Study On The Preparation And Physicochemical Properties Of Kudzu Resistant Starch

Starch is the dominant resource of our country,the main carbohydrate of human diet,and the main energy source of human body.The sources and processes would influence its digestible properties.Starch is generally classified as rapidly digestible starch(RDS),slowly digestible starch(SDS),and resistant starch(RS)based on the rate and extent of in-vitro digestion.RS can’t be digested and absorbed by the small intestine of healthy human body,but it can be fermented and converted to short chain fatty acids in the large intestine.RS have special physiological functions beneficial to human health,so that it plays a very important role in the field of food nutrition.In this paper,the effect of pullulanase debranching-recrystallization,pullulanase debranchingectothermic crystallization,and pullulanase debranching-complex method with linoleic acids on the formation conditions of RS was studied with the kudzu starch as raw material.The structure and properties were also analyzed.This paper can provide a theoretical basis for further development and application of kudzu starch.Kudzu resisitant starch was prepared by pullulanase debranching-recrystallization.On the basis of single factor experiments,the response surface optimization method was used to analyze the optimal conditions of the preparation of Kudzu RS.The results showed that the highest yield of 90.46%was obtained when the enzymatic time was 4 h,the enzymatic temperature 56℃ and the amount of enzyme 57 U/g.After debranched,the content of RS was higher than native starch.The crystal structure of debranched starch changed from A type to a mixture of B+V type.The results of scanning electron microscope showed that the surface of the native starch granule was smooth and varied in size,showing a spherical or irregular polyhedral shape,while the debranched starch granule was irregular in shape and size and the surface was rough and gully.The granule morphology of the modified starch granule was obviously changed.Short chain amylose(SCA)was obtained by pullulanase debranching of gelatinized kudzu starch.SCA recrystallized under isothermal and ectothermic conditions to form kudzu resistant starch.Ectothermic crystallization(dual cycle of 4℃ and-20℃)produced a higher yield of resistant starch.The solubility and swelling degree of native starch and resistant starch samples increased with the increase of temperature.When the temperature was high(80℃),the water holding capacity of the native starch was much higher than that of the resistant starch samples.The transmittance and freeze-thaw stability of resistant starch were better than that of the native starch.The level of resistant starch fraction in samples which were treated under isothermal and ectothermic conditions was higher than that of native starch.The X-ray diffraction patters suggested that crystal structure of starch samples changed from A type to a mixture of B+V type.Attenuated total reflection-Fourier transform infrared(ATR-FTIR)spectroscopy showed that the peripheral regions of native starch were better organized than that of the resistant starch samples.The granule morphology of the resistant starch was obviously changed.It was irregular in shape and size and the surface was rough.The polarized cross of resistant starch also disappeared.Taking kudzu starch and linoleic acid as raw material,the starch was gelatinized and debranched before adding linoleic acid to compound to prepare the complex of kudzu starch and linoleic acids.The effects of different temperature,the amount of linoleic acid and the debranching time on the yields and digestibility were studied.The results showed that the yield of the complex and the content of RS were the highest(32.5%and 31.15%,respectively)at the temperature of 50℃.When the content of linoleic acid was 5%,the yield of the complex was the highest(48.4%),but the content of RS showed no difference.The yield of complex was the highest of 32.5%with RS content of 34.35%when the debranching time was set at 4h.Compared with the native starch,the hydrolysis rate of the complex starch samples was decreased,that is the enhancement of anti digestion.The extension of debranching time had led the crystal structure to change from A type to V type.The granule morphology of the starch-linoleic acid complex samples at different debranching time were irregular fragment and the polarization cross disappeared.