Optimization of sodium alginate production from Cystoseira crinita macroalgae using an environmentally friendly next-generation ultrasound-assisted extraction method by response surface methodology

In this study, sodium alginate was produced from the brown seaweed Cystoseira crinita annually collected from the Rize coasts of the Black Sea, and the quality of the extracted sodium alginate was evaluated. The collected samples were categorized into two groups—cold and warm seasons—based on seawater temperature. Compared to the conventional extraction process, an environmentally friendly, next-generation ultrasonic-assisted extraction method was employed using an ultrasonic water bath, which significantly reduced both extraction time and energy consumption. Using a Central Composite Design (CCD) under Response Surface Methodology (RSM), the extraction process was optimized separately for each season by considering the extraction time, extraction temperature, and Na₂CO₃ concentration as factors. The response variables were extraction yield, crude ash content, pH, viscosity, gel strength, and color parameters (a*, b*, and L*). The statistical significance of the independent variables on the responses was analyzed at a 95% confidence level using analysis of variance (ANOVA) and F-test, and the predicted conditions were experimentally validated. Additionally, the obtained responses were compared with those of three different commercial alginates. The optimum responses were determined as 36.47% (cold season) and 30.38% (warm season) for extraction yield, and 26.97% (cold season) and 28.27% (warm season) for crude ash content. The optimum pH values were 8.86 for the cold season and 9.04 for the warm season. Minimum viscosity values were optimized at 5.07 mPa·s (cold season) and 4.41 mPa·s (warm season), while maximum viscosity values reached 29.16 mPa·s and 19.17 mPa·s, respectively. Gel strength, another quality indicator, showed minimum values of 125.11 g (cold season) and 5.15 g (warm season), while maximum values reached 785.53 g and 693.75 g, respectively. The extracted alginate samples exhibited light coloration, and their moisture contents were comparable to those of alginates obtained from other species used in industrial production.