Optimization of yield and quality of agar polysaccharide isolated from the marine red macroalga Pyropia yezoensis

The marine red seaweed Pyropia yezoensis is grown on a large scale in Japan using mariculture for production of nori sheets. Here, we optimized the isolation of agar from P. yezoensis and evaluated its yield, physical properties, and product applications. An alkali pre-treatment of seaweeds before agar extraction increased the weight-average molecular weight of the agar and promoted the conversion of L-galactose sulfate to 3,6-anhydrogalactose, which in turn reduced the sulfate contents, thus altering the gel strength of the agar. This ability to adjust agar quality by altering the alkali concentration during material pre-treatment allowed production of agar with properties similar to those of agar from the red seaweed Gelidium sp., which is widely used for industrial agar applications. We demonstrate the suitability of P. yezoensis agar in production of solid plates for bacterial growth. In addition, the P. yezoensis agar was particularly useful as a gel material, with the capacity for excellent size separation of DNA by electrophoresis even without agarose purification, because of quite low contents of sulfate. These findings support the applicability and usefulness of P. yezoensis for agar production. The established large-scale cultivation methods for P. yezoensis can generate sufficient biomass to produce agar to support medical and biological studies