## 3 Results and Discussion
cereus_ (log\({}_{10}\); mean \(\pm\) standard deviation) in fresh cheese inoculated with three different concentrations of crude extract and its two corresponding subfractions. Figure 1: Behavior of _B. cereus_ inoculated in fresh cheeses stored at 8 \({}^{\circ}\)C under _E. elaginoides_ extract exposure at the three concentrations for the two independent batches performed. Symbols represent the experimental observed data and lines the mean of observed data. Antimicrobial activity, mainly with inhibitory effect, for these compounds and/or macroalgae extracts from brown macroalgae has been widely reported by many authors in in vitro assays [23]. The antimicrobial potential of _E. selaginoides_ extracts to inhibit various foodborne pathogens and spoilage bacteria, including _Bacillus subtilis_, _Escherichia coli_, _Listeria monocytogenes_, _Pseudomonas aeruginosa_, and _Staphylococcus aureus_, has been supported by several authors [27; 38; 39; 40; 41; 42]. Despite _B. cereus_ not having been extensively used as a target strain in antimicrobial assays so far in other studies, the in vitro antimicrobial activity of extracts from _E. selaginoides_ collected from the Atlantic coast of Spain against this foodborne pathogen was described previously by [PERSON] et al. (2007) [39] and [PERSON] et al. (2022b) [27]. Nevertheless, most of the research developed in this sense has been evaluated mainly through in vitro assays. Studies assessing the antimicrobial potential of algal extracts in food matrices are currently limited and they are mostly focused on their effect on total viable counts over time. In addition, the reported effects differed depending on the nature of the food model. Whereas in meat products such as pork patties with added extracts from _Laminaria digitata_ and _Ulva_ spp., no effect was observed on the microbial population [43; 44], total viable counts decreased when extracts from _Myagropsi mysnrogoides_, _Ecklonia cava_, or _Sargassum sagamianum_ were added to bakery products, including bread and muffins [45; 46; 47]. There is no available information about the application in cheese of macroalgae extracts for this purpose. However, the addition of _Ascophyllum nodosum_ and _Fucus vesicusus_ extracts in other dairy products, such as raw whole cow's milk and yogurt, did not affect the studied microorganisms, including total plate counts, total coliforms, yeasts or molds in the milk, and lactic acid bacteria in the yogurt [48; 49]. The composition of macroalgae is highly dependent on a wide range of factors, intrinsic (i.e., life stage) and extrinsic (i.e., environmental and experimental conditions), determining, therefore, the nature of the extracted chemical structures. The composition of crude extracts used in this study was previously described in [PERSON] et al. (2022b) [27], being a mixture of compounds with bioactive potential, including 0.73% of lipophilic pigments (such as chlorophyll a and fucoxanthin), 7.97% of polyphenols, 3.57% of polysaccharides, and other uncharacterized compounds. Phlorotannins constitute a wide and diverse family of compounds restricted to brown seaweeds (Phaeophyceae), which are derived from the polymerization of phloroglucinol units, with diverse molecular weights and different levels of complexity. The growth inhibition and bactericidal effects against Gram+ and Gram- bacteria reported in several in vitro studies are proposed to occur by suppressing oxidative phosphorylation, the permeability alteration in microbial cell membrane, and the interaction with target microbial proteins [50; 51]. Thus, the interaction of the phenolic aromatic ring and hydroxyl groups of various phlorotannins with bacterial enzymes and proteins can induce cell lysis [52]. Likewise, the active mechanism remains unclear, the available information about different existing structures in brown seaweeds is still limited, and only low-molecular-weight phlorotannins (2-8 phloroglucinol units) have been described in the literature. In vitro antimicrobial activity against _B.