Study On The Beany Favor And Its Revelance To The Quality Of Astragali Radix

Radix Astragali (RA), known as Huangqi in China, has been used as a traditional herb for more than one thousand years. The raw herb can be used as a tonic and diuretic. The traditional Chinese medicine pays particular attention on "Shape, Color, Energy and Taste" of medicinal materials. The beany flavor is a traditional sensory indicator for evaluating the quality of RA. It is widely accepted that RA with a strong beany flavor is in relatively good quality in Chinese medicine. However, this traditional identification method is not characterized by modern technology.The bean flavor is a common characteristic of legume family. Studies on Leguminosae indicates that the bean flavor was caused by the products of enzymatic reactions using polyunsaturated fatty acids (PUFAs) as substrate. Lipoxygenase (LOX), widely distributed in various plants, is a key enzyme catalyzing the hydroperoxidation of PUFAs containing cis, cis-1,4 pentadiene. PUFA hydroperoxides derived from the LOX activity are considered to be flavor precursors. Indeed, PUFA hydroperoxides are subsequently converted into flavor compounds (such as alcohol, ketone and aldehyde) by the action of hydroperoxide lyase (HPL). Therefore, the production of beany flavor is related to the forms and activities of LOX and HPL and crude fat in raw materials or processed products.In this study, RA with different origin, growth age or cultural manner were collected and used as experimental material. The activities and isoenzyme profiles of LOX-1 and HPL were first analyzed. Then major volatile components were isolated and analyzed using gas chromatography (GC) techniques. Quantitative determination and statistical analysis were also applied to study the relevance between major beany flavor-producing component (hexanal), beneficial compounds, and standard substances for quality evaluating of RA. The mice were feed with RA with different levels of beany flavor and were trained to have a weight-loaded swimming until they were exhausted. Finally, the action of tonifying Qi, anti-fatigue, and immunoregulation of RA water decotion on experimental mice was evaluated. The results were as follows:1) The extraction and characterization of lipoxygenase in RA. The wild RA samples with the heavy beany flavor were collected from Hunyuan County, Shanxi and LOX activity was examined in such herb. Then a modified method was established to isolate LOX and determine its activities in the herb. Radix Astragali was first 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℃. LOX crude extracts and the substrate solution (0.518 mg/mL) 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 further indicated that the enzyme was stable at the temperature from 0℃to 50℃for 15 min, but the enzymes rapidly became inactivated at 70℃for 2 min. The enzymes were activated by Fe3+, Fe2+ and Ca2+, but inhibited by Zn2+, Mg2+ and tartaric acid. Moreover, Radix Astragali grown for 5 years had the highest activity of LOX, suggesting that LOX activity was associated with the growth age in the plant.2) The analysis of the activities and isoenzyme profiles of LOX and HPL, and the contents of crude protein and crude fatty acids in RA. The results indicated that the LOX-1 was the main from of LOX isozyme. The activities of LOX-1 and HPL, and the isozyme profiles of LOX and HPL were positively related to beany flavor. Combined with the sensory evaluation, RA with heavy beany flavor was relatively higher in the content of crude fatty acid, the activities of LOX-1 and HPL, and the relative activities of LOX-1 and HPL.3) The isolation and identification of the major volatile components from raw RA materials using SDE/GC techniques. The results showed that the percentage of hexanal was more than 66% of the volatile substance in each sample, indicating that hexanal was a major component producing the beany flavor in RA. The value of hexanal was significantly related to the origin and growth age of RA, indicating that the component could be used as a volatile indicator for the distinction of RA. The beany flavor was positively correlated to hexanal and LOX activity, and the hexanal was also positively correlated to LOX activity.4) The relevance between beany flavor and the quality of RA by quantification and statistical analysis of hexanal and main bioactive metabolites. The results demonstrated that hexanal, astragaloside IV, and total polysaccharides were primary indicators and total isoflavonoids, astragalosides, calycosin, and formononetin were the secondary indicators for quality assessment of RA. Correlation analysis further showed that the level of hexanal was positively associated with the concentrations of astragaloside IV and total polysaccharides. The results also indicated that RA plants grown in Hunyuan, Shanxi contained relatively higher amounts of the components examined here, as well as hexanal. Meanwhile, RA plants grown in Sichuan and Heilongjiang contained lower content of hexanal and active components.5) The action of water decotion of RA materials with different origin on tonifying qi, anti-fatigue, and immunoregulation on the mouse in weight-loaded swimming test. The results showed that the RA derived from Hunyuan had an advantage in tonifying qi and anti-fatigue, extending the swimming time, reducing the levels of serum urea nitrogen and blood lactic acid, as well as improving the indices of immune organ and the amount of T cell subgroup in blood. In contrast, RA derived from Sichuan and Heilongjiang increased the amount of B cell and changed the ratio of CD4/ CD8.In conclusion, our study demonstrated that beany flavor is one of the most important attributes of RA quality and will help to understand the role of aroma in quality assessment of traditional Chinese medicines.