Characteristics of Functional Materials Recovered from Red Macro Algae(Kappaphycus alvarezii) using Pressurized Hot Water Extraction

Abstract

Two strains of Kappaphycus alvarezii were treated with pressurized hot water extraction (PHWE) at conditions ranging from 150oC/1MPa - 300oC/10MPa 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 (ABTS+ & DPPH), total phenolic content (TPC), total flavonoid content (TFC), total sugar, reducing sugar, monosaccharide composition, maillard reaction products (MRP), 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 156.21mg/L and 155.49mg/L respectively. Radical scavenging activity, polyphenol content and proteins increased from 150oC/1MPa to 270oC/8MPa but decreased at 300oC/10MPa 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. The best condition for all sugars and foaming properties was 150oC/1MPa, while antioxidants, TPC, TFC, total protein and emulsifying properties were best recovered at 270oC/8MPa for both strains. Extraction of ĸ-carrageenan was carried out using a single composite function converted from optimized conditions identified for various responses. A three level Box-Behnken response surface design (BBD) for optimization was employed to investigate the impact of independent variables (responses) including temperature, pressure, solid-liquid ratio and sonication time on the extraction yield. The optimum extraction conditions were 130oC, 5MPa, 0.0063mg/mL and 20 min sonication time. From the optimum conditions, the extraction yield was 74.72% crude ĸ- carrageenan close to the predicted value of 74.02% indicating that the optimized condition was valid within the specified range of process parameters. The extracted crude ĸ-carrageenan under the optimum condition was analyzed using FT-IR, TGA and XRD to affirm the features of ĸ- carrageenan. Physical properties including gel strength, viscosity and emulsification index of the crude ĸ-carrageenan recovered by PHWE was low compared to the conventional method. However, the antioxidant activity and purity was high due to high sulfate content and enhanced temperature employed in the extraction process. The molecular weight was reduced by thermal degradation in the PHWE process which enhanced its bioavailability and functional properties.