课件：食品加工新技术.ppt

Ultrasonic sterilization,Contents,Introduction ultrasonic Mechanism of ultrasound sterilization The influence of ultrasonic sterilization effect factors Ultrasonic sterilization technology Ultrasound with other technologies synergistic sterilization Ultrasonic sterilization equipment The problems existing in the ultrasonic sterilization,Introduction,Each year in the food industry because of the loss caused by microbial action is huge, and produced by microbial food deterioration caused by food safety problem increasingly prominent, so the sterilization is a key process the food processing and storage.,Food sterilization methods varied, in terms of its essence, is the sterilization and inhibit the growth of microorganisms in food, to food can be available for use in a long time. Chemical sterilization caused serious residues of harmful chemicals in foods,endanger the safety of food; The traditional low temperature heating can not kill all in food microbiology, and high temperature sterilization will destroy nutrients in the food and the food in different degrees of natural features, result in nutritional components of destruction, loss, or lead to bad flavor, color intensifies, loss of volatile components, etc.,In recent years, studies have shown that ultrasonic can in a very short period of time to kill and destroy microbes, also can have on food such as homogeneous, Chen, a variety of action such as cracking macromolecule material, which can improve and improve the food quality and better keep food original taste and flavor, so ultrasonic technology is becoming more and more attention.,ultrasonic,Ultrasonic belongs to the mechanical wave, as part of the sound waves, frequency is greater than 20 KHZ. Particle by mechanical force is generated by the medium effect of periodic vibration.,The two main parameters of ultrasonic wave: Frequency: F p 20 KHZ (similar because of the effect in practice, usually the F 15 k of sound waves, also known as ultrasonic or higher); Power density: p = transmission power (W)/launch area (cm2); Usually p acuity 0.3 w/cm2;,ltrasonic wave has the following features: 1) ultrasound can be in gas, liquid and solid, solid solution and other effective transmission medium. 2) ultrasound can pass strong energy. 3) the superposition of ultrasonic will produce reflection, interference, and resonance phenomenon. 4) the spread of ultrasound in liquid medium, can have a strong impact on the interface and cavitation phenomenon.,Ultrasonic effect when the ultrasonic wave propagation in the medium, because of the ultrasonic wave interaction with the media, physical and chemical changes in the medium, to produce a series of mechanical, thermal, electromagnetics and chemical effects of ultrasound, including the following four kinds of effects:,(1) mechanical effect. Ultrasonic mechanical action may contribute to a liquid emulsion and the liquid and solid dispersion of gel. When ultrasonic standing wave formed in the fluid medium of particles suspended in a fluid due to the effect of mechanical force and condensed in nodal,Ultrasonic wave propagation in piezoelectric materials and magnetostrictive materials, due to the mechanical action of ultrasonic wave caused by the induced polarization and electric induced magnetization (see the dielectric physics and magnetostriction).,(2) Cavitation effect (3) heat effect Due to the ultrasonic frequency is high, the energy is large, when absorbed by the medium can have a significant effect.,(4) chemical effect The role of ultrasound can make or speed up certain chemical reactions happen. For example, the pure distilled water after ultrasonic treatment to produce hydrogen peroxide; Water is dissolved nitrogen after ultrasonic treatment produce nitrite; Dye,aqueous solution after ultrasonic treatment can change color or fade. The occurrence of these phenomena with cavitation accompanied. Ultrasound can also accelerate the hydrolysis of many chemical substances, decomposition and polymerization process. Ultrasonic light chemical and electrochemical process,has obvious influence. Various amino acids and other organic material solution after ultrasonic treatment, the characteristic absorption spectrum with disappear and general absorption of homogeneously, this shows that the cavitation effect makes the molecular structure has changed.,Mechanism of ultrasound sterilization,Cavitation effect Ultrasonic cavitation is refers to the tiny air bubbles in the liquid core vibrate under the wave action, when the pressure reaches a certain value, the cheongsam will rapidly expand, then suddenly closed, the bubbles have repercussions when closed, this expansion, closure, oscillation and a series of dynamic process called ultrasonic cavitation.,The influencing factors of ultrasonic cavitation: (1) ultrasonic intensity Ultrasonic intensity refers to the ultrasonic power per unit area, have related to the intensity of the ultrasonic cavitation. For general liquid ultrasonic intensity increases,the cavitation intensity increases, but after reaching a certain value, cavitation tends to saturation, at this time in increasing the intensity of ultrasonic, can produce a large number of useless bubbles, thus increasing the scattering attenuation, reduce the intensity of cavitation.,(2) ultrasonic frequency Ultrasonic frequency is lower, the easier to produce cavitation in the liquid. That is to cause cavitation, the higher the frequency, the greater the need sound intensity. Generally USES the frequency range of 20-40 KHZ.,(3) the surface tension of the liquid and viscous coefficient The greater the surface tension of liquid, cavitation intensity is higher, the more it is not easy to produce cavitation. Viscous coefficient of liquid is difficult to produce cavitation bubble, and losses in the transmission of large, so also is not easy to produce cavitation.,(4) the temperature of the liquid Liquid temperature is higher, the better in the formation of cavitation, but at high temperature, air bubbles in the vapor pressure increases, thus enhances the cushion makes the cavitation bubbles closed.,It is generally believed that ultrasound have the sterilization effect is mainly caused by its produce cavitation. Tiny bubbles at the instant of the adiabatic compression and collapse,its internal can present above 5000 high temperature and the pressure of 50000 kpa, thus kill some bacteria in the liquid, and virus inactivation, and even some small microbial cell wall broken, but their range is limited.,The influence of ultrasonic sterilization effect factors,Ultrasonic effect parameters Microbial properties Other factors,Ultrasonic effect parameters Sound intensity General situation of sterilization intensity is 2 to 10 w/cm2; When the sound intensity exceeds a certain limit, cavitation effect will weaken, sterilization effect will decline.,Frequency Sterilization of ultrasound for 20 to 50 KHZ frequency; With the increase of frequency, sound wave propagation attenuation will increase, the sterilization effect will be reduced.,The amplitude In general amplitude increase bactericidal effect will also be enhanced.,The sterilization time Research has shown that with the increase of the sterilization time, sterilization effect is generally higher than increase, but to further increase the sterilization time, sterilization effect and no obvious increase, but tend to be a saturated value. So the general sterilization time is set within 10 minutes.,Microbial properties The concentration of bacteria in the sample When the sterilization time phase at the same time, the samples contain high concentrations of bacteria sterilization effect is slightly less than when low concentration.,The capacity of bacteria in the sample Ultrasonic wave exists in the process of media transmission attenuation phenomenon, will increase with the increase of propagation distance and, therefore, with the increase of sample processing, sterilization effect would be reduced.,Microbial species The effects of ultrasound on microbial with state of the structure and function of microorganisms in itself. Generally speaking, the killing effect of ultrasound on the microorganisms is kill bacillus is faster than kill bacteria; For big coli faster than small bacillus kill.,Other factors Sterilization, sample temperature can also affect the sterilization effect of temperature, ultrasonic effect on the destruction of the bacteria. Ultrasound in different coal quality, effects on different components of the food, the effect will be different. Lopez - Malo, etc.,The effects of pH, water activity, temperature and ultrasonic amplitude of finger mold bactericidal effect, found the water activity in 0.99, adding ultrasonic amplitude and lower pH can reduce D value; When pH values, water activity increased when D value decreased.,Ultrasonic sterilization technology,In the early 1930 s, ultrasonic and collaborative research on other means of sterilization has been put forward. Some results show that the single use of ultrasound sterilization effect is limited, but the ultrasound combined with other sterilization methods, has great potential, its sterilization effect is very significant.,Ultrasonic sterilization alone Soy sauce is a liquid by microorganism fermentation and get food, it is in the process of production easy to be contaminated with harmful bacteria, mold, etc, when the temperature above 20, white spots appear easily in the soy sauce surface, then upset, will form the wrinkled film, color from white to brown, this is the soy sauce mildew, mildew soy sauce concentration,freshness, nutrition is mixed bacteria consume, seriously affecting the quality of soy sauce. The manufacturers generally use the antibacterial, such as preservatives or heat sterilization measures. Preservative bacteriostasis will remain some harmful ingredients to human body, at the same time, still have a kind of bad taste, greatly reduces the quality of soy sauce. And heating sterilization is not only consumes a lot of,energy, and inevitablyconsume soy sauce ingredients. Ultrasonic sterilization technology applied to soy sauce preservation is to overcome these problems. With soy sauce has a basic characteristics of ultrasonic processing, it is a fall in its viscosity, colour and lustre is becoming clear.,Green tea drinks in the machining process, due to reasons such as the oxidation of tea polyphenols, color is darker, by initially yellowish gradually become brown, namely Browning, which makes the appearance of green tea beverage and drinks quality severely affected. Using ultrasonic wave to the beverage sterilization,can be well keeping tea polyphenol content in tea soup, is conducive to the stability of tea liquor color and transparency, sterilization and protection of tea is green tea polyphenols against losses as far as possible make it has good colour and lustre is a good tea processing technology.,Ultrasonic sterilization technology is a kind of cold sterilization technology, compared with traditional high temperature heating sterilization technology, ultrasonic action does not change the food color, aroma, taste, can well protect the colour and lustre of juice drinks. Ultrasound (500 KHZ, 500 w) was used for orange juice was studied, under the action of ultrasonic, limonin,brown pigment in orange juice without adverse effect upon product quality, the results show that the limonin in orange juice content did not change, also not Browning and color changes. Ultrasound applied to the processing of lemon juice, lemon juice tastes and the nutrient damage of colour and lustre, and obtained good effect.,Ultrasound with other technologies synergistic sterilization,Ultrasonic sterilization is characterized by fast speed, no external additive, harmless to human body, no damage to items. But the sterilization effect is not completely, still is mainly used for secondary sterilization. If want to further improve the efficiency of sterilization, the ultrasonic must be used,in combination with other sterilization technology together. Here is in recent decades, the synergy of ultrasound with other technologies in the research of sterilization: (1) Ultrasonic synergy ozone (2) Ultrasonic synergy nano titanium dioxide,(3) Ultrasonic synergy microwave (4) Ultrasonic synergy laser sterilization (5) Ultrasonic synergy ultraviolet sterilization (6) Ultrasonic synergy heat sterilization (7)