Changes in macroscopic viscosity do not affect the release of aroma aldehydes from a pectinaceous food model system of low sucrose content

The effects of pectin and viscosity on the release of a systematic series of aldehydes (alkanals, methyl-alkanals, alkenals, and alkandienals) were studied in a food model system of low sucrose content (10% w/w). The viscosity was varied by adding different amounts of Ca(2+) (0, 13.5, and 27 mg/g pectin) to the model system of constant pectin concentration (0.4% w/w). Air-liquid partition coefficients, K (37 degrees C), of the aroma compounds were determined in aqueous and pectin-thickened solutions. Diffusivities of the aroma compounds in water and three pectin-thickened solutions were estimated from release rate constants that were obtained via timed collection of volatiles in the gas phase and quantifications by dynamic headspace-gas chromatography. The partition coefficients increased as the carbon chain increased within each homologous series. Overall, no significant difference was found between partition coefficients of aldehydes in water and in pectin solutions except for 2-methyl-propanal and butanal that showed higher K values when pectin was present. Furthermore, the diffusional properties of the model system with a constant pectin level (0.4% w/w) remained constant when the viscosity was increased from 0.001 to 150 Pa s. It was concluded that neither pectin nor alterations in macroscopic viscosity as such influenced the release of aldehydes from the pectin-thickened food model system.