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

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 oC for 48 h. The successful preparation of quaternized agar was confirmed by different technologies. The water-soluble QA with different degree of substitution (DS) can be obtained by adding different amount of EPTMAC. The QA exhibited low gelling and melting temperature and higher DS resulted in lower melting and gelling temperature. 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.