Analysis of lipids in pelagic fish of Sicilian Channel and use of fatty acids as bacterial contamination markers

Lipids provide the expendable form of energy in marine ecosystem, and have an important role for the reproductive biology of fish. Also, lipids are important nutrients, versatile markers for marine trophic studies, bacteria markers etc. Among the lipids, several essential fatty acids are determinants for ecosystem health as well as for their known nutritional properties and prevention capacity of chronic diseases. Furan fatty acids (F - acids) are other important lipid bioactive compounds; for these is hypothesized a crucial nutritional role that is synergistic to polyunsaturated fatty acids omega 3 (PUFA ω 3), also if their mechanism is not yet clear. Source of essential fatty acid is the anchovy (Engraulis encrasicolus, Linneus 1758), which is the most important commercial coastal pelagic species of the Mediterranean Sea and highly recommended for human nutrition. Although in literature there are numerous studies on the lipid composition of the anchovy during seasonal changes, studies regarding the species caught in the Sicilian Channel (GSA 16), south Sicily (Italy) which represents an important reference point for the fishing of pelagic fish in all the Mediterranean, have not been carried out. This Ph.D. thesis presents and discusses the variables contributing to lipid composition of Engraulis encrasicolus of the Sicilian Channel, Central Mediterranean Sea (Italy); in particular investigates the tissues (edible muscle, gonads and liver) and fatty acids distribution during catching season (between December 2014 to November 2015) and correlates the data to environmental parameters obtained by satellite as Chlorophill-a and Temperature (≤ 100 m from surface). The specimens were analyzed for sex and size classes, and the analysis of fatty acids, furan fatty acids, cholesterol were performed by GC/MS while total lipids by gravimetric method. One of the first results concerns reproductive status. The anchovy season spawning ranged from April to September, also if was observed an advance of the peak reproductive than literature, probably due to increase of surface temperature sea in the last three years (about 3 %). The results showed that the period of the biggest accumulation of lipids, both for edible part than organs, is winter, with values higher (p < 0.05) for females than males (22.78 ± 0.86 % vs 16.48 ± 0.42 % in March) and for different size classes (age). For example the highest percentage for females of 130 - 139 mm size class was 22.78 ± 0.86 % which have mainly one year old and not yet subject to reproduction, vs 17.78 ± 0.42 % for individuals of 150-159 mm (mainly 2 year ald). An positive correlation between total lipid and cholesterol was observed. Unlike the lipid amount, the PCA showed that the fatty acid composition of anchovy depends mainly of the physiological states of animals regarding their reproductive status and no from also sex and size class. In fact, all fillets of anchovy and liver organ reported higher values (p < 0.05) of PUFA ω 3 and lower values of saturated fatty acids (SFA) during reproductive cycle than autumn - winter. For example, in edible muscle the highest percentage of PUFA ω 3 was observed in April 42.17 ± 0.46 % and the lowest in December 34.56 ± 0.30 % (p < 0.05), while % SFA from April to September was about 35 % vs December - March about 40 % (p < 0.05). At the same time, a decreasing trend was observed, specially for docosahexaenoic acid DHA in sexual organs. DHA dropped (p < 0.05) from April (29.33 ± 0.10 %) to September (23.83 ± 0.47 %). High concentration of PUFA ω 3 and PUFA ω 6, and the seasonal variation of F - acid both muscle than organs are the important fingerprints of anchovy of Sicilian Channel than literature. This thesis, in fact, is the first study that quantify the F - acids amount in Engraulis encrasicolus of Sicilian Channel and shows that higher percentage of F - acids is measured mainly during spring - summer (however small quantity < 1%) and traces in autumn - winter (< 0.001 %). In addition the high concentration of PUFA ω:6 has been compared with Chlorophill-a concentration, and its increase of about 20 % in the last three year respect to 1998 - 2002, could be cause of changes of diet of animal, supported also of decrease of specific monounsaturated fatty acids (MUFA) markers of animal food fraction than literature. This thesis represent an important study on physiological state of anchovy Engraulis encrasicolus (Linnaes 1758) of Sicilian Channel through lipid markers in relation to environmental variables. Another theme concerns the fish safety, in fact due to the high perish ability of the fish, new technologies and fast and low-cost methods are necessary to control the hygienic conditions during all seafood chain, and the analysis of fatty acids could help. The analysis were performed by GC/MS on samples fish preserved a 7.4 ± 0.1 °C for total two weeks (gut and muscle) and bacterial colture. This study shows that fatty acids with odd number of carbon atoms as C13:0, C15:0 and only one fatty acid with even number of carbon atoms as C12:0 displayed an increase during storage period. An increase of about 70 % al 7th day and 90 % at 14th in edible muscle was observed, while omega 3 decreased of about 50 % and 80 % in muscle and gut, respectively. The presence of these fatty acids in bacterial colture and mainly in literature, suggests them as bacteria markers, and so the fatty acids analysis could be applied to assess and distinguish the freshness as well as the improper storage of the fish product. This method appropriately improved, can be also used in situ and to be another means to investigate the fish safety.