Improving Spirulina protein purification by addressing polysaccharides and alcohol-soluble components interference in ultrafiltration

Although Spirulina protein can be effectively extracted by ultrasonic treatment, the subsequent ultrafiltration for protein purification is always inefficient. Several carbohydrases and/or ethanol were tested to improve the efficiency of ultrafiltration, and the key components that influence the purification were analyzed. The results showed that Viscozyme® L treatment enhanced the Spirulina protein extraction yield from 89 % to 99 %. Treated by Viscozyme® L, protein-polysaccharide complexes with a molecular weight of approximately 175 kDa had reduced leading to a reduction of particle size from 4800nm to 460nm. In comparison, individual carbohydrase had little effect on the crude extracts. In the subsequent ultrafiltration (100kDa MWCO), the Viscozyme® L treated crude extract had a purity of 74 % in the retentate only 10 % higher than that without enzyme. When alcohol-soluble components, including 97 % of chlorophyll, were removed by ethanol, the complex of the protein-polysaccharide complex (156 kDa) in Viscozyme® L treated crude extract was depolymerized to two fractions (protein of 132 kDa and polysaccharide of 99 kDa). This depolymerization facilitated the follow-up ultrafiltration, yielding a Spirulina protein fraction with a purity exceeding 96 %. The high-purified spirulina protein contained more than 45 % essential amino acids, which can be applied to functional foods and nutritional supplements.