Organic acids in nature.

Naturally occurring organic acids are acetic acid (a fermentation and metabolic by-product found in vinegar), citric acid (citrus fruits), malic acid (apples), niacin, all amino acids (although some are purely basic because they antagonize basic amino groups or closely related groups), fumaric and cinnamic acids, uric acid (nitrogen metabolism), cholic acid (as a steroid, which, among other things, acts as a detergent-like emulsifier), gluconic acid (glucose oxidation), etc.