NMR分析冷冻面团在低温下的水份特性

The Water Properties of Forzen Dough at Low Temperature Determined by NMR

运用NMR分析冷冻面团从-70℃升温到5℃过程中的水份特性,以及运用MRI图像显示了面团的解冻过程。面团中的水分可以分为两部分:半结合水,其横向弛豫时间(T2)约为10ms;深层结合水,其T2约为2ms。观察冷冻面团在升温过程中的质子信号幅度变化情况,可得出结论:半结合水在面团冻结时,一部分形成冰,另一部分转变成不可冻结水;深层结合水在面团冻结时不发生状态变化或迁移,提高面团中深层结合水的含量有利于冷冻面团的生产和抑制冰晶的生成。多种类型的NMR数据均可确定面团的玻璃化转变发生在约-30℃,而结晶温度为-9℃。冷冻面团中的水分可以分为三类:固态冰(29.71%);未冻结水(22.20%);深层结合水(33.81%)。

The water properties of frozen dough were measured by NMR over the temperature range from -70℃ to 5℃.The thawing process of dough was also studied by MRI.The water in dough can be divided into two portions ,that are the half-bound water, the T2 of which is ≈10ms, and the deep-bound water, the T2 of which is = 2ms. During freezing,the half-bound water partly form to ice and the other change to unfreezale water. The deep-bound water did not change or move. So improving the ratio of deep-bound water in dough is benefit to frozen dough production and inhibiting ice crystals generating. According different NMR data, it is confirmed that the glass transition of dough occurs at -30℃ and the ice melting at -9℃. The water in frozen dough can be classified into three parts and they are the solid ice （29.71%）, the real unfreezable water （22.2%）, the deep-bound water （33.81%）.