Investigating Greener Alginate Extraction Methods for Bioplastic Applications

Alginates extracted from brown seaweed can be used to make bioproducts for a range of applications from single-use packaging to tissue engineering. To scale alginate production for widespread use, a focus on advancing sustainable extraction methods is needed. This study aimed to investigate greener extraction methods and the effect on alginate properties, to advance sustainable methods suitable for bioplastic applications. Three alginate extraction protocols were selected by evaluating the hazard levels of different alginate extraction methods, solvents and reagents. The four protocols were tested using Macrocystis pyrifera and evaluated based on the efficiency of extraction, uronic acid composition (M/G ratio), molecular weight and carbohydrate composition. Finally, the extraction methods were assessed using life cycle perspective, and compared to conventional alkaline extraction.

The three extraction protocols widely affected the resultant alginate properties. Extraction protocols with high pH and temperature and short alkaline extraction times achieved high M/G ratio and beneficial high molecular weight (comparable to commercial alginate), however contributed to greater energy and water consumptions and emissions. Extraction protocols using ambient conditions, and aqueous sodium citrate as a chelate, produced alginates with valuable decreased M/G ratio. The most efficient (high yield) and green protocol was achieved using sodium citrate and acid precipitation, however produced alginates with lower molecular weight. This work demonstrated the possibility to adapt extraction protocols to achieve the desired alginate molecular weight and M/G ratio. Moreover, this study assessed the safety and environmental implications of selected protocols in comparison with the conventional methods.