Enrichment of polyphenol contents and antioxidant activities of Irish brown macroalgae using food-friendly techniques based on polarity and molecular size
Highlights
► Food-friendly antioxidant extracts were generated from three Irish macroalgae. ► Molecular-weight cut-offs enriched the phenolic and antioxidant profiles of extracts. ► Flash chromatography employed to purify the low molecular weight (LMW) fractions. ► Q-Tof mass analysis suggests phlorotannins may be responsible for antioxidant effect.
Introduction
The commercial potential of brown macroalgae has long been recognised (Tierney, Croft, & Hayes, 2010), particularly for species such as Ascophyllum nodosum (Linnaeus) Le Jolis that are currently used for the production of alginates and fertilizers, although these final products are typically of low-value. In contrast, antioxidant compounds in these macroalgae have sparked interest due to their potential use in the lucrative functional food market. The presence of antioxidants in brown macroalgae, specifically those from the Fucaceae family, including Ascophyllum nodosum (A. nodosum), Fucus spiralis (F. spiralis) Linnaeus and Pelvetia canaliculata (P. canaliculata) (Linnaeus) Decaisne & Thuret, arises from the inter-tidal habitat of these species. To mitigate against the environmental stresses they endure, brown macroalgae produce a unique group of polyphenols, called phlorotannins, which are essentially derived from the oligomerising decoupling of the phloroglucinol (1,3,5-trihydroxybenzene) monomer (Sailler & Glombitza, 1999). Phlorotannins are essential for cell-wall development at early phases of zygote growth in members of the Fucaceae family (Schoenwaelder, 2002) and for minimising oxidative damage that occurs in response to changes in nutrient availability and UV radiation, thus, reducing the impact these stresses on their physiological integrity (Hupel et al., 2011, Svensson et al., 2007).
Despite both their obvious potential and the fact that simple polyphenols derived from plants have found many uses in foods and pharmaceuticals there have been few examples of commercial uses for phlorotannins. This is most likely because phlorotannins are difficult to separate, purify and characterise due to their similar polarity and polymeric structure. Membrane separation technologies are widely applied in food processing to support the purification of bioactive food ingredients using techniques based on size and/or molecular shape (Cassano, Conidi, & Drioli, 2010). Furthermore, carbohydrates, such as the sugar alcohol mannitol, present in brown seaweed (Mian and Percival, 1973, Zubia et al., 2008) are often co-extracted with phlorotannins and, therefore, must be eliminated to improve the phlorotannin purification process.
Separation methods based on both polarity and molecular size for the fractionation of phlorotannins have been previously reported (Le Lann et al., 2012, Wang et al., 2012). However, these studies either lacked MS analysis indicating the presence of phlorotannins and the complexity of their MW profiles (Le Lann et al., 2012) that has been reported in our study, or the phlorotannin enrichment steps were solvent intensive and, therefore, less industry relevant (Wang et al., 2012). The aim of the current study was to generate highly antioxidant-enriched fractions from macroalgal SLE extracts using methods based on both size and polarity, and to profile their phenolic contents and antioxidant activities. Mass spectrometry was also employed to support the identification of phlorotannins in the LMW fractions. For macroalgal-derived polyphenols to be commercially viable for inclusion in the food and beverage sector they have to be isolated in a simple, non-time-consuming manner using food-friendly methods. This study demonstrates enrichment approaches that could be of value in the exploitation of macroalgae polyphenols.
Section snippets
Chemicals
All chemicals used were of reagent-grade. All solvents used were of HPLC-grade. 2,2-diphenyl-1-picrylhydrazyl (DPPH), phloroglucinol, ferrous chloride, ferrozine, 2,4,6-tris(2-pyridyl)-s-triazine (TPTZ), 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox) and ferrozine were obtained from Sigma–Aldrich Chemical Co. (St. Louis, MO, USA) and used without further purification. BioDesignDialysis Tubing™ with 3.5 kDa cut-off was acquired from Fisher Scientific. Spectra/Por® Biotech
General
In order to profile the TPC, antioxidant activities and metal chelating abilities of food-friendly CW, HW and EW extracts from the three brown macroalgae A. nodosum, P. canaliculata and F. spiralis an initial partitioning, followed by MWCO fractionation using 3.5 and 100 kDa membranes was carried out. The less than 3.5 kDa MWCO fractions of the CW and EW extracts were further fractionated by RP flash chromatography and the TPC, in vitro antioxidant activities and metal chelating abilities of the
Conclusion
In this study, the use of MWCO dialysis indicated that the most antioxidant fractions from the brown macroalgae studied and those with the highest TPC were the HMW fractions; however, further purification of the LMW fractions using RP flash chromatography revealed that the removal of other interfering compounds resulted in enhanced antioxidant activity. The employment of Q-Tof-MS supported the assumption that phlorotannins were present and likely to be responsible for the observed RSA and FRAP
Acknowledgements
Michelle Tierney is in receipt of Walsh Fellowship funding from Teagasc the Irish Agriculture and Food Development Authority and this funding is gratefully acknowledged.
This work has also been supported by the Marine Functional Foods Research Initiative (NutraMara project) which is a programme for marine based functional food development. This project (Grant-Aid Agreement No. MFFRI/07/01) is carried out under the Sea Change Strategy with the support of the Marine Institute and the Department of
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