THE BIOCHEMICAL AND SENSORY PROPERTIES OF GILTHEAD SEA BREAM (SPARUS AURATA) FROZEN AT DIFFERENT CHARACTERISTIC FREEZING TIMES

摘要

Skinned, vacuum-packed, postrigor gilthead sea bream fillets were frozen individually with characteristic freezing times of 2,18, 74 and 640 min (times to cool the thermal center of the fillets from -1 to -7C). Immediately after freezing, the fillets were thawed, and their quality was evaluated with tests related to muscle integrity, myofibrillar protein denaturation and aggregation, lipid degradation and changes in tenderness. The muscle integrity indices (activities of α-glucosidase, β-N-acetyl-glucosaminidase and (β-hydroxy-acyl-coenzyme-A dehydrogenase and the amount and protein content of centrifugal tissue fluids) showed that the freezing process itself clearly affected the integrity of muscles. Freezing of fillets with characteristic freezing time of 74 min caused more damage to muscles and hydrolysis of lipids than the other freezing times. Adenosine triphosphatase (ATP)ase activities and Ca~(2+) sensitivity of actomyo-sin extracts suggested that the freezing process itself, but not the freezing times, caused structural damage to myofibrillar proteins. No difference in the levels of salt-soluble proteins and sulfhydryl contents in actomyosin extracts was found between the fresh and frozen fillets. Sensory evaluations showed that the cooked frozen fillets were less tender than the cooked fresh ones.