| Starch is the second richest carbohydrate of the nature. It is widely used in theareas of food, chemical industry, textile, architecture and so on. But the qualitative ofnative starch has some inadequacies，such as insolubility, poor transparency, poorshearing, easy retrogradation in low temperature and so on. In order to improve theprocessing performance of the starch, chemical, physical or enzymatic methods wereused to modify starches. Ultra High Pressure as a new and physical method withadvantages of security, economic and pollution-free could produce modified starch.Areca taro starch was chosen as the research object in this paper. The starch granulestructure, physicochemical property and rheological property influenced by differentpressure, pressure-holding time and starch concentration were studied. The mainresults were concluded as follows.(1) The particle morphology of areca taro starch under500MPa was destroyedand polarization cross deformed and even disappeared。X-ray diffraction studiesshowed that the starches converted A-type patterns to the B-type-like pattern, afterUHP treatment Compared with the effect of pressure, there was relatively slight effectof pressure-holding time and starch concentration on granular structure。Whenpressure-holding time was25min， only a few starch granules aggregated andcollapsed and polarization cross of starch became unclear。When the starchconcentration was25%，the starch granules occurred a certain degree of adhesion.There was no change in the type of X-ray diffraction pattern, but the intensity of thepeaks decreased with the change of pressure-holding time and starch concentration.(2) The solubility and swelling of the starch treated by UHP were significantlylower than the native starch at a higher temperature. The light transmittance increasedsignificantly after UHP treatment. And the free-thawing ability improved obviouslyunder the suitable treatment conditions. UHP treatment changed the texturalproperties of areca taro starch。The hardness, gumminess and chewiness of the modified starch increased obviously after UHP treatment. There were no significantchanges of the springiness and cohesiveness. Gelatinization characteristics ofmodified starch were measured by RVA. The results showed that the peak viscosity ofthe modified starch was significantly increased with the increase of pressure,pressure-holding time and starch concentration. It indicated that UHP treatment hasthe thickening effect on the starch paste thicken. And the slight light increase ofbreakdown showed that the hot and cool stability of starch paste reduced. UHPtreatment has no significant influence on the value of setback. It indicated that thephysicochemical properties of Areca taro starch could be improved under certainpressure treatment.(3) Steady flow tests illustrated that the native and UHP-treated starches gels werenon-Newtonian flow with pseudoplastic flow characters. Based on the resultsobserved from flow curves, the Herschel-Bulkley rheological model can be used to fitthe flow behavior of all starches gels. Dynamic viscoelastic measurements revealedthat their storage modulus (G′) and loss modulus (G′′) increased with increasing ofpressure, pressure-holding time and starch concentration. The starch pastes exhibitedshear-thinning pseudoplastic behavior before or after UHP treatment. |
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