Water activity measures the available free water in food that is responsible for biochemical reactions and is an important index to determine microbial stability of food. The powder produced at the inlet temperature of 170 C had significantly (P < 0.05) higherwater activity than those produced at 180 or 190 C (Table 6). Normally food is considered microbiologically stable if the water activity is less than 0.6 (Quek et al., 2007).
The vitamin C content of the CJP was higher in the CJP1 than the juice powder produced at 180 or 190 C (Table 6). Vitamin oxidization during thermal processing is documented by Selman(1994) & Damodaran et al. (2008). CJP1 had significantly higher b-carotene than CJP3, A similar b-carotene loss was reported when watermelon juice spray dried at 190 C (Quek et al., 2007). The chemical structure of carotenoids is very susceptible to heat destruction and oxidation. Moreover, they may undergo isomerization during thermal processing