CN120203125A - A preparation method of donkey-hide gelatin and red date yogurt - Google Patents

Abstract

The invention discloses a method for preparing donkey-hide gelatin and red date yogurt, comprising the following steps: (1) preparing donkey-hide gelatin hydrolysate; (2) preparing red date extract; preparing kelp and tea seed hydrolysate, mixing the hydrolysate filtrate with the red date extract, and concentrating under reduced pressure to obtain a composite extract; (3) adding donkey-hide gelatin hydrolysate, the composite extract, and white sugar to a milk powder solution to obtain a mixed solution, stirring, adding a yogurt starter, and fermenting at a constant temperature; (4) after fermentation, placing the fermentation product in a 4°C environment for 10 hours to inhibit excessive fermentation from affecting the taste, and then taking it out to obtain the donkey-hide gelatin and red date yogurt. The yogurt prepared by the method of the invention has good organizational morphology, fine and uniform texture, moderate viscosity, and no whey precipitation; uniform and glossy color, good taste, and rich aroma. It also has good antioxidant activity.

Description

Preparation method of donkey-hide gelatin and red date yoghourt

Technical Field

The invention relates to the technical field of yogurt manufacturing, in particular to a preparation method of donkey-hide gelatin and red date yogurt.

Background

The yoghurt is prepared by adding fermentation bacteria such as lactobacillus bulgaricus and streptococcus thermophilus in the fermentation process after heat treatment of raw milk. The research shows that the metabolites of the lactic acid bacteria can play a certain role in inhibiting harmful bacteria in intestinal tracts and also have a certain effect on regulating human immunity. The long-term drinking of the yoghurt can also improve diseases such as dyspepsia, constipation and the like. The yoghurt has unique flavor and smell, and the produced acetaldehyde and other substances cause the yoghurt to have special aroma due to the fact that the lactic acid bacteria convert lactose into lactic acid. Although the range of yogurt products produced in China is expanded at present, the quality problems in the production and the production process need to be controlled more strictly to ensure the quality of the products. In the yoghurt, lactobacillus bulgaricus and streptococcus thermophilus are two strains which are required to be added in national standard, and other probiotics can be added to produce fermented milk with various flavors. However, the yogurt is easy to excessively acidify and form milk lumps in the production process, and whey is separated out. The influence on the mouthfeel of the yoghourt and the appearance of the yoghourt in the later period is obvious, and the mouthfeel of the yoghourt is problematic and damaged.

Disclosure of Invention

Therefore, the invention provides a preparation method of donkey-hide gelatin red date yoghourt, which comprises the following steps:

(1) Preparing an alkaline protease solution, heating the alkaline protease solution to 40+/-3 ℃ in a water bath, preserving heat, adding donkey-hide gelatin powder into the alkaline protease solution, regulating pH after the addition, continuing stirring at the constant temperature of 40+/-3 ℃ for enzymolysis for 4-6 hours, filtering to remove insoluble substances after the enzymolysis is finished, carrying out liquid phase enzyme deactivation treatment, and concentrating under reduced pressure to obtain donkey-hide gelatin enzymatic hydrolysate;

(2) Removing cores of dry red dates, grinding the dry red dates into powder to obtain red date powder, soaking the red date powder in deionized water, stirring the mixture for more than 20 minutes under an ultrasonic environment, heating the mixture to 70+/-5 ℃ in a water bath, extracting the mixture at a constant temperature for 3-4 hours, naturally cooling the mixture to normal temperature after the extraction is completed, performing solid-liquid separation to obtain red date extract, cutting kelp Cheng Haidai pieces and tea seeds into tea seed powder, adding the kelp pieces and the tea seed powder into aqueous solution of cellulase to obtain extract mixed solution, adjusting the pH of the extract mixed solution to 5-5.5, heating the extract mixed solution to 50+/-3 ℃ in the water bath, stirring the extract at the constant temperature for more than 15 hours, performing enzyme deactivation treatment, filtering, mixing filtrate and the red date extract, and concentrating the filtrate under reduced pressure to obtain composite extract;

(3) Adding the donkey-hide gelatin enzymatic hydrolysate, the composite extracting solution and the white granulated sugar into the milk powder solution to obtain a mixed solution, stirring the mixed solution for more than 20 minutes, then sterilizing the mixed solution, cooling to 40+/-3 ℃ in a sterile room, adding a yoghurt starter, and fermenting at a constant temperature of 40+/-3 ℃ for 7-8 hours;

(4) And after the fermentation is finished, placing the fermentation product in a 0-4 ℃ environment for refrigeration for 10-12 hours, inhibiting the influence of transitional fermentation on the taste, and taking out to obtain the donkey-hide gelatin and red date yoghourt.

Further, in the step (1), the enzyme adding amount of the alkaline protease is 5100-5200U/g, and the pH is 8.3.

Further, in the step (1), the concentration is performed under reduced pressure to 1/2 of the volume before the concentration.

Further, the enzyme deactivation treatment is carried out by heating to 90 ℃ and preserving heat for 5min to deactivate the enzyme.

Further, in the step (2), the red date powder is soaked in deionized water in a mass ratio of red date powder to deionized water=1g:30ml.

In the step (2), the kelp pieces and the tea seed powder are added into the aqueous solution of the cellulase in a mass ratio of kelp pieces to tea seed powder, wherein the aqueous solution of the cellulase comprises 10g, 3-5 g and 30mL, the enzyme concentration in the aqueous solution of the cellulase is 8-10U/mL, and the aqueous solution of the cellulase is concentrated under reduced pressure to 1/2 of the volume before concentration to obtain a composite extract.

In the step (3), the mass ratio of the whole milk to the warm water is that the whole milk is warm water=1:5-6, and the mass ratio of the donkey-hide gelatin enzymatic hydrolysate, the composite extracting solution, the white granulated sugar and the yoghurt starter is that the mass ratio of the milk powder solution to the donkey-hide gelatin enzymatic hydrolysate to the composite extracting solution to the white granulated sugar and the yoghurt starter=100:20-25:12-18:8-10:0.3-0.4.

The yoghurt prepared by the method has the advantages of good tissue morphology, fine and uniform texture, moderate viscosity, no whey precipitation, uniform and glossy color, good taste and rich fragrance. And has good antioxidant activity.

Drawings

FIG. 1 is a graph comparing DPPH radical scavenging rates of yogurt prepared by the methods described in the examples and comparative examples;

FIG. 2 is a graph comparing hydroxyl radical scavenging rates of yogurt prepared by the methods described in the examples and comparative examples;

figure 3 is a graph comparing ABTS radical scavenging rates for yogurt prepared by the methods described in the examples and comparative examples.

Detailed Description

The invention is further illustrated below with reference to examples.

Example 1

A preparation method of donkey-hide gelatin red date yoghourt comprises the following steps:

(1) Preparing an alkaline protease solution, heating the alkaline protease solution to 40 ℃ in a water bath, preserving heat, adding donkey-hide gelatin powder into the alkaline protease solution, regulating pH after the addition, continuing stirring at a constant temperature of 40 ℃ for enzymolysis for 4 hours, wherein the enzymolysis process comprises the steps of adding 5100U/g of alkaline protease and 8.3 of pH, filtering to remove insoluble substances after the enzymolysis is finished, heating a liquid phase to 90 ℃, preserving heat for 5min, inactivating enzyme, concentrating under reduced pressure to 1/2 of the volume before concentration, and obtaining donkey-hide gelatin enzymatic hydrolysate;

(2) Removing cores of dry red dates, grinding the dry red dates into powder to obtain red date powder, soaking the red date powder in deionized water, wherein the mass ratio of the red date powder to the deionized water is that the red date powder is deionized water=1g:30mL, stirring the mixture for 20min in an ultrasonic environment, heating the mixture to 70 ℃ in a water bath, extracting the mixture at a constant temperature for 3h, naturally cooling the mixture to the normal temperature after the extraction is completed, carrying out solid-liquid separation to obtain red date extract, cutting kelp Cheng Haidai pieces and tea seeds into tea seed powder, adding the kelp pieces and the tea seed powder into aqueous solution of cellulase to obtain an extraction mixed solution, wherein the mass ratio of the kelp pieces and the tea seed powder into the aqueous solution of cellulase is that the aqueous solution of the tea seed powder is that the cellulase=10g:3g:30mL, the enzyme concentration in the aqueous solution of the cellulase is 8U/mL, adjusting the pH of the extraction mixed solution to 5, heating the mixture to 50 ℃, carrying out constant temperature stirring and extracting the mixture for 15h, heating the mixture to 90 ℃ and carrying out enzyme deactivation treatment for 5min, filtering, mixing the filtrate and the red date extract and the aqueous solution to obtain a compound extract which is not concentrated to 1/2;

(3) Adding whole milk into warm water at 45 ℃, wherein the mass ratio of the whole milk to the warm water is (1:5) of the whole milk to the warm water, stirring and fully dissolving to obtain a milk powder solution, adding donkey-hide gelatin zymolyte, the compound extract and white granulated sugar into the milk powder solution, stirring the mixed solution for 20min, sterilizing the mixed solution at 95 ℃ for 5min, cooling the mixed solution to 40 ℃ in a sterile room, adding a yogurt starter (streptococcus thermophilus: bulgaricus=1:1), and adding the donkey-hide gelatin zymolyte, the compound extract, the white granulated sugar and the yogurt starter into the milk powder solution, wherein the mass ratio of the donkey-hide gelatin zymolyte to the compound extract to the white granulated sugar to the yogurt starter=100:20:12:8:0.3, and fermenting at a constant temperature of 40+/-3 ℃ for 7h;

(4) And after the fermentation is finished, placing the fermentation product in a4 ℃ environment for refrigeration for 10 hours, inhibiting the influence of transitional fermentation on the taste, and taking out to obtain the donkey-hide gelatin red date yoghourt.

Example 2

A preparation method of donkey-hide gelatin red date yoghourt comprises the following steps:

(1) Preparing an alkaline protease solution, heating the alkaline protease solution to 40 ℃ in a water bath, preserving heat, adding donkey-hide gelatin powder into the alkaline protease solution, regulating pH after the addition, continuing stirring at a constant temperature of 40 ℃ for enzymolysis for 5 hours, wherein the enzymolysis process comprises the steps of adding 5100U/g of alkaline protease and 8.3 of pH, filtering to remove insoluble substances after the enzymolysis is finished, heating a liquid phase to 90 ℃, preserving heat for 5min, inactivating enzyme, concentrating under reduced pressure to 1/2 of the volume before concentration, and obtaining donkey-hide gelatin enzymatic hydrolysate;

(2) Removing cores of dry red dates, grinding the dry red dates into powder to obtain red date powder, soaking the red date powder in deionized water, wherein the mass ratio of the red date powder to the deionized water is that the red date powder is deionized water=1g:30mL, stirring the mixture for 20min in an ultrasonic environment, heating the mixture to 70 ℃ in a water bath, extracting the mixture at a constant temperature for 3h, naturally cooling the mixture to the normal temperature after the extraction is completed, carrying out solid-liquid separation to obtain red date extract, cutting kelp Cheng Haidai pieces and tea seeds into tea seed powder, adding the kelp pieces and the tea seed powder into aqueous solution of cellulase to obtain an extraction mixed solution, wherein the mass ratio of the kelp pieces and the tea seed powder into the aqueous solution of cellulase is that the aqueous solution of the kelp pieces is that the aqueous solution of the tea seed powder is that the cellulase is=10g:30mL, the enzyme concentration in the aqueous solution of the cellulase is 9U/mL, adjusting the pH of the extraction mixed solution to 5, heating the mixture to 50 ℃, carrying out constant temperature stirring and extracting the mixture for 15h, heating the mixture to 90 ℃ and carrying out heat preservation for 5min, filtering, mixing the filtrate and the red date extract, and concentrating the mixed solution to a reduced pressure concentrated solution to 1/2, and concentrating the mixed solution to obtain a compound extractive solution;

(3) Adding whole milk into warm water at 45 ℃, wherein the mass ratio of the whole milk to the warm water is (1:5) of the whole milk, stirring and fully dissolving to obtain a milk powder solution, adding donkey-hide gelatin zymolyte, the compound extract and white granulated sugar into the milk powder solution, stirring the mixed solution for 20min, sterilizing the mixed solution at 95 ℃ for 5min, cooling the mixed solution to 40 ℃ in a sterile room, adding a yogurt starter (streptococcus thermophilus: bulgaricus=1:1), and adding the donkey-hide gelatin zymolyte, the compound extract, the white granulated sugar and the yogurt starter into the milk powder solution, wherein the mass ratio of the donkey-hide gelatin zymolyte to the compound extract to the white granulated sugar to the yogurt starter=100:22:14:9:0.3, and fermenting at a constant temperature of 40+/-3 ℃ for 7h;

(4) And after the fermentation is finished, placing the fermentation product in a4 ℃ environment for refrigeration for 10 hours, inhibiting the influence of transitional fermentation on the taste, and taking out to obtain the donkey-hide gelatin red date yoghourt.

Example 3

A preparation method of donkey-hide gelatin red date yoghourt comprises the following steps:

(1) Preparing an alkaline protease solution, heating the alkaline protease solution to 40 ℃ in a water bath, preserving heat, adding donkey-hide gelatin powder into the alkaline protease solution, regulating pH after the addition, continuing stirring at a constant temperature of 40 ℃ for enzymolysis for 5 hours, wherein the enzymolysis process comprises the steps of adding 5200U/g of alkaline protease and pH of 8.3, filtering to remove insoluble substances after the enzymolysis is finished, heating a liquid phase to 90 ℃, preserving heat for 5min, inactivating enzyme, concentrating under reduced pressure to 1/2 of the volume before concentration, and obtaining donkey-hide gelatin enzymatic hydrolysate;

(2) Removing cores of dry red dates, grinding the dry red dates into powder to obtain red date powder, soaking the red date powder in deionized water, wherein the ratio of the red date powder to the aqueous solution of cellulase is that the red date powder is deionized water=1g:30mL, stirring the mixture for 20min in an ultrasonic environment, heating the mixture to 70 ℃ in a water bath, extracting the mixture at a constant temperature for 4h, naturally cooling the mixture to the normal temperature after the extraction is completed, carrying out solid-liquid separation to obtain red date extract, cutting kelp Cheng Haidai pieces and tea seeds into tea seed powder, adding the kelp pieces and the tea seed powder into the aqueous solution of cellulase to obtain an extraction mixed solution, wherein the ratio of the kelp pieces and the tea seed powder into the aqueous solution of cellulase is that the aqueous solution of cellulase=10g:4g:30mL, the enzyme concentration of the aqueous solution of cellulase is 9U/mL, adjusting the pH of the extraction mixed solution to 5, heating the mixture to 50 ℃, carrying out constant temperature stirring and extracting the mixture for 15h, heating the mixture to 90 ℃ and carrying out enzyme deactivation treatment for 5min, filtering the mixture, and concentrating the filtrate and the red date extract to obtain a compound extract which is not concentrated to 1/2 before the mixed solution is concentrated;

(3) Adding whole milk into warm water at 45 ℃, wherein the mass ratio of the whole milk to the warm water is (1:6), stirring and fully dissolving to obtain a milk powder solution, adding donkey-hide gelatin zymolyte, the compound extract and white granulated sugar into the milk powder solution, stirring the mixed solution for 20min, sterilizing the mixed solution at 95 ℃ for 5min, cooling the mixed solution to 40 ℃ in a sterile room, adding a yogurt starter (streptococcus thermophilus: bulgaricus=1:1), and adding the donkey-hide gelatin zymolyte, the compound extract, the white granulated sugar and the yogurt starter into the milk powder solution, wherein the mass ratio of the donkey-hide gelatin zymolyte to the compound extract to the white granulated sugar to the yogurt starter is (100:24:16:9:0.4), and fermenting at a constant temperature for 8h at 40+/-3 ℃;

(4) And after the fermentation is finished, placing the fermentation product in a4 ℃ environment for refrigeration for 10 hours, inhibiting the influence of transitional fermentation on the taste, and taking out to obtain the donkey-hide gelatin red date yoghourt.

Example 4

A preparation method of donkey-hide gelatin red date yoghourt comprises the following steps:

(1) Preparing an alkaline protease solution, heating the alkaline protease solution to 40 ℃ in a water bath, preserving heat, adding donkey-hide gelatin powder into the alkaline protease solution, regulating pH after the addition, continuing stirring at a constant temperature of 40 ℃ for enzymolysis for 6 hours, wherein the enzymolysis process comprises the steps of adding 5200U/g of alkaline protease and pH of 8.3, filtering to remove insoluble substances after the enzymolysis is finished, heating a liquid phase to 90 ℃, preserving heat for 5min, inactivating enzyme, concentrating under reduced pressure to 1/2 of the volume before concentration, and obtaining donkey-hide gelatin enzymatic hydrolysate;

(2) Removing cores of dry red dates, grinding the dry red dates into powder to obtain red date powder, soaking the red date powder in deionized water, wherein the ratio of the red date powder to the aqueous solution of cellulase is that the red date powder is deionized water=1g:30mL, stirring the mixture for 20min in an ultrasonic environment, heating the mixture to 70 ℃ in a water bath, extracting the mixture at a constant temperature for 4h, naturally cooling the mixture to the normal temperature after the extraction is completed, carrying out solid-liquid separation to obtain red date extract, cutting kelp Cheng Haidai pieces and tea seeds into tea seed powder, adding the kelp pieces and the tea seed powder into the aqueous solution of cellulase to obtain an extraction mixed solution, wherein the ratio of the kelp pieces and the tea seed powder into the aqueous solution of cellulase is that the aqueous solution of cellulase=10g:5g:30mL, the enzyme concentration in the aqueous solution of cellulase is 10U/mL, adjusting the pH of the extraction mixed solution to 5, heating the mixture to 50 ℃, carrying out constant temperature stirring and extracting the mixture for 15h, heating the mixture to 90 ℃ and carrying out enzyme deactivation treatment for 5min, filtering the mixture, and concentrating the filtrate and the red date extract to obtain a compound extract which is not concentrated to 1/2;

(3) Adding whole milk into warm water at 45 ℃, wherein the mass ratio of the whole milk to the warm water is (1:6), stirring and fully dissolving to obtain a milk powder solution, adding donkey-hide gelatin zymolyte, the compound extract and white granulated sugar into the milk powder solution, stirring the mixed solution for 20min, sterilizing the mixed solution at 95 ℃ for 5min, cooling the mixed solution to 40 ℃ in a sterile room, adding a yogurt starter (streptococcus thermophilus: bulgaricus=1:1), and adding the donkey-hide gelatin zymolyte, the compound extract, the white granulated sugar and the yogurt starter into the milk powder solution, wherein the mass ratio of the donkey-hide gelatin zymolyte to the compound extract to the white granulated sugar to the yogurt starter is (100:25:18:10:0.4), and fermenting at a constant temperature for 8h at 40+/-3 ℃;

(4) And after the fermentation is finished, placing the fermentation product in a4 ℃ environment for refrigeration for 10 hours, inhibiting the influence of transitional fermentation on the taste, and taking out to obtain the donkey-hide gelatin red date yoghourt.

Comparative example 1

A method of preparing yoghurt for comparison comprising the steps of:

(1) Preparing an alkaline protease solution, heating the alkaline protease solution to 40 ℃ in a water bath, preserving heat, adding donkey-hide gelatin powder into the alkaline protease solution, regulating pH after the addition, continuing stirring at a constant temperature of 40 ℃ for enzymolysis for 5 hours, wherein the enzymolysis process comprises the steps of adding 5200U/g of alkaline protease and pH of 8.3, filtering to remove insoluble substances after the enzymolysis is finished, heating a liquid phase to 90 ℃, preserving heat for 5min, inactivating enzyme, concentrating under reduced pressure to 1/2 of the volume before concentration, and obtaining donkey-hide gelatin enzymatic hydrolysate;

(2) Removing the core of dry red dates, grinding the dry red dates into powder to obtain red date powder, soaking the red date powder in deionized water, stirring the red date powder in the deionized water with the mass ratio of the red date powder to the deionized water=1g:30mL under an ultrasonic environment for 20min, heating the mixture to 70 ℃ in a water bath, extracting the mixture at a constant temperature for 4h, naturally cooling the mixture to normal temperature after the extraction is finished, carrying out solid-liquid separation to obtain an extract, and concentrating the extract under reduced pressure to 1/2 of the volume before the concentration to obtain the red date extract;

(3) Adding full-fat milk into warm water at 45 ℃, wherein the mass ratio of the full-fat milk to the warm water is full-fat milk to warm water=1:6, stirring and fully dissolving to obtain a milk powder solution, adding donkey-hide gelatin enzymatic hydrolysate, red date extract and white granulated sugar into the milk powder solution, stirring the mixed solution for 20min, sterilizing the mixed solution at 95 ℃ for 5min, cooling to 40 ℃ in a sterile room, adding a yogurt starter (streptococcus thermophilus to bulgaricus=1:1), and adding the donkey-hide gelatin enzymatic hydrolysate, the red date extract, the white granulated sugar and the yogurt starter into the milk powder solution, wherein the mass ratio of the donkey-hide gelatin enzymatic hydrolysate to the red date extract to the white granulated sugar to the yogurt starter=100:24:16:9:0.4, and fermenting at a constant temperature of 40+/-3 ℃ for 8h;

(4) And after the fermentation is finished, placing the fermentation product in a 4 ℃ environment for refrigeration for 10 hours, inhibiting the influence of transitional fermentation on the taste, and taking out to obtain the yoghurt.

Comparative example 2

A method of preparing yoghurt for comparison comprising the steps of:

(1) Preparing an alkaline protease solution, heating the alkaline protease solution to 40 ℃ in a water bath, preserving heat, adding donkey-hide gelatin powder into the alkaline protease solution, regulating pH after the addition, continuing stirring at a constant temperature of 40 ℃ for enzymolysis for 5 hours, wherein the enzymolysis process comprises the steps of adding 5200U/g of alkaline protease and pH of 8.3, filtering to remove insoluble substances after the enzymolysis is finished, heating a liquid phase to 90 ℃, preserving heat for 5min, inactivating enzyme, concentrating under reduced pressure to 1/2 of the volume before concentration, and obtaining donkey-hide gelatin enzymatic hydrolysate;

(2) Removing cores of dry red dates, grinding the dry red dates into powder to obtain red date powder, soaking the red date powder in deionized water, wherein the weight ratio of the red date powder to the deionized water is that the red date powder is deionized water=1g:30mL, stirring the mixture for 20min in an ultrasonic environment, heating the mixture to 70 ℃ in a water bath, extracting the mixture at constant temperature for 4h, naturally cooling the mixture to normal temperature after the extraction is finished, carrying out solid-liquid separation to obtain red date extract, cutting the kelp to Cheng Haidai dices, adding the kelp dices into aqueous solution of cellulase to obtain an extraction mixed solution, adding the kelp dices into the aqueous solution of cellulase in the weight ratio of kelp dices to the aqueous solution of cellulase=10g:30mL, wherein the enzyme concentration in the aqueous solution of cellulase is 9U/mL, adjusting the pH of the extraction mixed solution to 5, heating the mixture in the water bath to 50 ℃, carrying out constant temperature stirring extraction for 15h, heating the mixture to 90 ℃ and preserving the temperature for 5min, filtering, mixing the filtrate and the red date extract, and concentrating the filtrate under reduced pressure to 1/2 of the volume before concentration to obtain the compound extract of the comparative example;

(3) Adding whole milk into warm water at 45 ℃, wherein the mass ratio of the whole milk to the warm water is (1:6), stirring and fully dissolving to obtain a milk powder solution, adding donkey-hide gelatin zymolyte, the compound extract and white granulated sugar into the milk powder solution, stirring the mixed solution for 20min, sterilizing the mixed solution at 95 ℃ for 5min, cooling the mixed solution to 40 ℃ in a sterile room, adding a yogurt starter (streptococcus thermophilus: bulgaricus=1:1), and adding the donkey-hide gelatin zymolyte, the compound extract, the white granulated sugar and the yogurt starter into the milk powder solution, wherein the mass ratio of the donkey-hide gelatin zymolyte to the compound extract to the white granulated sugar to the yogurt starter is (100:24:16:9:0.4), and fermenting at a constant temperature for 8h at 40+/-3 ℃;

(4) And after the fermentation is finished, placing the fermentation product in a 4 ℃ environment for refrigeration for 10 hours, inhibiting the influence of transitional fermentation on the taste, and taking out to obtain the yoghurt.

Comparative example 3

A method of preparing yoghurt for comparison comprising the steps of:

(1) Preparing an alkaline protease solution, heating the alkaline protease solution to 40 ℃ in a water bath, preserving heat, adding donkey-hide gelatin powder into the alkaline protease solution, regulating pH after the addition, continuing stirring at a constant temperature of 40 ℃ for enzymolysis for 5 hours, wherein the enzymolysis process comprises the steps of adding 5200U/g of alkaline protease and pH of 8.3, filtering to remove insoluble substances after the enzymolysis is finished, heating a liquid phase to 90 ℃, preserving heat for 5min, inactivating enzyme, concentrating under reduced pressure to 1/2 of the volume before concentration, and obtaining donkey-hide gelatin enzymatic hydrolysate;

(2) Removing cores of dry red dates, grinding the dry red dates into powder to obtain red date powder, soaking the red date powder in deionized water, wherein the weight ratio of the red date powder to the deionized water is that the red date powder is deionized water=1g:30mL, stirring the mixture for 20min in an ultrasonic environment, heating the mixture to 70 ℃ in a water bath, extracting the mixture at constant temperature for 4h, naturally cooling the mixture to normal temperature after the extraction is finished, carrying out solid-liquid separation to obtain red date extract, grinding tea seeds into tea seed powder, adding the tea seed powder into aqueous solution of cellulase to obtain an extraction mixed solution, adding the tea seed powder into the aqueous solution of cellulase in an amount ratio of tea seed powder to the aqueous solution of cellulase=4g:30mL, adjusting the pH of the extraction mixed solution to 5, heating the mixture in a water bath to 50 ℃, carrying out constant temperature stirring extraction for 15h, heating the mixture to 90 ℃ and preserving the temperature for 5min, filtering, mixing the filtrate and the red date extract, and concentrating the filtrate under reduced pressure to 1/2 of the volume before concentration to obtain the compound extract of the comparative example;

(3) Adding whole milk into warm water at 45 ℃, wherein the mass ratio of the whole milk to the warm water is (1:6), stirring and fully dissolving to obtain a milk powder solution, adding donkey-hide gelatin zymolyte, the compound extract and white granulated sugar into the milk powder solution, stirring the mixed solution for 20min, sterilizing the mixed solution at 95 ℃ for 5min, cooling the mixed solution to 40 ℃ in a sterile room, adding a yogurt starter (streptococcus thermophilus: bulgaricus=1:1), and adding the donkey-hide gelatin zymolyte, the compound extract, the white granulated sugar and the yogurt starter into the milk powder solution, wherein the mass ratio of the donkey-hide gelatin zymolyte to the compound extract to the white granulated sugar to the yogurt starter is (100:24:16:9:0.4), and fermenting at a constant temperature for 8h at 40+/-3 ℃;

(4) And after the fermentation is finished, placing the fermentation product in a 4 ℃ environment for refrigeration for 10 hours, inhibiting the influence of transitional fermentation on the taste, and taking out to obtain the yoghurt.

Example 5

The yogurt prepared in the above examples and comparative examples was subjected to sensory evaluation according to the following criteria, 10 persons were selected to score the texture, color, mouthfeel and odor of the yogurt, and the final data were averaged, and the results are shown in table 1.

DPPH radical scavenging of the yogurts prepared in each example and comparative example was tested according to the method described in paper Antioxidant activity of extracts from Gevuina AVELLANA AND Rosa rubiginosa DEFATTED SEEDS, hydroxyl radical scavenging of the yogurts prepared in each example and comparative example was tested according to the method described in paper "Water-soluble polysaccharide from the fruiting bodies of Chroogomphis rutilus(Schaeff.:Fr.)O.K.Miller:Isolation,structural features and its scavenging effect on hydroxyl radical", ABTS radical scavenging of the yogurts prepared in each example and comparative example was tested according to the method described in paper "Modified2,2-azino-Bis-3-ethylbenzothiazoline-6-sulfonic acid(ABTS)method to measure antioxidant capacity of selected small fruits and comparison to ferric reducing antioxidant power(FRAP)and 2,2-Diphenyl-1-picrylhydrazyl(DPPH)methods", and the results are shown in FIGS. 1 to 3.

TABLE 1

Test group	Tissue state	Color and luster of	Mouthfeel of the product	Smell of	Total score
						Example 1	25.3	17.7	25.8	16.1	84.9
Example 2	25.8	18.2	26.5	17.4	87.9
						Example 3	26.4	18.5	26.7	17.9	89.5
Example 4	26.1	18.0	26.1	17.7	87.9
						Comparative example 1	18.5	14.9	16.4	13.6	63.4
Comparative example 2	20.2	15.3	18.6	14.5	68.6
						Comparative example 3	21.1	16.8	19.3	15.0	72.2

As can be seen from Table 1 and the figures, the yogurt prepared by the method has good tissue morphology, fine and uniform texture, moderate viscosity, no whey precipitation, uniform and glossy color, good taste and rich fragrance. And has good antioxidant activity.

The foregoing detailed description of the embodiments of the present invention will be provided to those skilled in the art, and the detailed description and the examples should not be construed as limiting the invention.

Claims (7)

1. A method for preparing donkey-hide gelatin and red date yogurt, characterized in that the steps include: (1) preparing an alkaline protease solution, heating the alkaline protease solution to 40±3° C. in a water bath, then adding donkey-hide gelatin powder to the alkaline protease solution, adjusting the pH after the addition, continuing to stir and enzymolyze at 40±3° C. for 4 to 6 hours, filtering to remove insoluble matter after the enzymolysis is completed, performing liquid phase enzyme inactivation treatment, and concentrating under reduced pressure to obtain donkey-hide gelatin enzymolysate; (2) removing the pits from dried red dates, grinding them into powder to obtain red date powder, soaking the red date powder in deionized water, stirring it under an ultrasonic environment for more than 20 minutes, heating it in a water bath to 70±5°C, extracting it at a constant temperature for 3-4 hours, and naturally cooling it to room temperature after the extraction is completed, separating the solid and the liquid, and obtaining a red date extract; chopping kelp into kelp cubes, and grinding tea seeds into tea seed powder; adding the kelp cubes and the tea seed powder into an aqueous solution of cellulase to obtain an extraction mixture, adjusting the pH of the extraction mixture to 5-5.5, heating it in a water bath to 50±3°C, extracting it at a constant temperature with stirring for more than 15 hours, then inactivating the enzyme, filtering, mixing the filtrate with the red date extract, and concentrating it under reduced pressure to obtain a composite extract; (3) adding whole milk to warm water at 45±5°C, stirring to fully dissolve, and obtaining a milk powder solution; adding the donkey-hide gelatin hydrolysate, the composite extract, and white sugar to the milk powder solution to obtain a mixed solution, stirring the mixed solution for more than 20 minutes, and then sterilizing the mixed solution, cooling it to 40±3°C in a sterile room, adding a yogurt starter, and fermenting it at a constant temperature of 40±3°C for 7 to 8 hours; (4) After the fermentation is completed, the fermentation product is placed in a refrigerated environment at 0 to 4° C. for 10 to 12 hours to inhibit excessive fermentation from affecting the taste, and then taken out to obtain the donkey-hide gelatin and red date yogurt. 2. The method for preparing donkey-hide gelatin and red date yogurt according to claim 1, characterized in that in the step (1), the amount of alkaline protease added is 5100-5200 U/g and the pH is 8.3. 3. The method for preparing donkey-hide gelatin and red date yogurt according to claim 1, characterized in that in the step (1), the reduced pressure is concentrated to 1/2 of the volume before concentration. 4. The method for preparing donkey-hide gelatin and red date yogurt according to claim 1, characterized in that the enzyme inactivation treatment method is: heating to 90°C and keeping warm for 5 minutes to inactivate the enzyme. 5. The method for preparing donkey-hide gelatin and red date yogurt according to claim 1, characterized in that in the step (2), the red date powder is soaked in deionized water in a ratio of red date powder: deionized water = 1 g: 30 mL. 6. The method for preparing a donkey-hide gelatin and red date yogurt according to claim 1 is characterized in that in the step (2), the diced kelp and the tea seed powder are added to the aqueous solution of cellulase in a ratio of diced kelp: tea seed powder: aqueous solution of cellulase = 10 g: 3-5 g: 30 mL, and the enzyme concentration in the aqueous solution of cellulase is 8-10 U/mL; and the composite extract is obtained by concentrating under reduced pressure to 1/2 of the volume before concentration. 7. The method for preparing a donkey-hide gelatin and red date yogurt according to claim 1 is characterized in that, in the step (3), the mass ratio of whole milk added to warm water is whole milk: warm water = 1:5-6; the mass ratio of the donkey-hide gelatin hydrolysate, the composite extract, white sugar, and yogurt starter added to the milk powder solution is milk powder solution: donkey-hide gelatin hydrolysate: composite extract: white sugar: yogurt starter = 100:20-25:12-18:8-10:0.3-0.4.