Juice HACCP and Challenge study

Hello everyone!  So I have been out of juice HACCP for a while and now I am getting into it again. Where I am at we have a challenge study conducted. Can someone explain what the difference is between the challenge study and validation study is? Is it the same thing. Second, if we are keeping the same ingredients but changing the recipe do we need to do another challenge study? The ingredient being changed is ascorbic acid, we will be increasing it. I know per FDA, we need to accomplish a 5 log reduction but ascorbic acid shouldn't affect increasing this from the previous challenge study. Any help would be appreciated! 

The way you want to approach this is to group similar juices into a chemically equivalent group (i.e. pH & brix, or other factors) and use the study for your validation for the 5 log reduction.

Okay so my validation study is set to be below a certain pH therefore as long as this recipe change is below then I am okay. No new validation correct? 

 

Thank you!

Okay so my validation study is set to be below a certain pH therefore as long as this recipe change is below then I am okay. No new validation correct?

Thank you!

Not necessarily.
The answer is not that simple, since you are adding a new ingredient and more factors come into play.
However, you can reasonably conclude adding the ascorbic acid will not increase the pH & the chemical composition of the juice will not be significantly affected.