Enzymatic Synthesis And Antioxidation Of Ferulic Acid Starch Ester In Ionic Liquids

Esterified starch is one of the more widely used modified starches and has important applications in food,medicine,and textile industries.Ferulic acid is a class of plant phenolic acids with a wide range of antioxidant properties.Ferulic acid starch ester has biological functions such as anti-enzymolysis,nitrite removal,and antioxidant.Existing methods for synthesizing ferulic acid starch ester mostly use chemical synthesis methods.In this paper,ferulic acid starch ester was synthesized by ionic liquid[BMIm]Cl and enzyme catalysis,and its structure and properties were studiedFerulic acid starch ester was synthesized by lipase Novozym 435 in ionic liquid[BMIm]Cl by two-step method.Its structure was characterized by FT-IR,SEM and XRD.FT-IR showed that a new peak appeared at 1726 cm^-1,which was an ester based stretching vibration absorption peak.It indicated that ferulic acid group was introduced into the hydroxyl group of starch molecule to synthesize ferulic acid starch ester.SEM images show that the surface of the pretreated starch is rough and uneven,indicating that the starch particle structure may be completely destroyed;there are many dense pores on the surface of ferulic acid starch ester particles,indicating that the esterification process may further destroy the starch structure.XRD results showed that the crystal structure of the original corn starch was type A;the pretreated starch dissolved in the ionic liquid[BMIm]Cl lost its diffraction peak,and the crystal structure was completely destroyed;the ferulic acid starch ester showed only a broad peak.The effects of enzyme dosage,substrate molar ratio,reaction time and reaction temperature on the degree of substitution of ferulic acid starch ester were studied.The optimum reaction conditions were determined as follows:enzyme dosage 0.3 g,substrate molar ratio 1:1,reaction time 7 h,reaction temperature 70?,under which the degree of substitution of starch ferulate was 0.53%.The two-step synthesis of ferulic acid starch ester starch by ionic liquid[BMIm]Cl in the two-step process.Under the same esterification reaction conditions,starch ferulate can be synthesized with a degree of substitution of 0.59%.The results of FT-IR,SEM and XRD were basically the same as those of the two-step method.The extrusion process changed the shape and crystal structure of starch particles,and ferulic acid group was successfully introduced into the hydroxyl group of starch molecules.The effects of extrusion parameters,such as water content,extrusion temperature and screw speed,on the substitution degree of ferulic acid starch ester were discussed.The optimum process conditions were determined:when the water content of the material was 20%,extrusion temperature was 60?,screw speed was200 r/min,the substitution degree of ferulic acid starch ester was 0.59%.The antioxidation of ferulic acid starch ester was determined.The results showed that when the degree of substitution of ferulic acid starch ester was 0.09%,0.28%and 0.53%,the scavenging rate of DPPH free radical was 22.9%,42.7%and54.8%respectively,and the scavenging rate of ABTS free radical was 51.1%,64.3%and 77.8%respectively.The higher the degree of substitution,the higher the clearance.It was proved that starch ferulate had scavenging effect on DPPH and ABTS free radicals,which indicated that starch ferulate had certain antioxidant activity.