Correlation between the Flavor and Quality of Radix Astragali: The Extraction and Characterization of Lipoxygenase in Radix Astragali

Lipoxygenase (LOX) is a key biotic factor producing the bean flavor in Radix Astragali. LOX was studied through spectro-photometry and Linolic acid. Extraction samples and detection methods were developed to investigate a range of biotic and abiotic factors, including the temperature, metal ion, chelate and age, and to evaluate the LOX activity of Radix Astragali. The results showed that LOX exists in the Radix Astragali grown in the Hunyuan County of Shanxi Province, China. Radix Astragali was ground into fine powder using liquid nitrogen, followed by being soaked for 1 h in the borate buffer. LOX crude extracts were obtained through centrifugation at 4000 r/min for 10 min at 4°C. LOX crude extracts and the substrate solution were mixed at a ratio ranging from 1:10 to 1:3 when the LOX activity was detected at a wavelength of 236 nm. The results also suggested that the enzyme could be stable for 15 min at the temperature from 0°C to 50°C, but the enzymes rapidly became inactivated after 2 min at 70°C. The enzymes were activated by Fe3+, Fe2+ and Ca2+, but inhibited by Zn2+, Mg2+ and tartaric acid. The Radix Astragali plants of 5 years old had the highest LOX activity, suggesting that LOX activity was associated with the growth age. The findings were useful for further study of the mechanism of producing the bean flavor in Radix Astragali and for searching for authentic growing sites.