European flat oyster (Ostrea edulis) is a highly priced sea food product, while oysters from Mali Ston Bay (South Adriatic Sea) are labelled with designation of origin (PDO) due to interaction of environmental conditions and quality of the oysters. The aim of this work was to determine the changes of chemical composition in oysters preserved by using IQF technology, with a goal of freezing oyster during the period of the best quality (March/April).The oysters were sampled from the bivalve farms at Mali Ston area and the Krka River estuary in March 2023, when they are characterized by a high condition index, frozen in whole shell with liquid nitrogen at -80 °C, divided and stored at two temperatures: -18 °C and -60 °C for 3 months. No significant differences were observed in the increase in total volatile base nitrogen (TVB-N) with respect to freezing temperatures, while the pH value increased slightly only during the first month of storage, for both sites, respectively. Mass fraction of saturated fatty acids (SFA) in oyster samples from both sites increased slightly during storage or had values close to the initial ones at both temperatures. In both types of oysters and at both storage temperatures, the mass fraction of polyunsaturated α-linolenic fatty acid (C18:2 cis) decreased, while the proportions of α-linolenic (C18:3n3) and cis-13,16-docosadienoic acid (C22:2) increased during storage. The greatest change in the proportions of polyunsaturated fatty acids occurred with the decrease in the proportion of linoleic acid in Ston oysters, mostly during the first month at both temperatures. Compared to the initial samples, a higher mass fraction of monounsaturated fatty acids (MUFA), namely palmitoleic acid (C16:1) was quantified and the mass fraction of oleic acid (C18:1 cis) was quantified in a lower mass fraction, respectively. The results obtained show that the IQF technology is a good method for preserving oysters and that the storage temperatures of -18 °C and -60 °C do not affect their quality and remain acceptable to consumers.
Key words: Ostrea edulis, fatty acids, Individual quick freezing