The flourishing development of the dairy industry is inseparable from the development of society and the advancement of science and technology. Today milk has become an essential drink in human life. However, milk is not favored by human beings when it appears. Even for a long time, people talk about "milk" discoloration. Before the 19th century, due to the lack of sterilization technology, at the higher temperature, the milk that was just extruded was easily contaminated by bacteria, causing disease in drinking people. At the time, the mainstream view was that milk was a high-risk food. Until the 19th century, due to the development of technology, the promotion of pasteurization methods improved the safety of milk, making dairy products an unprecedented development, from which milk became a common drink on the residents' table. According to the 2018 National Economic and Social Development Statistical Bulletin, the milk production in 2018 was 30.75 million tons, which was only 1.2% higher than that in 2017. Domestic milk supply remained tight.
Nutritional value of dairy products
Milk is an important source of human protein, calcium, phosphorus, vitamin A and vitamin B2. The protein content of milk is about 3-4%, of which casein is the main case, and the rest are whey protein and lactoglobulin. Milk has a fat content of about 2.8 to 4%, which is present in the form of particulate fat globules and is easily digested and absorbed. Milk is rich in lactose, which promotes the body's absorption of minerals such as calcium, iron and zinc, regulates gastric acid, promotes gastrointestinal motility, and promotes secretion of digestive juice. It also plays an extremely important role in the normal work of our brain, intellectual development and so on. Milk also has the effect of calming the nerves. Drinking a cup of warm milk before going to bed can help sleep. In addition, milk is also rich in animal calcium. The human body is more likely to absorb animal calcium, which is the best source of calcium in the diet.
Membrane separation technology enhances dairy quality
Many people may experience uncomfortable stomach, bloating, diarrhea, and barking after drinking milk. This phenomenon is called "lactose intolerance." It is more appropriate to call lactose intolerance a "trait" because it is more common because it is a "trait". 70% of Asians do not absorb lactose, while more than 75% of our population is lactose intolerant.
How to remove lactose from milk without affecting the flavor and nutrients of milk? Here we use the membrane separation technology we are talking about. First, use ultrafiltration membrane to intercept the protein and fat in the milk and let other substances flow out. The nanofiltration membrane is used to intercept the lactose and let water, inorganic salts, minerals and the like flow out. After the milk passes through the two layers of film in turn, we add the portion trapped by the ultrafiltration to the final liquid to be mixed, and the lactose-free milk is pulled.
At present, the application of membrane separation technology in the dairy industry includes: dairy sterilization, dairy concentration, whey desalting, milk protein fractionation and the like.
The traditional method of sterilization of dairy products is heat sterilization, mainly pasteurization and ultra-high temperature instantaneous sterilization. Membrane technology has been developed to remove bacteria from dairy products in recent years. Microfiltration technology can replace bacteria and spores in dairy products in place of heat sterilization and chemical preservatives. The active ingredients in the dairy can be passed through without affecting the flavor of the dairy, while extending the shelf life of the dairy. The cross-flow filtration technique (film pore size 1.2 um) was used to remove bacteria from the degreased and low-fat milk, and the sterilization rate was >99.6%. The shelf life of dairy products produced by the membrane separation process is extended from 6-15 days to 16-21 days.
Membrane separation is concentrated in dairy products: concentrated whole milk, concentrated skim milk, concentrated whey protein, concentrated in yogurt, and the like. Natural milk contains about 87% water. Concentrate the milk before transportation, and add water to the whole milk when it is put into production, which can reduce the transportation cost of milk. At present, more than 60% of the water can be removed by the reverse osmosis method, and the skim milk with a protein content of up to 80% can be obtained by the ultrafiltration method. The most concentrated application of milk protein in dairy processing plants is ultrafiltration membranes, which use ultrafiltration separation technology to intercept proteins in raw milk and allow lactose and ash to pass through. The lactose and ash can be removed to the utmost by continuously adding water to the filtrate to obtain a high protein content of concentrated milk protein and lactose. Conventional concentration methods such as flashing require heating. This method has high energy consumption and can cause protein denaturation in milk, and the introduction of membrane separation technology can greatly reduce energy consumption.
The whey salt produced by the production of cheese has a high salt content and must be desalted before it can be recovered, evaporated and dried. Nanofiltration membrane separation technology can block the divalent ions and components in the whey to a certain extent, allowing the monovalent ions to pass through. For the concentrate, an appropriate amount of washing water can be added, and the whey is desalted to meet the product requirements, and the clear liquid can be directly discharged. Nanofiltration membrane separation technology can effectively remove the odor and salt taste without destroying the flavor and nutritional value of the milk.
Milk protein fractionation
Each milk protein has different nutritional and specific functional properties. Therefore, the fractionation of milk proteins in recent years has become the focus of attention in the dairy industry worldwide. The separation and classification of milk proteins includes separation and fractionation of whey proteins and fractionation of casein. The milk proteins are fractionated and purified using different molecular weight membranes to obtain different proteins such as whey protein, serum albumin, lactoglobulin, lactalbumin, egg albumin, and simian. At present, foreign research is being carried out to combine various membrane separation techniques with chromatographic methods, chemical treatments, and enzymatic treatments to separate various components of milk proteins.
In developed countries, membrane separation technology has matured in dairy production and continues to expand its range of applications. China's membrane separation technology is in the preliminary stage of application in dairy products. However, with the improvement of the living standards of our people and the increasing demand and quality of dairy products, modern membrane separation technology, with its unique properties, has broad prospects in the development of dairy industry.