Multiple-response optimization of the acidic pretreatment of the brown alga Sargassum cristaefolium for the alginate extraction using twin screw extruder

The first step in the alginate extraction from brown seaweed is the acidic pre-treatment. The acidic pretreatment affected physical characteristics of brown seaweed in alkaline solution and physicochemical properties of alginate. The aim of this study to investigate the effects of pH and time of the acidic pretreatment on the multiple response of alginate from brown seaweed Sargassum cristaefolium extracted using twin-screw extruder (TSE). Central composite design in Response Surface Method (RSM) was used to find the optimum condition of the acidic pre-treatment based on these responses namely residence time distribution (RTD), yield, intrinsic viscosity, alginate molecule weight. Higher RTD was observed as pH level was approximately neutral, leading to degradation of alginate polymer chain. The results demonstrated that pH and duration of the acidic pre-treatment significantly showed quadratic effects on RTD, intrinsic viscosity, and molecule weight. The optimum condition of the acid pre-treatment was found at pH of 2.90 and time of 61.74 min, resulting in RTD 4.13±0.017 min, yield 35.58±0.23 %, intrinsic viscosity 418.77±1.74 ml/g, and molecule weight 198.15±2.47 kDa.