There's a myth that says certain foods are acid and others are alkali and this is somehow significant to health. This is not true, the body keeps pH controlled to a very fine degree.

The acid alkaline food hypothesis was part of the ptomaine theory of scurvy, whose cure had been discovered and lost over and over again.

The acid/alkali idea doesn't appear again in the scientific literature. It is a 100 year old bad guess that didn't pan out. There is no evidence it is true or meaningful in any way.

See paragraph 3 on Page 326 of:

"Sailors' scurvy before and after James Lind–a reassessment Jeremy Hugh Baron"
doi:10.1111/j.1753-4887.2009.00205.x
Nutrition Reviews® Vol. 67(6):315–332
http://idlewords.com/sailors_scurvy.pdf

"In 1897, the Norwegian polar explorer Fridtjof Nansen cited Dr. Torup, professor of physiology at Oslo, as proposing that scurvy was a form of ptomaine poisoning (an Italian term of 1870) from badly preserved meat and fish, and a subsequent Lancet editorial called scurvy “a condition of acid intoxication”. By 1900, this ptomaine theory was tested in monkeys who developed diarrhea and spongy gums on tainted, but not on fresh, meat.179 However, the chief advocate of the acid intoxication hypothesis was the distinguished immunologist Almroth Wright, professor of pathology at the Army Medical School, Netley from 1892.180,181 Wright blamed scurvy on eating acid meat and cereals, rather than alkaline green vegetables, tubers, and fruit. He described seven patients with such acidity that were treated with salts of organic acids such as sodium lactate or bicarbonate with improvement in their acidity, but four died, and perhaps only patient no. 1 had a history typical of scurvy. Wright persisted with his acid intoxication model and its corollary, the treatment with alkalies,182,183 so that the 1911 Encyclopaedia Britannica favored this suspect unknown microorganism of “the more chemical school of pathologists”.

All these models were abandoned with the isolation of ascorbic acid as vitamin C (see above)."