As an amateur soda maker, I have noticed an odd phenomenon: lemon juice sodas do not foam. Virtually every juice I have tried foams to some degree when mixed with carbonated water. Lemon juice does not. I have read "folk" explanations for this as being due to the "acidity" of the lemon juice, but this is not correct because other acidic juices like lime and orange juice foam. Why is it that lemon juice has an anti-foaming action?
Further information: it should be noted that "pasteurized" (ie, boiled) lemon juice does foam. Only fresh-squozen lemon juice is anti-foaming. Therefore, what is doing the anti-foaming may likely be some volatile compound.
My understanding of anti-foaming is that it is caused primarily by localized depression of surface tension, and that liquids having heterogeneous species promote anti-foaming because of the surface tension differential between those species at the surface. Therefore, one possible theory is that the lemon juice has some volatile oil which populates the surface of the water only in spots and is causing the surface tension breakage. Even if this theory is correct, it remains to determine what this mysterious volatile oil is that is the cause.