不同工艺真空冷冻干燥桂花的品质比较分析

为获得较高品质的干燥桂花,本实验采用电阻法测定桂花的共晶点和共熔点,分析了物料厚度、预冻温度和时间、隔板升温程序等因素对桂花冻干效率的影响,并比较不同工艺真空冷冻干燥和烘干桂花的复水比、活性成分和微观结构等指标进行品质分析。结果表明:桂花的共晶点为-19℃,共熔点为-17℃;预冻温度-25℃,2.5 h可达到真空冷冻干燥的预冻要求;物料厚度和升温程序是影响干燥效率的重要因素;真空冷冻干燥桂花的组织形态较好,复水比为4.16~4.56 g/g,总黄酮含量为35.90~38.42 mg/g·DW,香气活性物质含量均显著高于烘干桂花;不同真空冷冻干燥工艺对桂花中活性成分含量的影响差异不大;快速升温的真空冷冻干燥桂花的复水比为4.16 g/g,显著高于烘干桂花2.98 g/g,但是显著低于慢速升温;微观结构分析发现,越慢的升温程序,花瓣表面越平整。采用-10℃1 h,5℃1 h,20℃1 h,35℃若干小时的升温程序,基本可以获得较高品质的干燥桂花。本研究为桂花的储藏保鲜及高品质干桂花的生产利用奠定了基础。

Comparative Analysis of Different Vacuum Freeze Drying Processes on Quality of Osmanthus fragrans

To obtain high quality dried Osmanthus fragrans flowers,the eutectic point and co-melting point of flowers were measured byelectrical resistance method.The effects of material thickness,pre freezing temperature and time,partition heating program on the freeze-drying efficiency of O.fragrans flowers were analyzed.And the rehydration ratio,active components and microstructure of O.fragrans flowers dried by vacuum freeze of different processes and hot air were compared.The results showed that the eutectic point was-19℃and the co-melting point was-17℃.When the pre-freezing temperature was maintained at-25℃for 2.5 h,the pre-freezing requirement reached.The material thickness and partition heating program in the drying stage were important factors affecting the drying efficiency.Compared with hot-air drying treatment,vacuum freeze-drying maintained good tissue shape with the rehydration ratio 4.16~4.56 g/g.The total flavonoid content in vacuum freeze-drying ranging from 35.90 to 38.42 mg/g·DW and the contents of aroma active compounds were all significantly higher than hot-air dried O.fragrans flowers.The effects of different vacuum freeze-drying processes on the content of total flavonoid and aroma active compounds in O.fragrans flowers were not significant.The rehydration ratio of fast heating vacuum freeze-drying O.fragrans flowers was 4.16 g/g,significantly higher than that of hot-air dried flowers 2.98 g/g,but lower than the slower heating vacuum freeze-dried flowers.Microstructure analysis showed that the slower the heating process,the smoother the petal surface.High quality of the dried O.fragrans flowers could be obtained using partition heating program at-10℃for 1 h,5℃for 1 h,20℃for 1 h,and 35℃for several hours.This study laid a foundation for the storage and preservation of fresh flowers,and the production and utilization of high-quality dried O.fragrans.