In the image on the top, the chemical standards (Manufacturer) for Glucuronic acid (Aldrich), Gluconic acid (Sigma), and Fructose (Sigma) are outlined by the dashed line. 2-keto-Gluconic acid (Sigma) is defined by the solid line. As you can see, Glucuronic acid and 2-keto-Gluconic acid are very close in retention times. The image on the bottom shows Kombucha contrasted against these chemical standards by the solid line. The reference material for 2-keto-Gluconic acid shown by the small dotted line is a perfect match to the 7.846 minute peak in Kombucha. Glucuronic acid peaks at 7.678 minutes, and without a reference material for the alpha-keto acid, it is easily confused with the peak found in many strains of Kombucha.

     It may be that the peak was originally identified as Glucuronic acid, because of the increased numbers of glucuronides in the urine of Kombucha drinkers. The theory being that an increase in glucuronides would be consistent with an increase in Glucuronic acid. There is another possible explanation for the increased glurcuronides in the urine of Kombucha drinkers ... the possible presence in Kombucha of a potent beta-glucuronidase inhibitor. Each Glucuronic acid molecule that forms a glucuronide with a toxin in the body is a one to one relationship (one Glucuronic acid molecule bound to one toxic molecule). Glucuronidase enzymes cleave the bond between the two molecules, but do not become bound themselves. A single glucuronidase enzyme can cleave hundreds of glucuronides. The presence of the beta-glucuronidase inhibitor, Saccharic acid 1,4-lactone, even in micro quantities can prevent the glucuronidase enzyme from cleaving the bound glucuronides.