Purification And Properties Of Flavonoids From The Wastes Of Asparagus(Officinalis L.)

Asparagus (officinalis L.) is one of the most important export vegetables in our country, which produces a quantity of wastes during the processing. Researches on the extraction, purification and propertity identification of flavonoids were carried out in this paper.The flavonoid composition and content of five varieties of asparagus (V-1, V-2, V-3, V-4 and V-5), bred by Beijing Academy of Agriculture and Forestry Sciences, were studied. Results showed that the composition of flavonoid from five asparagus were the same, while their contents were different. Among the five varieties V-4 had the highest flavonoid content (0.47%), revealing a potential for further research and processing.By comparing the effect of ethanol extraction and ultrasonic extraction of flavonoids, ethanol extraction was selected. The optimum parameters of ethanol extraction were as follows: extraction temperature was 70℃; extraction time was 90 min; solid-liquid ratio was 1:35 and ethanol concentration was 80%.After extraction, flavonoids were purified by AB-8 macroporous resin and LH-20 gel-colum. Two main components (R1 and R2) were obtained and their purities were 75.34% and 98.17%. The structures of R1 and R2 were indentified via color reaction, UV characteristic spectrum, infrared spectrum and MS. The structure of R1 was similar to quercetin-3-triglycosidase and R2 to rutin. Furthermore, two other kinds of flavonoids were found in Asparagus wastes, with structures like quercetin-triglycoside and diosmetin.The antioxidant ability of R1 and R2 were investigated in organic and inorganic system by liposome peroxidant method and ferric thiocyanate method. The results showed that R1 and R2 could delay and reduce the peroxidation of linoleic acid and liposome, and also showing a significant capacity of scavenging DPPH and hydroxyl radicals. However, R1 and R2 showed a weak scavenging ability of the oxygen radicals, with the highest scavenging rate of 40.37% and 29.08% respectively. Compared to R2, R1 showed a more significant influence for radical scavenging. The stability of the R1 and R2 were further evaluated at different temperature, pH, and another two influence factor (oxidant and light) were also studied. R1 and R2 had the same aglycone, so the stability was similar. R1 and R2 could be influenced by antioxidants, acid and alkaline in the aqueous solution; but they were stable in the aqueous solution of 30-70℃. Lighted for more than 16 h, R1 and R2 would have significant losses. Furthermore, the thermal character of R1 and R2 were analyzed. The results showed that the degradation temperature of R1 and R2 were similar, respectively 251.27℃and 250.85℃. The thermal properties of R2 were very similar with the standard product of rutin.