1058
Biomacromolecules 2008, 9, 1058–1063
Protection of Active Aroma Compound against Moisture and Oxygen by Encapsulation in Biopolymeric Emulsion-Based Edible Films Alicia Hambleton,† Fre´de´ric Debeaufort,*,†,‡ Laurent Beney,§ Thomas Karbowiak,4 and Andrée Voilley† ENSBANA-EMMA, Universite´ de Bourgogne, 1 esplanade Erasme, F-21000 Dijon, France, IUT-Gen´ie Biologique, Boulevard Dr. Petitjean, BP 17867, F-21078 Dijon, France, ENSBANA-GPMA, Universite´ de Bourgogne, 1 esplanade Erasme, F-21000 Dijon, France, and IUVV, Universite´ de Bourgogne, Rue Claude Ladrey BP 27877, 21078 Dijon Cedex, France Received November 8, 2007; Revised Manuscript Received December 21, 2007
Edible films made of ι-carrageenans display interesting advantages: good mechanical properties, stabilization of emulsions, and reduction of oxygen transfers. Moreover, the addition of lipids to ι-carrageenan-based films to form emulsified films decreases the transfer of water vapor and can be considered to encapsulate active molecules as flavors. The aim of this study was to better understand the influence of the composition and the structure of the carrageenan-based film matrices on its barrier properties and thus on its capacity to encapsulate and to protect active substances encapsulated. Granulometry, differential scanning calorimetry, and Fourier transform infrared spectroscopy characterizations of films with or without flavor and/or fat showed that the flavor compound modifies the film structure because of interactions with the ι-carrageenan chains. The study of the water vapor permeability (WVP), realized at 25 and 35 °C and for three relative humidity differentials (30–100%, 30–84%, 30–75%), showed that the flavor compound increases significantly the WVP, especially for the weaker gradients, but has no effect on the oxygen permeability. This study brings new understanding of the role of carrageenan as a film matrix and on its capacity to protect encapsulated flavors.
1. Introduction The conservation of food products requires the maintenance of their initial properties in protecting them from the environment and in limiting the transfers and losses of matter.1 To preserve the quality of the food product and to avoid its degradation, food packagings are used. Several works on the understanding of the mass transfer mechanisms in food product packaging (traditional and edible) have been published in recent years. Only edible packaging are effective to control the transfers within composite food.2 Edible packagings (films or coatings) have been defined as “a packaging as a film, a coating or a thin protective layer which is an integral part of the food and/or can be eaten with”. The oldest applications known were used in China since the 12th and 13th centuries to delay the dehydration of citrus.3 Edible films are obtained from hydrocolloids (protein, polysaccharides), which provide film cohesion, mechanical properties, and impermeability of aroma compounds and lipids4 but have low water barrier properties,2 often used for flavor encapsulation or for medicine tablets, and/or lipids, which have poor mechanical properties but greatly reduce water transfer. These films can be used to limit the superficial dehydration of humid and/or frozen food products and to reduce the moisture transfer between components of a multidomain food product.5 The concept of complex packaging, combining hydrocolloids and lipids, allows edible films with good mechanical and water * Author to whom correspondence should be addressed. E-mail:
[email protected]. † ENSBANA-EMMA, Universite´ de Bourgogne. ‡ IUT-Gen´ie Biologique. § ENSBANA-GPMA, Universite´ de Bourgogne. 4 IUVV, Universite´ de Bourgogne.
barrier properties. These edible films can either be bilayer or dried emulsion. Emulsified films improved water barrier properties, and their production is a single one-step process.6 ι-Carrageenan-based edible films have good mechanical characteristics, are emulsion stabilizers, and decrease oxygen transfer. The addition of lipids to form emulsified films decreases the water vapor transfer and could be used to encapsulate active molecules or aroma compounds.6 Interactions between the hydrocolloids and the lipids are going to determine the film’s stability and properties.7 Hydrocolloids usually form a homogeneous network in which the lipids are dispersed. Several authors have shown that lipids forming crystals such as waxes decrease water transfer. Anker et al.8 and Karbowiak et al.9 have shown that the water permeability decreases when the concentration of lipids is close to 30% and the fat globules have small diameter. Carrageenans are a class of sulfated polysaccharides, soluble in water, extracted from marine resources which are constituents of the cell of various red seaweeds (Rhodophyceae). The number and position of sulfate groups on the disaccharide repeated unit determine classification in three major types: kappa (κ), iota (ι), and lamda (λ). The κ-, ι-, and λ-carrageenans exhibit sulfate content of 20, 33, and 41% (w/w), respectively. They are widely used in the food industry to improve thickening and texture and to stabilize food products. Moreover they are a renewable resource and commercially available at a reasonable cost. ι-Carrageenan is composed of altering R(1,3)-D-galactose-4sulfate and β(1,4)-3,6-anhydro-D-galactose-2-sulfate. In aqueous solutions, ι-carrageenans produce thermoreversible gels (50–55 °C) forming a tridimensional network with double-helix chains, each pair of helixes being 13.9 Å laterally spaced, therefore a compact, dense, and organized film structure. ι-Carrageenan
10.1021/bm701230a CCC: $40.75 2008 American Chemical Society Published on Web 02/08/2008
Aroma Protection with Emulsion-Based Edible Films
gives hot soluble films contrary to κ-carrageenan and does not depend on the type of the cations present in the medium.10 The use of microcapsules (encapsulation of aroma compounds, vitamins, and additives) in hydrocolloid-based edible films confers to them the status of active films.11 Microencapsulation has been defined as “the technology of packaging solid, liquid and gaseous materials in small capsules that release their contents at controlled rates over prolonged periods of time”.12 The microencapsulated particle is formed of an active substance sourrounded by a coating,13 and its role is crucial in the aromatic industry. This encapsulation allows avoiding the release (or loss) of flavors, which are small organic molecules having high saturated vapor pressure. As the wax coatings are water repellent and not soluble in water, they are often recommended as a moisture barrier but also useful for flavor because of the capacity of aroma retention and slow release.14 The aim of this study was to better understand the influence of the composition and the structure of the film matrix on its barrier properties (water vapor and oxygen) and thus on its capacity to protect encapsulated active substances.
2. Experimental Section 2.1. Material. ι-Carrageenan was supplied by Degussa Texturant Systems (95% purity, DTS, Baupte, France) and constituted the film matrix. Anhydrous glycerol was supplied from Fluka (98% purity, Fluka Chemical, Germany) and used as a plasticizer in order to improve mechanical properties of carrageenan films. Fat used in this study, Grinsted Barrier System 2000 (GBS), supplied by Danisco (Bradbrand, Denmark) is an acetic acid ester of mono- and diglycerides blended with 20.2% w/w beeswax, having a melting point of 57 °C. Glycerol monostearate (GMS) employed as emulsifier was purchased from Prolabo (99% purity, Merck eurolab, France). Sodium dodecyl sulfate (SDS) (98% purity, Prolabo Merck eurolab, France) was used as surfactant for the characterization of film structure, owing to disperse aggregates of fat globules after film solubilization in water. Aroma compound n-hexanal (98% purity, Sigma-Aldrich, Germany) was used as an active molecule encapsulated. It has a melting point of 128 °C and a saturated vapor pressure of 14.203 Pa at 25 °C, and its solubility in water is 3.81 mg/mL. Two saturated salt solutions were used to fix water activity (aw): sodium chloride (Prolabo, France) giving a 0.75 aw at 25 °C and potassium chloride for a 0.84 aw. 2.2. Carrageenan-Based Film Preparation. A carrageenan-filmforming solution was prepared by dispersing 6 g of ι-carrageenan powder in 200 mL of distilled water at 65 °C for 15 min under magnetic stirring. A 1.8 g sample of glycerol was then added to the carrageenan solution under stirring. The aroma compound was presolubilized (10000 ppm) in 2.4 g of fat before being dispersed in the film-forming solution, then the mixture was homogeneized at 24000 rpm with an Ultra Turrax (T25 IKA) for 1 min. The film-forming solution was poured onto smooth poly(methyl methacrylate) (Plexiglas) plates. In order to obtain a film, the water was removed by drying in a ventilated climatic chamber (KBF 240 Binder, ODIL, France) for 8 h with temperature and relative humidity (RH) fixed at 30 ( 1 °C and 40 ( 2% RH, respectively. Film thickness after drying was about 50 µm and was measured with an electronic gauge (Multichek FE SODEXIM, France). The four types of film-forming solutions are presented in Table 1. 2.3. Characterization of Films. Before the characterization, all the film samples were conditioned at 25 ( 0.2 °C and 30 ( 1% of relative humidity (RH) for at least 7 days prior experiments in a ventilated climatic chamber (KBF 240 Binder, ODIL, France). 2.3.1. Laser Light Scattering Granulometry. This technique is based on measuring the scattered light intensity caused by the fat particles present within the sample. The diffraction angle is a function of the
Biomacromolecules, Vol. 9, No. 3, 2008 1059 Table 1. Types of Film-Forming Solutions Prepareda ι-carrageenans + glycerol woa:wof wa:wof woa:wf wa:wf
aroma compound (n-hexanal)
// // // //
fat (GBS)
// //
// //
a Key: woa, without aroma compound; wof, without fat; wa, with aroma compound; wf, with fat; //, tested.
fat particle size, shape, and wavelength of the incident light and is inversely proportional to particle size. This allows measurement of the distribution of the fat globules in the emulsions. The samples were prepared by dispersing 1 g of dried film in 50 mL of osmosed water at room temperature with moderate magnetic stirring, and measured using a Malvern Mastersizer Hydro 2000 SM (Malvern Instruments Ltd., Worcestershire, U.K.). To identify the incidence of fat globule aggregation, samples were also dispersed under moderate magnetic stirring in 50 mL of a 0.1% (w/w) SDS solution at room temperature.15 Reproducibility was tested by carrying out three measurements of each replicate. The mean diameter measured is the diameter of a hypothetical particle that represents the total number of particles in the samples. The volume-surface diameter (D3,2) represents the average size based on the specific surface per unit volume. These mean particle diameters were defined as
D3,2 )
∑ nidi3 ∑ nidi2
where ni is the number of droplets in each size class and di is the droplet diameter. The specific surface corresponds to the developed area of fat globules dispersed normalized by the volume of the lipid phase expressed as m2/mL. 2.3.2. Differential Scanning Calorimetry (DSC). This technique is based on measuring the energy necessary to establish a nearly zero temperature difference between the sample and an inert reference material. The energy required to preserve the same temperature is a measurement of enthalpy. Through the energy variation (endothermic if the energy its absorbed by the sample, exothermic if the energy its released by the sample) it is possible to study the phase transitions. The differential scanning calorimetry was performed using a PerkinElmer DSC-7 (Perkin-Elmer, France). An empty capsule was used as an inert reference. The heating and cooling rates were fixed at 10 °C/ min. The following temperature program ranged between 20 and 120 °C: (a) heating from 20 to 120 °C, (b) cooling down to 25 °C, (c) heating again to 120 °C, (d) and finally cooling down to 20 °C. Reproducibility was tested by carrying out two measurements for each replicate. 2.3.3. Fourier Transform Infrared Spectroscopy (FTIR). Infrared spectroscopy explores the interactions between the atoms and their vibrations. The vibrational frequencies are determined by the shape, by the mass of the atoms, and eventually by the associated vibronic coupling. The spectrum may be plotted, which shows at which wavelengths the sample absorbs in the infrared region, and allows an interpretation of which bonds are present. For Fourier transform infrared spectroscopy in transmission, a beam of infrared light is passed through the sample, and the amount of energy absorbed at each wavelength is recorded. The samples were cut with a surface of 6 cm2 and conditioned. With a Bruker Vector 22, the spectra of films were obtained by transmission whereas that of pure n-hexanal was measured by attenuated total reflectance (ATR). Reproducibility was tested by carrying out three measurement for each sample. 2.4. Mass Transfer Measurements. 2.4.1. Water Vapor Permeability (WVP). The WVP of films was measured gravimetrically according to Debeaufort et al.2 and Quezada et al.14 The method is
1060 Biomacromolecules, Vol. 9, No. 3, 2008
Hambleton et al.
Table 2. Mean Diameters (D3,2) and Specific Surfaces (Ss) of Fat Particules in Emulsified Films with and without Aroma Compounda water b
with aroma (wa:wf) without aroma (woa:wf)b
solution of SDS 2
D3,2 (µm)
Ss (m /mL)
D3,2 (µm)
Ss (m2/mL)
16.79 ( 0.47 a 11.85 ( 1.08 b
0.37 ( 0.09 d 0.50 ( 0.04 e
3.52 ( 0.42 c 10.26 ( 1.12 b
1.71 ( 0.22 f 0.58 ( 0.06 e
a Key: a, ..., f, the values with the same letter are not significantly different,
