Effects of developmental stage, seawater concentration and rearing temperature on cryopreservation of Pacific oyster Crassostrea gigas larvae

ABSTRACT: For the development of a stepwise cryopreservation technique for larvae of the Pacific oyster Crassostrea gigas , various conditions were examined. Larvae at 9, 12, 15, 18 and 21 h after insemination were cooled at a rate of −1°C/min (seeding at −8°C for 15 min) and then plunged into liquid nitrogen at −35 or −40°C using 1.5 M dimethyl sulfoxide (DMSO) and 250 mM trehalose as cryoprotectants. Among these larvae, 15 h after insemination (the trochophore stage before formation of the shell gland) showed the highest motility and the best external appearance after thawing. Trochophore larvae were cryopreserved in preservation media containing different dilutions (1/4, 1/6, 1/8, 1/10 and 1/30) of seawater. Larvae preserved in the 1/4 seawater medium showed the highest appearance of shelled larvae 4 days after thawing. Trochophore larvae reared in seawater at 21, 25 or 29°C were cryopreserved for 8 months and then reared at 26°C after thawing. Larvae reared at 25°C showed the highest survival rate and normal larval ratio at day 6 after thawing, although larvae reared at 21°C showed the highest rates until day 4. One larva developed at 25°C succeeded to settle.     

Assessing the end-point temperature of heated fish and shellfish meats

ABSTRACT: Attempts have been made to assess the end-point temperature (EPT) of heated fish and shellfish meats by using the coagulation method together with sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis and enzyme activity determination. Unfrozen and frozen fish and shellfish meats were heat-treated at different selected temperatures with 0, 15 or 30 min holding times. Proteins were extracted with NaCl solution. The coagulation method was able to determine EPT of heated fish and shellfish meats between 60 and 67°C. SDS-PAGE patterns of the filtrates from heated meats were closely related to the results of the coagulation method and enzyme activity determination. Two proteins responsible for producing coagulum of fish meat extracts seem to be lactate dehydrogenase (LDH) and glyceraldehyde phosphate dehydrogenase (GAPDH). End-point temperatures determined by these methods were not significantly different between unfrozen and frozen samples. On the contrary, a highly thermostable protein with a molecular mass of 35 kDa was detected in heated shellfish meats up to 108°C. In scallop adductor muscle, this highly thermostable protein was found to be the tropomyosin subunit from its amino acid composition and their partial sequences. Tropomyosin could be used as an EPT indicator up to 108°C for heated shellfish meats.