**4. Conclusion**

The study investigated seasonal changes in the quantities of macro-components and fatsoluble biologically active compounds in the edible tissue of the aquaculture mussels from the Bulgarian Black Sea coast. Regardless of the observed variations in the chemical composition, the mussels are rich in proteins (average 18.5%) and contain low levels of total lipids and carbohydrates, and a low energy value (average 104 kcal/100 g). A well-expressed tendency of decreasing levels of total lipids and carbohydrates during the summer season (July) was established, which correlates well with the reproductive cycle of the Black Sea shellfish. Additionally, significant variations were found for bioactive lipid components such as fatty acids, fat-soluble vitamins, cholesterol, and carotenoids. High levels of n3 PUFAs (average 0.786 g/100 g) were found during the whole study period. Mussels are a rich source of EPA + DHA n3LCPUFAs (average 0.74 g/100 g), supplying 148% of RDI for these FAs. An interesting trend was determined for the summer season: the highest levels of all three fat-soluble vitamins and carotenoids were observed at the lowest total lipid values. Within the study period of catching and distribution of mussels to the Bulgarian markets, the levels of cholesterol that were subject to control were low (average 68.4 mg/100 g). The functional properties of the lipids were estimated by FA ratios, FA indices, and interactions between cholesterol and SFA (low CSI levels), and vitamin E and PUFA (high alpha-tocopherol/PUFA levels). The results demonstrated very good hypocholesterolemic (high h/H values), anti-atherogenic (low levels of AI), and anti-thrombogenic (low levels of TI) potential of the lipids. Valuable new information on changes in beta-carotene and astaxanthin contents in the intestinal tissue was provided. Beneficial carotenoid contents confirm the very good antioxidant potential of the mussel lipids. Although proximate and FA composition, fat-soluble vitamins, cholesterol, and carotenoids contents of mussel tissue are multifarious and strongly dependent on biotic and abiotic environmental factors, we can summarize that the present results illustrate well the high potential of mussels as healthy food. Moreover, mussel consumption could promote dietary recommendations for the consumption of low-fat and cholesterol, rich in n3 PUFA, vitamin D3, and astaxanthin foods. In addition to the study of the bioactive lipid composition of aquaculture black mussels, more detailed investigations devoted to the seasonal changes of different lipid classes as phospholipids, sterols, waxes, carotenoids, etc., are needed. The assessment of the proximate composition and the lipid quality of the black mussel edible tissue may promote their consumption. The findings concerning aquaculture mussels in Bulgaria may support consumers' dietary regimes and help them make healthy food choices.
