Many types of fresh fruit, including pineapple, contain citric acid, which gives fruit its tart flavor. However, while numerous components of pineapple contribute to its nutritional value, citric acid does not. Citric acid won't hurt you, but it may contribute to acid reflux.
Pineapple, whether fresh or dried, contains large quantities of carbohydrates, which your cells use for energy. It also contains the antioxidant vitamin C, or citric acid. A statement from Columbia University explains that foods high in citric acid don't actually cause acid reflux, but the acid can make stomach contents more acidic, and therefore more irritating to your esophagus.
Citric acid is very common in nature, occurring not just in fruits, but also in the cells of almost every living organism. The cells of the human body make citric acid as they burn carbohydrates, fats and proteins for energy. However, this does not mean citric acid will make you feel more energetic.
Uses in the Body
When you consume pineapple, you absorb citric acid into your bloodstream via the intestine, explains Dr. A. Pajor in a 1999 article published in the scholarly journal "Seminars in Nephrology." From there, most of the citric acid you've eaten gets filtered into the urine. Some of your cells -- primarily liver cells -- use a very small amount of citric acid from the blood and convert it into fat. The quantity is nearly inconsequential, however, in the context of your diet.
Citric acid in pineapple, while rather unimportant from a nutritional perspective, has some industrial significance. In a 1995 article published in the scholarly journal "Biotechnology Letters" and written by Dr. Chau Tran and colleagues, pineapple scraps yielded very high levels of citric acid when the scraps were fermented by fungus. This is of interest in the food industry because citric acid is a common preservative in processed foods, and also increases foods' tartness.