Effect of Vacuum-Microwave Predrying on Quality of Vacuum-Fried Potato Chips

The effects of vacuum microwave predrying on the quality of vacuum-fried potato chips were studied. The results showed that vacuum microwave predrying had a significant effect on moisture and oil contents, as well as color parameters and structure of potato chips. Vacuum microwave predrying significantly decreased the oil and moisture contents of vacuum-fried potato chips. The rates of both mass transfer phenomena (water loss and oil uptake) that take place during the vacuum frying of potato chips decrease due to the vacuum microwave predrying. The vacuum microwave predrying had a negative effect on color of potato chips, which decreases the L value of potato chips and increases Hunter a and b values. Breaking force of fried potato chips is also significantly (P < 0.05) affected by the drying pretreatment, which decreases the breaking force at the beginning of predrying and then increases with vacuum microwave predrying time.     

Image Analysis,Homogenization, Numerical Simulation and Experiment as Complementary Tools to Enlighten the Relationship between Wood Anatomy and Drying Behavior

Abstract

This paper has been written for a special issue devoted to the works done in France in the field of drying. Therefore, it aims, through numerous examples, to show the spirit which initiates and guides the research work of the Forest Products Unit at ENGREF : how more and more microscopic information can be included in the study of the drying process ?

Two steps are involved :

?microscopic observation and experiments to predict the macroscopic properties

?use of the macroscopic properties (the previous step + experiments carried our at the macroscopic scale) to predict the drying behavior.

In this approach, each prediction comes from a model, that means assumptions, formulations, calculations and then validation.

Several tools (image analysis, homogenization, measurement of microscopic and macroscopic properties, numerical simulation of heat and mass transfer, refined drying experiments) are used to study the drying of wood.     

KINETICS ON COLOR CHANGES DURING DRYING OF SOME FRUITS AND VEGETABLES

Abstract

The effect of drying conditions on color changes of apple, banana, carrot and potato during conventional and vacuum drying was investigated. The Hunder color scale parameters redness, yellowness and lightness were used to estimate color changes during vacuum and conventional drying at 50, 70 and 90°C. Air humidity during conventional drying was regulated at 15, 30 and 40%. Air temperature and humidity affected redness and yellowness, but not lightness. A first order kinetic model was fitted to experimental data adequately for both redness and yellowness. The rate of color deterioration was found to increase as temperature increased and air humidity decreased, for both drying methods and all the examined materials.     

Preparation and Characterization of Antibacterial Ag2O-Coated HDPE Films Obtained by Vacuum Evaporation Technique

To obtain the antibacterial plastics films, the Ag₂O-coated HDPE films were prepared through vacuum evaporation technique via depositing Ag₂O on the substrate of high density polyethylene (HDPE) films pretreated by ion bombardment. The pretreatment made the surface polarity and roughness of the substrates improved. The coating was continuous and dense, being of about 17.2 nm thick, and the content of silver ions in it was 7.0020 µg/cm². The Ag₂O-coated HDPE films exhibited strong antibacterial activity for both gram-negative bacteria (E. coli) and gram-positive bacteria (S. aureus). However, the mechanical properties of the composite films slightly dropped in contrast with the HDPE films.     

Indeno-Polycyclic Aromatic Hydrocarbons: A Versatile New Synthetic Route

Acylation of a polycyclic aromatic hydrocarbon (PAH) adjacent to a ring junction with 2-bromobenzoyl chloride followed by Flash Vacuum Pyrolysis (FVP) of the resulting bromoketone affords the corresponding indeno-annulated PAH. The new method is illustrated by syntheses of indeno[1,2,3-cd]pyrene (1) from pyrene and indeno[1,2,3-cd]fluoranthene (2) from fluoranthene. The formation of indeno[1,2,3,4-defg]chrysene (11) from FVP of 8-(2-bromobenzoyl)-fluoranthene (10), and as a secondary product from FVP of 3-(2-bromobenzoyl)fluoranthene (9), reveals the ability of phenyl groups to migrate around the periphery of a didehydro-PAH. Mechanisms involving reversible hydrogen atom transfers are proposed. Diacylation of fluoranthene with 2-bromobenzoyl chloride followed by FVP gives the previously unknown, nonplanar, nonalternant, C₂₈H₁₄ PAH diindeno[1,2,3,4-defg: 1,2,3-rs]chrysene (21) in just two steps.     

A STUDY OF VACUUM FREEZE-DRYING OF FROZEN WET PAPERS

Vacuum freeze-drying of frozen wet papers was investigated experimentally. A freeze-drying facility was built to study the process by monitoring the various physical parameters (pressure, sample temperature, heater temperature, water content of the sample and cold panel temperature). A simple phenomenological model was developed to explain experimental results. The values of the physical parameters were optimized to make the process cost effective.     

MOISTURE DIFFUSIVITY BEHAVIOR DURING FREEZE DRYING UNDER MICROWAVE HEATING POWER APPLICATION

The necessary criteria for the design of a freeze-drying operation, where radiant and microwave heating are combined, are analyzed in this work. Microwave heating presents indubitable advantages for enhancing drying kinetics. Modifications of different value characteristics must be also considered. Different freeze-drying strategies using MW heating are analyzed taking into account kinetics and diffusivity behavior compared to a constant diffusivity model. A microwave on-off cycled strategy with simultaneous up-down modification of pressure was found an acceptable power regulation system when magnetrons, whose field strength exceeds the breakdown voltage of gas, are used. In this case, chamber pressure becomes a convenient control parameter to avoid plasma discharge and subsequent melting of product. Different evolutions of specific power inputs per gram were proposed depending on the size and disposition of the product.     

A Vacuum Drying Model for Mango Pulp

Abstract

Vacuum drying of mango pulp at varying conditions of pulp thickness (2, 3, and 4 mm) and vacuum chamber plate temperature (65, 70, and 75°C) was carried out under 30–50 mm of mercury absolute pressure. A model based on moisture diffusivity was found to give close prediction to moisture content of the pulp at different times of drying with correlation coefficient varying between 0.98–0.99 for pure mango pulp and pulp with ingredients. Color change of reconstituted pulp made from mango powder was found to depend more on pulp thickness than plate temperature. For getting low color change vacuum drying should be carried at maximum pulp thickness of 2.6 mm and vacuum chamber plate temperature of 72.3°C.     

Microwave-Vacuum Drying of Pharmaceutical Powders

Abstract

Due to their temperature sensitive nature, many pharmaceutical products are dried under vacuum to facilitate solvent evaporation at reduced temperatures. However, this necessitates long drying times and represents a processing bottleneck. Microwave heating of such materials at reduced pressures offers a more rapid method of moisture removal, without the risk of product damage. Within this study, the effect of vacuum on the rate of solvent evaporation was investigated, using a range of powders (pharmaceutical actives Paracetamol and Aspirin, and a range of bulk excipients) and solvents including water, ethanol, methanol, and acetone. In general, drying rate increased as system pressure decreased, however, the magnitude and duration was system specific. As expected, the diffusion coefficient decreased from the first to the second falling rate period, with the diffusivity in each drying period increasing with increased vacuum. The findings in this research have significant implications for drying operations in the pharmaceutical industry.     

Modeling Superheated Steam Vacuum Drying of Wood

Abstract

A two-dimensional mathematical model developed for vacuum-contact drying of wood was adapted to simulate superheated steam vacuum drying. The moisture and heat equations are based on the water potential concept whereas the pressure equation is formulated considering unsteady-state mass conservation of dry air. A drying test conducted on sugar maple sapwood in a laboratory vacuum kiln was used to infer the convective mass and heat transfer coefficients through a curve fitting technique. The average air velocity was 2.5 m s^?1 and the dry-bulb temperature varied between 60 and 66°C. The ambient pressure varied from 15 to 11 kPa. Simulation results indicate that heat and mass transfer coefficients are moisture content dependent. The simulated drying curve based on transfer coefficients calculated from boundary layer theory poorly fits experimental results. The functional relation for the relative permeability of wood to air is a key parameter in predicting the pressure evolution in wood in the course of drying. In the case of small vacuum kilns, radiant heat can contribute substantially to the total heat transfer to the evaporative surface at the early stages of drying. As for conventional drying, the air velocity could be reduced at the latter stage of drying with little or no change to the drying rate.