Influence of high-intensity ultrasound on rheological and thermophysical properties of starch suspensions

Cilj ovoga rada bio je istražiti utjecaj ultrazvuka visokog intenziteta, različitih frekvencija i snaga te vremena djelovanja na reološka, fizikalna, termofizikalna svojstva, morfološku strukturu škrobnih granula i teksturu gela škroba kukuruza, pšenice, krumpira i tapioke. Suspenzija škrobova (1%, 2% i 10%) testirane su ultrazvukom visokog intenziteta (nominalne snage 100 – 400 W) frekvencije 22 i 24 kHz u trajanju od 15 i 30 minuta. Za obradu ultrazvukom primijenjeni su ultrazvučni procesor (sonda) i ultrazvučna kupelj. Rezultati istraživanja pokazali su da su snaga i frekvencija ultrazvuka, kao i vrijeme tretiranja imali različit utjecaj na reološka svojstva škrobnih suspenzija. Sve ispitivane škrobne suspenzije imale su ne-newtonski karakter. Obrada ultrazvukom snage 150 – 300 W rezultirala je porastom koeficijenta konzistencije, dok je daljnje povećanje snage ultrazvuka uzrokovalo njegov pad. Maksimalna viskoznost ispitivanih škrobnih suspenzija značajno je porasla, a stabilnost tijekom miješanja pri visokim temperaturama i tijekom hlađenja su snižene nakon ultrazvučnih tretmana. Obrada ultrazvukom nije značajno utjecala na temperaturu želatinizacije ispitivanih škrobova, ali je uzrokovala sniženje entalpije želatinizacije. Osim toga, uočene su značajne promjene čvrstoće, elastičnosti, kohezivnosti, adhezivnosti i gumenosti škrobnih gelova. Obrada ultrazvukom uzrokovala je i značajne promjene kapaciteta bubrenja, indeksa topljivosti i bistroće škrobnih suspenzija.The goal of this research was to examine the effect of high intensity ultrasound of different frequencies and power intensities and of different treating times on the rheological, physical and thermophysical properties, morphological structure of starch granules and textural properties of corn, wheat, potato and tapioca starch gels. Starch suspensions (1%, 2% and 10%) were treated with high intensity ultrasound (nominal power 100-400 W) of 22 and 24 kHz frequency for a period of 15 and 30 minutes. Ultrasound treatments used in this research were ultrasound processor (probe) and ultrasound bath. Examination results have demonstrated how ultrasound power, frequency and time of treatment all had different influence on the rheological properties of starch suspensions. All starch suspensions that were put to test had non-Newtonian character. Ultrasound treatment using power of 150 and 300 W resulted in the increase of the consistency coefficient, and every further increase of the ultrasound power (400 W) resulted in the decrease of the consistency coefficient. Maximal viscosity of the tested starch suspensions has increased significantly after the ultrasound treatments. On the other hand, the stability of starch suspensions during the process of mixing at high temperatures and during the process of cooling were decreased after the ultrasound treatments. Ultrasound treatment did not significantly affect the gelatinization temperature of tested starches, but it did cause a decrease in the gelatinization enthalpy. Beside that, significant changes in hardness, cohesiveness, adhesiveness, elasticity and gumminess of the starch gels were detected. Ultrasound treatment also resulted in significant changes of starch suspensions swelling capacity and of their respective solubility and turbidity indexes