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Water Sorption Characteristics and Glass Transition Temperature of Freeze-Dried Cherry Tomatoes

LIU Hua1, ZHONG Yejun2,*, LI Ziling1,2, LI Jihua2,3, LIN Lijing3, ZHOU Wei3   

  1. 1. School of Life Science, Jiangxi Science and Technology Normal University, Nanchang 330013, China;
    2. State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang 330047, China; 3. Agricultural Products
    Processing Research Institute, Chinese Academy of Tropical Agricultural Sciences, Zhanjiang 524001, China
  • Online:2015-12-15 Published:2015-12-24

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Abstract:

Desorption and adsorption isotherms of freeze-dried cherry tomatoes were determined by gravimetric method at
water activities ranging from 0.11 to 0.90 at 25 ℃ based on sorption theory. The glass transition temperatures at different
moisture contents were measured by differential scanning calorimetry (DSC) and fitted with the Gordon-Taylor equation.
Results indicated that the desorption and adsorption isotherms belonged to type III behavior and the hysteresis loop in the
water activity range of 0.23 to 0.76 was type H3 according to the classification method proposed by the International Union
of Pure and Applied Chemistry (IUPAC). Both the GAB and Peleg models were suitable for fitting the moisture absorption
isotherm of freeze-dried cherry tomatoes. The glass transition temperature of freeze-dried cherry tomatoes significantly
decreased with increase in moisture content, and glass transition curve was well fitted with the Gordon-Taylor equation.
A comparison of product stability criteria based on the concepts of water activity and glass transition temperature revealed
that there was a considerable discrepancy in the temperature related to stability criteria predicted by the concepts of water
activity and glass transition.

Key words: cherry tomatoes, adsorption isotherm, glass transition, desorption isotherm

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