Method for directionally regulating and controlling fish-source protein soft gel by utilizing electrostatic deposition microcapsules

Abstract

The invention discloses a method for directionally regulating and controlling fish-source protein soft gel by utilizing electrostatic deposition microcapsules, and belongs to the technical field of aquatic product processing. The preparation method comprises the following steps: compounding pea protein isolate-beta-glucan complex coacervate and vegetable fat to obtain complex coacervation microcapsules, and coating the complex coacervation microcapsules with a carboxymethyl chitosan electrostatic deposition layer under a pH induction condition by utilizing electrostatic attraction; an electrostatic deposition microcapsule is added into a minced fillet raw material, and a soft minced fillet gel system based on fish source protein is constructed by utilizing the unique thickening characteristic and gel forming ability of the electrostatic deposition microcapsule. Directional regulation and control on the texture of the minced fillet are realized by utilizing the microcapsules, and the texture of the minced fillet gel is improved, so that the product is finer and softer, and is more suitable for the mouth feel requirements of special crowds such as old people and patients with dysphagia; the nutritional and healthy value of the minced fillet soft gel can be improved, and the nutritional value of the product is enhanced by adding specific nutritional ingredients into the microcapsules, so that the minced fillet soft gel becomes an ideal nutritional supplement source for the type of people.

Description

Technical Field

[0001] The present invention belongs to the technical field of aquatic product processing, and particularly relates to a method for directionally regulating fish-derived protein soft gels by electrostatic deposition microcapsules. Background Art

[0002] With the intensification of the global population aging trend, the proportion of the elderly population is increasing continuously. Their body functions are gradually declining, especially dental health problems (such as loose teeth and tooth loss) and reduced saliva secretion, resulting in a decline in chewing and digestion ability, affecting the quality of life and possibly leading to malnutrition. Therefore, effective improvement measures need to be taken to maintain the health of the elderly and improve their quality of life. Currently, medical tube feeding, intravenous nutrition, and food texture modification are three ways to solve the diets of the elderly, especially those of elderly patients with dysphagia. Among them, food texture modification can not only improve the dietary safety and nutritional intake of elderly patients with dysphagia, but also enhance their dietary experience and quality of life; at the same time, this method is easy to implement in the living environment, has low cost, low risk, high flexibility, and can be customized according to the swallowing ability and preferences of patients. Therefore, food texture modification is considered an effective means to improve the quality of life of the elderly with dysphagia and ensure swallowing safety.

[0003] As a high-quality "grain", marine foods provide nearly 20% of the edible animal protein for humans. Aquatic proteins have advantages such as high biological value and high digestibility and utilization rate, making them high-quality protein raw materials for special diets. Surimi products are popular among consumers because of their rich high-quality aquatic protein and high viscoelasticity. However, surimi products with high gel strength are not suitable for the elderly with weak chewing ability. With the enhancement of people's health awareness, the existing types of surimi products are difficult to meet the higher demand of consumers for the nutritional and functional value, especially for special groups such as the elderly and those with dysphagia, and special nutritional customization is required for them. Therefore, it is becoming increasingly important to reasonably apply nutritional supplements, explore appropriate texture regulation means, and develop high-quality functional gel foods based on easy swallowing.

[0004] Currently, existing technologies mostly achieve the regulation of surimi texture through physical methods (such as homogenization treatment, freezing and thawing) and chemical methods (such as adding protease, phosphate, polysaccharide substances). However, these technologies have problems such as increased energy consumption and addition amount limitations in actual production, and it is difficult to take into account both product texture improvement and nutritional enhancement. Therefore, how to overcome the problems that existing surimi products have high hardness, high elasticity, strong chewiness, and are not suitable for special groups such as those with dysphagia, and provide a surimi soft gel product suitable for industrial production, high in protein, high in nutrition, and easy to eat, is a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0005] [Technical Problem]

[0006] The technical problem to be solved by the present invention is that existing surimi products have high hardness, high elasticity and strong chewiness, and are not suitable for special populations such as those with swallowing difficulties to consume.

[0007] [Technical Solution]

[0008] To solve the above problems, the present invention provides a method for directionally regulating fish-derived protein soft gels using electrostatic deposition microcapsules. The present invention prepares complex coacervation microcapsules by compounding pea protein isolate-β-glucan complex coacervate with vegetable oil, and coats an electrostatic deposition layer of carboxymethyl chitosan on the outside of the complex coacervation microcapsules under pH-induced conditions using electrostatic attraction; adding the electrostatic deposition microcapsules to surimi raw materials, and using their unique thickening properties and gel-forming ability to construct a soft surimi gel system based on fish-derived proteins. The method of the present invention improves the texture properties of surimi gels by directionally regulating the gel behavior of surimi. By the method of the present invention, it is possible to effectively reduce the hardness and chewiness of surimi gels while preparing soft surimi gels that are easy to eat; it is also possible to load specific nutrients using the unique embedding properties of microcapsules to strengthen the nutritional properties of surimi gels, further enhancing the nutritional value and functionality of surimi products.

[0009] The present invention provides a method for preparing electrostatic deposition microcapsules, comprising the following steps:

[0010] (1) Mix an aqueous solution of pea protein isolate with an aqueous solution of β-glucan to form a wall material solution, and at the same time dissolve nutrients in oil to obtain an oil phase;

[0011] (2) Mix the wall material solution with the oil phase and emulsify it in a high-speed homogenizer, then slowly dropwise add an acetic acid solution while stirring to adjust the pH value to 3.5-4.5; after reacting for 25-35 min, add an aqueous solution of carboxymethyl chitosan and dropwise add a sodium hydroxide solution to adjust the pH to 5.0-6.0;

[0012] (3) Add transglutaminase and stir and react at 20-25 °C to obtain a microcapsule suspension, let it stand for stratification, remove the supernatant and then filter to obtain electrostatic deposition microcapsules.

[0013] In one embodiment of the present invention, in step (1), the concentration of the wall material solution is 0.5-2 wt%, preferably 1 wt%.

[0014] In one embodiment of the present invention, in step (1), the concentration of the aqueous solution of pea protein isolate is 0.5-2 wt%, preferably 1 wt%.

[0015] In one embodiment of the present invention, in step (1), the concentration of the aqueous solution of β-glucan is 0.5-2 wt%, preferably 1 wt%.

[0016] In one embodiment of the present invention, in step (1), the wall material solution is hydrated at 0 - 5°C for 6 - 10 h.

[0017] In one embodiment of the present invention, in step (1), the oil is at least one of perilla seed oil, soybean oil, walnut oil, linseed oil, rapeseed oil, peanut oil, and sunflower seed oil, preferably perilla seed oil.

[0018] In one embodiment of the present invention, in step (1), the nutrient is a fat-soluble nutrient, preferably vitamin D; the concentration of the nutrient in the oil phase is 0.5 - 1.5 mg / mL.

[0019] In one embodiment of the present invention, in step (2), the mass ratio of pea protein isolate, β-glucan, and carboxymethyl chitosan is 1 - 4:1:1, preferably 1:1:1.

[0020] In one embodiment of the present invention, in step (2), the mass ratio of the wall material solution to the oil phase is 2 - 4:1.

[0021] In one embodiment of the present invention, in step (2), the emulsification conditions are 8000 - 10000 rpm for 2 - 3 min, preferably 8000 rpm for 3 min.

[0022] In one embodiment of the present invention, in step (2), the concentrations of the acetic acid solution and the sodium hydroxide solution are 0.1 - 10 wt%, preferably 1 wt%.

[0023] In one embodiment of the present invention, in step (3), the addition amount of transglutaminase is 1 / 4 of the mass of pea protein isolate, and the enzyme activity of transglutaminase is 100 U / g.

[0024] The present invention provides the electrostatic deposition microcapsules prepared by the above-mentioned method.

[0025] The present invention provides the application of the above-mentioned electrostatic deposition microcapsules in the food field.

[0026] The present invention provides the application of the above-mentioned electrostatic deposition microcapsules in surimi products.

[0027] The present invention provides the application of the above-mentioned electrostatic deposition microcapsules in regulating the texture properties of surimi products.

[0028] The present invention provides a surimi soft gel containing electrostatic deposition microcapsules, and the preparation method includes the following steps:

[0029] After thawing the frozen surimi, put it into a food processor and stir it without adding anything. Then add salt and continue to stir. Next, add water and continue to grind it. Finally, add the electrostatic deposition microcapsules described above and perform the final grinding. Gelatinize the surimi by using a two-stage heating method. After heating, cool it in ice water. After cooling, the surimi soft gel is obtained.

[0030] In one embodiment of the present invention, the surimi is one or more of cod surimi, grass carp surimi, silver carp surimi, threadfin bream surimi, tuna surimi and hairtail surimi, and preferably cod surimi.

[0031] In one embodiment of the present invention, the thawing is carried out at 0-4°C for 10-14 hours.

[0032] In one embodiment of the present invention, the grinding process is carried out in an ice box to prevent the surimi from overheating.

[0033] In one embodiment of the present invention, the grinding process lasts for 2-4 minutes, the speed is 2000-3000 rpm, and the time interval is 20-30 seconds.

[0034] In one embodiment of the present invention, the addition amount of the electrostatic deposition microcapsules is 5-30% of the mass of the surimi.

[0035] In one embodiment of the present invention, the addition amount of salt is 2-3% of the mass of the surimi, and preferably 2%.

[0036] In one embodiment of the present invention, the water is one or any combination of mineral water, tap water, ionized water, and distilled water, and preferably distilled water.

[0037] In one embodiment of the present invention, the two-stage heating is as follows: first heat at 40°C for 20-30 minutes, and then immediately transfer to 90°C and heat for 30 minutes.

[0038] [Beneficial effects]

[0039] (1) The vitamin D microcapsules prepared by the complex coacervation method effectively solve the problem that vitamin D is easily affected by factors such as temperature during food processing. The microcapsules not only improve the encapsulation rate of vitamin D, making the microcapsule encapsulation efficiency reach 92%, and the loading efficiency is increased to 70%, but also significantly enhance its thermal stability and ultraviolet stability, providing a technical basis for the wide application of vitamin D in the food industry.

[0040] (2) In the present invention, the complex coacervation microcapsules are coated with a carboxymethyl chitosan electrostatic deposition layer, which can enhance the structural stability of the microcapsules and prevent the microcapsules from cracking or leaking during processing.

[0041] (3) The cod protein soft gel prepared by microencapsulation technology meets the standards of easy-to-eat foods. This gel is particularly suitable for the elderly and those with swallowing difficulties, effectively solving the problems of their nutrient deficiencies and special taste requirements, and providing an ideal form of nutritional supplement.

[0042] (4) The application of microencapsulation technology in food not only improves the stability and sustained release of active ingredients, but also constructs a soft and easy-to-eat gel system suitable for special populations such as the elderly through its unique thickening properties and gel-forming ability. This research opens up new ways for the application of microcapsules in the elderly food market and other functional food fields, meeting the higher demands for healthy nutrition. Brief Description of the Drawings

[0043] Figure 1 Optical microscope images (A), fluorescence inverted microscope images of protein and oil distribution (B), fluorescence inverted microscope images of bilayer structure (C), and cold field scanning electron microscope images (D) of the microcapsules in Examples 1 - 4;

[0044] Figure 2 Ultraviolet stability images (A), differential scanning calorimetry images (B), and thermogravimetry images (C) of the microcapsules in Examples 1 - 4;

[0045] Figure 3 Optical microscope image of Comparative Example 1;

[0046] Figure 4 Effects of different pH values on the turbidity (A) and morphology (B) of coacervates in Example 5;

[0047] Figure 5 Effects of different wall material compounding ratios on the turbidity (A, B) and morphology (C) of coacervates in Example 6;

[0048] Figure 6 Effects of different wall material compounding ratios on the circular dichroism (A) and secondary structure (B) of composite coacervates in Example 7;

[0049] Figure 7 Effects of different wall material compounding ratios on the encapsulation efficiency and loading rate of vitamin D microcapsules in Example 8;

[0050] Figure 8 IDDSI test images of the soft gels in Comparative Example 2 and Examples 9 - 14;

[0051] Figure 9 Gel strength images of the soft gels in Comparative Example 2 and Examples 9 - 14;

[0052] Figure 10Chromaticity diagrams (A), whiteness diagrams (B), and appearance diagrams (C) of the soft gels prepared in Comparative Example 2 and Examples 9 to 14. Detailed implementation manners

[0053] The preferred embodiments of the present invention are described below. It should be understood that the embodiments are for better explaining the present invention and are not used to limit the present invention.

[0054] Sources of raw materials

[0055] Pea protein isolate (purity 95%) was purchased from Beijing Baoxidi Co., Ltd.; oat-β-glucan (purity > 90%) and carboxymethyl chitosan (purity 90%) were purchased from Dalian Benuo Co., Ltd.; vitamin D (purity 98%) was purchased from Shanghai Aladdin Reagent Co., Ltd.; perilla seed oil (unsaturated fatty acid content 91.6%, oleic acid 15.4%, linoleic acid 16%, linolenic acid 60%) was purchased from Hebei Shanyifang Co., Ltd.; cod fish mince was purchased from Qingdao Tengbenwei Co., Ltd.; transglutaminase was purchased from Beijing Solarbio Science & Technology Co., Ltd., and the enzyme activity was 100 U / g.

[0056] Testing methods

[0057] 1. Microcapsule optical microscope testing method: Drop the microcapsule suspension on a glass slide and observe the microcapsules using an optical microscope with a magnification of 200x.

[0058] 2. Microcapsule oil and protein distribution testing method: Take 200 μL of the microcapsule sample, stain the oil phase and protein with 20 μL of nile red-acetone solution (0.1%, w / v, g / mL) and 20 μL of FITC-dimethyl sulfoxide solution (0.5%, w / v, g / mL), shake the sample in the dark for 20 min, drop it on a glass slide with a dropper, and observe the embedding situation of the core material using a fluorescence inverted microscope after equilibration for 1 min.

[0059] 3. Microcapsule bilayer structure testing method: Disperse 1 g of microcapsules in 10 mL of distilled water, stain the protein and polysaccharide with 20 μL of acetone-nile blue solution (0.1%, w / v, g / mL) and 20 μL of fluorescent brightener, shake the sample in the dark for 20 min, drop it on a glass slide with a dropper, and collect images using a fluorescence inverted microscope after equilibration for 1 min.

[0060] 4. Microcapsule cold field scanning electron microscope testing method: Observe the microstructure of the microcapsules using a scanning electron microscope. Place the wet microcapsules on the sample stage and observe at a voltage of 10 kv with a magnification of 1k.

[0061] 5. Analysis method for the ultraviolet stability of microcapsules: Take 0.1 g of microcapsules respectively and irradiate them under a 15 W ultraviolet lamp at a distance of 10 cm for 10 min, 20 min, 40 min, and 60 min, and then disperse them in 30 mL of n-hexane. Centrifuge at 3000×g for 10 min to obtain free VD 3 . Record the absorbance value of the supernatant at 264 nm using a UV-Vis spectrophotometer.

[0062] 6. Analysis methods for the thermogravimetry and differential scanning calorimetry of microcapsules: Use a thermogravimetric analyzer and a differential scanning calorimetry spectrometer to test the thermal stability of microcapsules. Weigh 1 mg of vitamin D and microcapsule samples and put them into crucibles, press and seal the tablets, and then put them into the TGA and DSC reaction cells for analysis respectively, with a blank crucible as a control. Thermogravimetric parameters: heating rate is 20 °C / min, nitrogen flow rate is 60 mL / min, heating range is 20 - 600 °C; differential scanning calorimetry parameters: heating rate is 10 °C / min, nitrogen flow rate is 30 mL / min, heating range is 20 - 90 °C.

[0063] 7. TPA test method for soft gels: Evaluate the texture properties of samples in the full texture analysis mode of a texture analyzer. Test conditions: P / 100 probe, the speeds before measurement, during measurement, and after measurement are all 1 mm / s, perform two consecutive compressions on each sample, compression ratio is 30%, and trigger force is 5 g.

[0064] 8. IDDSI test method for soft gels: Classify soft gels using the fork pressure test of the International Dysphagia Diet Standardization Initiative (IDDSI) test method. Actual tests using forks or spoons will be foods of transitional types 5 - 7 belonging to the IDDSI level. When using the bottom of a dinner fork to press down on the food (about 1.5 cm × 1.5 cm), the food can be flattened (the nails of the thumb and index finger turn white when applying force), and after moving the dinner fork away, the food will not return to its original shape.

[0065] 9. Gel strength test method for soft gels: Cut the ripened samples into cylinders with a diameter of 25 mm and a height of 30 mm, and measure the gel strength of the samples in the gel strength mode of a texture analyzer. Test conditions: P / 5S probe, the speeds before measurement and during measurement are 1 mm / s, the speed after measurement is 10 mm / s, penetration ratio is 50%, and trigger force is 5 g. The gel strength calculation formula is as follows:

[0066] Gel strength (g×mm) = breaking force (g) × breaking distance (mm).

[0067] 10. Soft Gel Chromaticity Test Method: Use a colorimeter to measure whiteness. After the temperature is balanced to room temperature, measure and record the color values of L* (brightness), a* (red-blue), and b* (yellow-green). All measurements are taken at three random positions on the surface of each sample, and the average value is used to indicate the color change of the sample.

[0068]

[0069] 11. Circular Dichroism Spectral Analysis

[0070] Adjust the concentration of the complex coacervate to 0.01 mg / mL. Accurately measure 450 μL of the complex coacervate solution and add it to a cuvette. Set the scanning wavelength range to 190 - 240 nm, the resolution to 0.2 nm, the scanning speed to 50 nm / min, and the bandwidth to 1 nm. Detect the sample at room temperature (25 °C) and in a nitrogen environment. Circular dichroism is expressed by the mean residue ellipticity [θ], with the unit of deg·cm 2 / dmol.

[0071] 12. Determination Method for Encapsulation Efficiency and Loading Rate of Microcapsules

[0072] Take 0.1 g of the microcapsule sample and disperse it in 30 mL of n-hexane. Use a centrifuge to centrifuge at 3000 × g for 5 min to separate the unencapsulated VD 3 . Record the absorbance value of the supernatant at 264 nm using a UV-Vis spectrophotometer, and record the concentration of the unencapsulated VD 3 as C 1 . Then continue to add the precipitate to 30 mL of n-hexane, and use a thermal ultrasonic cleaner to break the microcapsules for 30 min. The ultrasonic power is 1200 W, the frequency is 24 Hz, and the heating temperature is set to 100 °C. After the breaking is completed, use a centrifuge to centrifuge at 3000 × g for 5 min, record the absorbance value of the supernatant at 264 nm using a UV / Vis spectrophotometer, and record the concentration of the encapsulated VD 3 as C 2 .

[0073] The calculation formulas for EE (encapsulation efficiency) and LE (loading rate) are as follows, where WT is the total mass of the microcapsules.

[0074]

[0075] Example 1

[0076] A preparation method of electrostatic deposition microcapsules, comprising the following steps:

[0077] (1) Prepare 1 wt% aqueous solutions of pea protein isolate (PPI), oat-β-glucan (β-OG), and carboxymethyl chitosan (CMCS) separately, and stir them with a magnetic stirrer at 300 rpm for 6 h. The hydration temperature is 0 - 5 °C until complete hydration;

[0078] (2) Mix PPI and β-OG in a ratio of 1:1 (w / w) to form a wall material solution. At the same time, dissolve vitamin D in perilla seed oil to obtain an oil phase (1 mg / mL);

[0079] (3) Mix the wall material solution and the oil phase in a ratio of 2:1 (w / w), emulsify with a high-speed homogenizer at 10,000 rpm for 3 min, stop every 30 seconds, then stir at 350 rpm, and slowly add acetic acid solution (1 wt%) to adjust the pH to 4.0 for complex coacervation reaction. After the reaction is completed, continue to stir for 30 min;

[0080] (4) Slowly add CMCS to make the mass ratio of pea protein isolate, β-glucan, and carboxymethyl chitosan 1:1:1, and adjust the pH of the system to 5.0 with sodium hydroxide solution (1 wt%), and continue to stir for 30 min;

[0081] (5) Finally, add 0.25 g / g pea protein isolate of TG enzyme as a cross-linking agent, and stir at 300 rpm at room temperature for 4 h to obtain a double-layer microcapsule suspension.

[0082] Example 2

[0083] Adjust the mixing ratio of PPI and β-OG in step (2) of Example 1 to 2:1; other steps are the same as in Example 1.

[0084] Example 3

[0085] Adjust the mixing ratio of PPI and β-OG in step (2) of Example 1 to 3:1; other steps are the same as in Example 1.

[0086] Example 4

[0087] Adjust the mixing ratio of PPI and β-OG in step (2) of Example 1 to 4:1; other steps are the same as in Example 1.

[0088] Perform performance tests on the electrostatic deposition microcapsules prepared in Examples 1 - 4, and the test results are as follows:

[0089] Figure 1 Microscopic structure diagrams of the microcapsules: (A) Optical microscope image, (B) Fluorescence inverted microscope, (C) Fluorescence microscope image of the double-layer structure, (D) Scanning electron microscope image. As Figure 1As shown in (A), at a magnification of 200 times, microcapsules of all ratios presented a good spherical structure, and the internal structure of all microcapsules could be seen, which could be judged as spherical multi-core microcapsules. In addition, as the ratio of PPI increased, the number of microcapsules in the field of view gradually increased, and the diameter of some microcapsules became larger. Figure 1 (B), Nile red and fluorescein isothiocyanate (FITC) were used to stain the oil phase and PPI complex respectively to observe the embedding of the oil phase by the microcapsules. It can be seen that Examples 1-4 had a good spherical structure under a fluorescence inverted microscope. From the distribution of protein (green) and oil (red), it can be seen that the complex formed a relatively complete wall material and could well coat the core material. As the protein content increased, the microcapsules showed large-area aggregation and poor dispersibility. In addition, to further prove the bilayer structure formed by the electrostatic interaction between CMCS and PPI / β-OG, CMCS and PPI / β-OG were stained simultaneously. Figure 1 (C), Nile blue was used to fluorescently label PPI, which showed red at an excitation wavelength of 633 nm; a fluorescent brightener was used to fluorescently label CMCS, which showed green at an excitation wavelength of 402 nm. It can be seen in the figure that PPI and CMCS could completely overlap. Under the action of pH, CMCS formed a relatively complete wall material and could well coat the single-layer microcapsules, which further confirmed the successful preparation of the bilayer microcapsules. In addition, we can see that the CMCS shell formed in Example 1 was smooth, dense and relatively uniform, while holes appeared on the CMCS shells formed in Examples 2-4, and the wrapping was uneven in some areas. The reason for this phenomenon may be that the pH of the microcapsule suspension was raised to 5.0 when coating CMCS, and the reduction of the positive charge of the protein made some CMCS unable to bind well with PPI / β-OG. Figure 1 (D) The ultramicrostructure of the microcapsules was further observed by SEM. At a magnification of 1000×, the microcapsules presented a good spherical structure, with a slightly sunken surface but no cracks. In addition, a network structure could be observed between the spheres, which could maintain a safe distance between the microcapsules and make them stable. The microcapsules in Example 1 were of relatively uniform size and had a flat surface. As the ratio of PPI increased, the number of microcapsules increased and the surface attachments increased. In Examples 2-4, due to the imbalance of the charge ratio in the solution, a large amount of CMCS adhered to the surface of the microcapsules and showed a superimposed state, resulting in an increase in the overall size of the microcapsules; at this time, the network became disordered.

[0090] Figure 2UV stability graph (A), differential scanning calorimetry graph (B), and thermogravimetric graph (C) of the microcapsules of Examples 1 to 4. Vitamin D is a photosensitive substance. When it is irradiated with ultraviolet light, it is prone to photooxidation or isomerization reactions, resulting in the degradation and inactivation of the active ingredient. To clarify the barrier efficiency of the microcapsules to ultraviolet light at different compounding ratios and further investigate the effect of the wall material ratio on the UV stability of vitamin D microcapsules, the results are as Figure 2 (A) shown. It can be seen from the figure that as the irradiation time prolongs, the protective effect of the microcapsules on vitamin D gradually loses. In Example 1, when the wall material ratio is 1:1:1, as the ultraviolet irradiation time prolongs, the EE of vitamin D in the microcapsules gradually decreases to 48.54%, but it is still higher than other groups. At 0 min, as the amount of PPI increases, the retention rate of vitamin D in the microcapsules gradually decreases. In addition, during the irradiation process, as the amount of PPI increases, the microcapsules rupture and vitamin D is exposed outside, resulting in a decrease in the retention rate. When the irradiation time exceeds 20 min, the rupture of the microcapsules increases and the retention rate of vitamin D drops rapidly. To sum up, when the wall material ratio in Example 1 is 1:1:1, the complex coacervation microcapsules have the strongest anti-UV ability, the best retention rate of vitamin D, and the best effect of delaying structural isomerization. During the processing of some foods, heat treatment methods such as steaming, boiling, baking, and high-temperature sterilization will cause losses to the active substances, and it is necessary to improve the thermal stability of the active substances. To evaluate the thermal stability of the microcapsules, a differential scanning calorimeter and a thermogravimetric analyzer were used to evaluate the thermal stability of vitamin D microcapsules. DSC analysis can measure the relationship between the heat flux density difference of the microcapsules and vitamin D and temperature to evaluate the stability. Figure 2 (B) is the DSC curve of the microcapsules and vitamin D. It can be seen from the figure that the original vitamin D has a large absorption peak near 65.29 °C, which may be due to the thermal degradation of vitamin D, indicating that 65.29 °C is the melting temperature of vitamin D. No absorption peak is found in the microcapsule curve, indicating that the thermal stability of the microcapsules is improved and they have a better protective effect on vitamin D. Thermogravimetric analysis can reflect the relationship between the sample mass and temperature, Figure 2(C) is the TGA curve of vitamin D microcapsules. As shown in the figure, the original vitamin D has a mass loss at 240.00 °C. The degradation of the coacervate microcapsules loaded with vitamin D mainly occurs in two stages. The first stage is the heating stage from 20 to 124.81 °C. At this temperature stage, the mass of the microcapsules decreases, which is mainly due to the mass loss caused by the loss of moisture in the sample. Before the temperature reaches 342.34 °C, the mass of the coacervate microcapsules loaded with vitamin D only changes slightly. Subsequently, as the temperature rises, the stability of the microcapsules deteriorates and the mass decreases sharply. When the temperature reaches 476.95 °C, the microcapsules are completely lysed. The wall material ratio also has a great influence on the thermal stability of the microcapsules. Compared with Example 4, the microcapsules prepared under the wall material compounding ratios of Examples 1-3 have a low thermal loss rate as the temperature gradually increases, showing better thermal stability.

[0091] Comparative Example 1

[0092] The preparation method is the same as that of Example 1, with the only difference being that carboxymethyl chitosan is omitted, that is, step (4) in Example 1 is omitted.

[0093] The microscopic observation of Comparative Example 1 was carried out, and the test results are as follows:

[0094] Figure 3 Figure is the optical microscope image of Comparative Example 1. It can be seen from the figure that the microcapsules in Comparative Example 1 show a good spherical structure with a round edge, indicating that this coacervate compounding ratio can form microcapsules. The outer wall of the microcapsules is relatively thin and there are large size differences, which may be due to uneven dispersion during the emulsification process. In addition, obvious oil-phase substances can be seen in some solutions in the figure, indicating that the oil phase is not completely encapsulated. These oil-phase substances may be because the encapsulation film layer is thin, discontinuous or ruptured during the preparation process. Some of the oil-phase substances are aggregated together, which further indicates that the encapsulation effect is not good.

[0095] Example 5

[0096] Explore the effects of different pH values on the turbidity and morphology of the coacervate

[0097] The turbidity and morphology of the coacervate affect the encapsulation efficiency, stability and release performance of the microcapsules. Therefore, the turbidity and morphology of the coacervate should meet the standards of being uniform, stable and controllable. In addition, when embedding microcapsules, the optimal state of the coacervate is a liquid phase with good water solubility.

[0098] Prepare a binary complex coacervate solution (0.1%) with PPI:β-OG = 1:1, and use glacial acetic acid (10%, v / v) and NaOH (1 mol / L) to adjust the pH of the mixed system to 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5 respectively. Visualize the samples using a photography box, and measure the turbidity of different complex coacervates using a UV-visible spectrophotometer.

[0099] As the pH of the solution changes, the intensity of the complex coacervation reaction also changes, presenting different colloidal states; macroscopically, it is manifested as the agglomeration of substances driven by pH to form complex coacervates, making the solution more turbid. In the range of pH 2.5 - 6.5, the turbidity of the binary complex coacervate first increases and then decreases with the increase of pH. In the low pH region (2.5 - 3.5), the strong acidic environment of the system causes both PPI and OG to be in a highly protonated state, and the intermolecular electrostatic repulsion dominates, making it difficult to form a stable complex coacervation phase; in the range of pH 4.0 - 5.0, PPI and OG form a dense network structure through electrostatic interaction, manifested as a sharp increase in turbidity, and the turbidity value is relatively high at this time, and the turbidity value is the highest when pH = 4; in the high pH region (5.5 - 6.5), the degree of deprotonation of OG increases, resulting in the inversion of the surface charge of the complex, the re-enhancement of the electrostatic repulsion, and the dissociation or recombination of the composite particles. When embedding substances, the better complex coacervates are the groups with better water solubility. As Figure 4 shown, through the visual analysis of the samples, when pH = 3.5, 4, 4.5, the solution is relatively turbid and has good homogeneity, with only a small amount of precipitation. When pH = 4, the solution system is the most homogeneous, probably because the protonation of the amino side groups of PPI is enhanced, triggering the charge attraction with the negatively charged carboxyl groups of β-OG. Therefore, pH = 4 is selected as the reaction pH.

[0100] Example 6

[0101] Explore the effects of different wall material compounding ratios on the turbidity and morphology of complex coacervates

[0102] Prepare a binary complex coacervate solution with a concentration of 0.1%, and make the ratios of PPI:β-OG and β-OG:PPI be 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0 respectively. Use glacial acetic acid (10%, v / v) and NaOH (1 mol / L) to adjust the pH of the mixed system to 4.0. Visualize the samples using a photography box, and measure the turbidity of different complex coacervates using a UV-visible spectrophotometer. The results are as Figure 5 shown. From Figure 5As can be seen from (A), when the addition amount of PPI gradually increases, the number of positive charge groups in the complex coacervate solution increases, and the turbidity value also increases accordingly. However, due to the interaction between charges gradually reaching equilibrium, the overall change in turbidity is relatively small. Figure 5 (B) shows that as the addition amount of polysaccharide increases, the turbidity value of the solution gradually decreases. When the ratio of PPI to polysaccharide is 1:1, the turbidity of the solution is the highest and evenly distributed. At this time, the charge matching of the two is the most reasonable, and the structure of the complex coacervate is more stable. When the polysaccharide is in excess, the steric hindrance effect of its molecular chain is enhanced, resulting in a decrease in the formation efficiency of the complex and a further decrease in turbidity. The complex coacervation reaction is a process in which positive and negative charge groups react through ionic interactions. The best complex coacervate ratio should be the moment when the solution is electrically neutral.

[0103] Example 7

[0104] Explore the influence of the wall material compounding ratio on the secondary structure of the complex coacervate

[0105] Circular dichroism (CD) spectroscopy is a spectroscopic method. By using the differential absorption of left and right circularly polarized light by this chromophore, it can be used to deduce the structural information of protein conformation. During the formation of the complex coacervate, the internal structure of PPI also changes. As can be found from Figure 6 (A), PPI has a negative peak at 200 nm, which is attributed to the presence of secondary structures containing β-sheets and β-turns, indicating that a large amount of β-configuration exists in the PPI structure. With the addition of OG, the peak value of the binary complex coacervate at 200 nm gradually decreases. This may be due to the reduction of irregular coil structures and more conversion into other configurations. When the ratio of PPI:OG:CMCS in the ternary complex coacervate is 1:1:1, a lower peak appears at 209 nm, and as the PPI content increases, the peak value gradually decreases and redshifts, indicating that the addition of CMCS will change the conformation of PPI, and the protein molecular conformation gradually changes from a disordered random form to an ordered helical state. Further, the secondary structure information in PPI and the complex coacervate was calculated by the Young's equation, and the results are as Figure 6 (B) shows. The β-type of PPI accounts for 45%, and β-sheets account for 25%, indicating that the β-configuration dominates the change in the CD profile of PPI. The β-turn and random coil contents of the binary complex coacervate decrease by 3.37% and 3.77% respectively, and the increase in β-sheets (31.93%) indicates that the addition of OG makes the structure of PPI gradually develop towards a stable trend. After adding CMCS, the α-helix content of the ternary complex coacervate increases, and the β-sheet and random coil contents decrease; the α-helix content at a ratio of 1:1:1 is 14.43%, which is 2.38 times the α-helix content of the binary complex coacervate, and the α-helix content gradually increases with the increase of the ratio, indicating that the ternary complex coacervate has a more stable and ordered structure.

[0106] Example 8

[0107] Effect of the compounding ratio of wall materials on the encapsulation efficiency and loading rate of vitamin D microcapsules

[0108] In order to clarify the protection efficiency of wall materials for active ingredients and the actual loading amount of vitamin D under different compounding ratios, the effects of wall material ratios on the EE and LC of vitamin D microcapsules were further investigated. A series of standard solutions of vitamin D3 (the concentrations of the series standard solutions were 0.1, 10, 20, 50, 100, 150, 200, 250, 300 μg / mL respectively) were prepared by the gradient dilution method, and the absorbance was detected at the characteristic absorption wavelength of 264 nm using an ultraviolet-visible spectrophotometer, with each concentration measured in parallel three times. A standard curve was constructed by linear fitting of concentration-absorbance, and the results are as Figure 7 (A) shown, and its regression equation is y = 0.0048x + 0.0101, R 2 = 0.9992. It shows that there is a high linear correlation between the standard product concentration and the absorbance value. As Figure 7 (B) shown, with the increase of PPI in the wall material, the EE of the complex coacervation microcapsules gradually decreases, but the total concentration of the biopolymer remains at 1%. By comparing the microcapsules prepared with different wall material ratios, it was found that when the wall material ratio was 1:1:1, the EE of the complex coacervation microcapsules for vitamin D was the highest, at 92.52%. This result indicates that the microcapsules under this wall material ratio can well embed vitamin D. When the PPI content increases, due to the decrease in the polysaccharide content in the solution, the emulsifying property and stability of the emulsion are poor, and most of the vitamins are exposed in the free solution, resulting in a lower encapsulation rate. LC represents the amount of vitamin D that can be carried in the microcapsules with a fixed content (0.01 g), and it depends on the concentration of the bioactive compound used. As can be seen from the figure, when the wall material ratio is 2:1:1, the microcapsules have the highest LC (reaching 74.52%), indicating that the most vitamin D can be carried under this wall material. When the wall material ratios are 3:1:1 and 1:1:1, the LC decreases slightly but still remains at a relatively high level, and the loading rates are 71.46% and 70.41% respectively; when the wall material ratio is 4:1:1, the microcapsules have the smallest LC, and the loading rate is 52.60%, indicating that the proportion of interacting charges in the solution is uneven under this wall material ratio, resulting in a relatively small volume of macromolecules that can react in the solution.

[0109] Example 9

[0110] A preparation method of surimi soft gel containing electrostatic deposition microcapsules, comprising the following steps:

[0111] (1) Thaw the frozen cod surimi at 0 - 4°C for 10 - 14 h. Put the surimi into a food processor and conduct empty beating for 3 min. Add 2% salt based on the mass of the surimi and beat for 3 min. Then add water with the same mass as the surimi and beat for 3 min at a speed of 2500 rpm with a time interval of 20 s;

[0112] (2) Add 5% (by mass of the surimi) of the microcapsules (Example 1) to the surimi and continue beating for 3 min. Heat the surimi using a two - stage heating method, that is, heat at 40°C for 30 min, and then immediately transfer it to 90°C and heat for 30 min. After heating, cool the obtained surimi gel in ice water for 30 min and store it at 4°C until the next analysis.

[0113] Example 10

[0114] Adjust the addition of microcapsules in step (2) of Example 9 to 10% (w / w) and add it to the surimi; other steps are the same as in Example 9.

[0115] Example 11

[0116] Adjust the addition of microcapsules in step (2) of Example 9 to 15% (w / w) and add it to the surimi; other steps are the same as in Example 9.

[0117] Example 12

[0118] Adjust the addition of microcapsules in step (2) of Example 9 to 20% (w / w) and add it to the surimi; other steps are the same as in Example 9.

[0119] Example 13

[0120] Adjust the addition of microcapsules in step (2) of Example 9 to 25% (w / w) and add it to the surimi; other steps are the same as in Example 9.

[0121] Example 14

[0122] Adjust the addition of microcapsules in step (2) of Example 9 to 30% (w / w) and add it to the surimi; other steps are the same as in Example 9;

[0123] Comparative Example 2

[0124] Adjust the water addition amount in step (1) of Example 9 to 0%, and add 0% (w / w) of microcapsules in step (2) to the surimi; other steps are the same as in Example 9.

[0125] Conduct performance tests on the soft gels prepared in Examples 9 - 14 and Comparative Example 2. The test results are as follows:

[0126] Table 1 shows the full texture properties (TPA) of the soft gels in Examples 9 - 14 and Comparative Example 2. It can be seen from the table that the addition of microcapsules has significant effects on the hardness, chewiness, and resilience of the cod protein gel. In Comparative Example 2, the hardness value and chewiness are relatively high, being 2767.08 g and 1653.56 respectively, indicating that the texture of this gel is relatively hard. As the addition amount of microcapsules increases, the hardness value and chewiness of the gel decrease significantly, showing a trend towards a softer texture. Compared with Comparative Example 2, there is no significant change in the elasticity value of Examples 9 - 14, indicating that the addition of water and microcapsules does not reduce the elasticity of the gel. The hardness value and chewiness of the gel in Example 13 are the lowest, indicating that the addition amount of microcapsules in this example can make the gel reach the most suitable soft state for chewing.

[0127] Table 1 Full texture properties of the soft gels in Examples 9 - 14 and Comparative Example 2

[0128]

[0129] The IDDSI framework provides an internationally recognized evaluation standard and test method for the diet design of patients with dysphagia. Through methods such as fork pressure testing, fork separation experiment, and spoon pressure testing, the applicability of the gel as a dysphagia-friendly food can be scientifically evaluated and verified according to the IDDSI classification system to ensure that the food meets the IDDSI level requirements. Figure 8 , According to the analysis of the gel diagram under the IDDSI framework, the texture of Comparative Example 2 (pure cod surimi) is relatively hard. During the fork / spoon pressure test, it is extremely difficult to press, and the area where the thumb turns white is relatively large, about 1 / 3. Moreover, it immediately returns to its original shape after pressing and does not belong to any level in IDDSI. As the addition ratio of microcapsules increases (Examples 9 - 14), the texture of the surimi gradually becomes softer, and the samples can all be easily separated with a fork. In the fork and spoon pressure tests, by pressing the fork and spoon with the thumb, the fingertips of the thumb turn slightly white. After pressing the front end of the fork and spoon, the shape of the sample changes and breaks, and the sample fails to return to its original shape after removing the fork / spoon, with obvious indentations and cracks still remaining. This change indicates that the soft gel can belong to the "potential transitional food" in the IDDSI framework, and the soft gel can be classified as level 6, which means that the gel can be easily decomposed into a safe size through chewing and tongue pressure, reducing the risk of choking. In summary, the addition of microcapsules can effectively regulate the texture of surimi to meet the needs of patients with dysphagia, providing an important practical reference for the diet design of patients with dysphagia.

[0130] Figure 9Gel strength diagrams of the soft gels of Examples 9 to 14 and Comparative Example 2. As can be seen from the figure, with the increase in the addition amount of microcapsules, the gel strength shows a trend of first increasing and then decreasing, developing towards a softer texture. The gel strength of Comparative Example 2 is relatively high, at 1788.32 g·mm. Compared with Comparative Example 2, Examples 9 to 14 all show a significant downward trend. Between Example 9 (adding 5% microcapsules) and Example 13 (adding 25% microcapsules), the gel strength increases with the increase in the addition amount of microcapsules, indicating that an appropriate amount of microcapsules can effectively enhance the gel structure of surimi. The wall material components in the microcapsules may interact with the proteins in the surimi during heating, promoting the cross-linking between protein molecules, thus forming a more stable three-dimensional network structure, stabilizing the water in the gel, and then reducing the gel strength. However, when the addition amount of microcapsules further increases to 30% (Example 14), the gel strength begins to increase. This may be attributed to the interference of excessive microcapsules on the interaction between protein molecules. When the addition amount of microcapsules exceeds the appropriate range, the substances released by them may form local high-concentration regions in the surimi system, thus hindering the effective cross-linking and polymerization between protein molecules. In this case, the binding sites between protein molecules are occupied or shielded by microcapsules, resulting in the inhibition of the construction of the protein network structure. Furthermore, the water in the gel system cannot be effectively bound, resulting in water loss, and the gel strength increases. In summary, an appropriate addition of microcapsules can significantly reduce the gel strength of the gel, but excessive addition will have a negative effect. A decrease in gel strength means that the soft gel has a softer and more delicate taste, which is suitable for those with difficulty chewing.

[0131] Figure 10 Chromaticity diagrams (A), whiteness diagrams (B) and appearance diagrams (C) of the soft gels of Examples 9 to 14 and Comparative Example 2. A good surimi product usually needs to have a high-brightness, high-whiteness and uniform-color appearance in terms of color. Figure 10 (A), L * 、a * 、b * respectively represent the brightness of the gel, the color component on the red-green axis and the color component on the yellow-blue axis. The higher the L * value, the brighter the sample; when the a * value is positive, it means the more red components, and when it is negative, it means the more green components; when the b * value is positive, it means the more yellow components, and when it is negative, it means the more blue components. These parameters together determine the color characteristics of the surimi gel. As can be found from the figure, the addition of microcapsules can effectively improve the brightness of the soft gel; the brightness value of Comparative Example 2 is relatively low, and with the increase in the addition amount of microcapsules, the L *Gradually increasing means that the surimi is gradually developing towards a brighter trend. This phenomenon may be due to the interaction between the wall material in the microcapsules and the proteins in the surimi, which changes the optical properties of the surimi and thus improves its brightness. Whiteness is one of the important indicators for measuring the appearance quality of surimi products, and it directly affects consumers' visual perception and purchase intention. Figure 10 (B), as can be seen from the chart, compared with Comparative Example 2, as the addition amount of microcapsules increases, the whiteness of the surimi gel shows an upward trend. When the addition amount is 20% (Example 12), the overall whiteness value of the surimi is relatively good. This may be related to the fact that the microcapsules are filled into the gaps of the cod protein-based gel structure as the addition amount increases, making the gel network structure denser, enhancing the light scattering effect, and increasing the whiteness. From Figure 10 (C), it can be seen that the visual sense of the soft gel in Comparative Example 2 is yellowish, with low whiteness and no gloss; while the soft gel added with microcapsules (Examples 9-14) has good gloss and a white texture, which is more visually appealing and improves consumers' purchase intention. In summary, the addition amount of microcapsules has a significant impact on the appearance of the surimi gel. An appropriate amount of microcapsules can effectively improve the whiteness of the surimi. Therefore, in practical applications, it is necessary to conduct scientific and reasonable formulation design according to specific circumstances to obtain the best color quality.

[0132] The embodiments provided above are not intended to limit the scope covered by the present invention, nor are the described steps intended to limit their execution order. Obvious improvements made by those skilled in the art to the present invention in combination with the existing common general knowledge also fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing electrostatically deposited microcapsules, characterized in that: The steps include: (1) a pea protein isolate aqueous solution and a β-glucan aqueous solution are combined to form a wall material solution, and nutrients are dissolved in oil to obtain an oil phase; (2) The wall material solution and the oil phase are mixed and emulsified, acetic acid is added to adjust the pH, and a complex coagulation reaction is performed; then a carboxymethyl chitosan aqueous solution is added, and a sodium hydroxide solution is added dropwise to adjust the pH; finally, glutaminase is added to react, the mixture is allowed to stand for stratification, and the supernatant is removed to obtain electrostatically deposited microcapsules.

2. The method according to claim 1, characterized in that In step (1), the oil is at least one of perilla seed oil, soybean oil, walnut oil, linseed oil, rapeseed oil, peanut oil, and sunflower seed oil; the nutrient is a fat-soluble nutrient, and the concentration of the nutrient in the oil phase is 0.5-1.5 mg / mL; the concentration of the pea protein isolate aqueous solution is 0.5-2wt%; and the concentration of the β-glucan aqueous solution is 0.5-2wt%.

3. The method according to claim 1, characterized in that In step (2), the mass ratio of pea protein isolate, β-glucan and carboxymethyl chitosan is 1 to 4:1:

1.

4. The method according to claim 1, characterized in that: In step (2), acetic acid is added to adjust the pH to 3.5-4.5; sodium hydroxide solution is added dropwise to adjust the pH to 5.0-6.

0.

5. The method according to claim 1, characterized in that In step (2), the mass ratio of the wall material solution to the oil phase is 2 to 4:1; and the amount of transglutaminase added is 1 / 4 of the mass of the pea protein isolate.

6. Electrostatic deposition microcapsules prepared by the method according to any one of claims 1 to 5.

7. Use of the electrostatically deposited microcapsules according to claim 6 in the food field.

8. Use of the electrostatically deposited microcapsules according to claim 6 in regulating the texture characteristics of surimi products.

9. A surimi soft gel, characterized in that: The electrostatically deposited microcapsules described in claim 6 are added to the fish paste together with water, pounded, and heated to gelate, thereby obtaining the fish paste soft gel.

10. The surimi soft gel according to claim 9, characterized in that The method for preparing the surimi soft gel comprises the following steps: thawing the frozen surimi and then pounding it in an empty state, adding salt, wherein the amount of salt added is 2-3% of the mass of the surimi, adding water and continuing to pound it, and then adding the electrostatic deposition microcapsules described in claim 6 for final pounding, wherein the amount of electrostatic deposition microcapsules added is 5-30% of the mass of the surimi; subjecting the surimi to a two-stage heating method to gelation, first heating it at 40°C for 20-30 minutes, then immediately transferring it to 90°C and heating it for 30 minutes, and cooling it in ice water after the heating is completed, and obtaining the surimi soft gel after cooling.

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