The seasonal variation in nitrogen, amino acid, protein and nitrogen-to-protein conversion factors of commercially cultivated Faroese Saccharina latissima

The demands of new food sources are increasing with the increasing human population. Proteins are a main nutrient for human consumption and in animal feed, which will be in short supply in the near future. Many macroalgal species have shown to possess significant levels and quality of protein, comparable to conventional protein-rich foods. The brown macroalga Saccharina latissima was commercially cultivated in an open ocean area in the Faroe Islands. The effect of depth, cultivation site and seasonal variation in nitrogen, protein concentration, and the amino acid profile were investigated to study the potential of Faroese cultivated S. latissima as a protein source. Moreover, the nitrogen-to-protein conversion factor was calculated. The average nitrogen concentration was 2.1 ± 0.2% of dry weight (dw) with no significant variation between sites, a single month with significant variation between cultivation depths (March 2016), and a significant seasonal variation (among most months). The average protein concentration determined by summing up total amino acids was 4.3 ± 0.9% of dw, and comparable to or slightly lower than other studies. There was no depth, site or seasonal variation in AA-protein concentration for the cultivated S. latissima. The lack of seasonal variation was most likely a consequence of the year-round stable physical conditions in the Faroe Islands, and compared with other studies surprising as most found seasonal variation of AA-protein. The quality of the protein was high (EAA score > 100%) in March, although the low total concentration of protein limits the possibilities to use S. latissima solely as a protein source or for protein extraction and other nutrients should be investigated to understand its potential as a food or feed source. This study will recommend estimating total protein concentration by summing up the total amino acids (AA-protein), as the widely used 6.25 factor is highly overestimating the protein concentration.