Spatial and seasonal effects on physicochemical properties of native agar from Gracilaria parvispora (Rhodophyta) in the Tropical Mexican Pacific (Oaxaca-Chiapas)

Background: Gracilaria parvispora is an invasive red seaweed located in coastal lagoons along the Tropical Mexican Pacific. Gracilaria species are the main source of agar around the world. Goals: Spatial and seasonal trends of the properties of native agar from the invasive seaweed G. parvispora were determined in three localities in the states of Oaxaca and Chiapas belonging to coastal lagoons along the Tropical Mexican Pacific: Ballenato, Paredon, and San Vicente. Methods: Native agar was obtained from dry samples of seaweed and the agar yield, gel strength, melting and gelling temperatures, hysteresis, and sulfate and 3,6-anhydrogalactose content were determined for each sample. Moreover, the polysaccharide structures and the location of sulfate groups in agar samples were identified. Results: The phycocolloid is a polysaccharide agar type. The agar yield was significantly different between seasons and localities, with the highest values during the dry season (19.9 ± 0.004 %) at Paredon (20.6 ± 0.01 %). Gel strength, melting temperature and gel hysteresis showed significant spatial differences; the highest values were obtained in Ballenato (367.3 ± 14.2 g cm-2, 80.2 ± 1.4 °C, 44.3 ± 2.2 °C, respectively); gelling temperature did not show significant differences between localities or seasons. Chemical properties were significantly different between seasons: 3,6-anhydrogalactose content was higher during the dry season (36.2 ± 0.2 %), and sulfate content was higher during the rainy season (12.69 ± 0.21 %). Salinity was significantly different between seasons, and the highest was obtained during the dry season (38.7 ± 0.1). Surface water temperature varied between localities, and the highest mean value was recorded at Paredon (32.5 ± 0.2 °C). Conclusions: The chemical properties of the G. parvispora native agar were lower than the standards for food and industrial use.