阅读说明：本技术 一种防止乳清析出的酸奶制备方法 (Preparation method of yoghourt capable of preventing whey from separating out ) 是由 张凤 王静 洪阳 李婉竹 朱旭 王鹏杰 陈冲 蒋源渊 周鑫 于 2020-11-30 设计创作，主要内容包括：本发明属于食品技术加工领域,具体公开了一种防止乳清析出的酸奶制备方法。具体包括以下步骤：S1,取牛乳,并将牛乳的pH值调节到5.0～6.7,得到乳液A；S2,在步骤S1中所制备的乳液A中加入TG酶,并进行孵化,得到乳液B；S3,将步骤S2中所制备的乳液B的pH值调节到6.5～6.7,进行杀菌灭酶,加入发酵物质后进行保存。本发明的制备方法简单,易于操作,其能有效解决酸奶在发酵贮藏过程中脱水收缩的现象的发生,从而提高酸奶稳定性。(The invention belongs to the technical field of food processing, and particularly discloses a preparation method of yoghourt for preventing whey from separating out. The method specifically comprises the following steps: s1, taking cow milk, and adjusting the pH value of the cow milk to 5.0-6.7 to obtain emulsion A; s2, adding TG enzyme into the emulsion A prepared in the step S1, and incubating to obtain emulsion B; s3, adjusting the pH value of the emulsion B prepared in the step S2 to 6.5-6.7, sterilizing and inactivating enzymes, adding a fermentation substance, and storing. The preparation method is simple and easy to operate, and can effectively solve the problem of syneresis of the yoghourt in the fermentation and storage processes, thereby improving the stability of the yoghourt.)

1. A preparation method of yoghourt for preventing whey from separating out is characterized by comprising the following steps:

s1, taking cow milk, and adjusting the pH value of the cow milk to 5.0-6.7 to obtain emulsion A;

s2, adding TG enzyme into the emulsion A prepared in the step S1, and incubating to obtain emulsion B;

s3, adjusting the pH value of the emulsion B prepared in the step S2 to 6.5-6.7, sterilizing and inactivating enzymes, adding a fermentation substance, and storing.

2. The method for producing yogurt according to claim 1, wherein an acidity regulator such as citric acid, diluted hydrochloric acid or lactic acid is used for adjusting the pH in step S1.

3. A method for preparing yogurt with whey prevented from separating out as claimed in claim 1 or 2, wherein in step S3, NaOH solution is used for pH adjustment.

4. The method for preparing yogurt according to claim 1 or 2, wherein in step S3, the temperature of sterilization and enzyme deactivation is 80-100 ℃ for 3-8 min.

5. The method for preparing yogurt with whey separated out prevented according to claim 4, wherein in step S3, the temperature for sterilization and enzyme deactivation is 95 ℃ for 4 min.

6. A method for producing yogurt according to claim 1, 2 or 5, wherein in step S2, the incubation temperature is 30 to 60 ℃ and the incubation time is 1.3 to 1.8 hours.

7. A method for producing yogurt according to claim 3, wherein in step S2, the incubation temperature is 30 to 60 ℃ and the incubation time is 1.3 to 1.8 hours.

8. A method for producing yogurt according to claim 4, wherein in step S2, the incubation temperature is 30 to 60 ℃ and the incubation time is 1.3 to 1.8 hours.

9. The method for producing yogurt with whey prevented from separating out according to claim 1, wherein the fermentation substance in step S3 is a bacterial strain or glucono-delta-lactone.

Technical Field

The invention belongs to the technical field of food processing, and particularly relates to a preparation method of yoghourt for preventing whey from separating out.

Background

The yoghourt becomes a food with rich nutritive value which is generally popular in the world, has fresh and mellow flavor and special mouthfeel which is instantly melt in the mouth, and attracts wide consumer groups. The yoghurt is a kind of fermentation product formed by fermenting lactose in cow milk by using lactic acid bacteria to generate lactic acid. In the fermentation process of the yoghourt, more than 20% of sugar and protein in the cow milk are decomposed due to the action of the lactic acid bacteria, when the pH value of a milk system is reduced to the isoelectric point pI of casein, casein micelles are dissociated into casein monomers, and at the moment, the solubility of the protein is reduced, and the protein aggregates to form gel with a three-dimensional space network structure, so that the human body can more easily absorb nutrients such as protein, calcium and the like in the yoghourt.

Although the yoghourt is easy to be absorbed by human bodies, the yoghourt often has different product quality problems in the fermentation and storage processes, and particularly, the yoghourt generates syneresis and is accompanied with phenomena such as whey precipitation and the like, so that the experience of consumers is seriously influenced. The main reason for separating out whey from the yogurt is that casein molecules are dissociated from micelle structures firstly and then are polymerized into particles larger than natural micelles again in the process of cow milk acidification, and three-dimensional network structures are formed among the particles. Therefore, the strengthening of the intermolecular interaction of milk proteins is of great significance for preventing the whey from separating out.

At present, the conventional methods for strengthening the interaction between the milk protein molecules have the characteristics of physical condition change, chemical reagent action or enzyme catalysis, wherein the enzyme catalysis reaction is widely applied to strengthening the interaction between the milk protein molecules due to the characteristics of specificity and mild condition of the reaction. Transglutaminase (TG enzyme) is widely applied to the production and processing of yoghourt, is acyltransferase, and can catalyze protein molecules or intramolecular formation of epsilon- (gamma-glutamyl) lysine covalent bonds, thereby strengthening the interaction between milk protein molecules, reducing the phenomenon of dehydration shrinkage of the yoghourt, and enabling the yoghourt to have smoother texture and better stability. Although TG enzyme can obviously improve the water holding capacity of the yoghourt and reduce the syneresis phenomenon, the problem of whey separation in the fermentation and storage process of the yoghourt can not be completely solved. After the TG enzyme is added, the water holding capacity of the yoghourt can be improved by about 10 percent, the highest water holding capacity can reach 52 percent, but the whey separation rate is still kept about 15 percent, and the primary judgment is that the number of cross-linked bonds of casein micelles under the action of the TG enzyme is still not enough, so that the phenomenon that the milk protein is dehydrated and shrunk to form whey separation is caused. Therefore, enhancing the number of milk protein cross-links has a crucial effect on the stability of the yoghurt.

The content of calcium phosphate colloid in the casein micelles is reduced, the casein micelles are dissociated to form a monomer structure, and the stability of the gel is favorably improved. The state of casein and minerals in milk is influenced by pH value, temperature and calcium ion chelating agent. Related studies show that before transglutaminase crosslinks protein molecules, a chelating salt (such as sodium citrate, polyphosphate and the like) is added into milk to induce dissolution of colloidal calcium phosphate in casein micelles, so that the casein micelles are dissociated, and then transglutaminase crosslinked milk protein is used for fermentation to form yogurt. The texture of the yoghourt prepared by the method is superior to that of the yoghourt prepared by adding transglutaminase in the prior art, but the method still has the following defects:

(1) the addition amount of the chelating salt such as sodium citrate is large: according to a large amount of research data, when the addition amount of chelating agents such as sodium citrate is required to be more than or equal to 3g/L, the stability of the yoghourt prepared by utilizing TG enzyme crosslinking has a great improvement phenomenon, but the weight ratio of the calcium chelating agent to the milk is 0.003: 1-0.01: 1, so that the method has a great requirement on the addition amount of chelating salts such as sodium citrate;

(2) the mouthfeel of the yoghourt is influenced: the chelated salt such as sodium citrate has salty and spicy taste, the mouthfeel of the yoghourt can be changed due to the excessive adding amount in the process of preparing the yoghourt, and particularly, the influence on the mouthfeel is more remarkable for the sugar-free yoghourt.

Based on the analysis, the phenomenon of whey precipitation is easy to occur in the yogurt prepared by the existing method, and the problems that the number of casein micelle cross-links is still not enough, the addition amount of the chelating salt is large, the mouthfeel of the yogurt is affected and the like still exist in the solution method in the prior art. Therefore, there is a need in the art to develop a method for preparing yogurt that is effective in preventing whey from separating out.

Disclosure of Invention

The invention aims to provide a preparation method of yoghourt for preventing whey from separating out. The preparation method is simple and easy to operate, and can effectively solve the problem of syneresis of the yoghourt in the fermentation and storage processes, thereby improving the stability of the yoghourt.

The technical scheme for realizing the purpose of the invention is as follows:

a preparation method of yoghourt for preventing whey from separating out comprises the following steps:

s1, taking cow milk, and adjusting the pH value of the cow milk to 5.0-6.7 to obtain emulsion A;

s2, adding TG enzyme into the emulsion A prepared in the step S1, and incubating to obtain emulsion B;

s3, adjusting the pH value of the emulsion B prepared in the step S2 to 6.5-6.7, sterilizing and inactivating enzymes, adding a fermentation substance, and storing.

The cow milk is obtained from Dairy second factory of Tianyou Dairy Co., Ltd, Chongqing, and fresh cow milk with pH value of 6.7 is preferred. The surface of casein micelle in fresh milk contains negative charges, the pH value is reduced by adjusting, the quantity of the negative charges in the milk is less and less in the process of reducing the pH value, the repulsion force is reduced, the hydrophobic force is enhanced, and the calcium phosphate (for stabilizing the structure of the casein micelle) is gradually dissolved. Aiming at the phenomenon of dehydration shrinkage of the yoghourt in the fermentation and storage processes, the pH value of the milk is adjusted, the casein micelle structure is changed, the dehydration shrinkage of the yoghourt can be reduced by utilizing TG enzyme exchange after a casein monomer is formed, the stability of the yoghourt is improved, a large amount of addition of chelating salts such as sodium citrate is avoided, and the mouthfeel of the yoghourt is ensured.

The method comprises the following steps of placing fresh milk in a refrigerated centrifuge, centrifuging at the temperature of 3-6 ℃, and collecting the lower layer of milk. After the fresh milk is subjected to degreasing treatment, the protein and carbohydrate content is high, the fat content is reduced to about 1%, and the heat is low, so that the milk is suitable for people with low heat demand and children with fat indigestion; meanwhile, oxidation is not easy to occur after degreasing, and the storage time can be prolonged. Degreasing at 3-6 ℃ can make degreasing more thorough.

In addition, the pH value of the emulsion B prepared in the step S3 is adjusted to 6.5-6.7, and the pH value is preferably adjusted to 6.5, so that the adjusting process is convenient to adjust, and the adjusting time is saved.

The invention has the beneficial effects that: according to the invention, the pH value of cow milk is regulated and controlled, the casein micelle structure is dissociated, and TG enzyme is used for crosslinking milk protein, so that the dehydration shrinkage phenomenon of the yoghourt is reduced, and the stability of the yoghourt is improved. The yoghourt prepared by the method is instantly melted in the mouth and has fresh, fresh and mellow flavor; in addition, the whey precipitation phenomenon can be effectively prevented, and the storage life of the yoghourt is further prolonged.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.

FIG. 1 is a graph showing the effect of different amounts of acidity regulator on milk pH.

FIG. 2 is a graph showing whey separation in yogurt according to examples 2 to 4.

FIG. 3 is another representation of whey separation in the yogurt of examples 2-4.

FIG. 4 is a graph of the effect of clarification index of yoghurts obtained after different pH treatments.

Fig. 5 is a graph showing the effect of the transmittance of the yogurt obtained in example 2.

FIG. 6 is a graph showing the effect of the transmittance of the yogurt obtained in example 3.

FIG. 7 is a graph showing the effect of the transmittance of the yogurt obtained in example 4.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

A preparation method of yoghourt for preventing whey from separating out comprises the following steps:

s1, taking cow milk, and adjusting the pH value of the cow milk to 5.0-6.7 by using acidity regulators such as citric acid, dilute hydrochloric acid or lactic acid and the like to obtain emulsion A;

s2, adding TG enzyme into the emulsion A prepared in the step S1, and incubating to obtain an emulsion B, wherein the incubation temperature is 30-60 ℃, and the incubation time is 1.3-1.8 h;

s3, adjusting the pH value of the emulsion B prepared in the step S2 to 6.5-6.7 by using a NaOH solution, sterilizing, inactivating enzymes, adding a fermentation substance, and storing; wherein the temperature of sterilization and enzyme deactivation is 80-100 ℃, and the time is 3-8 min; the fermentation substance is strain or gluconic acid-delta-lactone.

Example 2

A preparation method of yoghourt for preventing whey from separating out comprises the following steps:

s1, placing 4000g of fresh milk in a refrigerated centrifuge, centrifuging for 25min at 4 ℃, and collecting the milk at the lower layer;

s2, adjusting the pH value of the milk obtained in the step S1 by using 1mol/L citric acid to make the pH value of the milk be 6.7, obtaining emulsion A, and recording the required amount of the citric acid;

s3, adding 3U/g TG enzyme into the emulsion A prepared in the step S2, stirring for 3 minutes under the action of a magnetic stirrer to completely disperse the TG enzyme, and incubating for 1.5 hours at the temperature of 45 ℃ to obtain emulsion B;

s4, adjusting the pH value of the emulsion B prepared in the step S3 to 6.5 by adopting 1mol/L diluted NaOH solution, sterilizing and inactivating enzymes for 5min at 95 ℃, adding 100DCU/T strains, placing in a thermostat at 43 ℃ for 4h, cooling to obtain a yoghourt sample, and finally placing the sample at 4 ℃ for later use.

Example 3

A preparation method of yoghourt for preventing whey from separating out comprises the following steps:

s1, placing 4000g of fresh milk in a refrigerated centrifuge, centrifuging for 25min at 4 ℃, and collecting the milk at the lower layer;

s2, adjusting the pH value of the milk obtained in the step S1 by using 1mol/L citric acid to make the pH value of the milk be 6.0, obtaining emulsion A, and recording the required amount of the citric acid;

s3, adding 3U/g TG enzyme into the emulsion A prepared in the step S2, stirring for 3 minutes under the action of a magnetic stirrer to completely disperse the TG enzyme, and incubating for 1.5 hours at the temperature of 45 ℃ to obtain emulsion B;

s4, adjusting the pH value of the emulsion B prepared in the step S3 to 6.5 by adopting 1mol/L diluted NaOH solution, sterilizing and inactivating enzymes for 5min at 95 ℃, adding 1-2% of gluconic acid-delta-lactone, placing in a thermostat at 43 ℃ for 4h, cooling to obtain a yogurt sample, and finally placing the sample at 4 ℃ for later use.

Example 4

A preparation method of yoghourt for preventing whey from separating out comprises the following steps:

s1, placing 4000g of fresh milk in a refrigerated centrifuge, centrifuging for 25min at 4 ℃, and collecting the milk at the lower layer;

s2, adjusting the pH value of the milk obtained in the step S1 by using 1mol/L diluted hydrochloric acid to enable the pH value of the milk to be 5.2, obtaining emulsion A, and recording the amount of the diluted hydrochloric acid;

s3, adding 3U/g TG enzyme into the emulsion A prepared in the step S2, stirring for 3 minutes under the action of a magnetic stirrer to completely disperse the TG enzyme, and incubating for 1.5 hours at the temperature of 45 ℃ to obtain emulsion B;

s4, adjusting the pH value of the emulsion B prepared in the step S3 to 6.5 by adopting 1mol/L diluted NaOH solution, sterilizing and inactivating enzymes for 5min at 95 ℃, adding 100DCU/T strains, placing in a thermostat at 43 ℃ for 4h, cooling to obtain a yoghourt sample, and finally placing the sample at 4 ℃ for later use.

Example 5

A preparation method of yoghourt for preventing whey from separating out comprises the following steps:

s1, placing 4000g of fresh milk in a refrigerated centrifuge, centrifuging for 25min at 4 ℃, and collecting the milk at the lower layer;

s2, adjusting the pH value of the milk obtained in the step S1 by using 1mol/L lactic acid to enable the pH value of the milk to be 5.0, obtaining emulsion A, and recording the required amount of the lactic acid;

s3, adding 3U/g TG enzyme into the emulsion A prepared in the step S2, stirring for 3 minutes under the action of a magnetic stirrer to completely disperse the TG enzyme, and incubating for 1.5 hours at the temperature of 45 ℃ to obtain emulsion B;

s4, adjusting the pH value of the emulsion B prepared in the step S3 to 6.5 by adopting 1mol/L diluted NaOH solution, sterilizing and inactivating enzymes for 5min at 95 ℃, adding 1-2% of gluconic acid-delta-lactone, placing in a thermostat at 43 ℃ for 4h, cooling to obtain a yogurt sample, and finally placing the sample at 4 ℃ for later use.

Experimental verification

1. Calculation of acid addition

The pH of the milk of examples 2-4 was adjusted with the acidity regulator to 6.7, 6.0, 5.2, 5.0, respectively, and the required addition of the acidity regulator was recorded.

2. Diameter measurement of milk particles

Emulsion a prepared in step S2 of example 2 to example 4 was diluted 500 times with ultrapure water at normal temperature, and the particle size distribution of each set of samples (i.e., sample 1, sample 2, and sample 3) after pH adjustment was measured by a particle size analyzer, and the environmental temperature of the samples was 25 ℃ and the refractive index was 1.529.

3. Determination of whey separation rate of yoghourt

60g of each of the yogurts prepared in the embodiments 2 to 4 is taken, the supernatant of the yoghurt is respectively sucked by a syringe needle with the diameter of 2mm, the weight of the supernatant is weighed, and the precipitation rate of the whey of the yoghurt is calculated according to the following formula:

the yogurt whey separation rate (%) -. supernatant weight (g)/sample weight (g). times.100%

4. Determination of the stability of the yogurt

Examples 2-4 were analyzed using a Lumisizer analyzer, the sample particles were moved under gravity or centrifugal force by the centrifugal principle, the sedimentation rate was calculated by near infrared light observation, the stability of the different samples was compared by analyzing the separation time course of sedimentation and suspension, according to the result data. Wherein the test conditions are as follows: the rotation speed is 2000rmp, the time is 100min, and the temperature is 4 ℃.

Effects of the implementation

1. The pH value of the milk is influenced by the acid adding amount

The pH value of normal milk is 6.4-6.8, the average is 6.6, the pH value of milk used in the experiment is 6.7, the influence of the addition amount of the acidity regulator on the pH value of milk is shown in figure 1, when the addition amount of the acidity regulator is 0.0099mol/L (1.9g/L), the pH value of milk is 5.2, and when the addition amount of the acidity regulator is 0.0040mol/L (0.76g/L), the pH value of milk is 6.0, but the research of the invention shows that the precipitation phenomenon is easily formed when the pH value of milk is 5.0, and the reason may be that under the condition, dissociated casein monomers are mutually aggregated and re-polymerized to form colloidal particles, so that the solubility of a system is reduced, and the viscosity is increased. Therefore, when the dosage of the acidity regulator is equal to the additive amount (more than or equal to 3g/L) of the conventional calcium chelating agent, the effect is obviously reduced.

2. Influence of different pH values on milk particle diameter

The diameters of the milk particles treated at different pH values are measured, the pH values of the milk are respectively 6.7, 6.0 and 5.2, and the measurement results are shown in Table 1:

TABLE 1 Effect of different pH on milk particle diameter

In the table, a to c show the significant difference of different pH values to milk particle size (P <0.05)

As can be seen from Table 1, the lower the pH of the milk, the smaller the diameter of the milk particles, indicating that adjusting the pH of the milk reduces the average milk particle size. The reason may be that calcium phosphate combines with α s1-, α s2-, β -and κ -casein monomers in casein to form a casein micelle structure, and by reducing the pH value of milk, the negative charge on the surface of the casein micelle is reduced, the repulsion force is reduced, the hydrophobic force is enhanced, and calcium phosphate (which stabilizes the structure of the casein micelle) is gradually dissolved, so that the degree of connection between proteins in the micelle is reduced, which is visually shown as a significant reduction in the particle diameter of milk.

3. Effect of different pH values on whey separation of yogurt

The whey separation rates of the yoghurts obtained by different treatment modes are shown in fig. 2 and 3:

as can be seen from fig. 2 and 3, in the case of cow's milk treated at different pH values, the whey precipitation phenomenon of the yoghurt is reduced with the decrease of the pH value under the cross-linking of TG enzyme, but when the pH value is lower than 5.2, the casein protein in cow's milk is aggregated, which is not good for the stability of the product, as can be seen from the effect 1. When the pH of the milk is 5.2, the whey phenomenon of the yoghourt is remarkably reduced, because the casein micelles are fully dissociated after the milk is subjected to pH treatment, the cross-linking sites with TG enzyme are increased, water is not easily separated out from the gel network of the yoghourt, and the whey separation phenomenon of the yoghourt is improved.

4. Effect of different pH treatments on yogurt stability

The clarity index and transmittance of the yogurt obtained by the different treatment methods are shown in fig. 4 to 7:

according to Stocks' rule, when the particles in solution are smaller and the viscosity is higher, the particles float slower and therefore the stability of the polymer increases. Stability of the aggregates the particle behaviour over time was recorded by measuring the particle displacement rate in relation to the penetration of light. As the eccentricity increases, the greater the light transmission, the higher the clarity index, indicating that the material is less stable.

As can be seen from fig. 4, the clarification indexes of the yoghurts prepared from cow milk treated at different pH values are significantly different, and the clarification index of the yoghurt decreases with the decrease of the pH value, which indicates that the stability of the yoghurt increases significantly with the decrease of the pH value. Fig. 5 to 7 also demonstrate the phenomenon, and as shown by combining fig. 1 to 7, the stability of the yogurt is significantly enhanced and has better stability at a pH value of 5.2.

The above-mentioned embodiments are further described in detail for the purpose of illustrating the invention, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the invention and are not intended to limit the invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit of the invention should be included in the scope of the invention.