Sources/Uses
"Isocitric acid is a protonated form of isocitrate, which is a substrate of the citric acid cycle. . . . Isocitric acid is commonly used as a marker to detect the authenticity and quality of fruit products, most often citrus juices. In authentic orange juice, for example, the ratio of citric acid to D-isocitric acid is usually less than 130. An isocitric acid value higher than this may be indicative of fruit juice adulteration." [Wikipedia]