4-Hydroxy-2,5-dimethyl-3(2H)-furanone Formation in Buffers and Model Solutions of Citrus Juice

4-Hydroxy-2,5-dimethyl-3(2H)-furanone (DMHF, furaneol) is formed in stored citrus juice and has been reported to reduce juice quality. The source and pathways by which DMHF is formed in citrus products have not been delineated. In model orange juice solutions, DMHF was formed only when rhamnose (6-deoxyhexose) was present. Arginine was the major amino acid to react with rhamnose via the Maillard reaction. In buffer solutions, the formation of DMHF was affected by pH, temperature, and time of storage. Under acidic conditions, DMHF is formed only from arginine and rhamnose, whereas at pH 6-8, DMHF was also formed (as verified by GC-MS) from glucose and fructose, albeit in smaller amounts. The formation of DMHF from hexoses required a reducing step, which was apparently contributed by Maillard-producing reductones. It is concluded that the accumulation of DMHF to above taste-threshold levels, which occurs under the acidic conditions of citrus juices, is related, at least in part, to the reportedly small amounts of rhamnose interacting with arginine via the Maillard reaction.