草莓玻璃化转变温度的DSC测量

The measurement of glass-transition temperature of fresh strawberries by differential scanning calorimetry

在测量溶液的部分玻璃化转变温度时,往往无法直接测得溶液在最大冻结浓缩状态下的部分玻璃化转变温度(Tg’),而是测得部分结晶玻璃化转变温度(Tgf)。本文用差示扫描量热仪,采用不经过退火处理的连续扫描法、分步扫描法对草莓打浆液、榨汁草莓经抽滤的草莓汁液和浓缩掉三分之一水分的浓缩草莓汁进行了玻璃化转变温度的测量。研究发现,用同一种方法测得的三者的玻璃化转变温度相差不大。在-48℃以下退火,玻璃化转变温度随着退火温度的增大而增大,在-48℃以上退火,玻璃化转变温度随着退火温度的增大而减小,并有很好的线性关系,从Tgf确定Tg’的新方法是两侧Tgf的交点对应的温度为Tg’。得到草莓的Tg’为-52.8℃。

The glass-transition temperature of the maximally freeze-concentrated solution （Tg＇） often can not be obtained directly, although there are many methods to measure it. Otherwise the glass-transition temperature of the partially freeze-concentrated solution （Tgf） can always be obtained directly. In this paper, DSC （Differential Scanning calorimeter） and different scanning methods are used .Three kinds of samples are obtained by using different pretreatment methods. It is found that the glass transition temperatures of these three samples have little difference gotten by a same method. It is also found that the Tgf increases initially with annealing temperature up to -48℃, and decrease as the temperature continues to increase and exhibition linear relation obviously. It is concluded that the Tg＇ can be determined by intersection of the two curves reflecting the Tg, change with annealing temperature. The glass transition temperature （Tg＇, -52.8℃） of the concentrated strawberry juice is obtained.