Effect of pH Shift in the Stationary Phase of Growth on the Incorporation of Exogenous Docosahexaenoic Acid into Euglena gracilis

Abstract

The effects of pH shift in the stationary phase of growth on the incorporation of exogenous docosahexaenoic acid (DHA) into Euglena cells and lipid classes were examined. At pH 6.57.5 the incorporation of DHA was maximum, and content of DHA in the cells at pH 6.5 (35.7 % in the dry cells) was 2.5 times as much as that at pH 2.5. The percentage of DHA in total fatty acid in the cells was 70% at pH 4.57.5, but decreased at pH 2.53.5 and 8.5.The abundant component of total lipids in Euglena cells, incorporated exogenous DHA, was triacylglycerols (TG). But TG in the cells decreased and free fatty acids increased at pH 8.5.DHA in the cells was mainly incorporated into TG. DHA was partially incorporated into polar lipids and the acyl moiety of wax esters. Only a small amount of docosahexaenoyl alcohol could be detected in the alkoxy moiety of wax esters.It thus follows that, with sufficient shift of pH in the stationary phase, Euglena cells progressively incorporate DHA, to promote the production of more useful fishery feed from Euglena.