Abstract: One-factor-at-a-time method and orthogonal array design were employed to optimize four process conditions for microwave-assisted extraction of polysaccharides from Isochrysis galbana such as pH, microwave power, temperature and extraction time. One-factor-at-a-time experiments showed that each of the four conditions had a marked effect on polysaccharide extraction, and their optimal levels were identified by orthogonal array design to be: pH 9, microwave power of 600 W, extraction temperature of 90 ℃ and extraction time of 20 min. Under these conditions, the extraction rate of crude polysaccharides was 96.8 mg/g compared with 47.7 mg/g for hot water extraction, and the contents of protein and polysaccharides were respectively 1.08% and 43.6% in the crude polysaccharide sample obtained compared with 1.18% and 22.1% for hot water extraction. The crude polysaccharides obtained by both extraction methods revealed similar IR spectra, demonstrating that microwave did not destroy the chemical structures of polysaccharides. In summary, microwave-assisted extraction is greatly superior to hot water extraction.

Key words: Isochrysis galbana, polysaccharide, microwave-assisted extraction, hot water immersion extraction, IR spectrum