Clay/chitosan biocomposite systems as novel green carriers for covalent immobilization of food enzymes

In this work, innovative green composite systems, based on high amounts of montmorrilonite (MMT) and low amounts of chitosan in different relative ratios (70:30, 75:25, 80:20, % w/w), were proposed as potential alternatives to the free nanoclay particles, commonly used as carriers for enzymes covalent immobilization. In details, two different MMT were selected, i.e. SMP (a high purity unmodified MMT) and Optigel (OPT, an activated food-grade MMT). The chitosan was used both to make the clays appropriate supports for the enzymes covalent binding, and to maintain the clay particles together in a unique structure, acting as a binder. The mechanical, thermal, and chemical properties of the obtained composite systems were studied. Moreover, the catalytic properties of a protease covalently immobilized on these carriers were investigated in a model wine-like medium toward a synthetic substrate. OPT based composite systems presented higher σmax and Young modulus values with respect to the SMP based ones, due to OPT better distribution and interaction with the chitosan. Irrespective of nanoclays amount, SMP and OPT composite systems appeared suitable carriers for the covalent immobilization of protease, with an immobilization yield of 18% and 14–17%, respectively. The highest product release velocity was detected when the protease was immobilized on OPT carriers (Vmax 10.49-10.74 mIU mg−1IP), and the greatest apparent affinity when it was linked to SMP composite systems (Ka 2.19–3.10 min−1 μM).