Green Enzymatic Preparation,in Vitro Digestion And Oxidative Stability Evaluation Of Docosahexaenoic Acid-enriched Fish Oil Microcapsules

Docosahexaenoic acid(DHA)is the major long-chain polyunsaturated fatty acid in marine animals.It contains many healthful properties such as reducing inflammation and decreasing risk of cardiovascular disease.Due to slow metabolism of DHA in human body,it is necessary to obtain DHA from marine-based food such as tuna oil.DHA content in natural fish oil is rather low(<25%).Therefore,it is of scientific interest to develop a green enzymatic method for enriching DHA content in fish oil.In addition,DHA also suffers from poor digestion and absorption efficiency,and prone to oxidation.Present study developed a green enzymatic method to enrich DHA content in tuna oil,prepared high DHA fish oil microcapsules and evaluated the in-vitro digestibility and oxidative stability of the high DHA fish oil microcapsules.Firstly,molecular simulation software(Discovery Studio)was used to predict the binding affinity of lipase to different fatty acids.The predicted lipase selectivity was verified experimentally.Results show Candida rugosa lipase(CRL)preferentially hydrolyzes saturated(25.21% to 16.88%)and monounsaturated fatty acids(45.25% to 32.17%)in fish oil,while it has catalytic restrictions on DHA,Meanwhile,DHA content in the fish oil were enriched from 17.34% to 39.15%.Secondly,lipase hydrolysis conditions were optimized to obtain high-DHA fish oil.Melting and crystallization properties,oxidative stability and volatile substances of the high DHA fish oil were also evaluated.Results showed that the optimal process conditions were: water-oil ratio of 1: 6,hydrolysis temperature of 45 ° C,and hydrolysis time of 4h.Under these conditions,the DHA content increased from 22.84% to 43.63%.In comparison to tuna fish oil,high DHA fish oil did not have significant changes in terms of melting and crystallization behavior.Nevertheless,the oxidation stability of high DHA fish oil has decreased.In addition,the fishy smell of fish oil was significantly reduced due to decreased in 2,4-heptadienal content.Thirdly,high DHA fish oil microcapsules were prepared using sunflower phospholipids(SPL),protein(Whey protein concentrate,Sodium caseinate and Soy protein isolated)and maltodextrin.The in-vitro digestibility of the high DHA fish oil microcapsules was evaluated.Results showed SPL can expose the whey protein hydrophobic site,change the secondary structure of whey protein,and reduce the viscosity and surface tension of the emulsion,which is beneficial to enhance the stability of the emulsion.In-vitro digestion of the spray dried DHA microcapsules showed SPL-WPC DHA microcapsules were able to effectively resist gastric proteolysis and protect its bioactivity enroute to intestine.The lipid digestibility(77.58%)and DHA hydrolysis rate(74.3%)of SPL-WPC DHA microcapsules are also significantly higher than commercial DHA microcapsulesFinally,the effects of spray drying methods(electrostatic spray drying technology and conventional high temperature spray drying)on DHA microcapsules quality(encapsulation efficiency,water content,dissolution properties and lipid oxidation)were evaluated.Results showed that there is no significant difference in terms lipid encapsulation efficiency and water content between the two spray-drying methods.High DHA fish oil microcapsules prepared by electrostatic spraying are significantly better than conventional high temperature spray-drying in terms of dissolution properties and lipid oxidation.High DHA fish oil microcapsules with SPL-sodium caseinate(SC)-maltodextrin membrane structure demonstrated best lipid oxidation stability.