摘要
The red seaweed Melanothamnus somalensis was investigated as potential economic source of agar. The effect of different conditions of alkali pre-treatment on chemical properties of agar was evaluated. Agar was extracted by various concentrations of NaOH （4%, 6% and 8%） and heated at different temperatures （70 ℃, 75 ℃ and 80 ℃） for different durations （2 h, 2.75 h and 3.5 h）. The yields-molecular weight （Mw） and sulfate contents of extracted agar were analysed and characterized by FTIR spectroscopy. The yield was significantly increased at these treatments from 23.29% to 30.86%. Mw studied by HPLC ranged from （.12.45 ± 0.21） × 10^5 to （8.60 ± 2.40） × 10^5 Da. FTIR bands show sulfate groups in C4 and C6 ofgalactose and no sulfate group were found on both C2 of galactose and C2 of 3,6-anhydrogalactose. All treatments showed a high sulfate content that ranged from 5.4% to 10.1%. These properties were found to be significantly affected by the alkali pre-treatment concentration （p 〈 0.05）. In conclusion, agar extracted in this study was considered acceptable for industrial application and the optimal conditions for extraction were found to be at 6% NaOH at 70 ℃ for 2 hours.
