Influence of high intensity ultrasound on rheological and pasting properties of wheat starch

Svrha ovog rada je ispitati utjecaj ultrazvuka visokog i niskog intenziteta na reološka i pastozna svojstva suspenzija škroba pšenice. Ispitivane suspenzije sadrže 10 % pšeničnog škroba te su neposredno nakon pripreme procesirane ultrazvukom. Sva ispitivanja provedena su prije i nakon ultrazvučne obrade u ultrazvučnoj kupelji frekvencije 22 kHz, nominalne snage 150 W te ultrazvučnom sondom frekvencije 24 kHz, nominalne snage 100, 300 i 400 W. Vrijeme ultrazvučne obrade svih uzoraka bilo je 15 i 30 minuta. Reološka svojstva određena su primjenom rotacionog reometra Rheometric Scientific RM-180 pri temperaturi od 20 ˚C, a pastozna svojstva škrobnih suspenzija određena su primjenom Micro Visco-Amylo-Graph, Brabender Ohg Duisburg, Njemačka po metodi ICC Standard 126/1. Ultrazvučna obrada uzrokuje mehaničko oštećenje škrobne granule čime njena unutrašnjost postaje dostupnija vodi tijekom zagrijavanja što ima za posljedicu značajne promjene reoloških i pastoznih svojstava škrobnih suspenzija. Reološki parametri pokazuju da sve suspenzije imaju ne-Newtonski karakter, a ultrazvučni tretmen uzrokovao je značajno povećanje koeficijenta konzistencije svih ispitivanih sustava. Ultrazvučnim procesiranjem došlo je do značajnog sniženja temperature želatinizacije kod svih škrobnih suspenzija. Značajno smanjenje početnih temperatura želatinizacije upućuje na raniji stupanj bubrenja granule tijekom zagrijavanja.The aim of this paper was to examine the influence and effect of high and low power ultrasound on rheological and thermophysical properties of wheat starch suspensions. Suspensions containing ten percent of potato starch have been treated with ultrasound. All analysis have been carried out before and after power ultrasound treatment. Ultrasound bath of 22 kHz frequency and nominal power of 150 W has been used, as well as ultrasound probe of 24 kHz frequency and nominal power of 100, 300 and 400 W for 15 and 30 minute treatments. Rheological parameters have been determined with rheometer Rheometric Scientific RM-180 at 20 ºC. Pasting properties have been determined with Micro Visco-Amylo-Graph, Brabender Ohg Duisburg at method ICC Standard 126/1. Ultrasonic treatment caused disrupting of starch granules by mechanical forces and made the granule more permeable to water during the heating step. Because, significant changes of rheological and pasting properties were observed. Rheological parameters showed that all suspensions exhibited non-newtonian (dilatant) character. Also, ultrasonic treatment has affected a significant increase of consistency coefficient of starch suspension. Ultrasonic treatment caused significant lowering of the beginning gelatinization temperatures, which indicated an earlier state of granule swelling during heating