Fluorescence kinetics of soybean flour oxidation

Changes in fluorescence and oxidation indices of soybean flour were studied during storage at 37, 50, and 60 degrees C. The peroxide value and 2-thiob arbituric acid value did not increase in proportion to the extent of oxidat ion. The front-surface fluorescence of oxidized soybean flour had an excita tion maximum around 350 nm and an emission maximum between 420 and 430 nm. The fluorescent compounds were soluble in the organic phase of chloroform/m ethanol (2:1, vol/vol) after addition of water, and the solution showed exc itation and emission maxima around 360 and 440 nm, respectively. The fluore scent compounds might have been produced from interactions of oxidizing soy bean oil with other constituents of soybean flour. The fluorescence intensi ty in the organic phase increased steadily throughout the storage period. F luorescence kinetics of soybean flour oxidation showed a zero-order increas e, and the rate followed an Arrhenius relationship with an activation energ y of 47.8 kj/mol. These results suggest that analysis of fluorescence inten sity in the organic phase is a useful indicator for determination of the ox idative deterioration of soybean flour.