T and a as criteria for the oxidative stability of spray-dried encapsulated paprika oleoresin.

Moisture sorption isotherms and glass transition temperature ( T) of paprika oleoresin microcapsules were evaluated. Microcapsules were produced by spray drying using modified starch (Capsul) as encapsulating agent. The differential and integral thermodynamic functions of enthalpy and entropy were estimated from the sorption data for paprika oleoresin microcapsules. T of microcapsules conditioned at various water activities ( a's) were determined by modulated differential scanning calorimetry. The critical water content or water activity (RHc) was estimated from T values. Both a and T 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 (Δ S) was found at a = 0.241 at 35 °C, and at this point the system was within the glassy state. RHc was founded at a = 0.789 at 35 °C; all microcapsules stored at a's ≤ 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 = 0.742, which was near to RHc; however, microcapsules stored at this a showed incipient caking and agglomeration. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]