Study On The Antioxidant Activity And Anti-fatigue Effect Of Soft-shelled Turtle Peptides

Soft-shelled turtle is a traditional Chinese nourishing food.With the in-depth research on the components of soft-shelled turtle,we find that its active effects far exceed the traditional value.Previous studies have found that soft-shelled turtle peptides have good in vitro antioxidant activity.However,there are few reports on the in vivo antioxidant and anti-fatigue effects of soft-shelled turtle peptide.Thus,in this paper,soft-shelled turtle peptide（STP）was prepared by enzymatic hydrolysis with soft-shelled turtle as raw material.The antioxidant activity and anti-fatigue effects of STP were evaluated through in vitro chemical models and in vivo animal models.The relationship between antioxidant activity and anti-fatigue effect was explored.The main results of this study were as follows:The nutrient composition and relative molecular mass distribution of STP were analyzed,and four in vitro chemical models were used to evaluate in vitro antioxidant activity of STP.The peptide content of STP was 87.90%,and it mainly has peptides with molecular mass lower than 1000 Da,accounting for 93.23%.The content of essential amino acids was 32.41%,and the content of hydrophobic amino acids closely related to antioxidant capacity was 38.81%.The results of in vitro antioxidant activity showed that the IC₅₀ of STP in scavenging DPPH free radicals,ABTS free radicals and hydroxyl free radicals were 6.22 mg/m L,6.63 mg/m L and 24.86 mg/m L,respectively,and the total antioxidant capacity was 9.00μmol/g,which was higher than whey protein peptides.Thus,STP has certain in vitro antioxidant activity.Fruit flies（Drosophila melanogaster）were used as the model.Fruit flies were fed with different doses of STP（0.2%,0.4%and 0.8%）.The antioxidant enzyme activities and malondialdehyde（MDA）and survival experiments were used to evaluate the in vivo antioxidant activity of STP.The results showed that the superoxide dismutase（SOD）activity of female and male fruit flies in the high-dose group was significantly increased by 28.40%and 15.08%（p<0.01）,and catalase（CAT）activity was significantly increased by 33.50%（p<0.05）and 38.50%（p<0.01）,respectively.The MDA content were significantly decreased by 33.33%and 34.62%（p<0.01）,respectively.Compared with control group,the average lifespan of female and male fruit flies in the high-dose group was increased by 10.80%and 14.01%.The average maximum lifespans were increased by 6.35%and 13.22%,respectively.The results show that STP has the effect of improving the antioxidant activity of female and male fruit flies,and can extend the life of female and male fruit flies.The anti-fatigue effect of STP was studied through the experimental models of exhausted swimming and free swimming of mice,and the potential anti-fatigue mechanism was analyzed.Compared with the blank control group,the exhaustive swimming time of mice in the low,medium,and high STP dose groups were extended by 35.5%,57.1%,and 51.5%,respectively（p<0.05）,and the grip of the forelimbs was increased by 20.7%,22.6%and 27.6%,respectively（p<0.05）.The levels of metabolites lactic acid（LA）,urea nitrogen（BUN）and blood ammonia（NH3）in mice were reduced.The content of blood glucose（Glu）,muscle glycogen（MG）and liver glycogen（MG）were increased.The extravasation of lactate dehydrogenase（LDH）and creatine kinase（CK）were reduced,and muscle tissue was protected from damage.At the same time,the activity of SOD and GSH-Px in the liver were significantly increased and the level of MDA was significantly decreased.The expression of Nrf2 and HO-1protein were up-regulated,and the expression of Keap1 was down-regulated.The results show that STP inhibits the body’s oxidative stress by activating the Nrf2/Keap2signaling pathway,thereby exerting anti-fatigue effect.