Mineralized gel type physalis alkekengi leavening agent and application thereof in preparation of physalis alkekengi bean curd

Abstract

The invention provides a mineralized gel type physalis alkekengi leavening agent and application thereof in preparation of physalis alkekengi tofu. The method comprises the following steps: firstly, forming an EGCG-Ca < 2 + > complex from epigallocatechin gallate and tricalcium phosphate in soybean clear water, inducing TCP nanosheets to be self-assembled, and interpenetrating with a soybean protein network to construct a mineralized gel skeleton; the mineralized gel type sour slurry leavening agent is prepared by firstly preparing a skeleton, then immobilizing lactic acid bacteria in micropores of the skeleton and finally performing electrostatic grafting on soybean peptide, so that the gel strength, the water binding capacity, the flavor and the like of sour slurry bean curds are improved, and the nutrition and the quality of the bean curds are further improved.

Description

Technical Field

[0001] The invention belongs to the field of physalis bean curd fermentation, and particularly relates to a mineralized gel-type physalis bean curd fermentation agent and application thereof in the preparation of physalis bean curd. Background Art

[0002] As a traditional soy product, the production of physalis tofu relies on the natural fermentation of physalis (yellow slurry). Traditionally, this process utilizes the metabolic activity of the natural microbial community within the soywater to produce acid, which then causes the soy protein in the soymilk to form a gel through electrochemical precipitation. However, natural fermentation has inherent drawbacks, including uncontrollable microbial communities, long fermentation cycles, and wide fluctuations in product quality. To improve standardization, modern industry has attempted to enhance fermentation by introducing pure lactic acid bacteria. While this has improved acid production efficiency to some extent, the use of a single lactic acid bacteria strain still has significant limitations. Firstly, its single metabolic spectrum results in a lack of physalis flavor compounds, making it difficult to replicate the complex flavor characteristics of natural fermentation. Secondly, the acid production capacity of a single strain is easily inhibited by the environment, and actual fermentation efficiency still fails to meet the requirements of industrial continuous production.

[0003] Existing technologies for tofu texture control generally rely on exogenous calcium salts (such as calcium chloride and calcium sulfate) as coagulants. These calcium salts transiently release high concentrations of calcium ions during the slurrying process, triggering intense cross-linking of soy proteins and leading to uneven size distribution of protein aggregates. This over-aggregated gel network forms coarse pores at the microscopic level, which manifests as a roughened and gritty tofu texture at the macroscopic level, severely degrading the taste quality. Despite attempts to mitigate the aggregation rate through gradient addition of calcium salts, these efforts have failed to fundamentally address the issue of matching the calcium ion release kinetics with the protein cross-linking rate.

[0004] Furthermore, the shelf life and water retention of tofu from Physalis sylvestris also face technical bottlenecks. Traditional products lack an effective antioxidant system, and the aldehyde and ketone odors produced by lipid oxidation during storage generally result in a shelf life of less than 72 hours. Furthermore, insufficient gel network strength and reduced free water retention make tofu susceptible to water loss during storage and transportation, resulting in a loss of hardness of over 30%. Existing solutions, such as adding chemical preservatives or thickeners, not only contradict the clean label trend but also potentially introduce odors and destroy the tofu's natural flavor.

[0005] In recent years, while research has explored the use of composite bacterial fermentation or polysaccharide modification to improve tofu quality, these efforts have failed to synergistically address multiple requirements, including acid production efficiency, calcium release control, network strengthening, and antioxidant activity. In particular, the damage to the bacteria caused by the acidic fermentation environment has not been effectively addressed, resulting in low survival rates and high inoculum requirements. Therefore, there is an urgent need to develop a new Physalis starter system that integrates controlled fermentation, sustained-release cross-linking, structural strengthening, and antioxidant functions to achieve a breakthrough in improving the quality of Physalis tofu. Summary of the Invention

[0006] Technical problems to be solved: In view of the above problems, the purpose of the present invention is to provide a mineralized gel-type Physalis fermentation agent and its application in the preparation of Physalis tofu. First, epigallocatechin gallate (EGCG) and tricalcium phosphate (TCP) are used to form EGCG-Ca in bean clear water. 2+ The complex induces TCP nanosheets to self-assemble and interpenetrate with the soybean protein network to construct a mineralized gel skeleton; the lactic acid bacteria are then immobilized in the micropores of the skeleton, and finally, soybean peptides are electrostatically grafted to obtain a mineralized gel-type Physalis fermentation agent, which is beneficial to improving the gel strength, water retention and flavor of Physalis tofu.

[0007] Technical solution: A method for preparing a mineralized gel-type Physalis leavening agent, the specific preparation steps are as follows: S1. Add epigallocatechin gallate to soy protein water and stir at 40-45°C to dissolve. Then add tricalcium phosphate and continue stirring for 30 minutes. Then, incubate in a 50-55°C water bath for 1-3 hours to form an EGCG-TCP / soy protein interpenetrating mineralized gel. S2. Inoculate the composite lactic acid bacteria solution into the EGCG-TCP / soy protein interpenetrating mineralized gel, stir evenly, let it stand at 4°C for 30 minutes, and then anaerobically ferment it at 37°C for 24-36 hours to obtain a mineralized gel containing active lactic acid bacteria; S3. Add soybean peptide to the mineralized gel containing active lactic acid bacteria, stir at 35-45°C for 10-15 minutes, and then ultrasonically treat at 200-300W for 10-30 minutes. Then add propylene glycol alginate and stir at 35-40°C for 0.5-1.5 hours to obtain a mineralized gel-type Physalis starter.

[0008] Furthermore, in step S1, the amount of epigallocatechin gallate added is 0.1-0.15 wt %; and the amount of tricalcium phosphate added is 0.1-0.2 wt %.

[0009] Furthermore, the composite lactic acid bacteria solution in step S2 is a mixed solution of Lactobacillus plantarum, Lactobacillus bulgaricus and Lactobacillus acidophilus in a ratio of (1-5): (1-5): (1-5), and the concentrations of the three bacteria solutions are 1×10 9 -1.5×10 9 CFU / mL, with an inoculum size of 2-7%.

[0010] Furthermore, in step S3, the amount of soybean peptide added is 0.2-0.5 wt %; and the amount of propylene glycol alginate added is 0.05-0.2 wt %.

[0011] The mineralized gel-type Physalis alkekengi fermentation agent prepared by the above preparation method.

[0012] Application of the mineralized gel-type Physalis alkekengi fermentation agent in the preparation of Physalis alkekengi tofu.

[0013] Furthermore, the preparation method of the tofu is as follows: (1) Soaking: Weigh soybeans, add water, soak at 25°C for 12-24 hours, filter, and obtain soaked soybeans; (2) Grinding: Add water to the soaked soybeans, beat and remove foam to obtain a homogenous slurry; (3) Cooking: Filter the homogenate and boil for 5-10 minutes to obtain cooked soy milk; (4) Soymilk: Cool the cooked soymilk to 60-85°C, add 20-30% mineralized gel-type Physalis fermentation agent and 2-10% complex polysaccharide, stir, and stop stirring when tofu curd precipitates; (5) Simmering and pressing into shape: After the tofu pudding has solidified for 10-15 minutes, simmer for 20-30 minutes and press into shape to obtain the tofu.

[0014] Furthermore, in step (1), the mass volume ratio of soybean to water is (1-2) g: (3-6) mL.

[0015] Furthermore, the mass volume ratio of soybeans to water after soaking in step (2) is (1-3) g: (4-8) mL.

[0016] Furthermore, the complex polysaccharide in step (4) is any one of galacto-oligosaccharide, fructo-oligosaccharide and inulin, or a complex of two or more thereof. Beneficial effects

[0017] The present invention first prepares an EGCG-TCP / soy protein interpenetrating mineralized gel skeleton, which can be used to immobilize lactic acid bacteria and graft soybean peptides to prepare a mineralized gel-type Physalis soja starter for the preparation of Physalis soja tofu. First, epigallocatechin gallate (EGCG) and tricalcium phosphate (TCP) are added to soy water. The phenolic hydroxyl group of EGCG is ionized in soy water (unfermented soy water is weakly alkaline) and preferentially adsorbs calcium ions in TCP through electrostatic interaction to form EGCG-Ca 2+ The complex inhibits the growth of TCP crystals along the c-axis and promotes the self-assembly of two-dimensional nanosheet structures. Secondly, TCP nanosheets interpenetrate with the soybean protein network through a triple force to form an EGCG-TCP / soy protein interpenetrating mineralized skeleton: (1) Hydrophobic interaction: the aromatic ring of EGCG is embedded in the hydrophobic core of β-conglycinin (7S) or soybean globulin (11S globulin); (2) Hydrogen bond network: the phenolic hydroxyl group of EGCG binds to the polar amino acids of the protein (such as glutamine), inducing the transformation of β-folding to random coil; (3) Calcium ion crosslinking: EGCG-Ca 2+ Slow-release Ca in the complex 2+The bridge protein carboxyl groups strengthen the network rigid structure; finally, the interpenetrating mineralized skeleton acts as a rigid support, which is beneficial to improve the gel strength of the tofu; it can also intercept free water, which is beneficial to improve the water holding rate of tofu; in addition, it gradually dissolves in the acidic environment of lactic acid bacteria fermentation and continuously releases Ca 2+ Strengthened tofu gel.

[0018] The present invention introduces a composite lactic acid bacteria liquid into an EGCG-TCP / soy protein interpenetrating mineralized gel to prepare a mineralized gel containing active lactic acid bacteria. The microporous structure of the interpenetrating mineralized skeleton immobilizes the lactic acid bacteria community, physically blocking the direct impact of the external acidic environment on the community, and significantly improving the survival rate of the live bacteria. In addition, the acid production capacity of the composite lactic acid bacteria fermentation is stronger than that of traditional natural fermentation and single lactic acid bacteria fermentation. While taking into account the acid production, the types and contents of flavor substances can be increased, thereby improving the limitations of the current use of single lactic acid bacteria to ferment soy water.

[0019] The present invention adds soybean peptides to a mineralized gel containing active lactic acid bacteria to prepare a mineralized gel-type Physalis fermentation agent, and grafts soybean peptides onto the mineralized skeleton with the assistance of ultrasound. The soybean peptides are positively charged in the Physalis environment, while the EGCG-modified TCP nanosheets are negatively charged, so the soybean peptides can be bound to the gel through electrostatic interaction. The soybean peptides have good emulsifying and gelling properties. During the pulping process, the soybean peptides can be interwoven with functional polysaccharides to form a more uniform and dense gel network structure. This structure gives the Physalis tofu a delicate and smooth taste, while improving the elasticity and toughness of the tofu, making it less likely to break during the cooking process. In addition, the soybean peptides have antioxidant capacity and can cooperate with EGCG to scavenge free radicals in the tofu system, delay oxidative deterioration, and extend the shelf life of the Physalis tofu. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 This is a sensory radar chart of the Physalis tofu prepared in Example 8 and Comparative Examples 6-11. DETAILED DESCRIPTION

[0020] The present invention will be further described below with reference to the accompanying drawings and embodiments. The following embodiments are intended to explain the present invention, but the present invention is not limited to the following embodiments: Bacteria activation:

[0021] Under sterile conditions, 50 μL of glycerol-frozen bacterial suspension of Lactobacillus plantarum, Lactobacillus bulgaricus, and Lactobacillus acidophilus were respectively aspirated and inoculated into 10 mL of sterile MRS liquid culture medium, and cultured at 37°C at a speed of 60 r / min for 20 h to obtain a first-level activated bacterial solution; under sterile conditions, the first-level activated bacterial solution was transferred to 50 mL of sterile MRS liquid culture medium at a 1% inoculum volume, and cultured at 37°C at a speed of 60 r / min for 12 h to obtain a second-level activated bacterial solution. After the culture was completed, the concentration of each bacterial solution was adjusted to 1×10 9CFU / mL, reserve for future use.

[0022] Example 1 A method for preparing a mineralized gel-type Physalis alkekengi fermentation agent, the specific preparation steps are as follows: S1. Add 0.1 wt% epigallocatechin gallate to soy protein water and stir at 40°C to dissolve. Then add 0.1 wt% tricalcium phosphate and continue stirring for 30 minutes. Then, incubate in a 50°C water bath for 2 hours to form an EGCG-TCP / soy protein interpenetrating mineralized gel. S2. A composite lactic acid bacteria solution (Lactobacillus plantarum, Lactobacillus bulgaricus, and Lactobacillus acidophilus = 1:1:1) was inoculated into the EGCG-TCP / soy protein interpenetrating mineralized gel at a 2% inoculum concentration. The gel was stirred evenly, allowed to stand at 4°C for 30 minutes, and then anaerobically fermented at 37°C for 30 hours to obtain a mineralized gel containing active lactic acid bacteria. S3. Add 0.2 wt% soybean peptide to the mineralized gel containing active lactic acid bacteria, stir at 40°C for 10 min, and then ultrasonicate at 200W for 30 min. Then, add 0.1 wt% propylene glycol alginate and stir at 35°C for 1 h to obtain a mineralized gel-type Physalis starter. Example 2

[0023] A method for preparing a mineralized gel-type Physalis alkekengi fermentation agent, the specific preparation steps are as follows: S1. Add 0.15 wt% epigallocatechin gallate to soy protein water and stir at 40°C to dissolve. Then add 0.2 wt% tricalcium phosphate and continue stirring for 30 minutes. Then, incubate in a 50°C water bath for 2 hours to form an EGCG-TCP / soy protein interpenetrating mineralized gel. S2. A composite lactic acid bacteria solution (Lactobacillus plantarum, Lactobacillus bulgaricus, and Lactobacillus acidophilus in a 1:1:1 ratio) was inoculated into the EGCG-TCP / soy protein interpenetrating mineralized gel at a 3% inoculum concentration. The gel was stirred evenly, allowed to stand at 4°C for 30 minutes, and then anaerobically fermented at 37°C for 30 hours to obtain a mineralized gel containing active lactic acid bacteria. S3. Add 0.2 wt% soybean peptide to the mineralized gel containing active lactic acid bacteria, stir at 40°C for 10 min, and then ultrasonicate at 200W for 30 min. Then, add 0.1 wt% propylene glycol alginate and stir at 35°C for 1 h to obtain a mineralized gel-type Physalis starter. Example 3

[0024] A method for preparing a mineralized gel-type Physalis alkekengi fermentation agent, the specific preparation steps are as follows: S1. Add 0.1 wt% epigallocatechin gallate to soy protein water and dissolve with stirring at 40°C. Then add 0.2 wt% tricalcium phosphate and continue stirring for 30 minutes. Then, incubate in a 50°C water bath for 2 hours to form an EGCG-TCP / soy protein interpenetrating mineralized gel. S2. A composite lactic acid bacteria solution (Lactobacillus plantarum, Lactobacillus bulgaricus, and Lactobacillus acidophilus in a ratio of 2:1:1) was inoculated into the EGCG-TCP / soy protein interpenetrating mineralized gel at a 3% inoculum concentration. The gel was stirred evenly, allowed to stand at 4°C for 30 minutes, and then anaerobically fermented at 37°C for 30 hours to obtain a mineralized gel containing active lactic acid bacteria. S3. Add 0.2 wt% soybean peptide to the mineralized gel containing active lactic acid bacteria, stir at 40°C for 10 min, and then ultrasonicate at 200W for 30 min. Then, add 0.1 wt% propylene glycol alginate and stir at 35°C for 1 h to obtain a mineralized gel-type Physalis starter. Example 4

[0025] A method for preparing a mineralized gel-type Physalis alkekengi fermentation agent, the specific preparation steps are as follows: S1. Add 0.1 wt% epigallocatechin gallate to soy protein water and dissolve with stirring at 40°C. Then add 0.2 wt% tricalcium phosphate and continue stirring for 30 minutes. Then, incubate in a 50°C water bath for 2 hours to form an EGCG-TCP / soy protein interpenetrating mineralized gel. S2. A composite lactic acid bacteria solution (Lactobacillus plantarum, Lactobacillus bulgaricus, and Lactobacillus acidophilus = 1:2:1) was inoculated into the EGCG-TCP / soy protein interpenetrating mineralized gel at a 5% inoculum concentration. The gel was stirred evenly, allowed to stand at 4°C for 30 minutes, and then anaerobically fermented at 37°C for 30 hours to obtain a mineralized gel containing active lactic acid bacteria. S3. Add 0.2 wt% soybean peptide to the mineralized gel containing active lactic acid bacteria, stir at 40°C for 10 min, and then ultrasonicate at 200W for 30 min. Then, add 0.1 wt% propylene glycol alginate and stir at 35°C for 1 h to obtain a mineralized gel-type Physalis starter. Example 5

[0026] A method for preparing a mineralized gel-type Physalis alkekengi fermentation agent, the specific preparation steps are as follows: S1. Add 0.1 wt% epigallocatechin gallate to soy protein water and dissolve with stirring at 40°C. Then add 0.2 wt% tricalcium phosphate and continue stirring for 30 minutes. Then, incubate in a 50°C water bath for 2 hours to form an EGCG-TCP / soy protein interpenetrating mineralized gel. S2. A composite lactic acid bacteria solution (Lactobacillus plantarum, Lactobacillus bulgaricus, and Lactobacillus acidophilus in a ratio of 1:1:2) was inoculated into the EGCG-TCP / soy protein interpenetrating mineralized gel at a 7% inoculum concentration. The gel was stirred evenly, allowed to stand at 4°C for 30 minutes, and then anaerobically fermented at 37°C for 30 hours to obtain a mineralized gel containing active lactic acid bacteria. S3. Add 0.2 wt% soybean peptide to the mineralized gel containing active lactic acid bacteria, stir at 40°C for 10 min, and then ultrasonicate at 200W for 30 min. Then, add 0.1 wt% propylene glycol alginate and stir at 35°C for 1 h to obtain a mineralized gel-type Physalis starter. Example 6

[0027] A method for preparing a mineralized gel-type Physalis alkekengi fermentation agent, the specific preparation steps are as follows: S1. Add 0.1 wt% epigallocatechin gallate to soy protein water and dissolve with stirring at 40°C. Then add 0.2 wt% tricalcium phosphate and continue stirring for 30 minutes. Then, incubate in a 50°C water bath for 2 hours to form an EGCG-TCP / soy protein interpenetrating mineralized gel. S2. A composite lactic acid bacteria solution (Lactobacillus plantarum, Lactobacillus bulgaricus, and Lactobacillus acidophilus in a 1:1:1 ratio) was inoculated into the EGCG-TCP / soy protein interpenetrating mineralized gel at a 3% inoculum concentration. The gel was stirred evenly, allowed to stand at 4°C for 30 minutes, and then anaerobically fermented at 37°C for 30 hours to obtain a mineralized gel containing active lactic acid bacteria. S3. Add 0.5 wt% soybean peptide to the mineralized gel containing active lactic acid bacteria, stir at 40°C for 10 min, and then ultrasonicate at 200 W for 30 min. Then, add 0.1 wt% propylene glycol alginate and stir at 35°C for 1 h to obtain a mineralized gel-type Physalis starter. Comparative Example 1

[0028] The difference between this comparative example and Example 6 is that only a single Lactobacillus plantarum was added, as follows: A method for preparing a mineralized gel-type Physalis alkekengi fermentation agent, the specific preparation steps are as follows: S1. Add 0.1 wt% epigallocatechin gallate to soy protein water and dissolve with stirring at 40°C. Then add 0.2 wt% tricalcium phosphate and continue stirring for 30 minutes. Then, incubate in a 50°C water bath for 2 hours to form an EGCG-TCP / soy protein interpenetrating mineralized gel. S2. Inoculate 3% Lactobacillus plantarum into the EGCG-TCP / soy protein interpenetrating mineralized gel, stir evenly, let stand at 4°C for 30 minutes, and then anaerobically ferment at 37°C for 30 hours to obtain a mineralized gel containing active lactic acid bacteria. S3. Add 0.5 wt% soybean peptide to the mineralized gel containing active lactic acid bacteria, stir at 40°C for 10 min, and then ultrasonicate at 200 W for 30 min. Then, add 0.1 wt% propylene glycol alginate and stir at 35°C for 1 h to obtain a mineralized gel-type Physalis starter. Comparative Example 2

[0029] The difference between this comparative example and Example 6 is that the composite lactic acid bacteria are Lactobacillus plantarum and Lactobacillus bulgaricus, specifically as follows: A method for preparing a mineralized gel-type Physalis alkekengi fermentation agent, the specific preparation steps are as follows: S1. Add 0.1 wt% epigallocatechin gallate to soy protein water and dissolve with stirring at 40°C. Then add 0.2 wt% tricalcium phosphate and continue stirring for 30 minutes. Then, incubate in a 50°C water bath for 2 hours to form an EGCG-TCP / soy protein interpenetrating mineralized gel. S2. A composite lactic acid bacteria solution (Lactobacillus plantarum and Lactobacillus bulgaricus = 1:2) was inoculated into the EGCG-TCP / soy protein interpenetrating mineralized gel at an inoculum density of 3%. The gel was stirred evenly, allowed to stand at 4°C for 30 minutes, and then anaerobically fermented at 37°C for 30 hours to obtain a mineralized gel containing active lactic acid bacteria. S3. Add 0.5 wt% soybean peptide to the mineralized gel containing active lactic acid bacteria, stir at 40°C for 10 min, and then ultrasonicate at 200 W for 30 min. Then, add 0.1 wt% propylene glycol alginate and stir at 35°C for 1 h to obtain a mineralized gel-type Physalis starter. Comparative Example 3

[0030] The difference between this comparative example and Example 6 is that soybean peptide is not grafted, specifically as follows: A method for preparing a mineralized gel-type Physalis alkekengi fermentation agent, the specific preparation steps are as follows: S1. Add 0.1 wt% epigallocatechin gallate to soy protein water and dissolve with stirring at 40°C. Then add 0.2 wt% tricalcium phosphate and continue stirring for 30 minutes. Then, incubate in a 50°C water bath for 2 hours to form an EGCG-TCP / soy protein interpenetrating mineralized gel. S2. Inoculate a composite lactic acid bacteria solution (Lactobacillus plantarum, Lactobacillus bulgaricus, Lactobacillus acidophilus = 1:1:1) into the EGCG-TCP / soy protein interpenetrating mineralized gel at an inoculum density of 3%. Stir evenly, let it stand at 4°C for 30 minutes, and then anaerobically ferment it at 37°C for 30 hours to obtain a mineralized gel-type Physalis fermentation agent. Comparative Example 4

[0031] The difference between this comparative example and Example 6 is that no interpenetrating mineralized gel-supported lactic acid bacteria was prepared, but lactic acid bacteria were directly inoculated into soy water, specifically as follows: A method for preparing a Physalis alkekengi starter, the specific preparation steps are as follows: S1. Inoculate a 3% inoculum of a composite lactic acid bacteria solution (Lactobacillus plantarum, Lactobacillus bulgaricus, and Lactobacillus acidophilus in a ratio of 1:1:1) into soy water. Stir evenly, incubate at 4°C for 30 minutes, and then anaerobically ferment at 37°C for 30 hours to obtain a Physalis starter. Comparative Example 5

[0032] The difference between this comparative example and Example 6 is that the natural fermentation method is used to prepare the Physalis alkekengi starter, which is as follows: A method for preparing a Physalis alkekengi starter, the specific preparation steps are as follows: S1. Ferment the soybeans and water naturally for 30 hours to obtain the Physalis starter. Performance testing:

[0033] 1) Ca 2+ Release rate: The mineralized gel-type Physalis alkekengi ferment prepared in Examples 1-6 and Comparative Examples 1-5 were immersed in a pH 4.5 buffer solution to simulate the environment of Physalis alkekengi, and the Ca 2+ The release of Ca 2+ Cumulative release amount; 2) Lactic acid bacteria survival rate: Prepared mineralized gel-type Physalis alkekengi starter culture was added to sterile phosphate buffer, ultrasonically disrupted, graded diluted, and spread on MRS medium. Anaerobically cultured at 37°C for 48 hours, the number of viable cells was counted, and the number of viable cells in the culture solution was also measured before inoculation to determine the lactic acid bacteria survival rate. Table 1 Ca content of mineralized gel-type Physalis alkekengi starter 2+ Release rate and lactic acid bacteria survival rate

[0034] As shown in Table 1, the Ca content of the mineralized gel-type Physalis alkekengi ferment prepared by the present invention is 2+ The release rate is 60.4-63.1%. In Comparative Example 3, due to the lack of electrostatic shielding effect of soybean peptide, Ca 2+ The dissolution is slightly faster; the survival rate of lactic acid bacteria in the mineralized gel-type Physalis fermentation agent prepared in the embodiment is 86.8-88.4%. The single strain of comparative example 1 has weak stress resistance and lacks bacterial community cooperation, and the survival rate of lactic acid bacteria is the lowest; the dual strains of comparative example 2 partially retain the cooperative effect, but are weaker than the synergy of the three lactic acid bacteria in the embodiment; comparative example 4 has no mineralized skeleton protection, and the lactic acid bacteria are directly exposed to the acidic environment, and the bacteria are seriously damaged; in comparative example 5, competition from miscellaneous bacteria and environmental fluctuations in natural fermentation lead to an insufficient proportion of target lactic acid bacteria.

[0035] Therefore, the mineralized gel-type Physalis alkekengi starter prepared in Example 6 was selected for the subsequent preparation of Physalis alkekengi tofu.

[0036] Example 7 The preparation method of Physalis tofu is as follows: (1) Soaking: Weigh 500 g of soybeans, add water at a mass volume ratio of 1 g:3 mL, soak at 25 °C for 12 h, and filter to obtain the soaked soybeans; (2) Grinding: Add water to the soaked soybeans at a mass-to-volume ratio of 1 g:6 mL, beat and defoam to obtain a homogenous slurry; (3) Cooking: Filter the homogenate and boil for 5 minutes to obtain cooked soy milk; (4) Soymilk: Cool the cooked soymilk to 85°C, add 30% of the mineralized gel-type Physalis starter culture prepared in Example 6 and 5% of a complex polysaccharide (fructooligosaccharide: inulin = 2:1), and stir. Stop stirring when bean curd precipitates. (5) Simmering and pressing into shape: After the tofu pudding has solidified for 10 minutes, simmer for 25 minutes and press into shape to obtain the tofu. Example 8

[0037] The preparation method of Physalis tofu is as follows: (1) Soaking: Weigh 500 g of soybeans, add water at a mass volume ratio of 1 g:4 mL, soak at 25 °C for 12 h, and filter to obtain the soaked soybeans; (2) Grinding: Add water to the soaked soybeans at a mass-to-volume ratio of 1 g:6 mL, beat and defoam to obtain a homogenous slurry; (3) Cooking: Filter the homogenate and boil for 5 minutes to obtain cooked soy milk; (4) Soymilk: Cool the cooked soymilk to 85°C, add 30% of the mineralized gel-type Physalis starter culture prepared in Example 6 and 5% of a complex polysaccharide (fructooligosaccharide: inulin = 2:1), and stir. Stop stirring when bean curd precipitates. (5) Simmering and pressing into shape: After the tofu pudding has solidified for 10 minutes, simmer for 25 minutes and press into shape to obtain the tofu. Example 9

[0038] The preparation method of Physalis tofu is as follows: (1) Soaking: Weigh 500 g of soybeans, add water at a mass volume ratio of 1 g:6 mL, soak at 25 °C for 12 h, and filter to obtain the soaked soybeans; (2) Grinding: Add water to the soaked soybeans at a mass volume ratio of 1 g:8 mL, beat and defoam to obtain a homogenous slurry; (3) Cooking: Filter the homogenate and boil for 5 minutes to obtain cooked soy milk; (4) Soymilk: Cool the cooked soymilk to 85°C, add 25% of the mineralized gel-type Physalis starter culture prepared in Example 6 and 5% of a complex polysaccharide (fructooligosaccharide: inulin = 2:1), and stir. Stop stirring when tofu curd is precipitated. (5) Simmering and pressing into shape: After the tofu pudding has solidified for 10 minutes, simmer for 25 minutes and press into shape to obtain the tofu. Example 10

[0039] The preparation method of Physalis tofu is as follows: (1) Soaking: Weigh 500 g of soybeans, add water at a mass volume ratio of 1 g:4 mL, soak at 25 °C for 12 h, and filter to obtain the soaked soybeans; (2) Grinding: Add water to the soaked soybeans at a mass volume ratio of 1 g:4 mL, beat and defoam to obtain a homogenous slurry; (3) Cooking: Filter the homogenate and boil for 5 minutes to obtain cooked soy milk; (4) Soymilk: Cool the cooked soymilk to 85°C, add 20% of the mineralized gel-type Physalis starter culture prepared in Example 6 and 5% of a complex polysaccharide (fructooligosaccharide: inulin = 2:1), and stir. Stop stirring when bean curd precipitates. (5) Simmering and pressing into shape: After the tofu pudding has solidified for 10 minutes, simmer for 25 minutes and press into shape to obtain the tofu. Comparative Example 6

[0040] The difference between this comparative example and Example 8 is that the mineralized gel-type Physalis alkekengi fermentation agent prepared in Comparative Example 1 was used. Comparative Example 7

[0041] The difference between this comparative example and Example 8 is that the mineralized gel-type Physalis alkekengi fermentation agent prepared in Comparative Example 2 was used. Comparative Example 8

[0042] The difference between this comparative example and Example 8 is that the mineralized gel-type Physalis alkekengi fermentation agent prepared in Comparative Example 3 was used. Comparative Example 9

[0043] The difference between this comparative example and Example 8 is that the mineralized gel-type Physalis alkekengi fermentation agent prepared in Comparative Example 4 was used. Comparative Example 10

[0044] The difference between this comparative example and Example 8 is that the mineralized gel-type Physalis alkekengi fermentation agent prepared in Comparative Example 5 is used. Comparative Example 11

[0045] The difference between this comparative example and Example 8 is that no complex polysaccharide is added, specifically as follows: The preparation method of Physalis tofu is as follows: (1) Soaking: Weigh 500 g of soybeans, add water at a mass volume ratio of 1 g:4 mL, soak at 25 °C for 12 h, and filter to obtain the soaked soybeans; (2) Grinding: Add water to the soaked soybeans at a mass-to-volume ratio of 1 g:6 mL, beat and defoam to obtain a homogenous slurry; (3) Cooking: Filter the homogenate and boil for 5 minutes to obtain cooked soy milk; (4) Soymilk: Cool the cooked soymilk to 85°C, add 30% of the mineralized gel-type Physalis starter prepared in Example 6, and stir. Stop stirring when bean curd precipitates. (5) Simmering and pressing into shape: After the tofu pudding has solidified for 10 minutes, simmer for 25 minutes and press into shape to obtain the tofu.

[0046] Performance test of Physalis tofu: (1) Texture characteristics and gel strength The prepared tofu was cut into 4 cm × 4 cm × 1 cm cubes and the textural properties of the tofu were determined using texture profile analysis (TPA). The test parameters were as follows: test speed: 60 mm / s, post-test speed: 200 mm / s, probe recovery height: 15 mm, extrusion distance: 5 mm, test interval: 3 s, and initial force: 0.4 N. The test was repeated 10 times for each sample.

[0047] Table 2 Texture data of the tofu prepared in Examples 7-10 and Comparative Examples 6-11

[0048] As shown in Table 2, the hardness, elasticity, cohesion, stickiness and chewiness of the tofu prepared in Example 8 are the greatest, while the tofu prepared in Comparative Example 9 lacks a mineralized skeleton and is therefore lacking in Ca. 2+ The soy protein gel was slow to release, the gel network was loose, and the texture of the tofu was soft. The hardness of the tofu in Comparative Example 10 was relatively low, which may be because the natural fermentation made the soy protein gel more slowly, and the protein network structure was relatively loose, resulting in a softer texture of the tofu.

[0049] (2) Protein content The determination of protein content refers to GB 5009.5-2016.

[0050] Table 3 Protein content of the tofu prepared in Examples 7-10 and Comparative Examples 6-11

[0051] As can be seen from Table 3, the protein content of the tofu prepared in the examples of the present invention is 19.6-20.7 g / 100 g, while the protein content of Comparative Examples 6, 7, and 11 is lower, indicating that the fermentation of lactic acid bacteria and the addition of functional oligosaccharides promote the destabilization of protein particles, thereby improving the protein dissolution process and increasing the chance of soy protein hydrolysis reaction, thereby increasing the total protein content.

[0052] (3) Water retention The moisture content (MC) of tofu was determined by direct drying according to GB 5009.3-2016 “National Food Safety Standard - Determination of Moisture in Foods”.

[0053] A special 50 mL centrifuge tube with a meshed bottom was used. A piece of filter paper was placed inside the tube. The mass of the filter paper and the tube was measured as m1. Approximately 1 g of tofu was placed on the filter paper. The mass of the tube was then measured as m2. After centrifugation at 4000 rpm for 10 minutes, the mass of the tube was measured as m3. The water retention of tofu was determined according to the following formula:

[0054] Table 4 Water retention of Physalis tofu prepared in Examples 7-10 and Comparative Examples 6-11

[0055] As can be seen from Table 4, the water retention of the tofu prepared in the embodiment of the present invention is relatively high. The tofu prepared by using a single strain or a double strain of bacteria in the tofu fermentation agent has insufficient bacterial metabolic capacity (Comparative Examples 6 and 7), small secretion of extracellular polysaccharides, sparse water holding network, and corresponding water loss. Comparative Example 8 does not graft soybean peptides and cannot electrostatically complex with PGA, resulting in reduced gel network strength and increased water separation rate. The tofu fermentation agents prepared in Comparative Examples 9 and 10 have no mineralized skeleton and cannot release Ca. 2+ , tofu has a soft texture and cannot hold water efficiently.

[0056] (4) Antioxidant capacity The tofu samples prepared in the examples and comparative examples were vacuum freeze-dried for 24 h and ground. 300 mg of the sample powder was placed in a test tube, 20 mL of anhydrous ethanol was added, and ultrasonic extraction was performed for 2 h. The supernatant was filtered through a 0.45 μm membrane and the filtrate was stored at 4° C. for later use.

[0057] DPPH free radical scavenging activity: First, the concentration was 2×10 -4 mol / L DPPH anhydrous ethanol solution, store in the dark; take 2mL of sample and mix with 2mL DPPH anhydrous ethanol solution, react at room temperature in the dark for 30min, and then measure the absorbance value of the sample at 517nm A i The blank group was replaced with an equal volume of anhydrous ethanol solution instead of DPPH anhydrous ethanol solution, and the absorbance value was recorded as A j The control group was replaced by an equal volume of distilled water, and the absorbance value was recorded as A0. The DPPH free radical scavenging rate was calculated using the following formula: DPPH free radical scavenging rate / %=(1-(A i -A j ) / A0)×100 ABTS free radical scavenging activity: Refer to the method of Re et al. (1999) and make appropriate modifications. Prepare ABTS stock solution in advance: Mix 7mmol / LABTS solution and Mix the ABTS solution with 50 mmol / L potassium persulfate solution in a 1:1 ratio and allow to react in the dark at room temperature for 12-16 hours to obtain an ABTS stock solution. Then, dilute the ABTS stock solution with anhydrous ethanol so that the absorbance of the ABTS solution at 734 nm falls within the range of 0.70±0.02.

[0058] Pipette 0.1 mL of the sample dilution into a 10 mL centrifuge tube, add 3.9 mL of ABTS solution, vortex mix, and react at room temperature for 6 minutes. Measure the absorbance (AE) of the reaction solution at 734 nm by spectrophotometry. Simultaneously, pipette 0.1 mL of 70% ethanol solution, add 3.9 mL of ABTS solution, and measure the absorbance (AB) of the blank solution at 734 nm. The ABTS free radical scavenging efficiency (%) is calculated as follows: ABTS free radical scavenging rate (%) = (AB-AE) / AB×100 Table 5 DPPH and ABTS free radical scavenging rates of Physalis tofu prepared in Examples 7-10 and Comparative Examples 6-11

[0059] As can be seen from Table 5, the antioxidant capacity of Example 8 is higher than that of the comparative example, which may be because after lactic acid bacteria fermentation, more hydrogen ions are generated, which combine with the cationic radicals generated after oxidation of ABTS to improve its antioxidant performance; the secretion of superoxide dismutase in the Physalis tofu prepared in Comparative Example 6 (single lactic acid bacteria) and Comparative Example 7 (compound of two lactic acid bacteria) is reduced, and the antioxidant capacity is reduced; the Physalis fermentation agent in Comparative Example 8 is not grafted with soybean peptides, lipid oxidation is accelerated, and the antioxidant capacity is reduced; the antioxidant capacity of the Physalis tofu prepared in Comparative Examples 9 and 10 is significantly worse than that of the examples. It can be seen that the Physalis fermentation agent prepared by the mineralized skeleton-immobilized probiotics of the present invention has a significant effect on improving the antioxidant capacity of Physalis tofu.

[0060] (5) Sensory evaluation The Physalis tofu prepared in Example 8 and Comparative Examples 6-11 were selected for sensory evaluation.

[0061] Table 6 Sensory score table for Physalis tofu

[0062] The sensory radar graphs of the Physalis tofu prepared in Example 8 and Comparative Examples 6-11 are as follows: Figure 1 As shown, the overall sensory score of Example 8 is higher than that of several other types of Physalis tofu. It has a delicate and smooth taste, good elasticity, and a tofu aroma, showing a good sensory effect. The overall sensory score of the Physalis tofu prepared by the natural fermentation method in Comparative Example 10 is relatively poor.

[0063] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Any person skilled in the art can, without departing from the spirit and technical solution of the present invention, use the methods and technical contents disclosed above to make many possible changes and modifications to the technical solution of the present invention, or modify it into an equivalent embodiment with equivalent changes. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a mineralized gel-type Physalis leavening agent, characterized in that: The specific preparation steps are as follows: S1. Add epigallocatechin gallate to soy protein water and stir at 40-45°C to dissolve. Then add tricalcium phosphate and continue stirring for 30 minutes. Then, incubate in a 50-55°C water bath for 1-3 hours to form an EGCG-TCP / soy protein interpenetrating mineralized gel. S2. Inoculate the composite lactic acid bacteria solution into the EGCG-TCP / soy protein interpenetrating mineralized gel, stir evenly, let it stand at 4°C for 30 minutes, and then anaerobically ferment it at 37°C for 24-36 hours to obtain a mineralized gel containing active lactic acid bacteria; S3. Add soybean peptide to the mineralized gel containing active lactic acid bacteria, stir at 35-45°C for 10-15 minutes, and then ultrasonically treat at 200-300W for 10-30 minutes. Then add propylene glycol alginate and stir at 35-40°C for 0.5-1.5 hours to obtain a mineralized gel-type Physalis starter.

2. The method for preparing a mineralized gel-type Physalis alkekengi fermentation agent according to claim 1, characterized in that: In step S1, the amount of epigallocatechin gallate added is 0.1-0.15 wt %; the amount of tricalcium phosphate added is 0.1-0.2 wt %.

3. The method for preparing a mineralized gel-type Physalis alkekengi fermentation agent according to claim 1, characterized in that: The composite lactic acid bacteria solution in step S2 is a mixed solution of Lactobacillus plantarum, Lactobacillus bulgaricus and Lactobacillus acidophilus in a ratio of (1-5): (1-5): (1-5), and the concentrations of the three bacteria solutions are 1×10 9 -1.5×10 9 CFU / mL, with an inoculum size of 2-7%.

4. The method for preparing a mineralized gel-type Physalis alkekengi fermentation agent according to claim 1, characterized in that: In step S3, the amount of soybean peptide added is 0.2-0.5 wt %; the amount of propylene glycol alginate added is 0.05-0.2 wt %.

5. The mineralized gel-type Physalis alkekengi fermentation agent prepared by the preparation method according to any one of claims 1 to 4.

6. Use of the mineralized gel-type Physalis alkekengi fermentation agent according to claim 5 in preparing Physalis alkekengi tofu.

7. The use according to claim 6, characterized in that The preparation method of the tofu is as follows: (1) Soaking: Weigh soybeans, add water, soak at 25°C for 12-24 hours, filter, and obtain soaked soybeans; (2) Grinding: Add water to the soaked soybeans, beat and remove foam to obtain a homogenous slurry; (3) Cooking: Filter the homogenate and boil for 5-10 minutes to obtain cooked soy milk; (4) Soymilk: Cool the cooked soymilk to 60-85°C, add 20-30% mineralized gel-type Physalis fermentation agent and 2-10% complex polysaccharide, stir, and stop stirring when tofu curd precipitates; (5) Simmering and pressing into shape: After the tofu pudding has solidified for 10-15 minutes, simmer for 20-30 minutes and press into shape to obtain the tofu.

8. The use according to claim 7, characterized in that The mass volume ratio of soybean to water in step (1) is (1-2) g: (3-6) mL.

9. The use according to claim 7, characterized in that The mass volume ratio of soybeans to water after soaking in step (2) is (1-3) g: (4-8) mL.

10. The use according to claim 7, characterized in that: The complex polysaccharide in step (4) is any one of galacto-oligosaccharide, fructo-oligosaccharide and inulin or a complex of two or more thereof.

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