Method for detecting stability of normal-temperature milk

Abstract

The invention relates to the technical field of dairy product detection, in particular to a method for detecting the stability of normal-temperature milk, which comprises the following steps of: detecting the stability of the normal-temperature milk according to the sample appearance, the grain diameter and pitch diameter change rate and the centrifugal precipitation rate under the conditions of temperature and humidity sufficient to induce protein denaturation or fat oxidation, the method is simple to operate, does not need complex instruments and equipment, greatly shortens the detection time, and is rapid and efficient.

Description

Technical Field

[0001] The present invention relates to the technical field of dairy product detection, in particular to a method for detecting the stability of milk at room temperature. Background Art

[0002] UHT milk, also known as ambient temperature milk, is milk that has undergone ultra-high temperature instantaneous sterilization (UHT) and is then bottled under aseptic conditions, allowing it to be stored at room temperature for long periods of time. Due to its convenient storage and portability, ambient temperature milk is increasingly popular among consumers. However, ambient temperature milk has a long shelf life and can be affected by temperature fluctuations, light exposure, and other factors during storage and transportation, leading to decreased stability, resulting in fat buoyancy and protein precipitation, which in turn affects product quality and consumer experience.

[0003] Currently, the main methods for testing the stability of room-temperature milk include accelerated testing and long-term storage. The accelerated testing method accelerates the deterioration of milk by increasing temperature, light exposure, and other conditions, allowing its stability to be determined in a shorter period of time. However, this method suffers from difficulties in controlling test conditions, low accuracy of results, and the requirement for at least 30 days of storage and observation. The long-term storage method requires storing milk at room temperature for several months or even longer to observe its changes. This method is time-consuming and costly, and cannot meet the needs of rapid testing.

[0004] Therefore, there is an urgent need to develop a method for detecting the stability of milk at room temperature with controllable test conditions, high accuracy, short time consumption and low cost. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a method for detecting the stability of milk at room temperature, so as to solve the problems in the prior art.

[0006] To achieve the above-mentioned and other related purposes, the present invention provides a method for detecting the stability of milk at room temperature, the method comprising the following steps:

[0007] 1) Place the sample at a temperature and humidity sufficient to induce protein denaturation or fat oxidation, and observe whether the sample has any changes in appearance. If any changes are visible to the naked eye, the product does not meet the stability standards;

[0008] 2) The samples that did not change in appearance in step 1) were subjected to index testing, and the particle size (D50) of the samples was measured.

[0009] rate of change and centrifugal sedimentation rate;

[0010] 3) If the sample particle size change rate is less than 10% and the centrifugal sedimentation rate is less than 5%, the sample stability meets the standard.

[0011] As described above, the method for detecting the stability of milk at room temperature of the present invention has the following beneficial effects:

[0012] The method provided by the present invention no longer requires room temperature milk to undergo accelerated testing for at least 30 days to obtain preliminary test results. The stability test of room temperature milk can be completed in a short time (5 to 7 days), which greatly shortens the test time and is fast and efficient.

[0013] This method is simple to operate, does not require complex instruments and equipment, and is easy to promote and apply. Through qualitative observation and quantitative analysis, it can objectively and accurately reflect the stability of room temperature milk. DETAILED DESCRIPTION

[0014] The present invention provides a method for detecting the stability of milk at room temperature, the method comprising the following steps:

[0015] 1) Place the sample at a temperature and humidity sufficient to induce protein denaturation or fat oxidation, and observe whether the sample has any changes in appearance. If any changes are visible to the naked eye, the product does not meet the stability standards;

[0016] 2) The samples that did not change in appearance in step 1) were subjected to index testing, and the particle size (D50) of the samples was measured.

[0017] rate of change and centrifugal sedimentation rate;

[0018] 3) If the sample particle size change rate is less than 10% and the centrifugal sedimentation rate is less than 5%, the sample stability meets the standard.

[0019] In the present invention, the stability of the sample meets the standard means that the ambient temperature milk will not show visible system instability during its actual shelf life; the stability of the sample does not meet the standard means that the ambient temperature milk will show visible system instability during its actual shelf life. Specific system instability phenomena include but are not limited to stratification, precipitation, browning or gelation.

[0020] In certain embodiments of the present invention, in step 1), the temperature sufficient to induce protein denaturation or fat oxidation is 40-45°C.

[0021] In a preferred embodiment of the present invention, in step 1), the temperature sufficient to induce protein denaturation or fat oxidation is 40-43°C.

[0022] In certain embodiments of the present invention, in step 1), the humidity sufficient to induce protein denaturation or fat oxidation is 80-95% relative humidity.

[0023] In certain embodiments of the present invention, in step 1), the standing time is 5 to 7 days.

[0024] In certain embodiments of the present invention, in step 1), the appearance change includes a color change and a uniformity change.

[0025] In a specific embodiment of the present invention, the color change refers to a visible change in color compared to a reference product placed in a room temperature environment, specifically, the color of the product may be yellowing, browning, etc. compared to the reference product.

[0026] More specifically, any of the following indicators is detected. If any of the conditions is met, the color of the milk changes:

[0027] a) CIE b* value increases by ≥3.0 compared to the initial state;

[0028] b) 5-hydroxymethylfurfural (5-HMF) content ≥ 2.0 mg / kg;

[0029] c) The absorbance at 420 nm wavelength increases by ≥0.15.

[0030] In certain embodiments of the present invention, in step 1), the change in homogeneity includes surface stratification, bottom precipitation, or gelation. Specifically, surface stratification is manifested as an upper lipid-rich layer and a lower, thinner layer; bottom precipitation is manifested as particles or flocculent matter at the bottom; and gelation is manifested as the overall or partial formation of gel masses.

[0031] In certain embodiments of the present invention, in step 2), the median diameter of the particles is measured using a laser particle size analyzer.

[0032] In certain embodiments of the present invention, step 2) further includes setting a control group, and the calculation formula for the change rate of the particle diameter is as follows:

[0033] D50 change rate (%) = (D50x - D50con) / D50con × 100%

[0034] Wherein, D50x represents the median diameter of the particles of the experimental group samples obtained by the same detection method, in μm; D50con represents the median diameter of the particles of the control group samples obtained by the same detection method, in μm.

[0035] In certain embodiments of the present invention, in step 2), the calculation formula for the centrifugal sedimentation rate is as follows:

[0036] Centrifugal sedimentation rate = m 沉淀 / m 总 ×100%

[0037] Among them, m 沉淀 Indicates the mass of the precipitate obtained after centrifugation, in g; m 总 It represents the total mass of the sample before centrifugation, in g.

[0038] In certain embodiments of the present invention, in step 2), the sample is centrifuged when the centrifugal sedimentation rate is determined. When the amount of the centrifuged sample is 25-50 g, the centrifugal speed is 3000-5000 rpm; and the centrifugal time is 10-20 min.

[0039] In the present invention, the centrifugal speed and time can be flexibly adjusted according to the sample amount.

[0040] In certain embodiments of the present invention, in step 3), if the change rate of the mean diameter of the sample particle size is greater than 12% and the centrifugal sedimentation rate is greater than 6%, the stability of the test sample does not meet the standard.

[0041] In certain embodiments of the present invention, in step 3), if the sample median diameter change rate is 10-12% and the centrifugal sedimentation rate is less than 5%; or the median diameter change rate is less than 10% and the centrifugal sedimentation rate is 5-6%; or the median diameter change rate is 10-12% and the centrifugal sedimentation rate is 5-6%, then a 37°C accelerated stability test (i.e., standing at 37°C for 30 days) is performed to retest the stability.

[0042] The specific steps of the 37°C accelerated stability test are as follows: the sample is placed in a 37°C environment for 30 days. If there is no system instability, the stability of the ambient temperature milk meets the standards; if there is system instability, the stability of the ambient temperature milk does not meet the standards.

[0043] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention.

[0044] Before further describing the specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific specific embodiments described below; it should also be understood that the terms used in the examples of the present invention are for describing specific specific embodiments rather than for limiting the scope of protection of the present invention; in the present specification and claims, unless otherwise expressly stated herein, the singular forms "a", "an" and "the" include plural forms.

[0045] When the embodiments provide numerical ranges, it should be understood that, unless otherwise specified in the present invention, both endpoints of each numerical range and any numerical value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those generally understood by those skilled in the art. In addition to the specific methods, equipment, and materials used in the embodiments, according to the understanding of the prior art by those skilled in the art and the description of the present invention, any methods, equipment, and materials of the prior art similar or equivalent to the methods, equipment, and materials described in the embodiments of the present invention may also be used to implement the present invention.

[0046] Ambient temperature milk was purchased from Bright Dairy Co., Ltd. This study employed a controlled experimental design, with two treatment groups established: an experimental group and a control group. Each experiment was replicated three times (n = 3), and all data are presented as the mean of three independent replicates.

[0047] Example 1

[0048] The test method for the stability of milk at room temperature is as follows:

[0049] 1) Sample grouping: The samples were divided into two groups. The experimental group was placed under conditions of 40° C. and 95% relative humidity for 7 days, and the control group was not treated.

[0050] 2) Sample testing:

[0051] a) Appearance test: There was no significant change in the appearance of samples in the experimental and control groups;

[0052] b) Particle size median diameter test: The particle size median diameter of the experimental group samples was 0.35 μm, and the particle size median diameter of the control group samples was 0.32 μm, with a change rate of 9.4%;

[0053] c) Centrifugal Sedimentation Rate Test: 25 g of sample was centrifuged at 3000 rpm for 20 min. The centrifugal sedimentation rate of the experimental group sample was 3.2%, while that of the control group sample was 2.8%.

[0054] 3) Stability evaluation: According to the above test results, the change rate of the particle diameter is less than 10%, and the centrifugal sedimentation rate is less than 5%. The room temperature milk has good stability.

[0055] Example 2

[0056] The test method for the stability of milk at room temperature is as follows:

[0057] 1) Sample grouping: The samples were divided into two groups. The experimental group was placed under conditions of 43° C. and 80% relative humidity for 5 days, and the control group was not treated.

[0058] 2) Sample testing:

[0059] a) Appearance test: There was no significant change in the appearance of samples in the experimental and control groups;

[0060] b) Particle size median diameter test: The particle size median diameter of the experimental group samples was 0.344 μm, and the particle size median diameter of the control group samples was 0.32 μm, with a change rate of 7.5%;

[0061] c) Centrifugal Sedimentation Rate Test: 50 g of sample was centrifuged at 5000 rpm for 10 min. The centrifugal sedimentation rate of the experimental group sample was 2.9%, while that of the control group sample was 2.8%.

[0062] 3) Stability evaluation: According to the above test results, the change rate of the particle diameter is less than 10%, and the centrifugal sedimentation rate is less than 5%. The room temperature milk has good stability.

[0063] Example 3

[0064] The test method for the stability of milk at room temperature is as follows:

[0065] 1) Sample grouping: The samples were divided into two groups. The experimental group was placed under conditions of 40° C. and 90% relative humidity for 5 days, and the control group was not treated.

[0066] 2) Sample testing:

[0067] a) Appearance test: There was no significant change in the appearance of the samples in the control group, while the liquid surface of the sheared bags in the experimental group showed stratification.

[0068] 3) Stability assessment: Based on the appearance test results, the room temperature milk has poor stability.

[0069] Example 4

[0070] The test method for the stability of milk at room temperature is as follows:

[0071] 1) Sample grouping: The samples were divided into two groups. The experimental group was placed under conditions of 43° C. and 80% relative humidity for 5 days, and the control group was not treated.

[0072] 2) Sample testing:

[0073] a) Appearance test: There was no significant change in the appearance of samples in the experimental and control groups;

[0074] b) Particle size median diameter test: The particle size median diameter of the experimental group samples was 0.358 μm, and the particle size median diameter of the control group samples was 0.32 μm, with a change rate of 11.9%;

[0075] c) Centrifugal Sedimentation Rate Test: 50 g of sample was centrifuged at 3000 rpm for 15 min. The centrifugal sedimentation rate of the experimental group sample was 4.8%, while that of the control group sample was 2.8%.

[0076] 3) Stability evaluation: According to the above test results, the particle size median diameter change rate of the sample was higher than 10%, but not higher than 12%. Therefore, the sample was retested for stability according to the 37°C accelerated stability test.

[0077] Example 5

[0078] The test method for the stability of milk at room temperature is as follows:

[0079] 1) Sample grouping: The samples were divided into two groups. The experimental group was placed under conditions of 40° C. and 80% relative humidity for 7 days, and the control group was not treated.

[0080] 2) Sample testing:

[0081] a) Appearance test: There was no significant change in the appearance of samples in the experimental and control groups;

[0082] b) Particle size median diameter test: The particle size median diameter of the experimental group samples was 0.35 μm, and the particle size median diameter of the control group samples was 0.32 μm, with a change rate of 9.4%;

[0083] c) Centrifugal Sedimentation Rate Test: 50 g of sample was centrifuged at 4000 rpm for 20 min. The centrifugal sedimentation rate of the experimental group sample was 6.5%, while that of the control group sample was 2.8%.

[0084] 3) Stability evaluation: According to the above test results, the change rate of the median diameter of the particle size is less than 10%, but the centrifugal sedimentation rate is higher than 5% and higher than 6%, so the sample stability is poor.

[0085] The above examples are intended to illustrate the embodiments disclosed herein and are not to be construed as limiting the present invention. In addition, the various modifications listed herein and variations of the methods in the invention will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. Although the present invention has been specifically described in conjunction with various specific preferred embodiments of the present invention, it should be understood that the present invention should not be limited to these specific embodiments. In fact, various modifications apparent to those skilled in the art as described above to obtain the invention should be included within the scope of the present invention.

Claims

1. A method for detecting the stability of milk at room temperature, characterized in that: The detection method comprises the following steps: 1) Place the sample at a temperature and humidity sufficient to induce protein denaturation or fat oxidation, and observe whether the sample has any changes in appearance. If any changes are visible to the naked eye, the product does not meet the stability standards; 2) performing index testing on the samples that did not change in appearance in step 1), respectively measuring the particle size median diameter change rate and centrifugal sedimentation rate of the samples; 3) If the sample particle size change rate is less than 10% and the centrifugal sedimentation rate is less than 5%, the sample stability meets the standard.

2. The method according to claim 1, characterized in that The temperature sufficient to induce protein denaturation or fat oxidation is 40-45°C.

3. The method according to claim 1, characterized in that The humidity sufficient to induce protein denaturation or fat oxidation is 80-95% relative humidity.

4. The method according to claim 1, wherein The standing time is 5 to 7 days.

5. The method according to claim 1, wherein The change in appearance includes a change in color and / or a change in uniformity.

6. The method according to claim 5, characterized in that The change in homogeneity includes stratification of the liquid surface, precipitation at the bottom or gelation.

7. The method according to claim 1, characterized in that When determining the centrifugal sedimentation rate, the sample is centrifuged. When the amount of sample to be centrifuged is 25 to 50 g, the centrifugation includes any one or more of the following characteristics: a) The speed of centrifugation is 3000-5000 rpm; b) The centrifugation time of the centrifugation treatment is 10 to 20 minutes.

8. The method according to claim 1, characterized in that In step 3), if the change rate of the mean diameter of the sample particle size is greater than 12% and the centrifugal sedimentation rate is greater than 6%, the stability of the sample does not meet the standard.

9. The method according to claim 1, characterized in that If the sample's particle size median diameter change rate and centrifugal sedimentation rate have any of the following conditions, the 37°C accelerated stability test shall be used to test its stability: a) The mean diameter change rate of the sample particle size is 10-12%, and the centrifugal sedimentation rate is less than 5%; b) The change rate of the particle size median diameter is less than 10%, and the centrifugal sedimentation rate is 5-6%; c) The change rate of the mean diameter of the particles is 10-12%, and the centrifugal sedimentation rate is 5-6%.

10. The method according to claim 9, characterized in that The 37°C accelerated stability test is to place the sample in a 37°C environment for 30 days. If no system instability occurs, the stability of the ambient temperature milk meets the standard; if system instability occurs, the stability of the ambient temperature milk does not meet the standard.