A steady increase in activity from pH 4.8 up to pH 5.4 and a
gradual decline at higher pH levels were observed for the enzyme
(Fig. 4). This narrow pH range was previously shown to be
desirable for phytase applied to fermented calcium-fortified
soymilk (Tang et al., 2010) and the diet for broiler chickens
(Elkhalil et al., 2007). As expected, the change in the free
calcium concentration in the soymilk samples followed the same
trend as the enzyme. Therefore, the release of calcium ions
resulting from the action of phytase was pH-dependent. Such a
phytase activity–calcium release relationship was similar to that
observed at different temperatures (Fig. 3). Namely