Study On Antioxidant Activity Of Tibetan Yak Milk Residue Peptides

The research of milk and dairy products has always been a hot topic at home and abroad,and the research of small molecule peptides is an important topic of current concern.The purpose of this topic is to understand yak milk residue,develop yak milk residue products,and find out the peptides of milk residue with antioxidant activity.This topic takes the yak milk residue at different altitudes in Tibet(Naqu NA:2800 m above sea level,Lhasa NB:3500?4000 m above sea level,and announced Jiangda County Nc:4300 m above sea level)yak milk residue as the research object,and studied(1)the difference in yak milk residue at different altitudes.Physicochemical,nutritional and flavor characteristics;(2)Peptidomic changes of yak milk residue polypeptide;(3)Cell experiments to verify the antioxidant properties of milk residue polypeptide T10.This study provide a theoretical basis for the development and application of milk residue products.The specific results are as follows:Altitude had significant effect on physicochemical,nutritional and flavor of yak milk residue(P<0.05).Compared with NA and NB,Nc had.the highest average protein content(71.00 g/100 g),vitamin a content(0.33 ug/100 g),vitamin E content(0.33 mg/100 g),vitamin D3 content(0.66 ug/100 g),iron content(55.51 g/kg),total amino acid content(79.32 g/100 g)and essential amino acid content(36.40 g/100 g).Compared with NA and NC,NB had the lowest extreme temperature(129.68?)and the highest Tan ?,indicating that NB had the best fluidity.The main volatile components of yak milk residue were aldehydes(Vmin>37%).The main volatile components of NA and NB were nonanal with rose fragrance.The main volatile component of NC was hexanal with grass fragrance.The peptides were identified by nESI-LC-MS/MS at the altitude of 2800 m and 4300 m,and the proteomics of the peptides before and after two-step enzymatic hydrolysis with trypsin and pepsin was analyzed.The results showed that there were 84 kinds of differentially expressed peptides(up-regulated 32 kinds,down regulated 52 kinds)at 2800 m and 4300 m altitude before enzymolysis,and 888 kinds of differentially expressed peptides(up-regulated 397 kinds,down regulated 491 kinds)after enzymolysis.There were 456 differentially expressed peptides(107 up-regulated and 349 down regulated)in Na and 498 in NC before and after enzymolysis.The different peptides of milk residue before and after enzymatic hydrolysis were analyzed by go function annotation.It was found that the milk residue polypeptide mainly activity in the extracellular region and Golgi.The main molecular functions involved are the same protein binding,lactose synthetase activity,enzyme binding,signal receptor binding,antioxidant activity,etc.The main biological processes involved are the reaction to dehydroepiandrosterone,the reaction to 11-deoxycorticosterone,the reaction to corticosteroids,the reaction to progesterone,the reaction to estradiol,the reaction to ketone,the reaction to corticosteroids,the reaction to alcohol,etc.The results show that the main metabolic pathways of milk residue peptides are PPAR signal pathway,cholesterol metabolism,glycerin metabolism,complement and coagulation cascade,galactose metabolism,fat digestion and absorption,caffeine metabolism and so on.The yak milk residue polypeptide(T10)identified from the milk residue was synthesized,and the oxidative stress induced by H2O2 in HUVEC cells was used to verify its protective effect.The results showed that MTS method and flow cytometry detected that T10 protected HUVEC from damage caused by H2O2 in a dose-dependent manner,and attenuated the cell death induced by H2O2.T10 reduces the levels of lipid peroxidase and reactive oxygen species,increases the activities of superoxide dismutase and glutathione reductase,and inhibits cell apoptosis.T10 treatment reduced the mRNA and protein expression levels of Bax and Keapl in HUVEC cells,and increased the mRNA and protein expression levels of Bcl-2,Nrf2,p Nrf2,HO-1,and NQO1.This means that T10 can regulate the Nrf2 signal path.Using the Nrf2 inhibitor ML385 to block the Nrf2 pathway,the protective function of T10 is partially lost in the injury model.These results indicate that T10 isolated from milk residue has a protective effect on HUVEC cells induced by H2O2,and its mechanism of action is related to the regulation of Nrf2 signaling pathway and cell apoptosis.This research provides basic research for the application of Tibetan yak milk residue,which is beneficial to the development of functional foods.