Histamine formation during processing of Missoltino, a traditional fish preparation

Histamine is the molecule responsible of the sgombroid syndrome or histamine fish poisoning (HFP), an allergy-like form of food poisoning. Histamine presence in food is related to the histidine content, the presence of bacterial histidine decarboxylase and environmental conditions. Some fishes, like tuna, mackerel, herrings and sardines, characterized by an high level of histidine in their flesh, are associated with the hazard of causing HFP. In order to prevent HFP, histamine level is regulated by European Union (100mg/kg for fresh fish and 200 mg/kg for enzyme maturated product)(EU, 2005) and US (50mg/kg) (FDA, CFSAN, 2001) for fish products. European legislation specifies fish families associated with high amount of histidine (Scombridae, Clupeidae, Engraulidae and Coryphenidae). Missoltino is a traditional Italian product obtained from salted and dried twaite. Twaite (Alosa fallax lacustris) is a landlocked subspecies of shad (Alosa fallax), an endemic fish of northern Italian lakes. This fish belongs to the Clupeidae family then it is to be considered for the histamine risk. In this study we monitored the levels of histamine in various stages of processing and ripening of missoltino. We also investigated the bacterial contamination of the product. Seven producers of missoltini have been involved in this study, everyone worked with its own traditional technique. Ten samples from each producer were collected after evisceration, at the end of salting, at the end of drying, after 15, 60 and 120 days of ripening. We measured histamine levels, salt concentration, moisture, water activity (aw), water phase salt (WPS) ((salt/salt + moisture)100), the amount of total mesophilic bacteria, enterobacteriacae, lactobacilli, staphylococci. Bacterial colonies were identified and we determined their ability to produce histamine by passage on Nivens medium. Missoltini were produced using an amount of salt ranging from 50 to 80 g/kg of product. Salt at the end of ripening varies from 8.2 g/100g to 12.5g/100g, depending on the amount used and on the drying technique. Most producers used to dry the product into the oven, at 28for 5 days, resulting in a driest product. Aw and WPS followed this trend, driest missoltini showed a value of aw of 0.709 and WPS of 22.82 at the end of ripening, while the less dried was 0.786 and 15.75 respectively. Histamine level increased during the processing for all the seven producers, with differences according to different levels of drying. In driest missoltini the histamine remains always within European legal limit, while in less dry missoltini histamine reaches the average value of 1977.33 ppm. The first stage of production in which histamine exceeded legal level is at the end of drying for a producer and after 60 days of ripening for the other two producers who had histamine value above 200 ppm. Bacterial load reached the highest level at 15 days of ripening, Enterobacteriacae were present at the beginning stage of production, while staphylococci and lactobacilli were higher during ripening. Several of the isolated bacteria showed the ability of producing histamine. The more active bacteria in decarboxylation of histidine were Citrobacter and Enterobacter aerogenes.