Structure characterization by means of rheological and NMR experiments as a first necessary approach to study the l-(+)-ascorbic acid diffusion from pectin and pectin/alginate films to agar hydrogels that mimic food materials (original) (raw)
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Journal of Food Science and Technology, 2020
Films were prepared by casting 2% w/v apple pectin, 0.5% w/v low-acyl gellan and 2.2% w/v glycerol as plasticizer. Bioactive film (BF, films with 3912 International Units (IU) nisin/cm 2) and control films (CF, films without nisin) were elaborated. The objective was to analyze the release kinetics of nisin from films to a food model, to determine the period of film bioactivity and potential use as antimicrobial packaging. The release of nisin from BF to a food model was determined at 5°C and 30°C. The release kinetics of nisin was fitted to the analytical solution of the Fick's second law for an infinite plate. The diffusion coefficients of nisin (D) were 5.22 9 10-14 and 7.36 9 10-14 m 2 /s for 5°C and 30°C, respectively. Besides, both films were characterized in their mechanical properties and gas permeabilities [oxygen (PO 2) and water vapour permeability (WVP)]. The mechanical properties were reduced by the nisin incorporation, whereas PO 2 was increased, and no significant effect on WVP was observed.
Development of a High Methoxyl Pectin Edible Film for Retention of l -(+)-Ascorbic Acid
Journal of Agricultural and Food Chemistry, 2009
An edible film to carry L-(þ)-ascorbic acid (AA) was formulated for natural antioxidant food protection. Considering previous works where films based on the "rigid" structure of gellan (deacylated) or on a mixture of acylated-deacylated (more "disordered") gellan were used for network development, pectin was herein chosen by considering that the alternating presence of "disordered" (hairy) regions together with ordered (homogalacturonan) ones could sufficiently immobilize water for better AA retention and lower browning. High methoxyl pectin (HMP) was first investigated. AA stability and browning were studied during film storage at 33.3, 57.7, or 75.2% relative humidity (RH) and 25°C; their dependence on water mobility determined through 1 H NMR analysis as well as the correlation between browning and AA degradation were again found. Network characteristics and glycerol (plasticizer) interactions were analyzed through X-ray diffraction and Fourier transform infrared spectroscopy as well as through uniaxial tensile assay. From all results obtained, it was hypothesized that browning development in solidlike systems may be directly related to the water molecules more closely adsorbed on the hydroxyl-polymeric (active) surfaces. The HMP film microstructure produced the best immobilization of water molecules except at 75.2% RH, where it showed lower AA stability than acylated-deacylated gellan film. It is suggested that disordered regions of this pectin network may not be adequately counterbalanced by more transient junction zones of alternating hydrophilic (water) and hydrophobic (methyl ester) interactions, also disturbed by glycerol molecules, for accomplishing enough water immobilization in the whole network at 75.2% RH.
Gellan gum films as carriers of l-(+)-ascorbic acid
Food Research International, 2007
Edible gellan films were evaluated as carriers for stabilizing L-(+)-ascorbic acid (AA) for nutritional purposes and antioxidant effect on foods. AA retention during film casting (initial value), as well as stability and non-enzymic browning (NEB) development along film storage (25°C) at 33.3%, 54.7% or 75.2%-relative humidity (RH) were assessed. Initial AA retention was around 100%, and half-lives were 36, 26 and 11 days, respectively. AA destruction followed a pseudo-first order kinetics in gellan matrices. A water activity map was built for AA losses and NEB. AA and NEB kinetics were attributed to the restricted mobility of water molecules.
Food Chemistry, 2008
Mass transfers of various molecules in multiphasic food products lead to quality modification and thus require the use of edible films or coatings in-between the foodstuff. Consequently, it is important to assess the barrier properties and efficiencies of edible films as well as to determine the diffusivities of the migrants. Translational diffusion of a reference molecule such as fluorescein, determined by the fluorescence recovery after photobleaching (FRAP) method, displays a threshold of a critical water content inducing an increase of the molecular mobility, and demonstrates that multiple populations of a single molecular specie can be involved in different diffusion kinetics. Further investigations at a molecular scale through high resolution solid state nuclear magnetic resonance (NMR) enables to go deeper into the understanding of the interactions involved in such a system, in particular on the identification of the possible binding sites of the diffusant on the polymer and on the overall effect of interactions on the polymer organization. Therefore, the appraisal of transport properties in foods by means of reference molecules constitutes a relevant approach to use in combination with molecular investigation of physicochemical interactions with the diffusing substances.
Relation between structural and release properties in a polysaccharide gel system
Biophysical Chemistry, 2007
The potential utility of κ-carrageenan gels for preparing drug release devices is here shown. Structural properties of κ-carrageenan gels prepared with different salt composition and containing Ketoprofen sodium salt, as model drug, have been evaluated with static light scattering and rheological measurements. These properties have been correlated with release profiles in vitro at pH 5.5. Release properties from gelled matrices have been compared with those obtained by two commercial products containing the same drug. Results show that: i) in this system it is possible to easily control the gel texture by using different cationic concentration; ii) the kinetics of drug release by κ-carrageenan gels are dependent on the structural properties of matrices; iii) in the typical interval time used in classical local applications, all gel samples release the loaded drug almost completely, at difference with the commercial products. All these findings can provide useful suggestions for the realization of classical topical release systems.
Polymers
The release of a spin probe (nitroxide radical) from polymer films was studied by electron paramagnetic resonance (EPR). The films were fabricated from starch having different crystal structures (A-, B-, and C-types) and disordering degrees. Film morphology (analysis of the scanning electron microscopy (SEM)) depended on the presence of dopant (nitroxide radical) to a larger extent rather than on crystal structure ordering or polymorphic modification. The presence of nitroxide radical led to additional crystal structure disordering and reduced the crystallinity index from the X-ray diffraction (XRD) data. Polymeric films made of amorphized starch powder were able to undergo recrystallization (crystal structure rearrangement), which manifested itself as an increase in crystallinity index and phase transition of the A- and C-type crystal structures to the B-type one. It was demonstrated that nitroxide radical does not form an individual phase during film preparation. According to the ...
Bicomponent Solutions of Food Polysaccharide and Edible Films on Their Basis
Food and Nutrition Sciences, 2015
The study of the rheological properties of aqueous solutions of corn starch (CS) blends with sodium alginate (SA) and agar-agar (AA) as well as the physical and mechanical properties of bicomponent films on their basis has been carried out. The data show that adding of both polymers to starch solution causes an increase in viscosity which is higher in the case of SA. Activation energy for viscosity flow of solutions of CS blended with SA has minimum value at CS:SA ratio = 98:2. The above mentioned dependence is not typical for AA, as flow activation energy in this case raises steadily with the growth of AA content in the solution, like viscosity of the CS:AA. The extreme behavior of polymer blends with low content of one of the polymers is described in terms of mutual solubility or thermodynamic compatibility. There is a tendency that mechanical properties and water solubility increase with the increasing of SA and AA polymers in corn starch matrix. Obtained data evidence the benefits of bicomponent films production instead of starch-based films.
Food and Bioprocess Technology, 2011
L-(+)-Ascorbic acid (AA) was compartmentalized into a low methoxyl pectin (LMP) film in view of localized antioxidant activity at food interfaces. The AA hydrolysis was specifically studied in the present work in order to determine the ability of the formulated LMP film to stabilize AA. Hence, films were stored at controlled relative humidity (RH) in the absence of air. A commercial LMP characterized by a 40% degree of methylesterification (DM) was used. Since sucrose is normally added for its standardization, films were also made with the dialyzed LMP in order to determine the sucrose effect. Glycerol was used for plasticization. Kinetics of AA loss and subsequent browning development were determined, which are dependent on the RH. Considerable AA retention (t 1/2 =744, 727, and 185 days) was achieved at 33.3%, 57.7%, or 75.2% RH, respectively, at 25°C. Browning rate constants decreased in one order of magnitude with respect to kinetic constants determined from films previously developed with high methoxyl pectin (HMP; DM of 73%). Absence of sucrose in the LMP network only affected the browning kinetics at 75.2% RH. The glass transition temperature (T g) decreased with the increment of moisture content of the films and in a similar degree (T g ≈−90°C) to that observed for the HMP films, indicating the contribution of water to the network plasticization. However, water was more confined in the LMP network as inferred from the water availability determined by the 1 H-NMR and DSC. This was attributed to the water interaction at the Ca 2+ junction zones. Sucrose seemed to hinder the retention of water molecules by the polymeric network at 75.2% RH.