Yoghourt as well as preparation method and application thereof

Abstract

The invention relates to the technical field of food, and particularly discloses yoghourt as well as a preparation method and application thereof. The invention provides a preparation method of yoghurt, the yoghurt is prepared by fermenting a substrate through zymophyte, the substrate comprises a milk base material and protease, and the milk base material comprises concentrated animal milk and a fat raw material; the milk base material is subjected to lipase enzymolysis before fermentation and then is used for fermentation; the protease comprises flavourzyme or further comprises neutral protease; the fat raw material comprises one or more of cream cheese, fermented butter and single cream; the zymophyte is composed of lactobacillus helveticus, lactococcus lactis subsp. Lactis (diacetyl type), lactococcus lactis subsp. Cremoris, streptococcus salivarius subsp. Thermophilus and lactobacillus delbrueckii subsp. Bulgaricus. The content of flavor substances in the yoghourt can be increased, and the quality of the yoghourt is improved.

Description

Technical Field

[0001] The invention relates to the technical field of food, in particular to yogurt and a preparation method and application thereof. Background Art

[0002] Due to the requirement of a long shelf life, room temperature yogurt needs to be secondary pasteurized to inactivate the lactic acid bacteria in the system after fermentation. The secondary pasteurization process will cause the loss of some flavor substances in the yogurt system. In addition, in order to pursue a stable system during the shelf life, a variety of stabilizers are added to room temperature yogurt. Due to the addition of stabilizers and the heat sterilization process, there are obvious differences in fermentation aroma, milk aroma and freshness between room temperature yogurt and low-temperature yogurt. In the production process of room temperature yogurt, in order to give it a rich and real yogurt fermentation flavor and a smooth taste, some raw materials with flavor or taste contributions are usually added, including cream, protein powder, fermented butter, cream cheese, etc. These raw materials provide a certain flavor presentation for room temperature yogurt, but under complex process conditions, the flavor performance of room temperature yogurt still has no obvious improvement.

[0003] In addition, in order to give yogurt a variety of flavors, different flavors are usually given to yogurt by adding jams and flavors. The long shelf life and aseptic requirements of room temperature yogurt make the flavor ingredients of room temperature yogurt usually added simultaneously with other ingredients during batching. It needs to go through ultra-high temperature sterilization, fermentation, second pasteurization and other processes. Products containing jam can add flavors to the jam, but they also need to go through a jam heat sterilization process. Sterilization will cause the loss of some flavor substances in the yogurt system and reduce the freshness of the fruit flavor, making the room temperature yogurt have obvious differences in fermentation aroma, milk aroma and fruit freshness compared with low temperature yogurt.

[0004] Therefore, it is necessary to further study the preparation process of ambient temperature yogurt. Summary of the invention

[0005] One of the purposes of the present invention is to provide a yogurt having an ideal flavor after being sterilized.

[0006] The invention provides a method for preparing yogurt. The yogurt is prepared by fermenting a substrate with fermentation bacteria. The substrate comprises: a milk base and a protease, wherein the milk base comprises concentrated animal milk and a fat raw material; the milk base is firstly hydrolyzed by lipase before fermentation and then used for fermentation; the protease comprises a flavor protease, or further comprises a neutral protease; the fat raw material comprises one or more of cream cheese, fermented butter and light cream; and the fermentation bacteria comprises Lactobacillus helveticus, Lactococcus lactis lactis subsp. lactis (diacetyl type), Lactococcus lactis subsp. cremoris, Streptococcus salivarius subsp. thermophilus and Lactobacillus delbrueckii subsp. bulgaricus.

[0007] The present invention has found that the content of flavor substances in yogurt can be increased by adding fat raw materials to the yogurt fermentation substrate, performing enzymatic hydrolysis before fermentation, and then fermenting with a combination of specific proteases and fermentation bacteria.

[0008] In particular, the present invention has found that there is a mutual promotion and synergistic flavor enhancement effect between the selected fermentation bacteria: Lactococcus lactis subsp. lactis (diacetyl type) can effectively improve the synergistic growth promotion between the composite bacteria and increase the number of live bacteria during fermentation, which is beneficial to reduce the fermentation time; Lactobacillus helveticus and Lactobacillus delbrueckii subsp. bulgaricus can cooperate to produce lactic acid synergistically; Lactobacillus helveticus and Lactococcus lactis subsp. lactis (diacetyl type) help to increase the fat decomposition rate and improve the concentration of flavor substances; auxiliary fermentation agents (Lactobacillus helveticus, Lactococcus lactis subsp. lactis (diacetyl type), Lactococcus lactis subsp. cremoris) combined with fermentation agents (Streptococcus salivarius thermophilus subsp., Lactobacillus delbrueckii subsp. bulgaricus) can effectively improve the concentration of flavor substances in the system.

[0009] The present invention also found that the intracellular peptidase and extracellular protease of Lactococcus lactis subsp. cremoris in combination with the exogenously added specific protease of the present invention can perform a specific hydrolysis process on the protein in the fermentation substrate, thereby helping to improve the fermentation effect and product flavor. Specifically, the present invention found that during the fermentation process, the intracellular peptidase of Lactococcus lactis subsp. cremoris (diacetyl type) can degrade the bitter peptides produced by the hydrolysis of neutral proteases, thereby improving the product flavor (the accumulated bitter components are characterized by the valine content).

[0010] The animal milk of the present invention refers to the milk of mammals such as cow's milk, goat's milk, horse's milk, camel's milk, deer's milk, and donkey's milk.

[0011] Preferably, the ratio of the number of live bacteria of Lactobacillus helveticus, Lactococcus lactis subsp. lactis (diacetyl type), Lactococcus lactis subsp. cremoris, Streptococcus salivarius subsp. thermophilus and Lactobacillus delbrueckii subsp. bulgaricus is (1.8-2.2): (1.8-2.2): (0.9-1.1): (2.8-3.2): (1.8-2.2); And / or, the neutral protease is added at 0.08-0.4AU per ton of the milk base, and the flavor protease is added at 0-250LAPU per ton of the milk base; And / or, the yogurt also includes a water base, the water base includes polysaccharides and a filtrate obtained when concentrating animal milk; the polysaccharides are citrus fiber and / or high-ester pectin; the cream cheese accounts for 0-0.5% of the total mass of the milk base and the water base, the fermented butter accounts for 0-0.5% of the total mass of the milk base and the water base, and the light cream accounts for 0-1% of the total mass of the milk base and the water base; the mass percentages of the cream cheese, fermented butter, and light cream in the total mass of the milk base and the water base are not 0% at the same time.

[0012] Preferably, the protease comprises a neutral protease and a flavor protease, the neutral protease is added at 0.28 AU per ton of the milk base, and the flavor protease is added at 75 LAPU per ton of the milk base; The addition of enzymes according to the preferred embodiment of the present invention can better cooperate with the fermentation bacteria, so that the flavor substances are optimally presented and the bitter peptides produced are minimized.

[0013] Preferably, the fat raw material comprises cream cheese and fermented butter, and the mass ratio of the cream cheese to the fermented butter is (0.8-1.2):(0.8-1.2) preferably, 1:1.

[0014] The present invention has found that after the liquid containing cream cheese and fermented butter is hydrolyzed by lipase, the fat in the substrate is further decomposed in the subsequent fermentation process with the help of Lactobacillus helveticus and Lactococcus lactis subsp. lactis (diacetyl type), thereby improving the aroma production effect; after changing the fat raw materials (such as cream) or changing the addition ratio of cream cheese and fermented butter, the effect is reduced. In addition, the lactone precursors hydroxy acids, ethyl isobutyrate and γ-octanolactone in fermented butter (the fermentation strains are Lactococcus lactis subsp. cremoris, Lactococcus lactis subsp. lactis, and Lactococcus lactis subsp. lactis (diacetyl type)) also help to provide the product with a sweet cream aroma.

[0015] In the method for preparing yogurt of the present invention, the milk base material further comprises one or more of a sweetener, a thickener, a protein supplement, and citric acid; The sweetener includes: one or more of sugar, xylitol, erythritol, and maltitol; the thickener includes: one or more of starch, pectin, agar, and gellan gum; and the protein supplement includes: whey protein powder and / or casein.

[0016] The present invention preferably adds protein supplements (such as whey protein powder, casein, milk protein (including whey protein powder and casein) etc.) to the ingredients, which, in addition to increasing the protein content of the product, can also promote the growth of thermophilic subspecies of Streptococcus salivarius and shorten the fermentation time.

[0017] The present invention preferably adds citric acid to the substrate to facilitate increasing the concentration of acetoin during the fermentation process.

[0018] The preparation method of yogurt of the present invention comprises: (1) Concentrating the animal milk to obtain a filtrate and concentrated animal milk; the protein content of the concentrated animal milk is 3.1%-3.4%; (2) The mixture of the concentrated animal milk and other components of the milk-based material is fully enzymatically hydrolyzed by the lipase to obtain a milk-based material; the polysaccharide material and the filtrate are mixed to obtain a water-based material; (3) homogenizing and pasteurizing the milk-based material and the water-based material respectively; (4) mixing the homogenized and pasteurized milk base with the protease and fermentation bacteria, and then fermenting and demulsifying to obtain fermented milk; (5) The fermented milk and the water-based material treated in step (3) are mixed, homogenized, and secondary pasteurized to obtain a mixed material.

[0019] In the preparation method of yogurt of the present invention, the sweetener accounts for 2-8% of the total mass of the milk base and the water base; the thickener accounts for 1-2% of the total mass of the milk base and the water base; the protein supplement accounts for 0.4-1% of the total mass of the milk base and the water base; the polysaccharide accounts for 0.1-0.6% of the total mass of the milk base and the water base; the citric acid accounts for 0-0.25% of the total mass of the milk base and the water base; And / or, the protein supplement is whey protein powder.

[0020] The present invention preferably selects whey protein powder as a protein supplement, which can be obtained commercially or prepared by methods known in the art. For example, the whey protein powder can be made from cheese-derived whey liquid, and high-valent ions (such as Ca) are removed by electrodialysis. 2+ Mg 2+ ) is removed. Specifically, commercially available whey protein WPC30 can also be used as a protein supplement. Compared with other whey protein powders, WPC30 is preferentially separated from high-valent ions during the production process, which can better retain the flavor components in the protein powder.

[0021] In step (2) of the method for preparing yogurt of the present invention, the concentrated animal milk is first mixed with lipase, and after enzymatic hydrolysis at 5-8°C for 16-24 hours, it is mixed with other components of the milk base at 45-55°C for 30-60 minutes to obtain a milk base; 20000-100000U of the lipase is added per ton of the concentrated animal milk.

[0022] Preferably, the fat enzymatic hydrolysis step of the present invention can be carried out in combination with the raw milk storage link. Generally, in industrial large-scale production, the raw milk will be continuously transported to the factory until the single processing volume is reached before subsequent processing. During this period, the raw milk transported first needs to be refrigerated to prevent deterioration and affect the variety. The method of the present invention utilizes the storage time of the raw milk waiting for processing before formal production, first performs the first step of low-temperature long-time fat enzymatic hydrolysis, effectively improves the alanine content in the raw milk (alanine, as one of the precursors of acetoin, can effectively increase the content of acetoin in the system), and then realizes the second step of high-temperature short-time fat enzymatic hydrolysis in the material process, and enzymatic hydrolysis of the fat raw materials added to the ingredients is performed to ensure that the enzymatic hydrolysis produces enough free fatty acids (especially short-chain free fatty acids), increase the concentration of flavor substances, and then cooperates with the fermentation process to perform the third step of high-temperature long-time proteolysis for yogurt preparation. All enzymatic hydrolysis processes are combined with the product production sequence time, and the enzymatic hydrolysis process is completed without increasing the product production time, which effectively reduces the production time and simplifies the production process.

[0023] In step (2) of the method for preparing yogurt of the present invention, the temperature at which the polysaccharide substance and the filtrate are mixed is 65-75° C.; In step (3) of the method for preparing yogurt of the present invention, the secondary pressure of the homogenization is 30-50 bar, the total pressure is 130-150 bar, and the pasteurization conditions are: 121° C., 4-6 s; In step (4) of the method for preparing yogurt of the present invention, 50U-200U of the fermentation bacteria are added to each ton of the milk base; the fermentation temperature is 42±1°C, the acidity of the final fermentation product is not higher than 85°T, and the pH is not higher than 4.6; demulsification is a conventional operation in the art, and the stirring speed during demulsification can be 20-30r / min.

[0024] In step (5) of the method for preparing yogurt of the present invention, the homogenization pressure is 10-40 Bar; and the conditions for secondary pasteurization are: 75° C., 20-30 s.

[0025] The method for preparing yogurt of the present invention further comprises, after step (5), the step of aseptically adding flavors online at a temperature below 30° C.; the flavors comprise: one or more of fruit flavors, milk flavors, and mouthfeel flavors; and the amount of the flavors added is 0.05-0.3% by mass of the mixture.

[0026] In the present invention, mouthfeel flavors refer to flavor products known in the art that can increase oral perception, or enhance fullness or fruitiness, such as mono- and di-glycerol fatty acid esters, pectin, L-alanine, glycine, yeast extract, etc.

[0027] The present invention uses the flavor post-aseptic addition technology to avoid the reduction in the freshness of the flavor after multiple sterilization and fermentation processes, and can effectively reduce the amount of flavor added while maintaining the flavor, so that the fruit flavor intensity and fruit flavor freshness are ideal, and the quality of room temperature yogurt is improved in terms of multiple flavor perception and oral fullness.

[0028] Preferably, in the method for preparing yogurt of the present invention, when adding flavors online in an aseptic manner, the mixed material and the flavors are added simultaneously by flow contact mixing.

[0029] According to the ratio of the essence to the mixed material, the flow rates of the two liquid materials can be set so that they can be mixed at the same time, which is beneficial to ensure the uniformity of the mixing of the two materials.

[0030] The present invention also provides a yogurt, which is prepared by the above-mentioned yogurt preparation method.

[0031] The yogurt prepared by the preferred process of the present invention not only has a good flavor, but also has an ideal taste and stability.

[0032] The present invention also provides application of the yogurt preparation method in improving the flavor of yogurt.

[0033] The method of the present invention can be applied to the preparation of room temperature yogurt and low temperature yogurt, and is preferably applied to the preparation of room temperature yogurt to more obviously improve the product flavor.

[0034] The beneficial effects of the present invention are at least: The invention, on the basis of adding milk raw materials, increases the characteristic flavor concentration of room-temperature yogurt through step-by-step enzymolysis technology and the combination of specific fermentation bacteria, while adding some unique flavor substances of low-temperature yogurt, thereby improving the flavor of the yogurt as a whole. DETAILED DESCRIPTION

[0035] The preferred embodiments of the present invention will be described in detail below in conjunction with examples. It should be understood that the following examples are provided only for the purpose of illustration and are not intended to limit the scope of the present invention. Those skilled in the art may make various modifications and substitutions to the present invention without departing from the purpose and spirit of the present invention.

[0036] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, etc. used in the following examples, unless otherwise specified, can be obtained from commercial sources or prepared according to conventional methods in the art. In the present invention, Lactobacillus helveticus, Lactococcus lactis subsp. lactis (diacetyl type), and Lactococcus lactis subsp. cremoris were purchased from Chr. Hansen; Streptococcus salivarius subsp. thermophilus and Lactobacillus delbrueckii subsp. bulgaricus were purchased from DSM (DELVO®FRESH PIONEER-02). Fermented butter was purchased from Einstein Morning. Flavor protease selected flavor enzyme Flavourzyme, and neutral protease selected neutral enzyme Neutrase, both purchased from Novozymes.

[0037] The acid value test method is: Acid value (AV) is the number of milligrams of potassium hydroxide required to neutralize 1g of free fatty acids in milk fat, and is determined according to the method specified in GB 5009.229-2016.

[0038] The peroxide value test method is: Peroxide value (PV) is the number of millimoles of active oxygen in 1 kg of sample, and is determined according to the method specified in GB 5009.227-2016.

[0039] The test method for free fatty acids (FAAs) is as follows: determination by gas chromatograph (GC, Agilent) equipped with a flame ionization detector (FID), referring to GB 5009.168-2016, and the results are expressed in mg / 100g fat.

[0040] Example 1 This embodiment provides a method for preparing yogurt, which is as follows: The formula (per 100 parts by weight) includes: 4 parts by weight of sweetener (white sugar), 1.3 parts by weight of thickener (starch), 0.7 parts by weight of protein supplement (whey protein powder) (purchased from Davidlin, protein content 30%), 0.4 parts by weight of polysaccharide (citrus fiber), 0.2 parts by weight of cream cheese, 0.2 parts by weight of fermented butter, 0.15 parts by weight of citric acid, and the balance of raw milk.

[0041] 1. Enzymatic pretreatment of raw milk: The raw milk was concentrated through an RO membrane (pore size 1nm, NaCl retention of about 97%) to obtain a filtrate and concentrated milk with a protein content of 3.4%. The concentrated milk was stored at a temperature of 5°C and enzymatically hydrolyzed. Specifically, 60,000U of Palatase 20,000L fat hydrolase was added to each ton of concentrated milk, and the lipase was evenly distributed by stirring. The stirring speed was controlled to ensure that the dissolved oxygen content in the concentrated milk was less than 15ppm. After stirring thoroughly, it was left to stand for 18 hours.

[0042] The acid value, peroxide value and volatile free fatty acid (C<10) content were tested. The results showed that the acid value (average value of three tests) was 3.902±0.004mgKOH / g; the peroxide value (average value of three tests) was 0.244±0.004mg / g; the volatile free fatty acid content (average value of three tests) was 327.14mg / 100g.

[0043] 2. Fermentation preparation: (1) Raw material mixing Mixing of fermented raw materials (milk-based materials): Heat the concentrated milk after enzymatic hydrolysis to 50°C, and mix it with sweetener, thickener, protein supplement, cream cheese, fermented butter and citric acid at 45°C-55°C for 30 minutes.

[0044] Mixing of non-fermented raw materials (water-based materials): Heat the filtrate to 65°C, add the polysaccharide slowly and evenly, and mix well.

[0045] (2) Liquid homogenization and pasteurization The milk-based material and the water-based material were homogenized (secondary pressure 40 bar, total pressure 140 bar) and pasteurized (121°C, 5s) respectively. After pasteurization, the milk-based material was cooled to 42°C, and the water-based material was cooled to room temperature.

[0046] (3) Milk-based yogurt fermentation + proteolysis Flavour enzyme Flavourzyme and neutral enzyme Neutrase are selected for protein hydrolysis, and composite fermentation bacteria are selected for fermentation bacteria, which include Lactobacillus helveticus, Lactococcus lactis subsp. lactis (diacetyl type), Lactococcus lactis subsp. cremoris, Streptococcus salivarius subsp. thermophilus and Lactobacillus delbrueckii subsp. bulgaricus, and their live cell count ratio is 2:2:1:3:2.

[0047] In the pasteurized milk base, 75 LAPU of flavor enzyme Flavourzyme, 0.28 AU of neutral enzyme Neutrase and 100 U of composite fermentation bacteria were added at 42±1°C to the final product with an acidity of 80°T and a pH of 4.35.

[0048] (4) Demulsification After fermentation, the fermented product was demulsified at a stirring speed of 25 r / min and a demulsification time of 5 min. The demulsified yogurt was temporarily stored in a sterile tank at a temperature of 10±1°C.

[0049] (5) Mixed ratio The demulsified yogurt and the water base were mixed using a dynamic mixer and homogenized at 25 Bar.

[0050] (6) Secondary pasteurization After mixing, the sample was sterilized at a temperature of 75°C for 25 seconds. After sterilization, it was cooled to 22°C to obtain a mixed material for use.

[0051] 3. Aseptic filling Aseptic cold filling technology is used to fill the sterilized yogurt (mixture), that is, aseptic canning is carried out at 20~25℃, the nitrogen concentration is 99.999%, the nitrogen pressure is 1.5±0.2bar, and the nitrogen flow rate is 1.5±0.2slm.

[0052] Example 2 This embodiment provides a method for preparing yogurt, which is basically the same as the method in Example 1, except that: in step 1, 20000U of Palatase 20000L fat hydrolase is added to each ton of concentrated milk, and the mixture is stirred thoroughly and then left to stand for 24 hours. The acid value, peroxide value and volatile free fatty acid (C<10) content are tested (the average value is taken from three tests). The results show that the acid value is 2.179±0.028 mgKOH / g; the peroxide value is 0.187±0.008 mg / g; and the volatile free fatty acid content is 213.7 mg / 100 g.

[0053] Example 3 This embodiment provides a method for preparing yogurt, which is basically the same as the method in Example 1, except that: in step 1, 100,000 U of Palatase 20,000 L fat hydrolase is added to each ton of concentrated milk, and the mixture is stirred thoroughly and then left to stand for 16 hours. The acid value, peroxide value and volatile free fatty acid (C<10) content are tested (the average value is taken from three tests). The results show that the acid value is 4.458±0.045 mgKOH / g; the peroxide value is 0.281±0.032 mg / g; and the volatile free fatty acid content is 307.9 mg / 100 g.

[0054] Example 4 This embodiment provides a method for preparing yogurt, which is basically the same as the method in Embodiment 1, except that citric acid is not added to the formula.

[0055] Example 5 This embodiment provides a method for preparing yogurt, which is basically the same as the method in Embodiment 1, except that the amount of citric acid in the formula is 0.25 parts by weight.

[0056] Example 6 This embodiment provides a method for preparing yogurt, which is basically the same as the method in Embodiment 1, except that: cream cheese is not added to the formula, but 0.2 parts by weight of fermented butter and 0.5 parts by weight of light cream are added instead.

[0057] Example 7 This embodiment provides a method for preparing yogurt, which is basically the same as the method in Embodiment 1, except that: fermented butter is not added in the formula, but 0.2 parts by weight of cream cheese and 0.5 parts by weight of light cream are added instead.

[0058] Example 8 This embodiment provides a method for preparing yogurt, which is basically the same as the method in Example 1, except that the total amount of cream cheese and fermented butter added in the formula remains unchanged at 0.4 parts by weight, but the mass ratio of the two is changed to 0.15:0.25.

[0059] Example 9 This embodiment provides a method for preparing yogurt, which is basically the same as the method in Example 1, except that the whey protein powder in the formula is replaced with casein.

[0060] Example 10 This embodiment provides a method for preparing yogurt, which is basically the same as the method in Embodiment 1, except that: during fermentation, instead of adding the neutral enzyme Neutrase, the flavor enzyme Flavourzyme is added at 250 LAPU per ton.

[0061] Embodiment 11 This embodiment provides a method for preparing yogurt, which is basically the same as the method in Embodiment 1, except that during fermentation in step 2, a flavor enzyme Flavourzyme is added at 250 LAPU per ton and a neutral enzyme Neutrase is added at 0.08 AU per ton.

[0062] Example 12 The present embodiment provides a method for preparing yogurt, which is basically the same as the method in Example 1, except that during the fermentation in step 2, the composite fermentation bacteria include: Lactobacillus helveticus, Lactococcus lactis subsp. lactis (diacetyl type), Lactococcus lactis subsp. cremoris, Streptococcus salivarius subsp. thermophilus and Lactobacillus delbrueckii subsp. bulgaricus, and their viable cell count ratio is 2.5:1.7:0.8:3.4:1.6.

[0063] Example 13 The present embodiment provides a method for preparing yogurt, which is basically the same as the method in Example 1, except that the formula (per 100 parts by weight) includes: 8 parts by weight of a sweetener (xylitol), 1 part by weight of a thickener (0.67 parts by weight of starch, 0.15 parts by weight of pectin, 0.15 parts by weight of agar, 0.03 parts by weight of gellan gum), 0.4 parts by weight of a protein supplement (milk protein powder), 0.6 parts by weight of a polysaccharide (high-ester pectin), 0.5 parts by weight of cream cheese, 0.5 parts by weight of fermented butter, 0.15 parts by weight of citric acid, and the remainder of raw milk.

[0064] In step 2, the fermented raw materials (milk-based materials) are mixed for 1 hour; the non-fermented raw materials (water-based materials) are mixed at 75°C. The milk-based materials and the water-based materials are homogenized at a secondary pressure of 50 bar and a total pressure of 130 bar. During fermentation, 200 U of composite fermentation bacteria are added per ton. The stirring speed of demulsification is 30 r / min. The demulsified yogurt and the water-based materials are mixed using a dynamic mixer and homogenized at 40 Bar. The other unrecorded conditions are the same as those in Example 1.

[0065] Embodiment 14 The present embodiment provides a method for preparing yogurt, which is basically the same as the method in Example 1, except that the formula (per 100 parts by weight) includes: 8 parts by weight of a sweetener (xylitol), 2 parts by weight of a thickener (1.85 parts by weight of starch, 0.15 parts by weight of pectin), 1 part by weight of a protein supplement (whey protein powder), 0.1 parts by weight of a polysaccharide (high-ester pectin), 0.2 parts by weight of cream cheese, 0.2 parts by weight of fermented butter, 1 part by weight of light cream, 0.15 parts by weight of citric acid, and the remainder of raw milk.

[0066] In step 2, the milk-based material and the water-based material are homogenized at a secondary pressure of 30 bar and a total pressure of 150 bar. During fermentation, 50 U of composite fermentation bacteria are added per ton. The stirring speed of demulsification is 20 r / min. The demulsified yogurt and the water-based material are mixed using a dynamic mixer and homogenized at 10 Bar. The other unrecorded conditions are the same as those in Example 1.

[0067] Embodiment 15 This embodiment provides a method for preparing yogurt, which is basically the same as the method in embodiment 1, except that before aseptic filling, it also includes an aseptic online addition step of flavors, specifically, after the strawberry flavors are mixed evenly, they are filled into aseptic bags under aseptic conditions, and the flavor flow rate is set according to the flavor addition amount under the aseptic system, so that the mixture after secondary pasteurization (temperature below 30°C) and the flavors are mixed by flow contact, and both are ensured to be fed at the same time. In this embodiment, the amount of flavors added is 0.15% of the mass percentage of the mixture.

[0068] Example 16 This embodiment provides a method for preparing yogurt, which is basically the same as the method in Example 1, except that no protein supplement is added.

[0069] Comparative Example 1 This comparative example provides a method for preparing yogurt, which is basically the same as the method in Example 1, except that no protease is added during fermentation.

[0070] Comparative Example 2 This comparative example provides a method for preparing yogurt, which is basically the same as the method in Example 1, except that during fermentation in step 2, no flavor enzyme Flavourzyme is added, and instead only 0.4AU per ton of neutral enzyme Neutrase is added.

[0071] Comparative Example 3 This comparative example provides a method for preparing yogurt, which is basically the same as the method in Example 1, except that during the fermentation in step 2, the composite fermentation bacteria only include: Streptococcus salivarius thermophilus subspecies and Lactobacillus delbrueckii subspecies bulgaricus, and the ratio of their live bacteria count is 3:2.

[0072] Comparative Example 4 This comparative example provides a method for preparing yogurt, which is basically the same as the method in Example 1, except that during fermentation in step 2, Lactobacillus paracasei (purchased from Yupide Bio) is used to replace Lactococcus lactis subsp. lactis (diacetyl type) in the composite fermentation bacteria.

[0073] Comparative Example 5 This comparative example provides a method for preparing yogurt, which is basically the same as the method in Example 1, except that during fermentation in step 2, Lactobacillus reuteri (purchased from Yupide Biotechnology) is used to replace Lactobacillus helveticus in the composite fermentation bacteria.

[0074] Comparative Example 6 This comparative example provides a method for preparing yogurt, which is basically the same as the method in Example 1, except that the formula does not contain cream cheese and fermented butter.

[0075] Experimental example This experimental example tests the products of the above embodiments and comparative examples, and the specific method is as follows: 1. Determination of volatile flavor substances: The types and contents of volatile substances in the samples were determined by dynamic headspace solid phase microextraction-gas chromatography-olfaction-mass spectrometry (DHS-GC-O-MS), and the key odor active compounds were determined by olfactory analysis. The concentrations of key odor active compounds in each sample were compared. The results are shown in Tables 1 to 4, and the concentration unit is μg / kg.

[0076] 2. Yogurt stability test method: Use LUMisizer stability analyzer to conduct dynamic stability analysis on the sample, set the speed to 3500r / min, set the contour line to 100, analyze the sample clarification index, and judge the sample stability. The results are shown in Table 5.

[0077] 3. Sensory tasting method: 30 professional tasters were invited to score the overall flavor intensity, fermented flavor, milk flavor, smoothness, and sweet-sour ratio of the product, and additionally score the characteristic fruity flavor and freshness (for the solution of adding flavors) of Example 15. The scoring range is 1 to 5 points, and 3 points is the most suitable (wherein a sweet-sour ratio greater than 3 points indicates sourness, less than 3 points indicates sweetness, and other indicators greater than 3 points indicate strongness, and less than 3 points indicate weakness). The obtained scores were averaged to obtain the results of sensory tasting. The results are shown in Table 6.

[0078] 4. Determination of amino acid content: Ultra high performance liquid chromatography (UHPLC) was used for determination. The results are shown in Table 7.

[0079] 5. Determination of fermentation degree: When the fermentation is carried out for 360 minutes, the pH value of the yogurt is tested (the lower the pH value, the faster the fermentation is). The results are shown in Table 8.

[0080] Table 1

[0081] Table 2

[0082] Table 3

[0083] The higher the concentration of acetaldehyde, hexyl butyrate, and leaf acetate, the higher the freshness of the product. The higher the concentration of peach aldehyde, R-γ-decanoic acid, ethyl butyrate, and linalool, the better the fruity taste of the product. For Example 15 of adding flavors, this experimental example also additionally tested the concentrations of peach aldehyde, hexyl butyrate, R-γ-decanoic acid, ethyl butyrate, leaf acetate, and linalool, and the results are shown in Table 4.

[0084] Table 4

[0085] Table 5

[0086] Table 6

[0087] The characteristic fruity flavor score of Example 15 is 3.2, and the freshness score is 3.1. If the flavor in Example 15 is mixed with other milk-based ingredients during batching and then prepared subsequently, the intensity of the characteristic flavor and the freshness of the final product will be affected, and the scores will be reduced to 2.7 and 2.5 respectively. Even if the amount of flavor is increased to 20% on the basis of Example 15 and then mixed with other milk-based ingredients during batching and then prepared subsequently, the characteristic flavor score is 3.2, and the freshness cannot be effectively improved, with a score of 2.7.

[0088] Table 7

[0089] Table 8

[0090] According to the experimental results, we can know that: The selection and addition amount of lipase affect the content of free fatty acids (such as butyric acid and caproic acid) and the formation of ketones (such as 2-heptanone and 2-nonanone), and have a significant impact on the final flavor of yogurt. The type and amount of protease added affect the degree of protein hydrolysis. When protease is not used for hydrolysis or only endo-enzyme is used, resulting in incomplete protein hydrolysis, the peptide chains in the system cannot be completely hydrolyzed into amino acids, the content of flavor substances in the system is relatively low, and the content of bitter peptides (such as valine) is relatively high. Under appropriate enzymatic conditions of compound flavor protease + neutral protease (endo-enzyme + exo-enzyme), the degree of protein hydrolysis is high, the concentration of flavor substances in the system is high, and the content of bitter peptides is relatively low. 3. The addition of citric acid affects the content of ketones (acetoin) and alcohols and the stability of the product. If too much citric acid is added, the pH of the system will rise, casein in the milk system will precipitate prematurely, affecting the fermentation process of the strain, thus affecting the organizational state and stability of the product. 4. The type and amount of fat raw materials affect the content of ketone compounds and the smoothness of the taste; if fat raw materials are not added, the product will not perform well in terms of milk flavor and smoothness; 5. Lactobacillus helveticus and Lactococcus lactis subsp. lactis (diacetyl type) in the starter can promote fat decomposition. Without the addition of Lactobacillus helveticus and Lactococcus lactis subsp. lactis (diacetyl type), the content of fatty acids, ketones and γ-lactones is low, the overall flavor intensity of the product is weak, and the fermentation taste is weak; 6. Acetoin has a buttery smell and can be formed through citric acid metabolism and the decomposition of aspartic acid and alanine. Therefore, the alanine content in the system after enzymatic hydrolysis affects the content of acetoin, a key flavor substance; methionine can generate various sulfides through a series of specific redox reactions during the preparation of yogurt, and the concentration of sulfides also affects the final flavor formation of the product. In the enzymatic hydrolysis system of the present invention, the ratio of cysteine, alanine and methionine is relatively high, which is conducive to improving the flavor of the product.

[0091] Although the present invention has been described in detail above with general descriptions and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements may be made thereto based on the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing yogurt, wherein the yogurt is prepared by fermenting a substrate with a fermentation bacteria, characterized in that: The substrate comprises: a milk-based material and a protease, wherein the milk-based material comprises concentrated animal milk and a fat raw material; the milk-based material is first enzymatically hydrolyzed by lipase before fermentation and then used for fermentation; The protease includes flavor protease, or further includes neutral protease; The fat raw material includes one or more of cream cheese, fermented butter, and light cream; The fermentation bacteria are composed of Lactobacillus helveticus, Lactococcus lactis subspecies lactis (diacetyl type), Lactococcus lactis subspecies cremoris, Streptococcus salivarius subspecies thermophilus and Lactobacillus delbrueckii subspecies bulgaricus.

2. The method for preparing yogurt according to claim 1, characterized in that: The ratio of the number of live bacteria of Lactobacillus helveticus, Lactococcus lactis subsp. lactis (diacetyl type), Lactococcus lactis subsp. cremoris, Streptococcus salivarius subsp. thermophilus and Lactobacillus delbrueckii subsp. bulgaricus is (1.8-2.2): (1.8-2.2): (0.9-1.1): (2.8-3.2): (1.8-2.2); And / or, the neutral protease is added at 0.08-0.4AU per ton of the milk base, and the flavor protease is added at 0-250LAPU per ton of the milk base; And / or, the yogurt also includes a water base, the water base includes polysaccharides and a filtrate obtained when concentrating animal milk; the polysaccharides are citrus fiber and / or high-ester pectin; the cream cheese accounts for 0-0.5% of the total mass of the milk base and the water base, the fermented butter accounts for 0-0.5% of the total mass of the milk base and the water base, and the light cream accounts for 0-1% of the total mass of the milk base and the water base; the mass percentages of the cream cheese, fermented butter, and light cream in the total mass of the milk base and the water base are not 0% at the same time.

3. The method for preparing yogurt according to claim 2, characterized in that: The protease comprises a neutral protease and a flavor protease, wherein the neutral protease is added at 0.28 AU per ton of the milk base material, and the flavor protease is added at 75 LAPU per ton of the milk base material; And / or, the fat raw material includes cream cheese and fermented butter, and the mass ratio of the cream cheese to the fermented butter is (0.8-1.2): (0.8-1.2).

4. The method for preparing yogurt according to any one of claims 1 to 3, characterized in that: The milk base material further comprises one or more of a sweetener, a thickener, a protein supplement, and citric acid; The sweetener includes: one or more of sugar, xylitol, erythritol, and maltitol; the thickener includes: one or more of starch, pectin, agar, and gellan gum; the protein supplement includes: whey protein powder and / or casein; The preparation method of the yogurt comprises: (1) Concentrating the animal milk to obtain a filtrate and concentrated animal milk; the protein content of the concentrated animal milk is 3.1%-3.4%; (2) The mixture of the concentrated animal milk and other components of the milk-based material is fully enzymatically hydrolyzed by the lipase to obtain a milk-based material; the polysaccharide material and the filtrate are mixed to obtain a water-based material; (3) homogenizing and pasteurizing the milk-based material and the water-based material respectively; (4) mixing the homogenized and pasteurized milk base with the protease and fermentation bacteria, and then fermenting and demulsifying to obtain fermented milk; (5) The fermented milk and the water-based material treated in step (3) are mixed, homogenized, and secondary pasteurized to obtain a mixed material.

5. The method for preparing yogurt according to claim 4, characterized in that: The sweetener accounts for 2-8% of the total mass of the milk base and the water base; the thickener accounts for 1-2% of the total mass of the milk base and the water base; the protein supplement accounts for 0.4-1.0% of the total mass of the milk base and the water base; the polysaccharide accounts for 0.1-0.6% of the total mass of the milk base and the water base; the citric acid accounts for 0-0.25% of the total mass of the milk base and the water base; And / or, the protein supplement is whey protein powder.

6. The method for preparing yogurt according to claim 4, characterized in that: In step (2), the concentrated animal milk is first mixed with lipase, and after enzymatic hydrolysis at 5-8°C for 16-24 hours, it is mixed with other components of the milk base at 45-55°C for 30-60 minutes to obtain a milk base; 20000-100000U of the lipase is added per ton of the concentrated animal milk; and / or, in step (2), the temperature at which the polysaccharide and the filtrate are mixed is 65-75°C; And / or, in step (3), the secondary pressure of the homogenization is 30-50 bar, the total pressure is 130-150 bar, and the pasteurization conditions are: 121° C., 4-6 s; And / or, in step (4), 50U-200U of the fermentation bacteria is added to each ton of the milk base; the fermentation temperature is 42±1°C, the acidity of the fermentation final product is not higher than 85°T, and the pH is not higher than 4.6; And / or, in step (5), the homogenization pressure is 10-40 Bar; the secondary pasteurization conditions are: 75° C., 20-30 s.

7. The method for preparing yogurt according to claim 4, characterized in that: After step (5), the method further includes the step of adding flavors online aseptically at a temperature below 30° C.; the flavors include: one or more of fruit flavors, milk flavors, and mouth-feel flavors; and the amount of flavors added is 0.05-0.3% of the mass percentage of the mixture.

8. The method for preparing yogurt according to claim 7, characterized in that: When the flavor is added online in an aseptic manner, the mixed material and the flavor are added simultaneously through flow contact mixing.

9. A yogurt, characterized in that: The yogurt is prepared by the method for preparing the yogurt according to any one of claims 1 to 8.

10. Use of the yogurt preparation method according to any one of claims 1 to 8 in improving the flavor of yogurt.

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