Mechanoenzymatic Depolymerization of Alginate Yields Oligosaccharide Profiles Different from Standard Aqueous Conditions

Abstract Alginate oligosaccharides (AOS) are widely used in the pharmaceutical, food, and agricultural industries. AOS are typically generated by the partial depolymerization of alginate through chemical acid hydrolysis or enzymatic alginate lyase catalysis. These methods require large volumes of water, which results in significant wastewater production and in the case of acid hydrolysis, generates hazardous waste. Enzymes are biodegradable, renewable, nontoxic and proceed under mild conditions, properties that make them attractive catalysts. Mechanoenzymology, which involves the use of enzymes in low-water mixtures with intermittent mechanical mixing (e.g., by ball milling), is an emerging technique reported to offer several advantages over the standard dilute aqueous conditions typically used with enzymes. Not only does it often provide higher reaction yields, but it also generates minimal wastewater, avoids solubility issues, proceeds in much smaller volumes, and enables the direct transformation of highly crystalline polymeric substrates without pretreatment. Herein, mechanoenzymology was applied to the depolymerization of alginate by alginate lyase with only 1.5 μL of water per mg of alginate, corresponding to a solids loading of 40% w/w. Reaction kinetic profiles were similar in moist-solid and in traditional dilute aqueous mixtures. Remarkably, the mechanoenzymatically generated AOS products exhibited both lower molecular weights and a narrower polydispersity. This study showcases mechanoenzymology as a more sustainable approach for producing AOS of complementary properties to those produced by traditional routes.