Preparation Of V-type Porous Starch By Ethanolic Extrusion And Enzymolysis Of Maize Starch And Its Applications In Encapsulation Of Fisetin

V-type porous starch（VPS）is a new type of porous starch with V-type single helix cavity structure and excellent adsorption properties.Compared with traditional porous starch,besides its own porous structure with adsorption capacity,the special V-type single helix cavity structure of VPS can also form complexes with the small molecules guest,which has a wider range of application.However,VPS is prepared by enzymatic hydrolysis V-type cold water swelling starch（VCWSS）modified by ethanol-aqueous treatment under elevated pressure and temperature.The harsh reaction conditions and high cost of the ethanol-aqueous treatment under elevated pressure and temperature limit the further industrial application of VPS.To solve this problem,in this study,VPS was prepared from normal maize starch（NMS）in a green and efficient way by ethanolic extrusion together with enzymatic hydrolysis,the physiochemical properties of VPS and the application of VPS in encapsulation of fisetin were further explored.The main research results are as follows:Firstly,the effects of extrusion temperature,ethanol concentration,proportion of starch to ethanol and rotational speed on the V-type relative crystallinity and hydrolytic degree of VCWSS and the oil absorption rate of VPS were studied,the correlation between V-type relative crystallinity of VCWSS and oil absorption rate of VPS was analysed,and the orthogonal test was carried out to optimize the ethanolic extrusion process.The optimum ethanolic extrusion process was as follows:extrusion temperature was 90°C,ethanol concentration was 40%,proportion of starch to ethanol was 1:0.9,and rotational speed was 110r/min.The V-type relative crystallinity of VCWSS prepared under these conditions was 9.75%and the oil absorption rate of VPS obtained by further enzymatic hydrolysis was 261.63%.Next,ethanol concentration,substrate concentration,complex enzyme ratio,complex enzyme content,enzymolysis temperature and enzymolysis time on the hydrolytic degree of VCWSS and oil absorption rate of VPS were explored.On this basis,a response surface test was carried out to determine the optimal hydrolytic conditions:ethanol concentration of 40%,substrate concentration of 20%,complex enzyme ratio of 1:7.79,complex enzyme content of0.30%,enzymolysis temperature of 55°C and enzymolysis time of 6.33 h.Under these conditions,the oil absorption rate of VPS reached 316.04%,which was 2.06 times of normal porous starch（NPS）.Then,the changes in the physicochemical properties of NMS before and after the ethanolic extrusion together with enzymatic hydrolysis were compared and analysed by X-ray diffraction（XRD）,differential scanning calorimetry,fourier transform infrared spectroscopy（FTIR）,scanning electron microscopy（SEM）and rapid viscosity analyzer,using the traditional method of direct enzymolysis and ethanol free extrusion and enzymolysis as controls.Results showed that the crystalline structure of NMS changed from A-type to V-type by ethanolic extrusion,with complete disappeared of gelatinization endothermic peak and significant decreased in short-range order.Compared with pre-gelatinized starch（PGS）obtained by ethanol free extrusion,VCWSS had some pores on the surface,more loose structure,higher V-type relative crystallinity,improved hydration and swelling capacity,easier enzymatic hydrolysis,and significantly improved degree of hydrolysis（from 15.36%to 36.54%）.After the enzymatic hydrolysis of VCWSS,the V-type relative crystallinity increased from 9.75%to 16.20%,indicating that the enzymatic hydrolysis mainly occurred in the amorphous region.Compared with NPS obtained by direct enzymatic hydrolysis of NMS and pre-gelatinized porous starch（PPS）obtained by enzymatic hydrolysis of PGS,VPS had the largest specific surface area（22.46 m²/g）and total pore volume(130.92×10^-3 cm³/g),as well as the highest oil absorption rate（316.04%）.In addition,VPS had good water absorption and water solubility,could quickly swell in cold water to form stable,low-viscosity paste that was less likely to regenerate.Finally,fisetin inclusion complexes were prepared using VPS as a carrier by ultrasound and grinding.According to the results of single-factor experiments,the optimal preparation conditions for the ultrasound method were determined:VPS content was 400 mg,fisetin content was 24 mg,ultrasonic time was 40 min and ethanol concentration was 10%.The load capacity and entrapment efficiency of fisetin inclusion complex under these conditions were 50.15 mg/g and 83.59%,respectively.Under the same conditions of VPS and fisetin addition,the fisetin inclusion complex prepared by grinding for 30 min had load capacity and entrapment efficiency of 54.38 mg/g and 90.63%,respectively.The results of XRD,FTIR and SEM showed that the fisetin in both inclusion complexes was encapsulated in an amorphous form and formed hydrogen bonds with VPS.The in vitro evaluation results showed that the saturated solubility of fisetin in the inclusion complexes was significantly higher in deionized water,artificial gastric juice and artificial intestinal juice than that of unencapsulated fisetin,and the saturated solubility and cumulative release of fisetin in the inclusion complex prepared by the grinding were higher than that of the ultrasound.In addition,the results of 1,1-Diphenyl-2-picrylhydrazyl radical scavenging ability indicated that the antioxidant capacity of fisetin in the inclusion complexes was retained.