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CHEMICAL ENGINEERING TRANSACTIONS
VOL. 43, 2015
A publication of
The Italian Association
of Chemical Engineering
Online at www.aidic.it/cet
Chief Editors: Sauro Pierucci, Jiří J. Klemeš
Copyright © 2015, AIDIC Servizi S.r.l.,
ISBN 978-88-95608-34-1; ISSN 2283-9216
Effect of Rosemary Oil and an Emulsion of Essential Oils on
Structure and Physical Properties of Chitosan Film
Elena Torrieri*,a, Silvana Cavellaa, Paolo Masia,b
a Food and Agricultural Department -University of Naples Federico II –Naples, Italy
bCAISIAL-Centre of Food Innovation and Development in the Food Industry University of Naples Federico II – Naples, Italy
elena.torrieri@unina.it
The objective of this work was to study the effect of Rosemary oil (Resemary Officinalis) and an emulsion at
68 % of EOs (EA3) on chitosan (CH) film forming dispersion (FFD) and CH films properties. FFD were
characterized in terms of rheological properties and particle size distribution. In order to study the impact of
EOs into the CH matrix, microstructure (SEM), film thickness, equilibrium moisture content (EMC) and water
vapour permeability (WVP) of the dried film were evaluated. Results showed that oil concentration did not
affect particle size distribution whereas the type of EO have an effect on the particle size dimension. The
rheological properties of the FFD were significantly affected by the presence of the EOs. While a continuous
structure was observed for the CH film, the presence of EOs caused discontinuities associated with the
formation of two phases in the matrix: lipid droplets embedded in a continuous polymer network. The
dimension of the oil droplet were higher in the film respect to the FFD. Moreover, it was showed that the
higher the EOs content, the higher the film thickness and the lower the film moisture sorption capacity. The
WVTR of CH film has an average value of 2.3x10-3 g m-2 s-1. The study revealed that an active chitosan film
could be obtained by using the EA3 emulsion of EOs.
1. Introduction
Active packaging technologies involve interactions between the food and the packaging material to extend the
shelf life of foods while maintaining their quality and safety. These materials are designed to deliberately
incorporate ‘active’ components intended to be released into the food or to absorb substances from the food
(Regulation (EC) No 1935/2004; regulation (EC) No 450/2009). Recently, given the increasing health
concerns of consumers, current packaging research has focused on the use of natural compound, such as
essential oil, as active agents in active edible coating materials to preserve and prolong the shelf life of food
as meat, fish or minimally processed fruit (Azevedo et al., 2014; Bonilla et al., 2014; Fuenmayor et al., 2013;
Higueras et al., 2014; Raybaudi-Massilia et al., 2008; Valencia-Chamorro et al., 2009). Among the most
common oils that have been proven antimicrobial properties against spoilage microorganisms the main are
Cilantro oil, Coriander oil, Oregano oil, Rosemary oil, Sage oil, Clove (bud) oil and Thyme oil (Burt, 2004).
Chitosan has been studied extensively in the food industry due to its excellent film-forming, antimicrobial,
physical and mechanical properties (Elsabee and Abdou, 2013) and an active antimicrobial film based on
chitosan has been recently developed (Lago et al., 2014). The functional properties of edible film depend on
the type of constituents and also on their interaction (Giancone et al., 2008, 2011). According to the
application of EOs, it is also important to evaluate their effects on the physical and structural properties of the
resulting film (Sánchez-González et al., 2010). About the role of EOs on film functional properties the results
reported on literature are still contradictory, in particular regarding the effect of the oil on the water barrier
properties of the film. However, it has been reported that a major role can play the type of polysaccharide or
the type of oil added and their interaction on the effective structure of the film and thus on the diffusivity of the
water. In fact, if by adding the oil the matrix results more open, an higher diffusion of water in the matrix can
be expected and thus a negative impact on the water barrier properties expected (Perone et al., 2014). The
DOI: 10.3303/CET1543005
Please cite this article as: Torrieri E., Cavella S., Masi P., 2015, Effect of rosemary oil and an emulsion of eos oils on structure and physical
properties of chitosan film, Chemical Engineering Transactions, 43, 25-30 DOI: 10.3303/CET1543005
25
composition of the film and the interaction between the constituent (polysaccharides, oil, emulsifier) began a
critical aspect to design active film with desired properties (Perone et al., 2014). In this work the relation
between structure and properties of chitosan film obtained with rosemary oil and an emulsion of EOs at 68 %
has been investigated.
2. Material and methods
2.1. Material
Medium molecular weight Chitosan (CH MMW) with a degree of deacetylation higher than 75 – 85 %, acetic
acid puriss. p.a., rosemary essential oils (Rosemary Officinalis- REO) and Tween 80 were purchased from
Sigma-Aldrich (Milan, Italy). EA3 Emulsion (68 % of essential oils, 0.8 % Polisorbate Tween 80, 0.8 % Myverol
18-92, 1 % Citric Acid, 3 – 5 % CaCl2) was provided from Kerry Ingredients & Flavours (Bergamo, Italy). The
composition of EA3 EO were: Coriander (>10%), Clove (>10%), Caraway (10%), Cardamon (>10%), White
Thyme (5-10%), Cinnamon Distilled Fraction (Nutmeg (5-10%), Black Pepper (2-5%), Anise (2-5%), Anise
(<2%), Sage (<2%), Oregano (<2%), Mint (<2%).
2.2 Emulsion and Film making procedure
CH 1% (w/v) was prepared by dispersing chitosan powder in acetic acid solution (1%, v/v) at room
temperature for 12 hours. Then, the dispersion has been centrifuged for 4 min at 5,000 rpm to eliminate the
solid impurity suspended. Then, essential oils emulsion (EA3) or a mixture of REO and tween - 80 (4:1) were
added to polymer solutions to reach a final concentration of 0.5 %, 1 %, and 2 % (w/v). CH-EA3 and CH-REO-
tween-80 mixtures were emulsified for 4 min at 15,500 rpm at room temperature using a rotor-stator
homogenizer (Ultra TurraxR, T 18, IKA, Milan, Italy) and then the solutions were de-aerated under vacuum for
15 minutes to prevent pinhole formation. 20 ml of FFD were poured onto levelled 56.7 cm2 polystyrene Petri
dishes and allowed to dry at 20° C and 50 % relative humidity (RH) for 48 h under air circulation. The dried
films were peeled from the dishes and stored at 20°C and 50 % relative humidity prior to testing.
2.3. Characterization of the FFD
The particle size analysis of the FFDs was carried out by means of a laser diffractometer (Mastersizer 3000,
Malvern Instruments, Worcestershire, UK). The samples were diluted in deionised water at 1,800 rpm until an
obscuration rate of 10 % was obtained. Mie theory (Merkus, 2009) was applied considering a refractive index
of 1.48 and absorption of 0.001 for essential oils emulsion samples (EA3) and 1.48 and 0.01 for REO
samples. Three replications for formulation were made. The tenth, fiftieth and ninetieth percentile (D10, D50,
D90), has been calculated and indicated the percentage of particles with dimension inferior to the value
reported.
Flow curves were obtained using of a strain controlled rheometer (RFS II, Rheometric Inc. Piscataway, NY),
fitted with a coaxial cylinders. The viscosity versus shear rate was recorded at 25 °C. The shear rate ranged
between 0.04-103 s-1.
2.4. Characterization of the film
Microstructure of film samples was examined using an LEO EVO 40 scanning electron microscope (Zeiss,
Oberkochen, Germany). Film thickness was measured using a micrometer model HO62 with a sensitivity of ±2
µm (Metrocontrol Srl, Casoria, NA, Italy). The moisture content of samples was determined by the gravimetric
method. film samples were oven-dried at 105°C and accurately weighed at regular time intervals until constant
weight was reached. Three measurements were performed for each sample. The moisture content was
expressed as grams of water over grams of total weight (g/100g). Water vapour transmission rate (WVTR) of
films was evaluated by gravimetric test according to ASTM E96 (1993) by means of a Fisher or Payne
permeability Cup (Carlo Erba, Milan, Italy) at 25 °C (RH%= 0 – 85 %).
3. Results
3.1. Characterization of the FFD
Particle size of EA3 dispersion without and with polymer showed monomodal particle size distributions, and
CH-EA3 dispersion showed bigger particle dimension respect to EA3 emulsion. Whereas for REO essential oil
the particles dimension are reduced once they are dispersed into chitosan. Moreover, the particle size
distribution changes by bimodal in absence of chitosan to monomodal in its presence. The D10, D50, D90 values
are reported in Table 1.
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Table 1: Particle size dimension of CH-EA3 and CH-REO
Samples
(wt%) D10 (μm) D50 (μm) D90 (μm)
CH-EA3 mean value and standard deviation
0,5 1.92 (0.27) 3.02 (0.26) 4.87 (0.15)
1 1.99 (0.24) 3.25 (0.48) 5.83 (1.59)
1,5 1.82 (0.39) 2.85 (0.53) 4.55 (0.99)
EA3 1.20 (0.01) 2.75 (0.01) 4.68 (0.01)
CH-REO
0,5 0.120 (0.020) 0.263 (0.053) 0.566 (0.107)
1 0.128 (0.018) 0.295 (0.055) 0.672 (0.099)
1,5 0.130 (0.006) 0.283 (0.012) 0.596 (0.017)
REO 0.325 (0.022) 0.620 (0.040) 3.11 (0.711)
The typical flow curves for CH and CH-EOs FFD are shown in Figure. 1. Flow curves showed a shear-thinning
behaviour for all samples. At the contrary of what expected (Vargas et al., 2011; Floury et al., 2000; Otsubo et
al., 1994), as the oil content increases the viscosity decreases. The minor effect of concentrations of REO
samples on viscosity can be explained by the lower size of REO particles.
Figure 1: Viscosity (Pa s) of chitosan film added with EOs as function of shear rate (s-1)
3.2. Characterization of the film
Characteristic SEM images of cross section of the films are shown in Figure 2. The oil droplets were uniformly
distributed along the thickness but its sizes are not homogenous and it are bigger than in the FFD.
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Figure 2: SEM micrographs of 1 % Chitosan film at 0% EA3 (A), 0.5% oil (B), 1.5 % oil (C), and of 1 %
Chitosan film at 0.5 % REO (D), 1.5 % REO oil (E).
As reported in Table 2, the addition of EOs led to an increase of films thickness. The films made from CH-
REO, which showed a smaller particle sizes, were thinner than the others.
In general, equilibrium moisture content (EMC) at aw equal to 0.5 decreased as EO was incorporated into
chitosan-based film (Table 2). Chitosan-based films containing REO essential oil had less equilibrium moisture
content than those containing EA3 essential oils when the same level of essential oil was present (0.5, 1 %) in
each film. Lipid fraction caused to formation of covalent bonds between the functional groups of chitosan
chains, leading to a decrease in the availability of hydroxyl groups and limiting polysaccharide–water
interactions by hydrogen bonding and resulting in a decrease of moisture content value of edible films.
Chitosan film had a WVTR value of 2.3x10-3 g m-2 s-1 (Table 2). EA3 did not have a significant effect on the
WVTR of chitosan film. Different results have been obtained when REO has been added to chitosan film. The
WVTR of chitosan film increased to almost 50 % when REO has been added. The higher particle size of REO
in CH film by disrupting the compact structure of the polymer can enhance moisture passing through the films
and thereby increase the water vapour transmission rate values of the films. Moreover, as suggested by
Perdones et al. (2014), possible interactions of the EO compounds with CH, as also deduced from water
sorption data and SEM results, make the matrix more open to the transport of water molecules, despite the
theoretical increase of the hydrophobic nature of the matrix due to the presence of lipids. Anyway, the
differences between CH film with EA3 and REO EOs can be attributed to the different dimension of the oil
particle in the film. Thus, the good stability of the emulsion during casting is very important for the WVTR of
the film.
4. Conclusions
EOs concentration did not showed any effect on the particle size dimension in chitosan FFD. All the
dispersion CH-EA3 showed bigger particle dimension respect to EA3 emulsion, whereas for REO essential oil
the particles dimension are reduced once they are dispersed into chitosan. The oil had a significant effect of
viscosity of FFD that decreased as oil concentration increased. The structure of the CH film has been well
observed by SEM images: A continuous structure was observed for the CH film while the presence of EOs
caused discontinuities associated with the formation of two phases in the matrix: lipid droplets embedded in a
continuum polymer network. The oil droplets were uniformly distributed along the thickness but its sizes were
not homogenous and it were bigger than in the FFD. The addition of EOs led to an increase of films thickness
and a decreased of moisture content as the oil concentration increased. EA3 did not have a significant effect
28
on the WVTR of chitosan film, but the WVTR of chitosan film increase of almost 50 % when REO has been
added. Chitosan is a promising biopolymer for active food packaging and chitosan-EA3 film showed better
properties that chitosan-REO film.
Table 2: EMC (0.5 aw), WVTR, WVP and thickness of Chitosan film with different concentration of EO
Samples
(EOs wt %)
EMC
(gw/gdm)
Thickness
(μm)
WVTR x 10-3
(g m-2 s-1)
CH-EA3
0 22 (2) 46 (9) 2.6 (0.4)
0,5 15 (2) 63 (5) 2.19 (0.03)
1 13 (1) 86 (4) 2.04 (0.05)
1,5 10 (1) 97 (9) 2.28 (0.07)
CH-REO
0 22 (2) 46 (9) 2.6 (0.4)
0,5 12 (1) 53 (4) 5.6 (0.1)
1 10 (1) 65 (5) 5.2 (0.6)
1,5 9 (1) 69 (4) 4.3 (0.9)
Acknowledgements
This work was supported by VIVOPACK project (MISE, Industria 2015, Bando PII Made in Italy).
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