Gross Chemical Profile and Calculation of Nitrogen-to-Protein Conversion Factors for Five Tropical Seaweeds

Despite decades of research on marine algae, there are still significant gaps in basic knowledge about chemical com-position of these organisms, especially in tropical environments. In this study, the amino acid composition and contents of total nitrogen, phosphorus, lipid, carbohydrate and protein were determined in Asparagopsis taxiformis, Centro-ceras clavulatum, Chaetomorpha aerea, Sargassum filipendula and Spyridia hypnoides. The seaweeds showed low lipid contents (lower than 5.5 % d.w. in all species) and were rich in carbohydrates (more than 16 % d.w. in all sea-weeds). The percentage of nitrogen, phosphorus and protein varied widely among species, which red algae showed the highest concentrations. The amino acid composition was similar among the seaweeds, which glutamic acid, aspartic acid and leucine as the most abundant. All species are poor in histidine. An average of 24.2 % of the total nitrogen is non-proteinaceous. From data of total amino acid and total nitrogen, specific nitrogen-to-protein conversion factors were calculated for each species. The nitrogen-to-protein conversion factors calculated ranged from 4.51 to 5.21, with an overall average of 4.86. These findings show that the traditional conversion factor of 6.25 should be avoided for seaweeds, since it overestimates the actual protein content