Application of Stable Isotope Ratio Analysis Explaining the Bioformation of 2,5-Dimethyl-4-hydroxy-3(2H)-furanone in Plants by a Biological Maillard Reaction

[1- 13 C]- d -Fructose and [U- 13 C 6 ]- d -fructose were applied to detached ripening strawberry fruits, and the incorporation into 2,5-dimethyl-4-hydroxy-3(2 H )-furanone 1, 2,5-dimethyl-4-methoxy-3(2 H )-furanone 2, 2,5-dimethyl-4-acetoxy-3(2 H )-furanone 3, 2,5-dimethyl-4-hydroxy-3(2 H )-furanone β- d -glucopyranoside 4, and 2,5-dimethyl-4-hydroxy-3(2 H )-furanone 6‘- O -malonyl β- d -glucopyranoside 5 was determined by HRGC−MS and HPLC−ESI MS−MS. The data clearly showed the direct conversion of d -fructose to the furanones without cleavage of the carbohydrate prior to the formation of 1 − 5, as expected for a biological Maillard reaction. Both, the furanone and the d -glucose moiety of 4 and 5 contained the labels. However, the label was primarily incorporated into the furanone moiety, indicating that d -fructose is a more efficient precursor of the furanones than d -glucose.