STABILITY STUDIES OF PAPAYA PECTINESTERASE

Stability studies were carried out on the purified papaya (Carica papa ya L. var. exotica) pectinesterase (EC 3.1.1.11). The enzyme preparati on was stable at 4 degrees C in 0 . 02M sodium phosphate buffer (pH 7 . 5) solution containing 0 . 2M NaCl and 0 . 02% sodium azide and the loss in activity was less than 5% after storage for 1 year. The thermo stability studies showed that enzyme was more heat-stable at pH 7 . 5 than at pH 4. After heating at 60 degrees C for 5 min, 65 . 6 and 82% activity still remained at pH 4 and pH 7 . 5, respectively. It was com pletely inactivated by heating for 5 min at 70 and 75 degrees C at pH 4 and pH 7 . 5, respectively. The D values (time to inactivate 90% of the enzyme) at 55, 60, 65 and 70 degrees C at pH 4 . 0 were estimated to be 112 . 14, 23 . 78, 8 . 33 and 1 . 71 min, respectively. Lower in activation rates were observed for pH 7 . 5, with the D values ranging from 143 . 27 to 1 . 67 min for temperatures between 60 and 75 degree s C. The Z values, which indicate the rise in temperature necessary to observe a 10-times faster rate of heat-inactivation, were estimated t o be 7 . 8 degrees C and 8 . 38 degrees C at pH 7 . 5 and pH 4 . 0, re spectively. The inactivation energies and Q(10) values were calculated as 256 . 9 kJ/mol and 15 . 59 at pH 4 . 0 and 284 . 76 kJ/mol and 19 . 21 at pH 7 . 5, respectively. pH stability studies showed that the e nzyme was stable from pH 4-11 after exposure of the enzyme to these pH s for 24 h at 30 degrees C. More than 85% of the activity was retained in all of these cases. However, at pH 1 and 12, the enzyme was unstab le and it completely lost its activity after 24 h of incubation at 30 degrees C.