Antioxidant capacity of cranberry and blueberry nectar after ultrasound treatment

Svrha ovog rada je ispitati utjecaj ultrazvuka visoke snage, određene amplitude i vremena tretiranja, na antioksidativni kapacitet voćnih nektara brusnice i borovnice. Također je određivan i utjecaj ultrazvuka na boju, ukupne fenole te stupanj neenzimskog posmeđivanja voćnih nektara brusnice i borovnice prije i nakon tretmana ultrazvukom. Uzorci su tretirani ultrazvukom visoke snage pri 100%, 75% i 50% amplitude i vremenima obrade 3, 6, i 9 minuta. Za planiranje i optimiranje parametara tretiranja korišten je potpuni faktorijalni dizajn te metoda odzivne površine (RSM). Antioksidativni kapacitet je određen pomoću DPPH i ABTS metode čijom usporedbom se vidi pozitivna korelacija u vrijednostima antioksidativnog kapaciteta. Kod ABTS metode uočeno je da vrijeme tretiranja ima statistički značajan utjecaj na antioksidativni kapacitet voćnog nektra borovnice. Boja voćnog nektra brusnice je bila najtamnija i sa najvećim udjelom crvene te najmanjim udjelom žute boje kod netretiranog uzorka, dok kod borovnice slična svojstva ima uzorak tretiran ultrazvukom amplitude 100% kroz 6 minuta. Stupanj neenzimskog posmeđivanja je određivan spektrofotometrijski te je najizraženiji kod uzoraka tretiranih 9 minuta pri 100% amplitude, a pri sličnim uvjetima dolazi i do porasta koncentracije ukupnih fenola.The object of this paper is to determine the effect of power ultrasound, its amplitude and treatment time on blueberry and cranberry nectar antioxidant capacity and also its effect on color, total phenolic compounds and degree of nonenzymatic browning. Samples were treated with power ultrasound at 100%, 75% and 50% amplitude during treatment time of 3, 6 and 9 minutes. For planning and optimizing treatment parameters full factorial design and response surface method was used. Antioxidant capacity was determined by DPPH and ABTS methods. Their comparison shows a positive correlation between the values of antioxidant capacity. For ABTS method it was observed that treatment time has statistically significant impact on blueberry nectar antioxidant capacity. The untreated sample of cranberry nectar has the darkest color and the highest level of red and the lowest level of yellow while in blueberry nectar similar features has the sample treated with ultrasound at 100% amplitude for 6 minutes. The degree of nonenzymatic browning was determined spectrophotometric and it was highest for samples treated with ultrasound at 100 % amplitude for 9 minutes, and in these similar conditions also total phenolic compounds concentration increases