Abstract
Phlorotannins are bioactive polyphenols in brown macroalgae that make these algae interesting as healthy food. Specific phlorotannins are, however, seldom identified, and extracts from different species are often only analysed for total phenolic content (TPC). In this study, our focus was to identify phlorotannin molecules from Saccharina latissima and Ascophyllum nodosum (a species rich in these compounds) using ultra-high-performance liquid chromatography coupled to high-resolution tandem mass spectrometry (UHPLC-HRMS2). Water and ethanol (30 and 80% v/v) were used at solid:liquid ratios, extraction times and temperatures, proposed to result in high TPC in extracts from other species. The S. latissima extracts, however, did not allow phlorotannin detection by either UHPLC-UV/Vis or UHPLC-HRMS2, despite a TPC response by the Folin–Ciocalteu assay, pinpointing a problem with interference by non-phenolic compounds. Purification by solid phase extraction (SPE) led to purer, more concentrated fractions and identification of four phlorotannin species in A. nodosum and one in S. latissima by UHPLC-HRMS2, using extracts in ethanol 80% v/v at a solid:liquid ratio of 1:10 for 20 h at 25 °C with an added 10 h at 65 °C incubation of remaining solids. The phlorotannin with the formula C12H10O7 (corresponding to bifuhalol) is the first identified in S. latissima.
Highlights
Polyphenols are one of the essential micronutrients in the human diet due to their health effects, antioxidant properties, and prevention of diseases associated with oxidative stress such as cancer, cardiovascular, and neurodegenerative diseases [1]
Despite being a species that is successfully cultivated in the North Atlantic, phlorotannin compounds from Saccharina latissima have not yet been identified
The highest yield of total phenolic content (TPC) from macroalgae has far been reported in extractions using either water or ethanol as solvent
Summary
Polyphenols are one of the essential micronutrients in the human diet due to their health effects, antioxidant properties, and prevention of diseases associated with oxidative stress such as cancer, cardiovascular, and neurodegenerative diseases [1]. They are produced as secondary metabolites that exhibit protective functions against: (i) Environmental (abiotic) factors via their antioxidant properties by protection against reactive oxygen species produced as a consequence of high UV exposure and (ii) herbivores (biotic factors) by complexing proteins and decreasing digestive efficiency [1,2,3,4]. Marine brown macroalgae (seaweeds) have been recognized as one of the main natural sources for biologically active polyphenols [5]. In brown seaweeds (Phaeophysa), the major types of polyphenols are phlorotannins which are oligomers and polymers of phloroglucinol and have unique structures, different from terrestrial plants. The natural variety of structural linkages between phloroglucinol units (PGU) and the number of hydroxyl groups present in the phlorotannins ensure a broad range of potential biological activities of these heterogeneous poly/oligomers [6,7,8]. The specific types of the compounds are seldomly reported, often limiting evaluations to comparisons of total phenolic content, and rather few studies have focused on the identification of individual phlorotannins [9,10,11,12]
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