A low-sodium hollow salt supplemented with astaxanthin for dietary use and its preparation method

Abstract

The present invention provides a method for preparing a low-sodium hollow salt capable of dietary supplementation with astaxanthin, comprising the following steps: dissolving Haematococcus pluvialis protein and food-grade polysaccharide in water, adjusting the pH and stirring to obtain a complex solution; adding NaCl and oil to the complex solution, dispersing at high speed and performing high-pressure homogenization treatment to obtain an oil-in-water Pickering emulsion; spray-drying the oil-in-water Pickering emulsion to obtain a low-sodium hollow salt loaded with astaxanthin. The low-sodium hollow salt capable of dietary supplementation with astaxanthin according to the present invention does not contain any surfactants, and can achieve a sodium reduction effect of 30-50%; astaxanthin is encapsulated in the oil phase, solving problems such as poor water solubility and low bioavailability of astaxanthin, and increasing the daily dietary supplementation of astaxanthin; under long-term storage, the low-sodium hollow salt has good astaxanthin retention rate and lipid oxidation stability; it can effectively prevent the oxidation of the grease in fried steak and is beneficial to maintaining its food quality.

Description

Technical Field

[0001] The present invention belongs to the technical field of hollow microspheres, and particularly relates to a low-sodium hollow salt loaded with astaxanthin and a preparation method thereof. Background Art

[0002] Sodium chloride (NaCl) is the main source of the salty taste in food and is the most widely used condiment in daily diet, which is beneficial to the texture and preservation of food. According to the report of the World Health Organization, the current global average daily sodium intake is 4.5 - 6 grams per day, far exceeding the recommended 2.4 grams per day. Excessive sodium intake in the diet is closely related to hypertension and an increased risk of stroke and cardiovascular diseases. Therefore, there is an urgent need to reduce the sodium content in processed foods.

[0003] Spray-dried salt microspheres with emulsion as the carrier are considered a new salt substitute. By controlling the structure and distribution of the microspheres, they can reduce sodium without losing the taste. For example, Mint Company developed hollow salt using amphiphilic biopolymers such as gum arabic. In applications such as bread and savory snacks, this polymer can reduce sodium by 25 - 50%. Hollow microspheres with smaller size and high specific surface area can increase the accessibility of NaCl to the target receptors on taste bud cells, thus enhancing the perception of saltiness. Yang Xiaoquan et al. prepared hollow salt by spray drying using nanoemulsion droplets as the carrier and the oil phase as the flavor source. However, the existing spray-dried hollow salt still has problems such as poor structural stability, single nutritional components, poor antioxidant performance, and lack of rich flavors.

[0004] Astaxanthin is a beneficial carotenoid, famous for its antioxidant properties, and plays a crucial role in human health. It is mainly used to combat oxidative stress and prevent various diseases such as cardiovascular diseases, inflammation, and cancer. However, astaxanthin has poor water solubility, low bioavailability, and is easily degraded by oxygen, light, and high temperature. These limitations have hindered its widespread use as a nutritional supplement in the food industry. Summary of the Invention

[0005]

Technical Problem

[0006] Hollow salt can reduce sodium intake and is beneficial to human health. However, the existing spray-dried hollow salt has problems such as single nutritional components, poor antioxidant performance, and lack of rich flavors. Astaxanthin can be used to combat oxidative stress and prevent various diseases, but it has poor water solubility, low bioavailability, and is easily degraded by oxygen, light, and high temperature, making it difficult to be used as a nutritional supplement in the food industry. There is a need for a hollow salt that can provide dietary supplementation of astaxanthin, has antioxidant properties, and has rich flavors.

[0007]

Technical Solution

[0008] To address the above technical problems, the present invention utilizes an emulsion as an effective delivery system for astaxanthin to improve its stability and bioavailability. Based on the Haematococcus pluvialis protein-chitosan complex, a low-sodium hollow salt loaded with astaxanthin with antioxidant properties and rich flavors is prepared to provide a salt substitute for dietary supplementation of astaxanthin.

[0009] The present invention provides a method for preparing a low-sodium hollow salt for dietary supplementation of astaxanthin, comprising the following steps:

[0010] (1) Preparation of the complex: Dissolve Haematococcus pluvialis protein and food-grade polysaccharide in water, adjust the pH and stir to obtain a complex solution;

[0011] (2) Preparation of the salt Pickering emulsion: Add NaCl and oil to the complex solution, disperse at high speed and perform high-pressure homogenization treatment to obtain an oil-in-water Pickering emulsion;

[0012] (3) Preparation of the hollow salt: Spray-dry the oil-in-water Pickering emulsion to obtain a low-sodium hollow salt loaded with astaxanthin.

[0013] In one embodiment of the present invention, in step (1), the extraction method of Haematococcus pluvialis protein is as follows: Dissolve Haematococcus pluvialis and NaCl in water, perform ultrasonic treatment to obtain a dispersion system, extract Haematococcus pluvialis protein by ammonium sulfate precipitation method, and dialyze to remove ammonium ions.

[0014] In one embodiment of the present invention, in the extraction method of Haematococcus pluvialis protein, the concentration of Haematococcus pluvialis in the dispersion system after ultrasonic treatment is 4-6 wt%, and the concentration of NaCl is 1.5-3 wt%.

[0015] In one embodiment of the present invention, in the extraction method of Haematococcus pluvialis protein, the ammonium sulfate precipitation method is to add ammonium sulfate (0.662 g / mL) to the dispersion system to precipitate the protein in the supernatant, and after centrifugation at 12000 rpm at 4°C, collect the precipitate of Haematococcus pluvialis protein.

[0016] In one embodiment of the present invention, in the extraction method of Haematococcus pluvialis protein, the dialysis method is to dissolve the precipitate of Haematococcus pluvialis protein in deionized water and dialyze using a 3500 Da dialysis bag at 4°C for 48 h.

[0017] In one embodiment of the present invention, in step (1), the food-grade polysaccharide is one or several of chitosan, gum arabic, carrageenan, maltodextrin, β-glucan, xanthan gum, konjac gum mannose.

[0018] In one embodiment of the present invention, in step (1), the food-grade polysaccharide is chitosan, and 0.4% of glacial acetic acid based on the mass of water is added when dissolving chitosan in water.

[0019] In one embodiment of the present invention, in step (1), the mass ratio of Haematococcus pluvialis protein to food-grade polysaccharide is 1:0.5 to 1:4.

[0020] In one embodiment of the present invention, in step (1), the mass ratio of Haematococcus pluvialis protein to food-grade polysaccharide is preferably 1:2.

[0021] In one embodiment of the present invention, in step (1), the total mass fraction of Haematococcus pluvialis protein and food-grade polysaccharide in the complex solution is 0.5 to 2%.

[0022] In one embodiment of the present invention, in step (1), the pH is adjusted to 3 to 7, the stirring temperature is 20 to 50 °C, and the stirring time is 4 to 8 h.

[0023] In one embodiment of the present invention, in step (1), the pH is adjusted to 5, the stirring temperature is preferably 25 °C, and the stirring time is preferably 6 h.

[0024] In one embodiment of the present invention, in step (2), the NaCl concentration of the complex solution is 20 to 30 g / 100 mL.

[0025] In one embodiment of the present invention, in step (2), the NaCl concentration of the complex solution is preferably 25 g / 100 mL.

[0026] In one embodiment of the present invention, in step (2), the oil is one or more of soybean oil, corn oil, and sunflower oil.

[0027] In one embodiment of the present invention, in step (2), the mass ratio of the complex solution to the oil is 85:15 to 95:5.

[0028] In one embodiment of the present invention, in step (2), the oil is soybean oil, and the mass ratio of the complex solution to soybean oil is preferably 90:10.

[0029] In one embodiment of the present invention, in step (2), the rotation speed of high-speed dispersion is 10000 to 15000 rpm, and the dispersion time is 3 to 10 min.

[0030] In one embodiment of the present invention, in step (2), the high-speed dispersion is carried out in a high-speed disperser, and the model of the high-speed disperser is MICCRA D-4.

[0031] In one embodiment of the present invention, in step (2), the pressure of high-pressure homogenization is 200-1200 bar, and the cycle is 2-4 times.

[0032] In one embodiment of the present invention, in step (2), the high-pressure homogenization equipment is GEA.

[0033] In one embodiment of the present invention, in step (3), the spray drying conditions are as follows: the temperature at the sample injection port is 140-200 °C, the temperature at the output port is 70-100 °C, the sample injection rate is 4-16 mL / min, the rate of the air extractor is 70-100%, the air flowmeter is 20-30 mm, and the vacuum degree is -50 to -100 mbar.

[0034] In one embodiment of the present invention, in step (3), the spray drying equipment is BUCHI B-290.

[0035] The present invention also provides a low-sodium hollow salt loaded with astaxanthin prepared by the above preparation method.

[0036] In one embodiment of the present invention, the composition of the low-sodium hollow salt is as follows: 40-80 wt% of NaCl, 5-30 wt% of a mixture of protein and polysaccharide, 12-30 wt% of edible oil, and 0.2-2 wt% of water.

[0037] The present invention also provides the application of the above-mentioned functional salt loaded with astaxanthin in the food field.

[0038] In one embodiment of the present invention, the food includes dry sprinkle type and cold mix type food.

[0039] Beneficial effects:

[0040] The low-sodium hollow salt capable of dietary supplement of astaxanthin according to the present invention does not contain any surfactants.

[0041] The low-sodium hollow salt capable of dietary supplement of astaxanthin according to the present invention can achieve a sodium reduction effect of 30-50% without losing the salty taste.

[0042] The low-sodium hollow salt capable of dietary supplement of astaxanthin according to the present invention encapsulates astaxanthin in the oil phase to solve problems such as poor water solubility and low bioavailability of astaxanthin, and increases the daily dietary supplement of astaxanthin.

[0043] The spray-dried product obtained by using the emulsion as a carrier in the present invention has good astaxanthin retention rate and lipid oxidation stability during long-term storage.

[0044] The low-sodium hollow salt capable of dietary supplement of astaxanthin according to the present invention can effectively prevent the oxidation of the grease in fried steak and is beneficial to maintaining its food quality. Description of the drawings

[0045] Figure 1 Are the test results of the particle size (A), particle size distribution (B), appearance (C), and cryo-SEM (D) of the oil-in-water Pickering emulsion.

[0046] Figure 2 Are the thermogram (A), relaxation time (B), MRI (C), and relative signal intensity of MRI (D) of the oil-in-water Pickering emulsion.

[0047] Figure 3 Are the test results of the rheological properties of the oil-in-water Pickering emulsion.

[0048] Figure 4 Are the test results of the morphology and particle size of the low-sodium hollow salt loaded with astaxanthin.

[0049] Figure 5 Are the test results of the surface elements of the low-sodium hollow salt loaded with astaxanthin.

[0050] Figure 6 Are the test results of the astaxanthin stability and oil oxidation stability of the low-sodium hollow salt loaded with astaxanthin.

[0051] Figure 7 Are the Na of NaCl and 2% HPP-CS hollow salt (Example 4) + Release characteristics, XRD, and sensory test results.

[0052] Figure 8 Is the frying steak oxidation stability test of NaCl and 2% HPP-CS hollow salt (Example 4). Detailed implementation mode

[0053] The present invention will be described in detail below by combining examples, but the implementation modes of the present invention are not limited thereto.

[0054] The raw materials used in the examples and comparative examples of the present invention are: NaCl was purchased from Dalian Salt Chemical Group, Haematococcus pluvialis powder was purchased from Kunming Baiou Biotechnology Co., Ltd., chitosan was purchased from Shanghai Yuanye Bio-Technology Co., Ltd., and soybean oil was purchased from Jinlongyu. Test method for oil-in-water Pickering emulsion:

[0055] Particle size: The particle size of the emulsion sample was measured using a Zeta sizer Nano instrument (Malvern Instruments, UK). Before measurement, the emulsion sample was diluted to transparency and 1 mL of the sample was used for analysis.

[0056] SEM: The Hitachi SU8010 cryo-SEM was used to analyze the morphology of the emulsion. The emulsion was placed on the sample stage and quickly frozen with liquid nitrogen to maintain its initial state. Then the frozen droplet was cut to expose the cross-section and gold-coated using a cryo-preparation delivery system under vacuum. Subsequently, the sample was transferred to the SEM test chamber at -145 °C for detection.

[0057] Thermal properties: Differential scanning calorimetry (DSC) (DSC-250, TA, USA) was used to analyze the thermal properties of the samples. Approximately 10 mg of the sample was loaded into an aluminum pan, while an empty pan served as a control. During the programmed heating process, high-purity nitrogen gas was used as the protective gas, and the sample was heated from -40 °C to 40 °C at a rate of 5 °C / min.

[0058] Low-field NMR: Low-field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI) analyses of the samples were performed using an LF-NMR analyzer (Newmag Analytical Instruments Co., Ltd., Suzhou, China). The samples were inserted into the nuclear magnetic resonance probe, and signals were acquired through the Carr-Purcell Meiboom-Gill (CPMG) sequence to measure the transverse relaxation time (T2). The experimental parameters including P1 (90° pulse), P2 (180° pulse), TW (π value), and the number of echoes were set to 32 μs, 64 μs, 1500 ms, and 10000, respectively. MRI was performed through the spin echo sequence with specified acquisition parameters, the slice thickness was 2.5 mm, the repetition time (T R ) was 1600 ms, and the echo time (T E ) of the T1-weighted image was 50 ms. The permanent magnet was maintained at a temperature of 32 °C, and a magnetic field strength of 0.5 T was used. The gray-scale images of the MRI images were analyzed using OsiriX software (Pixmeo, Switzerland).

[0059] Rheological properties: The rheological properties of the salt Pickering emulsion were examined using a DHR-2 rheometer (TA Instrument, USA). Four scanning modes were adopted: (1) frequency scanning from 0.1 to 1 Hz at a constant strain of 0.5%; (2) strain scanning from 0.01% to 100% at 1 Hz and 25 °C; (3) measuring the apparent viscosity at a shear rate from 0.1 to 100 s -1 at 25 °C; (4) temperature rising from 10 °C to 80 °C at a frequency of 1 Hz and a strain of 0.1%.

[0060] Test method for astaxanthin-loaded functional salt:

[0061] Sodium content determination: Freshly spray-dried salt powder (0.5 g) was added to a mixed acid solution composed of perchloric acid and nitric acid in a ratio of 1:9, and then heated for digestion until the solution became clear and white smoke emerged. Then, the digested solution was diluted to 25 mL with deionized water for Na + content analysis. Cesium chloride solution (0.2% m / v) was introduced into the final determination solution and the corresponding blank solution. The Na content in the diluted sample was measured at 589 nm using AA-240 flame atomic absorption spectrometry + .

[0062] SEM and EDS: The morphology of the hollow salt was characterized by SEM (JSM-7800F, Japan). Approximately 50 particles were analyzed directly from the SEM images using ImageJ software (version 1.52a, National Institutes of Health, USA) while maintaining their original magnification to determine the particle diameter and size distribution. The surface elemental composition (Na, Cl, O, C, and N) of the hollow salt particles was examined using an SEM instrument equipped with an energy-dispersive X-ray spectroscopy (EDS) detector (X-Max50, UK).

[0063] XRD: The crystallinity and grain size of the salt particles were evaluated using an X-ray diffractometer (XRD-7000S, Japan). The samples were analyzed using CuKα radiation (wavelength ) under operating conditions of 40 mA and 45 kV. The 2θ scanning range was from 10° to 70°, the step size was 0.003°, and the scanning speed was 50 seconds / step. In addition, the Debye–Scherrer equation (Equation 1) was used to determine the grain size of the samples;

[0064] D = Kλ / (βcosθ) (1)

[0065] Here, D represents the grain size of the sample, K represents a dimensionless shape factor, λ represents the wavelength of CuKα radiation, β represents the full width at half-maximum intensity, and θ is the Bragg angle.

[0066] Moisture content and water activity: The moisture content of the newly spray-dried hollow salt powder was evaluated by gravimetry. Hollow salt powder with a mass of W0 was added to a crucible, and the total mass of the crucible and the hollow salt powder, W1, was recorded. Then, it was dried to a constant weight at 105 °C, and the total mass of the crucible and the hollow salt powder, W2, was recorded. The moisture content (%) was calculated as 100×(W1 - W2) / W0. The water activity (aw) was measured using a water activity meter (Aqua Lab 4TE, USA) with a sensitivity of ±0.001.

[0067] Chromaticity: The color values of the hollow salts were measured using a HunterLab spectrophotometer (ColorFlex EZ, USA). Before analysis, calibration was performed using a black glass and a white tile. The results were presented based on the L* (lightness), a* (red - green), and b* (blue - yellow) values (Lima et al., 2021). The color difference between the control sample and the modified sample was calculated using Equation (2).

[0068]

[0069] Total oil content: The total oil content of the hollow salts was determined by hexane extraction gravimetry. A 0.5 - g sample was dispersed in 15 mL of deionized water, 30 mL of hexane was introduced, and the mixture was shaken vigorously to ensure complete extraction of the oil. Subsequently, the mixture was centrifuged at 4500 rpm for 5 minutes. The upper layer containing the extracted oil was collected and dried at 60 °C until a constant weight was reached, and the total oil amount was weighed.

[0070] Surface oil content: 15 mL of hexane was added to 1.5 g of the hollow salt sample, and then the mixture was stirred at 150 rpm for 2 minutes. Subsequently, the mixture was filtered through a filter paper, and the residue was washed three times with 20 mL of hexane. The filtrate was collected and dried at 60 °C until a constant weight was reached, and the surface oil content was weighed.

[0071] The encapsulation efficiency was determined by Equation (3);

[0072] Encapsulation efficiency (%)=(TO - SO) / TO×100 (3)

[0073] where TO represents the total oil amount, and SO represents the surface oil content extracted per unit mass of the spray - dried powder.

[0074] Astaxanthin storage stability: The storage stability of the hollow salt powder was investigated by measuring the astaxanthin content of the hollow salt powder during storage at 50 °C for 15 days using an ultraviolet - visible spectrophotometer (Lambda 35, USA). Initially, 0.2 g of the astaxanthin - containing hollow salt was mixed with 4.8 mL of a mixed solvent (dichloromethane:methanol = 2:1 v / v). After stirring, the sample was centrifuged at 8000 rpm for 10 min, and then the absorbance of the organic phase was measured at 480 nm to determine the astaxanthin content.

[0075] LH measurement: The freshly spray-dried hollow salt powder was stored at 50 °C for 15 days to evaluate the oxidation of soybean oil. To detect the main lipid oxidation products, 0.2 g of the hollow salt powder was mixed with 1.5 mL of a mixed solvent (2-propanol: isooctane = 1:3 v / v) and stirred for 3 minutes. Subsequently, the suspension was centrifuged (8000 rpm, 5 min), and then 2.8 mL of methanol / 1-butanol (2:1, v / v) was added to the supernatant, and 15 μL of ferrous sulfate and ammonium thiocyanate solutions were introduced respectively. After a 20-min dark reaction, the absorbance at 510 nm was recorded. The LH content was determined using the standard curve of H2O2.

[0076] MDA measurement: 0.2 g of the hollow salt powder was mixed with a solution containing 4 mL of thiobarbituric acid (TBA) and 1.8 mL of deionized water. The TBA solution contained 0.375 g of TBA dissolved in 100 mL of 0.25 mol / L HCl and 15 g of trichloroacetic acid was added. Then the mixture was heated at 95 °C for 10 min and subsequently cooled. After centrifuging the solution (8000 rpm, 5 min) to obtain the supernatant, the absorbance was measured at 532 nm. The content of malondialdehyde (MDA) was quantified using the standard curve prepared with 1,1,3,3-tetraethoxypropane.

[0077] Electronic tongue measurement: An Astrie electronic tongue detection system (Alpha MOS, France) was used to identify the flavor intensity of the hollow salt. The powder sample was dissolved in a solution and incubated at 37 °C to simulate oral temperature. The sensor was immersed in the sample, and data was collected once per second. Principal component analysis (PCA) was performed using the built-in software.

[0078] Sensory panel evaluation: Eighteen healthy assessors aged between 18 and 35 years old without taste disorders were recruited. Before the main experiment, they underwent a series of screening tests, including triangle tests, ranking tests, and salinity threshold tests. Finally, 14 qualified sensory assessors (with a male-to-female ratio of 1:1) were selected to conduct all the sensory evaluations in this work.

[0079] Beef was purchased from Qianhe Market in Dalian, cut into small pieces of uniform size, and then fried at 180 °C for 3 min. The pre-measured salt samples were evenly sprinkled on the cooked beef. Sensory evaluations were conducted in a controlled sensory panel room under double-blind conditions. Each salt-seasoned steak was placed in a covered sensory bottle labeled with a randomly assigned three-digit number. Panelists were instructed to evaluate and score attributes such as salinity, appearance, off-odor, particle dispersibility, and oral texture using a 0-to-10 scoring scale.

[0080] Antioxidant Application of Astaxanthin Hollow Salt in Fried Steak: Fresh steak is fried at 180 °C for 3 min. Subsequently, an equal amount of NaCl and the hollow salt sample are evenly sprinkled on the surface of the steak. Then, it is stored overnight at 4 °C and 25 °C respectively. Finally, the steak with a fried surface is cut into small pieces, and 0.2 g of the steak sample is collected as the test sample. According to the method for lipid oxidation determination in Section 2.11, the lipid hydroperoxide (LH) and malondialdehyde (MDA) contents of the overnight steak are measured.

[0081] Example 1

[0082] A preparation method of a low-sodium hollow salt for dietary supplementation of astaxanthin, comprising the following steps:

[0083] (1) Extraction of Haematococcus pluvialis protein: Weigh 100 g of Haematococcus pluvialis powder, dissolve it in 2000 mL of water and stir continuously. Add 40 g of NaCl, sonicate for 2 h to obtain a dispersion system. Add ammonium sulfate at 0.662 g / mL to precipitate the protein in the supernatant. After centrifugation at 12000 rpm at 4 °C, collect the precipitate of Haematococcus pluvialis protein and dialyze it using a 3500 Da dialysis bag at 4 °C for 48 hours.

[0084] (2) Preparation of the complex: Prepare a 2 wt% Haematococcus pluvialis protein solution and a 2 wt% chitosan solution with an ice acetic acid concentration of 0.04 wt% in advance. Take 10 mL of the 2 wt% Haematococcus pluvialis protein solution and 20 mL of the 2 wt% chitosan solution, make up the solution to 120 mL, so that the total mass fraction of Haematococcus pluvialis protein and chitosan is 0.5%, adjust the pH to 5, and stir at 25 °C for 6 h to obtain a complex solution.

[0085] (3) Preparation of salt Pickering emulsion: Add 30 g of NaCl and 12 g of soybean oil to the complex solution, treat it with a MICCRA D-4 high-speed disperser at 12000 rpm for 3 min, and pass it through a GEA high-pressure homogenizer for 3 cycles at a high pressure of 600 bar to prepare an oil-in-water Pickering emulsion.

[0086] (4) Preparation of hollow salt: Connect the oil-in-water Pickering emulsion to the spray drying injection pump for spray drying. The spray drying conditions are: inlet port temperature 160 °C, outlet port temperature 90 °C, injection rate 8 ml / min, air extractor rate 90%, air flow meter 25 mm, vacuum degree -80 mbar. Collect the powder and store it in a cool and dry place to obtain a low-sodium hollow salt loaded with astaxanthin.

[0087] Example 2

[0088] A preparation method of a low-sodium hollow salt for dietary supplementation of astaxanthin:

[0089] The difference from Example 1 is that in step (2), 20 mL of 2 wt% Haematococcus pluvialis protein solution and 40 mL of 2 wt% chitosan solution are taken, and the solution is made up to 120 mL to make the total mass fraction of Haematococcus pluvialis protein and chitosan 1%.

[0090] Example 3

[0091] A preparation method of a low-sodium hollow salt for dietary supplementation of astaxanthin:

[0092] The difference from Example 1 is that in step (2), 30 mL of 2 wt% Haematococcus pluvialis protein solution and 60 mL of 2 wt% chitosan solution are taken, and the solution is made up to 120 mL to make the total mass fraction of Haematococcus pluvialis protein and chitosan 1.5%.

[0093] Example 4

[0094] A preparation method of a low-sodium hollow salt for dietary supplementation of astaxanthin:

[0095] The difference from Example 1 is that in step (2), 40 mL of 2 wt% Haematococcus pluvialis protein solution and 80 mL of 2 wt% chitosan solution are taken, and the solution is made up to 120 mL to make the total mass fraction of Haematococcus pluvialis protein and chitosan 2%.

[0096] Comparative Example 1

[0097] A preparation method of a hollow salt:

[0098] The difference from Example 1 is that 60 mL of 2 wt% Haematococcus pluvialis protein solution is taken, and the solution is made up to 120 mL to make the mass fraction of Haematococcus pluvialis protein 1%.

[0099] Comparative Example 2

[0100] A preparation method of a hollow salt:

[0101] The difference from Example 1 is that 60 mL of 2 wt% chitosan solution is taken, and the solution is made up to 120 mL to make the mass fraction of chitosan 1%.

[0102] The water-in-oil Pickering emulsions and functional salts loaded with astaxanthin prepared in Examples 1-4 and Comparative Examples 1 and 2 were subjected to performance tests, and the test results are as follows:

[0103] I. Characterization of water-in-oil Pickering emulsions

[0104] Particle size and SEM analysis

[0105] The droplet sizes and particle distributions of the oil-in-water Pickering emulsions in Examples 1-4 and Comparative Examples 1 and 2 are as Figure 1 shown in A-B. The droplet size range of the oil-in-water Pickering emulsion stabilized by the Haematococcus pluvialis protein-chitosan (HPP-CS) complex is from 750±59.15 nm to 1385±450.15 nm, and it decreases with the increase in the concentration of the HPP-CS complex. The smaller the droplet size, the higher the emulsion stability. The stable droplet sizes of Comparative Examples 1 and 2 are 1058.5±47.03 nm and 2098±122 nm, respectively. The reason is that the decrease in the sizes of the HPP-CS complex and HPP particles promotes the effective adsorption of the emulsifying particles at the oil-water interface, resulting in smaller droplet sizes.

[0106] Figure 1 C shows the appearance of the HPP-CS complex in stabilizing the oil-in-water Pickering emulsions in Examples 1-4 and Comparative Examples 1 and 2. All emulsions appear as flowing liquids, and the orange color of the emulsion deepens with the increase in the HPP content. The water-oil volume ratio of the emulsion is 90%, and the solid content is 25.5-27%. The cryo-SEM images ( Figure 1 D) show that the oil-in-water Pickering emulsions prepared at higher HPP-CS complex concentrations exhibit smaller droplets, more uniform distribution between droplets, less aggregation, and higher stability. The emulsion droplets in Comparative Example 1 show obvious fusion, indicating poor stability. The droplet size of the emulsion in Comparative Example 2 is significantly larger than that of the other groups.

[0107] Thermal properties and low-field NMR analysis

[0108] In the DSC measurement ( Figure 2 A), the temperature is gradually increased from -20 °C, and the heat flow signal initially decreases (exothermic), then increases (endothermic). The negative value indicates that the water phase in the oil-in-water Pickering emulsion undergoes supercooled water crystallization (exothermic) between -20 and 0 °C, and then the ice that has crystallized melts as the temperature continues to rise (endothermic). With the increase in the concentration of the HPP-CS complex, the temperature corresponding to the negative peak continuously shifts towards -20 °C. Compared with the other groups, the oil-in-water Pickering emulsion in Example 4 exhibits a lower crystallization temperature, indicating its higher stability.

[0109] The relaxation time (T2) distribution of the oil-in-water Pickering emulsion is as Figure 2As shown in B. The detected signals are divided into three regions: 0.1 - 10, 10 - 100, and 100 - 1000 ms, corresponding to strongly bound water, weakly bound water, and free water, respectively. In the transverse T2 relaxation spectra of the stable emulsions in Examples 1 - 4 and Comparative Examples 1 and 2, two characteristic peaks were observed in the ranges of 10.35 - 51.11 ms and 178.34 - 410.27 ms. With the increase in the concentration of HPP - CS, the peak in the range of 100 - 1000 ms shifted to the left, indicating that a larger proportion of free water became bound water through interactions with other components. This change in the water state indicates an improvement in the stability of the oil - in - water Pickering emulsion. Figure 2 C shows the MRI image sequence of the emulsion, where higher water content (hydrogen protons) corresponds to stronger signals in the MRI image ( Figure 2 D). With the increase in the concentration of HPP - CS composite particles, the color distribution of the MRI image becomes more and more uniform. In the emulsions of Comparative Examples 1 and 2, the non - uniform color distribution indicates uneven dispersion of the water and oil phases, which may lead to a decrease in stability.

[0110] Rheological behavior analysis

[0111] Rheological properties are crucial for the stability and functionality of emulsions containing high NaCl concentrations, especially in applications involving spray - drying hollow salts. In the frequency - sweep test ( Figure 3 A), except for Example 4, the G′ and G″ values of all samples remained below 60, and the observed differences were minimal. This may be because the weak micro - network structure formed by droplet aggregation under high ionic strength enables the emulsion to maintain a high - flow state. A high - flow state meets the prerequisite for the feed liquid of spray drying. A precursor liquid with too high viscosity is likely to block the spray - drying equipment, thus affecting the production and preparation of hollow salts. In the strain - sweep test ( Figure 3 B), in the strain range from 0.01% to 100%, the G′ value of all emulsions was higher than the G″ value at strains below 1%, indicating that in this strain range, there was mainly elastic behavior and strong structural stability. The increase in the oscillatory stress reflects the structural stability and elastic properties of the emulsion. The improvement of the emulsion's structural stability is beneficial to the stability of the hollow structure of the hollow salt. With the increase in strain, except for Comparative Example 1, the stress responses of all emulsions tended to stabilize in the range of 10 - 100% ( Figure 3 C). This observation may be due to the increase in NaCl concentration, which increases the viscosity of the system. Within the range that satisfies good fluidity, increasing the viscosity of the feed liquid helps to enhance the structural stability of the hollow salt and reduce the particle size. As Figure 3As shown in Figure 4, all emulsions exhibited typical shear thinning behavior, in which the network structure gradually deformed with increasing shear rate. At a shear rate of 3-10 1 / s, the apparent viscosity of the water-in-oil Pickering emulsion in Example 4 was less than 10, while for the other samples, the apparent viscosity was less than 1, indicating that all samples had strong fluidity. The apparent viscosity of the emulsion was positively correlated with the concentration of HPP-CS composite particles.

[0112] In addition, the thermal stability of the emulsions was evaluated by dynamic temperature sweep tests. Figure 3 As shown in Figure E, the G' values of all emulsions remain relatively unchanged in the temperature range of 20–70 °C, indicating reasonable thermal stability. The feed salt emulsion precursor has high thermal stability, which can reduce the thermal demulsification of emulsion droplets during spray drying, thereby improving the uniformity of the hollow salt powder. Figure 3 F shows that all emulsions exhibit typical shear-thinning behavior with increasing temperature. Specifically, the emulsions stabilized by 0.5% HC and 1% HPP maintain a low viscosity that remains stable during heating. The temperature at which the emulsions reach the lowest viscosity gradually increases with increasing HPP-CS complex concentration. Higher temperatures may weaken the stabilizing effect of ions on the emulsion structure, thereby further reducing the viscosity. In general, the emulsions stabilized by the HPP-CS complex exhibit excellent viscoelasticity and thermal stability. Based on these findings, increasing the concentration of the HPP-CS complex can enhance the rheological properties of emulsions containing high concentrations of NaCl.

[0113] 2. Characterization of the structure of low sodium hollow salt loaded with astaxanthin

[0114] SEM and EDS

[0115] Astaxanthin-loaded low-sodium hollow salt particles were prepared by spray drying a salt Pickering emulsion stabilized by HPP-CS complex. Figure 4 A shows the appearance of low sodium hollow salt. Figure 4 B~D show the microscopic morphology and average particle size of the low sodium hollow salt. Compared with Examples 1-2 and Comparative Examples 1-2, the low sodium hollow salt particles of Example 4 exhibit more uniform and smaller particle sizes and have a smooth surface. This shows that the content and size of the wall material are crucial to the stability of the surface structure of the low sodium hollow salt particles. Studies have shown that insufficient emulsification properties or low wall material content can cause cracks on the surface of low sodium hollow salt. Typically, NaCl particles are larger than 300 μm, while the smaller size and larger surface area of low sodium hollow salt particles contribute to the perception of saltiness because they dissolve faster during consumption. Figure 5 The EDS results showed that the surface of low-sodium hollow salt microspheres was mainly composed of Na and Cl. The low-sodium hollow salt with higher HPP-CS concentration showed lower Na content.

[0116] Physical properties

[0117] Water content and water activity are key parameters determining the shelf life of products. Generally, the water content of commercially available salts ranges from 0.91% to 7.36%. Excessive water content can easily lead to product deterioration. As shown in Table 1, the water content of the low-sodium hollow salts in Examples 1-4 is 0.33-1.18%. The water content of the low-sodium hollow salt particles increases with the increase in HPP content, which may be due to the hydrophilicity of HPP. The increase in temperature and the acceleration of the evaporation rate during the spray drying process will reduce the water activity (a w ). Higher aw levels are associated with reduced fluidity because they increase the interaction of low-sodium hollow salt particles. When a w is below 0.91, the growth of most bacteria can be inhibited. The aw of the low-sodium hollow salts in Examples 1-4 is 0.09-0.11.

[0118] Table 1 Physical properties of hollow salts

[0119]

[0120]

[0121] Different letters in the same column indicate significant differences (p<0.05).

[0122] Color is an important factor affecting consumers' acceptance of food. Table 2 shows the chromaticity of the low-sodium hollow salts. There are statistically significant changes in the L*, a*, and b* values among the samples (P<0.05), indicating that the HPP-CS complex concentration affects the color parameters. The HPP salts exhibit higher ΔE values and lower L* values, which are closely related to the presence of the natural pigment astaxanthin in the wall material (equivalent to 2% of the wall material).

[0123] Table 2 Chromaticity of hollow salts

[0124] L* a* b* ΔE Example 1 <![CDATA[36.39±0.01 b > <![CDATA[12.83±0.02 e > <![CDATA[38.68±0.03 a > <![CDATA[40.96±0.23 b > Example 2 <![CDATA[32.07±0.25 c > <![CDATA[15.88±0.30 d > <![CDATA[30.86±0.09 b > <![CDATA[38.19±0.30 c > Example 3 <![CDATA[29.63±0.54 d > <![CDATA[17.32±0.38 c > <![CDATA[27.54±0.05 c > <![CDATA[38.13±0.56 c > Example 4 <![CDATA[27.00±0.34 e > <![CDATA[20.58±0.52 b > <![CDATA[22.11±0.04 e > <![CDATA[38.56±0.25 c > Comparative Example 1 <![CDATA[22.54±0.19 f > <![CDATA[24.06±0.29 a > <![CDATA[25.64±1.32 d > <![CDATA[45.22±0.47 a > Comparative Example 2 <![CDATA[54.68±0.39 a > <![CDATA[0.68±0.03 f > <![CDATA[4.10±0.06 f > -

[0125] Different letters in the same column indicate significant differences (p<0.05).

[0126] It can be clearly seen from Table 3 that there is no significant difference in the total oil content (16 - 20%) of the low-sodium hollow salts in Examples 1 - 4 and Comparative Examples 1 - 2, indicating that an inlet temperature of 160 °C is more suitable for drying the HPP-CS hollow salts. Compared with Comparative Examples 1 - 2, the low-sodium hollow salts prepared from the HPP-CS complex exhibit a lower surface oil content, which decreases with an increase in the concentration of the HPP-CS complex. In addition, the encapsulation efficiency of the oil also follows a similar trend. For the hollow salt powder, a lower surface oil content and a higher encapsulation efficiency are beneficial for reducing the degradation of astaxanthin and lipid oxidation. This may be attributed to the electrostatic interaction between HPP and CS, which forms a thicker and tighter barrier around the oil droplets.

[0127] Table 3 Total oil, surface oil, and encapsulation efficiency of hollow salts

[0128]

[0129]

[0130] Different letters in the same column indicate significant differences (p < 0.05).

[0131] Astaxanthin and oxidative stability

[0132] The long-term stability of low-sodium hollow salts loaded with astaxanthin was investigated. Figure 6 A shows the astaxanthin retention rates of the low-sodium hollow salts in Examples 1 - 4 and Comparative Examples 1 - 2 within 15 days at 50 °C. After 15 days of storage, the astaxanthin retention rates of all low-sodium hollow salts showed a downward trend. Specifically, in the low-sodium hollow salts of Examples 1 - 4, the astaxanthin retention rates were 41.39 ± 2.88%, 47.42 ± 0.75%, 56.24 ± 1.32%, and 61.28 ± 0.75% respectively, and that of Comparative Example 1 was 36.02 ± 1.07%. The residual astaxanthin levels in Examples 1 - 4 were higher than that in Comparative Example 1. This indicates that with an increase in the complex concentration, the protective effect of the low-sodium hollow salts on astaxanthin is enhanced. At the same time, Figure 6 B gives a semi-logarithmic plot describing the astaxanthin retention rate. The research results show that the degradation behavior of astaxanthin can be effectively described by a first-order kinetic model. At 50 °C, the half-lives of astaxanthin encapsulated in the low-sodium hollow salts of Examples 1 - 4 were 12, 14, 18, and 21 days respectively, which were higher than the astaxanthin half-life of the comparative example (Table 4). This indicates that the incorporation of the HPP-CS complex significantly enhances the stability of astaxanthin, and the adsorption of the HPP-CS complex on the outer shell structure of the low-sodium hollow salt particles may affect the interaction between available oxygen and astaxanthin. In addition, the crude extract of HPP has the ability to scavenge free radicals, thus delaying the degradation of astaxanthin.

[0133] Table 4 Effect of HPP-CS complex on the storage stability of astaxanthin in hollow salts

[0134]

[0135] The levels of lipid hydroperoxides (LH) and malondialdehyde (MDA) were measured for all samples to evaluate the antioxidant efficacy of the functional salts against lipid oxidation. As Figure 6 shown in Figure 6 C, all samples exhibited similar LH levels, which then increased rapidly starting from the 3rd day of storage. After 15 days, the LH contents in the low-sodium hollow salts of Examples 2-4 were 43.77, 30.59, and 19.05 mmol / kg oil, respectively. The LH levels of Example 1 and Comparative Examples 1-2 were 2.82, 3.14, and 3.46 times that of Example 4, respectively. These findings indicate that the HPP-CS complex effectively inhibits the oxidation of the oil within the particles. The MDA levels (

[0136] Na + release and XRD determination

[0137] The Na + release characteristics of the low-sodium hollow salts were evaluated, as Figure 7 shown in + A. Specifically, compared with NaCl, the Na + release rate of the low-sodium hollow salts was significantly higher. The low-sodium hollow salts released 80% of their Na + content within 10 seconds, while NaCl required at least 30 seconds to reach the same release level. The faster release of Na + from the low-sodium hollow salts + might result in a stronger perception of saltiness. Therefore, compared with standard table salt with an equal sodium content, the low-sodium hollow salts can be considered to have a stronger saltiness. The perception of saltiness by taste receptors is closely related to the Na + release rate in foods. When Na +The release rate is very fast, which may activate these taste receptors faster, thus producing a stronger salty taste( Figure 7 B).

[0138] X-ray diffraction (XRD) analysis revealed the crystallinity and cubic lattice structure of the salt particles( Figure 7 C). The XRD spectrum showed a significant peak near 2θ = 31.60°, which is characteristic of their cubic structure. NaCl showed clear and strong peaks, indicating its crystal structure. In contrast, the XRD pattern of the low-sodium hollow salt showed a decrease in the intensity of the Bragg peaks, indicating a decrease in crystallinity. In addition, the XRD pattern of the low-sodium hollow salt showed a slightly distorted cubic phase with split reflections at the strong peaks. In addition, the crystallite sizes of NaCl and the low-sodium hollow salt were calculated to be 130.2 nm and 46.7 nm, respectively. These findings indicate that the atomization process significantly reduces the crystal size of the low-sodium hollow salt particles, facilitating the rapid release of Na + .

[0139] Sensory analysis

[0140] Figure 7 D shows the taste score results output by the electronic tongue for NaCl and the low-sodium hollow salt. The results show that the salty, astringent, bitter, umami, richness, and sour tastes of the low-sodium hollow salt are significantly higher than those of NaCl. In addition, Figure 7 the PCA results in E further show that there are significant differences in the overall taste between the low-sodium hollow salt and NaCl, and the sample differences have a cumulative variance of 99.7% (PC1: 96.0%, PC2: 3.7%). Equal amounts of NaCl and low-sodium hollow salt powder were sprinkled on the surface of freshly cooked steak, and the sensory evaluation results showed that there was no significant difference in the saltiness score of the steak, and no adverse effects were observed( Figure 7 F). It has been reported in the literature that the salinity of chitosan / acid / NaCl particles prepared at room temperature is 19.2 - 54.4% lower than that of NaCl with the same salinity. The enhanced saltiness of the low-sodium hollow salt may be attributed to the smaller NaCl crystals on the surface. Specifically, Na + is widely distributed on the surface of the low-sodium hollow salt microspheres, resulting in a larger specific surface area and a faster dissolution rate, thus enhancing the perceived saltiness.

[0141] Oxidation stability of fried steak after salting

[0142] Equal amounts of NaCl and low-sodium hollow salt powder were sprinkled on the surface of freshly cooked steak( Figure 8 A), and then left overnight at 4 °C and 25 °C to determine their LH and MDA contents, respectively, as shown in Figure 8As shown in Figures B and 8C, it can be seen that there are significant differences in the LH and MDA contents of fried beef steaks stored at 4 °C and 25 °C, indicating that there is a continuous oxidation reaction in fried foods after overnight storage. Compared with the NaCl sample, the LH and MDA contents of fried beef steaks with low-sodium hollow salt added are significantly reduced at 4 °C and 25 °C. The low-sodium hollow salt containing astaxanthin based on HPP-CS may be a potential salt product for fried foods, which can reduce the degree of oxidation before it enters the mouth.

[0143] The embodiments provided above are not intended to limit the scope covered by the present invention, nor are the described steps intended to limit the order of their execution. Obvious improvements made by those skilled in the art to the present invention in combination with the existing well-known common sense also fall within the protection scope defined by the claims of the present invention.

Claims

1. A preparation method of a low-sodium hollow salt capable of dietary supplement of astaxanthin, characterized in that, It includes the following steps: (1) Preparation of the complex: Dissolve Haematococcus pluvialis protein and food-grade polysaccharide in water, adjust the pH and stir to obtain a complex solution; the food-grade polysaccharide is chitosan; the mass ratio of Haematococcus pluvialis protein to food-grade polysaccharide is 1:0.5 - 1:4, and the total mass fraction of Haematococcus pluvialis protein and food-grade polysaccharide in the complex solution is 1.5 - 2%; adjust the pH to 3 - 7, the stirring temperature is 20 - 50 °C, and the stirring time is 4 - 8 h; (2) Preparation of the salt Pickering emulsion: Add NaCl and oil to the complex solution, disperse at high speed and perform high-pressure homogenization treatment to obtain an oil-in-water Pickering emulsion; the NaCl concentration of the complex solution is 20 - 30 g / 100 mL; the oil is one or several of soybean oil, corn oil and sunflower oil; the mass ratio of the complex solution to the oil is 85:15 - 95:5; the rotation speed of high-speed dispersion is 10000 - 15000 rpm, and the dispersion time is 3 - 10 min; the pressure of high-pressure homogenization is 200 - 1200 bar, and the cycle is 2 - 4 times; (3) Preparation of the hollow salt: Spray-dry the oil-in-water Pickering emulsion to obtain a low-sodium hollow salt loaded with astaxanthin; the spray-drying conditions are: the inlet port temperature is 140 - 200 °C, the outlet port temperature is 70 - 100 °C, the injection rate is 4 - 16 ml / min, the air extractor rate is 70 - 100%, the air flowmeter is 20 - 30 mm, and the vacuum degree is -50 - -100 mbar; Among them, the extraction method of Haematococcus pluvialis protein is: Dissolve Haematococcus pluvialis and NaCl in water, perform ultrasonic treatment to obtain a dispersion system, extract Haematococcus pluvialis protein by ammonium sulfate precipitation method, and dialyze to remove ammonium ions; the concentration of Haematococcus pluvialis in the dispersion system is 4 - 6 wt%, and the NaCl concentration is 1.5 - 3 wt%.

2. The preparation method according to claim 1, characterized in that, In step (1), add 0.4% of glacial acetic acid based on the mass of water when dissolving chitosan in water.

3. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of Haematococcus pluvialis protein to food-grade polysaccharide is 1:2; adjust the pH to 5, the stirring temperature is 25 °C, and the stirring time is 6 h.

4. The preparation method according to claim 1, characterized in that, In step (2), the NaCl concentration of the complex solution is 25 g / 100 mL; the oil is soybean oil, and the mass ratio of the complex solution to the oil is 90:

10.

5. The low-sodium hollow salt loaded with astaxanthin prepared by the preparation method according to any one of claims 1 - 4.

6. The low-sodium hollow salt according to claim 5, characterized in that, The components are: 40 - 80 wt% of NaCl, 5 - 30 wt% of the mixture of protein and polysaccharide, 12 - 30 wt% of edible oil, and 0.2 - 2 wt% of water.

7. The application of the low-sodium hollow salt according to claim 6 in the food field.

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