Study On Functional Components And Biological Activities Of Old Stem Extracts From Asparagus Officinalis L.

Asparagus officinalis L. is a kind of valuable vegetable, which is widely planted in China and mainly for export. Old stems are discarded in processing, which causes resource waste and environmental pollution. The functional components should be investigated in order to realize effective utilization of old stems, so asparagus juice was extracted from old stems and functional components were identified by qualitative tests. Flavonoids, polyphenols, saponins and polysaccharides were determined and the content differences of which in shoot tip, young stem and old stem juice were compared. The results indicated that flavonoids and polyphenols contents in shoot tip and young stem juice were significantly higher than those in old stem juice, but the saponins and polysaccharides contents in old stem juice had no significant differences compared with those in young stem juice, which suggest old stem juice still has high utilization values.Fresh asparagus juice deteriorates quickly at room temperature, so asparagus extracts from old stems (AEO) were obtained from asparagus juice. The various functional components of AEO were analyzed and the results showed the contents of total flavonoids, polyphenols, saponins and polysaccharides reached1.43mg/g dry weight,5.58mg/g dry weight,1.82mg/g dry weight and4.24mg/g dry weight respectively. Compared with the components in old stem juice, flavonoids and polyphenols contents were significantly decreased but polysaccharides and saponins contents did not change significantly. The contents of polyphenols, saponins and polysaccharides in AEO are higher relatively; therefore, the biological activities of AEO can be explored according to the physiological activities of the three components.Experiment systems in vitro were selected for biological activities. The antioxidant activities of AEO were evaluated by determining the scavenging effects on DPPH*and·OH. The role of cancer prevention was evaluated by exploring its scavenging nitrite and blocking synthesis of nitrosamine abilities. It was found that the scavenging effect of AEO on·OH was much stronger than that on DPPH·, and AEO could effectively remove nitrite and block nitrosamine synthesis. Because free radicals and nitrosamine may be carcinogenic to human and the special relationship between colorectal carcinoma cells and intestinal epithelial a-glucosidase, the cytotoxic activity of AEO on HCT1116cells and the activity of intestinal epithelial a-glucosidase of AEO were detected. The results showed AEO had activities of cytotoxicity and a-glucosidase inhibition and the half inhibitory concentrations were62.5mg/mL and0.156mg/mL respectively.The acute toxicity test was done to evaluate the security of AEO. Six groups of mice were administered with AEO one or several times within12hours and the doses were5.15g/kg,7.35g/kg,10.50g/kg,15g/kg,21.43g/kg and30.61g/kg respectively. The survival status had been observed for2weeks and the mice were killed at the end of experiment. The results suggest AEO has digestive, respiratory and nervous system toxicities on mice and its LD50is20.55g/kg. The safe dose is7.0g/kg body weight, which is equivalent to a70kg person taking19.6L asparagus juice and much higher than maximum dose for human.It had been proved that AEO inhibited intestinal α-glucosidase activity of rats in this study, so the effects of AEO on postprandial blood glucose were studied further. Rats were administered with AEO at dose of0.6,1.2,2.0g/kg body weight and killed after14days. The results showed0.6and1.2g/kg body weight of AEO lowered the postprandial blood glucose at0.5～1h after sucrose loading but not significantly. However AEO at the dose of0.6and1.2g/kg body weight could reduce fasting blood glucose and serum cholesterol content of normal rats.Due to the hypoglycemic effects of AEO in normal rats, effects of AEO on glucose metabolism were studied in STZ-induced diabetic rats. The results indicated that AEO showed restraining effects on rising of blood glucose and glycosylated serum protein in STZ-induced diabetic rats. In addition, liver hexokinase activity and glycogen content were raised, the weight loss was alleviated and the impaired sucrose tolerance was significantly improved by oral administration of AEO in diabetic rats. More importantly, AEO at the dose of1.2g/kg body weight could increase serum insulin level in diabetic rats, which suggest AEO could improve sucrose tolerance, increase hexokinase activity and accumulate hepatic glycogen through promoting insulin secretion in STZ-induced diabetic rats.AEO showed restraining effect on rising of serum cholesterol, suggesting the positive regulation of AEO on lipid metabolism. T-SOD activity was increased while MDA content was decreased by oral administration of AEO in diabetic rats, in addition, liver T-SOD, GSH-Px and CAT activities were increased in AEO treatment groups compared with model group, which suggest AEO could alleviate the oxidative damage caused by STZ through raising the level of antioxidant enzymes. Due to the liver injury induced by STZ in hyperglycemic rats, serum ALP, ALT and AST activities were significantly increased, however, AEO could alleviate the increasing of ALP and ALT activities, which suggest the protective effects of AEO on liver injury.