Process and Storage Quality of Quick Freezing Blueberries in LN_2-spraying Fluidized Bed

摘要

Liquid nitrogen spraying fluidized bed was used for Individual Quick Freezing (IQF) of blue berries; processing technology and quality change of frozen samples during storage stage were analyzed in this study. Regular and mixed experimental design were used to confirm the quick freeze process of blueberries by means of setting different freezing temperature, wind velocity and the height of bed-layer. Multiple linear regression analysis indicates that the suitable process conditions for quick-freezing blueberries in LN_2-spraying fluidized bed were -40℃ freezing temperature, 4.5 m/sec wind speed and 3.6 cm bed height. Environmental Scanning Electron Microscopy (ESEM) results show that the inner microstructure of the fluidized quick-frozen blueberries has better compactness, uniformity and destructiveness than that of the slow-frozen blueberries in -18℃ refrigerator. Texture Analysis (TPA) and the technology of image processing were used to analyze the different of blueberries in firmness and internal color between the fluidized quick-frozen and slow-frozen in -18℃ refrigerator. The results show that the quality of the fluidized quick-frozen blueberries has better than that of the slow-frozen blueberries in -18℃ refrigerator. The storage life of blueberry by LN_2 spraying fluidized quick-frozen was confirmed that is around 150 days which in much better than that of the slow-frozen sample with the storage life of 100 days.