Seasonal variations of antioxidants in the brown seaweed Saccharina latissima

Mainly the brown seaweeds are known for their high antioxidative capacity within the specific compounds such as phlorotannins, polyphenols, flavonoids, pigments, and these natural antioxidants are of high industrial interest. Previous studies have shown large seasonal variations in biomass composition.

The aim of this study was to see if there was a seasonal variation in the antioxidant content of sugar kelp (Saccharina latissima), compare two cultivation sites, REF and IMTA, and test different solvents applied for extractions, methanol or ethyl acetate. Rope cultivated sugar kelp were sampled both in close proximity to a blue mussel and fish farm (IMTA) and at a reference/control site (REF), both outside Horsens fjord in Denmark.

Sugar kelp biomass was measured (n=3) at 2 m depth in 2013-2014, and freeze dried and stored frozen for further analyses. In relation to the extraction, two solvents with different polarities were applied. Methanol was generally a better solvent for extracting the more polar compounds i.e. phenolics, whereas ethyl acetate tended more efficient for flavonoid extraction.

There was no significant variation in the TAC between the two cultivation sites, ranging between 1,531-5,135 μg GA/g DW, and with no clear pattern of seasonal variation. Within the phenolic content no significant difference was seen (258- 3,594 μg GA/g DW), and for IMTA the flavonoid concentration for September 2013 (4,830±1,048 μg rutin/g DW) was significantly higher than the other months.

The biological variability had a high impact revealed by large standard deviation. The pigment specimens did not change during the year, however the concentration did, and with fucoxanthin as the most interesting. No clear correlation was found between pigments and the antioxidants. This study showed high concentration of antioxidant in sugar kelp and in 100 times higher range than e.g. microalgae.

However, the large variations should be taken into account when aiming for industrial use.