Study On Pulsed Electric Fields-assisted Esterification Of Starch

Nowadays,starch esterification has some issues,such as low degree of substitution?DS?,long reaction time and poor reaction efficiency,which greatly reduces the economic benefits in food industry.In this study,a novel method of PEF-assisted esterification has been established.A-type and B-type maize starch with⁰.5-80%amylose content,A-type cassava starch and B-type potato starch were used as materials to explore the effects of PEF intensities,diverse crystalline structures,different chain structures on esterification.This study has focused on the result of DS value,the multi-scale structure and the functional characteristics of esterified starches modified by both conventional and pulsed electric fields?PEF?-assisted methods.The thermal stability,in vitro digestibility and emulsification and their emulsifiers'stability were also studied.And the potential application has been found in daily food processing and dietary regulation of metabolic disorders.The mechanism of PEF on esterification was explored.The conclusions were as follows.1)Based on the analysis of response surface methodology on potato starch and cassava starch,it was found that PEF intensity,PEF treatment time and the addition of acetic anhydride are significantly correlated with DS at level of P<0.01.The quadratic regression mathematical models were also provided.PEF treatment can effectively improve esterification efficiency and increase DS.Fourier transform infrared spectroscopy?FT-IR?showed that new bands at 1735 cm^-1?C=O?,1368 cm^-1?C-H?and 1230 cm^-1?C-O?were recommended after esterification reaction which represented the existence of ester-groups in starch granules.Obvious bulging and increased surface roughness were observed on the surface by scanning electron microscope?SEM?,especially for the starch with higher DS.When compared with native starches,higher solubility and gelatinization temperature but worse thermal stability were found in esterified starches.2)With DS increased,destroyed and rearranged crystalline structure was detected by the X-ray diffractometer?XRD?.Fractal structure of PEF-assisted starch esters changed from surface fractal structure to mass fractal structure as proved by small angle X-ray scattering?SAXS?and larger Blocket in size was observed by atomic force microscopy?AFM?.3)Different amylose content?⁰.5-80%?had obvious effects on both structures and properties of maize starch as modified by two esterification methods.Waxy starch with high amylopectin content changed its structure from A-type to B-type crystal structure,the stacking distance of the amorphous region with q=0.68 nm^-1 was significantly decreased and a new scattering peak was appeared at q=3.90 nm^-1.4)Emulsification stability showed that esterified starch assisted with higher PEF intensity?3.75 kV/cm?5.00 kV/cm?exhibited its excellent stability.The emulsifier had a lower separation level and narrower.PEF-assisted starch ester with higher amylose content possessed higher solubility and excellent freeze-thaw stability even after five repeated freeze-thaw cycles,indicating its potential applications in frozen food industry.In vitro digestion showed that the content of slowly digestible starch?SDS?increased with the increasing PEF intensity,and it was higher than that of conventional esterified-starch.5)Based on the effects of PEF treatment?PEF intensities and PEF treatment time?,crystalline structures,chain structures on esterification,the mechanism of PEF has been revealed in this study.The role of PEF can provide enough energy for the barrier transition of esterification.In addition,the high electric potential difference and the a direction of the electric field can not only destroy the structure in crystalline area,but also accelerate the motion of reaction particles thus promote more effective collisions.In this study,it firstly established a novel dual modification method by combining the PEF treatment and esterification together to alter properties of starch granules.,This dual method avoided the destruction of starch granules by high temperature and greatly improved the reaction efficiency and DS level.The esterified starch modified by PEF-assisted esterification showed its better freeze-thaw stability and improved of emulsification stability in the food processing industry providing a comprehensive analysis for technical support and theoretical principle.Its increased SDS content can effectively regulate the glucose content in blood by slowly releasing glucose and help maintain glucose balance.This discovery will be beneficial for people suffering metabolism disorder,including high blood pressure,obesity,diabetes etc.This study can promote the possibility of PEF-assisted esterification applied on large-scale industries.