Photometric extinction measurements to study dissolution kinetic of skim milk powder

Abstract

To study dissolution kinetic of spray dried skim milk powder (SMP), the change in light extinction was measured during dissolution of twenty-six commercial SMPs with different processing histories. SMP dissolution could be divided into two stages; the second stage could be described as a two–step process. In the first stage extinction increased up to maximum within 30–120 s. The second stage was characterised by a fast decrease in extinction followed by a slight decrease. To estimate dissolution times, the second stage was modelled using a biexponential function. The fast period was finished after 12–63 min, whereas the slower period took 9–23 h. Most of the observed changes in micelle size and soluble calcium occurred in the time frame of the fast period. SMP with low whey protein nitrogen index (WPNI) showed higher extinction values and micelle sizes, and tended to have longer dissolution times than SMP with high WPNI.