Histamine formation in a dry salted twaite shad (alosa fallax lacustris) product

Abstract

Landlocked shad is a freshwater clupeid fish (Alosa fallax lacustris) whose consumption is associated with the risk of scombrotoxin poisoning. Traditionally, fresh shad are subjected to an artisanal processing procedure, consisting of dry salting and maturation under pressure, to give a fish product named missoltino, which is stored in large metallic barrels and is sold to local consumers and restaurants. In recent years, the introduction of modern food packaging technologies has enabled this product to also be distributed in shops and supermarkets. Consequently, the determination of the safety of this product is an urgent issue. The aims of the present research were to measure histamine levels and histamine-forming bacteria in shad products collected at different phases of preparation and ripening, in order to minimize poison hazards, to provide technical information about risk, and to standardize the production process. One hundred twenty-six samples of shad (21 fresh fish and 105 dried) at different phases of preparation and ripening were collected from seven producers and were analyzed for chemical composition, histamine content, and microbiological properties. After 130 days of ripening, samples from three producers presented unacceptable amounts of histamine (>200 mg/kg), according to European Union legislation. A moderate negative correlation was found between histamine levels and salt content (r=-0.504, P < 0.01) and between histamine levels and water phase salt content (r=-0.415, P < 0.01). Several bacterial strains that were positive on Niven's medium were isolated during the early phases of production, whereas the extreme environment of salted shad at the end of ripening led to a drastic decrease of bacteria, but not of histamine. The most effective preventive measures for histamine formation and accumulation in salted shad were strictly related to fish handling and storage conditions during processing.