Over the temperature range tested, the concentration of free
calcium in phytase-treated soymilk was the greatest at 55 8C,
indicating that the calcium was most effectively liberated from
phytic acid at this optimum temperature (Fig. 3). Indeed, the
phytase activity assay produced a pattern of the curve that closely
paralleled that for free calcium, confirming that phytase is
responsible for the change of calcium from a bound state to a
free state. Therefore, this incubation temperature was ideal for
phytase-catalyzed release of calcium in soymilk. Previous studies
have also shown that temperatures between 50 and 60 8C provided
the optimum condition under which phytase functions to disrupt
phytate. Because the
conversion of bound calcium to free calcium remained moderately
strong (70.3%) even at the highest temperature tested (65 8C), the
enzyme appeared to be relatively tolerant to heat.