice gluten colloidal particles in the suspension B in step S3 is 2% to 5%.

[0018] In a preferred embodiment, the mass of the oil phase in step S3 accounts for 0.05% to 5% of the mass of the suspension B.

[0019] In a further preferred embodiment, the mass of the oil phase in step S3 accounts for 0.2% to 2% of the mass of the suspension B.

[0020] The food-grade capillary foam composition or the method for preparing the food-grade capillary foam system of the present invention can be applied to the field of food processing.

[0021] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: (1) In the present invention, rice glutenin is extracted from rice protein powder, and then subjected to alkali heat treatment to obtain rice glutenin colloidal particles, the particle size of which is significantly increased, and the particle contact angle is 92.63°±2.97°.

[0022] (2) The food-grade capillary foam system prepared using the rice gluten colloidal particles showed no significant difference from the foam just formed 2 months after formation, indicating good long-term stability.

[0023] (3) In the present invention, a small amount of immiscible secondary liquid (oil phase) is added to the primary liquid (mixture of rice gluten and water), and the mixture is dispersed by high-speed stirring to form foam by aeration, which breaks the traditional perception of using oil as a defoaming agent.

[0024] (4) In the system of the present invention, particles and oil are co-adsorbed on the surface of bubbles to stabilize the foam. Compared with the prior art, the raw material selected in the present invention is rice protein powder, which has a wide source, low price, high safety, high nutritional value, and low allergenicity; the preparation method is simple to operate, green and safe, and the foam formed has a longer stability period; therefore, both the raw materials and the method for preparing the capillary foam system can be used to produce stable foam in the food processing field. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a foam effect diagram of the food-grade capillary foam system prepared under different pH conditions in Example 1 of the present invention; Figure 2 This is a foam effect diagram of a food-grade capillary foam system prepared from rice gluten colloidal particle suspensions of different concentrations in Example 2 of the present invention; Figure 3 The foam effect diagrams of the food-grade capillary foam system prepared with different concentrations of the oil phase in Example 3 of the present invention after being placed for 0 days (Figure (a)) and 2 months (Figure (b)); Figure 4 A bar chart showing the foaming performance and foam stability evaluation of the food-grade capillary foam system prepared in Example 4 of the present invention; Figure 5 This is a confocal image of the food-grade capillary foam system prepared in Example 5 of the present invention; Figure 6 The figure is a result of three-phase contact angle measurement of rice gluten colloid particles prepared in the present invention; Figure 7The graph is a result of measuring the particle size and PDI (polymer dispersibility index) of the rice gluten colloid particles prepared in the present invention; Figure 8 This is a graph showing the zeta potential measurement results of the rice gluten colloid particles prepared in the present invention; Fig. 9 This is a foam effect diagram of the foam system prepared in Comparative Example 1 of the present invention; Fig.10 This is a foam effect diagram of the foam system prepared in Comparative Example 2 of the present invention; Fig.11 This is a foam effect diagram of the foam system prepared in Comparative Example 3 of the present invention; Fig.12 The statistical result diagram of the foamability and foam stability of the food-grade capillary foam system prepared with different concentrations of the oil phase in Example 6 of the present invention; Fig.13 These are the appearance pictures of milk cap prepared by using the food-grade capillary foam composition provided by the present invention, and the pictures (a), (b) and (c) are from different viewing angles. DETAILED DESCRIPTION

[0026] The following content is combined with the embodiments to clearly and completely describe the technical solution of the present application so that those skilled in the art can fully understand the present application. Obviously, the described embodiments are only some preferred embodiments of the present application, rather than all embodiments. Any equivalent transformation or substitution made to the following implementation modes by those of ordinary skill in the art without creative work belongs to the protection scope of the present application.

[0027] The raw materials used in the examples are all food grade and are common food raw materials on the market.

[0028] The foam stability evaluation method in the embodiment is as follows: The prepared foam was immediately poured into a 25 mL graduated cylinder to evaluate its foaming property (FA) and foam stability (FS). Foaming property was evaluated by comparing the foam volume at 2 min (V2) with the initial liquid volume of the sample (V0). Foam stability was evaluated by comparing the foam volume at 120 min (V 120 ) and the foam volume at 2 min (V2) to evaluate the foam stability, and the calculation formula is as follows:

[0029]

[0030] In the formula, V0, V2, V 120 The units are the same.

[0031] The specific embodiment of the present invention provides a method for preparing a food-grade capillary foam system that is stable for a long time, comprising the following steps: S1. Extraction of rice glutenin: Mix rice protein powder with 0.09mol / L NaOH solution in a mass volume ratio of (1g:4mL)~(1g:10mL), stir at 450~600rpm for 3~4h at room temperature, then centrifuge at 3~5℃ and 4000~6000rpm for 10~20min, and retain the supernatant. Adjust the pH of the supernatant to 4.8 with 2mol / L hydrochloric acid, then stand at 4℃ for 2 hours, centrifuge at 3~5℃ and 4000~6000rpm for 10~20min, and collect the precipitate. Wash the precipitate with deionized water, stir for 30 minutes, centrifuge at 3~5℃ and 4000~6000rpm for 10~20min, and collect the precipitate; repeat the washing and centrifugation twice to obtain rice glutenin.

[0032] S2. Preparation of rice gluten colloidal particles by alkaline heat treatment: Add rice gluten to deionized water to prepare a mixed solution A containing 1wt%~5wt% rice gluten. After the mixed solution A is gently stirred for 2 hours by a magnetic stirrer, it is placed in a 4°C refrigerator for hydration overnight (at least 8 hours). The pH of the mixed solution A is adjusted to 11.0~12.0, and then preheated in a 50~70°C water bath for 10~30 minutes, and continued to heat in a 80~90°C water bath for 10~20 minutes. After the heat treatment is completed, the heated denatured mixed solution A is quickly placed in an ice bath to cool, and then ultrasonically treated with an ultrasonic crusher (ultrasonic treatment conditions: 30% amplitude, power of 10W, ultrasonic one second stop, total treatment time of 20min; keep the mixed solution A in an ice water bath during the ultrasonic treatment to prevent the mixed solution A from overheating), and finally freeze-dried at -40°C to obtain rice gluten colloidal particles.

[0033] S3, preparing a capillary foam system: dispersing rice gluten colloidal particles in deionized water to prepare a suspension B containing 1wt%~5wt% of rice gluten colloidal particles, adjusting the pH of the suspension B to 2.0~8.0, adding an oil phase, and mixing uniformly; stirring at a high speed of 10000~16000 rpm for 1~10 min to disperse and foam, to obtain a food-grade capillary foam system.

[0034] As an example, in step S1, the rice protein powder is mixed with 0.09 mol / L NaOH solution according to a mass volume ratio of 1g:4mL, 1g:6mL, 1g:8mL, 1g:10mL; preferably 1g:10mL.

[0035] As an example, the rotation speed of each centrifugation in step S1 can be 4000 rpm, 4500 rpm, 5000 rpm or 6000 rpm, the centrifugation temperature can be 3°C, 4°C or 5°C, and the centrifugation time can be 10 min, 12 min, 15 min, 18 min, 20 min.

[0036] As an example, the stirring speed at room temperature in step S1 may be 450 rpm, 500 rpm, 550 rpm or 600 rpm, and the stirring time may be 3 hours, 3.5 hours or 4 hours.

[0037] As an example, the mass concentration of rice gluten in the mixed solution A in step S2 is 1wt%, 2wt%, 3wt%, 3.5wt%, 4wt% or 5wt%; preferably 2wt%~4wt%; most preferably 3.5wt%.

[0038] In a preferred embodiment, in step S2, the pH of the mixed solution A is adjusted to 12.0.

[0039] In a preferred embodiment, the preheating temperature in step S2 is 60° C. and the preheating time is 30 min.

[0040] In a preferred embodiment, the heating temperature in step S2 is 90° C. and the heating time is 15 min.

[0041] As an example, the mass concentration of the rice gluten colloidal particles in the suspension B in step S3 is 1wt%, 2wt%, 3wt%, 3.5wt%, 4wt% or 5wt%; preferably 2wt%~5wt%; further preferably 3wt%~5wt%; further preferably 3wt%~4wt%, and most preferably 3.5wt%.

[0042] In a preferred embodiment, in step S3, the pH value of the suspension B is adjusted to 4.0-5.0.

[0043] As an example, the oil phase in step S3 includes any one or a combination of coconut oil, peanut oil, soybean oil, wheat germ oil, sunflower oil, and olive oil.

[0044] As an example, the mass of the oil phase in step S3 accounts for 0.05%, 0.08%, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5% of the mass of suspension B; preferably 0.2% to 2%; most preferably 1.5%.

[0045] As an example, the speed of the high-speed stirring in step S3 is 10000 rpm, 11000 rpm, 12000 rpm, 13000 rpm, 14000 rpm, 15000 rpm or 16000 rpm; preferably 15000 rpm.

[0046] As an example, the time of high-speed stirring in step S3 is 1 min, 2 min, 3 min, 4 min, 5 min, 6 min, 8 min or 10 min; preferably 2 min.

[0047] Example 1 A method for preparing a long-term stable food-grade capillary foam system comprises the following steps: S1, extract rice glutenin: rice protein powder was mixed with 0.09mol / L NaOH solution at a mass volume ratio of 1g:10mL, stirred at 500rpm for 4h at room temperature, and then centrifuged at 4℃ and 4500rpm for 15min, and the supernatant was retained. The supernatant was adjusted to pH 4.8 with 2mol / L hydrochloric acid, then left to stand at 4℃ for 2 hours, and then centrifuged at 4℃ and 4500rpm for 15min to collect the precipitate. The precipitate was washed with deionized water, stirred for 30 minutes, centrifuged at 4℃ and 4500rpm for 15min, and the precipitate was collected; the washing and centrifugation were repeated twice to obtain rice glutenin. The mass concentration of rice glutenin was determined to be 89% by the Kjeldahl method.

[0048] S2. Preparation of rice gluten colloidal particles by alkali heat treatment: Rice gluten was added to deionized water to prepare a mixed solution A containing 3.5wt% rice gluten. After the mixed solution A was gently stirred for 2 hours by a magnetic stirrer, it was placed in a 4°C refrigerator for hydration overnight (at least 8 hours). The pH of the mixed solution A was adjusted to 12.0 with a 2.0mol / L NaOH solution, and then preheated in a 60°C water bath for 30 minutes, and continued to be heated in a 90°C water bath for 15 minutes. After the heat treatment, the heated denatured mixed solution A was quickly placed in an ice bath to cool, and then ultrasonically treated with an ultrasonic crusher (ultrasonic treatment conditions: 30% amplitude, power of 10W, ultrasonic one second stop, total treatment time of 20min; during the ultrasonic treatment, the mixed solution A was kept in an ice water bath to prevent the mixed solution A from overheating), and finally freeze-dried at -40°C to obtain rice gluten colloidal particles.

[0049] S3. Preparation of capillary foam system: rice gluten colloidal particles are dispersed in deionized water to prepare a suspension B containing 3 wt % of rice gluten colloidal particles, and after adjusting different pH values ​​(pH values ​​are 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, and 8.0, respectively), coconut oil (CO) accounting for 1.5% of the mass of the suspension B is added and mixed evenly, and the mixture is dispersed and foamed at a high speed of 15,000 rpm for 2 min to obtain a food-grade capillary foam system.

[0050] The foam system formed by the suspension B of 3 wt% rice gluten colloidal particles under different pH conditions is as follows: Figure 1 As shown. Figure 1 It can be seen that a stable capillary foam system can be formed under the condition of pH 4.0~5.0, but no stable capillary foam system can be obtained under other conditions.

[0051] Example 2 Steps S1 and S2 of preparing a long-term stable food-grade capillary foam system in this embodiment are the same as those in Example 1, except that step S3: S3. Preparation of capillary foam system: rice gluten colloidal particles are dispersed in deionized water to prepare suspension B containing rice gluten colloidal particles of different concentrations (1wt%, 2wt%, 3wt%, 4wt%, 5wt%), the pH of suspension B is adjusted to 5.0, and then coconut oil (CO) accounting for 1.5% of the mass of suspension B is added and mixed evenly, and the mixture is dispersed and foamed at a high speed of 15000 rpm for 2 min to obtain a food-grade capillary foam system.

[0052] The foam system prepared by the suspension of rice glutenin colloidal particles with different concentrations is as follows Figure 2 As shown. Figure 2 It can be seen that when the concentration of rice gluten colloidal particles in suspension B is 1wt%~5wt%, a stable capillary foam system can be formed; when the concentration is 3wt%~5wt%, the stability of the capillary foam system is better than that at a lower concentration.

[0053] Example 3 Steps S1 and S2 of preparing a long-term stable food-grade capillary foam system in this embodiment are the same as those in Example 1, except that step S3: S3. Preparation of a capillary foam system: dispersing rice gluten colloidal particles in deionized water to prepare a suspension B containing 3 wt % of rice gluten colloidal particles, adjusting the pH of the suspension B to 5.0, then adding coconut oil (CO) in different proportions (0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.5%) of the mass of the suspension B, mixing evenly, and stirring at a high speed of 15000 rpm for 2 min to disperse and foam, to obtain a food-grade capillary foam system.

[0054] Foam systems prepared with different concentrations of oil phase are as follows Figure 3 As shown; Figure 3 (a) shows the foam effect after 0 days, and (b) shows the foam effect after 2 months. Figure 3 It can be seen that when the mass of the oil phase is 0.2%~1.5% of the mass of suspension B, the foam formed can remain stable after two months, the bottom solution is transparent, and the stability increases with the increase of the oil phase concentration.

[0055] Example 4 Steps S1 and S2 of preparing a long-term stable food-grade capillary foam system in this embodiment are the same as those in Example 1, except that step S3: S3. Preparing a capillary foam system: dispersing rice gluten colloidal particles in deionized water to prepare a suspension B containing rice gluten colloidal particles of different concentrations (1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%), adjusting the pH of the suspension B to 5.0, then adding coconut oil (CO) accounting for 1.0% of the mass of the suspension B and mixing evenly, stirring at a high speed of 15000 rpm for 2 min to disperse and foam, and obtaining a food-grade capillary foam system.

[0056] The foamability (FA) and foam stability (FS) of the foam system prepared in this example were evaluated. Figure 4 As shown. Figure 4 It can be seen that when the concentration of rice gluten colloidal particles in suspension B is 1wt%~5wt%, the foaming property of the system increases with the increase of rice gluten concentration, but the stability of the foam increases first and then decreases. When the concentration of rice gluten colloidal particles in suspension B is 3wt%~5wt%, the foam stability is better; when the concentration is 3wt%~4wt%, the stability is further improved; when the concentration is 3.5wt%, the foam stability is the best.

[0057] Example 5 Steps S1 and S2 of preparing a long-term stable food-grade capillary foam system in this embodiment are the same as those in Example 1, except that step S3: S3. Preparing a capillary foam system: dispersing rice gluten colloidal particles in deionized water to prepare a suspension B containing 3.5 wt % of rice gluten colloidal particles, adjusting the pH of the suspension B to 5.0, then adding coconut oil (CO) dyed with Nile red dye solution accounting for 1.5 wt % of the mass of the suspension B and mixing evenly, stirring at a high speed of 15000 rpm for 2 min to disperse and foam, and obtaining a food-grade capillary foam system.

[0058] A small amount of the upper foam prepared in this example was taken and placed on a concave glass slide, covered with a cover glass, and the microstructure of the foam was observed using a confocal laser scanning microscope (FV3000, Olympus, Japan) equipped with an inverted microscope. The results are as follows: Figure 5 As shown in Figure 2, the excitation wavelength was set to 543 nm, and all experimental operations were performed at room temperature (25°C). Figure 5 It can be seen that the oil phase forms an oil film on the surface of the bubbles, and the rice glutenin colloid particles gather around the bubbles. The two work synergistically to stabilize the "capillary foam" structure.

[0059] Example 6 Steps S1 and S2 of preparing a long-term stable food-grade capillary foam system in this embodiment are the same as those in Example 1, except that step S3: S3. Preparing a capillary foam system: dispersing rice gluten colloidal particles in deionized water to prepare a suspension B containing 3.5 wt % of rice gluten colloidal particles, adjusting the pH of the suspension B to 5.0, then adding coconut oil (CO) in different proportions (0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%) of the mass of the suspension B, mixing evenly, and stirring at a high speed of 15000 rpm for 2 min to disperse and foam, to obtain a food-grade capillary foam system.

[0060] The foamability (FA) and foam stability (FS) of the foam system prepared in this example were evaluated. Fig.12 As shown. Fig.12 It can be seen that when the proportion of oil phase added to suspension B is 0.5wt%~5wt%, the foamability and foam stability of the foam increase first and then decrease with the increase of oil phase concentration. The best foamability and stability are shown when the oil phase concentration is 1.5%~2%.

[0061] Comparative Example 1 A method for preparing a foam system comprises the following steps: R1, add rice protein powder to deionized water to prepare a mixed solution C containing 3.5wt% rice protein powder. After the mixed solution C was gently stirred for 2 hours by a magnetic stirrer, it was placed in a 4°C refrigerator for hydration overnight (at least 8 hours). The pH of the mixed solution C was adjusted to 12.0 with a 2.0mol / L NaOH solution, then preheated in a 60°C water bath for 30 minutes, and continued to heat in a 90°C water bath for 15 minutes. After the heat treatment, the heated denatured mixed solution C was quickly placed in an ice bath to cool, and then ultrasonically treated with an ultrasonic crusher (ultrasonic treatment conditions: 30% amplitude, power of 10W, ultrasonic one second stop, total treatment time of 20min; keep the mixed solution C in an ice water bath to prevent the mixed solution C from overheating during the ultrasonic treatment), and finally freeze-dried at -40°C to obtain rice protein powder colloidal particles.

[0062] R2, the rice protein powder colloidal particles were dispersed in deionized water at a concentration of 3wt% to obtain a rice protein powder colloidal particle suspension D, and 1.5wt% coconut oil (CO) was added after adjusting different pH values ​​(pH values ​​were 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, and 8.0, respectively) and mixed evenly, and foam was prepared by frothing at a speed of 15000rpm using a high-speed disperser.

[0063] The foam system formed by the suspension D containing 3wt% rice protein powder colloidal particles under different pH conditions is as follows: Fig. 9 As shown. Fig. 9 It can be seen that when the unpurified rice protein powder is used for the experiment, the capillary foam structure can still be formed under the conditions of pH 4.0 and 5.0, but the bottom solution is milky white and has a low transmittance. Since about 80% of the rice protein powder is insoluble in water, part of the unpurified rice protein powder can still be modified to prepare the capillary foam, and the remaining part is dissolved in the solution.

[0064] Comparative Example 2 The preparation method of the foam system in this comparative example is basically the same as that in Example 1, except that: in step S2, after hydration in a refrigerator at 4°C overnight, the pH of the mixed solution A is adjusted to 2.0 with 2.0 mol / L hydrochloric acid, and then hydrothermal treatment is performed. In step S3, the pH is 4.0-6.0 (4.0, 5.0, 6.0).

[0065] The foam system formed by the rice gluten colloid particles prepared at pH 2.0 at different pH values ​​is as follows: Fig.10 As shown. Fig.10It can be seen that when rice glutenin is modified under acidic conditions, the modified rice glutenin colloidal particles cannot form a capillary foam structure at pH 4.0, 5.0, and 6.0.

[0066] Comparative Example 3 The preparation method of the foam system in this comparative example is basically the same as that in Example 1, except that: in step S2, after hydration in a refrigerator at 4°C overnight, the pH of the mixed solution A is adjusted to 7.0 with 2.0 mol / L hydrochloric acid, and then hydrothermal treatment is performed. In step S3, the pH is 4.0-6.0 (4.0, 5.0, 6.0).

[0067] The foam system formed by the rice gluten colloid particles prepared at pH 7.0 at different pH values ​​is as follows: Fig.11 As shown. Fig.11 It can be seen that when rice glutenin is modified under neutral conditions, the modified rice glutenin colloidal particles cannot form a capillary foam structure at pH 4.0, 5.0, and 6.0. The experimental results show that only when rice glutenin is heat-treated under alkaline conditions can a stable capillary foam structure be formed.

[0068] Determination of properties of rice glutenin colloid 1. Contact angle measurement of rice gluten colloid particles The mixed solution A after heat denaturation in step S2 of Example 1 was quickly placed in an ice bath to cool, and then subjected to ultrasonic treatment using an ultrasonic crusher (ultrasonic treatment conditions: 30% amplitude, power of 10 W, ultrasonication for one second and rest for one second, and a total treatment time of 20 min; during the ultrasonic treatment, the mixed solution A was kept in an ice water bath to prevent overheating of the mixed solution A), the pH of the mixed solution was adjusted to 5.0, and then freeze-dried at -40°C to obtain rice gluten colloidal particles.

[0069] The surface wettability of the above rice gluten colloidal particles was measured using a contact angle meter. Before the measurement, the freeze-dried rice gluten colloidal particles were pressed into thin sheets. During the measurement, the thin sheets were immersed in a square quartz dish filled with coconut oil, and finally the quartz dish was placed on a platform. The syringe needle was moved below the oil surface through the syringe system, and a drop of water was added to the surface of the oil surface. Then, a CCD (Charge Coupled Device) camera was used to quickly record the image of the droplet, and the contact angle was automatically calculated by the instrument software according to the Laplace-Young equation. The results are shown in Figure 2. Figure 6 As shown. Figure 6 From the above, it can be seen that the three-phase contact angle of rice glutenin colloid particles is 92.63°±2.97°, which meets the conditions for forming "capillary foam".

[0070] 2. Determination of particle size and potential of rice gluten colloid particles The rice gluten colloidal particles prepared in step S2 of Example 1 were dispersed in deionized water to prepare a suspension containing 0.1 wt% rice gluten colloidal particles, and the pH of the suspension was adjusted to 2.0-8.0 (pH was 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, and 8.0, respectively). The particle size, polydispersity index (PDI), and zeta potential of the rice gluten colloidal particles in the suspension were measured using a nanoparticle size potentiometer equipped with a He-Ne laser (633 nm). The suspension was placed in a cuvette for particle size and PDI measurements, and the suspension was placed in a potential tank for zeta potential measurements. All measurements were performed at 25°C. The results are shown in Figure 2. Figure 7 and Figure 8 As shown. Figure 7 It can be seen from the above that the particle size of the colloid particles of the rice gluten protein colloid particles with a concentration of 0.1wt% is larger (the particle size is greater than 7μm) when the pH is 4.0-5.0; when the pH is 4.0, the particle size of the colloid particles is the largest (the particle size is greater than 9μm), which is consistent with the conditions for forming a stable capillary foam system in Example 1. This shows that only when the particle size of the rice gluten protein colloid particles is at the micron level can a stable foam structure be formed. Figure 8 It can be seen from the above that the isoelectric point of the modified rice glutenin colloidal particles is around pH 4.0. Under this condition, the electrostatic repulsion between the particles is weak, and the particles attract each other to form larger particle aggregates.

[0071] In summary, the present invention successfully prepares a long-term stable food-grade capillary foam system, and the foam system can maintain a stable state when placed at room temperature for 2 months; the composition for preparing the foam system comprises rice gluten colloidal particles, an oil phase and water, the mass concentration of the rice gluten colloidal particles in water is 1% to 5%, and the mass of the oil phase accounts for 0.1% to 5% of the mass of the suspension formed by the rice gluten colloidal particles in water.

[0072] Application of long-term stable food-grade capillary foam system Protein is the main component of food and has an important influence on various properties of food such as texture, color, smell, etc. Rice protein has a high nutritional value, and its amino acid composition is most in line with the ideal model recommended by WHO / FAO (World Health Organization / Food and Agriculture Organization), which is more conducive to human digestion and absorption, and can be used as a substitute for animal protein. The preparation method of the food-grade capillary foam composition or food-grade capillary foam system prepared in this application can be used in cake baking, cream making, milk tea milk cap making, etc., so that rice protein can replace other proteins and provide unique taste and nutritional value for foam food.

[0073] The method for preparing milk cap using the food-grade capillary foam composition of the present application is as follows: take 100 mL of rice gluten colloidal particle suspension with a mass concentration of 1%, add coconut oil (shea butter) accounting for 5% of the mass of the suspension, shear pre-emulsify at 10000 r / min for 2 minutes to obtain an emulsion, and homogenize it at 15 MPa to obtain an emulsion. Mix the milk and the emulsion in a mass ratio of 1:2 to 1:3 (for example, 1:2, 1:2.5 or 1:3), add condensed milk accounting for 5% of the mass of the mixture of milk and emulsion, and use a whisk to beat to form a mixture such as Fig.13 The milk cap shown.

[0074] The above-described embodiments are only preferred embodiments of the present application and are not intended to limit the scope of protection of the present application. For any person skilled in the art, the present application may have various changes and modifications. Any simple equivalent changes and modifications made based on the scope of protection of the present application and the contents of the specification should be included in the scope of protection of the present application.

Claims

1. A food-grade capillary foam composition that is stable for a long time, characterized in that: The invention comprises the following components: rice gluten colloidal particles, an oil phase and water; the mass concentration of the rice gluten colloidal particles in water is 1% to 5%; the mass of the oil phase accounts for 0.05% to 5% of the mass of the rice gluten colloidal particle suspension.

2. The food-grade capillary foam composition according to claim 1, characterized in that The oil phase comprises at least one of coconut oil, peanut oil, soybean oil, wheat germ oil, sunflower oil and olive oil.

3. A method for preparing a long-term stable food-grade capillary foam system, characterized in that: The following steps are involved: S1, dissolving rice protein powder in an alkaline solution, mixing uniformly, centrifuging, adjusting the pH of the supernatant to acidic, centrifuging, and washing the precipitate with water to obtain rice gluten; S2, adding the rice gluten protein into water, mixing evenly, to obtain a mixed solution A; adjusting the pH of the mixed solution A to alkaline, heating in a water bath, and then rapidly cooling in an ice bath, ultrasonically treating, and freeze-drying to obtain the rice gluten protein colloidal particles described in claim 1 or 2; S3, adding the rice gluten colloidal particles into water, mixing uniformly, and obtaining a suspension B; adjusting the pH of the suspension B to 4.0-5.0, adding the oil phase described in claim 1 or 2, stirring, dispersing and foaming at a speed of 10000-16000 rpm, and obtaining a food-grade capillary foam system.

4. The method for preparing the food-grade capillary foam system according to claim 3, characterized in that: In step S1, the alkaline solution is a 0.09mol / L NaOH solution, and the mass volume ratio of rice protein powder to the alkaline solution is (1g:4mL)~(1g:10mL); or / and, in step S1, the pH of the supernatant is adjusted to 4.

8.

5. The method for preparing the food-grade capillary foam system according to claim 3, characterized in that: The mass concentration of rice gluten in the mixed solution A of step S2 is 1% to 5%.

6. The method for preparing the food-grade capillary foam system according to claim 3, characterized in that: In step S2, the pH of the mixed solution A is adjusted to 11.0-12.

0.

7. The method for preparing the food-grade capillary foam system according to claim 3, characterized in that: The conditions for water bath heating in step S2 are: preheating in a 50-70° C. water bath for 10-30 minutes, and continuing heating in a 80-90° C. water bath for 10-20 minutes.

8. The method for preparing the food-grade capillary foam system according to claim 3, characterized in that: The mass concentration of the rice glutenin colloid particles in the suspension B in step S3 is 2% to 5%.

9. The method for preparing the food-grade capillary foam system according to claim 3, characterized in that: The mass of the oil phase in step S3 accounts for 0.2% to 2% of the mass of the suspension B.

10. Use of the long-term stable food-grade capillary foam composition of claim 1 or the method for preparing the food-grade capillary foam system of any one of claims 3 to 8 in the field of food processing.

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