Synthesis and characterization of quaternized agar in KOH/urea aqueous solution

Abstract

In this article, agar was successfully dissolved in a KOH/urea mixture via freeze-thawing. Quaternized agar (QA) was synthesized by reacting agar with 2,3-epoxypropyltrimethylammonium chloride (EPTMAC) at 15 °C for 48 h. The successful preparation of quaternized agar was confirmed by different technologies. The water-soluble QA with different degrees of substitution (DS) can be obtained by adding different amounts of EPTMAC. The QA exhibited low gelling and melting temperatures and higher DS resulting in lower melting and gelling temperatures. In addition, the quaternized agar showed antibacterial properties. The QA with a DS of 0.45 can kill about 95% of Escherichia coli and 99% of Staphylococcus aureus. Thus, this work provides a simple, mild and green method to functionalize agar and the quaternized agar may have potential applications in different food and biomedical fields.