1. Color and texture: Normal milk is opaque milky white or yellowish, and its texture is uniform colloidal liquid, without precipitation, clots, impurities and foreign bodies.
2. Smell and taste: it has pleasant inherent fragrance of fresh milk and pure sweetness (from lactose), slightly salty; The salty taste caused by chloride ion (only 0.06-0. 12%) is often masked by fragrance. Normal milk sometimes has a little bitter taste, which is related to some amino acids, peptides and lipolytic enzymes it contains; But it is not allowed to have a strong bitter taste.
3, others: degreasing transparency is high, it will be slightly blue; Vitamin B2 in milk will make whey glow green. Milk is more fragrant when heated, but excessive heating will produce "boiling taste" and caramel taste; Milk easily absorbs all kinds of smells from outside. If it is not handled properly, it can sometimes smell the fishy, musty, astringent or fishy smell of cow dung, feed, onion and garlic and celery. , so it should be avoided.
4. Seasoned milk: Recently, several herbs were found in a grassland experimental field in Japan, and a small amount of herbs were fed to lactating cows. The milk they produce has the special fragrance and sweetness of herbs, which is better than ordinary milk and becomes the new favorite of the market. This fragrant milk and its preparation method have also been patented and popularized.
Second, the physical characteristics of milk
1, specific gravity: according to the number of ingredients contained, the specific gravity of milk at 20℃ is 1.028- 1.034.
2. Freezing point: The freezing point of milk is usually -0.54℃. The higher the content of lactose and inorganic salts in milk, the lower the freezing point, and vice versa. The commonly used and accurate classical method is to measure the freezing point of milk. When milk is mixed with 1% water, the freezing point can be increased by 0.0054℃, and when milk is mixed with fixed powder, soybean milk, CMC, etc. , can increase the freezing point, when the electrolyte urea and other soluble organic matter mixed, can reduce the freezing point.
3. Acidity: It is an important index reflecting the thermal stability of milk freshness. The pH value of normal milk is 6.5-6.7, mastitis milk with low acidity is above 6.7, and rancid milk and colostrum are below 6.5.
(1) Expression of milk acidity:
Thomet degree) (0T): that is, the consumption of 100ml milk is neutralized by titration with phenol as indicator. The acidity of normal milk is12-180t;
Lactic acid percentage
ML of 0. 1NnaOH solution
Lactic acid (%) = ————————————×100
Weight of milk to be measured (g)
Generally, the percentage of lactic acid in fresh milk is 0.11-0.17%.
(2) The source of milk acidity:
Natural acidity: the acidity of milk when it is just squeezed out is called it; Among them, about 3-50t comes from protein, about 1-20t comes from CO2, and 10- 1-20T comes from phosphate and citrate.
Fermentation acidity: during the storage of milk after extrusion, lactose is decomposed into lactic acid by microorganisms, which is called the increase of acidity.
The sum of these two acidity is called total acidity, which is usually expressed by acidity.
4. Other physical properties of milk: boiling point 100. 17℃, specific heat 0.938 kcal/kg℃, viscosity 1. 1-2.5 centipoise, as well as surface tension, refractive index and conductivity, all have certain parameter ranges, reflecting their normality.
Thirdly, the chemical composition and structure of milk
1, Overview: The main components of milk are water, fat, protein, lactose and minerals, and its trace components are vitamins, enzymes, fat, pigments, hormones and growth factors, organic acids, gases and somatic cells. In the 1960s, about 250 chemical components in milk were identified. Modern scientific research shows that milk is a mixture of about 3000 compounds.
After removing water and gas from milk, the remaining substances are called dry milk substances or total milk solids, and skimmed milk solids (SNF) refers to the solid content except fat.
Milk is a kind of biological nutrient solution with complex components, orderly structure and colloidal solution characteristics.
2. The main ingredients of milk
Due to the types and varieties of dairy cows (genetic factors), age and parity, lactation stage and season, feeding and management conditions, milk production level and milking technology, as well as individual characteristics and health status of dairy cows, the content of main components in milk varies greatly. See table 1 for the content of milk components in Shanghai recently.
Table 1 Content of main chemical components in milk (%)
average value
amplitude of variation
water
88.3
8.5.-89.5
total solids
1 1.7
10.5- 14.5
fat
3.3
2.5-5.2
protein
3.0
2.6-4.0
lactose
4.6
3.6-5.5
mineral
0.8
0.6-0.9
Milk fat is one of the most important ingredients in milk and dairy products. Chemical substances contain high thermal energy and a certain amount of essential fatty acids, and are carriers of vitamins A, D, E and K; It is closely related to the organizational structure, state and flavor of dairy products.
Protein content in milk is one of the most important quality indexes of milk. It is especially important for making dry, yogurt and other dairy raw materials; According to national regulations, only beverages with protein content ≥ 1% are allowed to be called milk-containing beverages. Milk protein can be divided into casein, albumin, globulin, globulin and lipid globule membrane protein. The same is true of the chemical properties of enzymes. Enzymes in milk come from breast tissue, plasma and white blood cells of dairy cows, which are called primary enzymes. Metabolites of microorganisms are called bacterial enzymes. Several enzymes are used to control and detect the quality of milk; The most important enzymes are catalase, acidophilic enzyme and lipolytic enzyme. Enzymes in milk have an influence on the processing of milk and the preservation of dairy products.
Lactose exists only in the milk of mammals. 1g lactose releases 16.7KJ of heat energy in the body, and lactose accounts for about 25-30% of the total calories of milk. It also has the functions of promoting calcium and phosphorus absorption and participating in body composition and cell activities. It is reported that 85-92% of adult yellow race people have very low intestinal lactase activity. After eating milk containing a lot of lactose, they will have abdominal distension, pain and even diarrhea, which is called lactose intolerance. Scientists and technicians have developed products such as low lactose milk and fermented dairy products to satisfy this group of people to enjoy milk.
Milk contains many vitamins, such as vitamins A, D, E, K, B 1, B2, nicotinic acid, B6, B 12, pantothenic acid, folic acid, biotin and vitamin C, etc. Mineral elements with a content of more than 0.0 1% in milk are Called macroelements or macroelements, such as sodium (Na), chlorine (CL), calcium (ca), phosphorus (p), magnesium (Mg) and sulfur (s). Trace elements include iron (Fe), copper (Cu), zinc (Zn), manganese (Mn), selenium (se), cobalt (Co), chromium (Cr), molybdenum (Mo), iodine (I), fluorine (F), nickel (Ni), vanadium (V) and silicon (V). The contents of vitamins and mineral elements in milk vary with varieties, heredity, environment, seasons, feed and drinking water, grazing land, feed additives and milk processing conditions.
3. Chemical structure of milk
Chemically, when one substance is dispersed into another in small particles, the dispersed substance is called dispersoid, such as lactose and inorganic salts in milk, and the substance receiving dispersoid is called dispersant, such as water. The mixed system composed of dispersoid and dispersant is called dispersion system. Milk is a mixture of four dispersion systems: (1) coarse dispersion system (suspension composed of solid particles such as protein with a particle size of 50- 100 nm); (2) Colloidal solution (fine dispersion system, particle size1-100 nm); (3) molecular solution (4) ionic solution.
4. Microbes and somatic cells in milk
1, milk is contaminated by pasture bacteria.
Milk is contaminated by bacteria before it leaves the breast; Because the lumens such as nipple duct and milk pool are communicated with the external scale. But these bacteria are generally harmless and have few counties (clinical mastitis milk is another matter). Milk is easily polluted during milking, storage and transportation. Many reports (such as 199 1 investigation of Shanghai 11th Ranch) think that the pollution caused by unclean surfaces of various containers contacting with milk is generally greater than the internal pollution. China's national standard GB 5408-85 allows super-grade, first-grade and second-grade fresh milk to contain 500,000,/kloc-0 and 2 million bacteria respectively. Commercially available sterilized milk is allowed to contain 30,000 bacteria. But no pathogenic bacteria can be detected. According to French raw milk quality standards, if the number of bacteria per milliliter is less than 60,000, score 3 points, score 2 points for 60,000-300,000, and score > 300,000 1 minute; Pricing according to quality. Canadian standards stipulate that the number of bacteria per milliliter of raw milk is below 6.5438+0.5 million. There are many bacteria in the nipple duct, and most of them are washed away when milking begins. Therefore, the milking operation rules often stipulate that milk should be squeezed into special cups (not mixed into milk storage tanks) at 1-3 in each milk area, which not only reduces the number of bacteria in raw milk, but also facilitates the detection of abnormal milk with clots and flocs. And the fat content of the first few handfuls of milk is much lower than that of the milk squeezed at the back.
In artificial milking, bacteria can enter milk from the surrounding environment and air (such as workers, cattle feed, ground feces and urine). Using milking machine to milk, especially milking platform or pipeline milking, can reduce pollution sources. But the milking equipment is not clean, and many bacteria will enter the milk.
Milk should be cooled to 4-0℃ as soon as possible after extrusion, which can inhibit the growth of microorganisms in milk and greatly improve the quality index of milk. For example, it is determined that freshly squeezed milk contains 40,000 bacteria per milliliter, and 90,000 bacteria can be stored at 5℃ for 24 hours. If stored at 10℃ and 15℃ for 24 hours, it will reach180,000 and 4.5 million respectively.
2. Mastitis in dairy cows and the number of somatic cells in milk.
Mastitis and recessive mastitis have great influence on the milk yield and quality of sick cows. There are more than 100 kinds of pathogenic bacteria that can cause mastitis, but 90-95% of them are caused by infection, such as Staphylococcus aureus, Streptococcus agalactiae, Streptococcus agalactiae and Escherichia coli. It is reported that the monthly incidence of clinical mastitis in the United States from 65438 to 0984 is 1-2%, and the positive rates of CMT for head and breast of subclinical mastitis are 40-50% and 20-25% respectively. From 65438 to 0988, the monthly incidence of clinical mastitis in adult dairy cows in Shanghai Dairy Company was about 65438 04%. The positive rate of head was 64.67%, and the positive rate of breast was 34.9 1%. It seems that the incidence of recessive mastitis is much higher than that of clinical type, and the influence of the former on milk yield and quality can not be ignored.
The effects of subclinical mastitis on milk composition are as follows: lactose decreased by 5-20%, casein decreased by 6- 18%, milk fat and total solids decreased by 5- 12% and 3- 12% respectively, and the contents of Ca, P, K and whey protein in milk also decreased, accounting for about 65433 of total protein.
Somatic cells in milk mainly come from white blood cells (formerly known as white blood cells), and a small number are epithelial cells shed from breast tissue, accounting for about 0-7% of the total number of cells (it is also reported that it can be as high as 25%). When the breast tissue is infected by bacteria, white blood cells gather here through the human immune system, and the number of somatic cells in the spilled milk increases immediately. Somatic cells in milk can be quickly determined by a special somatic cell fluorescence microscopic automatic analyzer. At present, it is recognized that this technology is highly correct and has been widely used. We can judge the degree of breast infection by bacteria according to the somatic cell count (SCC) in milk, which can directly reflect the health status of dairy cows' breasts, as well as the amount of milk loss and the quality of milk (see Table 2).
Table 2 Relationship between somatic cell number in milk and breast infection and milk loss
Total number of mastoid cells (× 1000ml)
Infected breast area (%)
Percentage of milk loss (%)
200
six
500
16
six
1000
32
18
1500
48
29
Excerpted from Aberhart et al. (1982)
Wells, S J( 1998), etc. It has been recognized by many scholars that the quality of milk in the United States today is measured by the total number of milk-like cells (short for BTSCC, sometimes called mixed milk SCC), which was developed in the United States, France, Germany, Sweden, the Netherlands and the United Kingdom in recent years.
3. Microbes in milk
(1) Type: The main microorganisms in milk are:
1) bacteria, which can distinguish lactic acid bacteria, Escherichia coli, butyric acid bacteria, propionic acid bacteria and spoilage bacteria, and each flora has multiple species and subspecies; 2) Fungi, which can be divided into yeast and mold; 3) Viruses, such as bacteria, destroy the quality of cheese, cream and fermented dairy products.
(2) Pathogenic microorganisms in milk
Sometimes there are many pathogenic microorganisms harmful to human health, such as mycobacterium tuberculosis, Brucella, Salmonella, anthrax, hemolytic or suppurative streptococcus, Staphylococcus, Listeria, some Escherichia coli and foot-and-mouth disease virus, etc., which should be strictly guarded against.
(3) Sources of microorganisms in milk:
1) Cows with systemic diseases or mastitis will undoubtedly have more germs in their milk.
2) Cattle are polluted, especially those with dirty breasts and their surrounding parts;
3) The ground, especially the places where cow dung and urine polluted by sewage, moisture or dust are not washed in high temperature season;
4) The milking utensils and milk containers have been measured. For example, if milk is washed with clean water, the content of bacteria in raw milk is 2.5 million per milliliter. If milk is sterilized by steam, there are only 23,000 bacteria in milk.
5) Mattress or pad of cattle bed, and forage;
6) Air: The bacterial content in the air of cowshed is usually ML50- 100, and the sanitary conditions can reach hundreds of thousands; Among them, Bacillus and cocci are the main ones, followed by mold and yeast.
7) Other pollution sources: such as milkman's hands and clothes, mosquitoes and flies, etc.
(4) Comprehensive measures must be taken to cut off the invasion route of microorganisms from the above sources in order to reduce the number of bacteria in milk. When milk leaves the pasture, it will also be contaminated by various microorganisms during storage, transportation and processing. Under suitable conditions, the bacteria originally existing in milk will grow and multiply in large numbers, and the microorganisms in milk must not be taken lightly.
5. Milk is polluted by chemicals.
There are many sources that milk is polluted by toxic and harmful chemicals. For example:
1, mycotoxins such as aflatoxin, Fusarium toxin and Corynebacterium toxin in feed can be excreted with milk by dairy cows after eating, which is harmful to human body.
2. Antibiotic residues: Antibiotics are used in dairy feed additives, or penicillin, streptomycin, gentamicin, chloramphenicol, neomycin, etc. In the treatment of cow diseases, the consequences of mixing the milk produced by these cows with edible milk are extremely serious. Both the Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization (WHO) suggest that milk expressed within at least three days after cows stop receiving antibiotic treatment should not be directly used as raw materials for edible milk. (It is best to stop taking medicine for 5-7 days). A number of inspection surveys conducted by health and epidemic prevention departments all over China found that the detection rate of antibiotic residues in fresh milk was 3.6%, that in sterilized milk was 1 1.48%, and that in milk powder was 39.58%. This problem must be solved practically.
3. Pesticide contaminated milk: There are more than 500 kinds of agricultural fungicides, insecticides, rodenticides and herbicides, among which organochlorine (such as BHC and DDT) and organophosphorus pesticides (such as trichlorfon) are commonly used and may be mixed into milk through various channels.
4. It is absolutely forbidden to excessively mix heavy metals and toxic salts such as mercury, cadmium, lead, arsenic, nitrate and nitrite in milk.
5. Other chemicals that are not allowed to enter milk, such as dioxins, disinfectants, detergents and neutralizers. 6. Adulterated substances: Some unscrupulous operators artificially add various adulterated substances to milk, which greatly reduces the quality of milk, which is even more unacceptable to national laws and ethics.
7. Detection example of this city: 1990, Shanghai Dairy Cow Research Institute cooperated with the Environmental Protection Monitoring Station of the Academy of Agricultural Sciences to detect milk samples evenly distributed at 30 sampling points in this city, and each milk sample detected 7 indicators. The results are listed in Table 3. Table 3 shows that 96.7% of the total milk samples tested are qualified, except for 1 sample, where the HCH residue exceeds the standard. According to the test items, 99.54% are qualified. At the same time, 9 feed samples, 5 water samples and 8 soil samples were tested in this project, and none of the above 7 indicators exceeded the standard.
Table 3 Test Results of Milk Samples and Standard Control (ppm)
test item
cadmium (Cd)
copper
lead to
Mercury
arsenic
horrible
DDT
Maximum allowable value in fresh milk
0.0 1
0.45
0. 1 1
0.0 1
0.2
0. 1
0. 1
Maximum allowable value in milk sample
0.005
0. 15
0.08
0.083
0.074
0. 158
0.0082
[Note] * The national standard for raw milk stipulates the above indicators of mercury, and other indicators are converted according to the indicators of milk powder and domestic water.
Six, milk and abnormal milk quality standards
1. Overview: The quality standard of milk and dairy products is to make technical provisions on the production, processing, quality grading, inspection methods, spoilage, storage and transportation of milk and dairy products. According to its publishing unit and scope of application, it is divided into national standards, Ministry (professional) standards and enterprise standards. In modern times, the standards of the International Dairy Federation (IDF) and the international quality certification system organized by the International Organization for Standardization (ISO) also appeared. It should be pointed out that product quality standards are not immutable, and should be revised and improved by the issuing and formulating departments with the development of production technology and the change of management level.
2, the quality standard of milk
(1) The raw milk purchasing standard GB69 14-86-86 was issued by China National Bureau of Standards 1986 and came into effect in July, 1987. Its content requires physical and chemical indicators, sensory and bacterial indicators.
(2) Twenty national standards for dairy products, such as sterilized milk, yogurt, whole milk powder, GB 2746-2747-85, GB-5408-5425-85, were issued in September 1985 and implemented in August 1. 0986. At the same time, "milk" was issued. According to 1998, the fourth annual meeting of China Dairy Industry Association decided that the current dairy quality standard is being revised, which will improve the milk protein rate and freshness.
(3) Abnormal milk: refers to milk whose composition and properties have changed and deviated from the prescribed quality standards in the process of milk production.
According to the causes of abnormal milk, it is often divided into four situations: (1) Physiological abnormal milk: colostrum, terminal milk and malnourished milk; (2) Pathological abnormal milk: mastitis milk contaminated by other pathogens; (3) Biochemical abnormal milk: high acidity milk, alcohol positive milk, low component milk and frozen milk; (4) adulterated milk: such as water, rice soup, soybean milk, lime water, etc.
There are still some ambiguities in abnormal milk, such as low acidity wine clear positive milk, and its causes and mechanism need to be studied. Abnormal milk is generally not suitable as raw material for processing dairy products, but it still has certain other utilization value.
Seven, the conventional nutritional value of milk
1, milk has comprehensive nutrition and good quality: all kinds of chemical components contained in milk are nutrients needed by human body, and milk has comprehensive nutrition and high quality. China Nutrition Society 1988 revised and published the "Daily Dietary recommended dietary allowance Recommendations", which stipulated energy, protein, fat, calcium, iron, zinc, selenium, iodine, vitamins A, D, E, B 1, B2, nicotinic acid, vitamin C and other items in milk. Milk protein, in particular, contains protein nutrition needed by the human body to meet the needs of infants, the elderly, the sick and the disabled, and is also an important supplement to plant protein in the diet of ordinary people: milk contains various vitamins needed by the human body, with vitamin A content of 180-400 ug/L and vitamin D content of 38-200 iu/L; Besides 1-2 mg/L nicotinic acid, milk is also rich in tryptophan (0.042-0.055%), and every 60mg of tryptophan can be converted into about 1mg nicotinic acid in human body. Milk contains many kinds of macroelements and microelements, especially the calcium available to human body is very rich.
2. Milk is digested, absorbed and highly utilized by human body: According to the measurement, the digestion and absorption rate of milk by human body reaches 92-98%. The physiological utilization rate of milk protein is 85% (fish 83%, meat 74%, rice 77%, flour 52%). The Food and Agriculture Organization of the United Nations (FAO)( 1973) has a tentative standard food with the optimal amount of amino acids needed by human body.
From another point of view, the fast-growing and extremely delicate mammalian newborns rely almost entirely on their mothers' milk for food. If the nutrition of milk is not complete or it is not easy to be absorbed and utilized, it is bound to be difficult to survive.
3. Milk is a kind of food with high nutrient concentration, that is, compared with their thermal energy value, milk contains higher concentration of main nutrients. For example, according to the data of the US Department of Agriculture (1980), the annual per capita consumption of dairy products is 240kg, and dairy products (excluding butter) provide about 10% of the total food consumption in the United States, while they provide 72% calcium, 36% vitamin B2, 33% phosphorus, 20% protein and 20%. In this sense, dairy products with high nutritional density, especially low-fat dairy products, are very suitable for patients with obesity, diabetes, hyperlipidemia and digestive system dysfunction.
4. Some nutritional defects of milk: The iron content in milk (500ug/L) is less than that in human milk (760ug/L), which is even less than the daily nutritional requirement of human body (10000- 18000 ug). Therefore, it is necessary to supplement iron and add more when breastfeeding the baby. There is no dietary fiber in milk, but dietary fiber is necessary for children over 6 months to have normal gastrointestinal function in old age.
Taurine is a metabolite of cysteine, which plays an important role in human vision, normal cell function, improving immunity and promoting infant brain development. Because the taurine content in normal milk and human milk often cannot meet the physiological needs of fast-growing children. At present, taurine is often added to infant milk powder and other dairy products.
Eight, the special nutritional function of milk
In addition to providing energy and conventional nutrition for human beings, milk also has many special functions, because milk is a special product of the tallest living mammal on the earth and contains many active substances involved in immune protection and physiological regulation. For example:
1. Milk can effectively supplement calcium for human beings. Calcium is the most abundant mineral element in human body, and it is also the most easily deficient nutrient element. People all over the world are short of calcium, especially in China, which is determined by the dietary structure of people in China. The absorption rate of calcium by fruits and vegetables, cereals, meat and fish is mostly lower than 25%, while milk is not only rich in calcium (850- 1300mg/L), but also rich in vitamin D, a factor that promotes calcium absorption and utilization. The absorption rate is significantly higher.
2. Milk can reduce the incidence of human hypertension. Studies have shown that insufficient calcium intake is one of the important factors leading to hypertension. Therefore, people are advised to eat a certain amount of dairy products to prevent hypertension.
3. Milk can lower people's cholesterol level. In common animal foods, the cholesterol content in milk is very low (only 140mg/kg, while in eggs and meat it is 4500 and 1000 mg/kg respectively). In addition, milk-based acids contained in milk can inhibit the synthesis of endogenous cholesterol in human body.
Drinking milk regularly can prevent intestinal cancer. Lecithin, superoxide dismutase (SOD) and Bifidobacterium proliferation factor in milk can directly or indirectly resist carcinogens. Another study believes that calcium in milk can convert carcinogens in the intestine into non-carcinogenic substances and excrete them, which can prevent colon cancer and rectal cancer.
5. Tryptophan in milk can be converted into 5- hydroxytryptamine in human body, which has sedative and hypnotic effects.
6. There are many special protein in milk, such as lactoferrin and vitamin B 12 binding protein, which can improve the absorption and utilization rate of milk and vitamin B 12 respectively.
7. Milk also contains dozens of protein, polypeptide or steroid hormones and growth factors, such as epithelial growth factor, nerve growth factor and erythropoietin. Many substances and their functions are still being explored.
8. Chinese medicine believes that milk is sweet and flat, and has the effects of tonifying deficiency, benefiting lung and stomach, promoting fluid production and moistening intestines. It can be used for physical weakness, strain, nausea, coughing, thirst quenching and constipation.
Nine, processed dairy products and their special health functions
Generally speaking, after leaving the breast, the quality of raw milk is getting worse and worse with the aggravation of microbial and chemical pollution. Timely and appropriate processing or adding legal food additives can increase the nutrition of raw materials, improve the color and flavor, improve the utilization rate of digestion and absorption, remove toxic and harmful factors and facilitate long-term preservation. Scientific processing can not only preserve the original nutritional components of milk, improve its quality, but also strengthen its health care function, and even give it new connotation, making it a functional or therapeutic food with extraordinary quality.
For example:
1, concentrated assembly line milk, condensed milk or diluted flavored milk, fruit and vegetable juice milk, milk-containing drinks, etc.
2. Milk and milk powder containing certain nutrients, such as low-fat milk, low-lactose (hydrolyzed) milk, fortified vitamins A and D, fortified calcium, zinc, iron and iodine, and dairy products added with taurine, immunoglobulin (Ig), docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA).
3. Fermented dairy products: Under the condition of artificial control, products fermented by adding some probiotics to milk have unique benefits to human physiological functions and become treasures in food. The typical representative of fermented dairy products is yogurt, which has been used in many countries in the world for thousands of years. In modern times, it has been endowed with many high-tech contents. For example, adding Lactobacillus acidophilus, Bifidobacterium or Lactobacillus Roy to the fermentation of mixed strains of Lactobacillus bulgaricus and Streptococcus thermophilus can produce more and stronger health care effects, such as inhibiting and killing spoilage bacteria, balancing intestinal microecology, improving digestive cavity flora and lowering serum cholesterol.
4. Further example of milk quality measurement: For example, Pellegrino, L.( 1996) reported that lactulose and furoic acid can provide lactose isomerization degree and early Maillard reaction (MR) respectively, and they are widely used to evaluate the heat applied in milk heating and sterilization, that is, these two indexes can be used to evaluate the heating process of dairy products.