Preparation And Characterization Of Monoglycerides Based On Mixed Fatty Acids As A By-product Of Rice Oil Refining

In this paper,rice oil refined by-products(mixed fatty acids)are used as the main raw material,and high-purity monoglycerides are prepared by boric acid protection method,acetone protection method and enzyme method which realize the high-value utilization of refining by-products.The main findings are as follows:(1)Process optimization and product structure characterization for synthesis of monoglycerides by boric acid protectionThe best process conditions for synthesizing monoglycerides by boric acid method are:n(boric acid diglyceride):n(mixed fatty acids)=4:1,esterification temperature220?,esterification time 3.5 h,catalyst addition amount 2.5%.Under these conditions,the yield of monoglycerides can reach 66.5%.GC analysis shows that mixed fatty acids are mainly composed of five fatty acids such as oleic acid and linoleic acid.The product was identified as monoglyceride by FTIR and HPLC.(2)Process optimization and product structure characterization for the synthesis of monoglycerides by acetone protectionThe best process conditions for synthesizing monoglycerides by acetone method are:group protection temperature 79?,esterification temperature 142?,n(glycerin):n(acetone):n(mixed fatty acids)=1:2:0.8,group protection time3 h,the esterification time 3 h.Under these conditions,the yield of monoglycerides can reach 79.5%.The product was identified as monoglyceride by FTIR,TOF-MS and ~1HNMR.(3)Enzymatic synthesis of monoglycerides and product structure characterization in the optimization of tert-butanol systemThe optimal process conditions for enzymatic synthesis of monoglycerides are:Lipozyme435 addition amount 8.5%,mass ratio of glycerol and tert-butanol=1:1.5,esterification temperature 54°C,n(glycerin):n(mixed fatty acids)=3.2:1.Under these conditions,the yield of monoglycerides can reach72.89%.The enzyme was repeatedly used 6 times in the experiment.After the sixth enzyme catalysis,the monoglyceride yield was still 50.5%,indicating that the enzyme has good repeatability.The product was identified as monoglyceride by FTIR,TOF-MS and ~1HNMR.(4)Research on the basic physical and chemical properties,HLB value and oxidation stability of monoglyceridesThe physical and chemical properties of triglycerides are determined with reference to relevant food standards.At the same time,the HLB value of monoglycerides was determined by turbidimetric method,and the storage stability of monoglycerides was studied by oven oxidation method.The research results show that the acid values of the products synthesized by the three methods are 3.4,2.6 and 2.5 mg/g,the peroxide values are 1.6,1.1 and 1.3 mmol/Kg,the saponification values are 168,165 and 171mg/g,and the iodine values are 77,74 and 75 mg/g.All physical and chemical indicators are in line with national safety food quality standards.The HLB values of monoglycerides measured by turbidimetric method were 3.7,4.3 and 5.2,respectively.Antioxidants L-ascorbyl palmitate,VE and citric acid can effectively inhibit the oxidation of monoglyceride products.The formula of the compound antioxidant obtained by orthogonal test is L-ascorbyl palmitate 200mg/Kg,VE 200mg/Kg,citric acid 175mg/Kg.Under this condition,the acid value and peroxide value of monoglyceride is 1.09mg/g and 1.68 mmol/Kg.After comparing with the blank group,it proved that the antioxidant effect is goodproving good antioxidant effect.