Cryobiology and Cryotechnology

Freeze-drying causes physicochemical changes in some materials and they acquire new properties different from their original ones as a result. We defined these freeze-dried materials as "Freeze-dried (FD) new material". In recent years, hinokitiol has been increasingly utilized as a natural bacteriocide and cell activator. This paper refers to properties of "FD new materials" namely the inclusion complexes of hinokitiol prepared with cyclodextrin, as well as those of hiba oil and hiba neutral oil which is raw material of hinokitiol obtained by steam-distilling the hinoki-asunaro plant (Thujopusis dorablata SlEBOLD et ZUCCARINI var. hondai MAKING). Hinokitiol crystal and hiba neutral oil were obtained from hiba oil. Then they were prepared as an inclusion complex with cyclodextrin and further freeze-dried to give a product which is easily soluble in water. Products were observed by electron microscopy and compared with antibiotics for their antibacterial activity.

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In order to obtain fundamental data for use in establishing an effective cryopreservation method, seasonal changes in resistance to freezing and survivability of cryopreserved pear leaf bud apices were examined. The survival rate of cryopreserved apices, excised, treated with cryoprotectants ( 8 % v/v DMSO and 3 % sucrose), cooled from 0℃ to-40℃ at a rate of 0.5℃/min, immersed in LN_2, thawed in warm water (38℃) and cultured, was high for apices treated in winter and low for spring. It decreased from March to April and increased from October to December. Seasonal changes of survivability by cryopreservation paralleled those of freezing resistance. A varietal difference in the level of resistance to freezing was found amoug apices collected in winter. The survivability by cryopreservation of apices excised from twigs, col-lected in winter and stored for 1-7 months at 0℃, was maintained at a high level. The fact that the rate of rosette-forming apices was relatively low in each material, suggested that dome tissue might be damaged by freezing.

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Equilibrium and nonequilibrium freezing behaviours of water in polymer gels were inves-tigated by DSC (differential scanning calorimetry). Ice crystallisation during rewarming, observed with the gels frozen under the nonequilibrium condition, i.e., frozen after the substantial undercooling, disappeared when observed with the gels frozen under the equilibrium condition which was induced by the addition of ice nucleating protein. Although ice crystallisation may proceed rather slowly under the equilibrium condition, most of the compartmentalised water crystallises without being vitrified. The different freezing behaviour depending on the freezing condition can be attributed to the different rate of ice crystal growth relative to that of the change in the polymer network.

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