Abstract
We recently demonstrated the monthly variation and antioxidant activity of mycosporine-like amino acids (MAAs) from red alga dulse in Japan. The antioxidant activity of MAAs in acidic conditions was low compared to that in neutral and alkali conditions, but we found strong antioxidant activity from the heated crude MAA fraction in acidic conditions. In this study, we identified and characterized the key compounds involved in the antioxidant activity of this fraction. We first isolated two MAAs, palythine, and porphyra-334, from the fraction and evaluated the activities of the two MAAs when heated. MAAs possess absorption maxima at around 330 nm, while the heated MAAs lost this absorption. The heated MAAs showed a high ABTS radical scavenging activity at pH 5.8–8.0. We then determined the structure of heated palythine via ESI-MS and NMR analyses and speculated about the putative antioxidant mechanism. Finally, a suitable production condition of the heated compounds was determined at 120 °C for 30 min at pH 8.0. We revealed compounds from red algae with antioxidant activities at a wide range of pH values, and this information will be useful for the functional processing of food.
Highlights
Marine organisms, e.g., dinoflagellates, cyanobacteria, and macroalgae, synthesize and accumulate mycosporine-like amino acids (MAAs) as natural compounds to protect themselves from UV radiation damages [1,2]
The peak pattern corresponded to heated palythine, suggesting that the usujirene was converted into palythine and dehydrated into heated palythine
We found that heated MAAs showed a high activity across a broad pH range
Summary
E.g., dinoflagellates, cyanobacteria, and macroalgae, synthesize and accumulate mycosporine-like amino acids (MAAs) as natural compounds to protect themselves from UV radiation damages [1,2]. It was previously reported that 97% of the light energy absorbed by shinorine and porphyra-334 is converted into heat [5]. These compounds hardly photodegrade and show high stability. Identified from algae and plants, e.g., catalaMsean[2y2a],nptihoyxcidoaenryt tahcrtiinve[1c5o]m, fpuocuoniddasnh[a2v3e],baesecnoribdiecnaticfiided[2fr4o],minasloglauebalendanptilaonxtids,aen.gts., catalase [22], phycoerythrin [15], fucoidan [23], ascorbic acid [24], insoluble antioxidants [25,26], phlorotannins [27,28], catechins [29], scytonemin [30], and phenolic compounds (e.g., gentisic acid, protocatechuic acid, and gallic acid) [31].
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