In vitro digestibility of proteins from red seaweeds: Impact of cell wall structure and processing methods.

This study aimed to assess the nutritional quality and digestibility of proteins in two red seaweed species, Gelidium corneum and Gracilaropsis longissima, through the application of in vitro gastrointestinal digestions, and evaluate the impact of two consecutive processing steps, extrusion and compression moulding, to produce food snacks. The protein content in both seaweeds was approximately 16 %, being primarily located within the cell walls. Both species exhibited similar amino acid profiles, with aspartic and glutamic acid being most abundant. However, processing impacted their amino acid profiles, leading to a significant decrease in labile amino acids like lysine. Nevertheless, essential amino acids constituted 35-36 % of the total in the native seaweeds and their processed products. Although the protein digestibility in both seaweed species was relatively low (<60 %), processing, particularly extrusion, enhanced it by approximately 10 %. Interestingly, the effect of the different processing steps on the digestibility varied between the two species. This difference was mainly attributed to compositional and structural differences. G. corneum exhibited increased digestibility with each processing step, while G. longissima reached maximum digestibility after extrusion. Notably, changes in the amino acid profiles of the processed products affected adversely the protein nutritional quality, with lysine becoming the limiting amino acid. These findings provide the basis for developing strategies to enhance protein quality in these seaweed species, thereby facilitating high-quality food production with potential applications in the food industry.

Characterization of the invasive macroalgae Rugulopteryx Okamurae for potential biomass valorisation.

This study aimed to examine the composition and properties of the invasive macroalgae R. okamurae and explore potential applications. The results showed that the seaweed biomass is mainly composed of structural carbohydrates, with alginate being the main constituent, accounting for 32 % of its total composition and with a mannuronic and guluronic acid ratio (M/G) ratio of 0.93. It also has a relatively high concentration of fucose, related to the presence of fucoidans that have important biological functions. Among the mineral contents, a high magnesium and calcium (7107 and 5504 mg/kg) concentration, and the presence of heavy metals above legislated thresholds, were notable. R. okamurae also contained a high lipid content of 17 %, mainly composed of saturated fatty acids, but with a significant fraction of n3 polyunsaturated fatty acids (18 %) resulting in a low n6/n3 ratio (0.31), that has health benefits. The protein content of R. okamurae was 12 %, with high-quality proteins, as essential amino acids (mainly leucine, phenylalanine and valine) constitute 32 % of the total amino acids. It also showed a high polyphenol content and outstanding antioxidant properties (106.88 mg TE/g). Based on these findings, R. okamurae has significant potential as a sustainable source of bioactive compounds that can add value to different sectors, including food, feed, pharmaceuticals and cosmetics.

Improved performance of less purified cellulosic films obtained from agar waste biomass.

The residues generated after the extraction of agar from Gelidium sesquipedale by means of a hot-water treatment, with (NaOH+HW residue) and without (HW residue) an alkali pre-treatment have been valorized to produce high performance cellulosic films. Both residues were mainly composed of structural carbohydrates (in particular, agar), ashes and lipids. The residual agar could only be completely removed by applying a two-step process based on bleaching and alkaline treatments. The application of the alkaline pre-treatment for the extraction of agar did not significantly affect the properties of the films produced from the extracted fractions, hence making the HW residue more sustainable and economically viable. The agar remaining in the less purified fractions had a positive effect on the performance of the films, improving their transparency, mechanical properties and water vapour barrier, outperforming benchmark biopolymers; in addition, these materials presented antioxidant capacity inhibiting the degradation of ß-carotene.