Paulo José do Amaral Sobral

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.

Glass transitions for freeze-dried and air-dried tomato

Univ Estadual Paulista, Dept Engn & Tecnol Alimentos, BR-15054000 Sao Jose do Rio Preto, SP, Brazil

Glass Transition Study of Nile Tilapia Myofibrillar Protein Films Plasticized by Glycerin and Water

Studies on glass transition of myofibrillar proteins based edible films are scarce. This work aimed to determine the Tg of edible films from Nile Tilapia myofibrillar proteins as a function of water content. Films with 30 or 70 g of glycerol/100 g of protein and several water content, were analyzed with a DSC TA 2010. Samples conditioned at water activity between 0.11 and 0.75, clearly showed one glass transition at low temperatures (<223 K), and another transition, less visible, above 273 K. DSC curves of samples conditioned ataw=0.84, also showed an endothermic peak below 273 K. These results rendered evidence of phase separation within edible films.

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).

Natural Additives in Bioactive Edible Films and Coatings: Functionality and Applications in Foods

Incorporation of natural additives to active packaging systems or biopolymer-based edible films can modify the film structure and, as a result, modify their functionality and application to foods. This paper reviews the effect of the incorporation of natural additives from plant extracts or their isolated active compounds and vitamins on the functionality of edible films and the application of these films to foods. The final functionality of edible films is related to their bioactive properties (such as antioxidant, antimicrobial, and antibrowning activities) and functional properties (such as barrier to oxygen, carbon dioxide, and UV–vis light); water vapor permeability; tensile stress; elongation at break; and physical properties (such as opacity and color). Several categories of natural antioxidants found in plant, spices, and herbs (organic acids, plant natural extracts, and plant essential oils) have been incorporated into edible films and coatings, resulting in an improvement of the bioactive properties of the films. However, a wide range of plant natural sources with bioactive properties has not yet been characterized with respect to their ability to be applied directly on foods and used to develop active packaging or biopolymer-based edible films for preserving and adding value to foods. In addition, in vivo studies of the use of bioactive films to preserve the quality, shelf life, and nutritional value of foods remain limited.

Preparo e caracterização de proteínas miofibrilares de tilápia-do-nilo para elaboração de biofilmes

The elaboration of edible films based on biopolymers, implies the knowledge of physicochemical properties of macromolecules. The objectives of this work were to describe a methodology of preparing Nile Tilapia myofibrillar proteins and study the properties related to formation and characterization of edible film elaborated with these proteins. Freshly slaughtered ground Nile Tilapia (Oreochromis niloticus) muscle was washed and processed until the formation of a homogeneous paste. Evolution of protein fractions during processing was followed by scanning differential calorimetry. Solubility of freeze-dried myofibrillar proteins was studied as a function of pH (2-7). Identification of protein fractions and that of the composition of amino acids were accomplished by SDS-PAGE and ion-exchange chromatography, respectively. Biofilms, thus formed, were submitted to puncture, solubility and scanning electron microscopy tests. The sample of freeze-fried proteins, constituted only of myofibrillar proteins, presented maximum solubility (96.9%), at pH around 3 and a high ionic interaction potential (74.4 kJ/100 kJ). Nile Tilapia myofibrillar protein based biofilms were not very soluble (lower than 20 g/100 g dry matter). Glycerol strongly influenced mechanical as well as solubility properties of biofilms.

Effects of drying temperature and relative humidity on the mechanical properties of amaranth flour films plasticized with glycerol

Biofilms are made of biopolymers. In the casting technique, biofilms are obtained by the drying of a polymer suspension in the final stage of processing. The aim of the present paper was to analyze the effect of this drying process on the mechanical properties of films produced with amaranth flour. Variables considered include glycerol content (30, 35 and 40%, g/g dry flour) and air-drying conditions (air temperatures of 30, 40 and 50oC and relative humidities of 40, 55 and 70%). As amaranth flour films constitute a complex mixture of amylopectin and amylose as well as native protein and lipid, certain unexpected results were obtained. The toughest films were obtained at the lowest temperature and the lowest relative humidity (30oC, 40%).

Avaliação físico-química e sensorial do iogurte natural produzido com leite de búfala contendo diferentes níveis de gordura

Palavras-chave: SUMMARY PHYSICO-CHEMICAL AND SENSORY EVALUATION OF PLAIN YOGURT MANUFACTURED FROM BUFFALO MILK WITH DIFFERENT FAT CONTENT. Yogurt can be considered an excellent alternative for utilization of buffalo milk. However, consumers may have some acceptance problems in relation to buffalo yogurt because of the original high fat content of the milk. The aim of the present study was to evaluate some characteristics of stirred plain yogurt produced from buffalo milk with the following fat levels: whole milk, 3.0% (standardized) and 0.5% (skim). Yogurts were stored in 1L polyethylene bottles at 5 C for 30 days. Samples were collected at 1, 15 and 30 days of storage and submitted to the following analysis: acidity, pH, viscosity and sensorial evaluation. Acidity and pH values showed no differences (P > 0.05) among treatments during storage. Viscosity was not influenced (P > 0.05) by fat content in yogurts on days 1, 15 and 30 after manufacture. Standardized yogurt obtained higher scores (P < 0.05) for taste in sensorial analysis at 15 and 30 days storage. It is concluded that skimming of buffalo milk does not alter the studied physical and chemical properties of yogurt during storage for 30 days, and that standardized yogurt at 3.0% fat shows a better sensorial quality. buffalo milk; fermented milks; analysis.

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.

Calculation of viscoelastic properties of edible films: application of three models

The viscoelastic properties of edible films can provide information at the structural level of the biopolymers used. The objective of this work was to test three simple models of linear viscoelastic theory (Maxwell, Generalized Maxwell with two units in parallel, and Burgers) using the results of stress relaxation tests in edible films of myofibrillar proteins of Nile Tilapia. The films were elaborated according to a casting technique and pre-conditioned at 58% relative humidity and 22oC for 4 days. The testing sample (15mm x 118mm) was submitted to tests of stress relaxation in an equipment of physical measurements, TA.XT2i. The deformation, imposed to the sample, was 1%, guaranteeing the permanency in the domain of the linear viscoelasticity. The models were fitted to experimental data (stress x time) by nonlinear regression. The Generalized Maxwell model with two units in parallel and the Burgers model represented the relaxation curves of stress satisfactorily. The viscoelastic properties varied in a way that they were less dependent on the thickness of the films.