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This study explores the potential of producing bioethanol from seaweed biomass and reusing the residues as antioxidant compounds. Various types of seaweed, including red (Gelidium amansii, Gloiopeltis furcata, Pyropia tenera), brown (Saccharina japonica, Undaria pinnatifida, Ascophyllum nodosum), and green species (Ulva intestinalis, Ulva prolifera, Codium fragile), were pretreated with dilute acid and enzymes and subsequently processed to produce bioethanol with Saccharomyces cerevisiae BY4741. Ethanol production followed the utilization of sugars, resulting in the highest yields from red algae > brown algae > green algae due to their high carbohydrate content. The residual biomass was extracted with water, ethanol, or methanol to evaluate its antioxidant activity. Among the nine seaweeds, the A. nodosum bioethanol residue extract (BRE) showed the highest antioxidant activity regarding the 2,2-diphenyl-1-picrylhydrazyl (DPPH) activity, ferric reducing antioxidant power (FRAP), and reactive oxygen species (ROS) inhibition of H2O2-treated RAW 264.7 cells. These by-products can be valorized, contributing to a more sustainable and economically viable biorefinery process. This dual approach not only enhances the utilization of marine resources but also supports the development of high-value bioproducts. [ABSTRACT FROM AUTHOR]

The study objective was to evaluate the potential production of polyhydroxyalkanoates (PHAs), a biodegradable plastic material, by Paracoccus haeundaensis for which PHA production has never been reported. To identify the most effective nitrogen-limited culture conditions for PHAs production from this bacterium, batch fermentation using glucose concentrations ranging from 4 g l -1 to 20 g l -1 with a fixed ammonium concentration of 0.5 g l -1 was carried out at 30°C and pH 8.0. A glucose supplement of 12 g l -1 produced the highest PHA concentration (1.6 g l -1 ) and PHA content (0.63 g g -1 ) thereby identifying the optimal condition for PHA production from this bacterium. Gas chromatography-mass spectrometry analysis suggests that P. haeundaensis mostly produced copolymer types of poly(3-hydroxybutyrate- co -3-hydroxyvalerate) [P(3HB- co -3HV)] from glucose concentrations at 12 g l -1 or higher under the nitrogen-limited conditions. When several other single carbon sources were evaluated for the most efficient PHA production, fructose provided the highest biomass (2.8 g l -1 ), and PHAs (1.29 g l -1 ) concentrations. Results indicated that this bacterium mostly produced the copolymers P(3HB- co -3HV) from single carbon sources composing a range of 93-98% of 3-hydroxybutyrate and 2-7% of 3-hydroxyvalerate, whereas mannose-supplemented conditions produced the only homopolymer type of P(3HB). However, when propionic acid as a secondary carbon source were supplemented into the media, P. haeundaensis produced the copolymer P(3HB- co -3HV), composed of a 50% maximum monomeric unit of 3-hydroxyvaleric acid (3HV). However, as the concentration of propionic acid increased, cell biomass and PHAs concentrations substantially decreased due to cell toxicity.