Physical stability of a Lactose-Trehalose matrix for nano-encapsulation of beta-carotene by spray drying

Mestrado em Engenharia Alimentar - Instituto Superior de Agronomia

The purpose of this work was to study the physical properties of a model sugar system of lactose and trehalose, related to its potential as an encapsulation matrix. The encapsulation was accomplished by spray-drying of an oil-in-water emulsion, with an oil phase with high content of β-carotene, representing the encapsulated molecule. This study aimed to relate the water content of the matrix sugars with the variation of the glass transition temperature (Tg) and the occurrence of crystallization over time. The influence of these changes on the structure of the rehydrated emulsion and the carotene content of the powder were also to be assessed. Characterization of physical changes was made by describing sorption behaviour, physical structure of the reconstituted emulsion from the encapsulate, determination of the thermal transition by DSC, DMA and DEA, and microscopical observation of the stored spraydried powder. It was shown that the matrix remains stable if kept under an aw of 0.33 or lower. Higher figures may lower the glass transition to below room temperature, causing spontaneous crystallization and collapse of the matrix structure, thus affecting the flowability of the encapsulate and exposing carotene to the environment. Sorption data of the spray-dried powder fitted fairly to the BET and GAB isotherms, indicating a monolayer moisture of 4.64% and 3.21%, respectively. DSC analysis on lactosetrehalose model sugar systems showed a glass transition temperature of 107.9ºC for anhydrous sample, 55.2ºC for 11% RVP storage and 30,2ºC for 33% RVP. These results could not be correlated to the results from DMA and DEA analysis, due to the highly irregular results shown by these methods. It is suggested that these methods are inadequate for hydrated samples with high Tg. The droplet sizes obtained with ultra-high pressure homogenization, and the physical stability of the lactose-trehalose amorphous matrix are satisfactory. However, it is still necessary to study the encapsulation efficiency of this matrix on this kind of core material, with more appropriate quantitative methods. As for DMA and DEA analysis, further development of the method is needed to establish a reliable relation with the DSC results.