Acceleration of pH variation in cloudy apple juice using electrodialysis with bipolar membranes

The purpose of this study was to accelerate pH variation in cloudy apple ju ice using electrodialysis (ED). The testing was conducted using two ED conf igurations. The bipolar and cationic membrane configuration showed that red ucing the spacing from 8 to 0.75 mm had little effect on treatment time, wh ereas stacking eight bipolar membranes reduced acidification time by 30%, a lthough the treatment still took too long (21 min). Furthermore, it was not possible to acidify apple juice to a pH of 2.0 to completely inhibit enzym atic browning. The bipolar and anionic membrane configuration helped to acc elerate the acidification step by a factor of 3, increasing the yield from 3.3 to 10 L of juice/m(2) membrane/min. Moreover, treatment time was invers ely proportional to the size of the membrane stack. The speed at which the pH of acidified juice returned to its initial value was, however, 4 times s lower than the speed of acidification, giving a yield of 2.5 L of juice/m(2 ) membrane/min. By accelerating the acidification step, ED treatment with b ipolar and anionic membranes results in more effective polyphenol oxidase a ctivity and more rapid control of juice browning at pH 2.0. Also, the treat ment has very little effect on the chemical composition and organoleptic qu ality of apple juice.