The bioactivities of polyhydroxyalkanoates have been
curtailed
owing to the lack of bioactive functional groups in their backbones.
In this regard, polyhydroxybutyrate (PHB) produced from new locally
isolatedBacillus nealsoniiICRI16
was chemically modified for enhancing its functionality, stability
as well as solubility. First, PHB was transformed to PHB-diethanolamine
(PHB-DEA) by transamination. Subsequently, for the first time, the
chain ends of the polymer were substituted by caffeic acid molecules
(CafA), generating novel PHB-DEA-CafA. The chemical structure of such
a polymer was confirmed by Fourier-transform infrared (FTIR) spectroscopy
and proton nuclear magnetic resonance (1H NMR). The modified
polyester demonstrated improved thermal behavior compared to PHB-DEA
as was shown by thermogravimetric analysis, derivative thermogravimetry,
and differential scanning calorimetry analyses. Interestingly, 65%
of PHB-DEA-CafA was biodegraded in a clay soil environment after 60
days at 25 °C, while 50% of PHB was degraded within the same
period. On another avenue, PHB-DEA-CafA nanoparticles (NPs) were successfully
prepared with an impressive mean particle size of 223 ± 0.12
nm and high colloidal stability. The nanoparticulate polyester had
powerful antioxidant capacity with an IC50of 32.2 mg/mL,
which was the result of CafA loading in the polymer chain. More importantly,
the NPs had a considerable effect on the bacterial behavior of four
food pathogens, inhibiting 98 ± 0.12% ofListeria
monocytogenesDSM 19094 after 48 h of exposure. Finally,
the raw polish sausage coated with NPs had a significantly lower bacterial
count of 2.11 ± 0.21 log cfu/g in comparison to other groups.
When all these positive features are recognized, the polyester described
herein could be considered as a good candidate for commercial active
food coatings.