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). Keywords: Clay, Chitosan, Food enzymes, Microstructure, Kinetic parameters

Pre-fermentative cold maceration in the presence of non-Saccharomyces strains: effect on fermentation behaviour and volatile composition of a red wine

Background and Aims This study evaluated the impact of pre‐fermentative cold maceration (PCM), in the presence of two non‐Saccharomyces yeasts, Metschnikowia pulcherrima MP 346 and Metschnikowia fructicola MF 98‐3, and of a commercial pectic enzyme, on fermentation kinetics and on the volatile composition of a Sangiovese red wine. Methods and Results Sangiovese grape must was inoculated with MP 346 or MF 98‐3 or treated with a pectic enzyme preparation during PCM, at 5°C for 24 or 72 h. A Control wine was produced by a pure culture of Saccharomyces cerevisiae. Both non‐Saccharomyces strains affected the initial yeast population dynamics and the persistence of S. cerevisiae at the end of malolactic fermentation. Irrespective of the duration of PCM, the inoculum of Metschnikowia strains did not influence the rate of sugar consumption or the kinetics of malolactic fermentation. The volatile composition of the final wines was evaluated with solid‐phase extraction, followed by GC/MS. The concentration of some terpenes and C13‐norisoprenoids, nerol, geraniol, 8‐hydroxy‐linalool (cis) and 3‐oxo‐α‐ionol, and of some esters, isoamyl lactate and ethyl isoamyl succinate, was higher in wines inoculated with Metschnikowia strains than in the Control and wine treated with pectic enzyme. Conclusions Metschnikowia yeast strains MP 346 and MF 98‐3 affect wine volatile composition. Significance of the Study This study shows for the first time that an inoculum of Metschnikowia strains MP 346 and MF 98‐3 during PCM is effective in modulating the volatile composition of a Sangiovese red wine