Chemical composition and ethanol production potential of Thai seaweed species

Abstract

This study evaluated the potential use of several Thai seaweed species for ethanol production. The high biomass of the green algae Ulva intestinalis and Rhizoclonium riparium and the red algae Gracilaria salicornia and Gracilaria tenuistipitata in an earthen pond culture led us to select these species for our study. The seaweed species were analyzed for chemical composition, resulting in ash contents of 37.62 ± 0.15 % and fiber of 11.93 ± 0.16 %, with the highest values in R. riparium. Low lipid values were found in all species, with the highest value (p < 0.05) in G. salicornia (1.69 ± 0.07 %) and the lowest in R. riparium (0.28 ± 0.01 %) and G. tenuistipitata (0.26 ± 0.01 %). The highest carbohydrate contents were found in G. tenuistipitata (54.89 %), and the lowest were in R. riparium (29.53 %). G. tenuistipitata (8.58 ± 0.36 %) and U. intestinalis (8.24 ± 0.28 %) had higher sulfate contents compared with G. salicornia (4.69 ± 0.04 %) and R. riparium (1.97 ± 0.20 %). The monosugar algal tissue components were analyzed by HPLC; rhamnose, xylose, fucose, arabinose, mannose, glucose, and galactose were used as reference sugars. Total sugar was found to be highest in G. tenuistipitata (98.21 %). Arabinose, glucose, and galactose were the main sugar components in all species. Glucose obtained from G. tenuistipitata (6.55 %) and R. riparium (6.52 %) was higher than in G. salicornia (0.27 %) and U. intestinalis (2.78 %). G. tenuistipitata fermentation gave a higher yield of ethanol (4.17 × 10⁻³ g ethanol g⁻¹ sugars; 139.12 μg ethanol g⁻¹ glucose) than R. riparium (0.086 × 10⁻³ g ethanol g⁻¹ sugars; 33.84 μg ethanol g⁻¹ glucose), U. intestinalis (0.074 × 10⁻³ g ethanol g⁻¹ sugars; 9.98 μg ethanol g⁻¹ glucose), and G. salicornia (0.031 × 10⁻³ g ethanol g⁻¹ sugars; 1.43 μg ethanol g⁻¹ glucose).