Seasonality: The Driving Force Behind the Antimicrobial and Antioxidant Activities and Biochemical Composition of Ericaria selaginoides Extracts, with Minimal Effect of High Hydrostatic Pressure Pretreatment.

The increasing interest in natural versus synthetic additives is a driving force for food industry innovation to develop alternative solutions for food safety and quality. Brown algae, described as containing potential antimicrobial and antioxidant compounds, are promising alternative sources. However, optimized food-grade extracts require preserving their bioactivity. In this study, the effects of seasonality and interannual variation, together with non-thermal high-hydrostatic-pressure (HHP) pretreatment, on the extraction of antioxidant and antimicrobial compounds from the macroalga Ericaria selaginoides, collected from the northwest of Spain between November 2021 and September 2023, were assessed. The HHP pretreatment of fresh algae did not significantly change the yield of the crude extracts and only slightly improved the antimicrobial activity of the extracts against L. monocytogenes, S. aureus and B. cereus, without significantly diminishing the antioxidant activity until 600 MPa for 5 min, the total polyphenol content (TPC), and the chlorophyll A content. Interannual and seasonal variations significantly influenced pigments and protein, carbohydrate and polyphenol contents, together with the antioxidant and antimicrobial activities, of the extracts. By NMR, phloroglucinol was identified as the major secondary metabolite, together with mannitol, alanine and a mixture of meroditerpenoids, which may contribute to the reported activities. The overall results demonstrated the role of environmental factors in driving seasonal and interannual changes in macroalgal metabolism, significantly influencing the bioactive properties of extracts, while the effect of HHP pretreatment was minimal.