Antioxidant Activity and Phenolic Content of Marine Dissolved Organic Matter and Their Relation to Molecular Composition

Teresa S Catalá,Thorsten Dittmar,Jan Tebben,Pamela E Rossel,Félix Álvarez-Gómez,Félix L Figueroa

doi:10.3389/fmars.2020.603447

Abstract

The potential of marine dissolved organic matter (DOM) for free radical scavenging has been extensively evaluated, however, the quantitative assessment of the antioxidant potential has been recently measured for the first time. The linkage of the DOM antioxidant potential to its molecular composition has not yet been examined. Following this line, this article takes a step forward by assessing, throughout a polarity-mediated fractionation, (1) the antioxidant capacity and phenolic content and (2) the molecular characterization of DOM in a more exhaustive manner. (3) The DOM antioxidant potential and phenolic content was linked to the molecular composition of DOM, which was molecularly characterized using ultrahigh resolution Fourier transform Ion Cyclotron Resonance mass spectrometry (FT-ICR MS). Antioxidant activity and phenolic content were quantified by the free radical 2,2’-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS⋅) and the Folin-Ciocalteu methods, respectively. We considered three types of different natural DOM samples: the deep North Pacific Ocean, the oligotrophic surface of the North Pacific Ocean and porewater from the sulfidic tidal flats of the Wadden Sea. Bulk porewater and its individual polarity fractions presented the highest antioxidant activity and phenolic content. DOM from the water column samples had lower antioxidant activity and phenolic content than porewater, but exceeded what it is commonly found in macroalgae, microalgae, fruits and vegetables with cosmeceutical purposes. Our values were similar to published values for terrestrial DOM. The variations in bioactivity were dependent on polarity and molecular composition. The high resolution and high mass accuracy used to determine the molecular composition of marine DOM and the chemometric and multistatistical analyses employed have allowed to distinguish molecular categories that are related to the bioactive potential. As a future perspective, we performed cytotoxicity tests with human cells and propose marine DOM as a natural ingredient for the development of cosmeceutical products.

Highlights

To maintain the health and integrity of an organism and neutralize the reactive species continuously produced during metabolic processes (Alscher et al, 2006), organisms use antioxidant substances to counteract this hazard imbalance
The fractionation yields (i.e., determine concentrations of non-purgeable organic carbon (DOC) recoveries of all fractions referred to the initial amount) were higher for PPL than for Silica, with values of 52, 81, and 84% for porewater, deep sea and sea surface, respectively, (Supplementary Table 1)
The DOC concentration and dissolved organic matter (DOM) recovery is within the range of what is commonly found in Wadden Sea porewater in previous studies (Seidel et al, 2015; Linkhorst et al, 2017)

Summary

Introduction

To maintain the health and integrity of an organism and neutralize the reactive species continuously produced during metabolic processes (Alscher et al, 2006), organisms use antioxidant substances to counteract this hazard imbalance. Marine dissolved organic matter (DOM) is among the least characterized natural organic matter mixtures known (Hedges and Oades, 1997; Dittmar and Kattner, 2003; Hernes and Benner, 2006). Given the molecular diversity of DOM, it is currently impossible to characterize this pool at the level of individual molecular structures. In this sense, the molecular structure of only 2–3% of bulk DOM is known (Dittmar, 2015). Despite of the limited knowledge of molecular structures in the DOM pool, non-targeted ultrahigh resolution mass spectrometry via Fourier transform Ion Cyclotron Resonance mass spectrometry (FT-ICRMS) provides information of individual molecular formulas, allowing DOM molecular characterization with an unprecedent detail. Tannins, and humic acids are examples found in the group of polyphenols (Klavins et al, 1999; Nebioso and Piccolo, 2013)

Methods

Results

Conclusion