Extraction, purification and antioxidant activity of Chlorella polysaccharide

The antioxidant activity of Chlorella polysaccharide has broad application prospect in healthcare. Ultrasound, hot water , microwave, freeze-thaw, alkali and enzyme assisted extraction methods can achieve high extraction efficiency of polysaccharide by optimizing extraction conditions. However, these methods may have risks of polysaccharide degradation, changes in polysaccharide structure and biological activity due to too long time (such as 6 h) or too high temperature (such as 170 °C). Therefore, mild, green and efficient extraction conditions need to be further studied during optimization process. This study extracted polysaccharide from Chlorella using four traditional methods (alkali, ultrasound, repeated freeze-thaw and hot water) and their combination, and optimized extraction process for the method with the highest polysaccharide extraction rate (alkali/hot water) using response surface methodology (Central Composite Design, CCD). We compared protein removal efficiency of Sevage reagent, trichloroacetic acid (TCA) and salting out for polysaccharide extracted by alkali-hot water method (AHP). Three components including neutral polysaccharide (AHP-1) and acidic polysaccharide (AHP-2 and AHP-3), were isolated and purified by DEAE-52 cellulose column chromatography , and their antioxidant activities were investigated. The results showed that Sevage reagent had the best protein removal efficiency (94.6 %, w /w) for AHP. In addition, three polysaccharide components exhibited different DPPH and ABTS free radical scavenging activities and iron reducing abilities (AHP-2 > AHP-3 > AHP-1). AHP-2 has great potential for the development of natural antioxidants and may serve as a component of functional foods. In summary, this study obtained high extraction rate and purity of Chlorella polysaccharide AHP through extraction and purification , and AHP exhibited high antioxidant activities. The results indicate that AHP has great potential for the development of natural antioxidants , laying the foundation for its application in food, medicine and beauty industries. • Alkali/hot water extraction had the highest polysaccharide yield (AHP, 10.09 %). • After response surface optimization, AHP yield was 12.11 %. • Sevage reagent removed 94.6 % protein and retained 61.12 % polysaccharide. • After purification by DEAE-52 column, for polysaccharide yield AHP-1 > AHP-2 > AHP-3. • For antioxidant activities: AHP-2 > AHP-3 > AHP-1, AHP-2 has potential as antioxidants.