Quality changes in the lotus root frozen under different conditions

This study was performed to optimize the preparation of frozen lotus roots. Prior to freezing, an optimal blanching condition at 100°C for 5 min was established, based on the microbial growth, texture, total phenolic content (TPC), and sensory evaluation results. The blanched samples were then frozen under various freezing conditions (-20°C in a freezer for 2 hr, -70°C in a gas nitrogen convection chamber for 7 min, and -196°C in liquid nitrogen for 20 sec), and their qualities after thawing were determined. The scanning electron microscopic analysis indicated that the microstructure of the sample frozen at -70°C was similar to that of the control sample, compared with the other freezing conditions (-20 and -196°C). The antioxidant activities of the frozen samples decreased compared to those of the control, but there was no significant (p<0.05) difference among the treatments. In terms of TPC, the samples frozen at -70 and -196°C had significantly (p<0.05) higher values than the sample frozen at -20°C. In addition, the drip loss of the sample frozen at -20°C was higher than those of the other frozen samples. These results suggest that freezing at -70°C in a gas nitrogen convection chamber can be an optimal freezing method of producing high-quality frozen lotus roots.