اثر ریبوفلاوین و lumichrome تخریب در پایداری اکسیداتیو چاشنی وادویه مخصوص سالاد
Abstract: Soybean oil is the major ingredient and easily oxidized in salad dressing, which makes the products less acceptable or unacceptable to consumers. Therefore, the addition of healthful antioxidant ingredients have been utilized to enhance the nutritional qualities while maintaining extended shelf-life of the salad dressing. Riboflavin, a water soluble essential vitamin, can be used to fortify processed foods because the human body has to obtain this compound from the diet. Although riboflavin has been known as a prooxidant in aqueous solution under light condition, its effect on the lipids in oil-in-water emulsion system is still not clearly known. The main purpose of this study was to evaluate the effects of riboflavin and its decomposed product (lumichrome) on soybean oils in salad dressing based on the changes in values from differential scanning calorimetry (DSC), headspace oxygen and solid phase microextraction (SPME), gas chromatography (GC) )-mass spectrometry (MS), high-performance liquid chromatography (HPLC) and peroxide analysis (PV). To determine the proposed mechanism of riboflavin activity, the data from antioxidant property analyses were also evaluated. Salad dressings with 0, 5, 20, 50 and 100 ppm added riboflavin were prepared and stored under light (3,000 lux) or in the dark at 25 °C for 5 days. The enthalpy and peak temperature corresponding to the exothermic peak area between -55 and -70 °C of the oil samples were calculated from the DSC runs and compared with the headspace oxygen depletion, peroxide value and headspace volatiles in samples. The crystallization peak shifted to lower temperature and its enthalpy decreased as the storage time increased under the light. As the riboflavin concentration increased from 0 to 100 ppm, (1) DSC crystallization enthalpy increased from 27.3 to 32.2 J/g, (2) DSC maximum crystallization temperature increased from -63.2 to -61.2 °C, DSC on-set temperature increased from 59.3 to 57.5 °C, and (4) peroxide value decreased after 5 day storage under light. The depletion of headspace oxygen and the formation of volatile compounds under light were also highest in the sample without riboflavin. Riboflavin in aqueous portion of salad dressing was analyzed by HPLC. The steady state kinetic study showed that the reaction rate of riboflavin with singlet oxygen in salad dressing was 3.2 x 108 M-1 sec-1 . HPLC also detected that riboflavin in aqueous portion gradually decreased during storage of 5 day. However, overall results showed that the decrease in lipid oxidation of salad dressing was accompanied with the increase in the concentration of added riboflavin indicating riboflavin acted as an antioxidant at the oil-in-water emulsion system under light storage condition. The mechanism of antioxidant effect of riboflavin on the emulsion system was investigated. In order to evaluate the antioxidant property of riboflavin, the radical scavenging activity of riboflavin was determined by DPPH and ABTS reaction. Reducing power and ion-chelating effect of riboflavin were also tested using trolox and sodium acetate. The results showed the antioxidant capacity of riboflavin is very low when compared with that of other known antioxidants such as tocopherol, butylated hydroxyanisole (BHA), and butylated hydroxytoluene (BHT). The result may suggest that the mode of action in antioxidant effect of riboflavin might be different from that of other antioxidants. There are two possible hypotheses. First, riboflavin under light may react with singlet oxygen to reduce the number of available free singlet oxygen. Second, the reduced-riboflavin reacts with the hydroperoxide on the chain of unsaturated fatty acids and oxidized to riboflavin. In that reaction, the hydroperoxide accepts an electron and decomposes thereby increasing the stability of the oil in present study. Considering lumichrome has been known to be the major photo-degradation products from riboflavin at low pH, the next area to investigate was whether the lumichrome could function as a photosensitizer or an antioxidant in salad dressing. DSC, headspace oxygen and peroxide value were subsequently analyzed in salad dressing samples that had been supplemented with lumichrome. There were significant reductions (P <0.05) in the peak temperature and the enthalpy of the crystallization transition of lumichrome added samples compared to that of the un-added samples in storage time up to 5 days under light. The addition of lumichrome also provoked a significant (p <0.05) decrease for the headspace oxygen content and increase for the hydroperoxide formation. The results showed that the addition of lumichrome accelerates the light-induced lipid oxidation of salad dressing.
Keywords: Health and environmental sciences, Riboflavin, Lumichrome, Lipid oxidation, Chromatography, Antioxidant