Study On The Oxidized Starch Acetate Used As An Emulsifier In Food

Starch-based emulsifiers have a good application prospect in the food industry becauseof their extensive sources and good compatibility with other food components. However, theirpractical application was restricted by their high cost and complex preparation. In this paper,oxidized starch acetates were prepared from economical corn starch by regulating denaturantadditions on the basis of the traditional process to solve the problems of the existingstarch-based emulsifiers. In order to obtain a modified starch having high emulsifyingproperties, the preparation conditions of the oxidized starch acetate were optimized byinvestigating the effects of oxidation on acetylation and the influences of the combinedmodification on the viscosity and shear stability of the starch paste, and the good emusifyingproperties of the oxidized starch acetate prepared under the selected conditions wereconfirmed. The main research contents and results are as followings:1. Selection of oxidant for preparing oxidized starch acetates: the production efficiencyof oxidized starch acetates using NaClO and H2O2as oxidants were evaluated from theaspects of the price, oxidation process and efficiency of the oxidants. Compared with H2O2,NaClO showed higher efficiency of the oxidation reaction, so selecting it as the oxidant isbeneficial to reducing the production cost of the oxidized starch acetate.2. Determination of the effects of oxidation on acetylation: the effects of oxidation on themorphology and crystallization characteristics of the starch particles were analyzed using ascanning electron microscope and a X-ray diffractometer, respectively, and the impactmechanism of the oxidation on acetylation was investigated by nuclear magnetic resonanceanalysis. According to the analysis results, the attack of the acetylation agent to the starchparticles was enhanced by the oxidation through partially destroying the particle structure ofthe starch, the occurrence of acetylation was promoted by low degree of oxidation butrestrained by high degree of oxidation, and a competitive reaction at the reactivity centers ofthe starch molecules existed between oxidation and acetylation. According to the effects ofoxidation on the acetylation, high acetyl contents (>1.54%) of the oxidized starch acetate canbe obtained by controlling its carboxyl content below0.52%, and the high acetyl content canfaciliate the enhancement of the emulsifying properties of the modified starch.3. Analysis on the pasting properties of the oxidized starch acetate: the effects of thecombined modification (oxidation and acetylation) on the pasting properties of the starch andthe viscosity and shear stability of its cold paste were analyzed using a rapid viscosityanalyzer and a rheometer. Compared with the original starch, the oxidized starch acetateshowed lower pasting temperature and shorter peak time, and the viscosity of its cold pastewas decreased while the shear stability was enhanced. The paste of the oxidized starchacetates with low degrees of oxidation showed higher shear stability than those with highdegrees of oxidation, and the structrue of the paste became more stable after shearing. Thus,starch pastes with high concentration and low viscosity, which are easy to be handled in anemulsification process and beneficial to the enhancement of the stability of the preparedemulsions, can be achieved by controlling the oxidation of the oxidized starch acetate at a lowdegree (carboxyl content <0.52%). 4. Investigation on emulsifying properties of the oxidized starch acetates: theHydrophilic Lipophilic Balance values of the oxidized starch acetates (0.26%of carboxylcontent, and0.42%,0.77%,1.23%or1.64%of acetyl content) were calculated using theDavis formula, and the stability of emulsions formed by the oxidized starch acetates, waterand conjugated linoleic acid (CLA) were evaluated using standing stratification observation,detection of CLA concentration, particle diameter distribution and the transformation point ofphase, and microscopic observation methods. The oxidized starch acetates can be used as oilin water emulsifiers as their HLB values were higher than10. The stability of the CLAemulsions increased with the increase of the acetylation degree of the oxidized starchacetates, and the emulsifying properties of the modified starch can be enhanced by thesynergism of oxidation and acetylation. Based on the above investigations, the oxidized starchacetate with0.26%of carboxyl and1.64%of acetyl has the best emulsifying propertiesamong the investigated samples in the study, which can be prepared by NaClO with1.5%available chlorine and8.0%acetic anhydride addition.