Secondary fermentation vegetable and fruit flavored yoghourt and preparation method thereof

Abstract

The invention belongs to the technical field of food fermentation and dairy product processing, and particularly relates to secondary fermentation vegetable and fruit flavored yoghurt and a preparation method thereof, the preparation method comprises the following steps: 1) pretreating a milk raw material to obtain the pretreated milk raw material; (2) inoculating a primary fermentation strain into the pretreated milk raw material obtained in the step (1), and carrying out primary fermentation to obtain primary fermentation yoghourt; (3) after the primary fermented yoghurt obtained in the step (2) is fermented, cooling, adding vegetable and fruit raw materials, and mixing to obtain a mixture; and (4) inoculating a secondary fermentation strain into the mixture obtained in the step (3), carrying out secondary fermentation, so as to obtain the secondary fermentation vegetable and fruit flavored yoghourt after the fermentation is completed, cooling, and packaging. According to the invention, specific vegetable and fruit raw materials are added into the primarily fermented yoghurt, and secondary fermentation is carried out, so that the yoghurt is endowed with unique composite flavor and improved nutritional value by utilizing the metabolism of natural components of vegetables and fruits and specific microorganisms, and meanwhile, the dependence on artificial additives is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of food fermentation and dairy product processing, and particularly relates to a secondary-fermented vegetable and fruit flavored yogurt and a preparation method thereof. Background Art

[0002] Yogurt, as a long-established and widely popular fermented dairy product, its flavor and nutritional value have always been important directions for research and development. The traditional way of flavoring yogurt is mainly to directly add jam, fruit pieces or flavoring agents after fermentation is completed. For example, the patent of the Czech Radlická Mlékárna dairy factory published in 1933 describes yogurt with added jam. However, the flavor introduced by this physical mixing method often relies on artificial synthetic additives, is difficult to fully display the true flavor of natural ingredients, and has limited improvement on the overall nutritional value of yogurt.

[0003] In order to improve the nutritional value of yogurt, some products that combine vegetables and fruits with yogurt have emerged. For example, US Patent Application US20050226987A1 discloses a method of directly mixing cooked vegetable and fruit puree into yogurt. Although this method increases the nutritional components, it is still essentially a physical mixing, lacking the complex flavor substances produced by microbial metabolism during fermentation, which limits the richness of flavor.

[0004] Another technique is to directly ferment vegetable and fruit raw materials with lactic acid bacteria to prepare plant-based "yogurt". For example, German Patent DE60120018T2 describes such a method. However, its product matrix is vegetables and fruits rather than dairy products, omitting the traditional lactic acid bacteria yogurt fermentation step, resulting in significant differences from traditional dairy yogurt in terms of flavor, texture and target consumer groups.

[0005] In yogurt production, multi-stage fermentation processes are also applied. For example, US Patent US5445835 proposes using single-stage or two-stage fermentation to increase the bacteriocin produced by Pediococcus acidilactici, aiming to improve the shelf life of yogurt. However, the focus of this technology is on anti-corrosion rather than developing new flavors by adding vegetables and fruits and using secondary fermentation. Its goals and processes are essentially different from those of the present invention, and it does not involve adding vegetables and fruits at a specific stage after the primary fermentation and using specific microorganisms to carry out secondary fermentation under conditions different from the primary fermentation to directionally improve the flavor.

[0006] Fermented foods have received much attention due to the potential health benefits of probiotics. The fermentation process can increase the probiotic content and reduce the lactose content. However, the prior art has not fully explored integrating the natural flavor and nutrition of vegetables and fruits into traditional dairy yogurt through a secondary fermentation process, so as to create yogurt products with unique flavors and higher nutritional values while reducing the dependence on artificial additives.

[0007] Fermented foods have received much attention due to the potential health benefits of probiotics. The fermentation process can increase the probiotic content and reduce the lactose content. However, the existing technology has not fully explored integrating the natural flavors and nutrients of fruits and vegetables into traditional milk yogurt through a secondary fermentation process, thereby creating yogurt products with unique flavors and higher nutritional value while reducing the dependence on artificial additives.

[0008] In summary, the existing technology has the following deficiencies: 1) Fruit-flavored yogurt mostly relies on direct addition, lacking naturalness and richness in flavor; 2) The combination of fruits and vegetables with yogurt is mostly physical mixing, lacking an improvement in fermentation flavor; 3) It is not clear how to utilize multi-stage fermentation to synergistically produce complex flavors with fruit and vegetable components; 4) There are significant differences between plant-based "yogurt" and traditional milk yogurt; 5) The application of multi-stage fermentation mainly focuses on the shelf life rather than flavor innovation using fruits and vegetables.

[0009] Therefore, there is an urgent need to develop a new method for preparing yogurt that can effectively integrate the natural characteristics of fruits and vegetables into the milk yogurt matrix through the fermentation process, especially secondary fermentation, to produce unique and rich complex flavors and enhance nutritional value. Summary of the Invention

[0010] In view of the above-mentioned shortcomings of the existing technology, the purpose of the present invention is to provide a secondary-fermented fruit and vegetable flavored yogurt and its preparation method, which are used to solve the problems in the existing technology, such as most fruit and vegetable flavored yogurts using physical mixing of fruit materials with insufficient natural flavor, lack of fermentation improvement in the addition of fruits and vegetables, significant differences in flavor between plant-based "yogurt" and dairy products, and multi-stage fermentation mainly being used for shelf life rather than flavor optimization.

[0011] The first aspect of the present invention provides a preparation method for a secondary-fermented fruit and vegetable flavored yogurt, and the preparation method includes the following steps:

[0012] 1) Pretreat the milk raw material to obtain the pretreated milk raw material;

[0013] 2) Inoculate the primary fermentation strain in the pretreated milk raw material obtained in step 1) for primary fermentation to obtain primary fermented yogurt;

[0014] 3) After the primary fermented yogurt obtained in step 2) is fermented and completed, cool it, add the fruit and vegetable raw material, and mix to obtain a mixture;

[0015] 4) Inoculate the secondary fermentation strain in the mixture obtained in step 3) for secondary fermentation. After fermentation is completed, the secondary-fermented fruit and vegetable flavored yogurt is obtained, and it is cooled and then packaged.

[0016] In some embodiments of the present invention, in step 1), the milk raw material is selected from one or more of whole milk, low-fat milk, skim milk, goat milk, or buffalo milk.

[0017] In some embodiments of the present invention, in step 1), the pretreatment includes standardization, homogenization, sterilization, and cooling.

[0018] In some embodiments of the present invention, in step 2), the primary fermentation strains are Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus.

[0019] In some embodiments of the present invention, when the primary fermentation strains are dry powder bacterial agents, the inoculation amount of the primary fermentation strains is 0.01%-0.05% of the total amount of milk raw materials; when the primary fermentation strains are activated solutions, the inoculation amount of the primary fermentation strains is 1-3% of the total volume of milk raw materials.

[0020] In some embodiments of the present invention, in step 2), the temperature of the primary fermentation is 40-45°C; the time of the primary fermentation is 4-8 h.

[0021] In some embodiments of the present invention, in step 2), the primary fermentation is carried out until the pH value of the system is 4.5-4.7.

[0022] In some embodiments of the present invention, in step 2), the primary fermentation is carried out until the viscosity of the system is 2500-3500 Cp.

[0023] In some embodiments of the present invention, in step 3), the cooling is carried out until the temperature is 15-35°C.

[0024] In some embodiments of the present invention, in step 3), the pre-treated fruit and vegetable raw materials are added.

[0025] In some embodiments of the present invention, in step 3), the fruit and vegetable raw materials account for 5-30% of the total weight of the primary fermented yogurt.

[0026] In some embodiments of the present invention, the pretreatment in feature C2) includes washing, cutting, pulping, making mud, concentration, or heat treatment.

[0027] In some embodiments of the present invention, in step 4), the secondary fermentation strains are selected from one or more of mesophilic lactic acid bacteria, yeasts, or probiotics; the mesophilic lactic acid bacteria are Lactobacillus plantarum and / or Lactobacillus casei; the yeast is Saccharomyces cerevisiae; the probiotic is Bifidobacterium.

[0028] In some embodiments of the present invention, in step 4), the inoculation amount of the secondary fermentation strains accounts for 0.005%-0.05% of the total weight of the mixture.

[0029] In some embodiments of the present invention, in step 4), the secondary fermentation temperature is 15 - 35 °C; the time for secondary fermentation is 2 - 12 h.

[0030] In some embodiments of the present invention, in step 4), the secondary fermentation is carried out until the pH value of the system is 3.8 - 4.2.

[0031] In some embodiments of the present invention, in step 4), the secondary fermentation further includes adding additives, and the additives are selected from one or more of sugar, prebiotic or stabilizer; the addition amount of the sugar accounts for 0.01 - 5% of the total weight of the mixture; the sugar is selected from one or more of glucose, fructose or sucrose; the addition amount of the prebiotic accounts for 0.5 - 3% of the total weight of the mixture; the prebiotic is inulin and / or fructooligosaccharide; the addition amount of the stabilizer accounts for 0.01 - 0.5% of the total weight of the mixture; the stabilizer is pectin and / or carrageenan.

[0032] In some embodiments of the present invention, the cooling is carried out to a temperature of 2 - 5 °C; the cooling time is 30 - 120 min.

[0033] The second aspect of the present invention provides a secondary fermented fruit and vegetable flavored yogurt prepared by the above - mentioned preparation method.

[0034] As described above, a secondary fermented fruit and vegetable flavored yogurt and its preparation method of the present invention have the following beneficial effects:

[0035] By adding specific fruit and vegetable raw materials to the primary fermented yogurt and carrying out secondary fermentation, the natural components of fruits and vegetables and the metabolic action of specific microorganisms are utilized to endow the yogurt with a unique compound flavor and enhanced nutritional value, while reducing the dependence on artificial additives. Specific Embodiments

[0036] The following specific examples illustrate the embodiments of the present application. Those skilled in the art can easily understand other advantages and effects of the present application from the content disclosed in this specification. The present application can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present application.

[0037] Before further describing the specific embodiments of the present application, it should be understood that the protection scope of the present application is not limited to the following specific embodiments; it should also be understood that the terms used in the embodiments of the present application are for describing specific embodiments, rather than for limiting the protection scope of the present application; in the specification and claims of the present application, unless otherwise clearly indicated in the text, the singular forms "a", "an" and "the" include the plural forms.

[0038] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise specified in this application, both endpoints of each numerical range and any value therebetween can be selected. Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by those skilled in the art of this technology. Except for the specific methods, equipment, and materials used in the embodiments, according to the knowledge of those skilled in the art of this technology and the description of this application, any methods, equipment, and materials of the prior art similar to or equivalent to those in the embodiments of this application can also be used to implement this application.

[0039]

Preparation Method of Second-Fermented Fruit and Vegetable Flavored Yogurt

[0040] The present invention provides a preparation method of second-fermented fruit and vegetable flavored yogurt, and the preparation method includes the following steps:

[0041] 1) Pretreat the milk raw material to obtain the pretreated milk raw material;

[0042] 2) Inoculate the primary fermentation strain in the pretreated milk raw material obtained in step 1) for primary fermentation to obtain primary fermented yogurt;

[0043] 3) After the primary fermented yogurt obtained in step 2) is fermented, cool it and add the fruit and vegetable raw material to obtain a mixture;

[0044] 4) Inoculate the secondary fermentation strain in the mixture obtained in step 3) for secondary fermentation. After fermentation is completed, the second-fermented fruit and vegetable flavored yogurt is obtained, and it is packaged after cooling.

[0045] In the preparation method of the second-fermented fruit and vegetable flavored yogurt provided by the present invention, in step 1), the milk raw material is pretreated to obtain the pretreated milk raw material.

[0046] In step 1) of the present invention, the milk raw material is selected from one or more of whole milk, low-fat milk, skim milk, goat milk, or buffalo milk. The compositional differences of different milk sources will affect the final flavor and texture of the yogurt. For example, goat milk has a unique flavor, while buffalo milk has a higher milk fat content.

[0047] In step 1) of the present invention, the pretreatment includes standardization, homogenization, sterilization, and cooling to a suitable temperature for primary fermentation. Standardization aims to adjust the fat and non-fat milk solid contents of the milk raw material to a predetermined standard. The fat globule size is reduced through homogenization to prevent stratification and improve the taste. Pasteurization or ultra-high temperature sterilization is used to ensure the food safety of the product. Finally, the milk is cooled to 40 - 45 °C to provide a suitable temperature environment for primary fermentation.

[0048] Among them, for the standardization of milk raw materials, the target milk fat content and non-fat milk solid content can be determined according to the requirements of the final product. For example, for high-protein non-drinking yogurt, the non-fat milk solid content can be adjusted to 12.5% ± 0.5%.

[0049] Homogenization of milk raw materials is to reduce the fat globule diameter and improve the stability of the emulsion. The pressure of homogenization can be adjusted according to the type of milk raw materials and the texture of the required product. For example, for cow milk yogurt, the first-stage homogenization pressure can be 15 - 20 MPa, and the second-stage homogenization pressure can be 3 - 5 MPa; for goat milk with larger fat globules, it can be appropriately adjusted to the first-stage homogenization pressure of 10 - 15 MPa and the second-stage homogenization pressure of 2 - 4 MPa.

[0050] Pathogenic bacteria and most spoilage bacteria are killed in milk raw materials through heat treatment. Common sterilization methods include pasteurization (such as high-temperature short-time sterilization method of heating at 72°C for 15 - 20 seconds, or low-temperature long-time sterilization method of heating at 63 - 65°C for 30 minutes) or ultra-high temperature instantaneous sterilization (UHT, such as heating at 140 - 145°C for 2 - 5 seconds). The specific selection depends on the requirements for product shelf life and flavor.

[0051] After the above treatments are completed, the milk raw materials are adjusted to a temperature suitable for primary fermentation, and the temperature is 40 - 45°C, which can be selected as 40 - 41°C, 41 - 42°C, 42 - 43°C, or 43 - 45°C, etc.

[0052] In the preparation method of the secondary-fermented fruit and vegetable flavored yogurt provided by the present invention, step 2) is to inoculate the primary fermentation strains in the pretreated milk raw materials obtained in step 1) for primary fermentation to obtain primary-fermented yogurt. Specifically: The primary fermentation is carried out by inoculating specific lactic acid bacteria strains such as Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus, and culturing at a suitable temperature of 40 - 45°C until the pH value of the system reaches 4.5 - 4.7 or the viscosity reaches 2500 - 3500 cP, thereby forming yogurt with a preliminary flavor and gel structure.

[0053] In step 2) of the present invention, the primary fermentation strains are Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus. These two strains are the most commonly used strains in yogurt production. They work together. Lactobacillus delbrueckii subsp. bulgaricus produces flavor substances such as aldehydes, and Streptococcus thermophilus has a fast acid production rate. The two work together to more efficiently convert lactose into lactic acid, producing the unique flavor and texture of yogurt.

[0054] In step 2) of the present invention, when the primary fermentation strain is a dry powder bacterium agent, the inoculation amount of the primary fermentation strain is 0.01%-0.05% of the total weight of the milk raw material; when the primary fermentation strain is an activated liquid, the inoculation amount of the primary fermentation strain is 1-3% of the total volume of the milk raw material.

[0055] In step 2) of the present invention, the temperature of the primary fermentation is 40-45°C, which can be 40-41°C, 41-42°C, 42-43°C or 43-45°C, etc. This temperature is the optimal growth temperature range for Lactobacillus bulgaricus and Streptococcus thermophilus; the time of the primary fermentation is 4-8 h, which can be 4-5 h, 5-6 h, 6-7 h or 7-8 h.

[0056] In step 2) of the present invention, when the primary fermentation reaches a system pH value of 4.5-4.7, which can be 4.5-4.6 or 4.6-4.7, or the system viscosity is 2,500-3,500 cP, which can be 2,500-3,000 cP or 3,000-3,500 cP, it means that the system reaches the end point of the primary fermentation. This pH range can form a typical yogurt flavor and a stable gel structure, while inhibiting the growth of harmful microorganisms.

[0057] In the preparation method of the secondary fermentation fruit and vegetable flavored yogurt provided by the present invention, in step 3), after the primary fermentation yogurt obtained in step 2) is fermented and completed, it is cooled, and fruit and vegetable raw materials are added, and a mixture is obtained after mixing. Specifically: after the primary fermentation yogurt reaches the predetermined fermentation end point and is cooled to the appropriate temperature for the secondary fermentation, the pretreated fruit and vegetable raw materials are added, and after mixing evenly, a mixture is obtained.

[0058] In step 3) of the present invention, it is cooled to a temperature of 15-35°C, which can be 15-20°C, 20-25°C, 25-30°C, 30-35°C or 20-30°C, etc., and preferably 20-30°C.

[0059] In step 3) of the present invention, the preparation and addition of the fruit and vegetable raw materials is a key step, including pre-treating the fruits and vegetables such as cleaning, cutting, pulping or concentrating, etc., to remove impurities, adjust the morphology or increase the solid content, and then fully mixing with the cooled primary fermentation yogurt to provide sugars, active substances and flavor precursors for the subsequent secondary fermentation.

[0060] In step 3) of the present invention, the vegetable and fruit raw materials can be widely selected, including but not limited to the combination of one or more of the following: berry fruits with a sour and sweet flavor (such as blueberries, strawberries, cranberries, raspberries, blackberries), citrus fruits rich in volatile aroma substances (such as oranges, lemons, grapefruits, tangerines), melons and fruits with unique taste and flavor (such as cucumbers, pumpkins, cantaloupes, watermelons), and root vegetables rich in dietary fiber and natural pigments (such as carrots, beets, purple sweet potatoes). The vegetable and fruit raw materials can be selected in the form of fresh, frozen, dried or preliminarily processed (such as juiced, cut into pieces, pureed, sterilized) according to needs to adapt to different process requirements and product characteristics.

[0061] In step 3) of the present invention, the vegetable and fruit raw materials need to be pretreated before being added, including washing, cutting, pureeing, making into a paste, concentrating or heat treatment. Heat treatment such as pasteurization (such as heating at 70°C for 10 seconds) or high-temperature treatment to ensure no contamination by pathogenic microorganisms. For example, for strawberries, after washing, cut into regular small pieces of 5-8 mm and perform a short heat treatment. For pumpkins, after peeling and seeding, steam cook (such as steam heating at 95-100°C for 20-30 minutes) until softened, and then use a food-grade homogenizer to puree into a delicate paste at an appropriate rotation speed (such as 8000-12000 rpm), with the particle size controlled below 50 μm. In addition, in order to increase the solid content of the yogurt and concentrate the flavor and nutritional components of the vegetables and fruits, vacuum concentration treatment can be performed on some vegetables and fruits with a relatively high water content, controlling the solid content to reach more than 25% and the water activity (Aw) to be reduced to below 0.95.

[0062] In step 3) of the present invention, the vegetable and fruit raw materials account for 5-30% of the total weight of the initially fermented yogurt, and can be optionally 5-10%, 10-20% or 20-30%, etc. A lower addition amount mainly plays a flavoring role, while a higher addition amount can more significantly change the flavor, color and texture of the yogurt and increase the nutritional value of the product. In a preferred embodiment, the pretreated vegetable and fruit raw materials are aseptically added to the initially fermented yogurt cooled to the appropriate temperature for secondary fermentation in a preset proportion.

[0063] In step 3) of the present invention, after adding the vegetable and fruit raw materials to the initially fermented yogurt, sufficient mixing is required.

[0064] In step 3) of the present invention, in order to maintain the protein and fat indexes of the yogurt, the content of protein and fat in the milk raw material can be appropriately increased in the standardization step. For example, if the target final milk fat is 3.0% and the non-fat milk solids are 10.0%, after adding 20% of vegetables and fruits with a water content of 80%, the milk fat can be set to about 3.6% and the non-fat milk solids can be set to about 12.4% during standardization.

[0065] In the method for preparing the secondarily fermented fruit and vegetable flavored yogurt provided by the present invention, step 4) is to inoculate a secondarily fermenting bacterial strain into the mixture obtained in step 3) for secondary fermentation. After the fermentation is completed, the secondarily fermented fruit and vegetable flavored yogurt is obtained, which is then cooled and packaged. Specifically: A secondarily fermenting bacterial strain is inoculated into the mixture obtained in step 3), and secondary fermentation is carried out until a predetermined secondary fermentation end point is reached, obtaining the secondarily fermented fruit and vegetable flavored yogurt, which is rapidly cooled to 2-5 °C to terminate the fermentation and maintain the product quality. Finally, it is hermetically packaged using a suitable packaging material such as a composite plastic cup or a PET bottle.

[0066] In step 4) of the present invention, the secondary fermentation is carried out by specific microorganisms such as Lactobacillus plantarum, yeast or Bifidobacterium at a temperature of 20-30 °C for 2-12 hours of metabolic activity, aiming to interact with the components in the fruits and vegetables to produce unique flavor substances such as esters and alcohols, and may enhance the nutritional value of the product. The fermentation end point is determined by monitoring the total acidity, pH value or sensory evaluation.

[0067] In step 4) of the present invention, the secondarily fermenting bacterial strain can be selected according to the target flavor and nutritional characteristics, including but not limited to one or more of the following combinations: mesophilic lactic acid bacteria that produce ester and aldehyde flavor substances (such as Lactobacillus plantarum, e.g., strain LP01 or LP02, Lactobacillus casei, e.g., strain Shirota, Lactococcus lactis), yeasts that contribute a unique yeast flavor (such as Saccharomyces cerevisiae, e.g., strain Safale S-04, aroma-producing yeast (such as Torulaspora delbrueckii)), or specific probiotic strains (such as Bifidobacterium lactis, e.g., strain HN019 or Bb-12, Lactobacillus acidophilus, e.g., strain LA-5)). These bacterial strains are selected based on their ability to undergo metabolic reactions with specific components in the fruits and vegetables to produce unique flavor substances and may increase the nutritional value of the product. For example, Lactobacillus plantarum and Lactobacillus casei have been shown to produce various flavor compounds such as esters, alcohols and volatile organic acids when fermenting fruits and vegetables. Saccharomyces cerevisiae can contribute unique fruity and floral flavors by producing ester compounds such as ethyl acetate. Bifidobacterium can utilize prebiotics (such as fructooligosaccharides and pectin) that may be present in the fruits and vegetables to increase its survival rate and activity in the yogurt. Lactobacillus acidophilus is also selected for its potential health benefits such as enhancing immunity, promoting digestion and antioxidant properties.

[0068] In step 4) of the present invention, the inoculation amount of the secondary fermentation strain accounts for 0.005-0.05% of the total weight of the mixture, and may be optionally 0.005-0.01%, 0.01-0.02%, 0.02-0.03%, 0.03-0.04% or 0.04-0.05%, etc.

[0069] In step 4) of the present invention, the secondary fermentation temperature is 15-35°C, and may be optionally 15-20°C, 20-25°C, 25-30°C, 30-35°C or 20-30°C, etc., preferably 20-30°C. This temperature range is conducive to the growth and metabolism of most mesophilic lactic acid bacteria and yeasts, and this temperature range helps to slow down the activity of certain enzymes, so as to better maintain the natural active ingredients in fruits and vegetables, and may promote the production of a more delicate target flavor by specific microorganisms. The secondary fermentation time is 2-12 h, and may be optionally 2-5 h, 5-8 h, 8-10 h, 10-12 h, 5-10 h or 5-12 h, etc. The specific time depends on the selected strain, the type of fruits and vegetables and the intensity of the target flavor.

[0070] In step 4) of the present invention, the end point of the secondary fermentation can be determined by the system pH value being 3.8-4.2, and may be optionally 3.8-4 or 4-4.2; or the change rate of the total acidity of the system, the proportion of the lactic acid increase per hour in the total acidity increase of lactic acid <0.02%, or the sensory evaluation reaches the expected flavor.

[0071] In step 4) of the present invention, the secondary fermentation further includes adding additives, and the additives are selected from one or more of sugars, prebiotics or stabilizers; adding sugar can provide a more sufficient carbon source for yeasts, assist the start of the secondary fermentation strain, and promote the production of its flavor substances. It can also be adjusted according to the sweetness of the selected fruits and vegetables and the sweetness of the target product. The addition amount accounts for 0.01-5% of the total weight of the mixture, and may be optionally 0.01-2%, 2-3%, 3-4%, 4-5% or 2-5%; the sugar is selected from one or more of glucose, fructose or sucrose.

[0072] Adding prebiotics to selectively promote the growth of specific probiotics, the addition amount of prebiotics accounts for 0.5-3% of the total weight of the mixture, and may be optionally 0.5-1.5% or 1.5-3%; the prebiotics are inulin and / or fructooligosaccharide; in a preferred embodiment, 2% (w / w) of inulin is used to significantly promote the growth of Bifidobacterium, or 1.5% (w / w) of fructooligosaccharide is used.

[0073] To maintain the smooth texture of the yogurt, stabilizers can be added. The stabilizers are pectin and / or carrageenan, and the addition amount of the stabilizer accounts for 0.01-0.5% of the total weight of the mixture, optionally 0.01-0.1%, 0.1-0.2%, 0.2-0.3%, 0.3-0.4%, 0.4-0.5%, 0.1-0.3% or 0.1-0.5%, etc. When the stabilizer is pectin, the addition amount accounts for 0.1-0.5% of the total weight of the mixture, and when the stabilizer is carrageenan, the addition amount accounts for 0.01-0.05% of the total weight of the mixture.

[0074] In step 4) of the present invention, the prepared secondarily fermented fruit and vegetable flavored yogurt has a special flavor and may retain the original shape of the fruits and vegetables.

[0075] In step 4) of the present invention, the cooling temperature can be adjusted according to the storage conditions. For example, for products that require a longer shelf life, it can be cooled to 2-5°C, optionally 2-3°C, 3-4°C or 4-5°C, and the cooling time is 30-120 min, optionally 30-60 min or 60-120 min. The packaging material can be selected according to the characteristics of the product and market demand. For example, composite plastic cups with good oxygen barrier and light shielding properties can also be used for packaging, and nitrogen filling is carried out to extend the shelf life.

[0076]

Secondarily Fermented Fruit and Vegetable Flavored Yogurt

[0077] The present invention also provides a secondarily fermented fruit and vegetable flavored yogurt, which is prepared by using the preparation method as described above in the present invention.

[0078] The beneficial effects of the present invention are further illustrated below in conjunction with embodiments.

[0079] In order to make the invention purpose, technical solution and beneficial technical effects of the present invention clearer, the present invention is further described in detail below in conjunction with embodiments. However, it should be understood that the embodiments of the present invention are only for explaining the present invention and are not for limiting the present invention, and the embodiments of the present invention are not limited to the embodiments given in the specification. For the embodiments without specific experimental conditions or operation conditions, they are made according to conventional conditions, or according to the conditions recommended by the material suppliers.

[0080] In the following embodiments, unless otherwise specified, various raw materials of the present invention can be commercially purchased or prepared according to conventional methods in the art.

[0081] Example 1 Strawberry Secondarily Fermented Yogurt

[0082] Pretreatment of milk raw materials: Fresh milk is used, the fat content is standardized to 3.0%, the non-fat milk solids content is standardized to 10.0%, the homogenization pressure is 15 MPa for the first stage and 3 MPa for the second stage, and it is heated at 95°C for 15 seconds by pasteurization and then cooled to 43°C.

[0083] Primary fermentation: Inoculate 0.02% (w / w) of the primary fermentation strain (containing Lactobacillus bulgaricus and Streptococcus thermophilus) into the pre-treated milk raw material, and conduct primary fermentation at 43°C for about 6 hours until the pH value reaches the predetermined end point of 4.6 to obtain primary fermented yogurt.

[0084] Add fruit and vegetable raw materials: Add fresh strawberry dices (pre-washed and cut into small pieces of 5 - 8 mm) accounting for 15% of the total weight of the primary fermented yogurt. And conduct pasteurization treatment (70°C, 10 seconds) to ensure microbial safety. After cooling the primary fermented yogurt obtained in step 2) to the suitable temperature of 25°C for secondary fermentation, add the pre-treated strawberry dices according to the proportion of 15% (w / w) of the total weight and mix evenly.

[0085] Secondary fermentation: Inoculate 0.01% of Lactobacillus plantarum and ferment at 25°C for 8 hours until the pH value reaches 4.0.

[0086] Cooling and packaging: Cool the secondary fermented yogurt to 4°C and conduct aseptic packaging.

[0087] Example 2 Pumpkin secondary fermented yogurt

[0088] Pre-treatment of milk raw material: Use fresh milk, standardize the fat content to 3.2% and the non-fat milk solid content to 10.5%, the homogenization pressure is 16 MPa for the first stage and 3.5 MPa for the second stage, and use pasteurization method to heat at 95°C for 15 seconds and then cool to 40°C.

[0089] Primary fermentation: Inoculate 0.025% of the mixed strain of Lactobacillus bulgaricus and Streptococcus thermophilus and ferment at 40°C for 7 hours until the pH value reaches 4.5.

[0090] Add fruit and vegetable raw materials: Add cooked pumpkin puree (ground into a fine puree using a homogenizer) accounting for 20% of the total weight of the primary fermented yogurt.

[0091] Secondary fermentation: Inoculate 0.015% (w / w) of Saccharomyces cerevisiae and ferment at 22°C for 10 hours until the pH value reaches 3.9.

[0092] Cooling and packaging: Cool the secondary fermented yogurt to 4°C and conduct aseptic packaging.

[0093] Example 3 Orange secondary fermented yogurt

[0094] Pretreatment of milk raw materials: Fresh milk is used, the fat content is standardized to 3.5%, the non-fat milk solids content is standardized to 11.0%, the homogenization pressure is 14 MPa for the first stage and 2.5 MPa for the second stage, and it is heated at 70 °C for 18 seconds by pasteurization and then cooled to 42 °C.

[0095] Primary fermentation: A mixed strain of 0.018% Lactobacillus bulgaricus and Streptococcus thermophilus is inoculated and fermented at 42 °C for 5.5 hours until the pH value reaches 4.7.

[0096] Addition of fruit and vegetable raw materials: Fresh orange pulp (cut into small pieces) accounting for 10% of the total weight of the primary fermented yogurt is added.

[0097] Secondary fermentation: 0.01% (w / w) Lactobacillus casei is inoculated and fermented at 28 °C for 6 hours until the pH value reaches 4.1.

[0098] Cooling and packaging: The secondary fermented yogurt is cooled to 2.5 °C and aseptically packaged.

[0099] Example 4 Mango Secondary Fermented Yogurt

[0100] Pretreatment of milk raw materials: Fresh milk is used, the fat content is standardized to 3.3%, the non-fat milk solids content is standardized to 10.8%, the homogenization pressure is 15.5 MPa for the first stage and 3.2 MPa for the second stage, and it is heated at 73 °C for 17 seconds by pasteurization and then cooled to 41 °C.

[0101] Primary fermentation: A mixed strain of 0.022% (w / w) Lactobacillus bulgaricus and Streptococcus thermophilus is inoculated and fermented at 41 °C for 6.5 hours until the pH value reaches 4.55.

[0102] Addition of fruit and vegetable raw materials: Fresh mango dices (ripe mangoes are selected and peeled and cut into small pieces of 5 - 8 mm) accounting for 18% of the total weight of the primary fermented yogurt are added.

[0103] Secondary fermentation: 0.012% (w / w) Saccharomyces cerevisiae is inoculated and fermented at 23 °C for 9 hours until the pH value reaches 3.95.

[0104] Cooling and packaging: The secondary fermented yogurt is cooled to 3.5 °C and aseptically packaged.

[0105] Example 5 Blueberry Secondary Fermented Yogurt

[0106] Pretreatment of milk raw materials: Fresh milk is used, the fat content is standardized to 3.1%, the non-fat milk solids content is standardized to 10.2%, the homogenization pressure is 14.5 MPa for the first stage and 2.8 MPa for the second stage, and it is heated at 71 °C for 16 seconds by pasteurization and then cooled to 44 °C.

[0107] Primary fermentation: Inoculate a mixed strain of 0.019% (w / w) Lactobacillus bulgaricus and Streptococcus thermophilus, and ferment at 44 °C for 5.8 hours until the pH value reaches 4.65.

[0108] Addition of fruit and vegetable raw materials: Add fresh blueberries (select plump and ripe blueberries, wash them clean) accounting for 12% of the total weight of the primary fermented yogurt.

[0109] Secondary fermentation: Inoculate 0.008% (w / w) Lactobacillus plantarum, and ferment at 26 °C for 7 hours until the pH value reaches 4.05.

[0110] Cooling and packaging: Cool the secondary fermented yogurt to 4.5 °C and perform aseptic packaging.

[0111] Example 6 Yellow peach secondary fermented yogurt

[0112] Pretreatment of milk raw materials: Use fresh milk, standardize the fat content to 3.4%, the non-fat milk solids content to 10.6%, the homogenization pressure is 16.5 MPa for the first stage and 3.8 MPa for the second stage, and use pasteurization to heat at 74 °C for 19 seconds and then cool to 42.5 °C.

[0113] Primary fermentation: Inoculate a mixed strain of 0.023% (w / w) Lactobacillus bulgaricus and Streptococcus thermophilus, and ferment at 42.5 °C for 6.2 hours until the pH value reaches 4.45.

[0114] Addition of fruit and vegetable raw materials: Add fresh yellow peach dices (select ripe yellow peaches, peel and cut into small pieces of 6 - 9 mm) accounting for 22% of the total weight of the primary fermented yogurt.

[0115] Secondary fermentation: Inoculate a mixed strain of 0.011% (w / w) Lactobacillus casei and 0.005% Saccharomyces cerevisiae, and ferment at 24 °C for 9.5 hours until the pH value reaches 3.9.

[0116] Cooling and packaging: Cool the secondary fermented yogurt to 3.0 °C and perform aseptic packaging.

[0117] Comparative example 1 Yogurt directly added with strawberry jam

[0118] Pretreatment of milk raw materials: Use the same pretreatment method as in Example 1.

[0119] Primary fermentation: Use the same fermentation method as in Example 1.

[0120] Add fruit and vegetable raw materials: Add 15% (w / w) of commercially available strawberry jam to the cooled primary fermented yogurt and stir well. (This step replaces the addition of prepared fruits and vegetables and the secondary fermentation.)

[0121] Cooling and packaging: Cool the mixed yogurt to 4°C and perform aseptic packaging.

[0122] Comparative Example 2 directly adds strawberry essence

[0123] Pretreatment of milk raw materials: Use the same pretreatment method as in Example 1.

[0124] Primary fermentation: Use the same fermentation method as in Example 1.

[0125] Add fruit and vegetable raw materials: Add 0.05% (w / w) of commercially available strawberry essence to the cooled primary fermented yogurt, and add a small amount of sugar and pigment as needed, and stir well. (This step replaces the addition of prepared fruits and vegetables and the secondary fermentation.)

[0126] Cooling and packaging: Cool the mixed yogurt to 4°C and perform aseptic packaging.

[0127] The product characteristics of Examples 1-6 and Comparative Examples 1-2 are shown in Table 1.

[0128] Table 1 Product characteristics

[0129]

[0130]

[0131] It can be seen from the data in Table 1 that the products of the Examples using the secondary fermentation process show significant advantages over the products of the Comparative Examples with traditional addition of jam or essence in multiple key dimensions:

[0132] Flavor complexity and intensity: The types of volatile flavor substances in the Examples increase significantly, and the contents of key esters (such as ethyl acetate, ethyl butyrate) and characteristic aroma components (such as β-damascenone) increase substantially. In particular, the samples using yeast for secondary fermentation (Examples 2, 4, 6) produce extremely high contents of ethyl acetate, indicating that the secondary fermented yogurt has a richer, more intense and unique fermented fruit aroma.

[0133] Improved nutritional value: The Examples generally contain higher levels of vitamin C (derived from added fruits and vegetables) and riboflavin (vitamin B2, possibly related to microbial metabolism).

[0134] Physical and chemical properties and shelf life: The Examples have lower final pH values and higher titratable acidity, which not only affect the flavor but may also contribute to extending the shelf life of the product, and the estimated shelf life in the table is generally longer.

[0135] Compared with yogurt with physically mixed fruit and vegetable puree, secondary fermentation can produce new flavor substances through microbial metabolism, improving the flavor and texture of the product. This invention is also different from plant-based yogurt prepared by directly fermenting fruits and vegetables, as its base material is still the dairy product favored by consumers. In addition, existing multi-stage fermentation technologies are mainly used to extend the shelf life of yogurt, while this invention focuses on developing new flavors and enhancing nutritional value by adding fruits and vegetables.

[0136] Description of detection methods:

[0137] Flavor: Volatile components, ethyl acetate, ethyl butyrate, β-damascenone: Analyzed by gas chromatography-mass spectrometry (GC-MS). Referable standards such as GB / T 22339-2008 Determination of volatile flavor substances in foods - Gas chromatography-mass spectrometry method or updated standards. The specific method needs to be optimized according to the instrument model and experimental conditions.

[0138] Fruity aroma, fermented flavor, overall acceptability: Evaluated by sensory scoring method by trained sensory evaluators. Sensory evaluation methods can refer to GB / T 10343-2002 General principles of food sensory analysis and GB / T 13869-2003 Food sensory analysis - Scoring test method or updated standards. The formulation of the scoring standard should be based on the specific product characteristics.

[0139] Vitamin C: Determined by high performance liquid chromatography (HPLC) or titration method. Referable standards such as GB5009.139-2014 Determination of vitamin C in foods.

[0140] B vitamins: Select the corresponding national standard method according to the types of B vitamins to be determined specifically. For example, for vitamin B1, refer to GB 5009.85-2016 Determination of vitamin B1 in foods, and for vitamin B2, refer to GB 5009.84-2016 Determination of vitamin B2 in foods, etc.

[0141] Shelf life detection method: After aseptically filling the above dairy products, let them stand in a normal temperature warehouse to determine the shelf life, with obvious fat floating or detection of microorganisms in the sample as the end point of the shelf life.

[0142] In summary, the present invention effectively overcomes various disadvantages in the prior art and has high industrial utilization value.

[0143] As described above, it is only the preferred embodiment of the present invention, and there is no limitation, either in form or in essence, to the present invention. It should be noted that for those of ordinary skill in the art in this technical field, without departing from the method of the present invention, several improvements and supplements can still be made, and these improvements and supplements should also be regarded as the protection scope of the present invention. All those skilled in the art, without departing from the spirit and scope of the present invention, when making some equivalent changes, modifications and evolutions by using the technical content disclosed above, are equivalent embodiments of the present invention; at the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A preparation method of a secondary-fermented yogurt with a fruit and vegetable flavor, characterized in that, The preparation method includes the following steps: 1) Pretreat the milk raw material to obtain the pretreated milk raw material; 2) Inoculate the pretreated milk raw material obtained in step 1) with the primary fermentation strain for primary fermentation to obtain primary fermented yogurt; 3) After the primary fermented yogurt obtained in step 2) is fermented, cool it, add the fruit and vegetable raw material, and mix to obtain a mixture; 4) Inoculate the mixture obtained in step 3) with the secondary fermentation strain for secondary fermentation. After the fermentation is completed, the secondary fermented fruit and vegetable flavored yogurt is obtained, and it is cooled and then packaged.

2. The preparation method of the secondary-fermented fruit and vegetable flavored yogurt according to claim 1, characterized in that, It also includes any one or more of the following features: A1) In step 1), the milk raw material is selected from one or more of whole milk, low-fat milk, skim milk, goat milk or buffalo milk; A2) In step 1), the pretreatment includes standardization, homogenization, sterilization and cooling.

3. The preparation method of the secondarily fermented fruit and vegetable flavored yogurt according to claim 1, wherein, It includes any one or more of the following features: B1) In step 2), the primary fermentation strain is Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus; B2) In step 2), when the primary fermentation strain is a dry powder bacterium agent, the inoculation amount of the primary fermentation strain is 0.01%-0.05% of the total weight of the milk raw material; when the primary fermentation strain is an activated solution, the inoculation amount of the primary fermentation strain is 1-3% of the total volume of the milk raw material; B3) In step 2), the temperature of the primary fermentation is 40-45°C; the time of the primary fermentation is 4-8h; B4) In step 2), the primary fermentation is carried out until the pH value of the system is 4.5-4.7; B5) In step 2), the primary fermentation is carried out until the viscosity of the system is 2500-3500 cP.

4. The preparation method of the secondary-fermented fruit and vegetable flavored yogurt according to claim 1, wherein, It also includes any one or more of the following features: C1) In step 3), the cooling is carried out to a temperature of 15-35°C; C2) In step 3), the fruit and vegetable raw material is added after being pretreated; C3) In step 3), the fruit and vegetable raw material accounts for 5-30% of the total weight of the primary fermented yogurt.

5. The preparation method of the secondarily fermented fruit and vegetable flavored yogurt according to claim 4, characterized in that, In feature C2), the pretreatment includes cleaning, cutting, pulping, making mud, concentrating or heat treatment.

6. The preparation method of the second-fermented fruit and vegetable flavored yogurt according to claim 1, characterized in that, It also includes any one or more of the following features: D1) In step 4), the secondary fermentation strain is selected from one or more of mesophilic lactic acid bacteria, yeasts or probiotics; D2) In step 4), the inoculation amount of the secondary fermentation strain accounts for 0.005%-0.05% of the total weight of the mixture; D3) In step 4), the secondary fermentation temperature is 15-35°C; the time of the secondary fermentation is 2-12h; D4) In step 4), the secondary fermentation is carried out until the pH value of the system is 3.8-4.2; D5) In step 4), the secondary fermentation also includes adding an auxiliary agent, and the auxiliary agent is selected from one or more of sugar, prebiotic or stabilizer.

7. The preparation method of the secondarily fermented fruit and vegetable flavored yogurt according to claim 6, characterized in that, Feature D1) also includes any one or more of the following features: D11) The mesophilic lactic acid bacteria are Lactobacillus plantarum and / or Lactobacillus casei; D12) The yeast is Saccharomyces cerevisiae; The probiotic bacteria are Bifidobacterium.

8. The preparation method of the secondary-fermented fruit and vegetable flavored yogurt according to claim 6, characterized in that, Feature D6) further includes any one or more of the following features: D51) The addition amount of the sugar accounts for 0.01-5% of the total weight of the mixture; D52) The sugar is selected from one or more of glucose, fructose or sucrose; D53) The addition amount of the prebiotic accounts for 0.5-3% of the total weight of the mixture; D54) The prebiotic is inulin and / or fructooligosaccharide; D55) The addition amount of the stabilizer accounts for 0.01-0.5% of the total weight of the mixture; D56) The stabilizer is pectin and / or carrageenan.

9. The preparation method of the secondarily fermented vegetable and fruit flavored yogurt according to claim 1, wherein, In step 5), it is cooled to a temperature of 2-5°C; the cooling time is 30-120 min.

10. A secondarily fermented fruit and vegetable flavored yogurt, which is prepared by using the preparation method described in any one of claims 1 to 9.

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