Pasteurization, also known as low-temperature sterilization, cold sterilization, is a disinfection method that uses lower temperatures to both kill germs and maintain the flavor of the nutrients in the article, often in a broad sense. Used to define heat treatment methods that require the killing of various pathogens.
Pasteurization is to heat the mixed raw materials to 68-70 ° C, and keep this temperature for 30 min and then rapidly cool to 4-5 ° C. Because the fatal point of common bacteria is 68 ° C and 30 min or less, the mixed raw materials can kill pathogenic bacteria and most non-pathogenic bacteria after being treated by this method; Cooling, sharp heat and cold changes can also cause bacterial death.
In a certain temperature range, the lower the temperature, the slower the bacterial reproduction; the higher the temperature, the faster the reproduction (the appropriate temperature for general microbial growth is 28 ° C - 37 ° C). But if the temperature is too high, the bacteria will die. Different bacteria have different optimum growth temperatures and heat and cold resistance. Pasteurization is actually the use of pathogens that are not very heat-resistant. They are treated with appropriate temperature and holding time to kill them all.
However, after pasteurization, a small number of harmless or beneficial, heat-resistant bacteria or bacterial spores are retained, so pasteurized milk should be stored at a temperature of about 4 ° C and can only be stored for 3 to 10 days. Up to 16 days.
There are a wide variety of pasteurization procedures in use today. The "Low Temperature Long Time" (LTLT) process is a batch process that is now used only by small dairy factories to produce some cheese products. The "High Temperature Short Time" (HTST) process is a "flowing" process, usually carried out in plate heat exchangers, and is now widely used in the production of drinking milk. The product obtained in this way is not sterile, i.e. still contains microorganisms, and requires refrigeration during storage and handling. "Quick pasteurization" is mainly used to produce yogurt dairy products. There are two main types of pasteurization methods commonly used in the world:
One is to heat the milk to 62~65 °C for 30 minutes. Using this method, it can kill various growth-type pathogenic bacteria in milk, and the sterilization efficiency can reach 97.3%~99.9%. After disinfection, only some thermophilic bacteria and heat-resistant bacteria and spores remain, but these Most of the bacteria are lactic acid bacteria, and the lactic acid bacteria are not only harmless to humans but also good for health.
The second method heats the milk to 75~90 °C and keeps it for 15~16 minutes. The sterilization time is shorter and the work efficiency is higher. However, the basic principle of sterilization is that the pathogen can be killed, and the temperature is too high, but there will be more nutrient loss.
Remarks: PU, which is kept at 60 ° C for one minute, is called a sterilization strength.
Main application of pasteurization
The degree of pasteurization heat treatment is relatively low, and is generally heated at a temperature lower than the boiling point of water, and the heated medium is hot water.
Different foods are pasteurized for different purposes. Some foods, especially cow's milk, whole eggs, egg whites and egg yolks, are mainly used to destroy possible pathogens such as Mycobacterium tuberculosis and Salmonella. In addition, most foods, such as beer, fruit wine (wine) and juice, are pasteurized to extend the shelf life of the product from a microbiological and enzymatic perspective.
Generally, pasteurized foods still contain many microorganisms that can grow, usually with thousands of live bacteria per milliliter or per gram, which is shorter than the commercial sterilization products. In addition to liquid foods (juice, milk), acidic foods and canned jams, pasteurization technology also penetrates into other fields. For example, steam treatment can reduce the number of bacteria in oysters when handling shelled oysters. It has the advantage of treating food at a lower temperature and in a shorter period of time, and maximizing the damage of the color, aroma, taste and nutrients of the food from long-term treatment at high temperatures.
It is mainly a sterilization method for milk, which can kill pathogens that are harmful to health and make the milk quality change as little as possible. That is, according to the difference principle between the heat lethal curve of the tuberculosis which is extremely resistant to high temperature and the heat-destructive curve of the cream which is most susceptible to heat in the milk, a kind of heat treatment for a short time at a low temperature for a long time or at a high temperature method. Among them, the method of heating at 60 ° C or lower for 30 minutes has been widely used as a standard for low-temperature sterilization. The use of high temperature treatment, although somewhat affecting the milk quality, can enhance the sterilization effect. This method is called sterilization, that is, heating at 95 ° C or higher for 20 minutes. Pasteurization can also be applied to fermented products in addition to milk.
Typically, bagged milk sold on the market is produced by pasteurization. Fresh milk is collected from the factory, first treated at low temperature and then sterilized by pasteurization. Bagged milk produced in this way can usually be stored for a longer period of time. Of course, the specific process and process are much more complicated, but the general principle is this.
It should be pointed out that drinking fresh milk (referred to as milk that has just been squeezed out) is not safe because it may contain bacteria that are harmful to our body. Another point is that pasteurization is not a panacea. The pasteurized milk is still stored at a lower temperature (generally <4 °C), otherwise there is still the possibility of deterioration. Therefore, many methods of selling bagged milk on the market are very irregular.
Pasteurized milk is the most consumed milk in the world. The consumption of pasteurized milk in the United Kingdom, Australia, the United States, Canada and other countries accounts for more than 80% of liquid milk. The varieties are fully degreased, semi-degreased or fully fat. In the US market, it is almost all pasteurized milk, and it is a large package (1 liter, 2 liters, 1 gallon). The public buys fresh milk for one week at a time in the supermarket. There are very few sterilized pure milk sold in the market, and some small towns cannot buy them at all.
Pasteurized pure milk preserves the nutritional and natural flavor of milk and is the best of all milk varieties. In fact, as long as the pasteurized milk is stored at a temperature of about 4 ° C, the reproduction of the bacteria is very slow, and the nutrition and flavor of the milk can remain unchanged for several days.
Pasteurization solves the problem of beer becoming sour. At the time, the French wine industry faced a headache: the wine would become sour after it was brewed and could not be drunk at all. And this acidification phenomenon often occurs. Pasteur was invited to study this issue. After a long period of observation, he found that the main culprit in making wine sour is Lactobacillus. Nutritious wines are a paradise for the growth of lactobacilli. A simple method of boiling can kill the lactobacillus, but the wine is boiled. Pasteur tried to use different temperatures to kill Lactobacillus without destroying the wine itself. Finally, Pasteur's research results: heating the wine at a temperature of 63.5 ° C for half an hour, you can kill the lactobacilli in the wine without boiling. This method saved the French wine industry.
Pasteurization ultra-high temperature sterilization
With the advancement of technology, people also use ultra-high temperature sterilization (UHT ultra-high temperature instant sterilization, higher than 100 ° C, but the heating time is very short, the damage to the nutrients is small) to treat the milk. The milk treated in this way will have a longer shelf life. Most of the milk in carton packs we see is in this way.
Pasteurization sterilization storage technology
In the liquid medium, the biological effect sterilization of pulse discharge is utilized. The sterilization equipment is generally composed of two parts: a pulse discharge power supply for supplying energy and a sterilization chamber for directly sterilizing liquid materials. Working principle: when the pulse discharge is sterilized, the liquid material is placed as a dielectric. In the gap between the two electrodes of the sterilization chamber or continuously flowing through the two electrode gaps of the sterilization chamber, when the two electrodes are applied with a pulse electric field of a certain intensity and frequency, a strong biological effect is generated in the liquid material to kill the bacteria therein.
In the conductive solution, due to the redox reaction caused by the exchange of electrons at the interface between the electrode and the solution, the reaction of this technology is divided into two types, one is caused by external electric energy, and the other is that there is no external power supply. It is inspired by the external light, heat or other forms of energy.
Generally speaking, it refers to a method of killing microbial bacteria through a low-frequency alternating current of several hundred hertz or less in a liquid material of a fruit and vegetable juice. One of the methods of expanding use uses the thermal effect of alternating current, also called resistance heating technology, which utilizes continuous flow. The electrical resistance of the conductive liquid is heated to achieve sterilization.
Pasteurization ultrasonic sterilization
A series of reactions using cavitation, mechanical, chemical, thermal, dispersion, acoustic flow, capillary, and thixotropic effects of ultrasonic waves propagating in solids, liquids, and gases to achieve sterilization purposes.
Pasteurization laser sterilization
A laser is an electromagnetic wave, also an energy flow (photon flow), which is sterilized by the working principle of some special biological effects (chemical reaction, thermal effect, electronic effect, pressure effect, bio-stimulating effect) produced by the organism.
Pasteurization pulse sterilizing
Sterilization is carried out using a strong white light flashing technique, which is generally used to treat the surface sterilization of foods and to extend the shelf life of prepackaged foods of transparent materials.
Pasteurization magnetic field sterilization
Both constant magnetic fields and pulsed magnetic fields can effectively inhibit the growth of certain microorganisms and bacteria. When a certain magnetic field strength is reached, enzymes, amino acids, nucleic acids, and proteins can be made by inhibiting the free radical activity of foods and affecting the activity of proteins and enzymes. The biological macromolecules lose their activity and kill the bacteria.
Pasteurization microwave sterilization
The thermal effect of microwave energy: Under the action of a certain intensity microwave field, the insects and bacteria in the food will be heated by the microwave energy due to the molecular polarization phenomenon, thereby denaturation of the protein and loss of biological activity. The thermal effect of microwave mainly plays a role in rapid temperature sterilization;
The non-thermal effect of microwave energy: The high-frequency electric field also changes the membrane potential and polar molecular structure; the microbial protein and physiologically active substances are mutated, and the vitality or death is lost. It has played a special role in conventional physical sterilization in sterilization and is one of the causes of bacterial death.
Louis Pasteur (1821-1895.9.25) French microbiologist
Pasteur, chemist, founder of modern microbiology. Like Newton's pioneering classic mechanics, Pasteur opened up the field of microbiology, created a unique set of basic microbiological research methods, and began to use the "practice-theory-practice" approach to start research. He is also a scientific giant.
Pasteurization personal achievement
Pasteur has conducted a number of exploratory studies throughout his life and has achieved significant results. He is one of the most accomplished scientists of the 19th century. He used his life's energy to prove four scientific problems:
(1) Each fermentation is due to the development of a microbacterium. The French chemist found that heating can kill the annoying microorganisms that make the wine sour. Soon, the pasteurization method is applied to a variety of foods and beverages.
(2) Every infectious disease is a development of microbacteria in the living body: Pasteur saved the French silk industry by discovering and eradicating a bacterium that invades silkworm eggs.
(3) The micro-organisms of infectious diseases can reduce the virulence under special cultivation, and make them from vaccines to vaccines for disease prevention. He realized that many diseases were caused by microorganisms, and established the theory of bacteria.
(4) The ingenious invention of the retort and the bacterial test prove that it is not caused by corrupt objects, but that the bacteria corrupt the objects, breaking the long-standing view of Newton and others.
Louis Pasteur was praised by the world as "the most perfect person to enter the kingdom of science". He is not only a theoretical genius, but also a person who is good at solving practical problems. Two papers he published in 1843, "Study on Twin Crystals" and "Crystal Morphology," pioneered the study of the optical properties of matter. From 1856 to 1860, he proposed a new theory of fermentation based on microbial metabolic activities. The "Record of Lactic Acid Fermentation" published in 1857 is a well-recognized classic paper in the field of microbiology. After 1880, a variety of vaccines such as chicken cholera vaccine and rabies vaccine were successfully developed. The theory and immunology have caused major changes in medical practice. In addition, Pasteur's work has successfully saved France's troubled wine, sericulture and animal husbandry.
In September 1854, the French Ministry of Education appointed Pasteur as Dean of the Lille Institute of Technology and Director of the Department of Chemistry. At this time, he became interested in the alcohol industry, and an important process in the production of alcohol was fermentation. At that time, an alcohol manufacturing plant in Lille encountered technical problems and asked Pasteur to help study the fermentation process. Pasteur went to the factory to investigate and bring various beetroot juices and fermentation liquids back to the laboratory for observation. After many experiments, he found that there is a spheroid in the fermentation broth that is much smaller than the yeast. When it grows up, it is yeast.
Soon, the buds grow on the cells, and the buds fall off and become new spheroids. In this cycle, the beetroot juice is "fermented". Pasteur continued to study and find out that the alcohol and carbon dioxide gas produced during fermentation are all yeasts that break down sugar. This process can occur even in the absence of oxygen. He believes that fermentation is the anaerobic respiration of yeast and controls their living conditions, which is a key link in winemaking.
The "Record of Lactic Acid Fermentation" published by Louis Pasteur in 1857 is a classic paper recognized by the microbiology community.