Study on the sterilization technology of the hotte

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Abstract: This paper comprehensively analyzes and introduces the mechanism, advantages and applications of new sterilization technologies in the food industry, such as high-voltage pulsed electric field, ultrasonic wave, electrified sterilization, high-voltage sterilization, far-infrared sterilization, pulsed strong light sterilization, etc., and points out that these new sterilization technologies have broad prospects for development and utilization, and deep research should be carried out to promote the development of the food industry

key words: food industry; New sterilization technology

0 preface

in the food industry, the annual loss caused by food spoilage accounts for more than 20% of food raw materials. Therefore, sterilization technology has always been one of the research hotspots in the food industry. In the food industry, traditional heating sterilization plays a very important role in the process of killing and inhibiting harmful microorganisms, but it will inevitably produce some side effects on the nutritional value, flavor and taste of food, especially for foods with heat sensitivity that better meet the needs of product utilization or special requirements, which are often difficult to achieve the desired effect. Therefore, some new sterilization technologies that limit the impact on food quality to a minimum and can quickly and effectively kill harmful microorganisms in food materials, save energy, improve product nutrition and sensory quality, and meet the requirements of product indicators came into being. These new sterilization technologies include high-voltage pulsed electric field, ultrasonic wave, power on sterilization, high-voltage sterilization, far infrared sterilization, pulse strong light sterilization, etc

1 high voltage electric pulse sterilization

high voltage electric pulse sterilization uses the appearance of negative pulse peaks to form a rapidly changing pressure on the cell membrane under the high voltage pulse electric field, which makes its structure loose. It can quickly destroy the permeability of the cell membrane by cooperating with positive pulse peaks. At the same time, the width of high-voltage electric pulse is only 2 μ s. It has no warming effect on food

this method has two characteristics,

first, due to the short sterilization time, the energy consumption in the treatment process is far less than that of heat treatment

second, because it is carried out under normal temperature and pressure, the processed food and fresh food have little change in physical properties, chemical properties and nutritional components, and there is no perceptible difference in flavor and taste. The sterilization effect is obvious and meets the requirements of commercial sterility. It is especially suitable for food with high heat sensitivity. Yue Chaoyang et al. Used the high-voltage pulse generator to sterilize milk. The results showed that the sterilization effect of high-voltage pulse electric field was remarkable

2 ultrasonic sterilization

the cavitation effect of ultrasound can produce micro jets and local high heat and pressure between the cell wall and the cell fluid. This has a strong killing effect on bacteria, bacteria and other microorganisms, and the heterogeneous interface will be finely broken due to the tangential force of ultrasonic vibration and micro jet, so it can easily sterilize and remove the dirt of food packaging and processing equipment. Zhou Yongchang and others used ultrasound to sterilize and preserve the salted duck, and achieved good results

3 electrified sterilization

electrified sterilization is also known as "ohmic sterilization, but the combustion performance of polyurethane insulation materials stays at the level of flammable B3 or flammable B2". It uses electrodes to pass current through objects. Due to the existence of impedance loss and medium loss, it finally converts electric energy into heat energy, so that heat is generated inside food and sterilization. The conventional method of heat sterilization is to use heat exchanger for indirect heat exchange, and its process rate depends on the heat transfer conditions of conduction, convection or radiation. In the case of inter wall heat exchange, the heat is first transferred by the heating medium (such as steam) through the export growth of China's extruder products, which will show a stable and progressive situation. The inter wall is transferred to the liquid in the food materials, and then transferred to the solid particles by convection and conduction between the liquid and solid particles. Finally, the conduction and heat transfer inside the solid particles make all materials reach the required sterilization temperature. Obviously, in order to make the interior of solid particles reach the sterilization temperature, the liquid part around them must be overheated, which will inevitably lead to soft and rotten texture and shape changes of food containing particles after sterilization, affecting the product quality. The heating rate of particles is close to that of liquid, and the heating rate of particles is faster than that of conventional methods. Therefore, the processing time can be shortened and high-quality products can be obtained

According to the preliminary discussion of the mechanism of sterilization with electricity, there are two reasons:

on the one hand, sterilization due to the temperature rise caused by heating with electricity

on the other hand, sterilization due to the destruction of the bacterial cell membrane between the two electrodes with electricity due to the effect of the applied electric field. Electric sterilization can kill E. coli, yeast and Bacillus in liquid food. For some microorganisms that are difficult to kill, the sterilization effect can be improved by high-voltage power on sterilization, that is, placing the power on heating device in a certain pressure of inert gas. One of the advantages of electrified sterilization is that it has less damage to nutrients such as vitamins. The electric heater can handle food materials with high particle density and high viscosity, which can be used to minimize the residence time distribution. Since 1991, the technology and equipment have been applied to the processing of low acid or high acid foods in Britain, Japan, France and the United States. At present, apvbaker company in the UK has manufactured industrial scale powered sterilization equipment for the processing of granular food

4 high pressure sterilization

compared with traditional thermal sterilization, high pressure sterilization can not only effectively kill microorganisms, but also maintain the unique flavor and quality of food, and avoid color change, heating odor and harmful substances caused by heating. High pressure sterilization is to pack food materials in a certain way and put them into a high-pressure (200MPa) device for pressure treatment to achieve the purpose of sterilization requirements. The basic principle of high-pressure sterilization is to use the lethal effect of pressure on microorganisms. High pressure leads to many changes in the morphological structure, biochemical reaction, genetic mechanism and cell membrane of microorganisms, which affects the original physiological function of microorganisms, and even destroys or irreversibly changes the original function. Meiji house food company of Japan adopts high-pressure sterilization technology to produce jam. The soft package sealed jam is treated at room temperature with a pressure of 400-600mpa for 10-30min, and the obtained product maintains the taste, color and flavor of fresh fruit

5 far infrared sterilization

far infrared sterilization does not need to go through the heat medium, and its heat transfer can directly penetrate from the surface to the interior. Therefore, far infrared sterilization can be used not only for the sterilization of general powdery and block foods, but also for the sterilization and sterilization of nut foods such as coffee beans, peanuts and grains, as well as the direct sterilization of bag foods. Far infrared ray sterilization effect is obvious. Far infrared sterilization has been applied in practical production abroad. For example, the surface of crops is often polluted by microorganisms. The most common way to eliminate this pollution is to pass toxic gases such as ethylene chloride, propylene chloride and the mixture of ethylene chloride and methyl bromide into crops, but the use of these toxic gases will bring a series of potential safety problems. However, there is no such problem when far infrared radiation is used to sterilize the surface of grains and fruits. And the production cost is lower than the above method. The use of far-infrared sterilization can not only kill the yeast and mold on the surface, reduce the microbial pollution on the surface to a certain extent, but also help shelling. Most food materials have the highest absorption rate of 149 trillion M2 data in 2016. Far infrared radiation can not only directly spread energy to the surface of objects, but also spread energy to a certain depth of objects. However, in the thermal radiation electromagnetic field, the photon energy level of far infrared is smaller than that of ultraviolet and visible light. Therefore, generally, it will only produce thermal effect and will not cause chemical changes of substances. In addition, the heating time is short, so it can reduce the loss of nutrients and color, flavor and fragrance during the heating process

6 pulse strong light sterilization

pulse strong light sterilization technology adopts the method of strong white light flash for sterilization. The main factors of pulse strong light sterilization effect are the number of flashes, the original concentration of bacterial solution and the input voltage. It is composed of a power unit and an inert gas lamp unit. The power unit is a component that can provide high voltage and high current pulses to provide the required energy for the inert gas lamp. The inert gas lamp can emit light in the ultraviolet to near-infrared region. Its spectrum is very similar to the sunlight, but its intensity is thousands to tens of thousands of times stronger. Because this technology only deals with the surface of food, it has little impact on the flavor and nutritional components of food. It can be used to extend the shelf life of food packaged with transparent materials and fresh food, and has a bright future. Josephdunn and other research results show that it can kill most microorganisms and has higher efficiency than traditional UV lamps. Therefore, the research on this technology was carried out. The results show that after 40 times of pulsed strong light flashing, the activity of amylase and protease decreased by 70% and 90%, which did not damage the main components of food, and the shelf life of bread was more than doubled

7 conclusion

with the development of modern science and technology, new sterilization technologies in the food industry continue to emerge. To vigorously develop these new technologies, we must thoroughly understand their mechanism, give full play to their advantages of high efficiency, low energy consumption and maintaining food nutrition and sensory quality, so that they can be more effectively applied in practice, so as to promote the development of the food industry

(author: zhanghongkang, East Campus of China Agricultural University)

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