Ebook Food physics (Physical properties – Measurement and applications): Part 2
➤ Gửi thông báo lỗi ⚠️ Báo cáo tài liệu vi phạmNội dung chi tiết: Ebook Food physics (Physical properties – Measurement and applications): Part 2
Ebook Food physics (Physical properties – Measurement and applications): Part 2
7 Thermal PropertiesMost of the food processing operations used to prolong the shelflife of foods involve heating foods to temperatures capable of ina Ebook Food physics (Physical properties – Measurement and applications): Part 2activating microbial and enzymatic activity. These heat treatments are based on controlled heat transfer that depends upon thermal properties of the food materials. In order to increase the internal temperature of a food product, heat must first be transferred to the outer surface of the food, and t Ebook Food physics (Physical properties – Measurement and applications): Part 2hen transmitted through the food material in order to reach the center of the food product. This is an example of heat transfer. In Section 7.6 heat tEbook Food physics (Physical properties – Measurement and applications): Part 2
ransfer is described in more detail. When heat is added to a material (heating), the temperature of that material will increase so long as it is not u7 Thermal PropertiesMost of the food processing operations used to prolong the shelflife of foods involve heating foods to temperatures capable of ina Ebook Food physics (Physical properties – Measurement and applications): Part 2rom a material (cooling), and transferred to a surrounding heat exchange medium at a lower temperature, the temperature of the material will decrease. Figure 7.1 illustrates these different directions of heat flow. In food processing, thermal process operations are very important for food safety. So Ebook Food physics (Physical properties – Measurement and applications): Part 2me examples of thermal process operations are listed in Table 7.1.In this chapter we want to focus on thermal properties of foods, such as heat capaciEbook Food physics (Physical properties – Measurement and applications): Part 2
ty, temperature and enthalpy of phase transition points (melting, freezing, glass transition, chemical reactions, evaporation, etc.), as well as theFi7 Thermal PropertiesMost of the food processing operations used to prolong the shelflife of foods involve heating foods to temperatures capable of ina Ebook Food physics (Physical properties – Measurement and applications): Part 2plesheat exchange mediumtemperature rangepasteurization/ sterilization -batch -continuous flow/ liquids (ƯHT/HTST)inactivation of pathogenic microorganisms for increasing shelflife. canned solids and liquids long-life aseptic packagingmeat, fish, soup, vegetables, fruit, cream milk, cream, custard, Ebook Food physics (Physical properties – Measurement and applications): Part 2desserts, soup, fruit, juice, beer, egg long-life milk, cream, fruit juiceselectricity, hot water, steam (direct or indirect steam)63-135 °CevaporatioEbook Food physics (Physical properties – Measurement and applications): Part 2
nremoval of water, production of liquid concentratemilk, fruit and vegetables, coffee, cheese wheysteam40-100 cdehydrationremoval of water, production7 Thermal PropertiesMost of the food processing operations used to prolong the shelflife of foods involve heating foods to temperatures capable of ina Ebook Food physics (Physical properties – Measurement and applications): Part 2eins,carbohydrates), evaporation of waterFrench fries, potatoes, doughnutshot oil100-150 ccooking/bakingreactions (proteins,carbohydrates), evaporation of watercatering operations, bread, meat pies, cakessteam, hot air, microwaves100-200 cchilling/freezingreducing spoilage reactions, microbial activ Ebook Food physics (Physical properties – Measurement and applications): Part 2itydairy products, meat, fish, fruit, vegetables, frozen dessertscold air, refrigerants, cryogenic fluids (liquid nitrogen)10-0°C (-18)-(-30)°C(-100)-Ebook Food physics (Physical properties – Measurement and applications): Part 2
(—200)°c2iz0'CÃ7.1 Temperature 259caloric value of foods. We will also introduce some methods and techniques for measuring some of these thermal prope7 Thermal PropertiesMost of the food processing operations used to prolong the shelflife of foods involve heating foods to temperatures capable of ina Ebook Food physics (Physical properties – Measurement and applications): Part 2ituent substances of the system. This kinetic energy increases with increasing temperature (molecules move about at greater speed). The mathematical product of absolute temperature T and Boltzmann’s constant k is called the thermal energy £ of a system.E = k-T-7.1whereEenergy in JkBoltzmann’s consta Ebook Food physics (Physical properties – Measurement and applications): Part 2nt inJ • K-1Ttemperature in KOn a molecular scale, the thermal energy is the kinetic energy of the molecules moving about within a system. Recall theEbook Food physics (Physical properties – Measurement and applications): Part 2
ideal gas where there velocity distribution of the gas atoms is a function of the temperature (see Appendix 15.2 about distribution functions). On a m7 Thermal PropertiesMost of the food processing operations used to prolong the shelflife of foods involve heating foods to temperatures capable of ina Ebook Food physics (Physical properties – Measurement and applications): Part 2les have high kinetic energy. At a hypothetical zero temperature, the molecules will be completely at rest with no kinetic energy. This is the lower limit (zero point) of the absolute temperature scale (thermodynamic temperature scale). It has no upper limit. The temperature unit chosen for this sca Ebook Food physics (Physical properties – Measurement and applications): Part 2le is 1 K (Kelvin), which is defined as —■ 16 of the triple point temperature of water. This triple point is the same at any point in the world, and iEbook Food physics (Physical properties – Measurement and applications): Part 2
s called a fixed point of the thermodynamic temperature scale. Figure 15.8 illustrates the triple point of water as a point in the state diagram that 7 Thermal PropertiesMost of the food processing operations used to prolong the shelflife of foods involve heating foods to temperatures capable of ina Ebook Food physics (Physical properties – Measurement and applications): Part 2temperature scales ( c, F, R) having other units and fixed points. For example, the Celsius scale is based on the fixed points for the temperatures at which water will freeze (freezing point) and boil (boiling point) at standard atmospheric pressure. The temperature difference between those fixed po Ebook Food physics (Physical properties – Measurement and applications): Part 2ints was defined to be 100 degrees. In a similar manner the Fahrenheit scale was based on two fixed points that could be recognized at the time. ZeroEbook Food physics (Physical properties – Measurement and applications): Part 2
on the Fahrenheit scale (-17.8 °C = 0°F) was the lowest temperature that could reached at that time, and the high point of the scale (100c'F) was set 7 Thermal PropertiesMost of the food processing operations used to prolong the shelflife of foods involve heating foods to temperatures capable of ina Ebook Food physics (Physical properties – Measurement and applications): Part 2ned to be 100 degrees. Likewise, there exists an absolute temperature scale based on each degree being the same as a Fahrenheit2607 Thermal PropertiesTable 7.2. Some fixed points for temperature, and related scalesabsolute zeroboiling temperature oi’N2freezing temperature ofH2Otriple point ofH2Otemp Ebook Food physics (Physical properties – Measurement and applications): Part 2erature of human body bloodboiling temperature ol’H2Otemperature scale name7 Thermal PropertiesMost of the food processing operations used to prolong the shelflife of foods involve heating foods to temperatures capable of ina7 Thermal PropertiesMost of the food processing operations used to prolong the shelflife of foods involve heating foods to temperatures capable of inaGọi ngay
Chat zalo
Facebook