Inhibitory effect of litchi pericarp procyanidins on advanced glycation end products formation in model system of α-Lactose/L-Lysine

Abstract: Industrial food processing induces protein glycation modifications and toxic advanced glycation end products (AGEs) which affect human health. Thus, it is an urgent problem in food process industry to control and inhibit the formation of AGEs during Maillard reaction. In this study, a model system consisting of lactose (as reducing disaccharide) and lysine (as very reactive amino acid) was established to monitor the AGE formation. Litchi pericarp procyanidins (LPPC), a natural antioxidant, was incubated in the simulated systems at different concentrations (0.02-0.10 mg/mL) and temperature levels (80 or 100℃) with or without various metal ions (Al3+, Ca2+, Fe2+, Cu2+, Mg2+ and Zn2+), which was to observe its inhibitory effect on AGEs. With all samples, the formation of fluorescent AGEs was quantitatively assessed using a spectrofluorimeter at excitation and emission wavelengths of 370 and 440 nm, respectively. The results showed that with the LPPC added, the formation of AGEs was significantly inhibited. The maximum relative inhibitory rate of LPPC on AGEs formation was up to 79.92%±5.21% after heated for 2.5 h at 80℃, while the relative inhibition rate of LPPC reached about 63.37%±4.12% after 30 min at 100℃. Moreover, there was the dose-effect relationship between the concentration of LPPC and its inhibition rate on AGEs formation: the half inhibitory concentration values of LPPC in the simulated food system at 80 and 100℃ were (0.081±0.006) and (0.144±0.009) mg/mL, respectively. After adding metal ions in the model system, the effect of metal ions on AGEs formation was found to depend on the heating time, as well as on the type of metal ion. The addition of 1.0 mg/L Al3+ promoted the formation of AGEs, whereas the addition of 0.1 and 10.0 mg/L Al3+ suppressed the AGEs formation. The 10.0 mg/L Al3+ had the highest inhibition ratio, up to 58.34%±2.93% and 55.92%±2.94% at 80 and 100℃, respectively. After 1 mg/mL LPPC was added, the inhibition ratio of the solution containing Al3+ with the concentration of 0.1 and 10.0 mg/L was increased significantly (P<0.05). And 1.0 mg/L Al3+ became to have an inhibition effect at the presence of LPPC. At the presence of Fe2+, the formation of AGEs was obviously promoted, except at 0.1 mg/L under 80℃. However, LPPC addition changed the effect of Fe2+ on the amount of AGEs at 0.1, 1.0, 10.0 and 50.0 mg/L. Moreover, the inhibition effect of LPPC on the AGEs was amplified. The addition of Ca2+, Mg2+ and Zn2+ with the concentration of 1.0 and 50.0 mg/L, increased the formation of AGEs in the lactose-lysine model system, especially for 50.0 mg/L Ca2+. However, the formation of AGEs could be suppressed when adding 0.1 and 10.0 mg/L Ca2+, Mg2+ or Zn2+. The addition of 10.0 mg/L Ca2+, 0.1 mg/L Mg2+ and Zn2+ had the highest inhibition ratios, which were 43.89%±4.13%, 38.29%±1.62% and 47.23%±2.82% at 80℃, and 28.52%±1.17%, 27.24%±1.37% and 6.35%±0.04% at 100℃, respectively. However, after LPPC was added, all concentrations of metal ions inhibited the formation of AGEs. For the Cu2+, only low level of 0.1 mg/L could suppress the formation of AGEs. Nevertheless, LPPC decreased the content of AGEs at the presence of Cu2+ even at 1.0, 10.0 and 50.0 mg/L. Overall, LPPC could be used as functional food ingredients to inhibit AGE formation.