The effect of dispersion mechanisms on aroma delivery
Dispersion of aroma compounds in food matrices is a common process in the production of many food products. However, the degrees of dispersion on the distribution and subsequent release of these compounds during consumption may have considerable consequences for perception of these flavours. This thesis investigates the effects of a range of dispersion techniques on the delivery and release of aroma compounds from several solid and semi-solid matrices which commonly contain added flavourings. Dispersion was achieved on three main scales ranging from molecular, through micro regions to physical separation or layering. The effects of different levels of mixing were assessed by measuring aroma release in vitro and in vivo via APci-MS. Having defined the stages of mixing, systems were developed to measure the influences of different dispersion techniques on aroma delivery. Layering to physically separate homogenous aroma-rich layers showed no significant effects on aroma release or perception from gelatine sucrose gels. It seems that mastication is very effective in re-mixing these systems and, in vivo there is no difference in aroma release. Although the degree of mixing could be controlled using a static mixer system for yoghurts, no effects of the different levels of mixing were observed on aroma release. Stirred yoghurts showed that mixing could influence equilibrium headspace concentrations but overall release in vivo was inconclusive. Sample selection in these systems may be important for influencing perception. Visual and textural cues may be more important for perception, in these mixing examples, than aroma release. Using co-solvents as dispersion agents significantly increased the ease of dispersion of a range of aroma compounds. Static headspace analysis confirmed that all the carrier solvents influenced the partition of aroma compounds and in vivo release from model confectionery systems. Increasing solvent concentration increased the solubility of a range of aroma compounds in the liquid phase. Release from gels was also influenced by the presence of solvents with hydrophobic aroma compounds showing patterns of release similar to those of hydrophilic compounds when dispersed using solvents. Finally, this work studied release from phase separated systems where the aroma compound was present as a microdroplet. Release was very intense and rapid and was investigated in aqueous solutions and gelatine-sucrose gels. In this case the release mechanism was not the conventional air-liquid partition but was based on direct release from the air-liquid interface. Release was dependent on both hydrophobicity and vapour pressure.