Lambros Farmakis

Size Analysis of Barley Starch Granules by Sedimentation/Steric Field Flow Fractionation

In the present work the relatively new technique of sedimentation/steric field-flow fractionation (Sd/StFFF) was used for the size analysis of the large, medium and small starch granules of barley grain. The experimental parameters varied were the time from the preparation of the starch sample dispersion - in order to study the disintegration or the aggregation of the starch granules - and the concentration of the sample -in order to study the sample overloading effect on the measured size of the starch granules. A bimodal or trimodal size distribution curve, depending on the experimental conditions used, was found by Sd/StFFF, and the number and weight average diameters of the starch granules were calculated. Finally, the experimental results are compared with those obtained by scanning electron microscopy and light scattering, and useful conclusions concerning the destruction or the aggregation of the starch granules, as well as the sample overloading effect on the granules size, measured by Sd/StFFF, are extracted.

Kinetic study of cell proliferation of Saccharomyces cerevisiae strains by sedimentation/steric field flow fractionation in situ.

The technique of Sedimentation/Steric Field Flow Fractionation (Sd/StFFF) is applied to the kinetic study of cells proliferation of Saccharomyces cerevisiae strains. The experimental parameter varied is the time from the preparation of the yeast sample dispersion in the culture medium. The determination of the size and mass distributions of the yeast cells is combined with the growth of the yeast cells and their life cycle. The experimental results are compared with those obtained by scanning electron microscopy (SEM) and those found in the literature. Useful conclusions concerning the budding and the fission of these yeast cells were extracted.

STUDY OF THE INFLUENCE OF IONIC STRENGTH AND pH OF THE SUSPENDING MEDIUM ON THE SIZE OF WHEAT STARCH GRANULES, MEASURED BY SEDIMENTATION/STERIC FIELD-FLOW FRACTIONATION

The sedimentation/steric field-flow fractionation (Sd/StFFF) technique has been approved as a simple and accurate method for the size separation and characterization of starch granules. In the present work, we further investigate this application by studying the influence of the ionic strength and the pH of the suspending medium on the size of the wheat starch granules measured by Sd/StFFF. A bimodal size distribution curve was found by Sd/StFFF for the starch granules, in accordance with the results obtained by scanning electron microscopy (SEM). The number and weight average diameters for the large (A-type) and small (B-type) starch granules are independent of the presence of the indifferent electrolyte KNO3 in the suspending medium, indicating that disintegration or aggregation phenomena of the starch particles are absent. The later was also verified by SEM. The fact that the suspension pH does not influence the number and weight average diameters of the starch granules is discussed, in relation to the zeta potentials of the particles, which were measured by a microelectrophoresis apparatus.

Dependence of Adsorption Rates with Lateral Interactions on Local Surface Coverage of Heterogeneous Surfaces

SummaryAs local adsorption isothermθf changes with time, it induces a changing with it of both, the net experimental adsorption rate∂θf/∂f with lateral molecular interaction, as well as the rate constants for adsorption (ko) and desorption (kd). All these changes are experimentally measured by applying the reversed-flow gas chromatographic method, and a relatively simple equation.These calculations have been applied to the adsorption of dimethyl sulfide on pieces of Penteli marble at 373 K and to the adsorption of heptane on γ-alumina at 383 K.

INVESTIGATION OF THE VARIATION OF THE MASS RATIOS FOR LARGE AND SMALL STARCH GRANULES WITH THE pH AND IONIC STRENGTH OF THE DISPERSING MEDIUM BY SEDIMENTATION/STERIC FIELD-FLOW FRACTIONATION

ABSTRACT The relatively new technique of Sedimentation/Steric Field-Flow Fractionation (Sd/St FFF) is a simple, fast, and accurate method for the size separation and characterization of starch granules. In the present work, the Sd/St FFF technique was used for the calculation of the mass ratios of the A-large and B-small granules from barley and wheat starch samples. The mass ratios were obtained from the distribution curves of the starch samples at various pH and ionic strength of the suspending medium, in the presence or the absence of the surfactant FL-70. The influence of the suspension pH and ionic strength on the mass ratios of A- and B-granules is discussed in relation to the zeta potentials of the particles, which were measured by a microelectrophoresis apparatus.

Potential-barrier field-flow fractionation: Potential curves and interactive forces

ABSTRACT Potential-barrier field-flow fractionation (PBFFF), a tool for the separation and size characterization of colloidal particles is based on the variation of the surface forces in the FFF process, which control particle adsorption–desorption on the channel wall. The latter phenomena depend on the total potential energy of interaction between the colloidal particles and the channel wall. Our results suggest, that at high ionic strengths of the suspending medium, the colloidal particles used (submicron monodisperse spherical particles of hematite and titanium dioxide) are retained within the secondary minimum even though the energy barrier is sufficiently high to inhibit attachment in the primary minimum of the interaction energy curve. This hypothesis is further supported by the particle detachment experiments at low ionic strengths of the suspension in which the total number of adhered particles was revealed when the secondary minimum was eliminated. The secondary minimum energies, φmn1, necessary for the separation of the colloidal particles used in PBFFF, which were computed using the electrical double layers and van der Waals expressions were found, approximately, in the range −4.7<φmn1<−3.2 kT, even though the energy maxima were much greater (φmax≈109 kT). As the secondary minimum energies depend not only on the size of the particles, but also on their nature, one could separate by PBFFF particles of different size, as well as of the same size but with different chemical constitution.

Reversed – Flow Gas Chromatography as a tool for studying the interaction between aroma compounds and starch

The versatile technique of reversed-flow gas chromatography was introduced to calculate physicochemical quantities for the interaction between aroma compounds and starch. Adsorption, adsorption/desorption, and surface reaction rate constants as well as surface diffusion coefficients for the vapors of aroma compounds over the different starch surfaces were calculated in the temperature range of 303.15-333.15 K. Enthalpies of adsorption between -45.5 and -109.0 kJ mol-1 and enthalpies of physicochemical interaction between 6.8 and 47.4 kJ mol-1 were also calculated for all the systems studied. From the obtained results, it is concluded that the interaction forces between aroma compounds and starch correspond to weak energy bonds such as hydrogen bonds and dipole-dipole interactions. For all the systems studied, except for the system heptanal/potato, physical sorption of aroma compounds on starch granules was indicated according to the calculated activation energies.