Robert G. Gilbert

Structure and physicochemical properties of octenyl succinic anhydride modified starches: A review

Starches modified with octenyl succinic anhydride (OSA) have been used in a range of industrial applications, particularly as a food additive, for more than half a century. Interest in these products has grown in recent years as a result of new methods and applications becoming available. Due to a combination of OSAs hydrophobic and steric contribution and starchs peculiar highly branched macromolecular structure, these starch derivatives display useful stabilizing, encapsulating, interfacial, thermal, nutritional and rheological properties. We review the synthesis procedures, structural characterization methods and physico-chemical properties, and the influences of the botanical origins and structural parameters of OSA starches on physico-chemical properties. A better understanding of these features has the potential to lead to products with targeted macromolecular structures and optimized properties for specific applications.

Characterization of Starch by Size-Exclusion Chromatography: The Limitations Imposed by Shear Scission

Shear degradation is examined in size-exclusion chromatography (SEC, or GPC) of native starch in an eluent system (dimethylsulfoxide and LiBr) in which the starch is completely dissolved. Changes in apparent size distribution with flow rate suggested extensive shear scission of the amylopectin region. For smaller sizes, largely amylose, there was no significant scission for lower flow rates. Quantification by analogy to shear breakup of dispersed droplets gives a scaling law for conditions for shear scission of highly branched polymers. This shows both that it is impossible to obtain reliable size distributions for the amylopectin component of starch using current SEC technology and also that the amylose region is not significantly polluted by degraded amylopectin for lower flow rates. Hence, the complete size distribution of starch can only be obtained with SEC for smaller sizes (largely amylose), plus a size-separation technique with very low shear, such as field-flow fractionation, for the amylopectin region.

Classical trajectory studies of the reaction CH4+H→CH3+H2

Trajectory data are reported for the reaction CH4+H→CH3+H2, designed to provide information that can be used to test approximate quantitative theories for the dynamics of abstraction reactions. A potential function was devised which properly reflects the nuclear permutation symmetry of the process. Microscopic reaction rate coefficients were obtained as functions of fixed rotational and vibrational energy, and of the angular momentum. The data indicated significant uncoupling between the various modes although, at a minimum, the symmetric stretch is directly coupled to the reaction coordinate at the transition state. The data were used to test the assumption that the total angular momentum, J, may be approximated by the orbital angular momentum, L. L is approximately conserved from the reactant to the saddle point configuration in reactive and nonreactive collisions and may be well approximated by J. The angular momentum about the long axis of the reacting system (equivalent to the K quantum number) is no...

Trajectory simulations of collisional energy transfer in highly excited benzene and hexafluorobenzene

Quasiclassical trajectory calculations of the energy transfer of highly vibrationally excited benzene and hexafluorobenzene (HFB) molecules colliding with helium, argon and xenon have been performed. Deactivation is found to be more efficient for HFB in accord with experiment. This effect is due to the greater number of low frequency vibrational modes in HFB. A correlation between the energy transfer parameters and the properties of the intramolecular potential is found. For benzene and HFB, average energies transferred per collision in the given energy range increase with energy. Besides weak collisions, more efficient ‘‘supercollisions’’ are also observed for all substrate–bath gas pairs. The histograms for vibrational energy transfer can be fitted by biexponential transition probabilities. Rotational energy transfer reveals similar trends for benzene and HFB. Cooling of rotationally hot ensembles is very efficient for both molecules. During the deactivation, the initially thermal rotational distribution heats up more strongly for argon or xenon as a collider, than for helium, leading to a quasi‐steady‐state in rotational energy after only a few collisions.

The importance of amylose and amylopectin fine structures for starch digestibility in cooked rice grains

Statistically and causally meaningful relationships are established between starch molecular structures (obtained by size-exclusion chromatography, proton NMR and multiple-angle laser light scattering) and digestibility of cooked rice grains (measured by in vitro digestion). Significant correlations are observed between starch digestion rate and molecular structural characteristics, including fine structures of the distributions of branch (chain) lengths in both amylose and amylopectin. The in vitro digestion rate tends to increase with longer amylose branches and smaller ratios of long amylopectin and long amylose branches to short amylopectin branches, although the statistical analyses show that further data are needed to establish this unambiguously. These new relationships between fine starch structural features and digestibility of cooked rice grains are mechanistically reasonable, but suggestive rather than statistically definitive.

Characterization of branched polysaccharides using multiple‐detection size separation techniques

The structure of branched polysaccharides involves a hierarchy of levels, from the constituent sugars, then the branching pattern, up to the macromolecular architecture, and then supramolecular organization. Finding causal relations between this complex structure/architecture and both (bio)synthetic mechanisms and final properties is needed for understanding the functionality of branched polysaccharides, which is important in fields ranging from improved nutrition and health through to papermaking and pharmaceuticals. The structural complexity makes this task especially challenging. This review focuses on the best current means to obtain reliable branch chain and size distributions using size-separation technologies coupled with number-, mass- and molecular-weight-sensitive detectors. Problems with current technologies are also critically appraised.

Modelling particle size distributions and secondary particle formation in emulsion polymerisation

An extensive model is given for the particle size distribution (PSD), particle number, particle size and amount of secondary nucleation in emulsion polymerisations. This incorporates what are thought to be all of the complex competing processes: aqueous phase kinetics for all radical species arising from both initiator and from exit (desorption), radical balance inside the particles, particle formation by both micellar and homogeneous nucleation mechanisms, and coagulation (the rate of which is obtained using the Healy-Hogg extension of DLVO theory). The predictions of the model are compared to extensive experimental results on rates, time evolution of the particle size distribution, and relative amounts of secondary nucleation, for styrene initiated by persulfate with sodium dodecyl sulfate and with sodium dihexyl sulfosuccinate as surfactants. For this system values of almost all of the many parameters needed for the model are available from independent measurements, and thus no significant parameter adjustment is plausible. Accord with experiment is imperfect but quite acceptable, supporting the validity of the various mechanisms in the model. Effects such as the experimental variation of particle number with ionic strength, as well as calculated coagulation rate coefficients as functions of particle size, suggest that coagulation of precursor (i.e., newly-formed) particles is a significant effect, even above the cmc. The modelling also suggests why secondary nucleation occurs readily in systems stabilised with polymeric surfactant.

Terminology of polymers and polymerization processes in dispersed systems (IUPAC Recommendations 2011)

A large group of industrially important polymerization processes is carried out in dispersed systems. These processes differ with respect to their physical nature, mechanism of particle formation, particle morphology, size, charge, types of interparticle interactions, and many other aspects. Polymer dispersions, and polymers derived from polymerization in dispersed systems, are used in diverse areas such as paints, adhesives, microelectronics, medicine, cosmetics, biotechnology, and others. Frequently, the same names are used for different processes and products or different names are used for the same processes and products. The document contains a list of recommended terms and definitions necessary for the unambiguous description of processes, products, parameters, and characteristic features relevant to polymers in dispersed systems.

Milling of Rice Grains. The Degradation on Three Structural Levels of Starch in Rice Flour Can Be Independently Controlled during Grinding

Whole polished rice grains were ground using cryogenic and hammer milling to understand the mechanisms of degradation of starch granule structure, whole (branched) molecular structure, and individual branches of the molecules during particle size reduction (grinding). Hammer milling caused greater degradation to starch granules than cryogenic milling when the grains were ground to a similar volume-median diameter. Molecular degradation of starch was not evident in the cryogenically milled flours, but it was observed in the hammer-milled flours with preferential cleavage of longer (amylose) branches. This can be attributed to the increased grain brittleness and fracturability at cryogenic temperatures, reducing the mechanical energy required to diminish the grain size and thus reducing the probability of chain scission. The results indicate, for the first time, that branching, whole molecule, and granule structures of starch can be independently altered by varying grinding conditions, such as grinding force and temperature.

New 1H NMR Procedure for the Characterization of Native and Modified Food-Grade Starches

A novel, fast, and straightforward procedure is presented for the characterization of starch (the largest energy component in food) and modified starches (such as octenyl succinic anhydride (OSA)-modified starches used as a dispersing agent in the food industry). The method uses (1)H NMR to measure the degree of branching and also, for modified starches, the degree of chemical substitution. The substrate is dissolved in dimethyl-d(6) sulfoxide; addition of a very low amount of deuterated trifluoroacetic acid (d(1)-TFA) to the medium gives rise to a shift to high frequency of the exchangeable protons of the starch hydroxyl groups, leading to a clear and well-defined (1)H NMR spectrum, which provides an improved way to determine the degrees of both branching and chemical substitution. Measurements of the size and molecular weight distributions by multiple-detector size exclusion chromatography show that degradation by TFA does not affect the accuracy of the method.