Capillary electrophoresis (CE) has been used for the separation and quantification of food polysaccharides including pectin, maltodextrin, carrageenan, and to study bulk phase separation in the pectin-starch-water system. Light scattering and optical rotation have been used to study kinetics of single and mixed protein-polysaccharide systems, in particular, gelatin-maltodextrin mixtures.
For pectins, it has been demonstrated that CE is capable of determining the degree of esterification (DE), irrespective of the pectin type and neutral sugar content. The effect of both DE and ionic strength on electrophoretic mobility are simulated using polyelectrolyte theory. Furthermore, this technique also allows the direct measurement of the intermolecular DE distribution (variation in DE between molecules). Results are compared with those obtained by ion-exchange chromatography in combination with size-exclusion chromatography (IEC-SEC). Both DE and DE distribution are obtained from CE in approximately 2 h, inclusive of sample preparation and calibration, in contrast to 2 days for the IEC-SEC method. For maltodextrin, after derivatising with the fluorescent reagent, 8- aminopyrene-1,3,6-trisulfonate (APTS), the distribution with resolution down to a single repeat residue up to DP 60 has been investigated by using CE with laser induced fluorescence (LIF) detection. Results for the mass distribution are compared with those obtained by size-exclusion chromatography using refractometric and light scattering detection. For carrageenan, a method for the quantitative analysis of K-, i- and 2- carrageenan has been developed using CE with LIF detection. Various carrageenan samples were first derivatised with APTS in both laboratory and commercial blend samples. Microcentrifuge filters (30 kDa) were then employed to separate derivatised samples into low (eluate) and high (retentate) molecular mass fractions which could each be assayed by CE with LIF detection. Quantitative aspects are evaluated and the method then applied to real commercial samples of food additive mixtures.
CE with diode-array detection (DAD) has been shown to be a useful analytical tool for studying the composition of bulk phase separated mixtures of two widely-used food biopolymers, starch and pectin. The limit of detection is approximately 0.5 mg ml1 for pectin and 0.2 mg ml'1 for starch (with added iodine/iodide to provide a charge and chromophore). CE has been shown to be an alternative to NMR in determining phase diagrams.
A novel technique has been used to perform polarimetry and turbidimetry at the same time and to simultaneously monitor the kinetics of gel formation and phase separation in gelatin- maltodextrin mixtures. Optical rotation tracks conformational change associated with gelation, whilst turbidity tracks the growth of sub-micron size domains during phase separation. Experiments on controlled cooling and heating cycles were used to determine the transition onset temperatures for conformational ordering and phase separation. Results suggest that the heating cycle is of particular importance to determine these temperatures under thermodynamic rather than kinetic control. Kinetics runs have been carried out using fast temperature quenching, monitoring time-dependent turbidity and optical rotation changes, with particular interest in the early phases of reaction.