Abstract
In our research, a composite film of whey protein isolate (WPI)/chitosan incorporated with TiO2 nanoparticles (NPs) and essential oil of Zataria multiflora (ZEO) was developed. The resulting composite films were evaluated by FTIR, SEM, and XRD, and also the physicochemical characteristics including color, mechanical properties, swelling ratio, and water vapor permeability (WVP) were studied. SEM graphs exhibited that the samples had a uniform and homogeneous structure where TiO2 NPs and ZEO were well dispersed. FTIR and XRD findings also show that the hydrogen bonds and hydrophobic interactions are the main interactions between the composite WPI/chitosan and TiO2. The crystalline nature of the composite samples increased with the increase of NP content. Nevertheless, ZEO had an insignificant effect on the functional groups and the crystallinity of composite samples. The film visual characterization revealed that, by adding and increasing the TiO2 and TiO2-ZEO, sample lightness and opacity significantly increased. Additions of TiO2 remarkably (p<0.05) improved the water vapor and mechanical properties of composite samples, although the loading of ZEO, regardless of TiO2 incorporation, led to a considerable decrement of these properties. Furthermore, composite films containing ZEO combined with 2% of TiO2 compared with 1% of NPs blended with ZEO had strong antimicrobial properties against Staphylococcus aureus, Escherichia coli, and Listeria monocytogenes. Generally, the findings proposed that the addition of TiO2 reinforces the properties of composite films with a synergistic effect of ZEO loading on the antibacterial ability, by which the resulting biodegradable composite samples can be used as a food active packaging material.
Highlights
Nowadays, the increase in the global concern of food quality and safety together with the environmental influences of nonbiodegradable plastic material wastes has led to the research and studies on the renewable and eco-friendly edible coating and films [1]
Our finding was in agreement with the results of Zhang et al [5] who evaluated the microstructure of chitosan/Whey protein isolate (WPI) films enriched by TiO2 nanoparticles containing sodium laurate. ey reported that the blend film made of chitosan and WPI had a ragged and rough surface attributing to the thermodynamic incompatibility and phase segregation of biopolymers. e Scanning Electron Microscopy (SEM) image shows that TiO2 NPs and ZEO incorporation into the composite films had no significant influence on the surface morphology of WPI/chitosan samples
WPI/chitosan films loaded with different concentrations of TiO2 nanoparticles and ZEO showed excellent potential to be applied for packaging. e nanoparticles were well distributed in the film structure, and the resulting composite films were homogeneous without any phase separation as observed by SEM. e X-Ray Diffraction (XRD) showed that the incorporation of nanoparticles gradually increased the crystalline structure of samples, which may be because of new bond formation between WPI/chitosan matrix and TiO2 NPs as investigated by Fourier-Transform Infrared (FTIR) spectroscopy
Summary
The increase in the global concern of food quality and safety together with the environmental influences of nonbiodegradable plastic material wastes has led to the research and studies on the renewable and eco-friendly edible coating and films [1]. Biopolymers including proteins, lipids, polysaccharides, and their mixtures are considered as the main engaged materials for this purpose due to their benefits such as biodegradability, high availability, and renewability [2, 3]. Chitosan is insoluble in usual solvent, but chitosan because of their amino groups is soluble in some acid solutions with a pH value lower than 6. It has an excellent film-forming capability and high antimicrobial activity and can be employed as an active antimicrobial coating agent or packaging film [6]. Whey protein isolate (WPI) is another biopolymer with good film-making
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