Chlorophyll stability in spinach dehydrated by freeze-drying and controlled low-temperature vacuum dehydration

Freeze-drying and controlled low-temperature vacuum dehydration were used f or the drying of both blanched and unblanched spinach. Monolayer moisture c ontent and solid surface area of dehydrated products were determined by usi ng moisture sorption isotherms and BET equation. Contents of chlorophylls a and b and TEA value were measured, and those variations in dried samples d uring storage were studied at different storage temperatures of 5, 20, 30, and 45 degreesC. Drying time of controlled low-temperature vacuum dehydrati on was much less than that of freeze-drying. Solid surface areas of product s from freeze-drying were higher than those from controlled low-temperature vacuum dehydration. and blanching also exerted an effect on the increase o f solid surface area of dried products. Chlorophyll contents decreased acid TEA value increased with the increase of storage temperature and time. Tho se phenomena were more significant in the products of freeze-drying than th ose from controlled low-temperature vacuum dehydration, and more marked in blanched samples compared to unblanched. (C) 2001 Elsevier Science Ltd. All rights reserved.