TWI519783B - Detection of Protein Thermal Stability in Milk Powder - Google Patents

Description

Method for detecting protein thermal stability in milk powder

The invention relates to the field of processing dairy products, in particular to a method for detecting the thermal stability of proteins in milk powder.

Milk-containing beverages are made from fresh milk or dairy products, which are fermented or unfermented. Because of their rich nutrients and unique taste, they are well received by consumers. However, due to the regional nature of dairy cows and other dairy farms, the production of fresh milk is subject to geographical restrictions. Because of the short shelf life of fresh milk products, it is necessary to carry out the corresponding process as soon as possible to complete the production of the products. Therefore, the milk of non-fresh milk producing areas Product processing enterprises generally use dairy products such as whole milk powder and skim milk powder as raw materials for processing milk-containing beverages. The product obtained by blending and ultra-high temperature transient sterilization (UHT) using dairy products such as whole milk powder and skim milk powder as raw materials is called a reconstituted milk product.

When the reconstituted milk product is subjected to UHT treatment during processing, the protein in the raw milk powder is easily denatured to form a precipitate under high temperature conditions, and adheres to the leaves or pipes of the sterilization device by mineral interaction to generate scale, and the pressure in the sterilization equipment system It will increase with the increase of the degree of fouling on the heated surface. When the pressure in the system rises to a certain extent, it will affect the heat transfer during the sterilization process, reduce the heat treatment efficiency, and finally reduce the protein index and the microorganisms in the product. The breeding has deteriorated, forcing production to be suspended, and intermediate cleaning (AIC) of the sterilization equipment. When the milk powder with excellent thermal stability of protein is used as a raw material, the sterilization equipment can be operated continuously for at least 6 hours. When the milk powder with poor thermal stability of the protein is used as the raw material, the sterilization equipment generally only needs to run A1.5 for 1.5~5h, which means that the protein is heat stabilized. Production of poorly defined milk powder will increase production costs. Therefore, the protein thermal stability of the milk powder can directly affect the continuous operation time of the sterilization equipment, the number of AICs, and the production cost.

In actual production, the thermal stability of proteins of different brands or different batches of milk powder may vary. Therefore, how to quickly select the milk powder with excellent thermal stability of protein in different brands or different batches of milk powder to carry out corresponding production, prolong the continuous operation time, reduce the number of AIC, and thus reduce the corresponding production cost, and become an urgent enterprise for dairy products processing. Demand. However, the current national standards for dairy products do not make special provisions for the thermal stability of proteins, and there is no publicly available method for quickly and accurately detecting the thermal stability of proteins in milk powder. Therefore, it provides a rapid and accurate method for detecting milk powder. The method of protein thermal stability has important practical significance.

In view of this, the present invention provides a method for detecting protein thermal stability in milk powder. The detection method has the advantages of simple detection device and low cost, and can quickly and accurately detect the stability of the protein in the milk powder, reduce the cost of the intermediate cleaning, and improve the production efficiency.

In order to achieve the above object, the present invention provides the following technical solution: The present invention provides a method for detecting protein thermal stability in milk powder, comprising the following steps: Step A: mixing milk powder with water to obtain a first sample solution; Step B The first sample solution is sealed in a stainless steel device, preheated at 50-90 ° C for 5-10 min, and subjected to high temperature treatment at 120-150 ° C for 5-15 min. After cooling and centrifugation, a second sample is obtained. Solution; Step C: obtaining the scaling rate of the milk powder according to the volume of the first sample solution and the second sample solution; the scaling rate of the milk powder = (the volume of the first sample solution - the volume of the second sample solution) / The volume of a sample solution × 100%; the scaling rate of milk powder <2.00%, the protein thermal stability is excellent; 2.00% The scaling rate of milk powder is <3.68%, the thermal stability of protein is general; the scaling rate of milk powder 3.68%, its protein has poor thermal stability.

The detection method provided by the invention adopts a specially designed stainless steel pipe material, and can accurately detect the thermal stability of the protein in the milk powder by accurately simulating the process of ultra-high temperature sterilization treatment.

In order to ensure the accuracy of the detection result, preferably, the weight percentage of the protein content of the milk powder in the first sample solution ranges from 3% to 7%.

The blades and pipelines of the ultra-high temperature sterilization device are made of stainless steel. In order to accurately compare the working state of the ultra-high temperature sterilization equipment, the invention uses stainless steel equipment to heat-treat the milk powder reconstituted milk sample. In some embodiments provided by the present invention, the stainless steel device is a stainless steel tube.

In some embodiments provided by the present invention, the stainless steel tubing is a specially designed stainless steel tubing. Stainless steel tubing includes stainless steel body, silicone gasket, stainless steel gasket and stainless steel spiral seal.

In the case of ultra-high temperature sterilization, the presence of gas adversely affects the processing of dairy products, and in actual production, degassing is required. In order to accurately simulate the ultra-high temperature sterilization process and ensure that the detection result is closer to the actual production, in some embodiments provided by the present invention, the first sample solution is sealed in the stainless steel device in step B to maintain the state of the full tube. Do not create voids in it.

Preferably, the heating medium treated in the high temperature in step B is a boiling point A fluid that does not generate smoke and coke at 300 ° C under continuous high temperature heating.

In some embodiments provided by the present invention, the heating medium treated in the high temperature in step B is methyl eucalyptus oil.

In order to ensure that the milk powder is sufficiently dissolved in water to obtain a reconstituted milk, preferably, the temperature of the water used to prepare the first sample solution in the step A is 50 to 70 °C.

In order to ensure the quality of the product and reduce the generation of scale, when preparing the reconstituted milk product in actual production, the water is preferably deionized water. In order to accurately simulate the ultra-high temperature sterilization process, the detection result is closer to the actual production, and the present invention provides In some embodiments, preferably, the water in which the first sample solution is formulated is deionized water.

In order to ensure that the milk powder is sufficiently dissolved in water to obtain reconstituted milk, in some embodiments provided by the present invention, the mixing in step A is specifically carried out at 50 to 70 ° C and 300 to 500 rpm / min for 8 to 12 minutes.

In some embodiments provided by the present invention, the cooling in step B is specifically to rapidly cool the first sample solution subjected to pre-heat treatment and high temperature treatment to 15 to 25 ° C with flowing water of 15 to 25 ° C.

In order to separate the protein precipitate, centrifugation is required. In some embodiments provided by the present invention, the centrifugation in step B is specifically carried out by centrifugation for 4-6 minutes under conditions of a relative centrifugal force of 140-180 g.

In some embodiments provided by the present invention, the milk powder is selected from whole milk powder or skimmed milk powder.

The invention provides a method for detecting the thermal stability of proteins in milk powder. The method comprises: mixing milk powder with water to obtain a first sample solution; taking the first sample solution sealed in a stainless steel device, preheating at 50 to 90 ° C for 5 to 10 minutes, at 120 to 150 ° C After high temperature treatment for 5~15min, the second sample solution is obtained by cooling and centrifugation; according to the volume of the first sample solution and the second sample solution, the scaling rate of the milk powder is obtained; the scaling rate of the milk powder=(the first sample) Volume of solution - volume of second sample solution / volume of first sample solution × 100%; fouling rate of milk powder <2.00%, excellent protein thermal stability; 2.00% The scaling rate of milk powder is <3.68%, the thermal stability of protein is general; the scaling rate of milk powder 3.68%, its protein has poor thermal stability. It can be seen from the protein thermal stability test in milk powder that the protein thermal stability of the milk powder standard can be accurately detected by the detection method provided by the present invention, and the thermal stability of the protein in the milk powder standard detected by the detection method provided by the invention is Actually consistent; the milk powder with excellent thermal stability of the protein detected by the detection method provided by the invention can continuously run for 5 hours, and the milk powder with poor thermal stability of the protein detected by the detection method provided by the invention can be used. The ultra-high temperature sterilization equipment has a continuous operation time of only 4.57h. The results show that the thermal stability of the milk powder protein detected by the detection method provided by the invention is consistent with the actual production, and the existing detection technology cannot accurately detect the protein thermal stability in the milk powder. Sexuality, the existing detection technology is less practical in actual production. It can be seen that the detection method provided by the invention has the advantages of simple detection device and low cost, can quickly and accurately detect the thermal stability of the protein in the milk powder, reduce the cost of the intermediate cleaning, and improve the production efficiency.

The invention discloses a method for detecting the thermal stability of proteins in milk powder, and those skilled in the art can learn from the contents of the paper and appropriately improve the process parameters. It is to be understood that all such alternatives and modifications are obvious to those skilled in the art and are considered to be included in the present invention. The method and the application of the present invention have been described by the preferred embodiments, and it is obvious that the method and application described herein may be modified or appropriately modified and combined without departing from the scope of the present invention. The technique of the present invention is applied.

The milk powder and the device used in the method for detecting the thermal stability of the protein in the milk powder of the present invention are commercially available; among them, the stainless steel pipe can be purchased from the market or can be referred to the literature (SOMMER, H. H. AND HART, E. B. The heat coagulation of milk. J. Biol. Chem., 40: 137-151.1919.) Designed.

The present invention is further illustrated below in conjunction with the embodiments:

Example 1 Test of protein thermal stability in whole milk powder standard

Three full-fat milk powder standards of known protein thermal stability were obtained. Among them, the standard A had excellent protein thermal stability, the standard B had high protein thermal stability, and the standard C had poor thermal stability. The content of protein in the standard was measured, and the results showed that the weight percentage of the protein content in the three standards was 25%. Weigh 30g of each of the above standards, weigh 220g of water at 50°C, slowly add the weighed standard to the water with an IKA mixer at 300rpm, stir for 12min, and obtain the protein content after the standard is completely dissolved. The first sample solution A, the first sample solution B, and the first sample solution C are 3% by weight. Wherein, the first sample solution A is prepared from the standard product A, the first sample solution B is prepared from the standard product B, and the first sample solution C is prepared from the standard product C.

Pour the first sample solution A, the first sample solution B, and the first sample solution C into the stainless steel pipe body, respectively, to maintain the full pipe state, without causing voids therein, and sequentially installing the rubber gasket, the stainless steel gasket, and The stainless steel spiral sealing cover makes the stainless steel pipe sealed and is set to repeat twice. The stainless steel tubing used is commercially available. The stainless steel pipe containing the first sample solution A, the first sample solution B, and the first sample solution C is placed in a heating device at 50 ° C for preheat treatment for 10 minutes, taken out and placed in a constant temperature device for high temperature. The heating medium of the constant temperature equipment is methyl eucalyptus oil, the set temperature is 120 ° C, and the high temperature treatment time is 15 min. After the end of the heating, the high-temperature treated stainless steel pipe was quickly taken out, and the temperature of the stainless steel pipe was quickly lowered to 15 ° C with flowing water at 15 °C. Open the stainless steel spiral sealing cap of stainless steel pipe, pour out the sample solution treated above in the centrifuge tube, carry out quantitative centrifugation at 160g, 6min, take the upper clear liquid in another centrifuge tube, and perform another 160g, 6min quantitative centrifugation to take the upper layer. The clear liquid is respectively obtained into the second sample solution A, the second sample solution B, and the second sample solution C, and is quantified to calculate the fouling ratio, and the fouling ratio = (the volume of the first sample solution - the second sample solution Volume) / volume of the first sample solution × 100%, the results are shown in Table 1.

It can be seen from the above test results that the average rate of the scale of the standard A is 1.00% and less than 2.00%, and the protein is excellent in thermal stability by the detection method provided by the present invention, and the detection result is in accordance with the actuality.

The average fouling rate of Standard B was 2.20%, and between 2.00% and 3.68%, the thermal stability of the protein was generally detected by the detection method provided by the present invention, and the results of the detection were consistent with the actual conditions.

The average fouling rate of the standard C was 4.02%, which was greater than 3.68%. The detection method provided by the present invention was used to detect the poor thermal stability of the protein, and the detection result was consistent with the actuality.

It can be seen that the detection method provided by the invention can accurately detect the thermal stability of protein in whole milk powder.

Example 2 Test of Protein Thermal Stability in Skim Milk Powder Standards

Three non-fat milk powder standards with known protein thermal stability were obtained. Among them, the standard D has excellent protein thermal stability, the standard E has good protein thermal stability, and the standard F has poor protein thermal stability. The amount of protein in the standard was measured and the results showed that the weight percentage of the protein content in the three standards was 32%. Weigh 28g of each of the above standards, weigh 100g of water at 70°C, slowly add the weighed standard to the water with an IKA mixer at 500rpm, stir for 8min, and obtain the protein content after the standard is completely dissolved. The first sample solution D, the first sample solution E, and the first sample solution F are 7% by weight. Wherein, the first sample solution D is prepared from the standard product D, the first sample solution E is prepared from the standard product E, and the first sample solution F is prepared from the standard product F.

Pour the first sample solution D, the first sample solution E, and the first sample solution F into the stainless steel tube body, respectively, to maintain the full tube state, without causing voids therein, and sequentially installing the silicone gasket, the stainless steel gasket, and The stainless steel spiral sealing cover makes the stainless steel pipe sealed and is set to repeat twice. The stainless steel tubing used was designed as a reference (SOMMER, H. H. AND HART, E. B. The heat coagulation of milk. J. Biol. Chem., 40: 137-151.1919.). The stainless steel pipe containing the first sample solution D, the first sample solution E, and the first sample solution F is placed in a heating device at 90 ° C for preheat treatment for 5 minutes, taken out and placed in a constant temperature device for high temperature. The heating medium of the constant temperature equipment is methyl eucalyptus oil, the set temperature is 150 ° C, and the high temperature treatment time is 5 min. Immediately after the end of the heating, the high-temperature treated stainless steel pipe was taken out, and the temperature of the stainless steel pipe was quickly lowered to 25 ° C with flowing water at 25 ° C. Open the stainless steel spiral sealing cap of stainless steel pipe, pour out the sample solution treated above in the centrifuge tube, carry out quantitative centrifugation at 180g, 4min, take the upper layer clear liquid in another centrifuge tube, and perform 180g, 4min quantitative centrifugation again, take the upper layer The clarified liquid obtains the second sample solution D, the second sample solution E, and the second sample solution F, respectively, and quantifies the scale ratio, and the fouling ratio = (the volume of the first sample solution - the second sample solution Volume) / volume of the first sample solution × 100%, the results are shown in Table 2.

It can be seen from the above test results that the average fouling rate of the standard D is 0.86% and less than 2.00%. The detection method provided by the present invention is excellent in thermal stability of the protein, and the detection result is consistent with the actual one.

The average fouling rate of the standard E was 2.47%, and between 2.00% and 3.68%, the thermal stability of the protein was generally detected by the detection method provided by the present invention, and the detection result was consistent with the actuality.

The average fouling rate of the standard F was 3.88%, which was greater than 3.68%. The detection method provided by the present invention was used to detect the poor thermal stability of the protein, and the detection result was consistent with the actuality.

It can be seen that the detection method provided by the invention can accurately detect the thermal stability of protein in skim milk powder.

Example 3 Test of protein thermal stability in whole milk powder

Take 3 different brands of whole milk powder, brand G, brand H, brand I, and test its protein content. The results show that the protein content of brand G, brand H, brand I whole milk powder is 25%, 24.8%, respectively. 24.5%. Weigh 50g brand G whole milk powder, weigh 200g 70°C water, stir with IKA At 400 rpm, the brand G whole milk powder was slowly added to water and stirred for 10 min. After completely dissolved, a first sample solution G with a protein content of 5% by weight was obtained; 50 g of brand H full fat was weighed. Milk powder, weigh 198g water at 70°C, slowly add brand H whole milk powder to water with IKA mixer at 400rpm, stir for 10min, after completely dissolved, get the same weight percentage of protein content as 5% Product solution H; weigh 50g brand I whole milk powder, weigh 195g water at 70 °C, use brand I I blender at 400rpm, slowly add brand I whole milk powder to water, stir for 10min, after completely dissolved, get protein The first sample solution I is 5% by weight of the content.

Pour the first sample solution G, the first sample solution H, and the first sample solution I into the stainless steel tube body, respectively, to maintain the full tube state, without causing voids therein, and sequentially installing the silicone gasket, the stainless steel gasket, and The stainless steel spiral sealing cover makes the stainless steel pipe sealed and is set to repeat twice. The stainless steel tubing used was designed as a reference (SOMMER, H. H. AND HART, E. B. The heat coagulation of milk. J. Biol. Chem., 40: 137-151.1919.). The stainless steel pipe containing the first sample solution G, the first sample solution H, and the first sample solution I is placed in a heating device at 70 ° C for preheat treatment for 8 minutes, taken out and placed in a constant temperature device for high temperature. The heating medium of the constant temperature equipment is methyl eucalyptus oil, the set temperature is 135 ° C, and the high temperature treatment time is 10 min. After the end of the heating, the high-temperature treated stainless steel pipe was quickly taken out, and the temperature of the stainless steel pipe was rapidly lowered to 20 ° C with flowing water at 20 ° C. Open the stainless steel spiral sealing cap of the stainless steel pipe, pour out the sample solution treated above in the centrifuge tube, carry out quantitative centrifugation at 160g, 5min, take the upper layer clear liquid in another centrifuge tube, and perform another 160g, 5min quantitative centrifugation to take the upper layer. The clarification liquid obtains the second sample solution G, the second sample solution H, and the second sample solution I, respectively, and quantifies the scale ratio, and the fouling ratio = (the volume of the first sample solution - the second sample solution Volume) / volume of the first sample solution × 100%, the results are shown in Table 3.

The continuous execution time of the ultra-high temperature sterilization equipment in actual production can directly reflect the thermal stability of the protein in the milk powder. If the continuous operation time of the ultra-high temperature sterilization equipment exceeds 6h, it can be judged that the protein thermal stability of the batch of milk powder is excellent; the continuous operation time of the ultra-high temperature sterilization equipment is 4h~6h, then the protein thermal stability of the batch of milk powder can be determined to be general; When the continuous operation time of the high-temperature sterilization equipment is below 4h, it can be judged that the protein thermal stability of the batch of milk powder is poor. The whole milk powder of the above three different brands (brand G, brand H, brand I) was put into the production of reconstituted milk with a protein content of 2.3%, and the ultra-high temperature sterilization equipment was continuously sterilized at 138 ° C for 4 s, when the proportion of steam When the valve is fully open and the sterilization temperature is less than 138 °C, the time for continuous operation of the ultra-high temperature sterilization equipment is recorded. The results are shown in Table 3.

It can be seen from the above test results that the average fouling rate of the brand G is 1.16%, and the detection method provided by the invention is excellent in thermal stability of the protein, and the ultra-high temperature sterilization equipment can be continuously operated for 7.54 h.

The average fouling rate of brand H is 1.92%. The detection method provided by the invention is excellent in thermal stability of the protein, and the ultra-high temperature sterilization equipment can be continuously operated for 6.08h.

The average fouling rate of brand I is 3.68%. The detection method provided by the invention detects that the protein has poor thermal stability, and the ultra-high temperature sterilization equipment can only run continuously for 4.57h.

It can be seen that the detection method provided by the invention can accurately detect the thermal stability of protein in whole milk powder.

Comparative Example 1 Test of protein thermal stability in whole milk powder

The whole milk powder of the three brands (brand G, brand H, brand I) in Example 3 was taken, and the thermal stability of the protein was detected by the existing detection method.

The specific detection method is as follows: Firstly, the protein content of the whole brand milk powder of three brands (brand G, brand H, brand I) is detected, and the results show that the weight percentage of the protein content of the three brands is 25%. Weigh 80g of each whole milk powder mentioned above, weigh 320g, 50°C water, slowly add the weighed standard to the water with IKA mixer at 400rpm, and obtain the weight percentage of protein content after the standard product is completely dissolved. It is a 5% whole milk powder solution. The whole milk powder solution was hydrated at 400 rpm for 10 min. 100 g of each whole milk powder solution was poured into three 250 mL serum bottles, and the outer lid was screwed to prepare three parallel whole milk powder solutions for use. The parameters of the experimental high-temperature autoclave were set to 90 ° C, 45 min, and the model of the high-temperature autoclave was: STURDY sa-300 vl. Three parallel whole milk powder solutions were processed in a high temperature autoclave at 90 ° C for 45 min. When the autoclave was cooled to below 70 ° C, the serum bottle was taken out, and the whole milk powder solution was taken up in a 10 mL sterile syringe and slowly dropped into a dosing cylinder containing 500 mL of water. The detection standard is as follows: after the whole milk powder solution is treated by high temperature and high pressure, it is dropped into a cylinder of 500 mL water by a syringe, and the whole milk powder solution is quickly and evenly dispersed in water, and the protein has excellent thermal stability; the whole milk powder solution It can be evenly dispersed in water, and the small granular coagulum visible in the naked eye is suspended therein, and the protein has thermal stability. The whole milk powder solution has serious flocculation phenomenon, the syringe is difficult to drip, and the flocculation quickly settles in the water when dripping. , its protein thermal stability is poor; whole milk powder soluble The tofu is agglomerated in the liquid, which can not be dispersed when dropped into water. The tofu flower-like agglomeration quickly settles to the bottom of the water, and its protein has poor thermal stability.

The test results show that the whole milk powder of three brands (brand G, brand H, brand I) is treated with high temperature and high pressure, and then dropped into a cylinder of 500 mL water by a syringe, and the whole milk powder solution can be quickly and evenly dispersed. In the water, the above-mentioned detection method was used to detect that the protein thermal stability of the brand G, brand H, and brand I whole milk powder was excellent.

In actual production, when the brand G is used to produce a reconstituted milk with a protein content of 2.3%, the ultra-high temperature sterilization equipment can be continuously operated for 7.54 h; when the brand H is used to produce a reconstituted milk with a protein content of 2.3%, the ultra-high temperature sterilization equipment can be continuously Running 6.08h; when using brand I to produce reconstituted milk with a protein content of 2.3%, the ultra-high temperature sterilization equipment can only run continuously for 4.57h, which shows that there are some differences in the scaling rate of the three brands of whole milk powder, inferring 3 There is also a certain difference in the stability of proteins in a brand of whole milk powder.

It can be seen that the above detection method cannot accurately detect the protein thermal stability of the milk powder, and the utility is low in actual production.

The above embodiments are intended to be illustrative only, and are not intended to limit the scope of the present invention. It is included in the scope of the following patent application.

Claims (10)

A method for detecting protein thermal stability in milk powder comprises the following steps: Step A: mixing milk powder with water to obtain a first sample solution; Step B: taking the first sample solution sealed in a stainless steel device at 50~ Preheating at 90 °C for 5~10min, high temperature treatment at 120~150°C for 5~15min, cooling and centrifugation to obtain second sample solution; Step C: according to the first sample solution and The volume of the second sample solution is obtained, and the fouling rate of the milk powder is obtained; the fouling rate of the milk powder = (the volume of the first sample solution - the volume of the second sample solution) / the volume of the first sample solution × 100%; the scale of the milk powder is <2.00%, and the protein thermal stability is excellent; 2.00% The scaling rate of the milk powder is < 3.68%, and the thermal stability of the protein is generally; the scaling rate of the milk powder 3.68%, its protein has poor thermal stability. The method for detecting the thermal stability of protein in the milk powder according to the first aspect of the invention, wherein the weight percentage of the protein content of the milk powder in the first sample solution ranges from 3% to 7%. The method for detecting the thermal stability of protein in a milk powder according to claim 1, wherein the stainless steel device is a stainless steel pipe. The method for detecting thermal stability of protein in a milk powder according to claim 3, wherein the stainless steel pipe comprises a stainless steel pipe body, a rubber gasket, a stainless steel gasket and a stainless steel spiral sealing cover. The method for detecting the thermal stability of protein in the milk powder according to the first aspect of the patent application, wherein the heating medium of the high temperature treatment in the step B is a boiling point A fluid that does not generate smoke and coke at 300 ° C under continuous high temperature heating. The method for detecting the thermal stability of protein in the milk powder according to the first aspect of the patent application, wherein the temperature of the water in the step A is 50 to 70 °C. The method for detecting the thermal stability of the protein in the milk powder according to the first aspect of the patent application, wherein the mixing in the step A is specifically carried out at 50 to 70 ° C and 300 to 500 rpm/min for 8 to 12 minutes. The method for detecting the thermal stability of protein in the milk powder according to the first aspect of the patent application, wherein the cooling in the step B is specifically cooled to 15 to 25 ° C with flowing water of 15 to 25 ° C. The method for detecting the thermal stability of the protein in the milk powder according to the first aspect of the patent application, wherein the centrifugation in the step B is specifically carried out by centrifugation for 4 to 6 minutes under the condition of a relative centrifugal force of 140 to 180 g. The method for detecting the thermal stability of protein in a milk powder according to claim 1, wherein the milk powder is selected from the group consisting of whole milk powder or skim milk powder.