T ^sub g^ and a ^sub w^ as criteria for the oxidative stability of spray-dried encapsulated paprika oleoresin

Moisture sorption isotherms and glass transition temperature (T ^sub g^) of paprika oleoresin microcapsules were evaluated. Microcapsules were produced by spray drying using modified starch (Capsul^sup ^) as encapsulating agent. The differential and integral thermodynamic functions of enthalpy and entropy were estimated from the sorption data for paprika oleoresin microcapsules. T ^sub g^ of microcapsules conditioned at various water activities (a ^sub w^'s) were determined by modulated differential scanning calorimetry. The critical water content or water activity (RHc) was estimated from T ^sub g^ values. Both a ^sub w^ and T ^sub g^ were used to determine the critical conditions for microcapsules storage. The GAB model provided a good fit to the experimental data. The point of maximum stability according to the minimum integral entropy ([Delta]S ^sub int^)^sub T^ was found at a ^sub w^ = 0.241 at 35 °C, and at this point the system was within the glassy state. RHc was founded at a ^sub w^ = 0.789 at 35 °C; all microcapsules stored at a ^sub w^'s [less than or equal to] 0.627 were able to maintain their structural integrity without caking and stickiness occurring. The lowest carotenoid degradation of microcapsules during storage at 35 °C proceeded at a ^sub w^ = 0.742, which was near to RHc; however, microcapsules stored at this a ^sub w^ showed incipient caking and agglomeration. [Figure not available: see fulltext.]