Padina gymnospora biorefinery: coalescing ultrasonic-assisted phenolic recovery and citric acid–mediated alginate extraction

The present study investigates the possibility of establishing a biorefinery strategy for comprehensive biomass utilization of Padina gymnospora by integrating ultrasonication and alginate extraction techniques. Ultrasonication experiments were carried out to optimize the process for recovering antioxidant-rich bioactive compounds from P. gymnospora by employing sample-to-solvent ratio and extraction time as independent variables using response surface methodology. A second-order response surface regression model was developed as a function of sample-to-solvent ratio and extraction time, and the optimum extraction condition was obtained by the desirability function. Biomass obtained after the ultrasonication process was then subjected to alginate extraction using the citric acid–based method (2 and 4%) as a step toward cascaded biorefinery. Employing a 2% citric acid–based method has shown improved viscosity of 5.41 cP and a higher zeta potential value of − 48.13 mV with a lower Polydispersity Index value of 0.359. Taking into consideration the commercial significance of natural antioxidants and alginate, the method developed can have significant implications in the food and nutraceutical industry. Further, the technology employed, viz., ultrasonication for seaweed extract production and citric acid for alginate extraction, is a greener process pointing toward the promising possibility of designing a greener biorefinery approach for seaweed biomass utilization.