Effect of different drying methods on the nutritional composition and phenolic compounds of the brown macroalga, Fucus vesiculosus (Fucales, Phaeophyceae)

The application of macroalgae for food and feed has been increasing continuously due to their nutritional and health-promoting properties. Efficient post-harvest drying is needed to remove moisture content from macroalgal biomass without negatively affecting its nutritional value. We hypothesized that low-temperature oven drying would preserve most of the nutrients and polyphenols in macroalgae. The polyphenol-rich brown macroalga, Fucus vesiculosus, was exposed to one of the following treatments: freeze-drying (FD; for 72 h), oven drying at 40 ℃ (OD40; for 24 h), and oven drying at 80 ℃ (OD80; for 24 h). The concentration of total fatty acids and the sum of saturated, mono-, and polyunsaturated fatty acids exhibited a decreasing trend with higher drying temperatures (FD > OD40 > OD80), indicating the sensitivity of fatty acids to a high drying temperature. However, the sum of total or essential amino acids was significantly higher (p < 0.05) in OD80 compared to OD40 and FD biomass.

In this study, the average N-protein-conversion factor for dried F. vesiculosus remained relatively stable (~ 4.64) across drying treatments. The total polyphenol content remained unaffected by the drying treatment, although it tended to decrease with increasing drying temperature. Targeted metabolomics revealed three classes of phenolic compounds: phenylpropanoids, flavones, and flavonols. A low-temperature oven drying appears to be a suitable method to preserve nutrients and polyphenols in brown macroalgae. Future studies are needed to evaluate the impact of drying methods on other bioactive compounds and to understand the economic sustainability of oven drying.