DEHYDRATION OF APPLES BY A COMBINATION OF CONVECTIVE AND VACUUM-MICROWAVE DRYING
 
More details
Hide details
 
Pol. J. Food Nutr. Sci. 2007;57(Special issue 4A):131–135
KEYWORDS
ABSTRACT
Apple cubes were dried with a convective method in a stream of air at the velocity of 4 m/s and temperature of 55˚C as well as with a combined method consisting in pre-drying the apples with the convective method and finish-drying with the vacuum-microwave method (VM). The time of convective pre-drying reached: 40, 100 and 160 min, and the wattage of microwaves accounted for 240, 480 and 720 W. Drying shrinkage was measured by means of a measuring cylinder filled with linseed, whereas rehydration of the dried material was carried out in distilled water with a temperature of 21˚C. Colour assessment was conducted based on results obtained with the use of a reflective colorimeter. The kinetics of apple cubes drying with the convective method was described using exponential functions. The VM finish-drying of the apples previously pre-dried with the convective method considerably shortened the total time of drying and decreased drying shrinkage. Apple cubes dried with the combined method demonstrated better rehydrating properties manifested by absorption capacity, dry mater holding capacity and rehydration ability as compared to the apples dried only with the use of the convective method. Drying resulted in the browning of apple cubes and shift of colour from green to red and a negligible shift of colour from yellow to blue. The colour of samples finish-dried with the VM method was more shifted towards red and blue when compared to the samples dried only under convective conditions.
ISSN:1230-0322