G.M. Rios

Simultaneous water and solute transport in shrinking media. Part 1 : Application to dewatering and impregnation soaking process analysis (osmotic dehydration)

ABSTRACT Agar model gel cubes, with initial low solute content, were soaked in higher concentration solutions. The influence of the concentration and molecular weight of the solute in the soaking solution, the temperature. the agar and solute content of the model food on water loss and solute gain rates were observed. The achievement of a prevailing dewatering effect with only marginal solute pick-up proved to be related to a inverse relationship between the cross-flows of water and solute, reinforced by shrinkage. As a preliminary to further modelling, reasonable assumptions were drawn from experimental result analysis.

Soaking process in ternary liquids : Experimental study of mass transport under natural and forced convection

Abstract Cross mass transport during the soaking process of model food gel (gelatin, carraghenan) in concentrated solutions (salt-sucrose-water) at 10 °C was investigated using a rotating gel disc device. The concentration profiles in gel were analyzed. The experimental results confirmed the theory that component concentrations are not functions of the disc radius. Two sets of experiments were carried out to study the influence of the main process variables (solute concentration, processing time) on mass transport under forced and natural convection. The results showed that the presence of sucrose enhanced water loss and hindered salt penetration whatever the hydrodynamic conditions. Rotation speed increased water loss as solute concentration increased but had no effect on salt gain, while it hindered sucrose gain. Photographs also showed the presence of very strong natural convection phenomena.

Simultaneous water and solute transport in shrinking media. Part 2 : A compartmental model for dewatering and impregnation soaking processes

ABSTRACT A simple compartmental model of simultaneous water and solute transport was developed on agar gel cubes, for particular situations in which high water loss is accompanied by shrinkage and flux interaction. The model provided a good fit for the different situations tested, and proved to behave adequately in a wider application field. Furthermore, it made it possible to obtain a simulation of the evolution of the solute contents in both compartments which was consistent with the previous studies.

Kinetics of cassava starch hydrolysis with Termamyl enzyme

Kinetic properties of Termamyl(R) 120L were investigated with respect to starch hydrolysis in a batch reactor at substrate concentrations of 50-270 g. dm(-3) and enzyme concentrations of 0. 17-1 cm(3). dm(-3) (i.e., cm(3) of Novo Nordisk enzymatic solution per dm(3) of raw cassava starch suspension). A general kinetic expression giving product concentration as a function of time was first developed; an equation relating the reaction rate of each product to the sum of the concentrations of oligosaccharides with a higher degree of polymerisation was then derived. The empirical model satisfactorily fits experimental data for oligosaccharides with a degree of polymerization ranging from 1 to 7.

Nanofiltration membrane behavior in a supercritical medium

Abstract The permeability values of “TN” organomineral nanofiltration membranes to water, L , and to supercritical CO 2 , G , were compared. The resulting values for G were an order of magnitude higher than for L . The difference may be directly related to the viscosity difference between the two fluids. Temperature- and pressure-related variations in G were also analyzed; for this purpose, Poiseuilles model satisfactorily accounts for experimental behavior, while Knudsens model is unsuitable. A hysteresis effect was observed on the isotherms corresponding to variations in G versus pressure, suggesting partially irreversible CO 2 adsorption on the micropore walls, that would diminish the radius. This phenomenon could be enhanced by an increased fluid density and viscosity.

Dynamic characterization and transport mechanisms of two inorganic membranes for nanofiltration

Abstract This article discusses the transport mechanisms of water and uncharged solute molecules (PEG) through two new nanofiltration membranes: a pure ceramic (γ-alumina) and a Nafion layer deposited on a mesoporous tita-nium oxide substrate. It is shown that in both cases the transport mechanisms are always predominantly convective rather than diffusive, even if the difference between the two components is less important with Nafion than with alumina due to specific chemical interactions between the membrane material and the solutes. This approach was also used to characterize the two membranes morphologically, notably the pore radius of ∼0.6 nm.

The effect of enzyme concentration and space time on the performance of a continuous recycle membrane reactor for one-step starch hydrolysis

Abstract In spite of minor limitations due to membrane fouling and catalyst inactivation, one-step hydrolysis of starch with termamyl enzyme in a continuous recycle membrane reactor appears to be a promising way to produce high DE sugar syrups. In addition to the main advantage over batch process to correctly integrating reaction and separation, this type of system opens up to process engineer tunable performance in terms of conversion, capacity and productivity. In this paper the effects of enzyme concentration and space time have been examined. As a whole it appears that by increasing these two parameters the conversion is improved; but the capacity and productivity are reduced leading to higher processing costs. Optimisation of enzyme concentration and space time needs that economic criteria are very carefully taken into account.

Preparation of hybrid membranes for enzymatic reaction

Two different active membranes were prepared by simple (membrane M1) or mixed-entrapping (membrane M2) covalent attachment of α-chymotrypsin onto an α-alumina tubular support coated with an inert protein. The derivatives were used as catalyst for the continuous kinetically controlled synthesis of kyotorphin in organic media. Contrary to adsorption, the covalent linkage of the enzyme to a dynamic membrane allows a continuous peptide synthesis and enhances operational stability towards the denaturative effects of organic solvents.

Modeling of dewatering and impregnation soaking process (osmotic dehydration)

Abstract Partial dewatering and simultaneous solute impregnation can be obtained by immersion of food pieces in concentrated solutions. Recently, further understanding of cross mass transfer was achieved by experimental study and modelling on agar model gel foods.

Kinetics of continuous starch hydrolysis in a membrane reactor

Following a previous study on kinetics of enzymatic starch hydrolysis with Termamyl 120l (Novo Nordisk) in batch reactor, this paper deals with kinetics in a continuous recycled membrane reactor (CRMR). Starting from results obtained in various working conditions, an equation relating the production rates of small oligosaccharides (DP ranging from 1 to 5) to the sum of concentrations of oligosaccharides with a higher degree of polymerisation is proposed. This equation looks like the one already reported for a batch system, with the exception that in the CRMR the enzyme activity varies: an exponential decay of activity as a function of time must be introduced to smooth carefully data points.