10.1080@02652040802175805

Prévia do material em texto

Journal of Microencapsulation, March 2009; 26(2): 97–103
Ascorbic acid retaining using a new calcium alginate-Capsul based edible film
DANIELE DA SILVA BASTOS1, KA´TIA GOMES DE LIMA ARAU´JO2, & MARIA HELENA
MIGUEZ DA ROCHA LEA˜O1
1Universidade Federal do Rio de Janeiro, Centro de Tecnologia, Bloco A, Instituto de Quı´mica, Ilha do Funda˜o, Cidade
Universita´ria, Rio de Janeiro, Brazil and 2Faculdade de Farma´cia, Departamento de Bromatologia, Universidade Federal
Fluminense, Laborato´rio de Bromatologia, Santa Rosa, Nitero´i, Rio de Janeiro, Brazil
(Received 15 March 2008; accepted 30 April 2008)
Abstract
This work aimed to produce a new calcium alginate-Capsul edible film with antioxidant incorporated in matrix. The vitaminic
stability was evaluated in the films during their storage under different conditions for 140 days. The films were characterized with
respect to their mechanical properties and surface morphology. The results indicated a 25.6% of vitamin C incorporation in
matrix during the film preparation. The films stored under refrigeration in the dark did not show a decrease in the vitaminic
retention. The films stored under room temperature in the dark and in the bright/dark cycles exhibited significant decreases in the
vitamin retaining from the 84th and 70th days, respectively. The vitamin C addition significantly decreased the tensile strength in
the new pellicle. The results of the microscopy revealed a cohesive matrix in the new edible films. These results support the
utilization of the new pellicle to protect ingredients, although more studies are necessary.
Keywords: Edible film, alginate, modified starch, ascorbic acid
Introduction
Edible films are pellicles obtained by natural and
synthetic substances which can be added in food
systems to control the water and fat migration, the
oxygen and carbon dioxide permeability, to maintain
the food sensory characteristics beyond to carry some
food additives such as antioxidants, anti-microbials,
colourants, flavours, fortified nutrients and spices
(Kester and Fennema 1986). Therefore, the edible
films or coatings are alternatives to increase the shelf-
life of a large variety of products, including fruits and
vegetables, protecting them from the deterioration
(Hardenburg 1997).
Alginate is of interest as a potential biopolymer film
or coating component because of its unique colloidal
properties, which include thickening, stabilizing, sus-
pending, film forming, gel producing and emulsion
stabilizing. It is a hydrophilic colloidal carbohydrate
extracted with dilute alkali from various species of
brown seaweeds (Phaeophyceae). In molecular terms,
it is a family of unbranched binary copolymers of
(1-4)-linked �-D-mannuronic acid and �-L-guluronic
acid residues of widely varying composition and
sequential structure (Santacruz et al. 2002). Alginic
acid is the only polysaccharide which naturally contains
carboxyl groups in each constituent residue and
possesses various abilities for functional materials.
The most useful and unique property of alginates is
their ability to react with polyvalent metal cations,
specifically calcium ions, to produce strong gels or
insoluble polymers (Rhim 2004). Considering the
potential amount available as a natural resource and
reproducibility of alginic acid, it is meaningful to
develop as a source for the biodegradable or edible
films. Although edible films prepared from hydrocol-
loids like alginate form strong films, they exhibit poor
water resistance because of their hydrophilic nature.
The ability of alginate to make strong and insoluble gels
with calcium ions can be utilized to improve such
properties of alginate films (Clark and Ross-Murph
1987; Llanes et al. 2000; Zactiti and Kieckbusch 2006).
Correspondence: Daniele da Silva Bastos, Universidade Federal do Rio de Janeiro, Centro de Tecnologia, Bloco A, Instituto de Quı´mica, Ilha do Funda˜o, Cidade
Universita´ria, Cep: 21949-900 Rio de Janeiro, RJ, Brazil. Tel.: þ55-21-2562-7351. E-mail: daninutr@ig.com.br
ISSN 0265–2048 print/ISSN 1464–5246 online � 2009 Informa UK Ltd.
DOI: 10.1080/02652040802175805
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Capsul is a modified amid developed by the National
Starch and Chemical Corporation from the US. This
modification consists of adding a lipophylic component
(octenyl-succinate) which increases the emulsion
stability in the formulations (King et al. 1976; Finotelli
2002). Furthermore, it is a polymer of a large application
in controlled release systems since it can contribute to
obtaining less porous materials. Of this form, Capsul is
widely used for a better entrapment and slow release of
many bioactive substances in filmogenic matrices and
microcapsules (Arburto et al. 1998).
Ascorbic acid is added extensively to many types of
food products for two quite different purposes: as a
vitamin supplement to reinforce dietary intake of this
vitamin and as an antioxidant to protect the sensory
and nutritive quality of the food itself. The vitamin role
is impaired by its high reactivity and, hence, poor
stability in solution, which can result in heavy losses
during food processing and storage (Kirby et al. 1991).
The vitamin C can degrade rapidly in food systems by
different mechanisms: in the presence of oxygen,
free-radical mediated oxidative processes produce a
series of reactive intermediates; in the presence of
transition metal ions, especially iron and copper; at
neutral pH and above and in the presence of ascorbate
oxidase and ascorbate peroxidase. Losses can also ocurr
by anaerobic mechanisms in strongly acid conditions, in
the presence of other substances, including fructose and
its derivates and indirectly amino acids. The latter route
can also result in the formation of coloured pigments
and offensive, carbonyl-derived odour (Gregory 1996;
Pierucci et al. 2004).
This is the first time that a mixture composed by
calcium alginate-Capsul was made to obtain an edible
film. This combination becomes sufficiently interesting
since the calcium alginate forms a reticulate polymer
and the Capsul may contribute to close the pores of this
polymeric matrix beyond allowing the retention of
many hydrophilic components in this material, like
ascorbic acid, because of its hydrophilic and hydro-
phobic nature.
The aim of this work was to produce a new edible
film with antioxidant incorporated in the matrix; to
evaluate the ascorbic acid stability in the films during
their storage at different conditions for 140 days and to
characterize the edible films with respect to their
mechanical properties and surface morphology.
Materials and methods
Materials
2,6-Diclorophenolindophenol (Sigma� (Germany)); Acetic
Acid (Reagen� (Brazil)); Ascorbic Acid (Basf� (Brazil));
Metaphosphoric acid (Merck� (Germany)); Sodium algi-
nate (ISP Alginates Inc. Keltone� LV (USA)); Capsul
(National Starch� (USA)); Sodium Citrate (H & R�
(USA)); Calcium chloride (Vetec� (Brazil)).
Methods
Production of edible film. Sodium alginate (0.3 g) and
Capsul (0.4 g) were separately dissolved in 5mL of
MilliQ water, with soft movements to avoid air bubbles
retention and, then, the solutions were mixed to obtain
a film-forming solution composed of sodium alginate
(3% w/v) and Capsul (4% w/v) (Dong et al. 2006).
Immediately, an antioxidant (vitamin C) was mixed
(20% Total Solids) in the film-forming solution. To
obtain the edible film, �2mL of film-forming solution
was cast onto an acrylic plate and, then, spread with an
extensor. Upon the edible film, 20mL of calcium
chloride solution (0.3M), containingthe same amount
of ascorbic acid present in the film-forming solution
(�140mg), was spilled on the newly-obtained film. The
film and the calcium chloride solution were conditioned
in a closed and dark protected packing during 10min.
After this period, the calcium chloride solution was
thrown up and the film dried with a paper to remove
the superficial moisture. These operations have
happened at 22�C. Then, the films were dried in an
air circulation heater (FANEM�; 330 model) at 38�C
for 15min and conditioned in closed and dark protected
packings for posterior analysis, which required a total
of 34 edible films.
Evaluation of the ascorbic acid stability in the edible
films. To evaluate the vitamin stability retained in
filmogenic matrix, calcium alginate–Capsul-based
edible films were conditioned in closed packings and
stored under different conditions: refrigeration (10�C)
in the dark (FRD) (control sample); room temperature
(27�C) in the dark (FRTD) (test sample) and room
temperature (27�C) in bright/dark cycles (12 h/12 h)
(FRTC) (test sample).
About 0.01 g of the edible film was rotary shaken
with 3mL of sodium citrate (0.15M), for 5min, to open
the filmogenic matrix and expose the vitamin C. The
vitamin analysis retained in the films was carried out for
�5months during 0, 7, 14, 28, 42, 56, 70, 84, 98, 112,
126 and 140 storage days. The vitamin contents were
fixed according to the Instituto Adolfo Lutz (1985)
analytical standards. The results were expressed by a
percentage of vitamin C retention. For each storage
condition, the experiment was carried out in duplicate
and the analysis was in triplicate.
Mechanical properties. Tensile strength (TS) and
percentage elongation at break (E) were evaluated
using a Universal Tensile Rehearsal Machine (EMIC
DL–10.000�) operated according to ASTM (1995)
D-882 standard method. The films were cut into
25� 100mm strips and held parallel with an initial
grip separation of 50mm. The cross-head speed was set
at 1mmmin�1. The tensile strength (Pa) was calculated
by dividing the maximum force at break (read from
machine or chart) by the cross-sectional area of film
98 D. da. S. Bastos et al.
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(Newton m�2¼Pascal). Percentage elongation at break
was calculated on the basis of length extended at the
moment of rupture as compared to the original length
of the film. The mechanical properties were checked in
calcium alginate–Capsul-based edible films with (test
film) and without vitamin C (control film) incorporated
on the matrix. TS and E, for each type of film, were
carried out in seven film samples to obtain a medium
for each measurement.
Scanning electronic microscopy. The calcium alginate–
Capsul-based edible films were kept in desiccators
containing silica gel (25�C) for a period of 7 days and
then fractured and fixed in stubs using copper
conducting adhesive tape. The samples were then
coated with gold and observed under a scanning
electron microscope (SEM) model JSM-6460LV
(JEOL�) at 10 kV according to Fakhouri and Grosso
(2003). For the surface morphology observation, newly-
obtained edible films (time 0), with and without vitamin
C addition, and calcium alginate–Capsul-based edible
films stored for 140 days under different conditions with
vitamin were utilized.
Statistics analysis
Statistical analyses were carried out using the Graph
Pad Prism Program (Version 2.0) and the differences
between the means were determined with the Tukey
multiple test (p5 0.05).
Results and discussion
Production of edible film
The calcium alginate and Capsul concentrations and the
producing method allowed the acquisition of a uniform
and flexible edible film with an antioxidant incorporated
in matrix. Visually, the edible films presented milky
colouration, probably explained by the Capsul addition
in the film-forming solution. The use of the extensor
made it possible to obtain calcium alginate–Capsul-
based films with 500 mm thickness. The film drying in air
circulation heater was necessary for its handling during
the vitamin C stability study. However, this step
modified the film texture through its water loss.
Evaluation of the ascorbic acid stability
in the edible films
Figure 1 presents the vitamin C retention percentage in
edible films stored under different conditions for
140 days (FRD, FRTD and FRTC).
Ascorbic acid was chosen as an antioxidant model
and thus to test the calcium alginate–Capsul film
efficiency to protect this unstable substance from the
adverse conditions and loss by different mechanisms.
According to Figure 1, it was verified that the
producing method allowed 25.6% of vitamin C incor-
poration in filmogenic matrix (time 0) with 74.4% of
vitamin being set free for the calcium chloride solution.
This initial vitamin C retaining did not differ among the
FRD, FRTD and FRTC. The control sample (FRD) did
not show significant decrease in the vitamin C retained
during the whole studied period and at the 140th storage
day this film exhibited 23.5% of vitamin C retention.
The FRTD showed a significant vitaminic reduction,
when compared to its initial average (time 0), at the 84th
storage day with 17.5% of vitamin C retention in this
moment and this significant reduction maintaining until
the 140th storage day. At this time, the FRTD exhibited
14% of vitamin C retention. In the FRTC, a significant
vitaminic reduction was verified, in relation to its initial
Figure 1. Vitamin C retention percentage in edible films stored at different conditions for 140 days (average� SD). FRD:
Edible film stored at refrigeration in the dark. FRTD: Edible film stored at room temperature in the dark. FRTC: Edible film
stored at room temperature in the bright/dark cycles. * Difference significantly average in comparison with the average at 0
storage day. ** Vitamin C retention percentage average on the filmogenic matrix connected with the film forming solution
vitaminic contents.
Ascorbic acid retaining using a new calcium alginate-Capsul based edible film 99
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retention (time 0), at the 70th storage day, when the
average retention was 16%. After this time, as well as
the FRTD, this significant reduction remained until the
140th storage. In this moment, the FRTC exhibited
12.4% of vitamin C retention.
Kirby et al. (1991) encapsulated ascorbic acid inside
liposomes and verified �15% of vitamin C within the
liposomes stored at room temperature in the dark, after
50 days. When the liposomes were stored for 50 days at
4�C, in the dark, it was observed that more than 50% of
vitamins survived. Compared with the results of the
present work, the active vitamin C percentage in the
films stored for 140 days at room temperature was
�52% while the active vitamin C percentage present in
the film stored at refrigeration for 56 days was 88%. So,
in both storage conditions, the vitamin C was more
stable when incorporated in calcium alginate (3%)–
Capsul (4%)-based edible films than within liposomes.
The average vitamin retention percentages of the
FRD, FRTD and FRTC had been also compared
between itself at each studied period. So, a statistics
difference was detected between the FRD and FRTC at
the 42th and between the FRD and FRTD at the 98th
storage day, with these differences remaining constant
until the end of the storageperiod (140 days), except at
the 56� storage day when no difference was observed
between the FRD and FRTC and at the 112� storage day
between the FRD and FRTD. It is important to point
out that at no moment was there a significant difference
between the vitamin C retentions of the FRTD and
FRTCwhen their averages were compared between itself
at each time. Probably, the Capsul was sufficiently
skillful, such as the plated paper, in keeping safe vitamin
C of the light action. So, the losses observed in the
FRTD and FRTC may be attributed to the room
temperature since the modified starch must have
contributed to diminishing the filmogenic matrix poros-
ity and its permeability to the light and humidity.
Mechanical properties
Figures 2(a) and (b) show, respectively, the results
obtained for the Tensile strength (TS) and Percentage
elongation at break (E) in edible films, with and
without vitamin C incorporated on the matrix (test
and control films, respectively), submitted to mechan-
ical tests. Tensile strength is a measure of film strength,
whereas elongation at break is a measure of film stretch
ability prior to breakage. Both properties are important
characteristics for packaging material.
As observed in Figure 2, it is verified that the average
TS of the test and control films were 100.4MPa and
179.4MPa, respectively. Incorporation of ascorbic acid
markedly affected calcium alginate–Capsul-based
edible film TS. The vitaminic addition, on the
filmogenic matrix, proportionated a TS reduction of
44%. Thus, this suggests that the vitaminic component
probably interfered with ionic interactions facilitated by
Ca ions, which help in forming a network. On the other
hand, the average E obtained in test and control
calcium alginate–Capsul edible films (Figure 3) did not
significantly differ, measuring 1.7% and 1.9%,
respectively.
Fakhouri and Grosso (2003) obtained an average TS
and E in simple films of gelatin (10%) and triacetin
(5–15%), varying from 88.3–99.7MPa and from 6.2–
8.9%, respectively. The composite films of gelatin
(10%) and fatty acids—lauric acid, palmitic acid and
stearic acid—(5–50%) showed a TS significant reduc-
tion according to the acids concentration increase. The
average TS was �29.9MPa in composite films of
gelatin (10%) and fatty acids (50%). On the other
hand, the E did not modify with the fatty acid addition
which average varied from 7.5–10.7%.
Rhim (2004) evaluated the mechanical properties of
calcium alginate films (2% w/v) obtained by direct
addition of CaCl2 (0.04, 0.08 and 0.12 g CaCl2/4 g
alginate) into film-making solution (mixing films) and
the immersion of alginate films into CaCl2 solutions
(1, 2, 3 and 5 g CaCl2/100mL water distilled)
(immersion films). It was verified that the average
TS and E were �40.5MPa and 10.5%, respectively,
in the mixing films. The immersion films showed a
significant TS increase (77.5MPa average) while its
average E showed an opposite effect (4.7% average).
Comparing with the present work, it is observed that
calcium alginate–Capsul film TS presented superior
Figure 2. (a) Average tensile strength (TS) obtained in test and control films; averages with different letters indicate significant
difference (p5 0.05); (b) Average percentage elongation at break (E) obtained in test and control films.
100 D. da. S. Bastos et al.
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values when compared with the immersion films. This
fact may be due to the glycerin use in the immersion
films (1%), the superior sodium alginate concentra-
tion utilized in the calcium alginate–Capsul films and
to the larger contact time between the calcium
alginate–Capsul film and CaCl2 solution.
Pranoto et al. (2005) analysed the TS and E in
calcium alginate-based edible films (1% w/v) added of
glycerol (0.4% v/v) and garlic oil at various concentra-
tions (0, 0.1, 0.2, 0.3 and 0.4% v/v). The garlic oil
addition markedly affected the TS, with values
decreased from 66.1 to 38.7MPa while the anti-
microbial concentration increased (0 and 0.4%, respec-
tively). On the other hand, the garlic oil addition
increases the E (4 to 4.8%) when the antimicrobial was
used at 0 and 0.3%, respectively. The 0.4% concentra-
tion of garlic oil significantly decrease this measure
(2.73%). Probably the garlic oil presence on the alginate
matrix interfered with ionic interactions and, conse-
quently, in forming a network. During film prepara-
tion, the garlic oil was incorporated before providing
Caþþ ions. Therefore, the higher amounts of garlic oil
incorporated caused a greater reduction of tensile
strength.
So, it can be affirmed that although the vitamin C
addition has decreased the mechanical resistance of
calcium alginate–Capsul edible film, its average TS
showed significantly superior when compared to some
TS described in the literature. Probably, the total solids
content and the producing method used in this work
beyond the lack of plasticizers like glycerol or triacetin
contributed to the obtainment of an edible film with
strong mechanical characteristics which include high TS
and minor E. Rhim (2004) and Pranoto et al. (2005)
affirm that edible films made by hydrocolloids, like
alginates, form very strong and brittle films although
they show poor barrier properties against water
molecules.
Scanning electron microscopy
According to Figure 3, which represents the surface
micrographs for the newly-obtained edible films
without and with vitaminic incorporation
(Figures 3a and b, respectively), a cohesive and
compact surface arrangement was observed in both
films with some irregularities which include mounts
and valleys for the newly-obtained film without
vitamin C and depressions and fissures for the
newly-obtained film with vitamin C. These cohesions
may be due to the ionic and electrostatic interactions,
between filmogenic components, which probably
contributed to the matrix reinforcement and can
explain the high results for the TS in these films when
compared to others in literature. The effect of vitamin
C addition could not be seen in these micrographs.
The irregularities present in the newly-obtained
calcium alginate–Capsul films may be a consequence
of the producing method which included an extensor
and acrylic plate use, which may possess microscopic
irregularities and also a consequence of the film
handling during its developing.
As observed in Figure 4, which represents the
surface micrograph for the calcium alginate–Capsul
film stored during 140 days at refrigeration in the
dark, it is verified that the filmogenic matrix
continues to be cohesive and compact. Therefore, it
is suggested that the filmogenic matrix was not
(b)(a)
Figure 3. (a) Scanning electron micrograph (SEM) of newly-obtained calcium alginate (3%)–Capsul (4%) edible film without
vitamin C addition; (b) SEM of newly-obtained calcium alginate (3%)–Capsul (4%) edible film with vitamin C addition.
Figure 4. SEM of calcium alginate (3%)–Capsul (4%) edible
film stored (140 days) at refrigeration in the dark.
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modified by the storage period at refrigeration in the
dark.
In the micrograph for the filmsstored under room
temperature in the dark and in bright/dark cycles
(Figures 5a and b, respectively), it is ascertained that
the filmogenic matrices still continues to be cohesive but
heterogeneous, mainly in Figure 5a which can be
related to the channels formed in the film frame when
the water migration was facilitated during the film
drying. It is important to accentuate that these surface
irregularities may alter the filmogenic structure and, so,
its functional properties like barrier properties (Souza
et al. 2004).
Conclusions
The new calcium alginate (3% w/v)–Capsul (4% w/v)
edible films were shown to be uniform, flexible and with
milky colouration. This film was able to retain 25.6%
of vitamin C in matrix during its development. The
FRD did not show a significant decrease in the vitamin
C retained during the studied period and the FRTD
and FRTC exhibited significant decreases in the
vitamin C retained, when compared to their initial
retentions (time 0), from the 84th and 70th storage
days, respectively.
These results show that the antioxidant model was
stable for nearly 5 months when incorporated in a
calcium alginate–Capsul-based matrix stored at
refrigeration in the dark and when incorporated in
films at room temperature it was maintained for nearly
3 months, thus suggesting excellent film efficiency to
protect this antioxidant mainly of the adverse condi-
tions of the light.
The vitamin C addition proportionated a significant
mechanical resistance reduction of calcium alginate–
Capsul edible film, although its TS showed a superior
measure when compared to other films in the literature.
The scanning electron microscopy revealed a contin-
uous filmogenic matrix with some irregularities, prob-
ably decurrent of its producing method.
Thus, the new calcium alginate–Capsul-based edible
film can be potentialy used by the food industry as a
pellicle to involve and increase the shelf-life of a variety
of products, although more studies about this edible
film are necessary.
Acknowledgement
We are grateful to CAPES for the financial support.
Declaration of interest: The authors report no conflicts
of interest. The authors alone are responsible for the
content and writing of the paper.
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(a) (b)
Figure 5. (a) SEM of calcium alginate (3%)–Capsul (4%) edible film stored (140 days) at room temperature in the dark;
(b) SEM of calcium alginate (3%)–Capsul (4%) edible film stored (140 days) at room temperature in bright/dark cycles.
102 D. da. S. Bastos et al.
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