Valorización del residuo del alga roja tras la extracción industrial de agar mediante tratamiento con agua subcrítica y extracción enzimática asistida

Abstract

Red alga Gelidium sesquipedale is the main resource in the Spanish agar industry for high-quality agar production. As a consequence of industrial agar extraction, great amounts of a solid residue are generated, and it still contains important valuable compounds such as proteins (21%) and carbo- hydrates (37%). It is possible to exploit this solid waste through a biorefinery concept by transforming into components of interest that can be reincorporated into the industrial process. To this purpose, the integral valorization of the by-product has been proposed through innovative and environmentally friendly technologies. Subcritical water extraction (SWE) consists of using water at high temperature, between 100ºC and 374ºC, and enough pressure to keep it in a liquid state. The effect of temperature and flow rate in the extraction of protein fraction, total organic carbon, total polyphenols and antioxidant activity has been studied. It has been observed that the increase in temperature from 129 to 185ºC led to higher extraction yields, of almost 70% for proteins, noting a degradation of proteins and free amino acids at higher temperatures. In the case of total organic carbon, no significant differences were seen between 185 and 200ºC. Regarding the extraction of phenolic compounds, the highest yields were reached at 200ºC with concentrations of 26mg GAE/dry residue (GAE, gallic acid equivalents). The extracts with the highest antioxidant ca- pacity were obtained at 200ºC and 6 ml/min, having determined a positive correlation between the antioxidant activity and the concentration of total polyphenols. On the other hand, the increase in water flow rate from 2 to 6 ml/ min led to faster extractions and higher yields due to a shorter residence time for all the components analyzed. The results obtained by using subcritical water have been compared with those obtained by enzyme assisted extraction (EAE). The hydrolytic capacity of cellulase has been studied at concentrations of 0.25, 0.5, 1, 2, 4, 6 and 8%, binary and ternary combinations of cellulase, xylanase and protease, as well as the effect of 6% protease at pH 5, 6 and 8. Higher cellulase concentrations resulted in a higher extraction of proteins and polyphenols. None of the enzymatic combinations generated better results than cellulase in the extraction of poly- phenols, while the best results in the protein extraction were obtained with the binary combination of cellulase and protease. In the extraction with proteases, a higher yield was observed at higher pH, close to 38% for the protein fraction and a concentration of 8.93mg amino acid / g protein.