(Fig. 4A) revealed surfaces that were as smooth as those samples
which were stored at 11.3% RVP. Again, samples stored at RVP
43.2% showed very few coarse particles, whereas rough surfaces
were clearly detected on the samples stored at 57.6% and 68.9%
RVP. This is an indication of the occurrence of physico-chemical
changes in freeze-dried mango powder, particularly sugar crystallization.
All SEM results were in agreement with the XRD analysis.
In conclusion, the coarse particles formed on the surface of the
mango powder were sugar crystals.
3.3. Degradation of b-carotene during storage
The b-carotene content in freeze-dried mangoes decreases over
time during storage. To compare the degradation of b-carotene
among different storage RVP values, the rate constants were plotted
as a function of storage RVP (Fig. 5). Fig. 5 also shows the state
of samples at 25 C. Freeze-dried mango powder was in a glassy
state while stored at 11.3% RVP, whereas it was plasticized by
water and subsequently rendered into a rubbery state while stored
above an RVP of 11.3%. The decrease in the rate constant was found
at higher levels of storage RVP of up to 43.2%, which coincided with
the transition into the rubbery state. This was in agreement with
Prado et al. (2006), who observed a decrease in the rate constant
of b-carotene degradation in the encapsulated freeze-dried polymeric
matrix when stored at higher RVP levels. In the glassy state,
the rate constant of b-carotene degradation was determined to be