Characteristics of functional materials recovered from Solomon Islands red seaweed (Kappaphycus alvarezii) using pressurized hot water extraction

In this study, two strains of Kappaphycus alvarezii were treated with pressurized hot water extraction (PHWE) at conditions ranging from 150 A degrees C/1 MPa to 300 A degrees C/10 MPa using three different solvents including water, 1% formic acid, and 1% sodium hydroxide. Hydrolysates obtained from the extraction were investigated for their hydrolysis efficiency, pH, radical scavenging activity (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS(+)) and 2,2-diphenyl-1-picrylhydrazyl (DPPH)), total phenolic content (TPC), total flavonoid content (TFC), total sugar, reducing sugar, monosaccharide composition, Maillard reaction products (MRPs), total protein, emulsifying properties, and foaming properties. The highest hydrolysis efficiency ranged from 81.47 to 97.18% showing a consistent increase with increasing temperature and pressure conditions. Major monosaccharide compounds recovered from the hydrolysates were glucose and galactose with concentrations of 156.21 and 155.49 mg L-1, respectively. Radical scavenging activity, polyphenol content, and proteins increased from 150 A degrees C/1 MPa to 270 A degrees C/8 MPa but decreased at 300 A degrees C/10 MPa due to decomposition and protein denaturation. Foaming and emulsifying properties were influenced by variation of protein with relation to temperature and protein-polysaccharide electrostatic interactions. Thus, this study showed that the best condition for all sugars and foaming properties is 150 A degrees C/1 MPa, while antioxidants, TPC, TFC, total protein, and emulsifying properties are best recovered at 270 A degrees C/8 MPa for both strains.