The Effect Of Refining Process Conditions On The Quality And Composition Of DHA Algae Oil

The algae oil extracted from Schizochytrium is a functional oil rich in DHA,and its DHA content is more than 40%(LS/T 3243-2015 DHA content?35%).In 2010,this algae oil was approved by the Ministry of Health of China as a new resource food,mainly used in infant formula and health care products.However,compared with crude oil,the content of DHA in the refined algae oil was significantly reduced by 2-5%(P<0.05),which became a bottleneck restricting the development of DHA algae oil companies.So this article focuses on the reasons for the decrease of DHA content in the refining process of DHA algae oil and its control methods:By exploring the effect of algal oil refining process on the quality and composition of DHA algae oil,the appropriate algae oil refining process conditions are determined so that the quality of algae oil meets the standard,and the loss of DHA is reduced as much as possible.At the same time,the loss form of DHA in the refining process was characterized,so as to provide theoretical and data support for the industrial production of DHA algae oil.Firstly,we analyzed the quality and composition of the crude algae oil,and found that the lower peroxide value and anisidine value of the crude algae oil indicate a lower degree of oxidation.However,the acid value,color and flavor(heavy algae smell)of crude algae oil cannot meet the corresponding industry and corporate standards.The content of sterols,phospholipids and VE in crude algae oil is very low.More than 97%of algal oil is triglycerides.The main fatty acids in triglycerides are DHA,palmitic acid and DPA.Among them,the content of DHA is 48.22%,and all fatty acids are randomly distributed in sn-1,2,and 3 positions.Risk factors and pollutants(trans fatty acids,plasticizers,3-chloropropanol and benzopyrene)meet the limit requirements of relevant regulations and standards.The analysis of the composition and physical and chemical indexes of the crude algae oil is helpful for the selection of the subsequent refining process and conditions.Secondly,using crude algae oil as raw material to investigate the effects of alkali refining process conditions on the quality,DHA content and glyceride composition of algae oil.The alkali refining was performed at temperature of 50?-90?,reaction time of 40 min-70 min,and excess alkali addition amount of 0.1%-0.4%.And the obtained alkali refining conditions are:the alkali refining temperature is 70?,the alkali refining time is 50 min,and the excess alkali(exceed the theoretical calculation value)addition amount is 0.1%(w/w).The obtained alkali refining conditions are as follows:the reaction temperature is 70°C,the reaction time is 50 min,and the amount of excess alkali is 0.1%(w/w).Under these conditions,the acid value of algae oil after alkali refining decreased significantly from 0.96 mg/g to 0.16 mg/g(in line with the requirements of DHA algae oil industry standards and enterprise internal control standards),although the degree of oxidation increased slightly but far below the limit of standard.The smell and color of algae oil decreased slightly.In addition,under optimal conditions,the phospholipid content of algae oil decreased significantly from373.50 mg/kg to 86.95 mg/kg,the triglyceride content increased to more than 98%,and the monoglyceride and glyceride content were less than 2%.Under all selected alkali refining conditions,the content of DHA did not change significantly(P>0.05).Since the flavor and color of the alkali-refined algae oil still does not meet the industry and enterprise internal control standards,it still needs to be decolorized and deodorized.Thirdly,using the oil refined through the optimal alkali refining conditions as the raw material,the effects of the decolorization process conditions on the quality,DHA content,and color of the algae oil were investigated.Decolorization is carried out at a temperature of 50-90?,a time of 10-50 min,and an additive amount of activated clay of 1-5%(w/w).The optimal decolorization process conditions optimized through orthogonal experiments are as follows:temperature is 70°C,time is 10 min,and the amount of activated clay is 3%(w/w).Under these conditions,the decolorized algae oil changes from orange-red to yellow,but it still does not meet the internal control standards of the enterprise.The acid value of algae oil after decolorization did not change significantly(P>0.05),and its oxidation degree increased slightly but still far below the standard limit.Both of them met the DHA algae oil industry standard and corporate internal control standards.The smell of algae has decreased,but the smell of activated clay has been introduced.Under all decolorization conditions,the content of DHA did not change significantly(P>0.05).Since the color and flavor of the decolorized algae oil still do not meet the requirements of the industry and the internal control standards of the enterprise,it needs to be deodorized.Finally,using the decolorized algae oil under the optimal decolorization process conditions as the raw material,the effect of the deodorization process conditions on the quality of the algae oil and DHA content was studied.Deodorization is performed at temperature of 150-240°C,time of 40-130 min,and nitrogen flow rate of 0.04-0.12m~3/h.The optimized conditions are as follows:temperature is 190?,reaction time is70 min,nitrogen flow rate is 0.08 m~3/h.Under these conditions,the physical and chemical indexes of refined algae oil meet industry standards and enterprise internal control standards,and the smell of algae is extremely weak and the quality is good.The content of risk factors such as trans fatty acids and pollutants such as benzopyrene are not excessive.However,the DHA content is slightly reduced(the loss is 0.6%).In order to explore the loss form of DHA,we selected deodorized algae oil with 0%,0.6%,and19%loss of DHA as raw materials,and characterized it in various forms:the results of ultraviolet spectroscopy showed that the double bond of DHA was conjugated,and the results of infrared spectroscopy showed that the cis double bond of DHA was transformed,the results of proton nuclear magnetic resonance spectroscopy further prove that the main loss form of DHA is conjugation and transformation.