Chemical characterization of a traditional fish preparation (missoltino) obtained from salted and dried twaite shad

Missoltino is a traditional Italian fish product obtained from salted and dried twaite shad (Alosa fallax lacustris), an endemic fish of northern Italian lakes. A large amount of these fish is caught near its reproductive period, during the end of spring. This reason had led local professional fishermen to find a way to preserve the fish for all the year using an old processing techniques. Briefly, the freshly-caught twaine shad, weighing about 80 g, are eviscerated and then salted using fine sea salt. The exceeding salt is removed by water washing and the fish are naturally dried in a room for 3-5 days. Afterwards fish are arranged in layers in metallic containers and pressed at ambient temperature for a long period, nearly 3 months. These containers are closed with a wooden lid and the pressure is progressively increased with a crank handle. The aim of this work was to chemically characterize this fish product, prepared using two different levels of salt and at different time of ripening, in order to identify the optimal processing technique that resulted in best quality properties. Thirty six samples of twaite shad caught in Como lake were collected and used to make missoltini with 2 different salt concentrations, 80 g kg-1 (A) and 40 g kg-1. (B). Four samples were sampled: after catching, during salting, after 30 days, after 60 days and after 90 days of pressing. Chemical composition, TBARS value, histamine, fatty acid composition and flavor volatile compounds were determined in all samples. Fresh twaite shad showed a lipid percentage of 6.7±2.41. This percentage increased progressively in missoltini while the moisture content decreased during drying and pressing. The salt percentage had a direct influence on the lipid content. In missoltini made using 80 g kg-1 of salt lipids were lower than in missoltini made using 40g kg-1 of salt. This difference was statistically significant (p<0.001) after 2 months of pressing (B 5.93±0.15, A 10.4 ±0.43) and after 3 months to the same extent. Moisture and protein did not show variations after the first month of pressing. TBARS values were statistically different after 60 days of pressing. Group A showed a higher TBARS (0.15±0.006 mM g-1) when compared to group B (0.13 ±0.012 mM g-1). These values were not correlated with lipid concentration. Histamine content of samples varied from 72 mg kg-1 to 1043 mg kg-1. The fatty acid profile of missoltini was characterized by the prevalence of oleic acid (25.5%±2.03), followed by palmitic acid (21.4%±2.04). The content of polyunsaturated fatty acid was also high, eicosapentaenoic acid (8,2%±0,70) and docosahexaenoic acid (5,7% ±0,90). Of the 93 volatile compounds identified, alcohols, aldehydes, ketones, hydrocarbons were the most prevalent groups of volatiles. Despite the high content of PUFA, amino acid catabolism led to larger changes in the composition of volatiles in the fish product than did lipid oxidation reactions.