| Summary: | This study analyzed the antimicrobial effect of aqueous extracts of flour obtained from red alga (<i>Gelidium</i> sp.) both in vitro, against most common food pathogenic and spoilage bacteria, and in a food model system during the chilled storage of Atlantic mackerel (<i>Scomber scombrus</i>). Results of in vitro assays allowed the conclusion that the aqueous flour extracts have antimicrobial activity against Gram-negative bacteria such as <i>Enterobacteriaceae</i> (<i>Escherichia coli</i>, <i>Enterobacter aerogenes</i>, and <i>Klebsiella pneumoniae</i>) and proteobacteria (<i>Vibrio alginolyticus</i>), and against Gram-positive bacteria such as <i>Bacillus cereus</i> and <i>B. subtilis</i>. In the food model study, different concentrations of the flour extract were present in the icing medium, microbial and chemical analyses being carried out in fish muscle at different storage times. An inhibitory effect (<i>p</i> < 0.05) on microbial growth (aerobes, psychrotrophs, <i>Enterobacteriaceae</i>, and proteolytic and lipolytic bacteria) and on chemical quality indices (pH, total volatile amines, and trimethylamine) was concluded. This effect was more pronounced when the flour extract concentration in the ice increased and at advanced storage times. This study provides a first approach to the beneficial use of flour of the alga <i>Gelidium</i> as a new preserving strategy for chilled fish.
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