Study On Varying Patterns Of Flavonoids Of Lycium Barbarum L.during Drying And Its Antioxidant Activities

Flavonoids possessing various bioactivities can change on contents when plant is during drying. Lycium barbarum L. is rich of flavonoid. In this study, with sodium carbonate solution and sodium sulfite solution as wax removers being used to smear the surface of the pure fruit of Lycium barbarum L. and no wax removers as blank control, variations of the drying rate, phenylalanine ammonia-lyase (PAL) activity, the contents of total flavonoid, p-coumaric acid, kaempferol, rutin and quercetin from Lycium barbarum L. were determined at different stage of sun-drying and hot-air-drying, respectively. The differences on content of the total flavonoid of Lycium barbarum L. drying by different methods and wax removers were compared and the correlation analyses were conducted between the increasing rate of the total flavonoid and dry weight. Meanwhile, the correlations were analyzed between the content of total flavonoid and PAL activity, so did the contents of kaempferol, rutin and quercetin. The results showed as below.Drying methods affected the content of total flavonoid but wax removers influenced the increasing rate of total flavonoid. The total flavonoid of Lycium barbarum L. drying with hot air reached the highest content first, followed by sun-drying, freeze-drying and pure fruit, and the differences were significant Both sun-drying and hot-air-drying showed that the content of the total flavonoid became higher during drying, and made a positive correlation with the drying rate. The Lycium barbarum L. with sodium carbonate solution had a higher drying rate in early stage, and later caught up with the one treated by sodium sulfite solution and control blank respectively. Following the drying rate, the content of the total flavonoid with sodium carbonate solution increased faster, then it was the Lycium barbarum L with sodium sulfite solution and control blank.Continuous increases of PAL activity and total flavonoid were determined during drying. Contents of kaempferol, rutin and quercetin increased firstly and then decreased, but p-coumric acid presented irregular change. With the same wax remover and drying method, the content of the total flavonoid made a highly significant positive correlation with PAL activity. So did the variations on the content of kaempferol, rutin and quercetin. Wax removers affected the PAL activity and contents of total flavonoid, kaempferol, rutin and quercetin at the same drying time. And the time of reaching the highest value of kaempferol, rutin and quercetin was also influenced by wax remover.Antioxidant activities were compared before and after flavonoid purification by AB-8macroporous rein column chromatography. Flavonoid purified had improved the antioxidant properties. The reducing power and scavenging abilities of nitrite and ABTS+by flavonoid were stronger than the power of scavenging hydroxide radical.