Ana Mônica Quinta Barbosa Habitante

Characterization of some functional properties of edible films based on muscle proteins of Nile Tilapia

Recently, it was observed that the myofibrillar as well as the sarcoplasmatic proteins obtained from fish are capable to form films. The objectives of this work was to elaborate and to characterize the water vapor permeability (WVP), the color and opacity, the mechanical properties, and the viscoelastic properties of films made with muscle proteins of Nile Tilapia (Oreochromis niloticus). The proteins were obtained by finely grinding the fish muscle, followed by separation of the connective tissue and freeze-drying after liquid nitrogen freezing. The films were prepared from filmogenic solutions (FS) by the casting technique, as follows: 1 g of protein/100 g of FS, 15 ‐ 65 g of glycerin/100 g of protein, pH ¼ 2.7 (acetic acid) and FS thermal treatment of 40, 65 and 90 8C/30 min. The WVP was determined by a gravimetric method, and the color and opacity of the films were determined with a colorimeter (model MiniScan XE, HunterLab). The mechanical properties, force and elongation at puncture, were determined with the help of a texturometer (model TA.XT2i, TA Instruments), at 25 8C. The viscoelastic properties were determined by dynamic mechanical analysis, with a DMA2980 apparatus (TA Instruments) operating in the frequency scanning mode, at 30 8C, with the viscoelastic properties being calculated at 1 Hz. It was observed that the WVP increased with the concentration of glycerin ðCgÞ as expected and that an increase in temperature of FS thermal treatment also caused an increase in the WVP of the films. The color and the opacity of the films decreased with Cg; and were proportional to the thermal treatment temperature of the FS. In general, it was observed that increasing the Cg provoked linear reduction of puncture force and an increase on the elongation at break, due to its plasticizer effect. It was also observed that increasing the Cg caused depression on both the storage and loss moduli values but increased the tan d: The presence of sarcoplasmatic proteins did not affect the quality of functional properties of films based on muscle proteins of Nile Tilapia. q 2003 Elsevier Science Ltd. All rights reserved.

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 (aw=0.11–0.90) at 25°C. For the high moisture content region, samples were obtained by water addition. At aw≤0.75 two glass transitions were visible, with Tg decreasing with increasing water activity due to water plasticizing effect. The first Tg 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 aw between 0.80 and 0.90 a devitrification peak appeared after Tg and before Tm. At this moisture content range, the Gordon–Taylor model represented satisfactorily the matrix glass transition curve. At the higher moisture content range (aw>0.90), the more visible phenomenon was the ice melting. Tg 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 Tg remained practically constant around Tg′ (−56.6°C).

Influência do grau de hidrólise do poli(vinil álcool) nas propriedades físicas de filmes à base de blendas de gelatina e poli(vinil álcool) plastificados com glicerol

The aim of this work was to study the effect of the Degree of Hydrolysis (DH) of poly(vinyl alcohol) (PVA) on the properties of films based on blends of pigskin gelatin and PVA with two DH. The films were made with solutions with 2 g macromolecules/100 g solution, containing 23.1 g PVA.100 g-1 macromolecules and 25 g glycerol/100 g macromolecules. The mechanical and thermal properties, color, opacity, moisture and solubility of the films were studied, as well as Fourier Transform Infrared (FTIR) spectra. The solutions were analyzed by dynamic rheometry. The films containing PVA with lower DH were more hygroscopic and more soluble. However, the type of PVA did not affect color, but affected the opacity and the gloss of the films. The PVA of higher DH produced films which were more resistant to puncture and stress, and the PVA of lower DH produced films which were more deformable upon stress, although less deformable upon puncture. The DH of PVA did not affect the first scan glass transition temperature of the films, but did affect this property in the second scan. The results from the FTIR analysis were in conformity with the results of the thermal analysis. The viscoelastic properties of the solutions determined by rheometry were not affected by the DH of PVA, possibly because the solutions studied were diluted.

Propriedades de filmes comestíveis produzidos com diferentes concentrações de plastificantes e de proteínas do músculo de tilápia-do-nilo

The use of sarcoplasmic proteins with myofibrilar proteins might be an interesting alternative in edible films technology, because it would eliminate the muscle washing step during protein extraction. The aim of this work was to study physical properties of films based on muscle proteins, constituted by myofibrilar and sarcoplasmic proteins, from Nile Tilapia (Oreochromis niloticus), as influenced by the protein concentration and the plasticizer content of the filmogenic solution. The films were made from filmogenic solutions with 1 or 2 g of proteins/100 g of solution and 15 to 65 g of glycerin/100 g of proteins, with the pH maintained at 2.7 (acetic acid), thermal treated at 90° C for 30 min, and dehydrated at 30° C for about 24 hours. Films made from solutions with higher protein concentration were more colored, more resistant to puncture and strain, with higher elongation capacity under strain and visibly more opaque, although significant difference was not found for this last property. The viscoelastic properties and the puncture deformation were not influenced by protein concentration. All properties were affected by the plasticizer content.

Análise térmica da carne de coelhos

O objetivo deste trabalho foi avaliar o efeito da adicao de condimentos na carne de coelho, sobre a estabilidade termica de suas proteinas miofibrilares. Retalhos de 24 musculos Longissimus dorsis foram moidos e misturados, para a obtencao de um lote homogeneo. Foram adicionados, em aliquotas dessa carne: 1,0; 2,0 ou 3,0% de sal; 2,5; 5,0 ou 7,5% de sacarose e 1,5; 3,0 ou 4,5% de acido acetico 3% em solucao aquosa, e uma mistura perfazendo 3% de sal, 5% de sacarose e 3% da mesma solucao de acido acetico. Apos homogeneizacao manual, as amostras foram mantidas em repouso sob refrigeracao, por 30 minutos. Aliquotas da ordem de 10mg foram usadas para analise termica e o restante, para analises de pH, proteinas e umidade. As analises termicas foram realizadas em um calorimetro diferencial de varredura DSC-TA2010, a 10oC/min, entre 0 e 100oC. As curvas de DSC da carne pura apresentaram endotermas nas temperaturas de (Td) 58,4(0,7oC (miosina) e 78,2(0,2oC (actina), envolvendo entalpia (DHd) de 17,5J/g de proteinas. O sal e o acido acetico desestabilizaram as proteinas, provocando reducao da Td da miosina e actina, contrariamente a sacarose, que apresentou efeito estabilizante. A adicao da mistura dos condimentos desestabilizou as proteinas miofibrilares. Apenas o acido, adicionado acima de 1,5%, provocou desnaturacao das proteinas.