Influence of Freezing Rate on the Quality of Lyophilized “Tokoroten.”

Effect of pre-freezing rate on the quality of lyophilized “tokoroten”, gelidium jelly, was examined. The jellies were freeze-dried in a vacuum freeze dryer at a platen temperature of 60°C and chamber pressure of 20-300μHg after being frozen by the following methods: spraying with liquid nitrogen, vacuum freezing, air blast (3m/sec) freezing at -30°C freezing on a cold plate at -30°C and still air freezing at -21°C (Fig. 1). When the jelly was frozen at a higher rate, the shape of lyophilized product remained unchanged and its tissue was fine (Fig. 3-2), whereas the one frozen at a slower rate gave a shrinked product and its tissue was rough (Fig. 3-5). Although the ultra-quick freezing by spraying with liquid nitrogen gave a product whose tissue was very fine, remarkable cracks and projections resulted during the subsequent freeze-drying (Fig. 3-1). The colour of lyophilized jelly was more preferable as the rate of prefreezing was higher. A slight difference was observed in the distribution of ash and dissolution velocity in hot water. However, the freezing rate did not affect the reconstitution of the products: the quality of all the jellies made from the dried products was similar to that of original jelly. It may be concluded from these results as well as the simplicity in processing that the vacuum freezing is the most preferable method for pre-treatment of the jelly.