Optimized ultrasonication-redox process for controlled production of low molecular weight carrageenan

Carrageenans are linear sulfated polysaccharides widely used in industry, but their high molecular weight and limited solubility restrict broader biomedical and agricultural applications. This study presents a two-step process combining ultrasonic pretreatment with a H 2 O 2 -AH 2 redox system to produce low-molecular-weight carrageenan (LMWC) efficiently and controllably. Ultrasonication rapidly reduced molecular weight, homogenized polymer size, and preserved functional groups, as confirmed by HPSEC, rheology, FTIR and 1 H-NMR. Depolymerization kinetics followed a two-phase model, with the most energy-efficient ultrasonication at 60% amplitude for 8.67 min (54.2% MW reduction, 218.8 J/mL). Redox-assisted depolymerization was optimized via a quadratic model, showing strong effects of temperature and time, while intermediate reagent ratios maximized efficiency. Scaling from 150 mL to 2.2 L retained performance, producing ∼9.35 kDa LMWC with lower polydispersity, reduced reagent consumption, and faster processing than mild-acid hydrolysis controls. The purified fraction exhibited enhanced antioxidant activity (IC 50 0.96 g/L, 270 mg Trolox equivalents/g). The sequential US, H 2 O 2 -AH 2 method provides a scalable, controllable route to tailor LMWC for specific applications, outperforming conventional acid treatments and offering a robust alternative to enzymatic depolymerization. • A optimized two-step process produced low molecular weight carrageenan (MW) • Ultrasonication reduced molecular weight and preserved functional groups • An optimal energy-efficient ultrasonication was found at 8.67 min at 60% amplitude • A validated quadratic model described the redox-assisted depolymerization • Target molecular weights can be achieved at 49 °C with 10 min reaction time