Determination of the structural stability of a premix powder through the critical water activity

This paper analyses the structural stability of a premix powder that consists of a mixture of whey protein isolate, soy protein isolate, sodium caseinate, carrot juice, and honey bee, which are mixed together by spray-drying. The structural stability of the powder is determined by means of its critical water activity (RHc) at 25 degrees C, which is determined by three different procedures, namely, by the conventional graphical method, by calculating the inflection points in the adsorption isotherms, and by digital image analysis on the powders stored at different water activities (0.11aw0.53). These three methodological approaches can predict the value of RHc reliably.