Ulvan from green seaweed Ulva lactuca: Optimization of ultrasound-assisted extraction, structure, and cytotoxic activity

An ulvan was extracted from green seaweed Ulva lactuca by ultrasound-assisted extraction. The extraction conditions were optimized by response surface methodology. The optimal conditions were extraction temperature at 84.75 degrees C, extraction time of 30.51 min, solvent to material ratio of 60.51 mL/g to achieve the yield of 22.5%. The ulvan is composed of repeated sequences of three disaccharides: -> 4)-beta-D-Glucuronic acid(1 -> 4)alpha-L-Rhamnose-3-sulfate(1 ->, -> 4)alpha-L-Iduronic acid(1 -> 4)alpha-L-Rhamnose-3-sulfate(1 ->, and -> 4)alpha-D-Xylose-2-sulfate(1 -> 4)alpha-L-Rhamnose-3-sulfate(->. The ulvan showed cytotoxic activities against five human cancer cell lines, including human hepatocellular carcinoma, human breast cancer, human cervical cancer, human colorectal adenocarcinoma and human undifferentiated thyroid carcinomas.