Changes in protein composition and agar quality in irradiated Gracilaria asiatica (Rhodophyta)

The mainland of Vietnam a coastline of approximately 3260 km, there are also many islands. The Vietnam Sea is located in the northwest part of the South China Sea and the climate varies from subtropical in the northern part to tropical in the southern part of the country. In Vietnam, there are about 15 species of Gracilaria, most of them occur in the intertidal zone (rocky, sandy, muddy bottom) and have a distinct growing season (from November to May). Gracilaria asiatica is main seaweed for the manufacturing of agar in Vietnam. The total quantity of agar produced (powder and strips form) is estimated to be 80-100 tons/year, which mostly supplied the domestic requirement. Gracilaria asiatica is cultivated on a large scale in Northern Vietnam where it is influenced by the subtropical climate. Therefore, especially from May to October in the rainy season, the growth of G. asiatica is drastically reduced or even ceases due to very low salinity and high temperature. It is very important to improve the characteristic of Gracilaria for it to adapt to wide changes of salinity and temperature. In this paper, the authors presented results in researching variety of survival ratio, protein components, content and quality of agar of Gracilaria asiatica (which were selected at Quy Kim station at Hai Phong City, Vietnam) after irradiation. Gracilaria asiatica was irradiated with different dosages (0-control formula, 20, 60 and 100 krade-experimental formula) and then were grown on selected media (ESS-1 with 0% o and 23% o NaCl). The obtained results in this paper showed that G. asiatica radiated with 20 and 60 krade has a high survival ratio and protein content in both selected media, especially in 60 krade, than those using another dosage of radiation. Based on the obtained results, strains were selected which can adapt to wide changes of salinity and temperature. After irradiating, G. asiatica only had a higher survival ratio and protein content but also had a content and better quality of agar compared with the control both selected media, especially with the dosage of 60 krade. These were no remarkable differences in protein components (on polyacrylamide 9.5%) among experimental and control samples. But it was found that a 67 kDa protein band appeared clearly compared with the control samples grown on ESS-1 23% o NaCl. Comparison with protein components of the control samples grown on ESS-1 0% o NaCl, leads to the conclusion that the 67kDa protein band plays an important role in G. asiatica adaptation to wide changes of salinity and temperature conditions. For further understanding the role of the 67 kDa protein band, more detailed experiments using another methods, such as two-dimensional SDS-PAGE, Western blot analysis are needed. Gracilaria asiatica in the formula of control and experimental treatment are also similar in organic and inorganic contents. But content and quality of agar of G. asiatica in formula of experiment is quite better than in formula of control. The presence of a high content of 3,6 on hydro-alpha-L-galactose combined with a low content of sulfate caused G. asiatic in formula of the experiment having condensation, and quality of the agar better than that in control (showing that the freezing-point and melting-point of G. asiatica in formula of experiments are lower than those of the control). Fluids agar extraction from radiated G. asiatica, which was selected by selected medium ESS-1, contained the concentration of NaCl at 0% o and 23% o, which showed remarkable decrease in the content of Ca2, Mg2 and total Fe compared with G. asiatica in the formula of the control, and resulted in the increasing melt-capacity of agar extracted from G. asiatica in formula of experiment.