Abstract
Seaweeds are a recognized source of bioactive compounds and techno-functional ingredients. However, its protein fraction is still underexplored. The aim of this study was to determine the total and free amino acid profile and protein content of four seaweeds species (Porphyra dioica, Porphyra umbilicalis, Gracilaria vermiculophylla, and Ulva rigida) produced in an integrated multi-trophic aquaculture system, while assessing their protein quality. Samples were submitted to acid and alkaline hydrolysis (total amino acids) and to an aqueous extraction (free amino acids) followed by an automated online derivatization procedure, and analyzed by reverse phase-high performance liquid chromatography. Protein-, non-protein and total-nitrogen were quantified by the Kjeldahl method. Crude and true protein contents were estimated based on the nitrogen and amino acid composition. Protein quality was assessed based on the amino acids profile. Porphyra species presented the highest protein content compared to the remaining three seaweed species tested. All samples presented a complete profile of essential amino acids and a high quality protein profile, according to World Health Organization and Food and Agriculture Organization standards. Methionine and tryptophan were the first limiting amino acids in all species. Red species (Porphyra and Gracilaria) presented high levels of free alanine, glutamic, and aspartic acids. The results highlight the potential of using seaweeds as an alternative and sustainable source of protein and amino acids for human nutrition and industrial food processing.
Highlights
Seaweeds are a diverse group of marine species that have been part of the human diet for thousands of years, especially in Asian countries
The total and free amino acid profiles of four seaweed species (Porphyra dioica, Porphyra umbilicalis, Gracilaria vermiculophylla, and Ulva rigida) produced in an Integrated multi-trophic aquaculture (IMTA) system were assessed. Their protein content and protein quality based on the corresponding amino acid score (AAS)
The % EAA in Gracilaria vermiculophylla was lower than the values previously described for other species of Gracilaria, which ranged from 50–61% dw [31,32]. These results indicate that the seaweed species analyzed in this study present similar amounts of EAA compared to other plant-based protein sources, such as lupine (38.01% dw), faba bean (41.36% dw), hemp (39.52% dw), and flaxseed (38.82% dw) [48], or animal origin, as is the case with casein (43.6%), lower than those of ovalbumin (52.4%) [34]
Summary
Seaweeds are a diverse group of marine species that have been part of the human diet for thousands of years, especially in Asian countries. Some authors have reported that the use of a small quantity of different seaweed liquid extracts efficiently enhanced the in vitro mass propagation of an important crop of Solanum melongena L. This suggests the possibility of using it as an alternative to commercially available plant growth regulators that can be toxic and costly when compared with natural extracts [3]. The antimicrobial activity of seaweeds is often reported.
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