Enzymatic Coating Of Porous Starch And Its Application In Controlled Release Of Curcumin

Porous starch granules(PSGs)are a modified starch with a hollow structure,which can be used as a stable carrier of nutrients and has a wide range of application prospects in the food field.However,because of the microporous structure of PSGs,PSGs has the disadvantages of poor environmental isolation and low mechanical strength,resulting in the inability to achieve stable loading and controlled release of small molecules.Taking PSGs as the object of investigation,this project used the transglycosylation effect of amylosucrase(NpAS)to construct bio-enzymatically modified PSGs(mPSGs)and load curcumin nanoparticles to achieve controlled release of curcumin.The main results were as follows:The catalytic reaction mode of mPSGs by NpAS was studied.After waxy corn starch was hydrolyzed by amyloglucosidase,the surface of PSGs showed pores with 0.5?m-2.0?m,and the pores were connected to the inside of the granules.Under the conditions of PSGs concentration of 2.0%(w/v),sucrose concentration of 0.80 mol/L,enzyme activity of 0.40U/mg PSGs,and temperature of 35°C,the dynamic reaction process of PSGs modified by NpAS was studied.When the reaction time was increased from 8 h to 48 h,the sucrose content in the reaction system decreased from 0.75 mol/L to 0.36 mol/L,while the fructose content increased from 0.04 mol/L to 0.33 mol/L,the content of turanose increased from 4.59mmol/L to 57.18 mmol/L.In addition,when the reaction proceeded to 16 h,a trace amount of maltotriose(1.42?mol/L)appeared in the reaction system.Modified PSGs(mPSGs)were prepared at 8 h,16 h,24 h,36 h,and 48 h reaction time,and their fine structure was characterized by high performance size exclusion chromatography.The results showed that the modification of NpAS significantly extended the branch chain length of mPSGs.The above research results showed that the catalytic reaction mode of PSGs modified by NpAS was mainly branched chain extension modification,and at the same time,sucrose isomerization and linear synthesis side reactions were accompanied in the reaction process.The molecular mechanism of NpAS glycosyl transfer to apparently solidifying mPSGs was studied.The structure characterization results of starch granules showed that the microporous structure of mPSGs was gradually disappeared for the glycosyl transfer function of NpAS,and after 48 hours of NpAS treatment,the mPSGs particles appeared spherical or polygonal,and the surface was smooth and flat.Solid state nuclear magnetic resonance analysis showed that with the increase of reaction time,the double helix content and the total amount of single and double helix of mPSGs gradually increased.Compared with PSGs,the double helix content of 48 h mPSGs increased from 29.30%to 36.02%and the total amount of double helix increased from 34.86%to 39.55%.The analysis of crystal characteristics showed that mPSGs were still A-type after short-term modification treatment(8 h,16 h,24 h),and long-term modification treatment(36 h,48 h)converted mPSGs into A+B type.After 48h of modification treatment,the relative crystallinity(R_C)of mPSGs increased from 37.42%to 41.26%.Compared with PSGs,the gelatinization temperature of mPSGs showed an increasing trend,indicating that the modification of NpAS made the starch chain lengthen,which in turn made mPSGs had better thermal stability.With the increase of reaction time,the ratio of?-1,4-glycosidic bond/?-1,6-glycosidic bond of mPSGs increased significantly,and the surface ratio of starch granules was significantly higher than the internal structure.In vitro digestion showed that with the increase of the modification treatment time,taking 36 h as the breaking point,the content of rapid-digesting starch(RDS)of mPSGs increased first and then decreased,while the content of resistant starch(RS)showed the opposite trend.After48 h of modification,the RDS content of mPSGs decreased from 34.92%to 33.40%,and the RS content increased from 6.73%to 8.99%.The results of digestion kinetics fitting showed that the digestion process of 48 h mPSGs could be divided into two stages with 20 min as the breaking point.The reaction rate constant(k)of the first stage was 5×10^-2 min^-1.The rate constant of the first stage is 2.8 times that of the second stage.The rest of the samples showed a constant hydrolysis rate,with a value of k between 1.5×10^-2 min^-1-2.4×10^-2 min^-1.Short-term modification treatment increased the amorphous structure of mPSGs,and the loosely structured amorphous regions had poor resistance to enzymatic hydrolysis;long-term modification treatment made mPSGs have more compact crystalline structures and stronger resistance to digestive enzymes.Curcumin nanoparticles were encapsulated by mPSGs and the controlled release law of curcumin(Cur)was studied.Under the conditions of rice proteins(RPs)concentration of 1.0%(w/v)and Cur concentration of 0.15%(w/v),Cur-RPs nanoparticles were prepared by the pH cycle method.The nanoparticles size were 160.1 nm and the content of Cur reached 139.4ug/mg RPs.On this basis,PSGs and mPSGs were used to encapsulate Cur-RPs,and the slow-release effect of Cur in the simulated gastrointestinal system was investigated.The results showed that the release process of Cur with PSGs as a carrier was fast,and the retention rate of Cur after 20 min was only 18.72%.However,the Cur release process with mPSGs as a carrier(after 48 h modification treatment)was relatively gentle.After 120 min treatment,the retention rate of Cur was as high as 51.9%.The above results indicated that the glycosyl transfer effect of NpAS could regulate the particle structure of PSGs,and then achieve the targeted delivery of small molecules.