Effects of air drying and freezing and long-term storage on phytochemical composition of brown seaweeds

The effect of air drying and freezing at − 25 °C on the total phenolic content, fucoidan, alginate, and amino acids of brown algae Fucus vesiculosus, Fucus distichus, and Ascophyllum nodosum was studied over 365 days of storage every 90 days. The levels of total phenols and polysaccharides in frozen algae samples at 365 days of storage were 75–95% of fresh algae and were higher than in air-dried samples by more than 5–15%. The greatest differences between the fresh and dried samples were in the total phenolic contents. A strong correlation was found between the content of total phenolics and polysaccharides and the water content in frozen samples of F. vesiculosus and A. nodosum. The influence of air drying and freezing processing and storage on the total amino acid content is discussed using F. vesiculosus as an example. The total amino acid content in the air-dried samples increased during storage, but on the 365th day, 99% of the initial content in fresh algae remained. In contrast, the content in the frozen samples had decreased to 82% after the same storage duration. The ratio of the sums of the essential to the total amino acids during storage in the dry and frozen samples increased compared with that in fresh algae from 0.43 to 0.51 after 365 days of storage. Air drying and freezing are suitable procedures in terms of the levels of total phenols, polysaccharides, and amino acids, allowing a shelf life of at least 365 days.