TITLE:
Hot Air Drying and Quality of Red and White Varieties of Onion (Allium cepa)
AUTHORS:
Ayoola Olalusi
KEYWORDS:
Air Temperature, Onion, Drying Characteristics, Quality, Moisture Content
JOURNAL NAME:
Journal of Agricultural Chemistry and Environment,
Vol.3 No.4B,
October
28,
2014
ABSTRACT: This study was undertaken to
investigate the drying characteristics of red and white varieties of onion (Allium
cepa) in a convective dryer. The drying characteristics of onion slices were examined
at air temperatures of 50℃, 60℃ and 70℃ and sample thicknesses of 2 mm.
During the drying experiments, air velocity was held stable at 0.9 m/s. The
effects of air temperature on the drying characteristics and quality parameters
such as vitamins C and D, macro minerals (Mg, Na, P, Ca and K), non-enzymatic
browning and thiolsulphinate of the dried onion slices were determined. For
each of the plots of the drying curves from the mechanical drying tests, there
was an absence of or just a very brief appearance of a constant rate period
because onions are hygroscopic and hygroscopic foods tending to quickly enter
the falling rate period; drying time decreased considerably with increased
temperature. The time required to reduce the moisture content to any given
value was dependent on the drying conditions, being the longest at an air
temperature of 50℃, 0.9 m/s and the shortest at an air temperature of 70℃ and
air velocity of 0.9 m/s. The loss of vitamin C, which is a thermo-sensitive
compound, was the least at an air temperature of 50℃.