Micropores and Their Relationship with Carotenoids Stability: A New Tool to Study Preservation of Solid Foods

Carotenoids were encapsulated by means of coacervation by using a nanostructured material (NE) prepared with alginate/zeolite valfor 100 (1:3) and another that was non-nanostructured (AA) prepared with alginate at 2 %. The diameter of the AA and NE capsules was ≈1,200 μm. The NE protected the carotenoids at higher water activities (a _w) than the AA. The highest retention of carotenoids (7,200 mg/kg dry solids for NE and 2,230 mg/kg dry solids for AA) was observed at water activities corresponding to the minimal integral entropy (≈0.35-0.45 for NE and ≈0.1 for AA). According to the enthalpy-entropy compensation, the water adsorption in the AA capsules was enthalpy driven at a _w range of 0.115-0.973. However, the NE showed two zones: (1) at low a _w (0.115-0.4), the water adsorption was controlled by entropy and (2) over an a _w range of 0.4-0.973, controlled by enthalpy. Atomic force microscope images, moisture content corresponding to micropore volume and thermodynamic properties suggest that the adsorption process and the carotenoids stability were controlled by entropic barriers when the water molecules were adsorbed in the micropores (nanopores with pore diameter <2 nm). The practical use of these results is that increasing the number of micropores in the solid matrix of wall materials is possible to improve the preservation of nutrients and functional substances during processing and storage of foods.