The effect of different methanol concentrations and temperatures on the extraction of mycosporine-like amino acids (MAAs) in algae and Zooplankton

Abstract

Mycosporine-like amino acids (MAAs) are a family of intracellular UV-absorbing compounds involved in the protection of aquatic organisms against solar UV radiation. These compounds have been identified and quantified in many marine and freshwater organisms, however, no standard method to analyze these compounds is available. Consequently, protocols to extract MAAs largely differ, for example, in the type of solvent, concentrations, temperatures, and times used. In this study, we tested whether the concentrations of MAAs are affected by extraction at different temperatures and methanol (MeOH) concentrations. Natural assemblages of freshwater phytoplankton, the cyclopoid copepod Cyclops abyssorum tatricus, and the marine alga Porphyra sp. were used as test organisms. The MAAs shinorine, palythine, MAA 331, asterina-330, and porphyra-334 present in the organisms examined were generally best extracted at 45 °C in 25 % aqueous MeOH. In Porphyra sp. and natural freshwater phytoplankton, the mean total MAA concentrations obtained with this protocol were respectively -13 and ∼3 times higher than when extracted in 100% MeOH at 4 °C. In Cyclops, concentrations of MAAs were also highest when extracted in 25 % MeOH at 45 °C, but there was no statistically significant difference among the different protocols (P = 0.079). Depending on the organism examined, both MeOH concentration and temperature affected extraction efficiency and final MAA concentration. Our results stress the need for a priori testing the influence of these variables to assure that the highest concentration is obtained without altering the qualitative MAA composition. Based on these results, direct comparison of MAA concentrations reported in the scientific literature should be done with caution.