Pectin methylesterase activity and ascorbic acid content from guava fruit, cv. Predilecta, in different phases of development.

The guava pectin methylesterase (PME) specific activity and vitamin C were assayed in samples from different phases of guava fruit development. The PME enzyme from guava was extracted with borate-acetate buffer, 50 mol/l, pH 8.0, in the presence of NaCl 0.3 mol/l. The results showed PME optimum activity at pH 9 and 95 degrees C, and it is a thermostable enzyme. Guava PME retained 96.8% of activity after 300 min in 90 degrees C. Electrophoresis showed that guava PME contained two isoforms, one with 57 kDa molecular mass. The analyses of the different phases of guava maturation showed that ascorbic acid decreases during the maturation process, but PME activity increases with maturation.