Critical moisture content for successful cryopreservation of embryonic axes of Fortunella polyandra determined by differential scanning calorimetry (DSC)

Abstract

The relationships between water content of desiccated embryonic axes (using different methods of desiccation), the availability of water determined by differential scanning calorimetry (DSC) analysis and recovery percentage after liquid nitrogen (LN) exposure of Fortunella polyandra embryonic axes were investigated. The objectives were to understand thermal properties of desiccated embryonic axes during cryopreservation and to determine the critical moisture contents for successful cryopreservation of the embryonic axes. Excised embryonic axes were desiccated under laminar air flow (0, 10, 15, 30 and 45 min), over silica gel (0, 5, 15, 30 and 60 min), and ultra-rapidly (0, 5, 10, 20 and 25 min). Desiccation under laminar air flow resulted in an optimal water content of 0.150 gH2O g−1 dw and a survival of 50 % after cryopreservation, while the unfrozen water content (WCu) was 0.126 gH2O g−1 dw. After drying over silica gel, the optimal water content was 0.190 gH2O g−1 dw, where the survival was 40 % after cryopreservation and the WCu was determined as 0.177 gH2O g−1 dw. Using the flash-drying method, the optimal water content was found to be 0.145 gH2O g−1 dw, the survival was 50 % after cryopreservation and the WCu was 0.133 gH2O g−1 dw. Embryonic axes of F. polyandra showed low-to-moderate tolerance to desiccation. The results of the freezing transitions for all the desiccation times and methods showed that the onset temperature and the peak of the mean enthalpy decreased in size with decreasing water content. DSC elucidated the critical moisture contents and the cooling and melt enthalpies for successful cryopreservation of F. polyandra embryonic axes.