High-efficiency and low-energy-consumption liquid milk sterilization method

Abstract

The invention discloses a high-efficiency and low-energy-consumption liquid milk sterilization method, and belongs to the technical field of dairy product processing. The high-efficiency and low-energy-consumption liquid milk sterilization method comprises the following steps: carrying out heat treatment sterilization on raw milk to be sterilized at 60-70 DEG C for 13-18 seconds, and rapidly cooling to 4-10 DEG C; then enabling the raw milk to pass through a 1-5m streaming type ultraviolet sterilization device at the flow speed of 5.5-6.5 L / h to obtain sterilized raw milk. According to the method disclosed by the invention, the heat treatment strength of sterilization of the raw milk is reduced by combining a proper amount of ultraviolet radiation, so that the aim of reducing the energy consumption of sterilization of the milk is fulfilled while the sterilization effect of the raw milk is ensured, active ingredients in the milk are reserved and obvious protein oxidation is avoided.

Description

TECHNICAL FIELD

[0001] The application relates to a high-efficiency and low-energy liquid milk sterilization method, and belongs to the technical field of dairy product processing. BACKGROUND

[0002] Fresh milk contains rich bioactive substances and has important physiological functions in enhancing human immunity, especially for the newborn population. However, due to its rich nutritional composition, fresh milk is also easy to become a substrate for the growth and reproduction of microorganisms. At present, heat treatment is widely used in the dairy industry as the main sterilization method, which effectively kills microorganisms and eliminates pathogenic bacteria through high-temperature action, thereby prolonging the shelf life of cow milk. Common industrial heat treatment methods include pasteurization (72-85℃, 15s), high-temperature instantaneous sterilization (≥135℃, 4-7s), spray drying, and other shelf life extension treatments.

[0003] However, during the heat treatment process, heat-sensitive components in milk are prone to change, leading to loss of heat-sensitive components, protein denaturation and aggregation, Maillard reaction, and further affecting the biological activity, sensory properties and digestive performance of milk protein. In addition, the existing heat sterilization process usually relies on electricity or fuel to generate heating steam, and water is used as the heat exchange medium to complete the heating sterilization and cooling process of cow milk through “indirect heat exchange”. This method not only has high energy consumption, but also produces a large amount of wastewater, causing environmental burden.

[0004] Non-thermal treatment technology generally refers to a processing method that achieves effective sterilization at ambient temperature or sub-lethal temperature. With the development of emerging food processing technologies, these processes not only meet the needs of consumers for safe, healthy and minimally processed foods, but also have the advantages of environmental friendliness, strong sustainability, low energy consumption and low water consumption. In recent years, new non-thermal sterilization technologies such as high-pressure processing (HPP), ultraviolet radiation (UV-C), pulsed electric field (PEF) and cold plasma have received extensive research attention.

[0005] The wavelength range of ultraviolet radiation is 100-400 nm, and its penetration is strong. The sterilization effect varies significantly with different wavelengths and can be generally divided into four wavebands: UV-A (320-400 nm), UV-B (280-320 nm), UV-C (200-280 nm) and UV-D (100-200 nm). Among them, the UV-C waveband, also known as short-wave sterilization ultraviolet, has the strongest sterilization ability, especially when the wavelength is about 253.7 nm. Ultraviolet radiation can damage the DNA structure of microorganisms, making them rapidly inactivated or lose the ability to reproduce, thereby achieving efficient sterilization. As a pure physical sterilization method, ultraviolet radiation technology has the advantages of high efficiency, simple equipment structure, low cost, broad-spectrum sterilization and easy control. However, excessive ultraviolet radiation may also cause oxidation of proteins and other components in milk, which has an adverse effect on the quality of cow milk.

[0006] Therefore, how to reduce the heat treatment intensity or the ultraviolet irradiation intensity while ensuring the sterilization effect, maximize the retention of natural active ingredients in milk, and reduce energy consumption has become one of the key problems to be solved in the current dairy industry. SUMMARY

[0007] [TECHNICAL PROBLEM] The current milk sterilization process has the problems of serious loss of active protein and high energy consumption.

[0008] [TECHNICAL SCHEME] To solve the above problems, the present application provides a high-efficiency and low-energy consumption liquid milk sterilization method. Specifically, the present application reduces the heat treatment intensity of raw milk sterilization by combining with appropriate dose of ultraviolet irradiation, while ensuring the sterilization effect of raw milk, retaining active ingredients in milk, avoiding significant protein oxidation, and achieving the goal of reducing the energy consumption of milk sterilization.

[0009] The first object of the present application is to provide a high-efficiency and low-energy consumption liquid milk sterilization method, comprising the following steps: The raw milk to be sterilized is subjected to heat treatment sterilization at 60-70℃ for 13-18s and rapidly cooled to 4-10℃, and then passed through a 1-5m flow type ultraviolet sterilization device at a flow rate of 5.5-6.5L / h to obtain sterilized raw milk.

[0010] In an embodiment of the present application, the above parameters are adapted to 20L of raw milk to be sterilized. If the amount of raw milk to be sterilized is increased, the parameters also need to be adjusted.

[0011] In an embodiment of the present application, the heat treatment sterilization is 60℃ heat treatment sterilization for 15s, and the flow type ultraviolet sterilization device is 3m.

[0012] In an embodiment of the present application, the heat treatment sterilization is 65℃ heat treatment sterilization for 15s, and the flow type ultraviolet sterilization device is 2m.

[0013] In an embodiment of the present application, the heat treatment sterilization is 70℃ heat treatment sterilization for 15s, and the flow type ultraviolet sterilization device is 1m.

[0014] In an embodiment of the present application, the flow type ultraviolet sterilization device is disclosed in patent CN 112167337B.

[0015] In one embodiment of the present application, the power of the ultraviolet lamp in the flow-around ultraviolet sterilization device is 27 W, the outer diameter of the quartz sleeve is 23 mm; a PFA tube with an inner diameter of 1.5 mm and an outer diameter of 2.0 mm is selected; each winding of 1 m of the PFA tube is taken as a sterilization area; and the corresponding ultraviolet irradiation doses of 1 m, 2 m, 3 m, 4 m and 5 m are 15.11 mJ / cm 2 , 30.22 mJ / cm 2 , 45.33 mJ / cm 2 , 60.44 mJ / cm 2 , and 75.55 mJ / cm 2 , respectively.

[0016] In one embodiment of the present application, the heat treatment sterilization is performed by using a tube plate combined ultrahigh temperature sterilization machine.

[0017] In one embodiment of the present application, the sterilization refers to killing pathogenic bacteria such as Escherichia coli, Staphylococcus aureus and Enterobacter sakazakii.

[0018] The second object of the present application is raw cow milk after sterilization prepared by the method.

[0019] In one embodiment of the present application, the raw cow milk after sterilization retains active ingredients in milk and does not cause significant protein oxidation.

[0020] The third object of the present application is to provide a method for ensuring the sterilization effect of raw cow milk and retaining active ingredients in milk, which comprises the following steps: The raw cow milk to be sterilized is subjected to heat treatment sterilization at 60-70℃ for 13-18 s, and then rapidly cooled to 4-10℃; and then passed through a flow-around ultraviolet sterilization device with a flow rate of 5.5-6.5 L / h and a length of 1-5 m to obtain the raw cow milk after sterilization.

[0021] In one embodiment of the present application, the active ingredients in milk include the contents of total protein, lactalbumin, lactoglobulin, non-denatured whey protein, lactoferrin and immunoglobulin IgG.

[0022] The fourth object of the present application is to provide a method for reducing the content of furfuryl amino acid in sterilized milk without causing the loss of protein oxidation in milk, which comprises the following steps: The raw cow milk to be sterilized is subjected to heat treatment sterilization at 60-70℃ for 13-18 s, and then rapidly cooled to 4-10℃; and then passed through a flow-around ultraviolet sterilization device with a flow rate of 5.5-6.5 L / h and a length of 1-5 m to obtain the raw cow milk after sterilization.

[0023] A fifth object of the present application is to provide a method for preserving the content of total protein, lactalbumin, lactoglobulin, undenatured whey protein, lactoferrin and immunoglobulin IgG in milk, comprising the steps of: The raw milk to be sterilized is heat treated at 60-70 DEG C for 13-18s, and cooled rapidly to 4-10 DEG C; then passed through a 1-5m flow type ultraviolet sterilization device at a flow rate of 5.5-6.5L / h to obtain sterilized raw milk.

[0024] [Advantages] The present application achieves the goal of reducing the energy consumption of milk sterilization while ensuring the sterilization effect of raw milk, preserving active ingredients in milk and avoiding significant protein oxidation. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The process flow chart of the present application.

[0026] Figure 2 The effect of the method of Examples 4-6 and Comparative Examples 5-7 on the number of microorganisms in skimmed raw milk (different letters indicate significant differences, p<0.05, raw is the untreated control group).

[0027] Figure 3 The effect of the method of Examples 4-6 and Comparative Examples 5-7 on total protein (a), lactalbumin (b) and lactoglobulin (c) in skimmed raw milk (different letters indicate significant differences, p<0.05, raw is the untreated control group).

[0028] Figure 4 The effect of the method of Examples 4-6 and Comparative Examples 5-7 on the content of undenatured whey protein (a) and the type of whey protein (b) in skimmed raw milk (different letters indicate significant differences, p<0.05, raw is the untreated control group).

[0029] Figure 5 The effect of the method of Examples 4-6 and Comparative Examples 5-7 on the content of carbonyl (a) and sulfhydryl (b) in skimmed raw milk (different letters indicate significant differences, p<0.05, raw is the untreated control group).

[0030] Figure 6 The effect of the method of Examples 4-6 and Comparative Examples 5-7 on the content of lactoferrin (a) and IgG (b) in skimmed raw milk (different letters indicate significant differences, p<0.05, raw is the untreated control group).

[0031] Figure 7Effect of the method of examples 4-6 and comparative examples 5-7 on the content of furfurol in skimmed raw milk (different letters indicate significant differences, p <0.05, raw is the control group without treatment). DETAILED DESCRIPTION

[0032] The preferred embodiments of the present application are described below, it should be understood that the embodiments are for better explaining the present application, not for limiting the present application.

[0033] Test method: 1. Determination of total protein in milk Skim milk treated by sterilization combination was determined by Kjeldahl method, with pasteurization (75℃-15s and 85℃-15s) as control.

[0034] 2. Determination of un-denatured whey protein and protein electrophoresis Un-denatured whey protein in skim milk treated by sterilization combination was determined, with pasteurization (75℃-15s and 85℃-15s) as control, and the pH of milk was adjusted to 4.6 by 1 mol / L hydrochloric acid aqueous solution, then centrifuged at 100000g, 25℃ for 90 min, and the middle layer whey was collected, and the concentration of un-denatured whey protein in whey was determined by BCA method.

[0035] The whey solution was diluted 5 times with deionized water to obtain whey dilution solution; 5 μL of β-mercaptoethanol aqueous solution, 95 μL of 2x electrophoresis sample loading buffer were mixed, and then mixed with 100 μL of whey dilution solution in equal volume, and boiled in water for 5 min. After cooling to room temperature, 10 μL of sample was taken for reducing polyacrylamide gel electrophoresis (SDS-PAGE).

[0036] Concentrated gel and separation gel with mass fraction of 4% and 12% were configured. The running current was 60 mA for 4 h. The gel was stained and decolorized with Coomassie brilliant blue R-250, 10% ethanol aqueous solution and 7.5% acetic acid aqueous solution respectively, and then scanned by gel imaging instrument.

[0037] 3. Determination of α-lactalbumin and β-lactoglobulin concentration The α-lactalbumin and β-lactoglobulin in whey were determined by reverse phase high performance liquid chromatography.

[0038] 4. Determination of lactoferrin and immunoglobulin IgG in milk The sample was diluted 1000 times for standby.

[0039] Dilute an appropriate amount of goat anti-bovine lactoferrin antibody 100-fold in coating buffer (0.05 mol sodium bicarbonate, pH 9.6) and mix well. Pipette 100 µL of the diluted coated antibody into the standard well and sample well, and incubate at room temperature for 60 min. Add 250 µL of ELISA washing buffer to each well, aspirate, and pat dry on absorbent paper, avoiding contamination between wells. Repeat five times. Then add 200 µL of blocking solution, react at room temperature for 30 min, repeat the washing operation, and pat dry on absorbent paper; then add 100 µL of standard and test sample of gradient concentration, set up 3 replicates for each, react at room temperature for 1 h, repeat the washing operation and pat dry. After adding 100 µL of horseradish peroxidase-conjugated goat anti-bovine lactoferrin detection antibody, the plate was incubated at room temperature for 1 hour, and washed 5 times. After adding 100 µL of TMB (enzyme substrate), the 96-well plate was incubated at room temperature in the dark for 15 min. After adding 100 µL of stop solution (0.18 mol H2SO4), the plate was shaken in a microplate reader for 5 s and the absorbance was read at 450 nm.

[0040] Finally, Soft-Max Pro was used to fit a standard curve to a 4-parameter curve and calculate the concentration of active proteins in the sample. The sample dilution was used as a blank control, and the results were expressed as the retention rate (%) with fresh milk as the control.

[0041] 5. Determination of protein carbonyl and thiol content Carbonyl determination: Mix 0.5 mL of skim milk with 0.5 mL of 10 M DNPH dissolved in 2 M hydrochloric acid aqueous solution and react at room temperature for 1 h. Then add 1 mL of 20% TCA solution and centrifuge at 10000 g for 5 min. Discard the supernatant in the centrifuge tube and wash three times with ethyl acetate-ethanol solution (1:1, v / v) to remove unreacted DNPH. Then add 6 M 0.5 mL of guanidine hydrochloride solution to dissolve the precipitate. The blank group uses 2 M hydrochloric acid aqueous solution instead of skim milk, and its pretreatment is the same as that of the sample group. After complete precipitation, measure the absorbance of the solution at a wavelength of 370 nm.

[0042] Carbonyl content is expressed as the amount of carbonyl groups per milligram of protein, in nmol / mg·Pr. The molecular extinction coefficient of the carbonyl group is 22000 L / (mol·cm).

[0043] Thiol group determination: Mix 0.5 mL of skim milk with 4 mL of Tris-glycine solution, then add 0.5 mL of 10M DTNB solution and react for 30 min. The blank control group used Tris-glycine solution and DTNB reagent, with the remaining treatments the same as the sample group. After the reaction, measure the absorbance of the solution at 412 nm.

[0044] The thiol content is expressed as the amount of thiol groups per milligram of protein, in nmol / mg·Pr. The molecular extinction coefficient of thiol is 13600 L / (mol·cm).

[0045] 6. Determination of furosine content Mix 2 mL of the sample with 6 mL of 10.6 mol / L hydrochloric acid aqueous solution in a heat-resistant tube until homogeneous. Heat at 110℃ for 22 h. After cooling, filter the solution with filter paper and collect the filtrate. Take 2 mL of the filtrate and determine the protein content in the hydrolysate according to GB 5009.5. Then, take 1 mL of the filtrate and mix it with 5 mL of 6 g / L ammonium acetate solution. Filter the filtrate through a 0.22 μm filter membrane and perform instrumental testing.

[0046] C18 column (250 mm × 4.6 mm, 5 μm) was used, column temperature: 32℃, detection wavelength: 280 nm.

[0047] A 0.1% (v / v) aqueous solution of trifluoroacetic acid was used as mobile phase A, and methanol was used as mobile phase B.

[0048] Elution conditions: Flow rate: 0.5 mL / min; Phase B gradient elution program: 0 min–16 min, 0%–13.2%; 16 min–16.5 min, 13.2%–100%; 16.5 min–25 min, 100%–0%; 25 min–30 min, 0%. The furosine content in the final sample is expressed in mg / 100 g protein.

[0049] 7. Energy Consumption Calculation Based on the operating power (14 kW), processing capacity (20 L / h), cooling water flow rate (800 L / h), heat treatment time, UV lamp power (27 W), and flow rate (6 L / h) of the plate heat exchanger, calculate the electrical energy and water consumption for different sterilization treatment groups. The calculation formula is W(kW·h) = P(kW) × t(h), where P is the operating power and t is the treatment time.

[0050] Raw materials used in the examples: A flow-around ultraviolet sterilization device is disclosed in patent CN 112167337 B; the ultraviolet lamp in the flow-around ultraviolet sterilization device has a power of 27W, and the outer diameter of the quartz sleeve is 23mm; a PFA tube with an inner diameter of 1.5mm and an outer diameter of 2.0mm is selected; each 1m of PFA tube winding constitutes a sterilization zone; the ultraviolet irradiation dose corresponding to 1, 2, 3, 4, and 5m is 15.11mJ / cm². 2 30.22mJ / cm 2 45.33 mJ / cm 2 60.44 mJ / cm 2 75.55 mJ / cm 2 .

[0051] Raw milk to be sterilized (UHT skim milk): Take commercially available UHT sterilized skim milk and inoculate it with Escherichia coli, Staphylococcus aureus and Cronobacter sakazakii respectively, so that the final number is 6.26±0.01 log CFU / mL, 7.34±0.01 log CFU / mL and 8.19±0.01 log CFU / mL.

[0052] Heat treatment sterilization is carried out using a tube sheet combined ultra-high temperature sterilizer.

[0053] Example 1 A highly efficient and low-energy-consumption method for sterilizing liquid milk includes the following steps: 20L of raw milk (UHT skim milk) to be sterilized was heat-treated at 60℃ for 15s, with temperature fluctuations within ±1℃ during the heating process; it was then rapidly cooled to 4℃; and then passed through a flow-through UV sterilization device at a flow rate of 6L / h for 1, 2, 3, 4, and 5m respectively to obtain sterilized raw milk.

[0054] Comparative Example 1 UHT skim milk (raw milk to be sterilized).

[0055] Comparative Example 2 The ultraviolet treatment in Example 1 is omitted, and everything else remains the same as in Example 1.

[0056] The sterilized raw milk was subjected to performance tests, and the results are as follows: Table 1. Effects of 60℃-15s heat treatment combined with UV irradiation intensity on common pathogenic bacteria in milk.

[0057] Note: ND indicates undetectable. As shown in Table 1, in the 60℃-15s heat treatment group, the number of the three pathogenic bacteria in UHT-inoculated milk gradually decreased with the increase of ultraviolet irradiation intensity. When the ultraviolet irradiation path reached 3m, the number of the three pathogenic bacteria could all decrease by 5log, indicating that 60℃-15s combined with 3m irradiation (60℃+3m) is a combination that ensures the safety of milk sterilization.

[0058] Example 2 A highly efficient and low-energy-consumption method for sterilizing liquid milk includes the following steps: 20L of raw milk (UHT skim milk) to be sterilized was heat-treated at 65℃ for 15s, with temperature fluctuations within ±1℃ during the heating process; it was then rapidly cooled to 4℃; and then passed through a flow-through UV sterilization device at a flow rate of 6L / h for 1, 2, 3, 4, and 5m respectively to obtain sterilized raw milk.

[0059] Comparative Example 3 The ultraviolet treatment in Example 2 is omitted, and everything else remains the same as in Example 2.

[0060] The sterilized raw milk was subjected to performance tests, and the results are as follows: Table 2. Effects of 65℃-15s heat treatment combined with UV irradiation intensity on common pathogenic bacteria in milk.

[0061] Note: ND indicates undetectable. As shown in Table 2, in the 65℃-15s heat treatment group, the number of the three pathogenic bacteria in UHT-inoculated milk gradually decreased with the increase of ultraviolet irradiation intensity. When the ultraviolet irradiation path reached 2m, the number of the three pathogenic bacteria could all decrease by 5log, indicating that 65℃-15s combined with 2m irradiation (65℃+2m) is a combination that ensures the safety of milk sterilization.

[0062] Example 3 A highly efficient and low-energy-consumption method for sterilizing liquid milk includes the following steps: 20L of raw milk (UHT skim milk) to be sterilized was heat-treated at 70℃ for 15s, with temperature fluctuations within ±1℃ during the heating process; it was then rapidly cooled to 4℃; and then passed through a flow-through UV sterilization device at a flow rate of 6L / h for 1, 2, 3, 4, and 5m respectively to obtain sterilized raw milk.

[0063] Comparative Example 4 The ultraviolet treatment in Example 3 is omitted, and everything else remains the same as in Example 3.

[0064] The sterilized raw milk was subjected to performance tests, and the results are as follows: Table 3. Effects of 70℃-15s heat treatment combined with UV irradiation intensity on common pathogenic bacteria in milk.

[0065] Note: ND indicates undetectable. As shown in Table 3, in the 70℃-15s heat treatment group, the number of the three pathogenic bacteria in UHT-inoculated milk gradually decreased with the increase of ultraviolet irradiation intensity. When the ultraviolet irradiation path reached 1m, the number of the three pathogenic bacteria could all achieve a 5log decrease, indicating that 70℃-15s combined with 1m irradiation (70℃+1m) is a combination that ensures the safety of milk sterilization.

[0066] Example 4 60℃ + UV3 A highly efficient and low-energy-consumption method for sterilizing liquid milk includes the following steps: 30L of raw milk is skimmed using a disc centrifuge to form skim milk; 20L of skim milk was heat-treated at 60℃ for 15s to sterilize it, with temperature fluctuations within ±1℃ during the heating process; it was then rapidly cooled to 4℃; and then passed through a 3m flow-through UV sterilization device at a flow rate of 6L / h to obtain sterilized raw milk.

[0067] Example 5 65℃ + UV2 A highly efficient and low-energy-consumption method for sterilizing liquid milk includes the following steps: Raw milk is skimmed using a disc centrifuge to produce skim milk; 20L of skim milk was heat-treated at 65℃ for 15s to sterilize it, with temperature fluctuations within ±1℃ during the heating process; it was then rapidly cooled to 4℃; and then passed through a 2m flow-through UV sterilization device at a flow rate of 6L / h to obtain sterilized raw milk.

[0068] Example 6 70℃ + UV1 A highly efficient and low-energy-consumption method for sterilizing liquid milk includes the following steps: Raw milk is skimmed using a disc centrifuge to produce skim milk; 20L of skim milk was heat-treated at 70℃ for 15s to sterilize it, with temperature fluctuations within ±1℃ during the heating process; it was then rapidly cooled to 4℃; and then passed through a 1m flow-through UV sterilization device at a flow rate of 6L / h to obtain sterilized raw milk.

[0069] Comparative Example 5 raw The skim milk from Example 4 was used directly.

[0070] Comparative Example 6 75℃ The ultraviolet treatment in Example 4 is omitted, and the heat treatment sterilization is adjusted to be maintained at 75°C for 15 seconds. Everything else is the same as in Example 4.

[0071] Comparative Example 7 85℃ The ultraviolet treatment in Example 4 is omitted, and the heat treatment sterilization is adjusted to be held at 85°C for 15 seconds. Everything else is the same as in Example 4.

[0072] The sterilized raw milk was subjected to performance tests, and the results are as follows: Figure 2 The effects of the methods in Examples 4-6 and Comparative Examples 5-7 on the number of microorganisms in skim raw milk (different letters indicate significant differences, p<0.05, raw represents the untreated control group). From Figure 2 It can be seen that the methods in Examples 4-6 can achieve satisfactory sterilization effects in the sterilization of skimmed raw milk. They achieve the same sterilization effect as the common 75℃-15s pasteurization, meet the microbiological requirements stipulated in the national standard for pasteurized milk, and prove their applicability.

[0073] Figure 3 The effects of the methods used in Examples 4-6 and Comparative Examples 5-7 on total protein (a), lactalbumin (b), and lactoglobulin (c) in skim raw milk are shown (different letters indicate significant differences, p < 0.05, raw represents the untreated control group). From Figure 3 It can be seen that, compared with the control group raw, the sterilization combination of Examples 4-6 does not affect the total protein content of skim milk; however, it slightly reduces the content of lactalbumin and lactoglobulin in the milk. This effect is not significantly different from that of common 75℃-15s pasteurization, but is better than 85℃-15s heat treatment.

[0074] Figure 4 The effects of the methods used in Examples 4-6 and Comparative Examples 5-7 on the content (a) and type (b) of undenatured whey protein in skim raw milk (different letters indicate significant differences, p < 0.05, raw represents the untreated control group). From Figure 4 It can be seen that the sterilization combination in Examples 4-6 slightly reduces the concentration of undenatured whey protein in milk, but the reduction is still better than that of common pasteurization heat treatments of 75℃-15s and 85℃-15s. Electrophoresis results show that the main whey protein composition is not significantly different from that of the control group, indicating that more undenatured whey protein can be retained. Pasteurization causes the LTF and IgG-HC bands to lighten, indicating that the content of these two proteins may be reduced, proving that pasteurization has the strongest destructive effect on whey protein.

[0075] The carbonyl content of proteins is a common marker of protein oxidation. It is generated by multiple free radicals and singlet oxygen (secondary reactants) and can be produced in most amino acids. Heat treatment can lead to the formation of protein oxidation products. The thiol groups of sulfur-containing amino acids such as cysteine ​​in milk are easily attacked by free radicals under the influence of light or heat, reacting with other amino acids or substances to form disulfide bonds or sulfides. Figure 5 The effects of the methods used in Examples 4-6 and Comparative Examples 5-7 on the carbonyl (a) and thiol (b) content in skim raw milk (different letters indicate significant differences, p < 0.05, raw represents the untreated control group). From Figure 5 It can be seen that, compared with the control group (raw), the three sterilization combinations did not significantly increase the carbonyl content or decrease the sulfhydryl content in milk. Therefore, they did not cause oxidative loss of milk protein and had no adverse effect on milk protein quality.

[0076] Figure 6 The effects of the methods used in Examples 4-6 and Comparative Examples 5-7 on the content of lactoferrin (a) and IgG (b) in skim raw milk (different letters indicate significant differences, p<0.05, raw is the untreated control group). From Figure 6 It can be seen that, compared with pasteurization at 75℃-15s and 85℃-15s, the sterilization combinations in Examples 4-6 can retain more lactoferrin and immunoglobulin IgG, and have less impact on active proteins in milk.

[0077] Furfuryl is a primary product of the Maillard reaction in milk and can be used as an indicator of the degree of Maillard reaction. Figure 7 The effects of the methods in Examples 4-6 and Comparative Examples 5-7 on the furosine content in skim raw milk (different letters indicate significant differences, p<0.05, raw represents the untreated control group). From Figure 7 It can be seen that, compared with pasteurization at 75℃-15s and 85℃-15s, all three pasteurization combinations produced less furosine (less than or equal to conventional pasteurization), indicating that the Maillard reaction in the milk was less severe under this treatment method, and had a smaller impact on the components of the milk.

[0078] Table 4 shows the electrical energy and water consumption data for the methods in Examples 4-6 and Comparative Examples 6-7, as detailed below: Table 4. Electricity and water consumption per liter of milk processed

[0079] Note: Only the power consumption during the thermal sterilization stage and the water consumption during the cooling stage are calculated.

[0080] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A highly efficient and low-energy-consumption method for sterilizing liquid milk, characterized in that, Includes the following steps: The raw milk to be sterilized is heat-treated at 60-70℃ for 13-18 seconds and then rapidly cooled to 4-10℃. After that, it is passed through a 1-5m flow-through ultraviolet sterilization device at a flow rate of 5.5-6.5L / h to obtain sterilized raw milk.

2. The method according to claim 1, characterized in that, Heat treatment sterilization involves heat treatment at 60℃ for 15 seconds, followed by passing through a 3m flow-through ultraviolet sterilization device.

3. The method according to claim 1, characterized in that, Heat treatment sterilization involves heat treatment at 65℃ for 15 seconds, followed by passing through a 2m flow-through ultraviolet sterilization device.

4. The method according to claim 1, characterized in that, Heat treatment sterilization involves heat treatment at 70℃ for 15 seconds, followed by passing through a 1m flow-through ultraviolet sterilization device.

5. The method according to claim 1, characterized in that, The UV lamp in the flow-through UV sterilization device has a power of 27W and an outer diameter of 23mm for the quartz sleeve. A PFA tube with an inner diameter of 1.5mm and an outer diameter of 2.0mm is used. Each 1m section of the PFA tube constitutes a sterilization zone. The UV irradiation dose corresponding to 1m, 2m, 3m, 4m, and 5m sections is 15.11mJ / cm². 2 30.22mJ / cm 2 45.33 mJ / cm 2 60.44 mJ / cm 2 75.55 mJ / cm 2 .

6. The method according to claim 1, characterized in that, Sterilization refers to killing pathogenic bacteria such as Escherichia coli, Staphylococcus aureus, and Cronobacter sakazakii.

7. The sterilized raw milk prepared by the method according to any one of claims 1-6.

8. A method for ensuring the sterilization effect of raw milk while retaining the active ingredients in the milk, characterized in that, Includes the following steps: The raw milk to be sterilized is heat-treated at 60-70℃ for 13-18 seconds and then rapidly cooled to 4-10℃. After that, it is passed through a 1-5m flow-through ultraviolet sterilization device at a flow rate of 5.5-6.5L / h to obtain sterilized raw milk.

9. A method for reducing the furosine content in sterilized milk without causing oxidative loss of milk proteins, characterized in that, Includes the following steps: The raw milk to be sterilized is heat-treated at 60-70℃ for 13-18 seconds and then rapidly cooled to 4-10℃. After that, it is passed through a 1-5m flow-through ultraviolet sterilization device at a flow rate of 5.5-6.5L / h to obtain sterilized raw milk.

10. A method for preserving the content of total protein, lactalbumin, lactoglobulin, undenatured whey protein, lactoferrin, and immunoglobulin IgG in milk, characterized in that, Includes the following steps: The raw milk to be sterilized is heat-treated at 60-70℃ for 13-18 seconds and then rapidly cooled to 4-10℃. After that, it is passed through a 1-5m flow-through ultraviolet sterilization device at a flow rate of 5.5-6.5L / h to obtain sterilized raw milk.

Images