Encapsulation of liquid flavours in low water content, glass-forming carbohydrates is largely used to prevent their evaporation and the occurrence of adverse chemical reactions.
In amorphous matrices the retention of aroma compounds during storage has been related to physical and structural properties that hinder their release in the vapour phase. Two mechanisms are recognised toexplain the retention of an aroma in glassy materials. Oneis the“selective diffusion” based on the significant decrease of the diffusion coefficient of the small organic compounds in low moisture and mobility systems. The formation during encapsulation and below a critical watercontent of “microregions”within an impermeable matrixwhere volatiles are entrapped has been also postulated.Aroma compounds include molecules with different polarity and hydrophilicity. Solubility, partition and phase separation of volatiles in the carbohydrate matrix have also to be, thus, taken into account.
Glass transition is the main threshold implied in the increased release of the entrapped volatiles from amorphous systems. An increase of either moisture or temperature favours changes in mobility of the glassy matrix and the transition to a rubbery state and, in some cases to a crystalline one, decreases the volatile retention ability. Flavour release from maltodextrins matrices (alone or mixed with small saccharides) has been studied while little is known on the aroma retention ability of glassy matrices made of disaccharides alone.
This study investigates the retention of limonene, taken as model of hydrophobic volatile compounds, in amorphous trehalose, maltose and sucrose glassy matrices and its release as function of the hydration degree. Matrices have been characterised for their physical state at different moisture content by DSC. Limonene retention in the glassy matrices has been quantified and its release as a function of moisture content determined by gas-chromatographic analysis.
Physical properties of the matrices as affected by the sugar type and drying technology and the effect of the increased mobility due to water sorption on the limonene release will be presented and discussed.
