Method for refreshing origanum vulgaris essential oil on pasteurized milk
阅读说明：本技术 一种牛至精油对巴氏乳保鲜方法 (Method for refreshing origanum vulgaris essential oil on pasteurized milk ) 是由 刘婷 文鹏程 张卫兵 刘海波 张炎 于 2020-07-08 设计创作，主要内容包括：本发明涉及食品保鲜技术领域,特别是一种牛至精油对巴氏乳保鲜方法,具体涉及巴氏乳货架期保鲜。通过巴氏灭菌与牛至精油相结合的试验研究中,发现巴氏乳添加2 mg/L牛至精油的乳样中pH值下降缓慢,吉尔涅尔度值在第8 d时才显著性的上升,且较对照组、1 mg/L浓度的试验组上升速度慢。添加2 mg/L牛至精油使牛奶中的丙二醛含量下降,SOD含量上升,使乳样中的微生物生长缓慢,延长了牛奶的保存期限,且牛奶的感官质量较对照组好。控制牛至精油质量浓度提升保存期限同时保持更好口感。(The invention relates to the technical field of food preservation, in particular to a method for preserving pasteurized milk by using oregano essential oil, and particularly relates to shelf-life preservation of pasteurized milk. In the experimental study of the combination of pasteurization and the oregano essential oil, the pH value of the milk sample added with 2mg/L of oregano essential oil in the pasteurized milk is slowly reduced, the Girlel value is obviously increased at the 8 d, and the increase speed is slower than that of the control group and the test group with the concentration of 1 mg/L. The addition of 2mg/L oregano essential oil reduces the malondialdehyde content in the milk, increases the SOD content, slows the growth of microorganisms in the milk sample, prolongs the storage life of the milk, and has better organoleptic quality than the control group. Controlling the mass concentration of the oregano essential oil improves shelf life while maintaining better mouthfeel.)
1. A method for refreshing pasteurized milk by using oregano essential oil is characterized by comprising the following steps:
pasteurization
Sterilizing at 63 deg.C for 30 min;
B. essential oil addition of origanum
Cooling the pasteurized milk to room temperature, and adding the oregano essential oil into the pasteurized milk; adding oregano essential oil into pasteurized raw milk according to the mass concentration of 0.5-2 mg/L to form a mixed solution;
C. cold chain fresh-keeping
The mixed solution is kept fresh at 4 ℃ in a cold chain.
2. The method as claimed in claim, wherein step B is carried out by adding oregano essential oil into pasteurized raw milk at a mass concentration of 2mg/L to form a mixed solution.
Technical Field
The invention relates to the technical field of food preservation, in particular to a method for preserving pasteurized milk by using oregano essential oil, and particularly relates to shelf-life preservation of pasteurized milk.
Background
Milk is a natural beverage with rich nutrition and is rich in a plurality of nutrient substances needed by human bodies. Including proteins, fats, carbohydrates, vitamins, minerals, etc. However, abundant nutrient substances can lead microorganisms to grow and reproduce in a large quantity, generate a plurality of toxic and harmful substances, change the physical and chemical properties of the milk and lose the edible value. Therefore, the microorganisms in the milk are controlled to be distributed to the market, so as to ensure the health of consumers. At present, the sterilization modes of milk mainly comprise ultrahigh temperature instant sterilization (UHT 135-. The first approach can achieve commercial sterility, but flavor and nutrition are destroyed. The second method retains the original nutrition and flavor of milk, but has poor sterilizing effect and short shelf life. The third method destroys the physical and chemical properties and nutritive value of milk.
Origanum contains more than 30 antibacterial compounds, has the effect of inhibiting the growth and reproduction of microorganisms, and can promote the growth of livestock and improve the utilization rate of feed. The origanum vulgaris can be used as a medicine and has the effects of clearing heat and detoxicating, regulating qi and eliminating dampness, inducing diuresis and reducing swelling and the like. The essential oil of origanum vulgaris extracted from plant has antibacterial and antioxidant effects. Zhang Rui et al found that the origanum vulgare essential oil can be directly smeared on the surfaces of fruits and vegetables through investigation and research to replace a synthetic bactericide for preventing rancidity and decomposition of the picked fruits and vegetables. The Yangjin research shows that the edible preservative film is coated on soft cheese, wherein the essential oil of origanum is used as a main antibacterial agent, and the antioxidant and antimicrobial properties of the essential oil of origanum are found to be better during the freezing storage of cheese. Zhang et al found that the use of oregano essential oil alone reduced the lipid oxidation rate of beef, extended shelf life, and exhibited higher antioxidant activity. Liu light et al have studied the preparation of oregano essential oil microcapsule, find that oregano essential oil has fine antibacterial effect. Liu Ting et al have studied the influence that the combination of oregano essential oil combines different packing modes to the fresh-keeping effect of cold bright mutton, found that the combination of oregano essential oil and vacuum packaging can prolong the retention period. These studies all demonstrated that oregano essential oil has bacteriostatic effects, and thus oregano essential oil was used as a main test object to study how to prolong the shelf life of pasteurized milk.
In the test, after raw milk is pasteurized, the origanum essential oil is added to detect the influence of the origanum essential oil on the fresh-keeping effect of pasteurized milk. So as to obtain whether the milk can be stored and kept fresh in the production process or not, and the shelf life of the pasteurized milk can be prolonged by using the oregano essential oil as a preservative.
Disclosure of Invention
The invention solves the technical problem of short shelf life of pasteurized milk in the prior art, and provides a method for preserving pasteurized milk by oregano essential oil.
The technical scheme adopted by the invention for solving the technical problems is as follows:
a method for refreshing pasteurized milk by using oregano essential oil comprises the following steps:
A. pasteurization
Sterilizing at 63 deg.C for 30 min;
B. essential oil addition of origanum
Cooling the pasteurized milk to room temperature, and adding the oregano essential oil into the pasteurized milk; adding oregano essential oil into pasteurized raw milk according to the mass concentration of 0.5-2 mg/L to form a mixed solution;
C. cold chain fresh-keeping
The mixed solution is kept fresh at 4 ℃ in a cold chain.
And step B, adding oregano essential oil into the pasteurized raw milk according to the mass concentration of 2mg/L to form a mixed solution.
The invention has the beneficial effects that:
in the experimental study of the combination of pasteurization and the oregano essential oil, the pH value of the milk sample added with 2mg/L of oregano essential oil in the pasteurized milk is slowly reduced, the Girlel value is obviously increased at the 8 d, and the increase speed is slower than that of the control group and the test group with the concentration of 1 mg/L. The addition of 2mg/L oregano essential oil reduces the malondialdehyde content in the milk, increases the SOD content, slows the growth of microorganisms in the milk sample, prolongs the storage life of the milk, and has better organoleptic quality than the control group. Controlling the mass concentration of the oregano essential oil improves shelf life while maintaining better mouthfeel. The milk sample added with 2mg/L of oregano essential oil can generate obvious different mouthfeel, and the storage life is not obviously improved.
Drawings
FIG. 1 is a flow chart of an experiment according to the present invention;
FIG. 2 is a schematic representation of a variation of pasteurized milk fat;
FIG. 3 is a schematic diagram of a variation of the pasteurized milk protein;
FIG. 4 is a schematic representation of a variation of pasteurized milk lactose;
FIG. 5 is a schematic representation of a variation of milk solids in pasteurized milk, non-fat;
FIG. 6 is a schematic representation of the variation of the dry matter of pasteurized milk;
FIG. 7 is a schematic diagram of the change in pH of pasteurized milk;
FIG. 8 is a graph showing the variation of Gillennel degree of pasteurized milk;
FIG. 9 is a schematic diagram of the change of the malondialdehyde of pasteurized milk;
FIG. 10 is a schematic diagram showing the change of SOD.
Detailed Description
A method for refreshing pasteurized milk by using oregano essential oil comprises the following steps:
A. pasteurization
Sterilizing at 63 deg.C for 30 min;
B. essential oil addition of origanum
Cooling the pasteurized milk to room temperature, and adding the oregano essential oil into the pasteurized milk; adding oregano essential oil into pasteurized raw milk according to the mass concentration of 0.5-2 mg/L to form a mixed solution;
C. cold chain fresh-keeping
The mixed solution is kept fresh at 4 ℃ in a cold chain.
Optimally, the origanum essential oil is added into the pasteurized raw milk in the step B according to the mass concentration of 2mg/L to form a mixed solution.
1 materials and methods
1.1 Main test materials
1.1.1 test reagents
Materials: pasteurized milk obtained by sterilizing fresh raw milk at low temperature for a long time is selected as a test material.
Reagent: essential oil of origanum vulgaris; agar culture medium; physiological saline (NaCl 0.85 g 100 ml water); the malondialdehyde kit is purchased from Nanjing to build a bioengineering institute; the SOD kit is purchased from Nanjing to build a bioengineering institute; 0.1 mol/LNaOH solution; 1% phenolphthalein indicator.
1.1.2 instruments and devices
A milk component analyzer; a constant-temperature incubator: 36 plus or minus 1 ℃ and 30 plus or
1.2 test methods
1.2.1 technical route
As shown in FIG. 1, origanum essential oil was stored in a refrigerator at 4 ℃ in a sealed manner to prepare 1200 ml of raw milk, the raw milk was treated by low-temperature long-time pasteurization, and the origanum essential oil was added to the pasteurized raw milk at concentrations of 0.5 mg/L, 1mg/L, and 2mg/L, and the test sample milk was stored in the refrigerator at 4 ℃ and then subjected to the following operations.
1.2.2 test methods
1.2.2.1 measurement of the major ingredients in milk
The indexes of fat, protein, lactose, dry matter, non-fat milk solid and the like of the pasteurized milk are measured by using a milk component analyzer, and the average value of each sample is taken after 3 times of measurement.
1.2.2.2 determination of pH
The pH value of the sample is determined according to the method in GB 5009.237-2016 national food safety standard for determination of pH value of food, and the average value of each sample is taken after 3 times of determination.
Measurement of 1.2.2.3 Gillennel degree
The method is characterized in that the sample titration acidity value is determined according to the method in GB 5413.34-2010 national standard for food safety milk and dairy product acidity determination, and the average value of each sample is taken after 3 times of determination.
1.2.2.4 assay of malondialdehyde
The malonaldehyde values of the samples were determined by reference to the method in a commercial kit of malonaldehyde (purchased from Nanjing Biotech Ltd.) and the mean value was taken 3 times per sample.
1.2.2.5 determination of SOD (superoxide dismutase)
The SOD values of the samples were determined by reference to the method of SOD commercial kit (purchased from Nanjing Biotech Co., Ltd.), and the mean value was taken for 3 times of each sample determination.
1.2.2.6 determination of the Total number of colonies
The total number of the bacterial colonies of the samples is measured according to the method in GB 4789.2-2016 food safety national standard food microbiological inspection total number of bacterial colonies measurement, and the average value is taken after 3 times of measurement of each sample.
1.2.2.7 determination of color
The colorimeter was calibrated to measure the a values (red-green bias), b values (yellow-blue bias), L values (brightness), and 3 determinations were made for each sample to take the mean.
1.2.2.8 data processing
Data were collated using Excel 2010, SPSS 25.0 for one-way anova, and differences between groups were examined using Duncan's multiple comparisons (P<0.05 orP<0.01), orgin 2019 software.
2 results and analysis
2.1 change in the major component of pasteurized milk during storage
The main components of the pasteurized milk comprise fat, protein, lactose and the like, which are one expression for evaluating the nutritional value of the milk, and the content of the milk components determines the action of the pasteurized milk on a human body. The nutrient content in the milk is gradually reduced along with the prolonging of the time, so that the value of the milk is lost.
2.1.1 changes in fat
When the preservation temperature is 4 ℃, the content of milk fat can be slowly reduced, and the change range is small. As can be seen from figure 2, the addition of oregano essential oil in pasteurized milk significantly affected the fat content. Under the same temperature conditions, the fat content of the control group increased at 2 d and decreased significantly at 4 d, resulting in a trough and then increased slowly. Compared with the control group, the content of fat is wavy and irregular by adding the oregano essential oil with the concentration of 1 mg/L. The content of fat was significantly increased at 2 d by adding oregano essential oil at a concentration of 2mg/L (P<0.05), a peak occurs, andthen slowly decreases. The significant effect of adding 2mg/L of oregano essential oil in the pasteurized milk on fat is demonstrated.
2.1.2 changes in proteins
Milk protein plays a very important role in the diet of people, and milk is used as a main protein source. As shown in FIG. 3, the protein content in pasteurized milk is related to both the refrigeration temperature and the time. Generally, the content of protein is reduced along with the time, and the content of protein is reduced to different degrees according to the concentration of the added oregano essential oil. Adding oregano essential oil with the concentration of 2mg/L into pasteurized milk, and the protein content is obviously lower than that of a control group and a test group with the concentration of 1mg/L at the 2 d time (P<0.05). The protein content at 6d is significantly higher than that of the control group (P<0.05) but no significant difference from the test group at the concentration of 1 mg/L: (P>0.05). Test group with protein content significantly higher than control group and 1mg/L concentration at 8 d: (P<0.05）。
2.1.3 changes in lactose
Lactose is the main carbohydrate required by humans and is an important nutritional ingredient. The content of lactose in milk was 4.6% of the total. As can be seen from fig. 4, the lactose content decreased significantly at 2 d with time (a)P<0.05) but no significant change at the later stage. Meanwhile, the lactose content is not changed along with the change of the concentration of the essential oil of the oregano. Therefore, the addition of different concentrations of oregano essential oil in the pasteurized milk has no significant difference to the change of lactose (P>0.05）。
2.1.4 changes in milk solids-not-fat
The nonfat milk solids are a generic term for substances other than fat and moisture in milk, and contain many substances such as proteins, saccharides, vitamins, and the like. The non-fat milk solids content is 9-12% of the total milk content. As shown in fig. 5, the content of milk solids-not-fat decreased with time, and the change was correlated with the concentration of the essential oil added to oregano. The content of milk solids not fat in the test group at the 2 d is obviously higher than that of the control group, and the content of milk solids not fat in the test group at the 6d is obviously lower than that of the control group when the oregano essential oil with the concentration of 1mg/L and 2mg/L is added into the pasteurized milkAccording to group (P<0.05). Addition of oregano essential oil at a concentration of 1mg/L, the milk solids nonfat content at 4 d was significantly lower than the control and the test group at a concentration of 2mg/L (P<0.05）。
2.1.5 Change in Dry matter
As can be seen from figure 6, the addition of 1mg/L and 2mg/L oregano essential oil in pasteurized milk resulted in a higher significance of dry matter content at 4 d than in the control group (P<0.05) in a milk sample with 2mg/L oregano essential oil added, the content of dry matter is the highest, making the content of dry matter a peak. The dry matter content at 8 d increased significantly with the addition of oregano essential oil concentration (S) ((S))P<0.05）。
2.2 changes in pH and Gillell degree of pasteurized milk during storage
China usually uses the Gillell degree to express the acidity of milk, namely DEG T. Acidity and pH are important indexes reflecting freshness and stability of milk, the lower the pH, the higher the concentration of free hydrogen ions, the higher the titration acidity, and the lower the freshness and poor thermal stability of milk with high acidity, so that acidity and pH are very important in production and processing[9]. The acidity of normal pasteurized milk should be less than 18 ° T, and the pH should be in the range of 6.5-6.7[11]。
As can be seen from FIG. 7, when different concentrations of oregano essential oil were added to pasteurized milk, the pH value tended to rise first and then fall and then slowly rise with time, and the test group to which 2mg/L oregano essential oil was added had a significantly lower pH value at 2 d than the control group and the test group at a concentration of 1mg/L (see the following table) (for example)P<0.05). Significant decrease in pH with increasing oregano essential oil concentration at 4 d: (P<0.05). The pH value of the test group added with 2mg/L oregano essential oil is obviously lower than that of the control group at 6d and 8 d (P<0.05), but no significant difference from the test group at the concentration of 1mg/L (P>0.05）。
As can be seen in FIG. 8, the value of Gilbert in pasteurized milk increases dramatically at 8 d over time. (ii) a tendency that the Gilles de la Lee value is significantly decreased at 6d with an increase in concentration: (P<0.05). Adding into pasteurized milk at a concentration of 2mg/LAt 8 d, the value of Gillennel degree is significantly lower than that of the control group and the test group with the concentration of 1mg/L (P<0.05). Meanwhile, at the 8 d, the Girlel value of the three test groups exceeds the acidity value of normal milk, so that the freshness of the milk is low, and the thermal stability is poor, but the storage life of the milk can be prolonged relatively by adding the oregano essential oil.
2.3 change of malondialdehyde during storage of pasteurized milk
The degree of lipid peroxidation in the body can be reflected by measuring Malondialdehyde (MDA), and the degree of cell injury can be indirectly reflected. The milk contains abundant fatty acid, and is easy to be oxidized and rancid, so that the flavor of the milk is deteriorated and the health of human bodies is harmed[13]. The level of MAD indirectly reflects the severity of free radical attack on body cells, thus reflecting the degree of oxidation of the body. As can be seen from FIG. 9, when 2mg/L oregano essential oil is added into milk, the content of malondialdehyde is significantly reduced at the 2 nd, 6 th and 8 th days (P<0.05). While the content of malondialdehyde in milk added with 1mg/L oregano essential oil has no significant change with the control group (P>0.05), each in a slow-rising process.
2.4 change in SOD during storage of pasteurized milk
SOD (superoxide dismutase) plays a crucial role in the balance of oxidation and antioxidation of organisms, and can remove superoxide anion free radicals (O)2-) Protecting cells from damage[13]. The measurement of MDA is often matched with the measurement of SOD, and the activity of SOD indirectly reflects the capability of organism to eliminate free radicals. As can be seen from FIG. 10, when 1mg/L and 2mg/L oregano essential oil is added into the pasteurized milk at the 2 nd day, the content of SOD is significantly higher than that of the control group (SOD)P<0.05), but there was no significant difference between the two: (P>0.05). At the 4 d, the content of SOD is obviously increased along with the increase of the concentration of the essential oil of the oregano (the content of SOD is obviously increased)P<0.05). At the 6d, 2mg/L concentration of oregano essential oil is added into the pasteurized milk, and the content of SOD is obviously higher than that of the control group and that of the test group with 1mg/L concentration (P<0.05), and control group andno significant difference between the test groups at 1mg/L concentration (P>0.05）。
2.5 changes in the Total colony count of the pasteurized milk during storage
The milk contains abundant nutrients such as fat, protein, lactose, dry matter, vitamins and enzymes besides water, has pH of 6.5-6.7, and is natural culture medium for microorganisms[9]. Although the test adopts a pasteurization treatment method, the sterilization effect is not obvious, and a large amount of microorganisms still exist in the pasteurized milk. As shown in tables 2-10, the test groups added with oregano essential oil at different concentrations in pasteurized milk and added with 1mg/L and 2mg/L concentrations at the 4 th day have a lower significance of the total number of colonies than the control group ((C)P<0.05). At 6d, the content of the total number of colonies is remarkably reduced along with the increase of the concentration of the essential oil of the oregano: (P<0.05). In the test group added with the concentration of 2mg/L at the 8 th day, the content of the total number of colonies is significantly lower than that of the control group and the test group with the concentration of 1mg/L (P<0.05）。
TABLE 2-10 changes in the total number of colonies of pasteurized milk
Note: data in the same column are marked with the same letter or no letter to indicate that the difference is not significant (P)>0.05), different letters indicate significant differences (P<0.05）。
2.6 change in color of pasteurized milk during storage
CLE L, a, b is the most complete color model that is routinely used to describe all colors visible to the human eye. L denotes the brightness value (L × =0 black generated, L × =100 white), a denotes between red and green (a × negative values indicate green less red, a × positive values indicate magenta less green), b denotes between yellow and blue (b × negative values indicate blue less yellow, b × positive values indicate yellow less blue)[14]。
As can be seen from tables 2-11, the value of color L in the test group with the addition of oregano essential oil at different concentrations in pasteurized milk and the addition of 2mg/L concentration at 4 d was significantly highIn a control group (P<0.05) but no significant difference from the test group at the concentration of 1 mg/L. The value of color L at 6d increased significantly with increasing concentration of oregano essential oil(s) ((r))P<0.05）。
Tables 2-11 change in pasteurized milk color L
Note: data in the same column are marked with the same letter or no letter to indicate that the difference is not significant (P)>0.05), different letters indicate significant differences (P<0.05）。
As can be seen from tables 2-12, the essential oil of origanum vulgaris at a concentration of 2mg/L was added to the pasteurized milk at 6 days, at different concentrations at the same time, and the a value was significantly lower than that of the control group and that of the test group at a concentration of 1mg/L (P<0.05). Significant increase in a-value with increasing concentration of oregano essential oil at 8 d ((ii))P<0.05）。
Tables 2-12 change in pasteurized milk color a
Note: data in the same column are marked with the same letter or no letter to indicate that the difference is not significant (P)>0.05), different letters indicate significant differences (P<0.05）。
As can be seen from tables 2-13, the addition of oregano essential oil at a concentration of 2mg/L to the pasteurized milk at 8 days at the same time in different concentrations, the significance of b is lower than that of the control group (B)P<0.05), but the b value will tend to increase with time.
Tables 2-13 change in pasteurized milk color b
Note: data in the same column are marked with the same letter or no letter to indicate that the difference is not significant (P)>0.05), different letters indicate significant differences (P<0.05）。
Discussion of 3
Through research, the plant essential oil extracted from oregano has a relatively obvious bacteriostatic effect. The phenolic compounds contained therein have a natural antimicrobial effect, and the antimicrobial effect of oregano essential oil is similar to that of other organic phenolic compounds. Phenolic compounds are most effective in plant-containing antimicrobial substances. Its antimicrobial effect is mainly achieved by changing the structure of bacterial cell wall and cell membrane, so that protein is denatured and coagulated, and then cell leakage, water imbalance and bacterial death are caused. Meanwhile, the phenolic compounds entering the bacteria can prevent the bacteria from absorbing oxygen to play a role in sterilization[15]。
3.1 Change in the Main ingredient in pasteurized milk
The results of this experiment show that milk requires an adaptive process for the addition of oregano essential oil, in which the content of the main components in milk is significantly increased or decreased, as the concentration of oregano essential oil increases, compared to the control group. The fat content in milk is related to the storage time and storage temperature, and when the milk is stored in a refrigerator at 4 deg.C, the fat content is slowly reduced, and the change range is small[12]. The protein content is slowly reduced after adaptation to oregano essential oil, which is related to the temperature of pasteurized milk storage and the content of residual enzymes and microorganisms in the milk, and can degrade the protein and reduce the protein content[9]. In the test group in which oregano essential oil was added to pasteurized milk at a concentration of 2mg/L, both dry matter and nonfat milk solids content were significantly higher than the control group and the test group at a concentration of 1mg/L over time. Illustrating the significant effect of oregano essential oil on dry matter and milk solids-not-fat of pasteurized milk: (P<0.05). The variation in lactose content is different from the variation in other ingredients. The addition of different concentrations of essential oil of oregano can not cause significant change of lactose, and the effect of the essential oil of oregano on the content of lactose in milk is not obvious (see that the essential oil of oregano has no significant effect on the content of lactose in milk)P>0.05). The analysis reason is as follows: the lactose content is related to the length of storage time and the refrigeration temperature.
3.2 changes in pH and Gillell degree in pasteurized milk
Is normalThe pasteurized milk should have an acidity of less than 18 ° T and a pH in the range of 6.5-6.7. The addition of different concentrations of oregano essential oil to pasteurized milk resulted in a significant adaptation phase of the pH of pasteurized milk to essential oil at 4 d. After adding 1mg/L oregano essential oil, the pH of the pasteurized milk decreased from 5.94 to 5.57 between 2 d and 8 d, and the acidity increased from 13.19 ° T to 29.91 ° T between 6d and 8 d. After 2mg/L oregano essential oil was added, the pH of the pasteurized milk decreased from 5.89 to 5.67 between 2 d and 6d, and the acidity increased from 12.39T to 27.15T between 6d and 8 d. It can be seen that the pH value is significantly decreased and the Gillell value is significantly increased. The results of this experiment show that the higher the concentration of oregano essential oil during storage, the slower the pH drop compared to the control. The reason for this analysis is: the milk is a multi-phase system, and the degradation and oxidation of substances such as fat, protein and the like contained in the milk and the growth and metabolism of microorganisms can cause the pH value and the titer value of the milk to generate various influences, and the change occurs in test measurement[9]. Therefore, the addition of the oregano essential oil in the pasteurized milk can inhibit the growth and reproduction of microorganisms in the milk and keep the milk fresh in a certain period.
3.3 Change in malondialdehyde and SOD in pasteurized milk
The malondialdehyde is used for reflecting the degree of lipid peroxidation of cells and the degree of damage of the cells, and the degree of malondialdehyde indirectly reflects the severity of free radical attack on body cells. The level of SOD reflects the level of free radical scavenging ability of the body[16]. In this test, a high malondialdehyde content indicates a high degree of lipid peroxidation of the cells in the emulsion and severe damage to the somatic cells in the milk. The addition of 2mg/L oregano essential oil into the pasteurized milk can obviously reduce the malondialdehyde content and increase the SOD content in the
3.4 Total colony count in Pasteur milk
Pasteurizing the raw milk at 63 deg.C for 30min to obtain pasteurized milkContains a large amount of microorganisms, so that the pasteurized milk has to be stored in a low-temperature environment, the storage period is short, and the content of the total number of bacterial colonies in the pasteurized milk is less than or equal to 30 cfu/L[17]. The test result shows that when 1mg/L and 2mg/L concentration of oregano essential oil is added into pasteurized milk, the content of the total number of colonies is remarkably reduced at 4 d and 6 d. When 2mg/L oregano essential oil is added, the content of the total number of colonies at 8 d is lower than that of the control group and the test group at the concentration of 1 mg/L. Compared with the control group, the growth rate of the microorganism is slower, and the total colony content<30 cfu/L. The origanum essential oil has the function of inhibiting the growth of microorganisms and can play a role in keeping fresh.
3.5 color change in pasteurized milk
In the test, 2mg/L of oregano essential oil is added into the pasteurized milk, and the L value is obviously higher than that of the control group and the test group with the concentration of 1 mg/L. The a values were significantly lower at 6d than the control and the test groups at 1mg/L concentration. b is significantly lower than control at 8 d. Description of the analysis: the color change of milk mainly occurs in Maillard reaction between protein and lactose contained in milk during storage, and other brown substances are generated, which affect the color of milk. The pasteurized milk can generate Maillard reaction at any temperature, so that the color of the milk is changed[18]. Therefore, a gradual increase in L and a gradual decrease in b are associated with the maillard reaction. The increasing L indicates the color is brighter and lighter, and the decreasing B indicates the color of the milk is more and more towards blue. The gradual decrease of a indicates that the color is more and more shifted to green.
4 conclusion
In experimental studies of combination of pasteurization and oregano essential oil, it is found that a fusion process is required for combination of pasteurized milk and oregano essential oil, the pH value of milk samples added with 2mg/L of oregano essential oil is slowly reduced, the Gillel value is obviously increased at the 8 th day, and the increase speed is slower than that of control groups and test groups with the concentration of 1 mg/L. The addition of 2mg/L oregano essential oil reduces the malondialdehyde content in the milk, increases the SOD content, slows the growth of microorganisms in the milk sample, properly prolongs the storage life of the milk, and has better organoleptic quality than the control group. It is recommended to preserve milk in practice by pasteurization (63 deg.C for 30 min) in combination with the addition of 2mg/L oregano essential oil.
The research adopts a single-factor experimental design, treats the pasteurized milk by using the oregano essential oil with different concentrations, and researches the changes of indexes such as main components, pH value, Girlell degree, malondialdehyde, SOD (superoxide dismutase), total bacterial count, chromaticity and the like of pasteurized milk stored at 4 ℃ for 0, 2, 4, 6 and 8 d. The results show that: when the pasteurized milk is stored to 8 d, in the treatment group added with 2mg/L of oregano essential oil, the pH of the pasteurized milk is reduced, and the speed of increasing the Girnel value is obviously lower than that of 0 mg/L and 1mg/L of oregano essential oil group (oil group)P<0.05); and the colorimetric value, the malondialdehyde content and the total colony content are obviously lower than 0 mg/L and 1mg/L (oregano essential oil group) ((P<0.05); the SOD content is obviously higher than 0 mg/L and 1mg/L of oregano essential oil group (P<0.05). Therefore, the effect of keeping the pasteurized milk fresh can be achieved by adding the oregano essential oil with different concentrations, and the effect of keeping the milk fresh is better by adding 2mg/L of oregano essential oil into pasteurized milk compared with the concentration of 1 mg/L.