Abstract
Himanthalia elongata is a brown oceanic seaweed rich in bioactive compounds. It could play an important role in food production because of its antimicrobial and antioxidant properties. Three strains belonging to the Lactobacillus casei group (Lactobacillus casei, Lactobacillus paracasei, and Lactobacillus rhamnosus) and a Bacillus subtilis strain were used for the solid-state fermentation of commercial seaweeds, and bacterial growth was monitored using the plate count method. High-pressure processing (HPP) was also employed (6000 bar, 5 min, 5 °C) before extraction. The antimicrobial activity of the extracts was tested in terms of the main food pathogenic bacteria (Salmonella spp., Listeria monocytogenes, Escherichia coli, Staphylococcus aureus, and Bacillus cereus), and the phenolic content was estimated using the Folin–Ciocalteau method. In addition, targeted UHPLC-MS2 methods were used to unravel the profile of phlorotannins. H. elongata allowed the growth of the L. casei group strains and B. subtilis, showing the fermentability of this substrate. Significant antimicrobial activity toward L. monocytogenes was observed in the extracts obtained from unfermented samples, but neither fermentation nor HPP enhanced the natural antimicrobial activity of this seaweed species. The content in the phenolic compounds decreased because of the fermentation process, and the amount of phenolics in both the unfermented and fermented H. elongata extracts was very low. Despite phlorotannins being related to the natural antimicrobial activity of this brown seaweed, these results did not support this association. Even if fermentation and HPP were not proven to be effective tools for enhancing the useful compounds of H. elongata, the seaweed was shown to be a suitable substrate for L. casei group strains as well as for B. subtilis growth, and its extracts exhibited antimicrobial activity toward foodborne pathogens.
Highlights
Over the centuries, various preservation techniques have been developed to increase food safety and avoid spoilage during storage and distribution
Even if fermentation and High-pressure processing (HPP) were not proven to be effective tools for enhancing the useful compounds of H. elongata, the seaweed was shown to be a suitable substrate for L. casei group strains as well as for B. subtilis growth, and its extracts exhibited antimicrobial activity toward foodborne pathogens
Contrary to Gupta et al [16], who observed that neither raw nor thermally processed H. elongata were able to support the growth of L. plantarum, in the present work the strains used for fermentation (L. casei 2240, L. paracasei 4186, L. rhamnosus 1473, and B. subtilis 5002) demonstrated the capacity to grow in this matrix, opening new avenues for novel fermented foods based on algae
Summary
Various preservation techniques have been developed to increase food safety and avoid spoilage during storage and distribution. Consumers, concerned about the potential side effects of synthetic antimicrobials, have started requesting food that contains preservatives of natural origin [1] This consumer choice has garnered interest in compounds extracted from natural sources, which are increasingly investigated for their antimicrobial activity. Different studies have attributed the antimicrobial and antioxidant capacity of seaweed extracts to the presence of bioactive compounds such as phlorotannins, flavonoids, steroids, and sulfated polysaccharides [6,7,8,9]. These secondary metabolites allow for the synthesizing organism to have a strong defense against pathogens and survive in stressful conditions. Antimicrobial compounds such as organic acids can be produced through fermentation [12]
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