研究预冻温度(-20、-30、-40、-50 ℃)对冻干猕猴桃片干燥特性及品质的影响,运用扫描电镜和图像分析技术测试不同预冻温度下冻干猕猴桃片的微观结构,分析预冻温度对冻干猕猴桃片孔隙和分形的影响。结果表明,对于干燥特性,预冻温度越低,猕猴桃片的干燥速率越小。在品质上,预冻温度越低,猕猴桃片的硬度和脆性越大,复水比越小。从感官结果来看,-40 ℃和-50 ℃预冻下的冻干猕猴桃片的感官评分显著高于-20 ℃和-30 ℃。扫描电镜和分形分析结果表明,预冻温度越低,冻干猕猴桃片形成的孔隙越小且多,平均孔隙面积、孔隙率、平均孔隙周长和平均孔隙直径越小,结构更规则,分布更均匀。综合以上各种指标,降低预冻温度使得冻干猕猴桃片的孔隙结构更小更均匀,一定程度上能够提高冻干猕猴桃片的感官品质,但降低了干燥速率,延长干燥时间,会使得能耗增加,生产成本增加。
The influence of pre-freezing temperature was studied on drying characteristics and quality of kiwifruit slices. The pore microstructure of kiwifruit slices were analyzed by scanning electron microscopy (SEM) in order to study the effect of pre-freezing temperature on porosity and fractal. The results showed that the drying rate reduced with the lower pre-freezing temperature. Quality factors, such as, the hardness and crispness increased on higher pre-freezing temperature; but the rehydration radio decreased. The sensory overall scores of kiwifruit slices processed by pre-freezing at -40 ℃ and -50 ℃ were significantly higher than -20 ℃and -30 ℃. According to the SEM, when the pre-freezing temperature was decreased, the pore structure of kiwifruit slices became smaller and their quantities increased. The pores were more regular and evenly distributed with smaller average pore area, pore perimeter, pore diameter and pore rate. It concluded that sensory quality of kiwifruit slices could be improved by reducing the pre-freezing temperature to some extent. However, the drying rate reduced, resulting in the increasing ost of energy and of production.
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