Contribution of Phosphorylation Modification to Stability and Antibacterial Activity of Egg White Protein Nanogels Loaded with Cinnamon Bark Essential Oil

Abstract

This study evaluated the potential usage of phosphorylated egg white protein (P-EWP) nanogels fabricated via microwave-induced phosphorylation modification and gel process and further ultrasonic nanometrization as novel delivery systems for cinnamon bark essential oil (CBEO). Compared to EWP-CBEO nanogels without chemical phosphorylation, the obtained P-EWP-CBEO nanogels have shown smaller average hydrodynamic diameter (133.6 nm), relatively uniform size distribution (polydispersity index around 0.265), enhanced negative surface charge (-35.4 mV), and improved stability under the conditions of high temperature (up to 90 °C) and ionic strength (up to 200 mM NaCl). Moreover, P-EWP-CBEO nanogels, with hydrophobic interactions and disulfide bonds as the main intermolecular forces, exhibited a remarkable conformational change in microstructures. In addition, the results of the antibacterial experiments on Escherichia coli, Staphylococcus aureus, and Listeria monocytogenes showed that the MIC values of P-EWP-CBEO nanogels were two times lower than those of EWP-CBEO nanogels and could completely inhibit the growth of pathogenic bacteria within 108 h. Hence, we have suggested that P-EWP-CBEO nanogels are successfully fabricated with improved physicochemical properties as novel potential natural preservatives in the food industry.

Keywords: antibacterial properties; cinnamon bark essential oil; egg white protein; nanogels; phosphorylation.

Figure 1

Particle size distribution of P-EWP-CBEO nanogels.

Figure 2

FTIR spectra of P-EWP-CBEO nanogels.

Figure 3

Differential scanning thermal analysis of P-EWP-CBEO nanogels.

Figure 4

Scanning electron micrography (SEM) of freeze-drying egg white protein powder (A1,A2), egg white protein-embedded cinnamon essential oil nanogels (EWP-CBEO) (B1–B3), and phosphorylation-modified egg white protein-embedded cinnamon essential oil nanogels (P-EWP-CBEO) (C1–C3).

Figure 5

Effect of different temperatures (30–90 °C) on the particle size and zeta potential of EWP-CBEO (A) and P-EWP-CBEO (B). A₁ and B₁ represent the particle size and Zeta-potential maps of EWP-CBEO and P-EWP-CBEO; A₂ and B₂ represent the morphology of EWP-CBEO and P-EWP-CBEO, respectively. Broken lines with different lower-case letters within the same panel are significantly different at p < 0.05 level according to Duncan’s multiple range test.

Figure 6

Effect of different ionic strengths on the particle size and zeta-potential of EWP-CBEO and P-EWP-CBEO nanogels. Samples were measured after being placed for 12 h at different ionic strengths (0–400 mM) for 30 min; EWP-CBEO (A) and P-EWP-CBEO (B) represent sample morphology, respectively. Samsamples were left for 12 h after 30 min at different ionic intensities (0–400 mM); (B): particle size and Zeta-potential map of the P-EWP-CBO; EWP-CBO (A) and P-EWP-CBO (B1) represent the morphology of the samples. Different superscript letters indicate statistically significant differences (p < 0.05).

Figure 7

Effects of LB, CBEO, EWP-CBEO, and P-EWP-CBEO nanogels on the time growth curves of Escherichia coli (A), Staphylococcus aureus (B), and Listeria monocytogenes (C).

Figure 8

Flow chart of P-EWP-CBEO nanogel preparation.