Drying Characteristics of Carrots Immersed in a Fluidized Bed of Fluidizing Particles Under Reduced Pressure

Abstract

The drying characteristics and properties (color and shrinkage) of carrots (as a representative agricultural product) were experimentally examined in a fluidized bed under reduced pressure. Dry hot air and superheated steam were used as the drying gases. Rice and carrot powders (0.125-0.355 mm in diameter) were used as the fluidizing particles, in addition to glass beads (0.12 mm in diameter).It was confirmed that the drying rate using a fluidized bed was much higher than without a fluidized bed (hot-air drying), regardless of the type of fluidizing particles used. Under reduced pressure, both with and without a fluidized bed, the drying rate was higher than that at atmospheric pressure using hot air. The drying rate was sufficiently high for fluidized-bed drying with superheated steam, though the drying rate was higher with hot air than with superheated steam. As the drying temperature increased, the volume ratio (befor/after drying) of the sample increased. At high drying temperatures (373 and 423 K in the present study), the color of the sample changed; in other words, a heat-induced change in the properties of the carrot was observed. At a low drying temperature (333 K in the present study), the drying method did not affect the color of the carrot; i.e., the color of the dried material was maintained even in a fluidized bed under reduced pressure when the drying rate was higher. INTRODUCTIONThe drying process affects the quality of a dried product. In particular, heat-sensitive materials such as food, agricultural products, and pharmaceuticals need to be kept at a low temperature while being dried. Vacuum and freeze dryers have been used for the low-temperature drying of such materials. However, these dryers have certain problems; a long drying time and a large amount of energy are required for drying. It is necessary to manufacture a dryer that has a low drying temperature, high drying rate, and high energy efficiency for drying heat-sensitive materials.

Reduction of Deoxynivalenol in Wheat with Superheated Steam and Its Effects on Wheat Quality

“…In recent years, researchers have tried to apply SS to the processing of food products. They mainly focus on the drying of foodstuffs, such as potato slices [18], oat groats [19], carrot [20], pork [21], beet, etc. What’s more, drying of beet with SS has been applied into some factories in the world [13].…”