冻干草莓内部孔隙率的分布及其影响的实验研究

冻干食品内部是多孔的疏松结构，针对不同预冻结速率和厚度的草莓，进行了冻干实验，采用微型CT扫描仪对冻干样品进行扫描和图像重构，计算得到了孔隙率。测量了冻干过程失水率，冻干后复水比，并且用二甲苯-二氯靛酚比色法测定了冻干前后抗坏血酸的值。结果表明：预冻结速率越快，孔隙率越小，且超速冻（速率大于10em／h）的孔隙率基本维持在一恒值10％。物料厚度越大，升华干燥速率越慢，孔隙率越大，复水比越大。8mm切片抗坏血酸保持得最好，并且孔隙率越大，抗坏血酸保持率越低。

Experimental study on porosity distribution and its eflect on freeze-dried strawberries

Freeze-dried foods have porous structure.Micro-CT was used to scan freeze-dried strawberries at different pre-freezing rates and thicknesses,porosity was calculated with those reconstruction images.The dehydration ratios during freeze-drying and the rehydration ratios after freeze-drying were measured.The content values of ascorbic acid(AA)were determined before and after freeze-drying using dimthylbenzene-two,six-dichlor indophenol's colorimetry method.The results showed that,the quicker tha pre-freezing rate,the smaller ths porosity.The porosity at ultra rapid frozen rate(10cm/h)is kept around 10%.When samples were thicker,sublimation rate was slower,porosity was higher,rehydration ratio was higher.8mm slice could get the best AA retaining rate,and the higher the porosity,the worse the AA retaining rate.