My Mother-In-Law can only eat low acid foods due to a medical condition. It is not an allergy but I assume this would include tomato and citrus, but I am not sure what else?
acidalkalinediet.com has things about alkaline (not acidic) foods.I’ve heard of this, but haven’t ‘done’ it.
The following page also has a nice chart of acidic versus alkaline food. This should be useful/handy for you.
http://www.essense-of-life.com/info/foodchart.htm