Effect of drying method on the adsorption isotherms and isosteric heat of passion fruit pulp powder

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Quality of natural coffee subjected to different rest periods during the drying process

O parcelamento da secagem pode ser eficiente tanto no que diz respeito à qualidade final do café, quanto na redução do consumo específico de energia. Diante disso, objetivou-se, com o presente trabalho, avaliar o efeito do teor de água dos frutos no momento da interrupção da secagem e do período de repouso até a retomada da secagem na qualidade do café natural, por meio da análise sensorial e dos testes de condutividade elétrica e lixiviação de potássio. Frutos de café maduros foram colhidos manual e seletivamente e, em seguida, secados ao sol em terreiros de concreto por dois dias e, então, submetidos à secagem mecânica em secadores de camada fixa. Quando o café atingiu os teores de água de 20%, 17% e 14% (base úmida, bu), a secagem foi interrompida e o café permaneceu em repouso por cinco, quinze e trinta dias e, posteriormente, foi secado em secadores mecânicos até o teor de água de 11% (bu). O controle constituiu-se na secagem completa em terreiro. Observou-se que as combinações entre o menor teor de água e o maior período de repouso e entre o maior teor de água e o menor período de repouso, proporcionam menores valores de lixiviação de potássio. A qualidade da bebida melhora progressivamente com o aumento do período de repouso. A interrupção da secagem com teores de água de 17% e 20% (bu) não altera a qualidade do café natural, comparativamente à secagem completa em terreiro.

Drying study of siloxane-PPG nanocomposites

This is a study of the structural transformations occurring in hybrid siloxane-polypropyleneglycol (PPG) nanocomposites, with different PPG molecular weight, along the drying process. The starting materials are wet gels obtained by the sol-gel procedure using as precursor the 3-(trietoxysilyl)propylisocyanate (IsoTrEOS) and polypropylenglycol bis(2-amino-propyl-ether) (NH2-PPG-NH2). The shrinkage and mass loss measurements were performed using a temperature-controlled chamber at 50 degreesC. The nanostructural evolution of samples during drying was studied in situ by small angle x-ray scattering (SAXS). The experimental results demonstrate that the drying process is highly dependent on the molecular weight of polymer. After the initial drying stage, the progressive emptying of pores leads to the formation of a irregular drying front in gels prepared from PPG of high molecular weight, like 4000 g/mol. As a consequence, an increase of the SAXS intensity due to the increase of electronic density contrast between siloxane clusters and polymeric matrix is observed. For hybrids containing PPG of low molecular weight, the pore emptying process is fast, leading to a regular drying front, without isolated nanopockets of solvents. SAXS intensity curves exhibit a maximum, which was associated to the existence of spatial correlation of the silica clusters embedded in the polymeric matrix. The spatial correlation is preserved during drying. These results also reveal that the structural transformation during drying is governed by capillary forces and depends on the entanglement of polymer chains.

Influence of different drying methods on tbe rheological properties of raisins

The rheological parameters of raisins were obtained after three different drying methods: convective, osmo-convective and solar drying. Compression tests were applied to rehydrated samples by using a Texture Analyzer TAXT2i. A mathematical trick was used to determine the stress and area was calculated along the deformation. A power law model could adequately fit stress-true strain curves and parameters; K (measure of stiffness) and n (solid behavior index) were obtained as a function of water activity between 0.755 to 0.432. Results showed that these parameters were strongly dependent on water activity for all drying methods. The constant K, which indicates the resistance against deformation, increased with decreasing water activity. on the other hand, increasing water activity resulted in higher solid behavior indexes, showing a large deviation from the Hookean behavior.

Changes of density, thermal conductivity, thermal diffusivity, and specific heat of plums during drying

The thermal properties of plums (Prunus domestica) and prunes were investigated in the moisture content of 14.2-80.4% (wet basis) near room temperature (approximately 28 degrees C). The apparent density of the fruits increased from 1042.9 to 1460.0 kg/m(3), and the bulk density increased from 706.6 to 897.5 kg/m(3) as the plums were dried, following classical empirical models as a function of moisture content. It was found that specific heat, effective thermal diffusivity, and effective thermal conductivity of the prunes increased with the moisture content of the samples, which can be represented by using different empirical models.

Influence of drying conditions on the rheological properties of prunes

Rheological properties of rehydrated prunes were obtained applying compression-relaxation tests by using a Texture Analyzer TAXT2i. A mathematical development was adopted to determine the stress and area, along the deformation. Experimental data of stress versus time was fitted by using three different rheological models: generalized Maxwell, Normand & Peleg and Maxwell. Results showed that generalized Maxwell model can be used to describe the viscoelastic behavior of the samples. The rheological parameters obtained indicated that prunes exhibited elastic behavior more pronounced at low moisture content and drying air temperature. At high moisture content and temperature the sample became a more viscous and less rigid.

Comparison of hexamethyidisilazane and critical point drying treatments for SEM analysis of anaerobic biofilms and granular sludge

We present a fast procedure for scanning electron microscopy (SEM) analysis in which hexamethyldisilazane (HMDS) solvent, instead of the critical point drying, is used to remove liquids from a microbiological specimen. The results indicate that the HMDS solvent is suitable for drying samples of anaerobic cells for examination by SEM and does not cause cell structure disruption.

SILICA MORPHOLOGY CHARACTERIZED BY SEM - THE EFFECTS OF THE SOLVENT TREATMENT AND THE DRYING PROCESS

Scanning electron microscopy (SEM) was used to investigated the effects of volatile solvents (such as water, propanone, ethanol, methanol or ethyl ether), treatment and drying processes, microwave ovens, drying ovens, and vacuum desiccators or freeze driers, on silica morphology. Silica gel was obtained from diluted sodium silicate (1:5 w/w SiO2:H2O). The results showed that the drying process based on freeze drying is more efficient for structural conservation of the precipitate. Treatment with volatile solvents does not change the shape of the aggregates, but has an important role in the determination of aggregate surface roughness.

Drying kinetics of tomato by using electric resistance and heat pump dryers

Drying kinetics of tomato was studied by using heat pump dryer (HPD) and electric resistance dryers with parallel and crossed airflow. The performance of both systems was evaluated and compared and the influence of temperature, air velocity, and tomato type on the drying kinetics was analyzed. The use of HPD showed to be adequate in the drying process of tomatoes, mainly in relation to the conversion rate of electric energy into thermal energy. The heat pump effective coefficient of performance (COPHT,EF) was between 2.56 and 2.68, with an energy economy of about 40% when compared to the drying system with electric resistance. The Page model could be used to predict drying time of tomato and statistical analysis showed that the model parameters were mainly affected by drying temperature.

The effect of drying and urea treatment on nutritional and anti-nutritional components of browses collected during wet and dry seasons

Fibre, crude protein and tannin concentrations were measured in browse species from the semi-arid region of Northeast Brazil during the dry and wet seasons. The effects of oven-, sun- and shade-drying and of urea treatment were also determined. Crude protein (CP) content varied from 103 to 161 g/kg dry matter (DM) and the browses had similar CP content in the two seasons (during 2002) (102-161 and 107-153 g/kg DM in the wet and dry seasons, respectively). Total tannin concentrations ranged from 13 to 201 g/kg DM amongst the browses and were higher in the dry season. A 30-d treatment with urea reduced extractable tannins significantly (P < 0.05). The urea treatment was also most effective at reducing the in vitro effects of tannins compared to the other drying treatments. This was demonstrated by measuring the effect of polyethylene glycol (PEG) on gas production. Addition of PEG increased gas production of oven- (81.4%), sun- (78.5%) and shade-dried (76.7%) samples much more compared to urea treated samples (10.9%). (c) 2005 Elsevier B.V. All rights reserved.

Effect of drying method on the sorption isotherms and isosteric heat of persimmon pulp powder

Moisture equilibrium data of persimmon pulp powders with 50% maltodextrin (dry basis) obtained with different drying methods were determined at 20, 30, 40 and 50 degrees C. The spray-dryer gave a dry product with a higher adsorption capacity than the other methods. The vacuum- and freeze-dried products had the same adsorption capacity. The highest isosteric heat of sorption was observed for powders produced by spray-drying. The isokinetic temperature (T(B)) calculated for persimmon pulp powder obtained by vacuum-, spray- and freeze-drying were 541.4 K, 616.3 K, 513.2 K, respectively. The sorption process was spontaneous and enthalpy controlled.

Influence of different drying temperatures on the amount of essential oils and citral content in Cymbopogon citratus (DC) Stapf. - Poaceae

Studies were conducted to show the effect of different temperatures in the drying process on the amount and quality of essential oils of Cymbopogon citratus (DC) Stapf. Leaves were harvested in the experimental field of the Agronomical Sciences College, UNESP, Botucatu, SP, Brazil in September, 1996. Blades of the leaves were cut in small parts (about 1-1,5 cm length), dried for several days at 30°, 50°, 70° and 90°C, until establishment of the weights. In the following process a hydrodistillation, during 2.5 hours, by Clevenger apparatus, was subsidized to extract the essential oils. A higher amount of oil could clearly be collected with the lower drying temperatures, except at 30°C, affected by fungus growing. Aspergillus sp., Penicillium sp., Rhyzopus sp., Cladosporium sp., Trichoderma sp. and Alternaria sp. were observed in the leaves. The analysis of the oil by GC-MS showed the variation of citral concentration of the treatments (86,1 to 95,2%). The results proved it is worthwhile to spend more time and effort in the production process using longer times of careful drying.

In vitro release of propolis from gelatin microparticles prepared by spray-drying technique

The purpose of this study was to investigate the in vitro release of propolis from gelatin microparticles. Gelatin microparticles containing propolis extractive solution (PES) were prepared by spray-drying technique. Microparticles with a mean diameter of 2.50 μm and with regular morphology were obtained. The entrapment efficiency of propolis in the microparticles was over 39%. Spray-drying showed to be a feasible method for the preparation of gelatin microparticles containing propolis. Comparing to PES, the in vitro release of propolis from gelatin microparticles in aqueous medium was slower, considering markers 1 and 2. Thus, it was possible to transform a liquid propolis dosage form into a solid one, improving manipulation, packaging and storage and with modified release in aqueous medium, comparatively to the ethanolic extract of the drug.

Beta-carotene stability during drying and storage of cassava and sweet potato

The effect of blanching on the β-carotene stability during drying and storage of cassava and sweet potato was evaluated. The orange-fleshed sweet potato showed good retention of β-carotene during the blanching and drying (100% and 96%, respectively), but lower retention (84% and 91%) was observed in cassava. Cassava also showed lower β-carotene stability than sweet potato during the storage of unblanched dried samples. β-Carotene content of dried cassava was reduced from 8.6 μg/g to traces in 20 days of storage while the initial amount of dried sweet potato (463 μg/g) was reduced by about 45% (210 μg/g). Blanching did not affect the β-carotene retention during the drying, but enhanced the stability of this carotenoid during the storage of dried samples at room temperature, especially in cassava. The initial levels of blanched-dried cassava and sweet potato (7.8 and 513 μg/g, respectively) took 70 days to fall by around 50%.

Effect of drying on the reproducibility of DIAGNOdent to detect caries-like lesions

The aim of this study was to verify the drying effect on the reproducibility of DIAGNOdent (Dd) devices to detect caries-like lesions. Three areas were created in each of the 34 bovine incisors: sound (S), demineralized (DE) and remineralized (RE). One examiner measured each area with two Dd devices (denominated X and Y), twice under humid, and twice under dry condition. Intra-rater agreement according each device and inter-device agreement were estimated by kappa statistics (κ). Intra-rater agreement for device Y was substantial under humid (κ DE=0.68 and κ RE+S=0.68) and dry condition (κ DE=0.64 and κ RE+S=0.67). For device X, it was substantial under humid condition (κ DE=0.57 and κ RE+S=0.49), and it was almost perfect after air drying (κ DE=1.0 and κRE+S=1.0). Inter-device agreement was slight (κ =0.17) under humid condition, and it was substantial under dry condition (κ =0.62). As reproducibility increased under dry condition, drying is advised to detect caries-like lesions on free smooth surfaces when different devices are used.