Microbiological contamination of ready to eat algae and evaluation of Bacillus cereus behavior by microbiological challenge test

Abstract

Consumption of seaweeds, often categorized as a superfood, is becoming popular in western countries. Algae can be marketed fresh, but are usually sold dehydrated to ensure longer shelf life. The consumption, often as ready to eat, open up possible risks for public health because of foodborne pathogens that can contaminate the raw material during harvesting or manipulation. In this study, fourteen ready to eat foods based on dehydrated algae, representative of the most consumed species, were considered. The microbial content, with a focus on Listeria monocytogenes and Bacillus cereus, was investigated by plate counts and B. cereus strains were isolated and identified by 16s rRNA gene sequencing. The microbiological quality was heterogeneous among the samples and, in particular, marine bacteria, Listeria spp., B. cereus and coliforms were detected. To contribute to related risk assessment, the ability of B. cereus to grow during refrigerated storage was evaluated, to our knowledge for the first time, by a microbiological challenge test on two ready to eat foods based on Undaria pinnatifida and Palmaria palmata.  Despite this study demonstrating the inability of B. cereus to proliferate in seaweed-based food, its presence in dehydrated foodstuffs cannot rule out the replication after rehydration before consumption, making it necessary to shed light on the possible risks for consumers.