The biochemical composition and its relation to color of Ulva spp. upon harvest time

Green seaweed species of the genus Ulva are promising protein sources for food production. Various factors affect the biochemical composition of Ulva spp. (hereafter Ulva) , which can complicate the utilization in a commercial scale food production. This study investigated the composition of Ulva harvested in 2021 in May (dark green/black biomass), June (light green biomass) and August (mixed colored biomass). The August harvest was divided into three different color codes: light green, green, and dark green/black, to explore a relation between color and composition as an indicator for biomass quality. The crude protein (CP) and ash contents were highest in the dark August biomass (16.4±0.4% and 35.9±3.0% of dry matter (DM), respectively) and in the dark biomass harvested in May (20.6±0.5% and 41.2±3.9% of DM, respectively). The light green Ulva harvested in June had a lower CP content (6.5±1.5% of DM) similarly to what was observed for light green biomass in August (7.7±0.1% of DM). The light green biomasses were found to have a higher nitrogen to amino acid (N-to-AA) conversion factor and proportion of essential amino acids (EAA). The lipid content ranged between 1.0-2.2±0.1-0.2% of DM for the different biomasses and a higher lipid content was related with a lighter biomass color. Phosphorus and potassium concentrations were highest in the green fraction, whereas the darker green/black biomass had higher contents of all other elements, including the toxic elements, arsenic and cadmium. Graphical abstract