Influence of 24 kHz frequency ultrasound on physical and rheological properties of cow's and goat's milk

Cilj ovog istraživanja bio je ispitati utjecaj ultrazvuka visokog intenziteta, snage 400 W konstantne frekvencije od 24 kHz, na promjenu fizikalnih i reoloških svojstava kravljeg i kozjeg mlijeka. Praćen je utjecaj ultrazvuka visokog intenziteta na temperaturu, pH vrijednost i gustoću pri slijedećim procesnim parametrima ultrazvuka: amplituda (A = 37,5; 50; 62,5; 75; 87,5; 100 %); vrijeme obrade (t = 2, 6, 10, 15 minuta); primijenjeni ciklus (c = 0,6; 0,8; 1). Promjene prividne viskoznosti, koeficijenta konzistencije, indeksa tečenja i koeficijenta regresije praćene su pri sljedećim procesnim parametrima ultrazvuka visokog intenziteta: amplituda (A = 37,5; 50; 62,5; 75; 87,5; 100 %); vrijeme obrade (t = 2, 15 minuta); primijenjeni ciklus (c = 1). Dobiveni rezultati statistički su obrađeni pomoću programskog paketa „Statistica 8“ i Mcrosoft Excel. Reološki parametri određeni su metodom linearne regresije na osnovi izmjerenih podataka (brzine smicanja i napona smicanja). Nakon obrade ultrazvukom nije došlo do promjene tipa tečenja kravljeg i kozjeg mlijeka. Oba mlijeka i dalje pokazuju nenewtonski karakter, tj. karakterizira ih dilatantan tip tečenja. Utjecajem ultrazvuka dolazi do povećanja temperature kravljeg i kozjeg mlijeka, a najjači utjecaj ima vrijeme obrade. Utvrđeno je da kod oba mlijeka dolazi do smanjenja pH vrijednosti. Nakon obrade ultrazvukom gustoća kravljeg mlijeka opada, dok gustoća kozjeg mlijeka raste.Main purpose of this research is to study the influence of high-intensity ultrasound (power 400 W) with constant frequency of 24 kHz on change of physical and rheological properties of cow's and goat's milk. The influence of high-intensity ultrasound on temperature, pH value and density was observed under following conditions: amplitude (A = 37,5; 50; 62,5; 75; 87,5; 100 %); processing time (t = 2, 6, 10, 15 minutes); applied cycle (c = 0,6; 0,8; 1). Changes in apparent viscosity, consistency coefficient, flow index and regression coefficient were observed during the following process parameters of high intensity ultrasound: amplitude (A = 37.5, 50, 62.5, 75; 87.5, 100%); processing time (t = 2, 15 minutes); applied cycle (c = 1). Obtained results are processed in the „Statistica 8“ software and Microsoft Excel. Rheological parameters were determined by linear regression based on measured data (shear rate and shear stress). After an ultrasound treatment there has not been found a change of flow type of cow's and goat's milk. Both milk continue to show non – Newtonian behaviour, that is characterized by dilatant type of flow. The influence of ultrasound is to increase the temperature of cow's and goat's milk, and the strongest impact has processing time. It was found that ultrasound treatment leads to decreasing of pH value of both mlik. After an ultrasound treatment density of cow's milk is decreasing, while density of goat's milk increases