Relationship between fluorescence and antioxidant activity of ethanol extracts of a maillard browning mixture

Abstract The relationship between the color and fluorescence of a Maillard browning mixture (0.1M glucose+0.1M glycine, heated at 100 C) and the antioxidant activity of ethnol extracts of the mixture was investigated. The activity was estimated by comparing the peroxide value development of soybean oil substrates containing the extracts with that of a control. The excitation and emission maxima of the mixture were 365 and 440 nm, and those of the extract 367 and 430 nm. The relative fluorescence (that of 1 µg quinine sulfate/mL 0.01N H2SO4=100) of the mixture after 16 hr browning was 450, whereas that of the corresponding extract was 175.8. The fluorescence of the mixture increased in parallel to the color (absorbance at 490 nm), which, in turn, was almost proportional to reaction time, except at the earlier stages of browning. The change of the fluorescence with the reaction time at the earlier stages was far greater than that of the absorbance at the same stages. Determination of fluorescence seems to provide a more sensitive method for tracing early browning than that of absorbance. The ethanol extracts from very early stages of the browning exhibited considerable antioxidant activity, and, unlike the absorbance of the mixture or the fluorescence of the extract, the activity of the extract changed very little with the reaction time. It appears that effective antioxidants with almost no color but with considerable fluorescence were already formed at the earlier stages of browning.