Optimization and Statistical Modeling of Ultrasonic Depolymerization of k-Carrageenan Using RSM: Predominant Role of pH, Temperature-Time Interactions, and Mechanistic Insights

Abstract

k-carrageenan is a sulfated polysaccharide from red seaweed widely used in the food and pharmaceutical industries. In its low-molecular-weight form (<20 kDa), it exhibits improved cellular uptake and more potent biological activity, making it highly attractive for biomedical applications. Ultrasonic-assisted depolymerization provides an effective method for reducing molecular weight while preserving functional sulfate groups. This study statistically modeled the effects of temperature, time, and pH on k-carrageenan depolymerization using Response Surface Methodology (RSM) with a Central Composite Design (CCD). Experiments were conducted at temperatures ranging from 40 to 60 C, with sonication times of 16 to 32 minutes, and at pH levels of 3 and 6. Molecular weight was estimated via intrinsic viscosity, and structural changes were analyzed by FTIR spectroscopy. The results showed that pH was the most influential factor, with acidic conditions (pH 3) promoting greater molecular weight reduction than near-neutral conditions (pH 6). Temperature and time also had significant effects, and the RSM model effectively captured both linear and quadratic interactions. ANOVA confirmed the model's reliability, with high coefficients of determination (R^2; = 0.9684 at pH 3 and R^2; = 0.9712 at pH 6). FTIR analysis revealed cleavage of alpha(1->3) and beta(1->4) glycosidic bonds, while sulfate ester groups remained stable. In conclusion, ultrasonic depolymerization coupled with RSM provides a predictive and reliable framework to optimize low-molecular-weight k-carrageenan production for biomedical applications.