Reginald H. Walter

The isolation and characterization of a water extract of konjac flour gum

Abstract An aqueous extract from konjac flour was dried, milled and redispersed in water, prior to its characterization by viscometry and rheometry. The rate of change of relative viscosity with reciprocal absolute temperature was of a magnitude less than that of some other polar polysaccharides by a factor approximating 2. The volume-concentration relationship was non-linear in water, but linear in 0·04 m tartaric acid. The hydrophilicity of this extract in 0·04 m tartaric acid was only 0·68 g g −1 solute/100 g dispersion, much less than that of many of the commonly used polysaccharides. The intrinsic viscosity was 1320 ml g −1 , among the highest of the polysaccharides. Considering the relatively low water affinity, the high viscosity of the konjac extract was attributed mostly to solute-solute interaction, rather than to hydration, at functional use-levels. The dried, redispersed extract was characterized in both steady and dynamic shear by the Carreau and Cross equations, and by the Cox-Merz rule. Deviation from the Cox-Merz rule was attributed to molecular associations of time scales longer than non-specific physical entanglements.

CHAPTER 7 – Isolation, Purification, and Characterization

This chapter discusses the isolation, purification, and characterization of polysaccharides. Polysaccharides are physically and chemically characterized in attempts to correlate their structure, properties, and function. Polysaccharides are isolated and extracted from vegetative milieu and concentrated in as high a concentration as possible, without serious structural modifications. Polysaccharides are usually separated from vegetable matter with the use of aqueous active solvents (hot dilute acids, alkalis, oxidants, etc). In isolation and purification, although water is the main solvent, when alcohol is included, it acts as an antidispersant of the hydrocolloidal solute. Numerous methods are available for analysis of polysaccharides, based either on their chemistry, occasionally involving unique fine structures and subunits, or on their response to ambient stimuli as chain molecules sensitive to altered environments. Neutral and ionic polysaccharides are distinguished from each other by charge on the latter, which originates from dissociation of acidic groups, complexation with ionic ligands, or adsorption of ions.

Pectin aggregation number by light scattering and reducing end-group analysis

Abstract Pectin determination by the copper-arsenomolybdate method is effectively a count of the total number of polymer molecules in a molar mass, ultimately yielding a number average molecular weight ( M n ). Light-scattering measurements yield a weight average ( M w ) of the number of light-scattering species that may be polymer molecules or aggregates of molecules, depending on solution (dispersion) conditions. Hence, the ratio M w / M n , may be interpreted as an aggregation number directly quantifying the molecules of pectin in the weight-average molar mass, under normal conditions of use of this polymer.

Quantitative definition of polysaccharide hydrophilicity

The increase in volume of a number of chain polysaccharides was measured with the aid of the density equation as a function of increasing concentration of polysaccharide. The hydrocolloids were carboxymethylcellulose, sodium alginate, a low-methoxyl and a high-methoxyl pectin, methylcellulose and guar gum. From the change of volume (converted to weight) of dispersion per g added polysaccharide per 100 g dispersion, a quantity defined as the hydrophilicity (H) was derived. On a molar basis, Hm = 5.56 · 10−3 · H · M kg, where M is the polysaccharide molecular weight. The magnitude of H was a property of the particular hydrocolloid, in every instance being substantially larger in pure water than in an electrolyte solution.

Molecular weight approximations of ionic polysaccharides by pH determinations

Abstract The molecular weight ( M ) of some ionic polysaccharides was determined by pH measurements inserted in an equation that was derived basically from the dissociation theory of low molecular-weight, weak acids. The equation contained a constant, f , defined as the segment factor, relating each carboxyl group to the repeating monomer. One f was common to the carboxylic acid polysaccharides, and another to the sulfuric acid polysaccharides. The universality of this new equation has not been determined, but M calculated with it gave molecular weights that were mostly in agreement with published M , and with M for pectin, measured by a conventional method (reducing-end-group analysis).

Volume fraction of a dispersed pectin

Abstract Foaming precludes direct volume ( V ) measurements of pectin dispersions, but the problem was overcome by calculating V from the density ( d ) of aliquot parts withdrawn from the interior volume, and substituting for d = W/V , where W = initial weight of the dispersion. By plotting V against moles for a series of pectin dispersions, the partial molal volume, denoted by the slope of the linear regression line, was determined. Thereby, thermodynamic equations developed for synthetic polymers, based on volume fractions, may be used to characterize the biopolymeric pectins.

CHAPTER 1 – Origin and Characteristics of Polysaccharides

This chapter discusses the sources and characteristics of polysaccharides,a class of biopolymers consisting of simple sugar monomers. Cellulose is the most abundant polysaccharide, which is the structural component of plant tissues. Polysaccharides used in commerce and industry are isolated from terrestrial and marine plants or are principally the exogenous metabolites of some bacteria; many are modified by partial organic synthesis and a few are the product of total biochemical synthesis. Polysaccharides are an important industrial, scientific, and medical commodity, and glycotechnology is a currently active area of pharmaceutical and medical research on oligosaccharides for drugs. Many polysaccharides are at the same time polyalcohols, polyacids, and polyesters composed of a topologically linear, main sequence of connected monomers in a variety of structures. The primary structure of a polysaccharide is the main sequence of connecting sugar monomers covalently linked as α and β glycosides. The molecular weight ( M ) of a polysaccharide is the gram mole or molar mass of 6.023 × 10 23 molecules (Avogadros number) that ideally are of a single size.

CHAPTER 5 – Additivity, Complementarity, and Synergism

This chapter discusses the additivity, complementarity, and synergism properties of polysaccharides. Mixed dispersions react by the same number-, weight-, and viscosity-average principles as single-solute dispersions, but combinations may evoke entirely new properties. When two polysaccharides are dispersed in water, under gelling conditions, the one more prone to gelation may develop a continuous reticulum throughout the solvent, embedding discrete volumes of the cosolute dispersion. The developed reticulum acquires the properties of the continuous phase polysaccharide and is filled with the cosolute. Additivity obtains when a measured property, e.g., viscosity, is the sum of the contributions made by each cosolute. The combined properties of the cosolutes in a single phase may exceed that of the additive property of each solute in separate phases in an identical volume of water, and this is referred to as synergism. The galactomannans, especially those with the least galactose substituents on the primary structure, display synergism with the broadest array of polysaccharides.

Derivation of a cooling-rate quotient for high-methoxyl pectin jelly sols

Abstract A common setting-rate index for pectin jelly sols was computed from an equation that was derived from consideration of the straight-line relationships between viscosity, reciprocal, absolute temperature and time, prior to gelation. The equation describes three major indices ( n ), that is, 0 n ⩽ 1 and n ⪢ 1, which should generally increase from slow-set to rapid-set pectins, according to the mathematical logic. This new system is mostly compatible with the existing trade classifications, while simultaneously eliminating the arbitrariness on which the latter are based. Inasmuch as the equation originates from a common time denominator, this mathematical method of classification requires fixed boundaries of the temperature-controlling events. The numerical values inserted in the derived equation have less significance than has the algebraic logic leading to n .

Application of intrinsic viscosity and the interaction coefficient to some ionic galacturonan dispersions

Abstract Aqueous dispersions of a number of galacturonans, commercially called pectins, were made to contain different concentrations of ethanol, and the corresponding slope ([η]2k′) of the viscosity number versus concentration graphs was factored into intrinsic viscosity ([η]) and an interaction coefficient (k′). Factoring was also done for purely aqueous dispersions at different temperatures. Low-OMe pectins appeared to be more susceptible to ethanol and heat than high-OMe pectins. This susceptibility is believed to arise from a tendency toward greater hydrogen bonding which in turn is quite sensitive to solution (dispersion) forces. At ethanol concentrations of 15–25%, all pectins exhibited large increases in [η]2k′, a development that is attributable to OMe—OMe bonding and a consequent increase in the frictional component of viscosity. Squaring or multiplication of small numerical differences in [η] and k′ leads to the conclusion that the slope is a more reliable index of dispersion behavior than is [η] or k′ separately. Although [η] is basically an inherent molecular property, theoretically free of interference in a given solvent system, and k′ is an independent property of that pectin-solvent system, any numerical value acquired by one will automatically impose a limit on the other. Comparisons of [η] or k′ under variable conditions are therefore meaningless without an appraisal of the impact of those conditions on the other parameter. Ageing the dispersions did not show any trend in either factor, but it was expected that OMe—OMe contacts would increase as a pre-condition of fractional deposition of solute.