Flavour-encapsulation and flavour-release performances of a commercial yeast-based delivery system

Empty yeast cells are used as a thermo-stable delivery system for flavour encapsulation. The flavour encapsulation efficiency was assessed regarding flavour molecule properties. A model based on passive transfer demonstrated the selectivity of the external cell wall and the attractive role of the internal yeast plasma membrane (phospholipid bi-layer). Not all the molecules can penetrate inside the yeast. Selection is based on the hydrophobic properties. The efficiency of encapsulation is higher than 50% for flavour compound log P higher than 2.0. Flavour release mechanism from yeast cells was characterized using a series of analytical techniques and limonene was used as a model representing a hydrophobic flavour. Dry loaded cells immersed "in water" or "in oil" or "in water and then in oil" showed different behaviours regarding the release performances leading to the careful study of the encapsulation barrier properties. Water is needed for release to occur. The modelling of the drying of the cell wall was consistent with a huge kinetic hysteresis between water sorption and water desorption isotherms. This also explained the unexpected reduction of the cell wall permeability as a function of temperature and water loss. Among others, these conditions insure flavour protection during specific application in cooking processes. Furthermore, organoleptic tests showed higher scores than conventional spray dry powders in battered products and in instant noodles, as expected from the stability conditions investigated. (c) 2007 Elsevier Ltd. All rights reserved.