Greek type high-protein normal-temperature yoghourt and preparation method thereof

Abstract

The invention relates to the field of dairy product fermentation, in particular to Greek type high-protein normal-temperature yoghourt and a preparation method thereof. The preparation method comprises the following steps: partially degreasing raw milk to obtain degreased raw milk, and then homogenizing, sterilizing and fermenting the degreased raw milk to obtain a fermented milk base material; mixing pectin and white granulated sugar, then adding RO water to obtain a pectin solution, sterilizing and cooling the pectin solution, and mixing with the fermented milk base material to obtain a mixture; performing secondary homogenization on the mixture to obtain a homogenized mixture, and sterilizing and cooling the homogenized mixture to obtain sterilized fermented milk; and performing concentration treatment on the sterilized fermented milk through freezing crystallization and filtering crystallization, and filling after concentration to obtain the Greek normal-temperature yoghourt. The problem of secondary sterilization of the high-protein yoghurt is solved, and freeze concentration is performed after secondary sterilization, so that the problems of difficulty in sterilization due to high protein content before sterilization and microbial pollution after sterilization are solved.

Description

Technical Field

[0001] This invention relates to the field of dairy product fermentation, and in particular to a Greek-style high-protein room-temperature yogurt and its preparation method. Background Technology

[0002] In the current dairy market, room-temperature yogurt (also known as "sterilized yogurt") meets consumer demand for convenience and wider distribution channels due to its advantages of not requiring a cold chain and easy storage, resulting in continuous growth in its consumption. Under this trend, high-protein yogurt further aligns with the global trend of health and nutrition consumption, demonstrating significant market potential and becoming an important direction for category upgrading. However, combining the "high-protein" attribute with the industrial production requirements of "room-temperature storage" presents significant technical contradictions, hindering the large-scale development of this niche product.

[0003] Traditional processes generally use two routes to prepare high-protein room-temperature yogurt, among which:

[0004] The first route is "pre-fermentation concentration." The core of this process is to pre-remove some water and small molecules such as lactose and minerals using membrane filtration (e.g., ultrafiltration) before inoculating raw milk with a starter culture, thereby increasing the protein and total solids content of the raw milk. This method is a direct means of increasing the protein content of the final product. However, it brings two chain reactions: high concentrations of substrate (milk protein, milk fat) and altered osmotic pressure generally slow down the fermentation rate of lactic acid bacteria, significantly prolonging the fermentation time and reducing production efficiency. More importantly, the fermented milk produced in this way has an abnormally dense gel network structure due to its extremely high protein content. After fermentation, the viscosity of the material increases dramatically to a very high level. This high-viscosity, non-Newtonian fluid-like gel material cannot be effectively sterilized using conventional tubular or plate-type ultra-high temperature instantaneous sterilization equipment used for liquid milk. High viscosity can cause uneven flow of materials within the equipment and a sharp drop in heat transfer efficiency, which can easily lead to local overheating and charring or incomplete sterilization, thus failing to meet the requirements of the aseptic post-sterilization process that room temperature yogurt must undergo.

[0005] The second approach is "post-fermentation concentration." To circumvent the slow fermentation problem, this process first uses raw milk with conventional solids for normal fermentation to obtain basal fermented milk. Then, some whey is removed using physical methods (such as using an ultrafiltration membrane system or a centrifugal whey separator), thereby concentrating the protein. While this method solves the fermentation rate problem, the core obstacle remains: the concentrated material ultimately has a protein concentration and total solids comparable to the product from the "pre-fermentation concentration" process, resulting in a similarly high viscosity (e.g., 3000-4000 centipoise or higher). As mentioned earlier, this high-viscosity material is also incompatible with existing, mature tubular / plate sterilization processes, making uniform and effective secondary sterilization impossible.

[0006] In addition, the existing process also poses a risk of microbial contamination. If the process from sterilization to filling is not properly controlled, microorganisms can easily grow, causing the product's shelf life to be shortened to less than 3 months, which cannot meet the market's demand for long-shelf-life, high-protein, room-temperature yogurt.

[0007] Therefore, there is an urgent need for an innovative process that can effectively reconcile the relationship between "high protein content", "industrially sterilizable" and "long shelf life stability" to break through the current development bottleneck. Summary of the Invention

[0008] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a Greek-style high-protein room-temperature yogurt and its preparation method, which solves the problem that in the prior art, the concentration ratio before or after fermentation is limited, and the protein content after concentration is too high to achieve secondary sterilization, resulting in a short shelf life at room temperature.

[0009] To achieve the above and other related objectives, the present invention is obtained through the following technical solution.

[0010] The first aspect of this invention is to provide a method for preparing Greek-style high-protein room-temperature yogurt, the method comprising the following steps:

[0011] (1) After partially defatting the raw milk, defatted raw milk is obtained. Then, the defatted raw milk is homogenized, sterilized, and fermented to obtain fermented milk base material.

[0012] (2) Mix pectin and white sugar, then add RO water to obtain a pectin solution. Sterilize and cool the pectin solution and mix it with the fermented milk base obtained in step (1) to obtain a mixture.

[0013] (3) The mixture obtained in step (2) is homogenized twice to obtain a homogenized mixture. The homogenized mixture is sterilized and cooled to obtain sterilized fermented milk. The pressure of the second homogenization is 200-300 bar.

[0014] (4) The sterilized fermented milk obtained in step (3) is concentrated by freezing crystallization and filtering crystallization. After concentration, it is bottled to obtain Greek-style room temperature yogurt. The freezing temperature is -3~0℃. Stirring is carried out simultaneously during freezing crystallization. The stirring speed is 10~30r / min. The stirring time is 1-2h.

[0015] A second aspect of the present invention is to provide a Greek-style high-protein room-temperature yogurt, which is prepared by the method for preparing Greek-style high-protein room-temperature yogurt as described above.

[0016] As described above, the Greek-style high-protein room-temperature yogurt and its preparation method of the present invention have the following beneficial effects:

[0017] (1) In the preparation of a Greek-style high-protein room temperature yogurt of the present invention, the problem of secondary sterilization of high-protein yogurt is solved by freezing and concentrating after secondary sterilization, thus avoiding the problem of high protein content and difficult sterilization before sterilization and microbial contamination after sterilization.

[0018] (2) In the preparation of a Greek-style high-protein room-temperature yogurt of the present invention, the freezing concentration reaches more than 4 times, which is higher than that of traditional single membrane concentration;

[0019] (3) In the preparation of a Greek-style high-protein room-temperature yogurt of the present invention, freezing and concentration are carried out at low temperature, so that flavor substances are preserved and the taste is better. Detailed Implementation

[0020] To make the inventive objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. Those skilled in the art can easily understand other advantages and effects of this invention from the content disclosed in this specification.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0022] When using “including,” “having,” and “contains” as described herein, the intention is to cover non-exclusive inclusion, unless an explicit qualifying term such as “only,” “consisting of,” etc., is used, in which case another component may be added.

[0023] In this invention, the terms "preferredly," "more preferably," "better," and "even better" refer to embodiments of the invention that provide certain beneficial effects under certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are unavailable, nor is it intended to exclude other embodiments from the scope of the invention. That is, in this invention, "preferredly," "more preferably," "better," and "even better" are merely descriptions of more effective implementations or examples, but do not constitute a limitation on the scope of protection of the invention.

[0024] In this invention, terms such as "further," "even more," and "particularly" are used for descriptive purposes and indicate differences in content, but should not be construed as limiting the scope of protection of this invention.

[0025] In this invention, "at least one" means one or more, such as one, two, or more. "Multiple" or "several" means at least two, such as two, three, etc., and "multi-layered" means at least two layers, such as two layers, three layers, etc., unless otherwise explicitly specified. In the description of this invention, "several" means at least one, such as one, two, etc., unless otherwise explicitly specified.

[0026] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0027] Unless otherwise specified, all steps of this invention may be performed sequentially or randomly. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0028] Unless otherwise stated, a singular term may include a plural term and should not be understood as having a quantity of one.

[0029] In this invention, "above" or "below" both include the number itself. For example, "below 1" includes 1.

[0030] In this invention, room temperature refers to 0~40°C, including but not limited to 10~40°C, or further to 20~30°C.

[0031] The technical problem this invention aims to solve is overcoming the limitations of existing pre-fermentation or post-fermentation concentration methods, which often result in excessively high protein levels after concentration, preventing secondary sterilization. This patent addresses this problem through the following method: first, high-flowability room-temperature yogurt is prepared; second, the concentration process is adjusted to achieve secondary sterilization; and finally, the yogurt is concentrated and packaged using freeze-concentration technology to obtain the desired finished product. This method involves freezing and controlling the ice crystal size after secondary sterilization in existing room-temperature yogurt processes, then using a membrane to separate the ice crystals for concentration. This avoids the problem of excessively high protein levels leading to sterilization issues caused by pre-sterilization concentration. Furthermore, freeze-concentration below the freezing point avoids microbial growth and contamination problems after sterilization. This application prepares materials with "extremely low viscosity and high stability." Based on this, it controls ice crystal growth to avoid the protein network being compressed and destroyed due to insufficient material flowability and rampant ice crystal growth. Freeze concentration involves cooling the material to below 0°C and controlling the ice crystal size by adjusting the stirring speed, freezing temperature, and ice crystal crystallization time. Water crystallizes into ice crystals of 0.2~1mm, which are then removed to achieve concentration. After sterilization, freeze concentration allows for immediate filling after concentration; it also achieves a higher concentration ratio than traditional concentration methods; and compared to traditional membrane concentration or separation processes, freeze concentration is carried out at temperatures below 0°C throughout the process, preventing microbial growth and avoiding microbial contamination problems caused by sterilization processes.

[0032] The first aspect of this invention is to provide a method for preparing Greek-style high-protein room-temperature yogurt, the method comprising the following steps:

[0033] (1) After partially defatting the raw milk, defatted raw milk is obtained. Then, the defatted raw milk is homogenized, sterilized, and fermented to obtain fermented milk base material.

[0034] (2) Mix pectin and white sugar, then add RO water to obtain a pectin solution. Sterilize and cool the pectin solution and mix it with the fermented milk base obtained in step (1) to obtain a mixture.

[0035] (3) The mixture obtained in step (2) is homogenized twice to obtain a homogenized mixture. The homogenized mixture is sterilized and cooled to obtain sterilized fermented milk. The pressure of the second homogenization is 200-300 bar.

[0036] (4) The sterilized fermented milk obtained in step (3) is concentrated by freezing crystallization and filtering crystallization. After concentration, it is bottled to obtain Greek-style room temperature yogurt. The freezing temperature is -3~0℃. Stirring is carried out simultaneously during freezing crystallization. The stirring speed is 10~30r / min. The stirring time is 1-2h.

[0037] The raw materials used in this invention—milk, pectin, white sugar, and RO water—are conventional raw materials in the art and are not specifically limited. The RO water in this invention is reverse osmosis pure water, which is high-purity water prepared from raw water through a reverse osmosis membrane treatment process.

[0038] In some embodiments of the present invention, the raw milk in step (1) has a fat content of 2.9-3.3% and a protein content of 2.6-2.9%.

[0039] In some embodiments of the present invention, the defatted raw milk in step (1) has a fat content of 1-1.5% and a protein content of 2.6-2.9%;

[0040] In some embodiments of the present invention, the raw milk in step (1) is raw cow's milk;

[0041] In some embodiments of the present invention, the degreasing process in step (1) is not specifically described, and conventional degreasing steps can be used. Specifically, the degreasing step is centrifugal degreasing.

[0042] In some embodiments of the present invention, the homogenization temperature in step (1) is 60~65℃, for example, 60-63℃ or 63-65℃; the homogenization pressure is 18-22MPa, for example, 18-20MPa or 20-22MPa.

[0043] In some embodiments of the present invention, the sterilization temperature in step (1) is 120-125°C, for example, 120-123°C or 123-125°C; and the sterilization time is 55-65s, for example, 55-60s or 60-65s.

[0044] In some embodiments of the present invention, the fermenting agent used in step (1) is selected from one or more of Streptococcus thermophilus, Lactobacillus acidophilus, Lactobacillus bulgaricus, Lactobacillus plantarum, Lactococcus lactis subsp. lactis, and Lactococcus lactis subsp. milk fat.

[0045] In some embodiments of the present invention, based on the mass of the defatted raw milk, the amount of starter culture added for the fermentation treatment is 1×10⁻⁶. 6 -1×10 9 CFU / mL; specifically, 1×10⁻⁶. 6 -1.5×10 6 CFU / mL, 1.5×10 6 -2×10 6 CFU / mL, 2×10 6 -5×10 6 CFU / mL, 5×10 6-1×10 9 CFU / mL.

[0046] In some embodiments of the present invention, the fermentation time in step (1) is 4-6 hours, the fermentation temperature is 40-44°C, and the final pH of the fermentation is 4.2-4.3.

[0047] In some embodiments of the present invention, the pectin solution in step (2) comprises the following raw materials by weight percentage: 4.5-5.5% pectin, 6-8% white sugar, and 85-90% RO water;

[0048] Specifically,

[0049] In step (2), the amount of pectin added is 4.5-5%, the amount of white sugar added is 6-7.5%, and the amount of RO water added is 88-90%.

[0050] In step (2), the amount of pectin added is 5-5.5%, the amount of white sugar added is 7.5-8%, and the amount of RO water added is 85-88%.

[0051] In some embodiments of the present invention, the mass ratio of yogurt to pectin solution in step (2) is 8.5-9.5:1. For example, it is 9:1.

[0052] In some embodiments of the present invention, the sterilization temperature in step (2) is 105-115℃, for example, 105-110℃ or 110-115℃; the sterilization time is 3-7s, for example, 3-5s or 5-7s.

[0053] In some embodiments of the present invention, the cooling temperature in step (2) is 40-43°C. For example, 40-42°C or 42-43°C.

[0054] In some embodiments of the present invention, the secondary homogenization temperature in step (3) is 40-44°C. For example, 40-42°C or 42-44°C. The secondary homogenization pressure is 200-300 bar, for example, 200-250 bar or 250-300 bar.

[0055] In some embodiments of the present invention, the sterilization temperature in step (3) is 75-77°C, for example, 76°C; the sterilization time is 20-30s, for example, 20-25s or 25-30s.

[0056] In some embodiments of the present invention, the cooling temperature in step (3) is 2-25°C, for example, 2-15°C or 15-25°C.

[0057] In some embodiments of the present invention, the viscosity of the sterilized fermented milk in step (3) is 15-30 mPa·s. For example, it is 15-25 mPa·s or 25-30 mPa·s.

[0058] In some embodiments of the present invention, the stirring speed in step (4) is 10-30 r / min; for example, 10-20 r / min or 20-30 r / min. The formation of ice crystals is the result of the competition between nucleation and growth processes. Slow cooling combined with moderate stirring is beneficial for the uniform dissipation of heat and moisture, forming a large number of small crystal nuclei, thereby obtaining small and uniform ice crystals. When the stirring speed is too fast, strong fluid shear and heat transfer will inhibit the stable formation of a large number of crystal nuclei. At the same time, it will accelerate the migration and adhesion of water around the formed crystal nuclei, causing a few crystal nuclei to grow rapidly and disorderly, eventually forming coarse, dendritic, and uneven ice crystals. When the stirring speed is too slow, the following two core problems will be mainly caused:

[0059] Slow stirring means that heat and moisture (solute) within the system cannot be dispersed promptly and evenly. This results in excessively low temperatures (high local supercooling) near the cooling surface, leading to the formation of numerous crystal nuclei; while areas farther from the cooling center remain at higher temperatures, hindering nucleation. Under these conditions, nucleation and growth processes are severely asynchronous spatially. Local areas have ample time and moisture to overgrow, forming large ice crystals; while other areas may only produce a small number of fine ice crystals. Ultimately, this results in severely uneven ice crystal size distribution in the product, which is also detrimental to subsequent efficient and uniform separation.

[0060] Heat transfer efficiency drops sharply: Slow stirring cannot generate sufficient fluid shear force to prevent ice crystals from adhering to and accumulating on the cooler walls (heat exchange surfaces). Once an ice layer forms, it becomes an insulating layer, severely hindering heat transfer from the material to the cooling medium, leading to a significant reduction in subsequent cooling efficiency and increased energy consumption. In extreme cases, the ice layer adhering to the vessel walls may continue to thicken, even causing blockages in pipes or equipment flow channels, interrupting production.

[0061] In some embodiments of the present invention, the stirring time in step (4) is 1-2 hours; for example, 1-1.5 hours or 1.5-2 hours.

[0062] In some embodiments of the present invention, the ice crystals obtained during crystallization in step (4) are spherical in shape.

[0063] In some embodiments of the present invention, the filtration method in step (4) is membrane filtration; the membrane material is selected from one or more of stainless steel and polyvinylidene fluoride; the membrane pore size is 50~100μm. For example, 50-80μm or 80-100μm.

[0064] In some embodiments of the present invention, the freezing temperature in step (4) is -2 to 0°C. For example, -2 to -1°C or -1 to 0°C. When the freezing temperature is low, the greater the supercooling, the higher the nucleation rate. "Freezing temperature" refers to the final equilibrium temperature reached by the material. The lower the temperature, the greater the temperature difference (supercooling) between the system and the freezing point. The nucleation rate increases exponentially with the supercooling. Therefore, at extremely low temperatures, the system will explosively form a huge number of extremely small ice crystal nuclei in a very short time and in various parts of space. These ice crystals formed at ultra-low temperatures are too numerous and have a short growth time (or growth is inhibited), and their size is too small, even flocculent or needle-like. For high-viscosity yogurt systems, these micro-ice crystals have a huge total surface area and colloidal properties, and cannot be effectively separated by gravity sedimentation or conventional filtration. They will be suspended in the concentrated phase, forming an "ice slurry" state. When these residual, unseparated micro-ice crystals completely melt during subsequent storage or rewarming, the pure water they contain is released back into the concentrated yogurt, directly causing a decrease in the solids and protein content of the concentrated yogurt, i.e., it is "diluted," thus reducing the protein content in the yogurt.

[0065] The stirring process is the process of ice crystal formation. After formation, the mixture consists of ice crystals and yogurt liquid. When the mixture is passed through a membrane, the ice crystals are trapped by the membrane, while the yogurt passes through. Yogurt is always in a fluid state.

[0066] In some embodiments of the present invention, the stirring speed in step (4) is 10-15 r / min. For example, 10-13 r / min or 13-15 r / min.

[0067] In some embodiments of the present invention, the size of the ice crystals obtained during crystallization in step (4) is 0.2-1 mm. For example, 0.2-0.6 mm or 0.6-1 mm.

[0068] In some embodiments of the present invention, the filling temperature in step (4) is 2~25°C. For example, 2-10°C or 10-25°C.

[0069] A second aspect of the present invention is to provide a Greek-style high-protein room-temperature yogurt, which is prepared by the method for preparing Greek-style high-protein room-temperature yogurt as described above.

[0070] In some embodiments of the present invention, based on the quality of Greek-style high-protein room-temperature yogurt, the yogurt has a protein content of 8-10%, for example, 8-9% or 9-10%; and a fat content of 3-6.5%, for example, 3-5% or 5-6.5%.

[0071] In some embodiments of the present invention, the yogurt is stored at a temperature of 18-25°C. For example, 20-23°C or 23-25°C.

[0072] The present invention will be further illustrated by the following examples, but these examples do not limit the scope of the invention.

[0073] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. All reagents or instruments whose manufacturers are not specified are conventional products that can be purchased commercially. In addition to the specific methods, equipment, and materials used in the embodiments, based on the knowledge of the prior art possessed by one of ordinary skill in the art and the description of this invention, any prior art methods, equipment, and materials similar to or equivalent to those described, used, and materials in the embodiments of this invention may be used to implement this invention.

[0074] The raw milk used in this invention is manufactured by Bright Dairy & Food Co., Ltd.

[0075] The pectin used in this invention is manufactured by IFF Ltd.

[0076] The fermentation agents of this invention are Lactobacillus bulgaricus and Streptococcus thermophilus, manufactured by IFF Ltd.

[0077] The viscosity test in this invention uses a viscometer, specifically a ProRheo viscometer. The specific test method involves measuring the viscosity at 25°C at a rate of 100 s⁻¹. -1 The sample was sheared at a constant shear rate, and the steady-state viscosity was read 10 seconds after the shearing began.

[0078] Example

[0079] Example 1

[0080] This embodiment provides a method for preparing Greek-style high-protein room-temperature yogurt, the method comprising the following steps:

[0081] (1) After partially defatting the raw milk, defatted raw milk is obtained. Then, the defatted raw milk is homogenized, sterilized, and fermented to obtain fermented milk base. The raw milk is raw milk with a fat content of 2.9% and a protein content of 2.6%. The defatted raw milk has a protein content of 2.6% and a fat content of 1.1%. The homogenization temperature is 60℃, the homogenization pressure is 20MPa, the sterilization temperature is 122℃, the sterilization time is 60s, the fermentation temperature is 40℃, the fermentation time is 5h, the pH at the end of fermentation is 4.2, and the amount of fermenting agent added is 1×10 based on the amount of defatted raw milk added. 6 CFU / mL; The defatting step is centrifugation defatting;

[0082] (2) Mix 4.5% pectin and 8% white sugar, then add 87.5% RO water to obtain a pectin solution. Sterilize and cool the pectin solution and mix it with the fermented milk base obtained in step (1) to obtain a mixture. The mass ratio of fermented milk base to pectin solution is 9:1. The sterilization temperature is 110℃, the sterilization time is 4s, and the cooling temperature is 40℃.

[0083] (3) The mixture obtained in step (2) is homogenized twice to obtain a homogenized mixture. The homogenized mixture is sterilized and cooled to obtain sterilized fermented milk. The pressure of the second homogenization is 200 bar, the temperature of the second homogenization is 40°C, the sterilization temperature is 75°C, the sterilization time is 25 s, the cooling temperature is 25°C, and the viscosity of the sterilized fermented milk is 28 mPa·s.

[0084] (4) The sterilized fermented milk obtained in step (3) is concentrated by freezing crystallization and filtration crystallization. After concentration, it is aseptically filled at 2°C to obtain Greek-style room temperature yogurt. The freezing temperature is -1.5°C. Stirring is carried out simultaneously during freezing crystallization. The stirring speed is 20r / min. The stirring time is 1h. The average size of the ice crystals after crystallization is 0.5mm. The filtration method is membrane filtration. The membrane material is stainless steel and the membrane pore size is 50μm.

[0085] The Greek-style high-protein room-temperature yogurt prepared using the above method has a protein content of 9% and a fat content of 3.9%. The yogurt is stored at 25°C.

[0086] Example 2

[0087] This embodiment provides a method for preparing Greek-style high-protein room-temperature yogurt, the method comprising the following steps:

[0088] (1) After partially defatting the raw milk, defatted raw milk is obtained. Then, the defatted raw milk is homogenized, sterilized, and fermented to obtain fermented milk base. The raw milk is raw milk with a fat content of 3.3% and a protein content of 2.9%. The defatted raw milk has a protein content of 2.9% and a fat content of 1.1%. The homogenization temperature is 65℃, the homogenization pressure is 20MPa, the sterilization temperature is 122℃, the sterilization time is 60s, the fermentation temperature is 40℃, the fermentation time is 5h, the pH at the end of fermentation is 4.2, and the amount of fermenting agent added is 1×10 based on the amount of defatted raw milk added. 6 CFU / mL; The defatting step is centrifugation defatting;

[0089] (2) Mix 5.5% pectin and 8% white sugar, then add 86.5% RO water to obtain a pectin solution. Sterilize and cool the pectin solution and mix it with the fermented milk base obtained in step (1) to obtain a mixture. The mass ratio of fermented milk base to pectin solution is 9:1. The sterilization temperature is 110℃, the sterilization time is 4s, and the cooling temperature is 40℃.

[0090] (3) The mixture obtained in step (2) is homogenized twice to obtain a homogenized mixture. The homogenized mixture is sterilized and cooled to obtain sterilized fermented milk. The pressure of the second homogenization is 300 bar, the temperature of the second homogenization is 40°C, the sterilization temperature is 75°C, the sterilization time is 25 s, the cooling temperature is 20°C, and the viscosity of the sterilized fermented milk is 15 mPa·s.

[0091] (4) The sterilized fermented milk obtained in step (3) is concentrated by freezing crystallization and filtration crystallization. After concentration, it is aseptically filled at 5°C to obtain Greek-style room temperature yogurt. The freezing temperature is 0°C. Stirring is carried out simultaneously during freezing crystallization. The stirring speed is 30r / min. The stirring time is 1h. The average size of the ice crystals after crystallization is 0.8mm. The filtration method is membrane filtration. The membrane material is stainless steel and the membrane pore size is 100μm.

[0092] The Greek-style high-protein room-temperature yogurt prepared using the above method has a protein content of 8% and a fat content of 3%. The yogurt is stored at 20°C.

[0093] Example 3

[0094] This embodiment provides a method for preparing Greek-style high-protein room-temperature yogurt, the method comprising the following steps:

[0095] (1) After partially defatting the raw milk, defatted raw milk is obtained. Then, the defatted raw milk is homogenized, sterilized, and fermented to obtain fermented milk base. The raw milk is raw milk with a fat content of 2.9% and a protein content of 2.6%. The defatted raw milk has a protein content of 2.6% and a fat content of 1.1%. The homogenization temperature is 60℃, the homogenization pressure is 20MPa, the sterilization temperature is 122℃, the sterilization time is 60s, the fermentation temperature is 42℃, the fermentation time is 6h, and the final pH of the fermentation is 4.3. Based on the amount of defatted raw milk added, the amount of fermenting agent added is 1×10 6 CFU / mL; The defatting step is centrifugation defatting;

[0096] (2) Mix 5% pectin and 8% white sugar, then add 87% RO water to obtain a pectin solution. Sterilize and cool the pectin solution and mix it with the fermented milk base obtained in step (1) to obtain a mixture. The mass ratio of fermented milk base to pectin solution is 9:1. The sterilization temperature is 110℃, the sterilization time is 4s, and the cooling temperature is 42℃.

[0097] (3) The mixture obtained in step (2) is homogenized twice to obtain a homogenized mixture. The homogenized mixture is sterilized and cooled to obtain sterilized fermented milk. The pressure of the second homogenization is 250 bar, the temperature of the second homogenization is 42°C, the cooling temperature is 18°C, the viscosity of the sterilized fermented milk is 18 mPa·s, the sterilization temperature is 75°C, and the sterilization time is 25 s.

[0098] (4) The sterilized fermented milk obtained in step (3) is concentrated by freezing crystallization and filtration crystallization. After concentration, it is aseptically filled at 8°C to obtain Greek-style room temperature yogurt. The freezing temperature is -3°C. The freezing crystallization is carried out simultaneously with stirring at a speed of 10 r / min. The stirring time is 1 h. The average size of the ice crystals after crystallization is 0.3 mm. The filtration method is membrane filtration. The membrane material is stainless steel and the membrane pore size is 80 μm.

[0099] The Greek-style high-protein room-temperature yogurt prepared using the above method has a protein content of 10% and a fat content of 4.3%. The yogurt is stored at 20°C.

[0100] Example 4

[0101] This embodiment provides a method for preparing Greek-style high-protein room-temperature yogurt, the method comprising the following steps:

[0102] (1) After partially defatting the raw milk, defatted raw milk is obtained. Then, the defatted raw milk is homogenized, sterilized, and fermented to obtain fermented milk base. The defatted raw milk has a protein content of 2.9% and a fat content of 1.1%. The raw milk is raw cow's milk with a fat content of 3.2% and a protein content of 2.9%. The homogenization temperature is 60℃, the homogenization pressure is 20MPa, the sterilization temperature is 122℃, the sterilization time is 60s, the fermentation temperature is 44℃, the fermentation time is 5h, the pH at the end of fermentation is 4.2, and the amount of fermenting agent added is 1×10 based on the amount of defatted raw milk added. 6 CFU / mL; The defatting step is centrifugation defatting;

[0103] (2) Mix 5% pectin and 8% white sugar, then add 87% RO water to obtain a pectin solution. Sterilize and cool the pectin solution and mix it with the fermented milk base obtained in step (1) to obtain a mixture. The mass ratio of fermented milk base to pectin solution is 9:1. The sterilization temperature is 110℃, the sterilization time is 4s, and the cooling temperature is 44℃.

[0104] (3) The mixture obtained in step (2) is homogenized twice to obtain a homogenized mixture. The homogenized mixture is sterilized and cooled to obtain sterilized fermented milk. The pressure of the second homogenization is 250 bar, the temperature of the second homogenization is 44°C, the cooling temperature is 25°C, the sterilization temperature is 77°C, the sterilization time is 25 s, and the viscosity of the sterilized fermented milk is 23 mPa·s.

[0105] (4) The sterilized fermented milk obtained in step (3) is concentrated by freezing crystallization and filtration crystallization. After concentration, it is aseptically filled at 8°C to obtain Greek-style room temperature yogurt. The freezing temperature is -1.5°C. Stirring is carried out simultaneously during freezing crystallization. The stirring speed is 20r / min. The stirring time is 2h. The average size of the ice crystals after crystallization is 0.6mm. The filtration method is membrane filtration. The membrane material is stainless steel and the membrane pore size is 80μm.

[0106] The Greek-style high-protein room-temperature yogurt prepared using the above method has a protein content of 9% and a fat content of 3.5%. The yogurt is stored at 20°C.

[0107] Example 5

[0108] This embodiment provides a method for preparing Greek-style high-protein room-temperature yogurt, the method comprising the following steps:

[0109] (1) After partially defatting the raw milk, defatted raw milk is obtained. Then, the defatted raw milk is homogenized, sterilized, and fermented to obtain fermented milk base. The defatted raw milk has a protein content of 2.9% and a fat content of 1.1%. The raw milk is raw cow's milk with a fat content of 3.2% and a protein content of 2.9%. The homogenization temperature is 60℃, the homogenization pressure is 20MPa, the sterilization temperature is 122℃, the sterilization time is 60s, the fermentation temperature is 42℃, the fermentation time is 5h, the pH at the end of fermentation is 4.2, and the amount of fermenting agent added is 1×10 based on the amount of defatted raw milk added. 6 CFU / mL; The defatting step is centrifugation defatting;

[0110] (2) Mix 5% pectin and 8% white sugar, then add 87% RO water to obtain a pectin solution. Sterilize and cool the pectin solution and mix it with the fermented milk base obtained in step (1) to obtain a mixture. The mass ratio of fermented milk base to pectin solution is 9:1. The sterilization temperature is 110℃, the sterilization time is 4s, and the cooling temperature is 42℃.

[0111] (3) The mixture obtained in step (2) is homogenized twice to obtain a homogenized mixture. The homogenized mixture is sterilized and cooled to obtain sterilized fermented milk. The pressure of the second homogenization is 250 bar, the temperature of the second homogenization is 42°C, the cooling temperature is 18°C, the sterilization temperature is 77°C, the sterilization time is 25 s, and the viscosity of the sterilized fermented milk is 20 mPa·s.

[0112] (4) The sterilized fermented milk obtained in step (3) is concentrated by freezing crystallization and filtration crystallization. After concentration, it is aseptically filled at 10°C to obtain Greek-style room temperature yogurt. The freezing temperature is 0°C. During freezing crystallization, stirring is carried out simultaneously at a stirring speed of 30 r / min. The stirring time is 2 h, and the average size of the ice crystals after crystallization is 1 mm. The filtration method is membrane filtration, and the membrane material is stainless steel with a pore size of 60 μm.

[0113] The Greek-style high-protein room-temperature yogurt prepared using the above method has a protein content of 8% and a fat content of 3.4%. The yogurt is stored at 25°C.

[0114] Comparative Example

[0115] Comparative Example 1

[0116] This comparative example provides a method for preparing Greek-style high-protein room-temperature yogurt, which differs from Example 1 in that the freezing temperature in step (4) is -5℃.

[0117] The Greek-style high-protein room-temperature yogurt prepared using the above method has a protein content of 7% and a fat content of 3.4%. In this comparative example, the ice crystals formed are smaller and can permeate the membrane, thus diluting the concentrated yogurt.

[0118] Comparative Example 2

[0119] This comparative example provides a method for preparing Greek-style high-protein room-temperature yogurt, which differs from Example 2 in that the stirring speed in step (4) is 100 r / min.

[0120] The Greek-style high-protein room-temperature yogurt prepared using the above method has a protein content of 5.6% and a fat content of 2.1%. In this comparative example, the ice crystals formed were relatively large, which hindered the yogurt from passing through the membrane and affected the separation effect between the ice crystals and the yogurt.

[0121] Comparative Example 3

[0122] This comparative example provides a method for preparing Greek-style high-protein room-temperature yogurt, which differs from Example 3 in that the secondary homogenization pressure in step (3) is 60 bar.

[0123] Because of its high viscosity (280 mPa·s), the yogurt adhered to the membrane surface during separation, making it impossible to effectively separate the ice crystals from the yogurt.

[0124] Comparative Example 4

[0125] This comparative example provides a method for preparing Greek-style high-protein room-temperature yogurt, which differs from Example 4 in that the freezing time in step (4) is 0.5 hours. No significant ice crystals formed in this comparative example, making concentration impossible.

[0126] Comparative Example 5

[0127] This comparative example provides a method for preparing Greek-style high-protein room-temperature yogurt, which differs from Example 1 in that it uses an ultrafiltration membrane to concentrate the sterilized yogurt at a concentration temperature of 42°C. The protein content and fat content of this comparative example are 7% and 7.8%, respectively.

[0128] Performance testing

[0129] Sensory evaluation

[0130] Ten professionally trained sensory evaluators were selected to conduct sensory evaluations on the yogurts prepared in Examples 1-5 and Comparative Examples 1-2. The scoring results are shown in Table 1. The scoring criteria had a full score of 100 points, including: texture (40 points): observation of smoothness, viscosity, presence of bubbles and layering; aroma (40 points): richness of milky aroma, sweetness and sourness, presence of steamed or cooked taste or off-flavors; color (20 points): uniformity of color.

[0131] Table 1. Sensory evaluation results of the yogurts prepared in Examples 1-5 and Comparative Examples 1-2.

[0132]

[0133] As can be seen from Table 1, the Greek-style high-protein room-temperature yogurts prepared in Examples 1-5 have better sensory evaluation.

[0134] Stability test

[0135] Yogurts prepared in Examples 1-5 and Comparative Examples 1-2 were stored at 25°C. The condition of the samples was observed at 0, 1, 2, 3, and 6 months, and the presence or absence of whey separation was recorded. The whey separation results are shown in Table 2.

[0136] Table 2. Results of room temperature stability tests on yogurts prepared in Examples 1-5 and Comparative Examples 1-2

[0137]

[0138] As can be seen from Table 2, the yogurt prepared in Examples 1-5 has a longer shelf life at room temperature and no whey separation occurs within 6 months.

[0139] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing Greek-style high-protein room-temperature yogurt, characterized in that, The preparation method includes the following steps: (1) After partially defatting the raw milk, defatted raw milk is obtained. Then, the defatted raw milk is homogenized, sterilized, and fermented to obtain fermented milk base material. (2) Mix pectin and white sugar, then add RO water to obtain a pectin solution. Sterilize and cool the pectin solution and mix it with the fermented milk base obtained in step (1) to obtain a mixture. (3) The mixture obtained in step (2) is homogenized twice to obtain a homogenized mixture. The homogenized mixture is sterilized and cooled to obtain sterilized fermented milk. The pressure of the second homogenization is 200-300 bar. (4) The sterilized fermented milk obtained in step (3) is concentrated by freezing crystallization and filtering crystallization. After concentration, it is bottled to obtain Greek-style room temperature yogurt. The freezing temperature is -3~0℃. Stirring is carried out simultaneously during freezing crystallization. The stirring speed is 10~30r / min. The stirring time is 1-2h.

2. The preparation method according to claim 1, characterized in that: It also includes one or more of the following features: 11) The raw milk in step (1) has a fat content of 2.9-3.3% and a protein content of 2.6-2.9%; 12) The fat content of the defatted raw milk in step (1) is 1-1.5%, and the protein content is 2.6-2.9%; 13) The raw milk in step (1) is raw cow's milk; 14) The homogenization temperature in step (1) is 60~65℃ and the homogenization pressure is 18-22MPa; 15) The sterilization temperature in step (1) is 120-125℃ and the sterilization time is 55-65s; 16) The fermenting agent used in step (1) is selected from one or more of Streptococcus thermophilus, Lactobacillus acidophilus, Lactobacillus bulgaricus, Lactobacillus plantarum, Lactococcus lactis subsp. lactis, and Lactococcus lactis subsp. milk fat. 17) Based on the quality of the defatted raw milk, the amount of starter culture added for the fermentation process is 1×10⁻⁶. 6 -1×10 9 CFU / mL; 18) The fermentation time in step (1) is 4-6 hours, the fermentation temperature is 40-44℃, and the final pH of the fermentation is 4.2-4.

3.

3. The preparation method according to claim 1, characterized in that: It also includes one or more of the following features: 21) The pectin solution in step (2) comprises the following raw materials by weight percentage: 4.5-5.5% pectin, 6-8% white sugar, and 85-90% RO water; 22) The mass ratio of yogurt to pectin solution in step (2) is 8.5-9.5:1; 23) The sterilization temperature in step (2) is 105-115℃ and the sterilization time is 3-7s; 24) The cooling temperature in step (2) is 40-44℃.

4. The preparation method according to claim 1, characterized in that: It also includes one or more of the following features: 31) The secondary homogenization temperature in step (3) is 40~44℃; 32) The sterilization temperature in step (3) is 75-77℃ and the sterilization time is 20-30s; 33) The cooling temperature in step (3) is 2-25℃; 34) The viscosity of the sterilized fermented milk in step (3) is 15-30 mPa·s.

5. The preparation method according to claim 1, characterized in that: It also includes one or more of the following features: 41) The ice crystals obtained during crystallization in step (4) are spherical in shape; 42) The freezing temperature in step (4) is -2~0℃; 43) The size of the ice crystals obtained during crystallization in step (4) is 0.2-1 mm. 44) The filling temperature in step (4) is 2~25℃; 45) The filtration method in step (4) is membrane filtration.

6. The preparation method according to claim 5, characterized in that: It also includes one or more of the following features: 451) In feature 45), the membrane material is selected from one or more of stainless steel and polyvinylidene fluoride; 452) In feature 45), the membrane pore size is 50~100μm.

7. The preparation method according to claim 1, characterized in that: The stirring speed in step (4) is 10-15 r / min.

8. A Greek-style high-protein room-temperature yogurt, characterized in that: It is prepared by the method for preparing Greek-style high-protein room-temperature yogurt as described in any one of claims 1-7.

9. The Greek-style high-protein room-temperature yogurt according to claim 8, characterized in that: Based on the quality of Greek-style high-protein room-temperature yogurt, the yogurt contains 8-10% protein and 3-6.5% fat.

10. The Greek-style high-protein room-temperature yogurt according to claim 8, characterized in that: The yogurt should be stored at a temperature of 25-30℃.

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