Study On The Screening Of Antioxidant Yeast From Tibetan Kefir Grain And Its Inhibition Of Lipid Oxidation In Fish

Grass carp meat is rich in unsaturated fatty acids,which is easy to be oxidized in the process of gastrointestinal digestion.The harmful products formed will be absorbed by the body and cause potential harm to the body’s health.Adding antioxidants is one of the most commonly used methods to inhibit lipid oxidation.Microbial antioxidants are popular because of their easy availability and high safety.In this paper,yeast strain with excellent antioxidant activity was screened from Tibetan Kefir Grain.Then,the effect of yeast strain on lipid oxidation during simulated gastrointestinal digestion of fish was explored based on lipidomics.Finally,the formula of freeze-drying protective agent for yeast was optimized to improve the cell activity of lyophilized powder.(1)The yeast with excellent antioxidant activity was screened from Tibetan Kefir Grain.It is found that strain KM-4 have the strongest comprehensive antioxidant capacity.The scavenging rate of hydroxyl radical in the cell-free extract group is(61.65±0.46)%,and the reducing power is(305.08±4.64)μmol/L L-cysteine equivalent,the scavenging rate of superoxide anion is(10.86±0.44)%,aldehyde dehydrogenase activity is(0.29±0.06)U/mg prot,superoxide dismutase(SOD)activity is(145.04±4.41)U/mg prot,catalase(CAT)activity is(210.93±28.44)U/mg prot.Strain KM-4 can inhibit the increase of peroxide value(POV)and thiobarbituric acid reactive-substances(TBARS)value of grass carp meat during cold storage,and has excellent anti-lipid oxidation characteristics.The effective components of strain KM-4 that played an antioxidant role are antioxi-dant enzymes:superoxide dismutase and catalase.The analysis of the growth characteristics of strain KM-4 shows that it has a good survival rate and a certain tolerance to bile salts in the simulated gastric and intestinal fluid environment.The results of strain identification show that KM-4 is Kluyveromyces marxianus.(2)Strain KM-4 can effectively reduce the POV,TBARS value and protein carbonyl content of grass carp meat during simulated gastrointestinal digestion,indicating that yeast have inhibited the lipid oxidation of grass carp meat.Based on UHPLC-QTOF-MS,it is found that the addition of strain KM-4 have not changed the lipid profile composition of grass carp meat,but have affected the lipid content of grass carp meat.The analysis results of differential metabolites have showed that LPC,LPE,PC,PE,FFA(18:4),FFA(16:1)and DGDG(O-22:4/8:0)can be used as differential metabolites related to lipid oxidation of fish during simulated gastrointesstinal digestion for 3 hours.FAHFA(18:2/20:4),FFA(16:1),FFA(18:2),FFA(18:3)and FFA(18:4)can be used as differential metabolites related to lipid oxidation of fish during simulated gastrointestinal digestion for 5 hours.(3)The formulation of freeze-drying protective agent for strain KM-4 is optimized to provide a theoretical basis for the preparation of lyophilized powder.The optimal preparation of the highly active strain KM-4 yeast lyophilized powder are:7.92%sucrose,7.49%skimmed milk powder,5.00%mannitol,3,72%monosodium glutamate,and the mixing ratio of slime and protectant is 1:1,the equilibrium time is 30 min,the maximum freeze-drying survival rate is(84.31 ± 0.83)%.