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Among the milk proteins, bovine beta-casein has the peculiarity of containing in its sequence some peptides liable to interfere in mineral nutrition and some peptides with opioid (casomorphines), antihypertensive, and immunomodulatory activities. In this work we propose a novel type of multicompartment enzyme reactor, operating under an electric field, for the continuous hydrolysis of milk proteins such as beta-casein. The enzyme trypsin is trapped, with zwitterionic buffering ions and its substrate beta-casein, in solution between two isoelectric membranes having pI values encompassing the isoelectric point of the enzyme. Additionally, beta-casein is captured inside the same reaction chamber with the aid of sieving membranes, since its pI is too far away from the pI of trypsin. This setup permits the continuous operation at the pH of optimum of activity. The peptides, arising from tryptic hydrolysis of beta-casein, are removed under the influence of the electric field and collected in different chambers in which they are isoelectric and isoionic as well. The purity of the peptides collected is ascertained by capillary zone electrophoresis and their identity confirmed by N-terminal sequencing and MALDI-TOF mass spectrometry. This setup allows continuous harvesting of some biologically-active peptides in a pure form. The major advantages of such a reactor system over conventional batch reactors are the great increase in enzyme utilization efficiency and the overall reactor productivity.

A novel type of immobilized enzyme reactor operating under an electric field is here reported: a multicompartment immobilized enzyme reactor (MIER). In this experimental set-up, the enzyme and zwitterionic buffering ions are trapped in between two isoelectric membranes, having isoelectric point (pI) values so far apart as to trap the enzyme by an isoelectric mechanism, while allowing operation at pH optima, even when the latter pH value is quite removed from the enzyme pI. As an example, urease (pI 4.9) is trapped between a pI 4.0 and a pI 8.0 membranes, thus permitting operation (via suitable amphoteric ions buffering at pH 7.5) at the pH of optimum of activity (pH 7.5). The charged product (ammonium ions) quickly leaves the enzyme chamber under the influence of the electric field, thus allowing sustained activity for much longer time periods than in conventional reactors. As an example, while in a batch reactor 90% of original enzyme activity is lost in 200 min, only 2% activity is lost in the same period in the MIER reactor. As an additional bonus, the MIER reactor allows conversion rates of ∼95% in a wide range of substrate concentrations, whereas batch-type reactors rarely achieve better than 50% conversion under comparable experimental conditions.

A novel type of immobilized enzyme reactor operating under an electric field is here reported: a multicompartment immobilized enzyme reactor (MIER). In this experimental set‐up, the enzyme and zwitterionic buffering ions are trapped in between two isoelectric membranes, having isoelectric point (pl) values so far apart as to trap the enzyme by an isoelectric mechanism, while allowing operation at pH optima, even when the latter pH value is quite removed from the enzyme pl. As an example, urease (pl 4.9) is trapped between a pl 4.0 and a pl 8.0 membranes, thus permitting operation (via suitable amphoteric ions buffering at pH 7.5) at the pH of optimum of activity (pH 7.5). The charged product (ammonium ions) quickly leaves the enzyme chamber under the influence of the electric field, thus allowing sustained activity for much longer time periods than in conventional reactors. As an example, while in a batch reactor 90% of original enzyme activity is lost in 200 min, only 2% activity is lost in the same period in the MIER reactor. As an additional bonus, the MIER reactor allows conversion rates of ∼95% in a wide range of substrate concentrations, whereas batch‐type reactors rarely achieve better than 50% conversion under comparable experimental conditions. © 1997 John Wiley & Sons, Inc.

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