Annual compositional variation in wild Osmundea pinnatifida (Hudson) Stackhouse from the west coast of Scotland

Osmundea pinnatifida (Pepper Dulse) is a commercially interesting red alga harvested from the wild and sold dried as seasoning due to its distinctive peppery taste. For the first time, this research highlights how the proximate composition, metal, antioxidant, pigment content, and C:N ratio of this species varied over a 12-month period in wild biomass collected from the same location on the west coast of Scotland. The nutritional profile varied across the seasons with high levels of carbohydrates (27.8%) observed in the summer, which coincided with low levels of proteins (11.4%). Antioxidant content was higher in the summer months compared to the autumn/winter. All pigments, but especially the phycobiliproteins, decreased in the summer samples. The levels of heavy metals such as arsenic, cadmium, and lead were low and do not represent a concern for the consumption of this species. Bivariate correlations showed links between the production of carbohydrates and antioxidant compounds and environmental factors such as maximum radiation/hours of light. Using principal component analysis (PCA) clearly discriminated between samples taken in the summer and winter months with the separation being substantiated by the carbohydrate and antioxidant levels in summer and pigments in winter. The results obtained are fundamental for predicting and planning biomass harvest and commercial management of this species, providing information on the variation in the biochemical and qualitative profile of the species.