Sugaring-out: a novel sample preparation method for determination of fucoxanthin in Icelandic edible seaweeds

Fucoxanthin is an oxygenated carotenoid with a broad spectrum of bioactivities, ranging from antioxidant activity to antimicrobial activities. Micro-algae are well-recognized resources for their production of fucoxanthin, which can be enhanced by cell culture and genetic engineering, and macro-algae or seaweeds are readily available natural resources for harvesting and fucoxanthin purification. Prior sample preparation methods from macro-alga matrix are tedious and time-consuming, usually involving repetitive chromatographic purification of fucoxanthin from co-extracted compounds, such as phlorotannins. This study focused on five Icelandic edible seaweeds and reported a novel sample preparation method—sugaring-out for the HPLC analysis of fucoxanthin. We aimed to determine fucoxanthin contents in Icelandic edible seaweeds and to evaluate the effects of drying process on fucoxanthin contents. An aqueous acetonitrile model system was developed to visualize fucoxanthin partition and to select optimal conditions for partition. Glucose was added to trigger phase separation. The highest yield of fucoxanthin was found when it is mixed with 70 mg mL⁻¹ glucose. Among three edible dry seaweeds sold in Icelandic food market, fucoxanthin was detected only in sugar kelp (18.76–38.13 μg g⁻¹ d.w.). Fresh brown algae can be good alternative sources of fucoxanthin (177.74–227.39 μg g⁻¹ d.w. in Ascophyllum nodosum and 120.39–147.86 μg g⁻¹ d.w. in Fucus vesiculosus). Seaweed freshness is critical for fucoxanthin extraction, as post-harvest drying process with light and air exposure can cause approximately 70–90% loss of fucoxanthin after a 4-week drying process.