Does cornstarch affect the pH of what I'm cooking? I'm considering canning some fruit compotes to use with yogurt, and the recipe I want to use (which was not designed with canning in mind, found here: http://www.simplebites.net/how-to-make-your-own-fruit-bottom-yogurt/ ) calls for cornstarch to be used to thicken everything up. 

Now, I do not have a pressure cooker, so I would be doing this with a water bath canner, and I'd like to know if the cornstarch is going to lower the acidity of the fruit mixture, or if I should use some other thickening agent or method.

Thanks!
I don't have any info on the affect of pH, but cornstarch can make your compote separate when canned: http://www.sbcanning.com/2011/08/canning-pie-filling-education-in-clear.html.

Two alternative thickeners are tapioca and clearjel.  I've used clearjel for canning with excellent results.  I haven't used tapioca to can, but do prefer it in my pies.

(posted as an answer per Sobachatina's recommendation)