Structural and dynamic aspects of plasticization and antiplasticization in carbohydrate glasses.

Carbohydrate glasses are widely used in the protection of active ingredients in pharmaceutics and in foods. In the pharmaceutical domain, bioactive proteins and peptides are commonly stabilized by amorphous matrices based on the discaccharide trehalose [1], whereas in the food domain, oxidation-sensitive active ingredients, such as polyunsaturated fatty acids and essential oils are often encapsulated in matrices based on starch hydrolysates and sucrose [2]. In recent years, it has become clear that, whereas the glass transition of the glassy matrix is relevant for the protective properties of the amorphous matrix, the glassy-state structure and dynamics excert a controlling role as well, specifically in relation to the antiplasticization of the main constituent of the glassy matrix by low-molecular weight diluents [2]. In this lecture, I am reviewing experimental evidence for the antiplasticization and plasticization in carbohydrate glasses. I will first be discussing recent insights in impact of low-moelcular weight diluents on the dynamics of the glassy matrix as probed by dielectric spectroscopy, neutron scattering and solid-state NMR [1, 3]. I will then turn to our recent insights in the dependence of the molecular packing of carbohydrate glasses on composition, pressure and temperature as determined by positron annihilation life time spectroscopy and volumetric measurements [2, 4]. Finally, I will attempt to link the regimes as identified via the structural and dynamic properties in order to formulate a general hypothesis for the mechanism of plasticization and antiplasticization of carbohydrate glasses by low molecular weight diluents. [1] M.T. Cicerone, M.J. Pikal, K.K. Qian, Stabilization of proteins in solid form, Advanced Drug Delivery Reviews, 93 (2015) 14-24. [2] J. Ubbink, Structural and thermodynamic aspects of plasticization and antiplasticization in glassy encapsulation and biostabilization matrices, Advanced Drug Delivery Reviews (in press), doi:10.1016/j.addr.2015.12.019 (2016). [3] M.T. Cicerone, J.F. Douglas, β-Relaxation governs protein stability in sugar-glass matrices, Soft Matter, 8 (2012) 2983-2991. [4] S. Townrow, M. Roussenova, M.I. Giardiello, A. Alam, J. Ubbink, Specific Volume-Hole Volume Correlations in Amorphous Carbohydrates: Effect of Temperature, Molecular Weight, and Water Content, J Phys Chem B, 114 (2010) 1568-1578

Delivery of Functionality in Complex Food Systems: Physically Inspired Approaches from Nanoscale to Microscale, Wageningen 18–21 October 2009

The Wageningen Delivery of Functionality symposium covered all aspects involved with food structural design to arrive at high-quality foods which meet demanding customer expectations and regulatory requirements. The symposium integrated aspects from the structural organization of foods at molecular and supramolecular scales to dedicated techniques required to describe and visualize such structures, the gastro-intestinal events and how to model these in a laboratory setting, and finally the impact those food structures and ingredients have on the consumer’s physiology and on the human perception. As an interdisciplinary platform, bringing together more than 160 researchers from academia and industry, the symposium meanwhile fulfills an important role in the food science communit

The Cell Wall of Lactic Acid Bacteria: Surface Constituents and Macromolecular Conformations

A variety of strains of the genus Lactobacillus was investigated with respect to the structure, softness, and interactions of their outer surface layers in order to construct structure-property relations of the Gram-positive bacterial cell wall. The role of the conformational properties of the constituents of the outer cell-wall layers and their spatial distribution on the cell wall is emphasized. Atomic force microscopy was used to resolve the surface structure, interactions, and softness of the bacterial cell wall at nanometer-length scales and upwards. The pH-dependence of the electrophoretic mobility and a novel interfacial adhesion assay were used to analyze the average physicochemical properties of the bacterial strains. The bacterial surface is smooth when a compact layer of globular proteins constitutes the outer surface, e.g., the S-layer of L. crispatus DSM20584. In contrast, for two other S-layer containing strains (L. helveticus ATCC12046 and L. helveticus ATCC15009), the S-layer is covered by polymeric surface constituents which adopt a much more extended conformation and which confer a certain roughness to the surface. Consequently, the S-layer is important for the overall surface properties of L. crispatus, but not for the surface properties of L. helveticus. Both surface proteins (L. crispatus DSM20584) and (lipo)teichoic acids (L. johnsonii ATCC332) confer hydrophobic properties to the bacterial surface whereas polysaccharides (L. johnsonii DSM20533 and L. johnsonii ATCC 33200) render the bacterial surface hydrophilic. Using the interfacial adhesion assay, it was demonstrated that hydrophobic groups within the cell wall adsorb limited quantities of hydrophobic compounds. The present work demonstrates that the impressive variation in surface properties displayed by even a limited number of genetically-related bacterial strains can be understood in terms of established colloidal concepts, provided that sufficiently detailed structural, chemical, and conformational information on the surface constituents is available

Poisson–Boltzmann theory of the charge-induced adsorption of semi-flexible polyelectrolytes

A model is suggested for the structure of an adsorbed layer of a highly charged semi-flexible polyelectrolyte on a weakly charged surface of opposite charge sign. The adsorbed phase is thin, owing to the effective reversal of the charge sign of the surface upon adsorption, and ordered, owing to the high surface density of polyelectrolyte strands caused by the generally strong binding between polyelectrolyte and surface. The Poisson–Boltzmann equation for the electrostatic interaction between the array of adsorbed polyelectrolytes and the charged surface is solved for a cylindrical geometry, both numerically, using a finite element method, and analytically within the weak curvature limit under the assumption of excess monovalent salt. For small separations, repulsive surface polarization and counterion osmotic pressure effects dominate over the electrostatic attraction and the resulting electrostatic interaction curve shows a minimum at nonzero separations on the Ångstrom scale. The equilibrium density of the adsorbed phase is obtained by minimizing the total free energy under the condition of equality of chemical potential and osmotic pressure of the polyelectrolyte in solution and in the adsorbed phase. For a wide range of ionic conditions and charge densities of the charged surface, the interstrand separation as predicted by the Poisson–Boltzmann model and the analytical theory closely agree. For low to moderate charge densities of the adsorbing surface, the interstrand spacing decreases as a function of the charge density of the charged surface. Above about 0.1 M excess monovalent salt, it is only weakly dependent on the ionic strength. At high charge densities of the adsorbing surface, the interstrand spacing increases with increasing ionic strength, in line with the experiments by Fang and Yang [J. Phys. Chem. B 101, 441 (1997)].BiotechnologyApplied Science

Water vapor sorption and glass transition temperatures of phase-separated amorphous blends of hydrophobically-modified starch and sucrose

This article contains water vapor sorption data obtained on amorphous blends of octenyl succinic acid-modified (denoted as hydrophobically modified starch; HMS) and sucrose (S) in the anhydrous weight HMS/S ratios between 100/0 and 27/75. The water vapor sorption data was obtained gravimetrically. The amorphous state of the blends was confirmed by X-ray diffraction. The glass transition temperatures of the phase-separated blends are listed; the blends show phase separation into a sucrose-rich phase and a HMS-rich phase, the composition of which varies with the blend ratios. The sucrose-rich phase is characterized by a glass transition temperature Tg,lower that is 40 to 90 K lower than the glass transition temperature Tg,upper of the HMS-rich phase

Biodegradable starch particles for controlled release applications : swelling and leaching mechanisms

Starch-extruded particles have only found infrequent use as delivery systems for active ingredients. We have previously shown that these particles are attractive for releasing hydrophobic compounds in water media. Here, we cover a range of amylose-amylopectin ratios and evaluate the presence of the thyme essential oil (TEO) as active compound to understand the dominant release mechanism in relation to the physicochemical properties of the starch matrices. Starch blends with high amylopectin content (1.8 and 15% amylose) could not be shaped into regular particles. For amylose contents higher than 28%, the equilibrium degree of swelling in water decreased with increasing amylose contents, from nearly 300% for an amylose content of 28-90% at an amylose content of 70%. For both lowest amylose contents, 1.8 and 15%, leaching of solids and disintegration of the particles resulted in a low apparent degree of swelling. The presence of TEO reduces the degree of swelling of the gelatinized starch matrix. This is explained by the formation of thymol-amylose complexes, which is confirmed by Fourier transform infrared spectroscopy analysis and X-ray diffractionCAPES - Coordenação de Aperfeiçoamento de Pessoal e Nível SuperiorFAPESP – Fundação de Amparo à Pesquisa Do Estado De São Paulonão tem16/09824-

Influence of Fermentation Medium Composition on Physicochemical Surface Properties of Lactobacillus acidophilus

The effect of the simple and complex basic components of a fermentation medium on the surface properties of Lactobacillus acidophilus NCC2628 is studied by physicochemical methods, such as electrophoresis, interfacial adhesion, and X-ray photonelectron spectroscopy, and by transmission electron microscopy. Starting from an optimized complete medium, the effect of carbohydrates, peptones, and yeast extracts on the physicochemical properties of the cell wall is systematically investigated by consecutively omitting one of the principal components from the fermentation medium at the time. The physicochemical properties and structure of the bacterial cell wall remain largely unchanged if the carbohydrate content of the fermentation medium is strongly reduced, although the concentration of surface proteins increases slightly. Both peptone and yeast extract have a considerable influence on the bacterial cell wall, as witnessed by changes in surface charge, hydrophobicity, and the nitrogen-to-carbon ratio. Both zeta potential and the cell wall hydrophobicity show a positive correlation with the nitrogen-to-carbon ratio of the bacterial surfaces, indicative of the important role of surface proteins in the overall surface physical chemistry. The hydrophobicity of the cell wall, which is low for the cultures grown in the complete medium and in the absence of carbohydrates, becomes fairly high for the cultures grown in the medium without peptones and the medium without yeast extract. UV spectrophotometry and sodium dodecyl sulfate-polyacrylamide gel electrophoresis combined with liquid chromatography-tandem mass spectrometry are used to analyze the effect of medium composition on LiCl-extractable cell wall proteins, confirming the major change in protein composition of the cell wall for the culture fermented in the medium without peptones. In particular, it is found that expression of the S-layer protein is dependent on the protein source of the fermentation medium

Drying of maltodextrin solution in a vacuum spray dryer

New drying strategies that use low temperatures can have a significant impact on the improvement of food quality, in particular regarding the retention of flavor compounds, bioactives and other thermosensitive components. The vacuum spray dryer (VSD) is a spray dryer that operates with a low-pressure drying chamber, which consequently reduces the increases the thermodynamic driving force for water removal and allows drying at significantly reduced temperatures. In order to understand the process behavior and define operational strategies, a mathematical model that encompasses mass and energy balances was validated with experimental measurements of pressure and temperature during drying of large chained maltodextrin (dextrose equivalent =10). Results from experiments carried out in a pilot VSD present a good fit with the proposed model and confirmed its underlying assumptions. In addition, comparative analyses were performed regarding physical aspects of particles produced by VSD and by conventional spray dryer (SD) in the same equipment, but without vacuum. Under the tested conditions, VSD particles presented a higher moisture content (8%) and smaller time of wettability than SD particles. The morphological changes were caused by the vacuum and can be interesting for technological applications1467886COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESnão te