The effect of polymer/plasticiser ratio in film forming solutions on the properties of chitosan films

In this work physical-chemical properties of chitosan/ glycerol film forming solutions (FFS) and the resulting films were analysed. Solutions were prepared using different concentrations of plasticising agent (glycerol) and chitosan. Films were produced by solvent casting and equilibrated in a controlled atmosphere. FFS water activity and rheological behaviour were determined. Films water content, solubility, water vapour and oxygen permeabilities, thickness, and mechanical and thermal properties were determined. Fourier transform infrared (FTIR) spectroscopy was also used to study the chitosan/glycerol interactions. Results demonstrate that FFS chitosan concentration influenced solutions consistency coefficient and this was related with differences in films water retention and structure. Plasticiser addition led to an increase in films moisture content, solubility and water vapour permeability, water affinity and structural changes. Films thermo-mechanical properties are significantly affected by both chitosan and glycerol addition. FTIR experiments confirm these results. This work highlights the importance of glycerol and water plasticisation in films properties.This work was supported by National Funds from FCT - Fundacao para a Ciencia e a Tecnologia, through project PEst-OE/EQB/LA0016/2011.Authors Joana F. Fundo, Andrea C. Galvis-Sanchez and Mafalda A. C. Quintas acknowledge FCT for research grants SFRH/ BD / 62176 / 2009, SFRH/BPD/37890/2007 and SFRH / BPD / 41715 / 2007, respectively

Glass transitions and state diagram for freeze-dried pineapple

Glass transition temperature of freeze-dried pineapple conditioned by adsorption at various water activities at 25 degreesC was determined by differential scanning calorimetry (DSC). High moisture content samples corresponding to water activities higher than 0.9, obtained by liquid water addition, were also analysed. The DSC traces showed a well-visible shift in baseline at the glass transition temperature (T(g)). Besides, no ice formation was observed until water activity was equal to 0.75. For water activities lower than 0.88, the glass transition curve showed that T(g) decreased with increasing moisture content and the experimental data could be well-correlated by the Gordon-Taylor equation. For higher water activities, this curve exhibited a discontinuity, with suddenly increasing glass transition temperatures approaching a constant value that corresponds to the T(g) of the maximally freeze-concentrated amorphous matrix. The unfreezable water content was determined through melting enthalpy dependence on the sample moisture content

EFFECT OF THE CHEMICAL TREATMENT ON THE MECHANICAL PROPERTIES, WATER VAPOR PERMEABILITY AND SORPTION ISOTHERMS OF GELATIN-BASED FILMS

Proteins contain hydrophilic groups which can bind to the water molecule through hydrogen bridges resulting in water adsorption. The increase of the cross-linking degree can be an alternative to improve the cohesiveness force and functional properties of protein based films. Thus, the objective of this work was to evaluate the effect of chemical treatment of gelatin with formaldehyde and glyoxal on the mechanical properties, water vapor permeability and water vapor sorption characteristics of gelatin based films. Films were produced using gelatin, with and without chemical treatment. The chemical treatments caused a reduction on the water vapor permeability, however, only the formaldehyde allowed a significant increase on the tensile strength. The GAB and Halsey models could be used to model the sorption isotherms of films. It was observed that the increase of the temperature produced a decrease in water sorption and the chemical modifications caused a slight reduction on the monolayer moisture content.19SI22122

Development of films based on blends of Amaranthus cruentus flour and poly(vinyl alcohol)

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)The aim of this work was to develop biodegradable films based on blends of Amaranthus cruentus flour and poly(vinyl alcohol). Five different PVA types were tested. Blends with higher hydrolysis (HD) degree PVA were more resistant, showing greater tensile strength (TS) and puncture force (PF). However, the films with PVA with lower HD showed more flexibility, greater elongation at break (ELO) and greater puncture deformation (PD), with the exception of PVA 325. The latter was chosen due to it superior mechanical performance (TS = 10.2 MPa, ELO = 89.8%, PF = 9.4 N and PD = 16.3%). When films based on blends of amaranth flour and PVA 325 (10-50%) were evaluated, all mechanical properties were enhanced with increase in PVA 325 content. The solubility in water of the films made with PVA and amaranth flour decreased with increasing PVA content, reaching 44% of soluble matter for the 50% PVA film. The formation of hydrogen bonds between the blend components was confirmed by the FTIR spectra analysis. (C) 2008 Elsevier Ltd. All rights reserved.754592598Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Water sorption and glass transition of freeze-dried camu-camu (myrciaria dubia (HBK) Mc Vaugh) pulp

Differential scanning calorimetry (DSC) was used to determine phase transitions of freeze-dried camu-camu pulp in a wide range of moisture content. Samples were equilibrated at 25 degrees C over saturated salt solutions in order to obtain water activities (a(w)) between 0.11-0.90. Samples with a(w)> 0.90 were obtained by direct water addition. At the low and intermediate moisture content range, Gordon-Taylor model was able to predict the plasticizing effect of water. In samples, with a(w)> 0.90, the glass transition curve exhibited a discontinuity and T-g was practically constant (-58.8 degrees C), representing the glass transition temperature of the maximally concentrated phase(T-g ).84243543

Denaturation and the glass transition temperatures of myofibrillar proteins from osmotically dehydrated tilapia: Effect of sodium chloride and sucrose

The effect of sodium chloride and/or sucrose content on the denaturation (T-d) and the glass transition (T-g) temperatures of osmotically dehydrated tilapia fillets using binary or ternary solutions at 20 degrees C, was evaluated. DSC analyses revealed that myofibrillar proteins denaturation temperatures and enthalpies decreased with increase in muscle salt content. Sugar produced a stabilizing effect on denaturation of the fillets proteins. When ternary solutions were used, sucrose did not protect the proteins against the ionic stress produced by the salt. Tg was affected by the residual moisture content of the samples. Influence of NaCl was important at low water activity values. Sucrose content did not influence on T-g.10479180

Phase diagram for freeze-dried persimmon

Phase transitions of freeze-dried persimmon in a large range of moisture content were determined by differential scanning calorimetry (DSC). In order to study this transitions at low and intermediate moisture content domains, samples were conditioned by adsorption at various water activities (a(w) = 0.11-0.90) at 25 degreesC. For the high moisture content region, samples were obtained by water addition. At a(w) less than or equal to 0.75 two glass transitions were visible, with T(g) decreasing with increasing water activity due to water plasticizing effect. The first T(g) is due to the matrix formed by sugars and water, the second one, less visible and less plasticized by water, is probably due to macromolecules of the fruit pulp. At a(w) between 0.80 and 0.90 a devitrification peak appeared after T(g) and before T(m). At this moisture content range, the Gordon-Taylor model represented satisfactorily the matrix glass transition curve. At the higher moisture content range (a(w) > 0.90), the more visible phenomenon was the ice melting. T(g) appeared less visible because the enthalpy change involved in glass transition is practically negligible in comparison with the latent heat of melting. In the high moisture content domain T(g) remained practically constant around T(g)' (-56.6 degreesC). (C) 2001 Elsevier B.V. B.V. All rights reserved

Development of films based on quinoa (Chenopodium quinoa, Willdenow) starch

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)The filmogenic solutions (FS) composed of quinoa starch (4.0 g/100 mL) were prepared, containing various concentrations of glycerol (GC; 16.6-33.4g glycerol/100 g of quinoa starch, dry weight basis) and alkaline pH values (9.7-11.3). To obtain quinoa starch films (QSF), the FS were dried using different temperature/time combinations (T degrees C/h) denoted as the drying conditions (DC; 30 degrees C/20 h-50 C/5 h). The influence of GC, pH and DC on the mechanical properties and solubility of QSF was evaluated using response surface methodology (RSM). According to the statistical analyses, the optimized conditions corresponded to 21.2 g of glycerol/100 g of quinoa starch, a pH value of 10.7 and 36 degrees C/14 h for the DC. The films produced under these conditions exhibited superior mechanical properties (7.05 +/- 0.37 N puncture force, 7.56 +/- 0.95 MPa tensile strength, and 58.14% +/- 3.16 elongation at break), low solubility (15.9%), and optimal barrier properties (WVP of 0.204 +/- 0.012 g mm m(-2) h(-1) kPa(-1) and oxygen permeability of 4.34 +/- 1.03 cm(3) mu m m(-2) d(-1) kPa). (C) 2010 Elsevier Ltd. All rights reserved.814839848Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Effects of plasticizers and their concentrations on thermal and functional properties of gelatin-based films

The objective of this paper was to study the effect of plasticizers and their concentrations on the thermal and functional properties of gelatin-based films. Four polyols (glycerol-GLY, propylene glycol-PPG, di- DTG and ethylene glycol-ETG) were tested in five concentrations: 10, 15, 20, 25, and 30 g plasticizer/100 g of gelatin. For thermal analysis, the films were conditioned in desiccators with silica gel and for functional properties (mechanical properties, water vapor permeability, color and opacity) characterizations, the films were conditioned at 25 degrees C and 58% relative humidity. The results were discussed in terms of `plasticizer efficiency' meaning plasticizer content effect and also in terms of 'plasticizer effect' meaning the plasticizer type effect on the properties. In a general manner, the higher plasticizing effect on thermal properties was observed with the DTG, followed by PPG, GLY and ETG, principally with low plasticizer content. However, also in terms of thermal properties, the ETG presented the higher plasticizer efficiency followed by the GLY, DTG and PPG. Concerning the mechanical properties, the GLY showed the greater plasticizing effect and efficiency, but the plasticizing efficiency of DTG on the puncture deformation was also considerable. The mechanical resistance could be related with the glass transition temperature of films. It was not possible to observe the plasticizer effect on the water vapor permeability (WVP), but the DTG had shown greater plasticizer efficiency, followed by GLY and ETG, while a counter effect was observed with PPG. The effect of the type and concentration of plasticizer on the color and opacity of films could be considered as negligible. In conclusion, the more important plasticizer effect and efficiency were observed with DTG and ETG on the thermal properties, and with the GLY in terms of functional properties. The behavior of the mechanical properties of films could be explained by its glass transition temperature. (c) 2005 Elsevier Ltd. All rights reserved.19589990