Optimization of alkali-treated Gracilaria verrucosa chips production using response surface methodology: Physicochemical characterization and agar quality assessment

Context: Agar, a hydrocolloid derived from red seaweed such as Gracilaria verrucosa, is widely used in food and pharmaceutical industries. In addition to dried seaweed, several countries now utilize alkali-treated Gracilaria (ATG) chips as a semi-finished product for agar production. However, the alkali pre-treatment process for producing ATG chips remains suboptimal and requires refinement for improved efficiency. Aims: To optimize the production of ATG chips from G. verrucosa using response surface methodology (RSM) to obtain optimal product quality. Methods: A central composite design was applied with two factors: alkali concentration and heating temperature, and six responses: ATG yield, moisture content, ash content, sulfate content, agar yield, and agar gel strength. Design Expert 11 software was used for experimental design, model selection, and process optimization. Results: Optimal conditions were found at 10.30% NaOH concentration and 67.76°C heating temperature, achieving a desirability value of 0.87. Under these conditions, the ATG chips showed a yield of 45.60%, 21.18% moisture, 4.42% ash, and 1.42% sulfate content. The derived agar had a yield of 54.74% and a gel strength of 100.91 g/cm². Conclusions: The validation results confirmed the predictive accuracy of the RSM model. The optimized alkali pre-treatment process improves the quality and efficiency of ATG chip production, offering a promising alternative for sustainable agar manufacturing.