Effect of High-Pressure Pretreatment and Drying Conditions on the Physicochemical and Antioxidant Properties of Carrageenan from <i>Kappaphycus alvarezii</i>

This study examines the impact of high-pressure pre-treatment (HPP) combined with various drying temperatures on the physicochemical and antioxidant characteristics of carrageenan extracted from Kappaphycus alvarezii . Samples were subjected to 200, 400, and 600 MPa HPP before undergoing freeze-drying (−50 °C) and hot-air drying (40 °C and 60 °C). Then, samples were extracted to produce semi-refined carrageenan (SRC). Semi-refined carrageenan was analyzed for colour, yield, gel strength, viscosity, total phenolic content (TPC), total flavonoid content (TFC), and antioxidant capacity using DPPH and FRAP assays. The optimal treatment was 600 MPa HPP combined with 40 °C drying which yielded superior results, including the highest carrageenan yield (85.28%), gel strength (193.23 g/cm²), viscosity (79.07 mPa·s), TPC (86.15 mg GAE/100 g), TFC (5.49 mg QE/100 g), FRAP (304.29 mg FeSO 4 /100 g), and DPPH radical scavenging (36.56%). While freeze-drying preserved higher TPC and TFC values under some conditions, oven drying at 40 °C consistently produced better functional performance of carrageenan. These findings highlight that combining HPP with moderate thermal drying significantly enhances the structural and bioactive quality of carrageenan, offering an efficient and scalable processing route for high-value seaweed-based products.