The water activity of the spray dried astaxanthin powders is in
the range of 0.2–0.3 for both WPI/SCF70 and SC/SCF70 wall systems
(Table 1). Water activity measures the availability of free
water responsible for microbial and other deteriorative reactions.
Higher aw means more free water available for biochemical reactions,
leading to reduced shelf life. Powders with aw < 0.6 is generally
considered to be microbiologically stable (Labuza and Shafiur
Rahman, 2007), and if any spoilage occurred at the above aw value,
it is induced by chemical reactions rather than by microorganism.
Current results indicate that the astaxanthin powders are relatively
stable in terms of microbial spoilage.