Ultrasonic-freeze-thaw-cycle assisted extraction was used to synchronously extract polysaccharide and phycobiliprotein from Gracilaria lemaneiformis. Firstly, different solvents (deionized water, sodium hydroxide, phosphate buffer solution (PBS) and calcium chloride solution) were screened, and PBS (1 mM, pH 6.8) was considered as the best solvent for its OD565 value (0.086±0.0003) and OD595 value (0.471±0.002), which was significantly higher than any other solvents (p<0.05). Moreover, an L9 (3)4 orthogonal test was carried out to optimize extraction conditions, based on the single-factor test. The results indicated that the optimized conditions were fixed as follows: the ratio of solid to liquid 1:25 (w/v), 2 times of freeze-thaw cycles, ultrasound power 320 W and ultrasound time 10 min, which obtained the optimum yield and purity of polysaccharide and phycobiliprotein, 30.54%, 1.36% and 0.296, respectively. As a result, ultrasonic-freeze-thaw-cycle assisted extraction is considered to be an effective, economic and eco-environmental method to extract polysaccharide and phycobiliprotein.

In the present study, the crude polysaccharides were extracted from the microalgae Gracilaria lemaneiformis with ultrasonic-assisted extraction method and purified by DEAE-52 cellulose chromatography and Sephadex G-100 size-exclusion chromatography in that order. Two main fractions, GPC-1and GPC-2, were obtained through the extraction and purification steps. Then partial characterizations, such as chemical composition, ultraviolet (UV) spectrum and infrared (IR) spectrum of the two fractions were analyzed in this study. The results indicated that the total sugar contents of GPC-1and GPC-2 were 89.32% and 88.79%, and the protein contents of these two fractions were only 0.35% and 0.76%, compared with that of crude polysaccharides of 75.49% and 1.92%, respectively. Moreover, both the UV spectrum and the IR spectrum demonstrated that the two fractions were typical purified polysaccharides. As a consequence, these investigated characterizations could be considered as a favorable evidence for the identification of polysaccharides from Gracilaria lemaneiformis.