Page "Kiwifruit" Paragraph 36

Actinidin also makes raw kiwifruit unsuitable for use in desserts containing milk or any other dairy products which are not going to be served within hours, because the enzyme soon begins to digest milk proteins.

This applies to gelatin-based desserts as well, as the actinidin will dissolve the collagen proteins in gelatin very quickly, either liquifying the dessert, or preventing it from solidifying.

However, the U. S. Department of Agriculture suggests cooking the fruit for a few minutes before adding it to the gelatin to overcome this effect.