Eugenol Nanoencapsulated by Sodium Caseinate: Physical,
Antimicrobial, and Biophysical Properties
Received: 6 November 2017 / Accepted: 7 December 2017 / Published online: 14 December 2017
Springer Science+Business Media, LLC, part of Springer Nature 2017
To improve the application of essential oils as natural antimicrobial preservatives, the objective of the present study was to
determine physical, antimicrobial, and biophysical properties of eugenol after nanoencapsulation by sodium caseinate (NaCas).
Emulsions were prepared by mixing eugenol in 20.0 mg/mL NaCas solution at an overall eugenol content of 5.0–137.9 mg/mL
using shear homogenization. Stable emulsions were observed up to 38.5 mg/mL eugenol, which had droplet diameters of smaller
than 125 nm at pH 5–9 after ambient storage for up to 30 days. The encapsulated eugenol had similar minimal inhibitory and
minimal bactericidal concentrations as free eugenol against Escherichia coli O157:H7 ATCC 43895, Listeria monocytogenes
Scott A, and Salmonella Enteritidis but showed better inhibition of E. coli O157:H7 than free eugenol during incubation at 37 °C
for 48 h. After 20 min interaction at 21 °C, bacteria treated with encapsulated eugenol had a greater reduction of intracellular ATP
and a greater increase of extracellular ATP than free eugenol, suggesting the enhanced permeation of eugenol after
nanoencapsulation. However, such overall trend was not observed when examining bacterial morphology and uptake of crystal
violet, suggesting the possible membrane adaptation. Findings from this study showed the feasibility of preparing nanoemulsions
with high loading of eugenol using NaCas.
Essential oils (EOs) are secondary metabolites of plants .
Many EOs and their components have excellent antimicro-
bial activities and can potentially be used as natural preser-
vatives to meet the increasing consumer demand for clean
labels . However, poor solubility and high volatility of
EOs limit their application in aqueous foods and beverages.
This has led to studies of delivery systems to improve their
applicability in food matrices. Emulsions , food biopoly-
mer particles [3, 4], and liposomes  are several groups of
colloidal systems studied to encapsulate EOs. In addition to
improving the dispersibility of EOs [6, 7], some studies
have reported the improved antimicrobial activity of EOs
after encapsulation . Conversely, other studies have
shown negative effects on antimicrobial activity after en-
capsulating EOs, which would nullify their practical appli-
cations [2, 8, 9]. Therefore, materials used to deliver EOs
are to be carefully studied.
For food applications, delivery systems should ideally be
fabricated from generally-recognized-as-safe (GRAS) ingre-
dients. To prepare emulsions, dairy proteins are extensively
studied as natural emulsifiers due to their abundance, low cost,
and amphiphilic properties. Sodium caseinate (NaCas) is a
commercially available ingredient that can be used to prepare
emulsions due to its excellent surface activity. The self-
assembly properties of caseins have been used to
nanoencapsulate hydrophobic molecules such as bixin and
curcumin [10, 11]. NaCas has been used to encapsulate EO
components with and without other ingredients such as zein
and lecithin [12–14]. Thymol nanoemulsified by NaCas
showed a significant improvement of anti-listerial activity in
milk with different fat contents when compared to free thymol
. However, much is unknown about the biophysical prop-
erties of EO components after nanoencapsulation.
Electronic supplementary material The online version of this article
(https://doi.org/10.1007/s11483-017-9509-0) contains supplementary
material, which is available to authorized users.
* Qixin Zhong
Department of Food Science, University of Tennessee, 2510 River
Drive, Knoxville, TN 37996, USA
Department of Food Science and Technology, University of
Nebraska-Lincoln, Lincoln, NE, USA
Food Biophysics (2018) 13:37–48