I assume you want to use something to keep the avocado from turning brown. That is a tough one as the only thing I know that does this is citrus. If you cannot eat citrus, can you eat ascorbic acid? I think Fruit Fresh is ascorbic acid. Don't know what else is in it.

The other alternative is to eat the avocado so quickly it doesn't have a chance to turn brown .

Sorry about not being able to eat citrus. That must really be difficult. I cannot have vinegar but am able to substitue lemon juice.
Anne