A Research On Ohmic Heating Properties Of Liquid Food Material With Fruit Granulae And Their Influencing Factors

Ohmic heating is also called resistance heating, Joule heating, direct resistance heating, electro-pure processing and electro heating . The conception of Ohmic heating was brought out in the early 19th . Then heating techniques were formed gradually ,in which electricity was the energy. Although in the early 20th , Ohmic heating device was produced in America ,which was used for milk sterilizing ,but it was defeated because there was no proper material to make inert electrode. It was not until APVBaker company, Britain developed a set of researching Ohmic heating apparatus in 1990s that Britain ,France ,Japan and America began to use this technique . The appearance ,flavor, smell and nutrient of food is required to be kept as much as possible during processing ,along with the development of food processing technology and improvement of living standard. Traditional food heating methods can′t fully cater these requirements in most circumstance . Ohmic heating has attracted much attentions from domestic and abroad food science researchers for its advantages:① temperature of material increse quickly and uniformly ;② pollution-free;③ manipulate freely;④heat energy used more efficiently;⑤ products quality is better. Now, in America, Ohmic heating is used in developing low acidity and high acidity food. While in Japan, it is introduced in lapper milk with strawberry, miced fish meat product and soybean curb processing. Sino-Japan food reaearching center, China Agriculture University has studied basic principles of Ohmic heating application from 1996. And it is utilized in soymilk heating, soybean curb making, starch gelatinizing, meat thrawing, okra heating as well as other processing fields. According to domestic and abroad researching status of Ohmic heating, it can be realized that its most properous application field is aseptic processing liquid food with solid granulae. Ohmic heating method has large potential to develop, and many topics still need further study:① controlling heating rate is a bottle-neck for Ohmic heating application. ② electric resistance differences between various parts of non-uniform liquid-solid mixture food will result in current distributs non-uniformly , which is a critical factor to impact products quality. ③ heating effect can′t be assure when the denisity of food with granulae is too high or too low. ④ much more deep, systematical and detailed studies on Ohmic heating properties and impact factors of liquid food material with fruit granulae are still needed , especially that of hydrophilic colloid solution with fruit granulae. There are merely relevant literatures published domestically and abroad .⑤ There are little science publishments about the influence of Ohmic heating on physic-chemical properties of liquid food with fruit granulae; ⑥Little researches were carried out on temperature changing regularities of liquid food material with fruit granulae during the procedure of Ohmic heating . And further studies are needed.Ohmic heating is a new kind of technology for sterilization and processing. It's also a new method for successive heat processing and treating of high sticky food and food with granulae. There are some essential differences between Ohmic heating and traditional techniques of sterilization and processing. In the procedure of conventional cooking, sterilizing and processing, food heating mostly depends on the heat transferred by convection, conduction and radiation. It will take a relatively long period to make the central temperature of granulae reach required level, which may increase food nutrient losing. Overheating liquid around these granulae will also boil out solid surface, destroy the integrity of granula and even degrade food quality as well as commercial value. Ohmic heating is the very technique to overcome former shortcomings. With the Ohmic method, heating rate of granulae approximates that of liquid phase, that is to say, the liquid phase and solid phase of food material are heated concurrently with a relatively high velocity(a...