3.4. Release of natamycin from films
The amount of NAT released from coatings was tested according
to European Regulation (10/2011) employing HPLC-DAD. The calibration
curve of the analyte of interest was linear from 0.05 to
10 lg/ml (correlation coefficient over 0.99). LOD and LOQ were
found to be 0.03 and 0.05 lg/ml, respectively. The CV% for precision
in term of repeatability (intraday) was found to be less than
6% for peak areas and 0.3% for migration time (n = 9). The intermediate
precision (interday repeatability) not exceeded 13% and 1%
for the peak areas and migration times (n = 15), respectively. The
results indicated that the method had good precision.
The kinetics of released NAT from four different coatings (CoD,
CoC, CoB and CoA) into food simulant liquid vs. time at 4 C are
reported in Fig. 3. As shown, for each coating, a process of diffusion
of NAT (solid line) and a final plateau can be observed, illustrating
that the initial release characteristics followed a Fickian behaviour
due to the release of uniformly distributed antimicrobial agent. For
these systems, based on hybrid silica obtained by the sol–gel
method, it is possible to use the semi-empirical equation (Alfieri,
Lorenzi, Montenero, Gnappi, & Fiori, 2010):