Effect On The Structure And Properties Of Corn Starch By Microwave And Lysine

Slowly digestible starch(SDS)is an ideal form of energy intake,and the SDS content is low in native starch.In this study,corn starch was modified by combining two green starch modification methods,lysine and microwave,to prepare corn starch with high SDS content.The effects of microwave power,microwave time and lysine addition on the structure,physicochemical and digestive properties of the modified starch with microwave and lysine(MC-Lys)were investigated,and the mechanism of the interaction between lysine and corn starch in the microwave field was investigated.The results were as follows.The SDS content of the native starch was 15.09% and 12.96% before and after pasting,respectively.The in vitro digestibility of corn starch was improved by microwave treatment,and the RDS(rapidly digestible starch)content was significantly increased,while the total SDS and RS(resistant starch)content was significantly decreased,where the SDS content was 14.82% and 11.53% before and after pasting,respectively.Peak viscosity,setback viscosity,disintegration viscosity,transparency,coagulability,freeze-thaw stability and gel enthalpy of starch were significantly reduced by microwave treatment.holes appeared on the surface of starch after microwaving,starch granules aggregated,and the particle size of starch increased.The inter-and intra-molecular hydrogen bonds of starch were also damaged by microwave treatment,which impaired the crystal structure of starch and reduced the short-range orderliness and relative crystallinity of starch.The SDS content of lysine-modified corn starch(ungelatinized)reached 18.86%,which was slightly increased compared with the native starch.The particle morphology as well as molecular structure of lysine-modified starch did not change significantly,and the short-range orderliness and relative crystallinity were basically the same as those of the native starch,but the peak viscosity,disintegration viscosity,setback viscosity,coagulability and pasting temperature of the starch decreased after the addition of lysine,and the swelling power,transparency,freeze-thaw stability and particle size were slightly enhanced.The slow digestibility of starch was significantly improved by modification with microwave and lysine.The SDS content of MC-Lys was 30.25% and 20.11% before and after pasting at the microwave power of 720 W,microwave time of 4 min and lysine addition of 3%,respectively.The peak viscosity,disintegration viscosity,setback viscosity,coagulability and pasting temperature of MC-Lys were significantly lower compared with the native starch,and the swelling power,transparency and freeze-thaw stability were significantly improved.The modification of microwave and lysine had significant effects on the granule morphology and molecular structure of corn starch,and some of the lysine was coated on the surface of starch granules or combined with starch molecules after microwave,which increased the granule size of starch.The lysine changed the molecular structure of starch,and the peak intensity of both the infrared characteristic peak and X-ray diffraction peak of MC-Lys were enhanced,and the short-range orderliness and relative crystallinity were increased.