Yield optimization, physicochemical characterizations, and antioxidant properties of food grade agar from Gracilaria tenuistipitata of Cox's Bazar coast, Bangladesh

The present study was aimed at investigating the optimization of extraction variables for food grade quality agar from Gracilaria tenuistipitata, so far, the first study on Bangladeshi seaweed. Water (native)- and NaOH (alkali)-pretreated agars were comparatively analyzed by several physicochemical parameters. All extraction variables significantly affected the agar yield in both extraction conditions. Alkali-pretreated agar provided a better yield (12-13% w/w) and gel strength (201 g/cm(2)) in extraction conditions as followed by 2% NaOH pretreatment at 30 degrees C for 3 h, seaweed to water ratio at 1:150, and extraction temperature at 100 degrees C for 2 h. Gelling and melting temperatures, color, and pH values of both agars were found to be comparable with commercial agar. Significantly higher sulfate contents including organic and inorganic and total carotenoids were reported in native (3.14% and 1.29 mu g/mL) than that in alkali-pretreated agar (1.27% and 0.62 mu g/mL). FTIR spectrum demonstrated the purity of the agar as characterized by the stronger relative intensity with higher degree of conversion of L-galactose 6-sulfate to 3,6-anhydrogalactose in alkali pretreatment group than that of native ones. Moreover, antioxidant activity (% DPPH scavenging) was observed and confirmed by IC50 values of 5.42 and 9.02 mg/mL in water- and alkali-pretreated agars, respectively. The results suggested that agar from G. tenuistipitata with optimized alkali extraction conditions could promote cost-effective yield with improved physicochemical characteristics and biofunctional values upon consumption by the consumers as food materials.

Automated summary

The present study aimed to optimize the extraction variables for obtaining food grade quality agar from Gracilaria tenuistipitata, which is the first study on Bangladeshi seaweed. Water- and NaOH-pretreated agars were compared based on several physicochemical parameters. The extraction variables significantly influenced the agar yield in both conditions. NaOH-pretreated agar showed better yield and gel strength compared to water-pretreated agar. Parameters such as NaOH concentration, temperature, and extraction time were optimized to obtain the highest agar yield. The obtained agar had comparable characteristics with commercial agar and showed antioxidant activity.