Study On The Functional Properties Of Starch Regulated By Pulsed Electric Field Assisted Esterification

Starch plays an important role in human life,it is the main source of human energy and one of the important industrial raw materials.However,due to some undesirable characteristics of natural starch,such as high pasting temperature,poor emulsification,easy retrogradation,and high glycemic index,the application of its original form in the food industry is subject to many restrictions.The functional properties of starch can be improved by physical,chemical or enzymatic modification to improve the processing performance of starch.Octenyl succinic anhydride modified starches(OSA starch)is obtained by introducing OSA groups to the starch molecular chain.It exhibits excellent pasting,emulsification,water retention and anti-digestion properties,thus receiving wide attention from the starch further processing industry.At present,in practical applications,the traditional aqueous phase method is usually used to produce octenyl succinate starch esters.However,the semi-rigid structure of starch is difficult to be destroyed,which limits the attack of chemical/enzyme reagents on starch molecular chains.Therefore,traditional aqueous phase method has the limitations of high reagent consumption and high energy consumption.This made an urgent requirement of development of rapid,efficient and economical modification techniques.The pulsed electric fields(PEF)treatment can destroy starch structure and promote the chemical reaction time.At present,the effect of PEF-assisted esterification on starch functional properties has rarely been reported,and its mechanism is still unclear.Based on this,this study took green and renewable starch as the research object,constructed a processing technology based on PEF physical field to enhance the efficient modification of starch.We systematically controlled the structure and functional characteristics of starch,analyzed the relationship between the morphology and multi-layer structure of modified starches and their functional properties,so as to elucidate the mechanism of PEF co-esterification in regulating the functional properties of starches.The main research contents and results are as follows.(1)In this chapter,PEF assisted esterification was used to regulate the pasting properties of potato starch.The results showed that PEF assisted esterification significantly improved the pasting properties of starch.Compared with native starch,the gelatinization temperature of PEF assisted esterified OSA starch decreased by 14.6-15.1~oC at 5-6 k V/cm,while that of non PEF treated OSA modified starch only decreased by 3~oC.PEF assisted esterification greatly shortened the esterification reaction time from several hours to 50 min.SEM,XRD and FTIR results showed that the high-intensity PEF assisted esterification seriously destroyed the starch dense shell barrier and the long/short range ordered structure.In addition,DS value showed that PEF promoted the grafting of more OSA groups onto starch molecules,and weakened the binding force between starch molecular chains.The above structural characterization shows that the starch structure assisted by high strength is conducive to water molecules entering the starch granules,thus accelerating the water absorption expansion of starch granules and reducing the gelatinization temperature.(2)In this chapter,PEF assisted esterification was used to regulate the emulsification properties of waxy corn starch.The results showed that the OSA starch granules prepared with PEF had excellent emulsifying ability.The stable gel-like Pickering emulsion with a moderate oil volume fraction(φ(oil)=50%)was successfully obtained using an OSA-modified waxy maize starch at a relative low starch concentration of 6%and treated with PEF at an intensity of 4.5 k V/cm.XPS analysis showed that high strength PEF assisted esterification produced more esterification sites on the surface of starch granules,which increased the number of graft groups on the surface of starch granules.Contact angle data analysis showed that PEF assisted esterification significantly improved the surface hydrophobicity of starch granules.The above structural characterization shows that the starch structure of high-strength PEF assisted esterification can effectively promote the accumulation of particles at the oil-water interface,and form a spatial barrier to prevent oil droplets from coalescence,thus promoting the formation of Pickering gel emulsion.(3)In this chapter,the influence of pulsed electric field(PEF)combined with octenyl succinic anhydride(OSA)on the freeze-thaw stability of corn starch gel was investigated.Dual-modified starch exhibited excellent freeze-thaw stability.The reduction in syneresis was 29.5%lower for OSA starch treated with synergetic modification for 15 min while 10.17%lower for the non-PEF control compared to that of native starch after five freeze-thaw cycles.HPAEC-PAD analysis showed that short-time PEF assisted esterification preferentially cracked the long B2 chains and long B3 chains in the inner amorphous region of amylopectin.XRD and DSC analysis showed that the starch structure under PEF assisted esterification for a short period of time in the freeze-thaw cycle prevented the formation of double helix conformation of starch long chains and inhibited starch retrogradation.In addition,PEF assisted esterification promoted the grafting of OSA groups onto starch molecular chains.During the freeze-thaw cycle,the applied steric hindrance effect inhibited the hydrogen bond force between starch molecular chains and the starch sedimentation.The above structural characterization shows that the starch structure assisted by PEF in a short period of time is conducive to reducing the water separation rate of starch gel,thereby improving the freeze-thaw stability of starch.(4)In this chapter,the effect of PEF assisted esterification on the digestibility of cassava starch was studied.The results showed that the content of rapid digestible starch(RDS)decreased and the content of resistant starch(RS)increased after PEF assisted esterification.Compared with native starch,the RS content of OSA starch assisted with esterification at 3k V/cm was significantly increased by 17.13%,but that of OSA starch without PEF assisted treatment was only increased by 5.91%.XPS analysis showed that the low strength PEF assisted esterification promoted the grafting of ester groups and long carbon chains onto the surface of starch granules,and increased the stereo blocking.Compared with PEF control group,Raman spectroscopy and XRD results showed that low intensity PEF assisted esterification enhanced the packing density of double helix.The above structural characterization shows that the starch structure assisted by low strength PEF retards the diffusion of enzyme molecules from the starch shell barrier to the inside of starch granules,thus reducing the digestion rate and increasing the content of resistant starch.In general,PEF can destroy the structure of starch granules,promote the directional migration of charged chemical reagents,and thus improving the rate of chemical modification of starch.There is a correlation between the electric field strength of PEF and the crystal structure integrity of starch,which can be briefly described as maintaining the crystal structure integrity at low field strength,destroying the crystal structure at medium field strength,and cracking the crystal structure at high field strength.The specific mechanisms are as follows:(1)the crystallinity of starch prepared by PEF-assisted esterification at low electric field strength(1.5-3 k V/cm)is relatively increased,the spatial site resistance effect is enhanced by increasing the OSA grafting degree,and the resistance to enzymatic hydrolysis is enhanced so that the starch digestibility is reduced;the increased ratio of short to long branches of branched starch inhibits starch aging and thus improves the freeze-thaw stability of starch;(2)PEF-assisted esterification at medium electric field strength(3-4.5 k V/cm)disrupts the crystal structure of starch and promotes the grafting of OSA groups to the surface of starch particles,which enhances the interfacial activity of starch and improves the emulsification properties of starch;(3)PEF-assisted esterification at high electric field strength(5-6 k V/cm)severely disrupts or even disintegrates the crystal structure of starch,and the grafted OSA groups further weaken the bonding force between molecular chains,improved the accessibility of water molecules to starch,and reduced the starch pasting temperature.