阅读说明：本技术 低脂低乳糖复合型酸奶及其制备方法 (Low-fat low-lactose composite yoghurt and preparation method thereof ) 是由 索超 尹小静 薛建岗 庞飞 张建斌 于 2020-04-30 设计创作，主要内容包括：本发明提供了一种低脂低乳糖复合型酸奶及其制备方法。该制备方法包括在杀菌后、发酵前采用未经灭菌的乳糖酶进行酶解,并且,以酸奶原料总重为100％计,所述酸奶原料包括酸度调节剂0.04-0.06％,细菌素0.0005-0.0015％,用于抑制乳糖酶中的杂菌。本发明还提供了一种低脂低乳糖复合型酸奶,其是由上述制备方法得到的。本发明提供的制备方法能够有效降低酸奶产品的乳糖含量及避免产品变质,制备得到的低脂低乳糖复合型酸奶具有较好稳定性和良好的风味口感。(The invention provides low-fat and low-lactose compound yogurt and a preparation method thereof. The preparation method comprises the steps of carrying out enzymolysis on the raw materials of the yoghourt by adopting non-sterilized lactase after sterilization and before fermentation, wherein the raw materials of the yoghourt comprise 0.04-0.06% of acidity regulator and 0.0005-0.0015% of bacteriocin by taking the total weight of the raw materials of the yoghourt as 100%, and are used for inhibiting mixed bacteria in the lactase. The invention also provides low-fat and low-lactose composite yoghurt which is prepared by the preparation method. The preparation method provided by the invention can effectively reduce the lactose content of the yoghurt product and avoid the product deterioration, and the prepared low-fat low-lactose composite yoghurt has better stability and good flavor and taste.)

1. A preparation method of low-fat and low-lactose compound yoghurt comprises the steps of carrying out enzymolysis on non-sterilized lactase after sterilization and before fermentation, wherein the raw materials of the yoghurt comprise 0.04-0.06% of acidity regulator and 0.0005-0.0015% of bacteriocin by taking the total weight of the raw materials of the yoghurt as 100% and are used for inhibiting mixed bacteria in the lactase.

2. The preparation method of claim 1, wherein the raw materials of the yogurt comprise, based on 100% of the total weight of the raw materials of the yogurt: 0.05-1% of compound stabilizer, 1000NLU/L of non-sterilized lactase 700-;

preferably, the content of the acidity regulator is 0.05%, and the content of the bacteriocin is 0.001%.

3. The preparation method according to claim 1 or 2, wherein the raw material of the yogurt further comprises 1.5-3.5% of sugar, preferably the sugar comprises white granulated sugar, based on 100% of the total weight of the raw material of the yogurt.

4. The preparation method of claim 2, wherein the compound stabilizer comprises pectin and starch in a mass ratio of 1:3-1: 6;

preferably, the compound stabilizer comprises 0.02-0.15% of pectin and 0.06-0.09% of starch by taking the total weight of the yoghourt raw material as 100%;

more preferably, the starch comprises physically modified starch and/or chemical starch;

further preferably, the chemical starch comprises hydroxypropyl distarch phosphate and/or acetylated starch.

5. The production method according to claim 1 or 2, wherein the acidity regulator comprises one or a combination of two or more of lactic acid, citric acid, malic acid, and tartaric acid.

6. The preparation method according to claim 1, wherein the fermenting agent used for fermentation comprises one or more of streptococcus thermophilus, lactobacillus bulgaricus, bifidobacterium lactis, lactobacillus acidophilus, lactobacillus plantarum and lactobacillus rhamnosus;

preferably, the weight of the leavening agent accounts for 0.002% of the total weight of the yoghourt raw material.

7. The method of claim 2, wherein the standardized milk has a fat content of less than or equal to 1%;

preferably, the standardized milk is obtained by standardizing raw milk;

more preferably, the standardization treatment comprises the operations of degreasing and hydrating the raw milk;

further preferably, the degreasing temperature is 55-58 ℃, the degreasing pressure is 0.4-0.6bar, the hydration temperature is 55-60 ℃, and the hydration time is 25-35 min.

8. A method of manufacturing as claimed in claim 7, wherein the raw milk has a fat content of less than 1%;

preferably, the raw milk comprises one of low fat milk, fully skimmed milk powder or partially skimmed milk powder.

9. The production method according to claim 1, wherein the production method comprises: preparing materials, degassing, homogenizing, sterilizing, performing enzymolysis and fermenting to obtain the low-fat and low-lactose compound yogurt;

preferably, the ingredients comprise the operations of stirring the standardized milk, the compound stabilizer, the concentrated whey protein, the acidity regulator and the bacteriocin, and when the yogurt raw material contains sugar, the sugar and the standardized milk are stirred together;

the degassing temperature is 60-70 ℃, and the degassing pressure is 18-20 MPa;

the pressure for homogenizing is 30 +/-2/180 +/-5 bar;

the sterilization temperature is 90-100 ℃, and the sterilization time is 280-320 s;

the temperature of the enzymolysis is 35-40 ℃, and the time of the enzymolysis is 35-45 min;

the fermentation temperature is 40-43 ℃, and the fermentation is carried out until the pH value reaches 4.5-4.6;

more preferably, the stirring temperature is 50-55 ℃, the stirring time is 30-60min, and the stirring speed is 500-800 rpm.

10. A low-fat and low-lactose composite yoghurt obtained by the production method according to any one of claims 1 to 9.

Technical Field

The invention relates to the field of food processing, in particular to low-fat and low-lactose compound yogurt and a preparation method thereof.

Background

Obesity is one of three diseases harmful to human health, and is more and more concerned by people, meanwhile, a part of people are lactose intolerant people, non-infectious diarrhea caused by lactose in breast milk or cow milk cannot be completely digested and decomposed due to lack of lactase in the body, which is also called lactase deficiency disease, lactase deficiency is a worldwide problem which exists widely, the incidence rate of people in the far east is high, and the normal life of people is seriously influenced. Therefore, the trend of low lactose and low fat has been developed, and the yoghurt containing a large amount of beneficial active bacteria is one of the ideal food for modern people with both nutrition and health care functions. Therefore, the development of a low-fat low-lactose compound yoghurt surely leads to market trend.

The fat content of the traditional yoghurt product is generally between 2.7 and 3.2 percent, the fat in the yoghurt is an important component for maintaining the texture and the taste of the yoghurt, and the low-fat yoghurt has the phenomena of sandy texture, rough taste, whey separation and layering due to low solid content, and lacks the characteristics of smoothness, fineness and the like of the yoghurt. Therefore, there is an urgent need for a method for improving the texture and mouthfeel of low-fat, low-lactose yogurt while reducing the lactose content of the yogurt.

Disclosure of Invention

In order to solve the problems, the invention aims to provide low-fat and low-lactose compound yoghurt and a preparation method thereof. According to the preparation method, lactase is added for enzymolysis, and the acidity regulator and the bacteriocin are added, so that the lactose content of the yogurt product can be effectively reduced, the product is prevented from deteriorating, and the low-fat and low-lactose compound yogurt with better stability, flavor and taste is obtained.

In order to achieve the aim, the invention provides a preparation method of low-fat low-lactose compound yoghurt, which comprises the steps of carrying out enzymolysis by using non-sterilized lactase after sterilization and before fermentation, wherein the raw materials of the yoghurt comprise 0.04-0.06% of acidity regulator and 0.0005-0.0015% of bacteriocin by taking the total weight of the raw materials of the yoghurt as 100% and are used for inhibiting mixed bacteria in the lactase.

In the preparation method, the lactase which is not sterilized is adopted for enzymolysis, so that the lactose content in the yoghourt product can be effectively reduced, and the consumption requirements of lactose intolerant people are met. Because lactase is not sterilized before being added and is added after being sterilized in the process of preparing the yoghourt, and the lactase is not subjected to high-temperature sterilization treatment after being added, the lactase activity in the yoghourt product is reserved, and the lactose in the yoghourt product can be continuously decomposed after the yoghourt product is filled, so that the product maintains a low-lactose state. The activity of the lactase filtered by the existing membrane treatment is generally 85 percent of that of the lactase not filtered by the membrane treatment, the cost is higher, and the economic efficiency of the industrial production is general. Compared with the prior art, the lactase without sterilization has higher enzyme activity, saves the cost and is suitable for industrial production.

In the preparation method, the bacteriocin has an antibacterial effect, can reduce the activity of mixed bacteria brought by non-sterilized lactase, and avoids the yogurt product deterioration caused by mixed bacteria pollution. In a specific embodiment, the bacteriocin can play a role in inhibiting miscellaneous bacteria in lactase on the premise of ensuring that the activity of a starter is not influenced by the added content of the bacteriocin in the yoghourt raw material.

In the preparation method, the acidity regulator is matched with the bacteriocin for use, so that the inhibition effect of the excessive bacteriocin on the activity of the starter can be avoided, the acidity of the yoghourt raw material can be synergistically regulated, cell membranes of mixed bacteria can be damaged, and the mixed bacteria can be effectively inhibited.

The bacteriocin adopted by the invention can also inhibit the propagation of lactic acid bacteria, reduce the post-acidification generation of the yoghourt and reduce the sterilization temperature and the heat treatment time in the preparation process of the yoghourt. The bacteriocin has strong heat stability under acidic condition, can be digested by human body acidolysis as a polypeptide, is harmless to human body, has no cross resistance with other antibiotics, and has no side effect on flavor and taste of the product, such as color, fragrance, taste, etc.

In the preparation method, preferably, the raw materials of the yoghurt comprise 0.05% of acidity regulator and 0.001% of bacteriocin, wherein the total weight of the raw materials of the yoghurt is 100%.

In the preparation method, the stability of the yoghourt product can be improved by adding the whey protein and the compound stabilizer. Preferably, the raw materials of the yogurt comprise, by taking the total weight of the raw materials of the yogurt as 100 percent: 0.05-1% of compound stabilizer, 0.5-0.8% of concentrated whey protein, 1000NLU/L of non-sterilized lactase 700-.

In the preparation method, preferably, the raw material of the yoghurt further comprises 1.5-3.5% of sugar, based on 100% of the total weight of the raw material of the yoghurt. In a specific embodiment, the sugar can be white granulated sugar.

In the preparation method, the compound stabilizer comprising pectin and starch is added, so that the problems of low viscosity, rough mouthfeel, whey precipitation and the like caused by low fat content of the yoghourt can be avoided. The consumption of pectin and starch is controlled within a reasonable proportion range, and the system stability of the low-fat low-lactose compound yoghurt can be further improved, the mouthfeel of the yoghurt is improved, and the phenomenon of whey separation and stratification is improved. Preferably, the compound stabilizer comprises pectin and starch in a mass ratio of 1:3-1: 6; more preferably, the compound stabilizer comprises 0.02-0.15% of pectin and 0.06-0.09% of starch, wherein the total weight of the yogurt raw materials is 100%.

In particular embodiments of the present invention, the starch may comprise physically modified starch and/or chemical starch. Preferably, the chemical starch comprises hydroxypropyl distarch phosphate and/or acetylated starch.

In particular embodiments of the present invention, the acidity regulator may include one or a combination of two or more of lactic acid, citric acid, malic acid, and tartaric acid.

In a specific embodiment of the present invention, the leavening agent used for fermentation may be one or a combination of two or more of probiotics. Preferably, the leavening agent comprises one or more of streptococcus thermophilus, lactobacillus bulgaricus, bifidobacterium lactis, lactobacillus acidophilus, lactobacillus plantarum and lactobacillus rhamnosus.

In the above preparation method, preferably, the weight of the leavening agent is 0.002% of the total weight of the yogurt raw materials.

In a particular embodiment of the invention, the fat content of the standardized milk is preferably ≦ 1%. In some embodiments, if the raw milk has a fat content higher than 1%, the standardized milk may be obtained by standardizing the raw milk, for example, by defatting and hydrating the raw milk to obtain the standardized milk. The degreasing temperature can be controlled to be 55-58 ℃, and correspondingly, the degreasing pressure can be controlled to be 0.4-0.6 bar; the hydration temperature can be controlled to be 55-60 ℃, and correspondingly, the hydration time can be controlled to be 25-35 min.

In a particular embodiment of the invention, the fat content of the raw milk is preferably below 1%. The raw milk can adopt fresh milk or reconstituted milk which meets the raw milk purchasing standard GB6914 of China, and preferably adopts one of low-fat milk, fully-skimmed milk powder or partially-skimmed milk powder.

In a specific embodiment of the present invention, the preparation method comprises: and (3) mixing, degassing, homogenizing, sterilizing, carrying out enzymolysis and fermenting to obtain the low-fat and low-lactose compound yoghurt.

In a particular embodiment of the invention, the ingredients may include operations of stirring standardised milk, a built-up stabiliser, concentrated whey protein, an acidity regulator and bacteriocins, when the yoghurt raw material contains sugar, the sugar is stirred together with the standardised milk. The stirring temperature can be controlled to be 50-55 ℃, the stirring time can be controlled to be 30-60min, and the stirring speed can be controlled to be 500-800 rpm.

In a specific embodiment of the present invention, the degassing temperature may be controlled to 60 to 70 ℃ and the degassing pressure may be controlled to 18 to 20 MPa.

In a specific embodiment of the invention, the pressure for homogenization can be controlled to 30. + -. 2/180. + -. 5 bar.

In the specific embodiment of the present invention, the sterilization temperature can be controlled to be 90-100 ℃, and the sterilization time can be controlled to be 280-320 s.

In the specific embodiment of the invention, the enzymolysis temperature can be controlled to be 35-40 ℃, and the enzymolysis time can be controlled to be 35-45 min.

In a particular embodiment of the invention, the temperature of the fermentation can be controlled between 40 and 43 ℃ and the fermentation is generally carried out until a pH of 4.5 to 4.6 is reached.

In a specific embodiment of the present invention, after the fermentation is finished, the preparation method may further include operations of filling and refrigeration. The filling generally comprises stirring the fermented milk and then filling the stirred milk into a buffer tank. The refrigerating temperature is controlled to be 2-6 ℃ generally, and the refrigerating time is controlled to be 12h generally.

According to a specific embodiment of the present invention, the method for preparing the low-fat and low-lactose composite yoghurt comprises the following steps:

1. degreasing and standardizing: defatting raw milk at 55-58 deg.C and 0.4-0.6bar to obtain defatted milk powder; and hydrating the skimmed milk powder at 55-60 deg.C for 25-35min to obtain skimmed standardized milk.

2. And (3) degassing the ingredients: adding sugar, concentrated lactalbumin, a compound stabilizer, an acidity regulator and bacteriocin into the standardized milk, mixing and circularly stirring for 30-60min at 50-55 ℃, wherein the stirring speed is 500 plus 800rpm, and obtaining a base material; then degassing the base material at 60-70 ℃ and 18-20 MPa.

3. Homogenizing and sterilizing: homogenizing the degassed base material at a pressure of 30 + -2/180 + -5 bar; then the homogenized base material is sterilized for 280-320s at the temperature of 90-100 ℃.

4. And (3) enzymolysis and fermentation: cooling the sterilized base material to 35-40 ℃, and adding lactase for enzymolysis for 35-45 minutes; then heating to 40-43 deg.C, adding starter until pH is 4.5-4.6, and ending fermentation to obtain yogurt.

5. Canning and refrigerating: stirring the fermented yogurt, filling in a buffer tank, refrigerating at 2-6 deg.C, and aging for 12 hr to obtain low-fat and low-lactose compound yogurt;

the preparation method comprises the following steps of (1) taking the total weight of the yoghourt raw materials as 100%, wherein the yoghourt raw materials adopted by the preparation method are as follows: 1.5 to 3.5 percent of sugar, 0.5 to 0.8 percent of concentrated whey protein, 0.05 to 1 percent of compound stabilizer (comprising pectin and starch), 0.04 to 0.06 percent of acidity regulator, 0.0005 to 0.0015 percent of bacteriocin, 1000NLU/L of lactase 700-fermented milk without sterilization, 0.002 percent of leavening agent and the balance of standardized milk.

The raw materials of the yoghourt can be obtained commercially and meet the requirements of relevant quality standards. The health index, the physical and chemical index and the like of the low-fat low-lactose compound yoghurt prepared by the invention also meet the regulations of relevant quality standards.

The packaging form of the product in the invention can adopt the common yogurt packaging form in the market at present. Such as glass bottle packaging, cup packaging, and the like.

In addition to the above description, the more specific operations such as compounding, degassing, homogenizing, sterilizing, etc., which are not specifically mentioned in the preparation method of the present invention, and the equipment used therefor may be conventional in the art.

The invention also provides low-fat and low-lactose composite yoghurt which is prepared by the preparation method.

The beneficial effects of the invention include:

1. according to the invention, lactase is added into the yoghourt raw material, so that a low-fat low-lactose compound yoghourt product with low lactose content can be prepared. The yoghourt product meets the requirements of people on the nutritive value of the yoghourt, eliminates the worry of people who need to control the intake of lactose and fat, and meets the market development trend.

2. According to the preparation method provided by the invention, the lactase is added after sterilization, and the lactase is not subjected to high-temperature sterilization and retreatment, so that the unstable phenomena of whey precipitation and the like caused by multiple high-temperature treatments of the yoghourt can be reduced, the final product can meet the index requirement of low lactose, the lactase can keep activity during the storage period of the product, the lactose content of the product is maintained at a lower level, the energy consumption is reduced, the cost is saved, and the effect of the lactase on decomposing lactose reaches the optimal state.

3. According to the preparation method provided by the invention, the acidity regulator and the bacteriocin are added at the same time, so that the acidity of the yoghourt raw material can be regulated on the basis of ensuring the normal activity of the starter, the mixed bacteria pollution caused by the non-sterilized lactase is avoided, and the product quality of the low-fat low-lactose compound yoghourt is ensured. The addition of the bacteriocin can also inhibit the propagation of lactic acid bacteria and the post-acidification generation of the yoghourt, reduce the heat treatment temperature and time in the preparation process of the yoghourt and save energy consumption.

4. According to the preparation method provided by the invention, pectin and starch are added and the proportion of the pectin and the starch is controlled, so that the obtained yoghourt product has high stability and good taste, and the phenomena of whey separation and layering are avoided in the quality guarantee period.

Detailed Description

The technical solutions of the present invention will be described in detail below in order to clearly understand the technical features, objects, and advantages of the present invention, but the present invention is not limited to the practical scope of the present invention.

In the following examples, the method for detecting lactose is GB5413.5-2010 first-method high performance liquid chromatography, and the lactose content of the base material before enzymolysis and the lactose content of the base material after enzymolysis are detected as a ratio to obtain the lactose hydrolysis degree. The alleged standard of the lactose limit is that the lactose-free content specified in the table C.1 in GB28050-2011 is less than or equal to 0.5g/100 ml.

Example 1

The embodiment provides a preparation method of low-fat and low-lactose compound yogurt. The total weight of the yoghourt raw materials is 1000g, and the yoghourt raw materials used by the preparation method are as follows:

20g of white granulated sugar, 5g of concentrated whey protein, 0.8g of compound stabilizer (comprising 0.2g of pectin and 0.6g of starch), 0.5g of lactic acid, 0.01g of bacteriocin, 700NLU/L of unsterilized lactase, 0.02g of leavening agent (comprising 0.01g of streptococcus thermophilus and 0.01g of lactobacillus bulgaricus) and the balance of standardized milk.

The preparation method comprises the following steps:

1. degreasing and standardizing: defatting whole fresh milk with a centrifugal separator at 56 deg.C and 0.5bar to obtain defatted milk powder; and hydrating the skimmed milk powder at 58 deg.C for 30min to obtain standardized milk.

2. And (3) degassing the ingredients: adding white granulated sugar, concentrated lactalbumin, stabilizer, lactic acid and bacteriocin into standardized milk, mixing and circularly stirring for 45min at 53 ℃, wherein the stirring speed is 650rpm, and obtaining a base material; the base material was degassed at 65 ℃ and 19 MPa.

3. Homogenizing and sterilizing: feeding the degassed base material into a homogenizing system, and homogenizing at 30/180 bar; then sent into a sterilization system for sterilization for 300s at 95 ℃.

4. And (3) enzymolysis and fermentation: cooling the sterilized base material to 38 ℃, adding lactase for enzymolysis for 35 minutes, wherein the hydrolysis degree of lactose after enzymolysis reaches 70%, and the limit declaration of low lactose is reached; and then heating to 40 ℃, adding a leaven until the pH value is 4.5, and finishing fermentation to obtain the yoghourt.

5. Canning and refrigerating: stirring the fermented yogurt, filling in a buffer tank, refrigerating at 2-6 deg.C, and aging for 12 hr to obtain low-fat and low-lactose compound yogurt product.

Example 2

The embodiment provides a preparation method of low-fat and low-lactose compound yogurt. The total weight of the yoghourt raw materials is 1000g, and the yoghourt raw materials used by the preparation method are as follows:

25g of white granulated sugar, 6g of concentrated whey protein, 4.8g of compound stabilizer (comprising 0.8g of pectin and 4g of starch), 0.5g of lactic acid, 0.01g of bacteriocin, 800NLU/L of non-sterilized lactase, 0.02g of leavening agent (comprising 0.01g of streptococcus thermophilus and 0.01g of lactobacillus bulgaricus) and the balance of standardized milk.

The preparation method comprises the following steps:

1. degreasing and standardizing: defatting whole fresh milk with a centrifugal separator at 56 deg.C and 0.5bar to obtain defatted milk powder; and hydrating the skimmed milk powder at 58 deg.C for 30min to obtain standardized milk.

2. And (3) degassing the ingredients: adding white granulated sugar, concentrated lactalbumin, stabilizer, lactic acid and bacteriocin into standardized milk, mixing and circularly stirring for 45min at 53 ℃, wherein the stirring speed is 650rpm, and obtaining a base material; the base material was degassed at 65 ℃ and 19 MPa.

3. Homogenizing and sterilizing: feeding the degassed base material into a homogenizing system, and homogenizing at 30/180 bar; and then sending the homogenized base material into a sterilization system, and sterilizing for 300s at 95 ℃.

4. And (3) enzymolysis and fermentation: cooling the sterilized base material to 35 ℃, adding lactase for enzymolysis for 40 minutes, wherein the lactose hydrolysis degree reaches 85%; and then heating to 41 ℃, adding a leaven until the pH value is 4.52, and finishing fermentation to obtain the yoghourt.

5. Canning and refrigerating: stirring the fermented yogurt, filling in a buffer tank, refrigerating at 2-6 deg.C, and aging for 12 hr to obtain low-fat and low-lactose compound yogurt product.

Example 3

The embodiment provides a preparation method of low-fat and low-lactose compound yogurt. The total weight of the yoghourt raw materials is 1000g, and the yoghourt raw materials used by the preparation method are as follows:

30g of white granulated sugar, 7g of concentrated whey protein, 6.2g of compound stabilizer (comprising 1.2g of pectin and 5g of starch), 0.5g of lactic acid, 0.01g of bacteriocin, 900NLU/L of unsterilized lactase, 0.02g of leavening agent (comprising 0.01g of streptococcus thermophilus and 0.01g of lactobacillus bulgaricus) and the balance of standardized milk.

The preparation method comprises the following steps:

1. degreasing and standardizing: defatting whole fresh milk with a centrifugal separator at 56 deg.C and 0.5bar to obtain defatted milk powder; and hydrating the skimmed milk powder at 58 deg.C for 30min to obtain standardized milk.

2. And (3) degassing the ingredients: adding white granulated sugar, concentrated lactalbumin, stabilizer, lactic acid and bacteriocin into standardized milk, mixing and circularly stirring for 45min at 53 ℃, wherein the stirring speed is 650rpm, and obtaining a base material; the base material was degassed at 65 ℃ and 19 MPa.

3. Homogenizing and sterilizing: feeding the degassed base material into a homogenizing system, and homogenizing at 30/180 bar; and then sending the homogenized base material into a sterilization system, and sterilizing for 300s at 95 ℃.

4. And (3) enzymolysis and fermentation: cooling the sterilized base material to 38 ℃, adding lactase for enzymolysis for 42 minutes, wherein the lactose hydrolysis degree reaches 88%; and then heating to 42 ℃, adding a leaven until the pH value is 4.55, and finishing fermentation to obtain the yoghourt.

5. Canning and refrigerating: stirring the fermented yogurt, filling in a buffer tank, refrigerating at 2-6 deg.C, and aging for 12 hr to obtain low-fat and low-lactose compound yogurt product.

Example 4

The embodiment provides a preparation method of low-fat and low-lactose compound yogurt. The total weight of the yoghourt raw materials is 1000g, and the yoghourt raw materials used by the preparation method are as follows: 35g of white granulated sugar, 8g of concentrated whey protein, 9.5g of compound stabilizer (comprising 1.5g of pectin and 8g of starch), 0.5g of lactic acid, 0.01g of bacteriocin, 1000NLU/L of unsterilized lactase, 0.02g of leavening agent (comprising 0.01g of streptococcus thermophilus and 0.01g of lactobacillus bulgaricus) and the balance of standardized milk.

The preparation method comprises the following steps:

1. degreasing and standardizing: defatting whole fresh milk with a centrifugal separator at 56 deg.C and 0.5bar to obtain defatted milk powder; and hydrating the skimmed milk powder at 58 deg.C for 30min to obtain standardized milk.

2. And (3) degassing the ingredients: adding white granulated sugar, concentrated lactalbumin, stabilizer, lactic acid and bacteriocin into standardized milk, mixing and circularly stirring for 45min at 53 ℃, wherein the stirring speed is 650rpm, and obtaining a base material; the base material was degassed at 65 ℃ and 19 MPa.

3. Homogenizing and sterilizing: feeding the degassed base material into a homogenizing system, and homogenizing at 30/180 bar; and then sending the homogenized base material into a sterilization system, and sterilizing for 300s at 95 ℃.

4. And (3) enzymolysis and fermentation: cooling the sterilized base material to 40 ℃, adding lactase for enzymolysis for 45 minutes, wherein the lactose hydrolysis degree reaches 92%; and then heating to 43 ℃, adding a leaven until the pH value is 4.58, and finishing fermentation to obtain the yoghourt.

5. Canning and refrigerating: stirring the fermented yogurt, filling in a buffer tank, refrigerating at 2-6 deg.C, and aging for 12 hr to obtain low-fat and low-lactose compound yogurt product.

Comparative example 1

The comparative example provides a preparation method of low-fat and low-lactose composite yoghurt. The total weight of the yoghourt raw materials is 1000g, and the yoghourt raw materials used by the preparation method are as follows: 20g of white granulated sugar, 5g of concentrated whey protein, 0.8g of compound stabilizer (comprising 0.2g of pectin and 0.6g of starch), 700NLU/L of unsterilized lactase, 0.02g of leavening agent (comprising 0.01g of streptococcus thermophilus and 0.01g of lactobacillus bulgaricus) and the balance of standardized milk. Compared with the yogurt raw material adopted in example 1, the yogurt raw material of the comparative example is not added with acidity regulator and bacteriocin.

The specific steps and operating parameters of the preparation method are the same as those of the preparation method of example 1.

Comparative example 2

The comparative example provides a preparation method of low-fat and low-lactose composite yoghurt. The total weight of the yoghourt raw materials is 1000g, and the yoghourt raw materials used by the preparation method are as follows: 20g of white granulated sugar, 5g of concentrated whey protein, 0.8g of compound stabilizer (comprising 0.2g of pectin and 0.6g of starch), 0.5g of lactic acid, 700NLU/L of unsterilized lactase, 0.02g of leavening agent (comprising 0.01g of streptococcus thermophilus and 0.01g of lactobacillus bulgaricus) and the balance of defatted standardized milk. Compared with the yogurt raw material adopted in example 1, the comparative example does not add bacteriocin to the yogurt raw material.

The specific steps and operating parameters of the preparation method are the same as those of the preparation method of example 1.

Comparative example 3

The comparative example provides a preparation method of low-fat and low-lactose composite yoghurt. The total weight of the yoghourt raw materials is 1000g, and the yoghourt raw materials used by the preparation method are as follows: 20g of white granulated sugar, 5g of concentrated whey protein, 0.8g of compound stabilizer (comprising 0.2g of pectin and 0.6g of starch), 0.01g of bacteriocin, 700NLU/L of unsterilized lactase, 0.02g of leavening agent (comprising 0.01g of streptococcus thermophilus and 0.01g of lactobacillus bulgaricus) and the balance of defatted standardized milk. Compared with the yogurt raw material adopted in example 1, the comparative example does not add bacteriocin to the yogurt raw material.

The specific steps and operating parameters of the preparation method are the same as those of the preparation method of example 1.

Test example 1

The low-fat and low-lactose composite yogurts obtained in examples 1 to 4 and comparative examples 1 to 3 were subjected to taste and flavor evaluation tests. The main sensory evaluation items included: texture (whey separation, viscosity, fineness, texture, etc.), color, flavor, and taste. The number of the test subjects was 60 persons, and the yogurt samples of examples 1 to 4 and comparative examples 1 to 3 were subjected to sensory evaluation. Table 1 shows sensory evaluation criteria, and table 2 shows sensory evaluation results.

TABLE 1

TABLE 2

Item	Organization and color	Flavor (I) and flavor (II)	Taste of the product	Total score
					Example 1	28	37	38	93
Example 2	29	38	38	95
					Example 3	27	38	39	94
Example 4	28	36	38	92
					Comparative example 1	15	25	25	65
Comparative example 2	18	26	26	70
					Comparative example 3	17	25	27	69

As can be seen from the sensory evaluation results in Table 2, the yogurt products of examples 1-4 were liked by most experimenters in terms of texture, color, flavor, and mouthfeel, and were accepted and liked by consumers. In contrast, comparative example 1, which did not contain an acidity regulator and bacteriocin, could not inhibit the entry of miscellaneous bacteria into the base material due to lactase, resulting in yoghurt spoilage, significant whey precipitation, off-flavor and inconsistent aroma. Comparative example 2 was not added with bacteriocin, comparative example 3 was not added with an acidity regulator, and the corresponding products showed whey precipitation and off-flavor during the shelf life, respectively. The results show that the simultaneous addition of the acidity regulator and the bacteriocin can effectively inhibit the mixed bacteria brought by lactase, and ensure the stability and good taste and flavor of the product. And if one of the acidity regulator and the bacteriocin is added alone or both are not added, the influence of the mixed bacteria on the quality, the flavor and the taste of the product cannot be inhibited.

Test example 2

The test example provides the effect of the composition of the compound stabilizer on the stability of low-fat low-lactose compound yogurt. The raw material composition and preparation process of the product used in this test example were the same as in example 1, except that pectin and starch were added in different ways. The yogurt products used in the tests differed by the compositional composition of the compound stabilizer and the ratio between the ingredients. The stability of the yogurt product over shelf life was observed and recorded and the test results are summarized in table 3.

TABLE 3

From the experimental results in table 3, it can be seen that when the mass ratio of pectin to starch used for preparing the yogurt is in the range of 1:3 to 1:6, the corresponding product starts to slightly whey out after 21 days of storage and has a fine and thick mouthfeel. When the mass ratio of pectin to starch is higher or lower than the above range, the corresponding yogurt product has poor stability over shelf life or exhibits a rough, grainy mouthfeel. When only pectin or starch is added, whey precipitation occurs in the corresponding product after 7 days of storage, and loose tissue state occurs in the product after fermentation is finished, so that the quality requirement of low-fat low-lactose compound yoghurt is not met.

Test example 3

The test example provides the effect of the treatment mode of lactase on the lactose content of low-fat low-lactose composite yoghurt. The raw material composition and preparation procedure of the product used in this test example were the same as in example 1, except that the lactase treatment was carried out in a different manner.

The yogurt products used for the tests were distinguished by enzymatic hydrolysis with non-sterilized lactase and sterilized lactase, respectively. The results of the testing of the lactose content of each yogurt product are summarized in table 4.

TABLE 4

As can be seen from the results in Table 4, the average lactose content of the product enzymatically digested with the unsterilized lactase was 1.65g/100 g. And the lactase after sterilization (enzyme deactivation at 95 ℃ for 20min) is used for enzymolysis, the average lactose content of the obtained product is 1.86g/100g, and the lactose content is higher than that of the product. This result is due to the fact that lactase, after sterilization, has a reduced catalytic capacity for reducing lactose content, a low capacity for degrading lactose, resulting in a higher final lactose content in the product. Therefore, the lactase which is not sterilized is adopted for enzymolysis, so that on one hand, the enzymolysis efficiency can be improved, the lactose content can be effectively reduced, on the other hand, the energy consumption in the production process can be reduced, and the resources and the cost can be saved.

The test example also used the above samples to test the effect of lactase treatment on the stability of low-fat and low-lactose composite yoghurt. The results of the lactose content test for each product are summarized in table 5.

TABLE 5

From the test results in table 5, it can be seen that the yogurt product prepared with the non-sterilized lactase had a slight lactose separation only after 21 days of storage, and the product had a smooth and thick mouthfeel. And the product prepared by adopting the sterilized lactase has whey precipitation after being stored for 7 days, has poor stability in shelf life, and does not meet the quality requirement of low-fat low-lactose compound yoghurt. Therefore, the stability of the product can be effectively improved by adopting the non-sterilized lactase for enzymolysis during the preparation of the low-fat low-lactose compound yoghurt.