Published on: Mar 3, 2016
Transcripts - Nanofilmes
Polysaccharide/Protein Nanomultilayer Coatings:
Construction, Characterization and Evaluation
of Their Effect on ‘Rocha’ Pear (Pyrus communis L.)
Bartolomeu G. de S. Medeiros & Ana C. Pinheiro &
José A. Teixeira & António A. Vicente &
Maria G. Carneiro-da-Cunha
Received: 15 November 2010 /Accepted: 28 December 2010 /Published online: 21 January 2011
# Springer Science+Business Media, LLC 2011
Abstract Nanolayered coatings of κ-carrageenan, a poly-
saccharide with good gas barrier properties, and lysozyme,
a protein with antimicrobial action, were in a first stage
assembled on aminolysed/charged polyethylene terephthal-
ate (PET) pieces, which acted as a support, by alternate
five-layer deposition. This was performed to allow the
characterization of the nanomultilayer system. PET ami-
nolysis was confirmed by Fourier transform infrared
spectroscopy and contact angle, and the subsequent layer
adsorption on aminolysed PET surface was confirmed by
absorbance, contact angle and SEM images. The water
vapour permeability and the oxygen permeability (O2P) of
the five layers were found to be 0.013±0.003×10−11
, respectively. The nano-
multilayer system was subsequently applied (without PET
support) directly on ‘Rocha’ (Pyrus communis L.) fresh-cut
pears and whole pears. Uncoated fresh-cut pears and whole
pears presented higher mass loss, higher total soluble solids
(TSS) and lower titratable acidity when compared with
coated fresh-cut pears and whole pears. Uncoated fresh-cut
pears also presented a darker colour. These results showed
that the nanolayered coating assembled on the fruits’
surface has a positive effect on fruit quality and contributed
to extend the shelf-life.
Keywords Nanocoatings . Layer-by-layer. κ-carrageenan .
Lysozyme . Shelf-life . Pear
Nanotechnology offers great potential to food packaging by
promising longer shelf-life, safer packaging and healthier
food (Neethirajan and Jayas 2011). There are several
advantages expected when using a nanotechnological
approach in the field of packaging materials, namely in
terms of the much lower amounts of functional ingredients
needed, the lesser impact in the sensory attributes of foods,
and improvements in both mechanical and gas and solutes’
Nanomultilayers of polyelectrolytes have been a highly
studied class of materials over the past decade due to their
potential interest on several fields of application. These
materials are obtained by alternating deposition of nano-
layers of polyelectrolytes on the surface of a solid substrate,
known as layer-by-layer technique. The interaction between
the successive layers is mainly due to the electrostatic
forces (Su and Li 2008) and is central to ensuring the
stability of the system.
These nanolayer systems are built aiming at a given set
of one or more functionalities. For this reason, the materials
selected for each nanolayer must have by themselves
specific properties (e.g. antioxidant, antimicrobial and
reduction of gas exchange) that justify its use or they must
B. G. d. S. Medeiros :A. C. Pinheiro :J. A. Teixeira :
A. A. Vicente
IBB-Institute for Biotechnology and Bioengineering,
Centre of Biological Engineering, Universidade do Minho,
Campus de Gualtar,
4710-057 Braga, Portugal
B. G. d. S. Medeiros :M. G. Carneiro-da-Cunha (*)
Department of Biochemistry/Keizo Asami Laboratory of
Immunopathology, Universidade Federal de Pernambuco,
Campus Universitário, s/n, Cidade Universitaria-CEP,
50.670-420, Recife, Pernambuco, Brazil
Food Bioprocess Technol (2012) 5:2435–2445
show such properties once combined in the nanostructure.
The assembly of the nanomultilayer systems can be
confirmed, e.g. by UV/VIS spectroscopy, contact angles
and scanning electron microscopy (SEM; Carneiro-da-
Cunha et al. 2010; Fu et al. 2005).
κ-carrageenan and lysozyme are two potential candidates
to be used in the assembly of nanolayered systems.
κ-carrageenan is a sulphated polyanionic polysaccharide
extracted from red algae and is formed by alternating (1-3)-
D-galactose 4-sulphate and α(1-4) 3,6-anhydro-D-galactose
units. Advantages of κ-carrageenan such as biocompatibility,
biodegradability and absence of toxicity have been pointed
out (Schoeler et al. 2006) and confirmed by its extensive
use in food, pharmaceutical and cosmetic industries.
κ-carrageenan has also shown good gas barrier and optical
properties (Ribeiro et al. 2007). The lysozyme is an
ellipsoidal protein extracted from chicken’s eggs, which
shows a good resistance to denaturation (Su et al. 1998) and
is well known for its antimicrobial properties (Su and Li
2008). Due to its physiological and functional properties,
lysozyme has been applied in medicine and in the food
industry (Benkerroum 2008).
The quality and the shelf-life of fruits and vegetables are
respectively impaired and reduced by several factors such
as water loss, enzymatic browning and deterioration of
texture. To minimize these alterations, many kinds of
packaging materials are being used by the food industry.
More recently, consumer concerns on environmental issues
have led to the search for biodegradable materials for food
packaging applications as replacement of the oil-based
polymers traditionally used (Rojas-Graü et al. 2009). In the
particular case of fruits, there have been research efforts in
the development of edible films and coatings because they
may provide not only the extension of shelf-life but may
also improve the organoleptic properties. In recent years,
edible coatings have been widely studied because of
evidence about their beneficial effects on fruits and
vegetables (Garcia et al. 2010). However, until now, the
potentialities of nanolayered films and coatings have not
been exploited at this level.
‘Rocha’ pear (Pyrus communis L.) is an exclusively
Portuguese certified pear cultivar commercialized world-
wide in countries like UK, Brazil, France, Ireland, Russia,
Poland, the Netherlands, Canada and Spain. Presently, it is
also very common to find it cut into pieces or sliced and
packaged in small sealed containers for convenience of
consumers, which are typically stored under refrigerated
The aim of this work was the construction and
characterization of a nanomultilayer coating system com-
posed of κ-carrageenan and lysozyme and the evaluation of
its effect on the shelf-life of fresh-cut ‘Rocha’ pear and
whole ‘Rocha’ pear.
Material and Methods
Films of polyethylene terephthalate (PET) were obtained from
Canson (Annonay Cedex, France). κ-carrageenan was
obtained from CPKelco (Genugel WR-78, Lille Skensved,
Denmark) and lysozyme was obtained from Sigma-Aldrich
(St. Louis, MO, USA). 1,6-Hexanediamine (98%) and
propanol (99.8%) were obtained from Sigma-Aldrich. Lactic
acid (90%) and hydrochloric acid were obtained from Merck
(Darmstadt, Germany). Ethanol (99.8%) and sodium hydrox-
ide were obtained from Riedel-de Haën (Seelze, Germany).
Semi-mature (titratable acidity=0.188±0.008%; total soluble
solids=10.60±0.30°Brix; L*=72.89±0.91, a=−2.14±0.45,
b=44.14±1.05) pears (cv. Rocha) were purchased at a local
retail store (Braga, Portugal).
Preparation of Nanolayered Coating Assembly
The nanolayered coating was initially built on an amino-
lysed/charged PET support film. Five alternate polysaccha-
ride and protein nanolayers were adsorbed onto the support
with the sequence Carra-Lyso-Carra-Lyso-Carra, where
Carra stands for κ-carrageenan and Lyso for lysozyme.
Aminolysis of Polyethylene Terephthalate Surface
PET films were cut into rectangular pieces of 0.8×5.0-cm
diameter and circular pieces of 5.0-cm diameter and were
aminolysed according to Fu et al. (2005) as concisely
follows. PET films were cleaned in ethanol/water (1:1, v/v)
solution for 3 h, followed by a thorough rinsing with
distilled water, and dried at 30 °C for 24 h. Afterwards, the
films were immersed into 0.06 gmL−1
propanol solution at 37 °C for 4 h, thoroughly washed with
distilled water to remove free 1,6-hexanediamine and
finally dried at 37 °C for 24 h. The aminolysed PET films
were treated with 0.1 M HCl solution for 3 h at room
temperature (20 °C), thoroughly washed with distilled
water, dried at 30 °C for 24 h and termed aminolyzed/
charged PET (A/C PET). This procedure was needed to
charge (positively) the otherwise neutral PET surface,
aiming at a stronger interaction with the negatively charged
Preparation of Polyelectrolyte Solutions
The κ-carrageenan (Carra) solution was prepared by
dissolving 0.2% (w/v) κ-carrageenan in distilled water
under agitation (using a magnetic stirrer) at 200 rpm for
2 h at 70 °C and after that for 22 h at 20 °C. The lysozyme
(Lyso) solution was also prepared dissolving 0.2% (w/v) of
2436 Food Bioprocess Technol (2012) 5:2435–2445
lysozyme in distilled water under agitation at 200 rpm for
2 h at 20 °C. The pH of κ-carrageenan and lysozyme
solutions was adjusted to pH 7.0 with a solution of 1 M
sodium hydroxide and to pH 3.8 with a 1 M lactic acid
Coating Procedure of A/C PET
A/C PET pieces were immersed into the Carra solution for
20 min and subsequently rinsed with deionized water with
the same pH (7.0). The samples were dried by hanging
them inside a chamber where nitrogen was gently flown in
order to speed up the process. This procedure was repeated
with Lyso solution as the polyelectrolyte (except that
rinsing was performed with deionized water at pH 3.8).
This process was repeated with the alternate deposition of a
total of five nanolayers. The obtained nanolayered coatings
on A/C PET films (A/C PET-Carra-Lyso-Carra-Lyso-Carra)
were finally maintained at 20±2 °C and 50±5% of relative
humidity (RH) provided by the laboratory air conditioning
system before analysis.
Characterization of Nanolayers
Fourier Transform Infrared Spectroscopy
To confirm PET aminolysis, Fourier transform infrared
spectroscopy (FTIR) analyses were carried out with a
Perkin Elmer 16 PC spectrometer (Perkin Elmer, Boston,
MA, USA) equipped with an ATR probe in the wave
number region of 600–4,000 cm−1
using 16 scans for each
The zeta potential of the polyelectrolyte solutions was
determined by dynamic light scattering (DLS; Zetasizer
Nano ZS, Malvern Instruments, UK). Each sample was
analysed in a folded capillary cell. Three true replicates
were conducted, with three readings for each of them.
To follow the multilayer assembly, UV/VIS analyses were
carried out using a UV/VIS spectrophotometer (Jasco 560,
Germany). The absorbance was measured at 296 nm on the
dried films. Three replications of the measurements were taken.
Contact Angle Analysis
Using the sessile drop method (Newman and Kwok 1999),
the contact angles of original PET, A/C PET and the
subsequent nanolayers’ surface were measured in a face
contact angle meter (OCA 20, Dataphysics, Germany). A
2-μL droplet of ultrapure water was placed on the horizontal
surface with a 500-μL syringe (Hamilton, Switzerland) with
a needle of 0.75-mm diameter. Measurements were made at
0, 15 and 30 s, and for each type of surface, three film
samples were used. For each film sample, ten contact angle
measurements were carried out at 20±0.3 °C.
Thickness of Coated A/C PET and of the Nanolayers
The thickness of A/C PET was measured with a digital
micrometer (Mitutoyo, Japan) and confirmed by SEM, and
the thickness of each of the five nanolayers was measured by
SEM. As a result of the immersion into polyelectrolyte
solutions, both sides of the A/C PET pieces were coated with
the same set of five layers. Therefore, for the determination of
water vapour and oxygen permeability, it was necessary to
multiply the thickness value of each of the five layers by 2.
Water Vapour Permeability
Based on the ASTM E96-92 method (Casariego et al.
2009), the measurements were carried out gravimetrically.
The films were sealed at the top of a permeation cell
containing 55 mL of distilled water (100% RH, vapour
pressure of 2,337 Pa at 20 °C). The supports were placed in
a desiccator at 20 °C and 0% of RH containing silica. The
cells were weighed during 10 h at time intervals of 2 h. The
slope of mass loss versus time was achieved by linear
regression. Three replicates were obtained for each film and
water vapour permeability (WVP) was determined by the
following equation (Cooksey et al. 1999):
where subscripts a, b and t correspond respectively to: A/C
PET support (a), nanolayers (Carra-Lyso-Carra-Lyso-Carra)
(b) and to the resulting A/C PET support coated with
nanolayers (A/C PET-Carra-Lyso-Carra-Lyso-Carra) (t). L
corresponds to the thickness of the films (in mm) and WVP
to the water vapour permeability (in g m−1
Oxygen permeability (O2P) was determined based on
ASTM (2002) method. The A/C PET (used as a reference)
and the coated A/C PET (A/C PET-Carra-Lyso-Carra-Lyso-
Carra) films were sealed between two chambers, each one
with two channels. In the lower chamber, the O2 was
supplied at a constant flow rate controlled by a gas flow
meter (JW Scientific, ADM 2000, USA) to keep its
pressure constant in the compartment. The other chamber
Food Bioprocess Technol (2012) 5:2435–2445 2437
was purged by a stream of nitrogen, also at controlled
flow. The nitrogen acted as a carrier for the O2. The flow
leaving this chamber was connected to an O2 sensor
(Mettler Toledo, Switzerland) which measured the O2
concentration in that flow online. The flows of the two
chambers were connected to a manometer to ensure the
equality of pressures (both at 1 atm) between both
compartments. As the O2 was carried continuously by
the nitrogen flow, it was considered that the partial
pressure of O2 in the upper compartment is null; therefore,
ΔP is equal to 1 atm. Three replicates were obtained for
each sample, and the O2P for the five nanolayers (Carra-
Lyso-Carra-Lyso-Carra) was determined by the following
equation (Cooksey et al. 1999)
where a, b and t correspond respectively to: the A/C PET
support (a), nanolayers (Carra-Lyso-Carra-Lyso-Carra) (b)
and to the resulting coated A/C PET support (A/C PET-
Carra-Lyso-Carra-Lyso-Carra) (t). L corresponds to the
thickness of the films (in mm) and O2P to the oxygen
permeability (in g m−1
The surface morphology of the studied material was
examined using a scanning electron microscope (Nova
130 NanoSEM 200, the Netherlands) with an accelerating
voltage from 10 to 15 kV. Before analysis, all samples were
mounted on aluminium stubs using carbon adhesive tape
and sputter-coated with gold (thickness of about 10 nm).
Whole and Fresh-Cut Pears Coating and Shelf-Life Evaluation
Twelve pears (cv. Rocha) with uniform size (between 65
and 70 mm), uniform colour, absence of physical damage
and apparent absence of fungal infection were washed with
abundant tap water, left to dry and randomly divided into
four groups (two control groups and two test groups) of
three pears each. The pears of one control group and of one
test group were peeled off, lengthwise sliced in eight pieces
and termed fresh-cut pears (CP). The pears of the remaining
two groups were termed whole pears (WP). Coating
solutions (Carra and Lyso) were applied on test groups of
CP and WP in a similar way as done on the A/C PET
surface. The immersion time into each polyelectrolyte
solution was 5 and 15 min for CP and WP test groups,
respectively. These immersion times were optimized in
preliminary tests. The immersion times for the two control
groups of CP and WP was the same (5 and 15 min,
respectively), but distilled water with the respective pH of
Carra (7.0) and Lyso (3.8) solutions was used instead of the
polyelectrolyte solutions used with test groups. After that, all
four groups were placed in open plastic boxes and stored at 4 °
C and 93% RH (in a temperature- and humidity-controlled
room), and the parameters mass loss, total soluble solids,
titratable acidity and colour were measured in triplicate over
the experimental period of time (7, 14, 21, and 28 days for
CP and 0, 1, 2, 3, 5 and 7 days for WP, respectively).
All fresh-cut pears and whole pears were individually
weighed at the beginning of the experiment and over the
experimental storage time with an analytical balance
(METTLER AE200, Mettler Toledo, Germany). The mass
loss (W) was expressed as:
W %ð Þ ¼
mi À mt
Â 100 ð3Þ
where mi is the initial mass and mt the mass at a certain time t.
TSS, TA and Colour Measurement
Juice samples of CP and of WP were obtained using a
domestic juice extractor (Moulinex Mx type 664, Spain)
and collected in sterilized jars in aseptic conditions. The
total soluble solids (TSS) were determined on this juice
using a refractometer (SCHMIDT+HAENSCH, GmbH
Co., series no. 4008).
Titratable acidity was determined by titrating 10 g of pear
flesh liquefied with 100 mL of distilled water (Becken max
mix II, Spain) with 0.1 N NaOH solution (Instituto Adolfo
Lutz 1985). The results were expressed as per cent (w/w).
The surface colour was measured throughout the
experimental storage period using a colorimeter (CR 400;
Minolta, Japan) and evaluated through the changes of L*
values. Three readings were made on randomly chosen
reading positions for each sample.
The statistical analyses were carried out using analysis of
variance, Tukey mean comparison test (p0.05) and linear
regression analysis (SigmaStat, trial version, 2003, USA).
Results and Discussion
Aminolysis on PET Support
FTIR analyses were carried out to confirm the presence of
amino groups on the A/C PET surface. Figure 1 shows two
differences between the A/C PET and the original PET,
2438 Food Bioprocess Technol (2012) 5:2435–2445
located at 1,647 and 1,558 cm−1
, which confirm that the
Original PET was successfully aminolysed. Similar results
were reported by Fu et al. (2005), and working with the
same aminolysed PET, Carneiro-da-Cunha et al. (2010)
confirmed the presence of a nitrogen peak through energy-
Aminolysed PET samples were purposely treated with
HCl to charge positively the support surface. The first
negatively charged layer (κ-carrageenan) will interact with
the support surface by electrostatic forces and the subse-
quent lysozyme layer (positively charged) will interact with
the κ-carrageenan’s oppositely charged surface. In order to
ensure that the interaction between the polyelectrolyte
solutions and the A/C PET surface would be sufficiently
strong, the pH values of polyelectrolyte solutions were
previously adjusted to obtain the adequate charges. The pH
values were determined based on κ-carrageenan’s dissoci-
ation constant (pKa=2.0; Jones et al. 2010) and lysozyme’s
isoelectric point (pI=11; Lvov et al. 1995).
The electrostatic properties were confirmed by the
determination of the solutions’ zeta potential by DLS. The
lowest zeta potential value of −60.53±0.15 mV was found
for κ-carrageenan at pH 7.0. The same pH value was used
by Schoeler et al. (2006) when preparing ultrathin films
with one cationic poly(allylamine hydrochloride) and two
anionic polysaccharides, λ- and ι-carrageenan. These
ultrathin films were compared with the films assembled at
pH 10.0, and the authors found that the thickness of the
films assembled at pH 7.0 was lower than the films
assembled at pH 10.0. The highest zeta potential value of
+25.67±2.27 mV was found for lysozyme at pH 3.8. A
similar pH value was used by Lvov et al. (1995).
The charge of some polysaccharides may be associated with
the number of sulphate groups in their structure. This is
possibly the case of κ-carrageenan (Reynaers 2003), putting it
in position to be a good candidate for electrostatic interactions.
The layers’ deposition was followed measuring the increase in
absorbance at 296 nm, the wavelength at which the highest
absorbance peak was found. The increase in absorbance due
to the layer’s deposition (Fig. 2a) is in agreement with other
works where deposition through layer-by-layer technique
was characterized by UV/VIS spectroscopy (Carneiro-da-
Cunha et al. 2010; Fu et al. 2005). These results confirm the
successful assembly of the nanolayered film.
The values of contact angles observed on the original PET,
A/C PET support and on the five successive layers added
are shown in Fig. 2b. The global trend is not affected by the
time of observation after drop application. After 15 and
Fig. 1 Raw data of FTIR spectra of A/C PET (black line) and of
original PET (grey line). Circles show the differences corresponding
to the amide I and II groups on aminolysed PET surface
Fig. 2 a UV/VIS spectroscopy analysis at 296 nm of A/C PET
support and after the addition of each of the five successive layers
containing κ-carrageenan (Carra) and lysozyme (Lyso). Each data
point is the average of nine determinations; error bars show the
standard deviation. b Contact angle measured on original PET, A/C
PET support and on each of the five successive layers containing κ-
carrageenan (Carra) and lysozyme (Lyso) after 0, 15 and 30 s of drop
application. Each data point is the average of 30 measurements; error
bars show the standard deviation
Food Bioprocess Technol (2012) 5:2435–2445 2439
30 s, the results are similar; therefore, 15 s was taken as the
The hydrophobicity of original PET was confirmed by
the contact angle of 78.55±1.7°, and the value of the
contact angle of the A/C PET of 73.93±1.72° is lower than
the original PET, being in agreement with Carneiro-da-
Cunha et al. (2010). From this behaviour, one can deduce
that the aminolysis of PET surface was well performed,
corroborating the result from the FTIR analyses.
The magnitude of contact angles illustrated in Fig. 2b shows
the evolution of the alternate deposition of κ-carrageenan and
lysozyme layers, suggesting that the film was progressively
assembled by alternate deposition of the polyelectrolytes. The
angles with small magnitude were observed for the layers
assembled at pH 7.0 and with great magnitude obtained for
the layers assembled at pH 3.8. Small contact angles
(κ-carrageenan layer) define a hydrophilic surface and great
contact angles (lysozyme layer) characterize a hydrophobic
surface. The hydrophobic character of lysozyme layers was
confirmed in our work with the contact angles ranging from
61.85±6.63° to 57.48±4.82° in comparison with the contact
angles of κ-carrageenan layers (from 15.47±3.65° to 34.20±
5.27°). It is possible that segments of chemical structure
of an underlying layer penetrate into the surface of the
outmost layer, when they differ from each other in
thickness and one is positively charged and the other
negatively charged, thus changing its hydrophobicity or
hydrophilicity (Yoo et al. 1998). The most wettable
surfaces present lower values of contact angles, and on
the contrary, the hydrophobic surfaces show higher values.
The wettability of a surface depends on the nature of the
outermost layer and not only on the initial or previous
substrate. The interpenetration of the layers may influence
this property (Yoo et al. 1998), especially at the nanoscale.
The wettability of a surface can be significantly affected
by changes of pH since they can affect the structure itself.
Scanning Electron Microscopy
The SEM images were captured to observe the A/C PET
surface and the A/C PET support with all five layers already
adsorbed (Fig. 3). Figure 3a, b shows the A/C PET before
layer deposition and the outmost surface of the five layers
already adsorbed on A/C PET, respectively. Figure 3c shows
the five layers of the two polyelectrolytes, κ-carrageenan and
lysozyme. These images confirm the construction of the
nanolayered film on the PET surface.
Water Vapour Permeability
Shelf-life and food quality can be improved by edible films
and coatings (Cerqueira et al. 2009; Souza et al. 2010),
providing a good and selective barrier to the moisture
transfer, oxygen uptake, lipid oxidation, losses of volatile
aromas and flavours. On the other hand, films or coatings
made of polysaccharides or proteins are reported to provide
high gas barrier properties (Miller and Krochta 1997).
Using Eq. 1 and the A/C PET thickness value of
0.103 mm, measured with a micrometer and confirmed by
SEM, and the five layers thickness value of 469.2 nm,
Fig. 3 Scanning electron microscopy images of surface morphology
of A/C PET (a), outmost surface of the five layers (b) and cross-
section of the five nanolayers (c) (scale bar, 1 μm)
2440 Food Bioprocess Technol (2012) 5:2435–2445
obtained by SEM, the WVP values determined for A/C
PET and for the five nanolayers were 1.51±0.07×10−11
, respectively. The WVP
value obtained for the multilayer film was much lower than
those that could be expected for edible films composed of
carrageenan and lysozyme. The reported values in literature
for carrageenan (±50 μm of thickness) and lysozyme
(±70 μm of thickness) films are 232.0 ± 9.9 ×
(Hambleton et al. 2008) and 192.0±
(Park et al. 2004), respectively.
The good water vapour permeability of the five nanolayers
may be explained based on the hydrophobic amino acid
chains of lysozyme that may contribute to the decrease of
the hydrophilicity of the κ-carrageenan/lysozyme nano-
layers and on interactions that are established between
adjacent κ-carrageenan and lysozyme layers that increase
the tortuosity of the material, thus decreasing its effective
permeability to the water molecules (Jang et al. 2008).
Since the WVP value of the five nanolayers was lower
than that found for A/C PET, it can be concluded that the
nanolayers of Carra and Lyso provide a good water barrier.
The WVP value found in this work is of the same order of
magnitude for the five nanolayers composed of alginate and
) found by Carneiro-
da-Cunha et al. (2010). Oms-Oliu et al. (2008) applied
different polysaccharide-based coatings on fresh-cut pieces
of pears P. communis L. (cv Flor de Invierno) and observed
a substantial increase of water vapour transport resistance.
Another parameter to take into account in the shelf-life of fruits
and vegetables is oxygen permeability (O2P). A reduction of
the oxygen flow rate promotes a reduction of oxidation. O2P
of edible films and coatings depend on several factors such as
the integrity of the film, the ratio between crystalline and
amorphous zones, the hydrophilic/hydrophobic ratio, and the
chain mobility (Miller and Krochta 1997).
Using Eq. 2 and the thickness values previously deter-
mined, an O2P value of 2.5±0.03×10−14
obtained for A/C PET and a lower O2P value of 0.1±0.01×
was obtained for the five nanolayers,
meaning that the nanolayers exhibit a significant barrier
against O2 flow. Conventional edible films composed of
κ-carrageenan exhibited significantly higher values of O2P:
(Ribeiro et al. 2007) and
(Hambleton et al. 2008).
These good results for the multilayer nanofilm may again be
explained based on the interactions that are established
between adjacent κ-carrageenan and lysozyme layers. In
fact, polysaccharide- and protein-based coatings or films are
usually characterized, among other things, for having low
oxygen permeability values (Lima et al. 2010).
Evaluation of Pear Shelf-Life
Taking into account the economical importance of pears in
natura and, more recently, the appearance of an important
market of semi-processed fresh-cut fruits, nanolayers of
κ-carrageenan/lysozyme were applied on the pears’ surface
(fresh-cut pears and whole pears) aiming at knowing how
this coating may extend their shelf-life. For such a purpose,
physicochemical analyses were carried out and the results
of coated CP and WP were compared with those obtained
with uncoated (control) fruits.
The modified atmosphere created by edible coatings
(between the coating and the fruit’s surface) protects the
fruits from the moment it is applied until they reach the
final consumer (Ribeiro et al. 2007; Souza et al. 2010). The
mass loss occurs manly due to water loss since the other
components that can be lost (e.g. aromas, flavours and
gaseous products of respiration) are practically undetectable
in terms of mass (Olivas and Barbosa-Cánovas 2005).
For that very reason, the mass loss of coated fresh-cut
pears and coated whole pears with κ-carrageenan/lysozyme
nanolayers was followed over the experimental storage
period to determine how effective this coating was as a
barrier against water loss.
The fruits’ skin is a good barrier against chemical and
physical damage and prevents microbial growth (Martín-
Belloso et al. 2006). Lysozyme was incorporated in the
nanolayer structure due to its well-known antimicrobial
properties (Gemili et al. 2009; Mecitoğlu et al. 2006) and to
protect mainly the fresh-cut pears against microbial action.
Over an experimental storage period of 7 days (Fig. 4a)
and 45 days (Fig. 4b) of CP and of WP, respectively, there
are statistically significant differences (p0.05) between
uncoated fresh-cut pears and whole pears (control groups)
and coated fresh-cut pears and whole pears (test groups).
On the other hand, the magnitude of mass loss between the
fresh-cut pears and the whole pears is not the same, as can
be observed comparing Fig. 4a, b.
At the end of the seventh day of storage (Fig. 4a), the
mass loss of fresh-cut pears was found to be 13.3±1.3%
and 3.5±0.6% for uncoated (control group) and coated (test
group) fruits, respectively, which demonstrates the effec-
tiveness of the nanolayers as a water loss barrier.
The same behaviour was found for whole pears
(Fig. 4b). On the 45th day of storage, uncoated (control
group) and coated (test group) fruits presented a mass loss
of 1.4±0.19% and 0.8±0.02%, respectively. These differ-
ences can be mostly related with the water vapour barrier
provided by the coating, leading to a lower water loss and,
consequently, to a lower mass loss.
Food Bioprocess Technol (2012) 5:2435–2445 2441
It is known that the skin of the fruits protects against
water loss and pathogen invasion and provides partial
barrier to gases; therefore, the mass loss observed after
45 days of storage for whole pears is much lower than that
for fresh-cut pears after 7 days of storage.
Total Soluble Solids
Total soluble solids (TSS) represent water-soluble substan-
ces like sugars, acids, vitamin C and some pectins (Oliveira
et al. 1999), and since sugar corresponds to 90% of TSS,
this parameter is used as an indicator of total sugar content
and maturation stage of the fruit.
At the beginning of the experimental period (day 0), both
fresh-cut pears (Fig. 5a) and whole pears (Fig. 5b) had a TSS
with a °Brix value of similar level (between 10.20±0.45 and
10.86±0.06°Brix) and without statistically significant differ-
ences (p0.05); these values are in agreement with those
found by Nicolaï et al. (2008) (between 10.4 and 15.4°Brix),
also for pears. The TSS content in fruits increases during the
maturation phase due to metabolic processes. When water loss
occurs, there is also an increase of TSS essentially due to the
increase of the concentration of sugar in the fruits (Bhattarai
and Gautam 2006). Both for uncoated fresh-cut pears (Fig. 5a)
and for uncoated whole pears (Fig. 5b), TSS increased until
the 5th and 28th days, respectively, and diminished at the end
of the experimental period to similar levels (p0.05). This
decrease is probably related to the slowing down of
polysaccharide degradation reactions and the corresponding
consumption of the resulting sugars by the living tissue of
the fruits. Although with a similar profile, TSS values
remained lower for both coated fresh-cut pears and coated
whole pears throughout the respective experimental period.
At the end of the experiment (days 7 and 45, respectively),
the coated fresh-cut pears exhibited a TSS value significantly
lower (p0.05) than the control pears; however, for whole
pears, a statistically significant difference (p0.05) was not
found between uncoated and coated groups.
The generally lower values of TSS for the coated fruits
are a direct result of the barrier to water vapour mass
transfer imposed by the coating. Also, the decreased O2 and
CO2 transfer rate due to the presence of the coating will
impose a reduction in the metabolic activity of the fruits,
thus leading to a further slowdown of polysaccharide
degradation reactions and, therefore, to a lower TSS value
for the coated fruits. In any case, the values of O2
permeability obtained here are sufficiently high to ensure
that no danger of anaerobiosis is at stake.
Titratable acidity is another parameter that changes with the
maturity phase due to organic acids that are usually
consumed during the fruits’ shelf-life.
Fig. 5 Total soluble solids (TSS) of fresh-cut pears over 7 days (a)
and of whole pears over 45 days (b). Each data point is the average of
three determinations; error bars show the standard deviation
Fig. 4 Mass loss of fresh-cut pear over 7 days (a) and of whole pears
over 45 days (b). Each data point is the average of three
determinations and the error bars show the standard deviation
2442 Food Bioprocess Technol (2012) 5:2435–2445
The final organic acid content of the fruit is determined
by the net balance of acid synthesis, degradation, utilization
and compartmentalization (Mϋller et al. 1996).
At the beginning of the experimental period, TA values
of both fresh-cut pears (Fig. 6a) and whole pears (Fig. 6b)
were around 0.20% and decreased until the end of both
experimental periods (7th and 45th days, respectively).
Silva et al. (2010) obtained values within the range from
0.28% to 0.14% for ‘Rocha’ pears at different stages of
maturation during storage at −0.5 °C for 250 days.
Although the four groups of samples showed a decrease
over the experimental period, the test groups exhibited
significantly higher (p0.05) TA values than the control.
The decrease of acidity with maturation during cold storage
of ‘Rocha’ pear was characterized by Galvis-Sánchez et al.
(2004). Kingston (1993) determined the maturity indices for
apples and pears, concluding that as the maturation goes on,
there is a decrease of TA until it stabilizes at the end.
According to Toğrul and Arslan (2004), the decrease in
titratable acidity may be due to the breakup of acids present
in fruit to sugars with respiration during storage.
The lower reduction of TA values of coated CP and coated
WP suggests that the maturation of test groups was retarded
by the application of the nanolayer coating as compared to
control (uncoated) groups due to reduced gas (O2 and CO2)
exchange owing to the presence of the coating.
Darkening of fruits is the result of oxidation processes that
occur at advanced maturation stages, and the changes of
colour can be evaluated through the L* parameter that
The fruit’s skin is a natural protection against environmen-
tal attacks. During the experimental period of 45 days,
uncoated and coated whole pears did not present significant
differences of L*. Uncoated whole pears presented a
reduction of 8.0%, whilst coated whole pears showed a
reduction of 4.6% for this parameter. However, the L* values
of uncoated fresh-cut pears decreased throughout the 7 days
of the experimental period: From an initial value of 66.3±
2.4, a final value of 43.7±6.1 was attained. Coated fresh-cut
pears exhibited a completely different behaviour, and no
significant changes in L* (p0.05) were observed during the
experimental period (L* varied from 70.0±1.2 at days 0 to
65.9±5.3 at day 7). Similar results were obtained by Abreu
et al. (2003) for ‘Rocha’ fresh-cut pears pretreated at 40 °C
for 105 min and subsequently stored at 2 °C during 7 days.
Lower values of L* are a consequence of darkening,
which occurs mainly due to the increase of respiration and
enzymatic processes, causing quality loss of the fruit. When
pears are cut, the tissue cells are broken and enzymes, such
as polyphenol oxidase, are liberated and brought into
contact with their substrates, causing browning (Olivas et
Fig. 6 Titratable acidity (TA) of fresh-cut pears over 7 days (a) and of
whole pears over 45 days (b). Each data point is the average of three
determinations; error bars show the standard deviation
Fig. 7 Images of uncoated (a) and coated (b) fresh-cut pears on the
seventh day of storage
Food Bioprocess Technol (2012) 5:2435–2445 2443
al. 2007). The reduction of the oxidation process may have
occurred in the present work in coated fresh-cut pears and
coated whole pears. Uncoated fresh-cut pears, as exhibited
in the Fig. 7a, presented a brownish colour in comparison
with coated fresh-cut pears (Fig. 7b).
The work presented here has established the proof-of-concept
of the use of nanolayered edible coatings for food preserva-
tion. Such coatings have adequate mass transfer properties
(the WVP), and the O2P of the five nanolayers was found to
respectively) and adequate surface properties (measured in
terms of contact angles) to be used as packaging materials
for ‘Rocha’ pears.
As a result of this, uncoated fresh-cut pears and whole pears
presented higher mass loss, higher TSS and lower TA when
compared with coated fresh-cut pears and whole pears.
Uncoated fresh-cut pears also showed a darker colour. These
findings suggest that the nanolayered coating of κ-carrageenan
and lysozyme assembled on the pears’ surface had a significant
positive effect on the quality of the fruits and therefore hold
potential for their shelf-life extension.
Acknowledgments Author Bartolomeu G. de S. Medeiros was a
recipient of a scholarship from the project Isac (Isac Mundus
Cooperation, European Union) and is also a recipient of a scholarship
from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
(Capes, Brazil). Author A.C. Pinheiro is recipient of a fellowship
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