Milk manufacturing methods

Abstract

The present invention aims to develop a technology for sterilizing milk products that ensures hygiene while suppressing the deterioration of milk product flavor due to light exposure during distribution and storage. [Solution] The present invention solves the above problem by a method for producing packaged milk products, which includes the following steps. (1) A process to reduce the dissolved oxygen concentration in the liquid of milk products to 3 ppm or less. (2) A process of heat-sterilizing milk products with a dissolved oxygen concentration of 3 ppm or less at 131°C to 135°C. (3) Process of filling pasteurized milk into containers Furthermore, the present invention relates to a manufacturing method having a homogenization step between steps (1) and (2).

Description

Technical Field

[0001] The present invention relates to a method for producing milk products. More particularly, it relates to a method for producing milk products in which deterioration of flavor due to light irradiation is suppressed.

Background Art

[0002] It is known that the flavor of milk products deteriorates when irradiated with light. Patent Document 1 describes a method for suppressing the generation of off-flavors in dairy products due to photooxidation and improving oxidative stability by adding ascorbic acid to dairy products such as milk. Patent Document 2 describes a beverage or food containing milk or a milk component that does not generate an off-flavor due to light induction, characterized in that milk or a beverage or food containing a milk component is heat-treated at 140°C for 30 to 120 seconds or under heat treatment conditions equivalent thereto. Patent Document 3 describes a method for producing milk products that suppresses the generation of off-flavors due to light induction, characterized in that milk products are subjected to vacuum degassing to reduce the dissolved oxygen concentration in the liquid to 3 ppm or less, and then heat-sterilized at 120 to 150°C for 2 to 4 seconds and filled into containers. However, according to the method of Patent Document 1, there is a problem that a flavor different from that of milk is imparted by the additive. In addition, in Japan, there is a problem that additives cannot be used for "milk", "modified milk", "low-fat milk", and "fat-free milk" according to the Milk and Milk Products Regulations. In the production of milk, usually, sterilization at 130°C for 2 seconds is performed to ensure hygiene. The sterilization conditions of 140°C for 30 to 120 seconds in Patent Document 2 are far from the production conditions of commercially available milk, and there are problems with both flavor and production efficiency. The method of heat-sterilizing at 130°C for 2 seconds described in Patent Document 3 is a sterilization method usually performed on commercially available milk products, but the suppression of the generation of off-flavors in light induction due to differences in other heating conditions has not been clarified.

Prior Art Documents

Patent Documents

[0003] [Patent Document 1] Japanese Patent Application Publication No. 10-84866 [Patent Document 2] Japanese Patent Publication No. 2002-262769 [Patent Document 3] Japanese Patent Publication No. 2006-42814 [Overview of the project] [Problems that the invention aims to solve]

[0004] According to the aforementioned prior art, the purpose of sterilizing milk products is to ensure hygiene. When storing milk products under refrigeration at 10°C or below, sterilization is performed at 130°C for 2 to 4 seconds, while milk products that can be distributed at room temperature are sterilized at 140°C for 2 seconds. The present invention aims to develop a technology for sterilizing milk products that ensures hygiene while suppressing the deterioration of milk product flavor due to light exposure during distribution and storage. [Means for solving the problem]

[0005] The inventors of this invention have discovered that in a method of producing milk by reducing the dissolved oxygen in milk and then heat-sterilizing the milk, the degree of flavor deterioration of the milk due to light irradiation after production differs depending on the sterilization temperature, and have completed the present invention. Specifically, they have discovered for the first time that by reducing the dissolved oxygen concentration in the milk liquid to 3 ppm or less, and then heat-sterilizing it at 131°C to 135°C for 2 to 10 seconds, it is possible to suppress flavor deterioration of the milk due to light irradiation after production. Specifically, the present invention has the following configuration. <1> A method for manufacturing packaged milk products, including the following steps. (1) A process to reduce the dissolved oxygen concentration in the liquid of milk products to 3 ppm or less. (2) A process of heat-sterilizing milk products with a dissolved oxygen concentration of 3 ppm or less at 131°C to 135°C. (3) The process of filling the heat-sterilized milk into containers. <2> The process of heat sterilization at 131°C to 135°C described in (2) above is a process of heat sterilization for 2 to 10 seconds. <1> The manufacturing method described above. <3> The heat sterilization step in (2) above is an indirect sterilization step using a plate heat exchanger. <1> or <2> The manufacturing method described above. <4> Between steps (1) and (2) above, there is a homogenization process. <1> or <2> The manufacturing method described above. <5> The step of reducing the dissolved oxygen concentration in the milk product liquid in (1) above to 3 ppm or less is a process of degassing under reduced pressure. <1> or <2> The manufacturing method described above. <6> The vacuum degassing process described in (1) above is a process in which milk products are pressurized and sprayed into a deaeration tank that has been pre-pressurized, so that they become fine particles, and the temperature is controlled so that the milk products do not reach their boiling point. <5> The manufacturing method described above. <7> The aforementioned <1> or <2> Milk products manufactured using the manufacturing method described above. <8> A method for suppressing the generation of flavor deterioration odors caused by light irradiation of milk products, including the following steps. (1) A process to reduce the dissolved oxygen concentration in the liquid of milk products to 3 ppm or less. (2) A process of heat-sterilizing milk products with a dissolved oxygen concentration of 3 ppm or less at 131°C to 135°C. (3) The process of filling the heat-sterilized milk into containers. [Effects of the Invention]

[0006] According to the present invention, by reducing the dissolved oxygen concentration in the liquid milk to 3 ppm or less, and then heat-sterilizing it at 131°C to 135°C before filling it into containers, it is possible to suppress the deterioration of flavor of the manufactured milk due to light exposure during storage and distribution. [Brief explanation of the drawing]

[0007] [Figure 1] The results of the evaluations of each example and comparative example sample on the day of manufacture (initial) are shown. [Figure 2] The results of each evaluation one day after light irradiation (D1) after the production of the samples of each example and comparative example are shown. [Figure 3] The results of each evaluation two days after light irradiation (D2) after the production of the samples of each example and comparative example are shown. [Figure 4] The results of each evaluation three days after light irradiation (D3) after the production of the samples of each example and comparative example are shown. [Figure 5] It is a graph showing the change over time of the evaluation of "overall preference" of the samples of each example and comparative example on the day of production (Initial), one day after light irradiation (D1), two days after light irradiation (D2), and three days after light irradiation (D3).

Mode for Carrying Out the Invention

[0008] (Milk products) The milk products in the present invention refer to liquids including "milk" or "dairy products" as defined in the Milk and Milk Products Order. For example, "milk", "formulated milk", "low-fat milk", "fat-free milk", "processed milk", "milk beverage", "fermented milk", "lactic acid bacteria beverage", "sterilized lactic acid bacteria beverage" by type can be mentioned, and among them, milk is preferably used. "Milk" refers to raw milk, cow milk, special cow milk, raw goat milk, sterilized goat milk, raw ewe milk, formulated milk, low-fat milk, fat-free milk, and processed milk. "Dairy products" refer to cream, butter, butter oil, cheese, concentrated whey, ice creams, concentrated milk, skim concentrated milk, unsweetened condensed milk, unsweetened skim condensed milk, sweetened condensed milk, sweetened skim condensed milk, whole milk powder, skim milk powder, cream powder, whey powder, protein concentrated whey powder, buttermilk powder, sweetened milk powder, prepared milk powder, fermented milk, lactic acid bacteria beverage (limited to those containing 3.0% or more of non-fat milk solids), and milk beverage. In the present invention, the milk products may be any liquid containing milk or dairy products, including cases where additives, flavors, etc. are also contained.

[0009] (Production method) The production method of the milk products of the present invention will be described. The production method of the milk products of the present invention includes the following steps. (1) A process of degassing milk products under reduced pressure to reduce the dissolved oxygen concentration in the liquid to 3 ppm or less. (2) A process of heat-sterilizing milk products with a dissolved oxygen concentration of 3 ppm or less at 131°C to 135°C. (3) The process of filling the heat-sterilized milk into containers.

[0010] (Dissolved oxygen reduction process) Step (1) is a step in which the dissolved oxygen concentration in the liquid milk is reduced to 3 ppm or less by vacuum degassing before heat sterilization of the milk, preferably to 2 ppm or less, and more preferably to 1 ppm or less. The step of reducing dissolved oxygen in the liquid as described in (1) above only needs to reduce the dissolved oxygen in the milk before pasteurization to 3 ppm or less, and any step that can reduce dissolved oxygen, such as degassing or nitrogen replacement, is acceptable. Among these, a step of vacuum degassing is preferred due to concerns about deterioration of flavor. To reduce the dissolved oxygen concentration in milk products by vacuum degassing, all known methods for degassing dissolved oxygen under reduced pressure can be applied. For example, membrane degassing and vacuum degassing methods can be used. Membrane degassing is a method in which milk products are passed through one side of a hydrophobic membrane that allows only gas to pass through, such as a hollow fiber membrane, and the gas in the liquid is separated and reduced by reducing the pressure on the other side of the membrane. Vacuum degassing is a method in which milk products are immersed in a vacuum to separate and reduce the gas in the liquid, and deaulators are typical vacuum degassing devices. The most preferred method for degassing under reduced pressure is to pressurize and spray milk into a deaeration tank that has been pre-pressurized, thereby reducing the dissolved oxygen concentration in the milk. Preferably, the milk is atomized to an average particle size of 50 μm to 1000 μm by pressurizing and spraying. Reducing the dissolved oxygen concentration in the milk means removing as much dissolved oxygen as possible (allowing it to escape from the milk), resulting in a dissolved oxygen concentration of 3 ppm or less after the treatment. This prevents damage to the flavor and color of the milk and eliminates problems such as corrosion or peeling of the inner surface of metal containers when the milk is filled into them. Furthermore, exposure to a reduced-pressure atmosphere means placing the atomized milk products in a reduced-pressure atmosphere. For example, when a degassing tank is used as equipment to provide a reduced-pressure atmosphere, the milk products are sprayed under pressure into the degassing tank, causing the atomized milk products to fly through the tank and be exposed to the reduced-pressure atmosphere. Furthermore, the step of pressurizing and spraying milk into a pre-pressurized diarator tank to form fine particles is preferably a temperature-controlled step that prevents the milk from reaching its boiling point.

[0011] (heat sterilization process) Step (2) is a process that follows step (1), in which milk products with a dissolved oxygen concentration of 3 ppm or less are heat-sterilized at 131°C to 135°C. The sterilization conditions for milk products are acceptable as long as they meet the regulations for sterilization of milk products under the Food Sanitation Act. However, sterilization by ultra-high temperature short-time sterilization (UHT) is preferred because it yields milk products with excellent shelf life. The sterilization method can be either indirect or direct. In this invention, indirect sterilization is preferred. For indirect heat sterilization, plate heat exchange systems, tubular heat exchange systems, and scraping heat exchange systems can be used. For direct heat sterilization, steam injection systems and steam infusion systems can be used. In this invention, the heat sterilization conditions are preferably 131°C to 135°C for 2 to 15 seconds, and more preferably 132°C to 135°C for 2 to 10 seconds. After heating, it is preferable to immediately cool the milk products to 10°C or below. In the manufacturing method of the present invention, preheating may be performed before the heat sterilization step. The preheating temperature is preferably 90°C or lower, and the holding time is, for example, 6 minutes or less.

[0012] (Container filling process) Step (3) is the process of filling containers with milk products that have been heat-sterilized in step (2) above. The material and shape of the container are not particularly limited, as long as they are commonly available. That is, containers for filling milk products obtained by the present invention include aseptic filling and packaging containers that allow for long-term storage, and containers that fill and package products in a state where refrigeration is required (non-aseptic packaging containers, chilled distribution product packaging containers), so as to accommodate various distribution methods. Furthermore, the filling container may be a container that transmits sunlight or fluorescent light. That is, it includes transparent containers made of glass or synthetic resin, containers made of semi-transparent glass or synthetic resin, containers made of polyethylene-processed paper, paper containers, etc. Furthermore, the form and shape of the container are not limited to bottles, boxes, etc. A transparent or semi-transparent light-transmitting window may be provided in part of the container. According to the present invention, since deterioration of the flavor of milk products can be suppressed even when exposed to light during storage after manufacturing, materials that transmit light to a certain extent can be suitably used.

[0013] (Homogenization process) In the manufacturing method of the present invention, homogenization treatment may also be performed in order to stabilize the quality by making the diameter of the fat globules contained in the raw milk uniform. The homogenization process can be performed before or after the preheating, or before or after the heat sterilization, but it is preferable to perform it between the dissolved oxygen reduction process (1) and the heat sterilization process (2). Homogenization can be carried out using conventionally known homogenization methods, and equipment such as homogenizers, microfull dizers, and colloid mills can be used. Preferred homogenization pressure and temperature conditions for the homogenization process are 10-30 MPa and 60-90°C, respectively.

[0014] (Method for suppressing the generation of off-flavors and odors) The present invention, through a manufacturing method comprising the steps (1) to (3) described above, can suppress flavor deterioration caused by light irradiation even when the manufactured milk products are stored or distributed under light irradiation conditions. Flavor deterioration typically refers to the generation of off-flavor odors, and suppression of flavor deterioration refers to suppression of the generation of off-flavor odors. Suppression of the generation of off-flavor odors includes not only suppression of the generation of off-flavor odors themselves, but also masking of the off-flavor odors that have been generated. In other words, it also includes suppression of the generation of apparent off-flavor odors. The manufacturing method of the present invention is a method of reducing the dissolved oxygen in the liquid milk products and then heat sterilizing them within a specific temperature range. Heat sterilization at this specific temperature generates a certain degree of heating odor, but this has been used to successfully mask the off-flavor odors that develop over time due to light irradiation. Therefore, the manufacturing method of the present invention can be rephrased as a method for suppressing the generation of off-flavor odors caused by light irradiation of milk products, including the steps (1) to (3). The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. [Examples]

[0015] [Test Example 1] 1. Method of manufacturing milk products (1) Dissolved oxygen reduction process Raw milk was pressurized and sprayed into a deaeration tank with a vacuum level adjusted to -0.098 to -0.100 MPa to form fine particles, and then degassed under reduced pressure at 10-15°C until the dissolved oxygen concentration was 3 ppm or less. A HACH dissolved oxygen meter was used to measure the dissolved oxygen. (2) Heat sterilization process After degassing under reduced pressure, the raw milk was preheated to 80°C in a plate heat exchanger and then homogenized in a homogenizer. The homogenization pressure was 15 MPa. After homogenization, the milk was heat-sterilized in a plate sterilizer at 120°C (Comparative Example 2), 130°C (Comparative Example 3), 132°C (Example 1), 135°C (Example 2), and 142°C (Comparative Example 4) for 10 seconds each, and then cooled to below 10°C in a plate heat exchanger. Similarly, raw milk that had not been degassed was heat-sterilized at 130°C (control) and 132°C (Comparative Example 1), and then cooled to below 10°C in a plate heat exchanger. (3) Container filling process The milk obtained through the above process was filled into plain white gable-top containers.

[0016] 2. Light irradiation test The milk, filled into containers, was stored in a refrigerator while being exposed to light. The illuminance was set to approximately 2,000 lux from the top of the milk container and a total of 4,000 lux from the four sides. The temperature inside the refrigerator was set to 10°C, and irradiation was carried out for 12 hours a day for 1 to 3 days.

[0017] 3. Evaluation Method The milk produced under each condition was evaluated by eight expert panelists on the day of production (initial), one day after light exposure (D1), two days after light exposure (D2), and three days after light exposure (D3), according to the following evaluation items and scoring method. (1) Evaluation items We evaluated the following aspects: "overall pleasantness," "quality of aroma in the mouth," "quality of aftertaste," "strength of heated odor," and "presence or absence of freshness." In this specification, "suppressing the generation of flavor-degrading odors" means that in this embodiment, the decrease in "overall desirability" is suppressed, resulting in an excellent rating. (2) Scoring method A control sample, obtained by heat-sterilizing raw milk at 130°C without degassing and storing it in the dark without light exposure, was assigned a score of "0". Each light-exposed sample was compared to the control and scored on a scale of -10 to +5 in increments of 1 point. For "overall likability," "quality of aroma in the mouth," "quality of aftertaste," and "presence or absence of freshness," a higher score indicates a more favorable evaluation, while for "strength of heat-induced odor," a lower score indicates a more favorable evaluation. The average score from the eight expert panelists was calculated, and the results were presented according to the following criteria. <Standards> "Overall pleasantness," "quality of aroma in the mouth," "quality of aftertaste," and "presence or absence of freshness." ◎: -2 or higher ○: -3 or greater and less than -2 △: Less than -3 "Strength of the heated smell" ◎: -1 or less ○: Greater than -1 and less than or equal to 1 △: Greater than 1

[0018] [Table 1]

[0019] 4.Results Table 1 shows the evaluation results for each sample three days after light irradiation. According to these results, among the milk samples obtained by heat sterilization after reducing the dissolved oxygen concentration to 3 ppm or less, samples with a heat sterilization temperature of 131°C to 135°C received good evaluations in all categories, and the overall preference also received a good evaluation (Examples 1 and 2). On the other hand, the sample that underwent heat sterilization at a dissolved oxygen concentration higher than 3 ppm without degassing (Comparative Example 1), the sample with a heat sterilization temperature of less than 131°C (Comparative Examples 2 and 3), and the sample with a temperature higher than 135°C (Comparative Example 4) all showed unfavorable results in at least one of the items, and received a low overall favorability rating.

[0020] 5. Discussion The evaluation results for each sample on the day of manufacture (initial), one day after light irradiation (D1), two days after light irradiation (D2), and three days after light irradiation (D3) are shown in Figures 1 to 4. Furthermore, Figure 5 shows the change in "overall preference" over time for the samples of Examples 1 and 2, and Comparative Examples 1, 2, 3, and 4. These results suggest that on the day of manufacture (initial), the flavor is dominated by the intensity of the heating odor, which is determined by the temperature of the heat sterilization. As the light exposure time progresses, the flavor gradually deteriorates, but in Example 1 (dissolved oxygen 0.97 ppm, heat sterilization temperature 132°C) and Example 2 (same 0.61 ppm, same 135°C), the deterioration of flavor is gradual. On the other hand, Comparative Example 2 (1.36 ppm, 120°C) gradually deteriorated in flavor to the same extent as Comparative Example 1 (sterilization at 132°C without reducing dissolved oxygen). Furthermore, Comparative Example 3 (1.09 ppm) showed significant differences compared to Example 1 in overall palatability, aftertaste quality, and freshness. This is likely because the moderate heating odor produced by sterilization at a suitable temperature range masks the flavor degradation odor caused by light irradiation. This is further supported by the fact that when the heat sterilization temperature in Comparative Example 4 is 142°C, resulting in a large amount of heat odor generation, the degree of flavor deterioration over time during light-irradiated storage is less. However, a problem arises when the heat sterilization temperature is high: the flavor is inferior to that of the day of manufacture (initial production) (the heat odor is too strong). From the above, it was found that by reducing the dissolved oxygen to 3 ppm or less and then sterilizing it by heating within an appropriate temperature range of 132 to 135°C, the deterioration of flavor when milk products are stored under light irradiation after production can be suppressed.

[0021] [Test Example 2] 1. Manufacturing method and evaluation Milk was produced and evaluated in the same manner as in Test Example 1, except that the heat sterilization temperature and the dissolved oxygen concentration in the liquid before heat sterilization were changed.

[0022] [Table 2]

[0023] 2.Results Table 2 shows the manufacturing conditions and evaluation results for each product. According to these results, the evaluation of milk obtained by reducing dissolved oxygen to 2.91 ppm and then heat sterilizing was good (Example 3), while the evaluation of milk obtained by reducing dissolved oxygen to 4.10 ppm and then heat sterilizing at the same temperature was unfavorable in some aspects (Comparative Example 6). From the results of Test Example 2, it was found that by reducing dissolved oxygen to 3 ppm or less and then heat sterilizing at an appropriate temperature range of 132 to 135°C, the deterioration of flavor of milk products due to storage under light irradiation after production can be suppressed, and this result supports the results of Test Example 1 in terms of the strictness of the dissolved oxygen concentration range.

Claims

1. A method for manufacturing packaged milk products, including the following steps. (1) A process to reduce the dissolved oxygen concentration in the liquid of milk products to 3 ppm or less. (2) A process of heat-sterilizing milk products having a dissolved oxygen concentration of 3 ppm or less at 131°C to 135°C. (3) The process of filling the heat-sterilized milk into containers.

2. The manufacturing method according to claim 1, wherein the step of heating and sterilizing at 131°C to 135°C in (2) above is a step of heating and sterilizing for 2 to 10 seconds.

3. The manufacturing method according to claim 1 or 2, wherein the heat sterilization step in (2) is an indirect sterilization step using a plate heat exchanger.

4. The manufacturing method according to claim 1 or 2, further comprising a homogenization process between steps (1) and (2).

5. The manufacturing method according to claim 1 or 2, wherein the step of reducing the dissolved oxygen concentration in the milk liquid in (1) above to 3 ppm or less is a step of degassing under reduced pressure.

6. The manufacturing method according to claim 5, wherein the vacuum degassing step (1) is a step of pressurizing and spraying milk into a pre-vacuumed deaeration tank so that it becomes fine particles, and the temperature is controlled so that the milk does not reach its boiling point.

7. Milk products produced by the manufacturing method described in claim 1 or 2.

8. A method for suppressing the generation of flavor deterioration odors caused by light irradiation of milk products, including the following steps. (1) A process to reduce the dissolved oxygen concentration in the liquid of milk products to 3 ppm or less. (2) A process of heat-sterilizing milk products having a dissolved oxygen concentration of 3 ppm or less at 131°C to 135°C. (3) The process of filling the heat-sterilized milk into containers.

Images