Thermal stability and deactivation energy of free and immobilized invertase

The thermal stability and the energy of deactivation of free invertase and the immobilized enzyme (IE) was measured at temperatures in the range of 35 to 65 degreesC for the hydrolysis of a 5% w/v sucrose solution. The free e nzyme at pH 5.0 is stable up to 50 degreesC for a period of 4 h. Invertase immobilized in controlled pore silica by the silane-glutaraldehyde covalent method is stable up to 55 degreesC, in pH 4.5 For the same period. For hig her temperatures the enzyme deactivation follows the exponential decay mode l and half-lives are 0.53, 1.80, and 13.9 h for free invertase, at 65, 60, and 55 degreesC, respectively. For the IE hair-lives are 0.48, 1.83, and 20 .9 h, at 65, 60, and 55 degreesC, respectively. The IE is more stable than the free invertase; the energy of deactivation being 83.1 kcal/mol for the IE and 72.0 kcal/mol for the free enzyme.