Identification and Content of Astaxanthin and Its Esters from Microalgae Haematococcus pluvialis by HPLC-DAD and LC-QTOF-MS after Extraction with Various Solvents.

Biljana Todorović,Veno Jaša Grujić,Jana Ambrožič-Dolinšek,Roman Kranvogl,Andreja Urbanek Krajnc

doi:10.3390/plants10112413

Abstract

Haematococcus pluvialis, a unicellular green microalga that produces a secondary metabolite under stress conditions, bears one of the most potent antioxidants, namely xanthophyll astaxanthin. The aim of our study was to determine the content of astaxanthin and its esterified forms using three different solvents—methyl tert-butyl ether (MTBE), hexane isopropanol (HEX -IPA) and acetone (ACE)—and to identify them by using high performance liquid chromatography coupled with diode array detection and the quadrupole time-of-flight mass spectrometry (HPLC-DAD and LC-QTOF-MS) technique. We identified eleven astaxanthin monoesters, which accounted for 78.8% of the total astaxanthin pool, six astaxanthin diesters (20.5% of total), while free astaxanthin represented the smallest fraction (0.7%). Astaxanthin monoesters (C16:2, C16:1, C16:0), which were the major bioactive compounds in the H. pluvialis samples studied, ranged from 10.2 to 11.8 mg g−1 DW. Astaxanthin diesters (C18:4/C18:3, C18:1/C18:3) were detected in the range between 2.3 and 2.6 mg g−1 DW. All three solvents were found to be effective for extraction, but MTBE and hexane-isopropanol extracted the greatest amount of free bioactive astaxanthin. Furthermore, MTBE extracted more low-chain astaxanthin monoesters (C16), and hexane-isopropanol extracted more long-chain monoesters (C18 and above) and more diesters. We can conclude that MTBE is the solvent of choice for the extraction of monoesters and hexane-isopropanol for diesters.

Highlights

Microalga Hematococcus pluvialis is a unicellular green microalga that produces the secondary metabolite xanthophilic astaxanthin, which accumulates under extreme stress conditions [1,2,3,4,5]
The analyses performed by using LC-QTOF-MS have better sensitivity and selectivity and are more accurate compared to those performed by HPLC-DAD
11 astaxanthin monoesters and Plants 2021, 10, 2413 six astaxanthin diesters were identified with their molecular weights (Tables 1 and 2)

Summary

Introduction

Microalga Hematococcus pluvialis is a unicellular green microalga that produces the secondary metabolite xanthophilic astaxanthin, which accumulates under extreme stress conditions [1,2,3,4,5]. It is a highly potent antioxidant with antioxidant activity, which is ten times stronger than in the case of β-carotene [6] and 500 times stronger than in the case of α-tocopherol [7]. Research related to astaxanthin from natural sources has visibly attracted the scientific community and has great potential in terms of application

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Conclusion