Abstract
Two kinds of single cell oils from thraustochytrids including Schizochytrium limacinum SR21 and Thraustochytrium sp. KK17-3 were hydrolyzed with Candida rugosa lipase to prepare the acylglycerols rich in docosahexaenoic acid (DHA, C22:6n-3). When the lipase at 800 units/g-oil was employed for a 24-h hydrolysis of SR21 oil at 37°C, DHA content in the glycerides fraction reached at up to 67.3%, being much higher than that in the original oil (40.5%), even in the absence of surfactants. In particular, monoacylglycerol contained DHA at 85.6%. After removal of free fatty acids, the glycerides fraction was further hydrolyzed to improve its DHA content to 81.3%. On the contrary, an incapability to concentrate docosapentaenoic acid (DPA, C22:5n-6) in the glycerides suggested that the lipase strictly discriminated in fine structure of respective fatty acids. Although the addition of either Triton X-100 or deoxycholate, but not Tween 20, facilitated the rapid production of monoacylglycerol rich in DHA, its accumulation level was not significantly improved. The lipase was also effective in enriching DHA (63.0%) in glycerides fraction from KK17-3 oil (30.7%). Eicosapentaenoic acid (EPA, C20:5n-3) and arachidonic acid (AA, C20:4n-6) present in this oil were released from glycerides faster than DPA and DHA by the hydrolysis. The resistance to hydrolysis of the predominant ester bonds composed of the polyunsaturates and palmitic acid (C16:0) in the oils from SR21 and KK17-3 was in the following order, DHA>>DPA>EPA>AA>C16:0. The thraustochytrid oils are therefore suitable source for the preparation of DHA-rich glycerides, especially monoglycerides.
