Microwave heating advantages - JFS: Food Engineering and...

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1976 JOURNAL OF FOOD SCIENCE —Vol. 68, Nr. 6, 2003 Food Engineering and Physical Properties © 2003 Institute of Food Technologists Further reproduction prohibited without permission JFS: Food Engineering and Physical Properties Temperature Profiles Within Milk after Heating in a Continuous-flow Tubular Microwave System Operating at 915 MHz P. CORONEL, J. SIMUNOVIC, AND K.P. SANDEEP ABSTRACT: Milk with different fat contents (0, 1, 2, 4%, and chocolate milk) were heated in a specially designed continuous-flow microwave applicator operating at 915 MHz. The nominal power was 5 kW and the flow rates were 2.0 and 3.0 L/min to attain laminar flow. Temperature profiles at the exit of the applicator were measured. The results showed that the average increases in temperature were similar to one another, being 42 °C at 2.0 L/ min and 29 °C at 3.0 L/min. Differences between the lowest and highest temperatures were 3.7 and 3.0 °C, respectively. The temperature profiles illustrated that slightly higher temperatures were achieved within seg- ments flowing close to the center of the tube. Keywords: continuous microwave heating, milk, temperature profile, dielectric properties Introduction C ONTINUOUS-FLOW MICROWAVE HEATING is a relatively new technology in the food industry, even though applications of microwave heating technology are highly evolved for household applications. Micro- waves are a part of the electromagnetic spectrum and have a frequency between 300 MHz and 3 GHz. They are primarily used for communications and radar. It has been long known that microwaves can be used for heating foods, and small batch mi- crowave oven units for household use are present in most kitchens in the U.S.A. Mi- crowaves heat foods in a rapid and direct manner, providing volumetric heating. In industrial applications, this could drastical- ly reduce the come-up time needed to achieve the required process temperature, thereby reducing the total cumulative ther- mal treatment and better preserving the thermo-labile constituents of the foods, such as aromas, vitamins, and pigments. The characteristic of instantaneous power- on and shut-off of microwave generators can help deliver energy very precisely into the food products (Metaxas and Meredith 1983; Meredith 1998). Due to the volumetric heating character- istic of microwaves, that is, heat is generated in the food as a result of the conversion of the electromagnetic energy, the cumulative heat treatment of the bulk of a product should be more uniform than in the case of conven- tional processing. In theory, volumetric heat- ing should minimize overcooking of the sur- face and undercooking of the center. This can be extremely beneficial for liquids, such as milk, in which fouling of the tubes occurs due to overheating of the product in contact with the tube wall (Kudra and others 1991). Continuous-flow microwave heating of
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Microwave heating advantages - JFS: Food Engineering and...

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