Recovery of the protein fraction with high antioxidant activity from red seaweed industrial solid residue after agar extraction by subcritical water treatment

In this work valorization of the underexploited industrial solid residue generated after agar extraction from Gelidium sesquipedale was studied by using subcritical water in a semicontinuous fix-bed reactor. First, complete characterization by-product carried out, determining up to 21% (w/w) protein content (for nitrogen factor 4.9) with high essential amino acids, 37% carbohydrate fraction and amount ash, 22% (w/w). The effect temperature, range 129 200 °C, flow rate, 2 6 mL min?1, on carbon extraction/hydrolysis studied. At constant rate maximum achieved at 185 °C. Higher temperatures led degradation or its hydrolysis products. Free acids release followed same trend as fraction. most temperature sensitive determined gas chromatography (EZ:faast Phenomenex), were serine aspartic glutamic acids. As consequence, selectivity towards non-polar increased working severity factors. A Pearson correlation between antioxidant capacity collected extracts bioactive compounds (total polyphenolic –TPC-, peptides free acids) established, being stronger for TPC. ash treatment steadily due non-solubilization possible application agriculture fertilizers.