Optimization Of Microalgal DHA Refining Technologies

Docosahexaenoic acid(DHA)is a kind of human body required omega-3 poly-unsaturated fatty acid(PUFA),and it can promote brain development in infants and children,protect eyesight and improve the human immunity,and other important physiological functions.With improvement of DHA algal oil quality standards in domestic and international market,the conventional algal oil refining process cannot obtained quality microalgal DHA production because of organic solvent residue,excessive heavy metals,the change of colour,melting point and flavor due to easily oxidation characteristics of DHA.In this study,the dry fractionation and applications of antioxidants in the algal oil were optimized in order to achieve high quality DHA product during the DHA algal oil refining process.First,dewaxing and dry fractionation process were applied to improve the purification of DHA algal oil.The optimal dewaxing process conditions were obtained as follows:The heating temperature was 65 ?,the crystallization temperature was 25?,and crystallization time was 12 h.Under these optimal conditions,the dewaxing rate up to 99.27%was achieved,and the wax content in DHA algal oil was only 0.7 mg/kg.Subsequentially,the optimal conditions for dry fractionation were determined as follows:equilibrium temperature was 60 ?,cooling rate for low temperature oil was 0.2 ?/h,seed load was 4%,cooling rate for winterization oil was 0.1 ?/h,and crystallization time was 15 h for winterization oil.Under the optimal conditions of the dry point method,the yield of normal oil was 73.24%,the melting ponit of normal oil was 16 ?,and the DHA oil content increased to 49.43%.The yield,the melting point,and DHA content of winterization oil were 64.92%,-4 ? and 54.98%,respectively.Second,the decolorization and deodorization process of DHA microalgal oil were optimized.Activated clay,decolorization sand and three kinds of active carbons were used in decolorization process,respectively.The effects of decoloring temperature,decoloring time and amount of decoloring agent addition on decolorization were investigated.The optimization decoloring conditions were obtained as the temperature of 50 ? time of 30 min,and addition of 3%of decoloring agent.In the deodorization process,the effects of deodorization temperature,time,and steam amount on peroxide and anisidine value,DHA content and flavor of algal oil were also investigated,The optimization deodorization conditions were deodorization temperature of 190?,time of 3 h,steam amount of 4 kg.Finally,the effects of citric acid,sodium ascorbate and natural vitamin E as antioxidant on stability of DHA algal oil were investigated by the single factor experiment and the central composite design.The optimal antixoidants combination was obtained by equation modeling and as follows:citric acid 0.09%,sodium ascorbate 0.04%,and natural vitamin E 0.10%.The theoretical and experimental POV values of DHA algal oil were 0.29 and 0.28 meq/kg,respectively.The results indicated that the antioxidant combination has good antioxidant effect for DHA algal oil.