The moisture absorption law of the wolfberry (Lycium barbarum) powder obtained by three different drying methods was determined by measuring the moisture absorption rate and adsorption isotherm curves. Low-field NMR technique was used to analyze the characteristics of moisture migration during moisture absorption process of the powder. The results showed that the moisture absorption isotherms of the wolfberry powder obtained by three different drying methods all belonged to type III isotherm. When the water activity was greater than 0.5, at the same water activity, the equilibrium water content was as follows: sun drying> heat-drying> freeze-drying, which indicated that wolfberry powder was easier to be stored when the water activity of the storage environment was less than 0.5. The NMR spectra showed that the powder made by three different drying methods had T21 increased significantly with time (P<0.05) during storage, while T22 did not change significantly during the first 15 days and increased dramatically (P<0.05) on day 30. There were no significant changes in T23, which indicated that the changes in moisture migration were mainly between bound water and immobile water during moisture absorption. It was found that the hygroscopicity characteristics of the powder obtained by freeze-drying was more stable in initial 15 days. These results are important for studying the moisture changes in Lycium barbarum powder during moisture absorption. This study also provided theoretical bases for explaining the mechanisms of moisture absorption of powder.
XU Hao
,
ZHANG Xikang
,
XIE Xianghong
,
KONG Weizhou
,
MA Haoran
,
LIU Dunhua
. Effects of different drying methods on moisture changes in wolfberry powder during moisture absorption[J]. Food and Fermentation Industries, 2019
, 45(5)
: 151
-156
.
DOI: 10.13995/j.cnki.11-1802/ts.017834
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