Optimization of electrodialysis with bipolar membranes applied to cloudy apple juice: minimization of malic acid and sugar losses.

摘要

In previous studies, we demonstrated the feasibility of using electrodialysis with a bipolar-anionic configuration to quickly inactivate the enzyme polyphenol oxidases and prevent the enzymatic browning of cloudy apple juice. The approach consisted of reducing temporarily the pH of cloudy apple juice to 2.0 then adjusting back to its initial value. However, losses in malic acid (19.8%) and sugars (9.7%) were observed in apple juice, especially during the pH adjustment step. The purpose of this work was to study the effect of different methods used to reduce the losses of malic acid and sugars during the inactivation of the enzyme by electrodialysis with a bipolar-anionic configuration. Anionic membranes with improved permselectivity to monovalent ions were tested. The use of an apple juice containing 0.1M HCl as an electrolyte instead of 0.1M HCl alone was also considered. Finally, the combination of the acidification and pH adjustment steps in one operation using an acidified apple juice (pH 2.0) as the electrolyte that circulates on the anion side of the bipolar membranes and an apple juice to acidify as the electrolyte on the cation side of the bipolar membranes was tested. Selective membranes had no effect on reducing the juice's malic acid and sugar losses which amounted to 19.1 +or- 2.1% and to 9.7 +or- 1.5%, respectively. The use of an apple juice-HCl electrolyte resulted in juice's malic acid and sugar losses of approximately 10% and less than 5%, respectively. The combination of acidification and pH adjustment of apple juices in a single ED operation successfully reduced the malic acid (0.9%) and sugar (1.1%) losses and preserved the integrity of cloudy apple juice. However the process productivity was decreased by approximately 2 times, when compared to the former approach. Industrial Relevance: Cloudy or unclarified apple juice is a natural food product with lots of pulp which enhances its sensory properties and it also provides fibre and nutrients that may be lacking in clarified juices. However, cloudy apple juice is very sensitive to enzymatic browning because it contains considerable quantities of polyphenols and polyphenol oxidases (PPO). Enzymatic browning reactions are catalyzed by PPO and result from the oxidation of phenolic compounds to o-quinones, which then polymerize to form dark pigments thereby changing the organoleptic and nutritional properties of the juice. In previous studies, we demonstrated the feasibility of using electrodialysis with a bipolar-anionic configuration to quickly inactivate the enzyme polyphenol oxidases and prevent the enzymatic browning of cloudy apple juice (Lam Quoc, Lamarche, & Makhlouf, 2000; Lam Quoc et al., 2006). The approach consisted of reducing temporarily the pH of cloudy apple juice to 2.0 then adjusting back to its initial value. However, losses in malic acid (19.8%) and sugars (9.7%) were observed in apple juice, especially during the pH readjustment step. In this work, we have studied the effect of different methods to reduce the losses of malic acid and sugars during the inactivation of the enzyme by electrodialysis with a bipolar-anionic configuration. The combination of acidification and pH readjustment of apple juices in a single ED operation successfully preserved the integrity of cloudy apple juice by reducing losses of malic acid and sugars to negligible level. As a result, the optimized process could be applied at industrial scale for the production of stable cloudy apple juice with good organoleptic and nutritional properties.