Abstract:

After 10 days of cultivation in f/2 medium under appropriate conditions, Isochrysis galbana cells and cultivation supernatant were separated by centrifugation and prepared into powders by freeze drying method for extracting intercellular and extracellular polysaccharides by hot water extraction, respectively. A series of single factor experiments was conducted to examine the effects of technological parameters such as extraction time, pH, extraction temperature and material/liquid on extraction of intercellular and extracellular polysaccharides. Subsequently, the optimal values of the parameters were determined using orthogonal array design. Finally, extracted intercellular and extracellular polysaccharides were analyzed for protein and polysaccharide contents. Single factor analysis showed that extraction time, pH and extraction temperature all had an obvious effect on extraction of intercellular and extracellular polysaccharides. For intercellular polysaccharide extraction, the optimal values of the three parameters were 180 min, 9 and 70 ℃, respectively; in contrast, an optimal extracellular polysaccharide extraction was obtained under the following parameters: pH 10 and 80 ℃ for 300 min extraction. Material/liquid ratio had little effect on extraction of intercellular and extracellular polysaccharides, and an appropriate value of 20:1 (mL/g) was found. Orthogonal array design analysis demonstrated that the optimal values of extraction time, pH and extraction temperature were 180 min, pH 8, 70 ℃ and 15:1 for intercellular polysaccharide extraction and 240 min, pH 9, 70 ℃ and 15:1 for extracellular polysaccharide extraction. The protein and polysaccharide contents in target products obtained under optimized technological parameters were 1.18% and 22.1% for crude intercellular polysaccharide and 0.82% and 18.6% for crude extracellular polysaccharide, respectively. So low protein content and so high polysaccharide content indicate high purity of target polysaccharides resulting from the orthogonal array optimization, which is favorable to further purification.

Key words: Isochrysis galbana, intracellular polysaccharides, extracellular polysaccharides, hot water extraction