Evaluation of health aspects of kojic acid in food

Kojic acid is a fungal metabolite commonly produced by many species of Aspe rgillus, Acetobacter, and Penicillium, The Aspergillus flavus group has tra ditionally been used in the production of a number of foods, including mise (soybean paste), shoyu (soy sauce), and sake. Kojic acid is widely used as a food additive for preventing enzymatic browning, and in cosmetic prepara tions as a skin-lightening or bleaching agent. Because kojic acid is often produced during the fermentation of historically used dietary staples, it h as a long history of consumption. Various types of compounds, such as gluco se, sucrose, acetate, ethanol, arabinose, and xylose, have been used as car bon sources for kojic acid production. Different Aspergillus species are kn own to produce variable amounts of kojic acid. The mechanism of action of k ojic acid is well defined and it has been shown to act as a competitive and reversible inhibitor of animal and plant polyphenol oxidases, xanthine oxi dase, and D- and some L-amino acid oxidases, The structure of kojic acid in dicates a relatively simple route of metabolism much like dietary hexoses, Acute or subchronic toxicity resulting from an oral dose has not been repor ted, but convulsions may occur if kojic acid is injected. Results of mutage nicity studies are mixed, but in the in vivo mammalian dominant lethal assa y, kojic acid was proven negative. Continuous administration of high doses of kojic acid in mice resulted in induction of thyroid adenomas in both sex es. Kojic acid reversibly affects thyroid function primarily by inhibiting iodine uptake, leading to decreases in T-3 and T-4 and increase in TSH. Inc reased TSH from pituitary gland in turn stimulates thyroid hyperplasia. Sev eral lines of evidence indicate that the proliferative effects of kojic aci d on thyroid are not related to a genotoxic pathway. The risk of functional inhibition of iodine uptake and its metabolism (organification) and thyroi d tumor induction by kojic acid in humans appears to be extremely low. Base d on the literature reviewed and discussed here, consumption of kojic acid at levels normally found in food does not present a concern for safety. (C) 2001 Academic Press.