Mustard or ketchup. Sometimes Mayo.

AND I just found this:
Fruits and fruit juices high in acid
Here’s a list of fruits and their pH from Clemson University. They are listed from most acidic to least:

lemon juice (pH: 2.00–2.60)
limes (pH: 2.00–2.80)
blue plums (pH: 2.80–3.40)
grapes (pH: 2.90–3.82)
pomegranates (pH: 2.93–3.20)
grapefruits (pH: 3.00–3.75)
blueberries (pH: 3.12–3.33)
pineapples (pH: 3.20–4.00)
apples (pH: 3.30–4.00)
peaches (pH: 3.30–4.05)
oranges (pH: 3.69–4.34)
tomatoes (pH: 4.30–4.90)