Estudo da desidratação de tomates em pedaços com pré-tratamento osmótico

Vegetables drying plays an important role in the field of food dehydration, being a very old practice that was originated from sun drying items of food in order to preserve them to be consumed during the periods of scarcity. One of these vegetables is the tomato, that was originally grown in South America. Tomatoes are easily perishable after being picked up from the tree and this makes the process of tomato dehydration a challenge due to the high amount of water (95%) contained in them. The present research work was mainly intended to develop alternative processes for tomato conservation, by drying slices of skinned and unskinned tomatoes in the in natura form or in the osmotically pre-dehydrated form. Firstly, the best conditions of the osmotic pre-dehydration process were defined including temperature, immersion time and concentration of the osmotic solution, based on the results of water loss, solids gain and weigh reduction of the pre-dehydration tomatoes at different processing conditions. The osmotic solution used was made up of NaCl (5 and 10%) and sucrose (25 and 35%) at different combinations. For a fixed conditions of osmotic pre-dehydration, the drying tests of the pre-processed and in natura tomatoes were carried out in a stove with air circulation and a convective dryer with trays, at two levels of temperature. The sensorial analysis of the osmotically pre-treated and unskinned dehydrated tomatoes was carried out as well as a study on the their shelf-live. The results obtained showed that the drying of the tomatoes took place as a result of the internal control of the water transport, and did not show a constant rate, while two distinct periods of the decreasing phase were observed. The osmotic pre treatment substancially reduced the initial amount of humidity in the tomatoes, thus reducing the necessary time for the product to attain levels of intermediate humidity. The impermeability of the tomato skin was identified as well as the unfavorable influence of the pre-treatment on the unskinned tomatoes, whose solid gain brought about a decrease in the water activity with subsequent reduction of the drying rate. Despite the various simplifications carried out during the development of this study, the proposed diffusive model adjusted to the experimental data satisfactorily, thus making it possible to determine the effective coefficients of diffusion, whose results were consistent and compatible with those found in the current literature. Concerning the higher rates of evaporation and the lowest processing time, the best results were obtained in the drying of the unskinned, in natura tomatoes and of the skinned, pre-dehydrated tomatoes, at 60ºC, both processed in the convective drier. The results of the sensorial analysis of the unskinned and pre-treated product did not prove to be satisfactory. Regarding the shelf-live of the tomatoes, for a period of 45 days, no physicochemical or microbiological alteration of the product was noted

Avaliação do ciclo térmico de conformação por compressão de peças em poli(sulfeto de fenileno) reforçado com fibras contínuas de carbono

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Conventional and microwave sintering of CaCu(3)Ti(4)O(12)/CaTiO(3) ceramic composites: non-ohmic and dielectric properties

The non-ohmic and dielectric properties as well as the dependence on the microstructural features of CaCu(3)Ti(4)O(12)/CaTiO(3) ceramic composites obtained by conventional and microwave sintering were investigated. It was demonstrated that the non-ohmic and dielectric properties depend strongly on the sintering conditions. It was found that the non-linear coefficient reaches values of 65 for microwave-sintered samples and 42 for samples sintered in a conventional furnace when a current density interval of 1-10 mA cm(-2) is considered. The non-linear coefficient value of 65 is equivalent to 1500 for samples sintered in the microwave if a current interval of 5-30 mA is considered as is shortly discussed by Chung et al (2004 Nature Mater. 3 774). Due to a high non-linear coefficient and a low leakage current (90 mu A) under both processing conditions, these samples are promising for varistor applications. The conventionally sintered samples exhibit a higher relative dielectric constant at 1 kHz (2960) compared with the samples sintered in the microwave furnace (2100). At high frequencies, the dielectric constant is also larger in the samples sintered in the conventional furnace. Depending on the application, one or another synthesis methodology is recommended, that is, for varistor applications sintered in a microwave furnace and for dielectric application sintered in a conventional furnace.

Efeito dos parâmetros de extrusão sobre as propriedades funcionais de extrusados da farinha de batata-doce

Farinha de batata-doce (Ipomoea batatas) foi extrusada em equipamento de rosca simples, mantendo-se fixas as temperaturas na 1ª e 2ª zonas de extrusão (20ºC e 60ºC, respectivamente). O efeito das variáveis umidade da farinha (15, 18 e 21%), temperatura na 3ª zona (100, 120 e 140ºC) e rotação da rosca (180, 210 e 240 rpm) sobre as características dos extrusados foi investigado utilizando-se metodologia de superfície de resposta. O teor de umidade e a temperatura de extrusão influenciaram significativamente a expansão dos extrusados. O índice de expansão apresentou valores crescentes com a temperatura sob baixos teores de umidade. A dureza dos extrusados e também o índice de absorção de água e o índice de solubilidade em água das farinhas extrusadas não mostraram modelo de regressão significativo com as condições de processo. Quanto à cor das farinhas, o componente L* (luminosidade) apresentou valores crescentes e o parâmetro a*, valores decrescentes com a elevação do teor de umidade até 20-21%. O parâmetro b* e a diferença de cor entre farinhas extrusadas e não extrusadas mostraram valores decrescentes com o aumento da umidade.

Avaliação nutricional, em tilápias-do-nilo, de farinhas de sangue bovino obtidas por três métodos de processamento

Avaliaram-se farinhas de sangue obtidas pelos métodos de processamento em tambor, convencional e atomização. As farinhas foram submetidas ao processo de extração e fracionamento da proteína para determinação do perfil do tamanho molecular, que foi comparado ao do sangue bovino in natura. Nas amostras, submetidas ou não ao processo de desengorduramento, foram realizadas análises da digestibilidade in vitro da proteína. Para determinação dos coeficientes de digestibilidade dos nutrientes in vivo, foram confeccionadas quatros rações, sendo uma sem farinha de sangue, denominada ração-referência purificada. Para essa etapa, juvenis de tilápia-do-nilo com peso médio inicial de 100,0±5,0 g foram estocados em aquários de 250 L, em delineamento de blocos casualizados, com quatro repetições e dez peixes/unidade experimental. As rações-teste foram obtidas com a introdução de 30% das farinhas de sangue em estudo. O processamento afetou a estrutura proteica original do sangue in natura em condições de alta temperatura e tempo prolongado, efeito traduzido pela alta proporção de peptídeos de baixo peso molecular e aminoácidos livres, correspondendo a baixos valores de digestibilidade da proteína da farinha de sangue nos testes in vivo e in vitro. A farinha de sangue atomizada e a de tambor são eficientemente utilizadas por tilápias-do-nilo. Na farinha de sangue convencional, a proteína teve valor biológico inferior ao das outras duas farinhas. Na formulação de rações contendo farinha de sangue para tilápias-do-nilo, a isoleucina deve ser considerada o primeiro aminoácido limitante, seguida pela metionina+cistina, arginina e treonina, que foram encontradas em níveis críticos para essa espécie, principalmente na farinha de sangue convencional.

The role of chain scission and chain branching in high density polyethylene during thermo-mechanical degradation

The mechanical and thermo-oxidative degradation of high density polyethylene (HDPE) was measured in a twin-screw extruder using various processing conditions. Two types of HDPE, Phillips and Ziegler-Natta, having different levels of terminal vinyl unsaturation were analysed. Mild screw profiles, having mainly conveying elements, have short mean residence times then profiles with kneading discs and left hand elements. Carbonyl and traps-vinylene group concentrations increased, whereas vinyl group concentration decreased with number of extrusions. Higher temperature profiles intensified these effects. The thermo-mechanical degradation mechanism begins with chain scission in the longer chains due to their higher probability of entanglements. These macroradicals then react with the vinyl terminal unsaturations of other chains producing chain branching. Shorter chains are more mobile, not suffering scission but instead are used for grafting the macroradicals, increasing the molecular weight. Increase in the levels of extrusion temperature, shear and vinyl end groups content facilitates the thermo-mechanical degradation reducing the amount of both, longer chains via chain scission and shorter chains via chain branching, narrowing the polydispersity. Phillips HDPE produces a higher level of chain branching than does the Ziegler-Natta type. (C) 2004 Elsevier Ltd. All rights reserved.

ZnO varistors from intensively milled powders

Two ways of application of intensive milling in ZnO varistors processing were compared. First was intensive milling of mixture of previously prepared constituent phases. In this case, intensive milling was applied only to obtain highly activated nanocrystalline varistor powder mixtures. Second application is intensive milling of simple mixture of oxides that could result not only in activation and formation of nanocrystal line powders, but also in mechanochernical reaction and synthesis of constituent phases. Powders and ceramics samples were characterized by XRD and SEM analysis. as well as by de electrical measurements (nonlinearity coefficients, leakage current and breakdown field). Differences in microstructural and electrical properties of obtained varistors were discussed and optimal milling and processing conditions were recommended. The best electrical characteristics were found in sample ZI -DMCP-m, which exhibited leakage current of 2.5 mu A/cm(2), nonlinear coefficient reaching 58 and breakdown field of 8950 V/cm. (c) 2007 Elsevier Ltd. All rights reserved.

Effects of powder preparation and sintering procedure on microstructure and dielectric properties of PLZT ceramics

PLZT ceramics belong to one of the very important groups of functional materials that make a basis for the production of a large range of electronic devices. The microstructure and properties of ceramics depend on the powder preparation and thermal processing conditions. Various techniques have been used to obtain chemically homogeneous and fine starting powders. PLZT powders have been prepared by two different production routes: by a modified Pechini method, using a polymeric precursor method (PMM) and by a partial oxalate method. A two-step sintering process, including a hot pressing, was carried out at 1100 and 1200degreesC Distinct phases obtained during the sintering process have been investigated by SEM and EDS techniques and dielectric properties such as permittivity and dielectric loss were measured in a frequency range from 1 to 20 kHz.. A significant difference in microstructure and dielectric properties, depending on powder origin and sintering procedure, has been noticed.

Evaluation of survival of Staphylococcus aureus and Clostridium botulinum in charqui meats

Charqui meats were prepared in laboratory conditions in order to carry out experiments to observe the possibility of development of enterotoxigenic Staphylococcus aureus and Clostridium bottilinum proteolytic type B spores and their toxins. Results demonstrated that the harsh processing conditions, high salt concentration, relative high temperature, a, values, inhibited the growth of both bacteria. Under our experimental conditions, S. aureus would survive throughout the sequence of salting steps i.e. brine followed by rock salting and the sunshine drying step. However, at final a(w) value of 0.70-0.75 would create conditions to inhibit its development. The other experiment revealed that C. botulinum spores germination also was impaired because of these low a(w) values. Under these conditions, charqui meats revealed to be safe products in relation to toxins from both enterotoxigenic S. aureus and C. botulinum. (C) 2003 Elsevier B.V. Ltd. All rights reserved.

PZT ceramics obtained from mechanochemically synthesized powders

PZT ceramics were obtained from the mechanochemically synthesized powders. Milling and sintering conditions were optimized based on results of density measurements, as well as on microstructural and electrical characterization. As a result, highly dense and homogeneous ceramics were obtained. Excellent microstructural properties resulted in good electrical properties. Samples showed values of dielectric constants reaching 12800 at the Curie temperature, as well as low dielectric loss under the optimal processing conditions. High values of remanent polarization, reaching 60 muC cm(-2), indicate high internal polarizability. (C) 2003 Kluwer Academic Publishers.

Dielectric and piezoelectric properties of the mechanochemically prepared PZT ceramics

Mechanochemical synthesis was applied to obtain nanocrystalline powders of composition Pb(Zr0.52Ti0.48)O-3 (PZT). Milling was performed in a planetary ball mill using vials and balls made of zirconia or steel-in order to investigate influence of milling media on the electrical properties of resulting ceramics. PZT ceramics showed high values for dielectric constant (epsilon(r)), reaching 970 at room temperature, as well as low dielectric loss (tandelta) under the optimal processing conditions. High values of remanent polarization (P-r) indicate high internal polarizability. The best samples showed piezoelectric strain constant d(33) = 347 pC/N and planar coupling factor k(P) = 0.44. Milling in ZrO2 medium prevents powder contamination and provides reproducibility of milling process. Also, PZT obtained from the powders milled in ZrO2 exhibited lower values of dielectric loss, in comparison with the PTZ obtained from the powders milled in Fe. This suggests that contamination of the powder with Fe could result in an increase of conductivity in final product. (C) 2004 Kluwer Academic Publishers.

Competition between anchoring and reversible photo-induced alignment of a nematic liquid crystal

We investigated the alignment induced on a nematic liquid crystal (LC) by a photo-aligned polymer film with azo-dye side groups. The orientation of the LC molecules can be manipulated in a reversible manner by irradiating the film with polarized light. We analyzed the competition between the orientation induced by the main chain, through rubbing of the film and that induced by the photo-aligned polymer. Anchoring strength for the different processing conditions are reported. The changes in film morphology caused by rubbing or photo-alignment could be captured by atomic force microscopy. The reversibility of the photo-induced alignment and the competition between the two anchoring mechanisms may allow recording and erasing of information in a LC display.

The Effects of Piece Size and Storage Temperatures on Minimally Processed 'Aurora-1' Peaches

The production of minimally processed fruit has increased significantly in the last few years due to the high nutritional value, convenience and safety of minimally processed fruit. The objective of the present study was to evaluate the effects of the conservation temperature and processing conditions on the quality and shelf-life of minimally processed peaches. The processing procedure consisted of washing, sanitization, peeling and stone removal. To remove the stone, the fruit was cut longitudinally, and three types of products were obtained, including halves, quarters and one-eighth segments. The fruit pieces were immersed in 2% ascorbic acid for 3 min and were packed in rigid polystyrene trays (Meiwa (c) M-54) coated with 14 mu m PVC film (Omnifilm (TM)) (about 200 g per pack). The pieces were stored at 65% RH at 3, 6 or 9 degrees C for 12 days, and were evaluated every four days. The appearance, fresh mass loss, color, O-2 and CO2 concentration, acidity, total soluble solids, total and soluble pectin content and ascorbic acid concentration were measured. Minimally processed peaches stored at 3 degrees C maintained higher quality due to control of ripening and senescence Moreover, an interaction effect between one-eighth segments and a temperature of 3 degrees C was observed, and fruit with a superior appearance and higher soluble solids content was obtained.

Sol-gel synthesis of mesoporous CaCu3Ti4O12 thin films and their gas sensing response

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Hydrodynamic aspects of the amorphous alloy ribbon fabrication

Conditions for as-quenched amorphous ribbon fabrication by a single roll-casting method are analyzed from a hydrodynamic standpoint. The analysis is based on the investigation of the processing conditions for Fe 4 0Ni 40P 14B 6 amorphous ribbons. It is shown that the dependence of ribbon thickness on the ejection pressure for different roll angular velocities and different dimensions of crucible and orifice can be obtained from general considerations on the melt flow regime.