Modification and comparison of three Gracilaria spp. agarose with methylation for promotion of its gelling properties

In order to improve the gelling properties of agarose, we modified it by methylation. The agarose was prepared from Gracilaria asiatica, G. bailinae, and G. lemaneiformis with alkaline, treated with diatomaceous earth and activated carbon, and anhydrous alcohol precipitation. The methylation reaction process of agarose was performed with dimethyl sulfate while the chemical structure of low-gelling temperature of agarose was also studied by ¹³C-NMR and FT-IR spectra. Results showed that the quality of agarose from G. asiatica is optimal. Its electroendosmosis is 0.116, sulfate content is 0.128%, and its gel strength (1.5%, w/v) is 1024 g cm^-2, like those of the Sigma product (A9539). The gelling temperature, melting temperature, and gel strength of the low-gelling temperature agarose is 28.3, 67.0 °C, and 272.5 g cm^-2, respectively. FT-IR Spectra and ¹³C-NMR spectra also showed that agarose was successfully methylated. Overall, this work suggests that low-gelling temperature agarose may have potential uses as an agar embedding material in various applications such as biomedicine, food, microbiology, and pharmaceutical.