| Tea cakes contain various functional ingredients such as tea saponin,polysaccharides,tannins,proteins and flavonoids,which have been directly discarded as fuel or waste,resulting in wasted resources.Therefore,in this study,a new extraction technology,subcritical water,was used to extract tea saponin,and macroporous resin was used for preliminary purification.The antioxidant capacity was evaluated by scavenging free radicals,and the antibacterial mechanism was described by means of morphological observation,enzyme activity determination and metabolomics.Tea saponin was applied to the preservation of chicken breast,and salmonella dynamics model and its shelf life model parameters were set up at 25℃,4℃ and-18℃,respectively.The results will provide theoretical guidance for the reuse of tea cake.The main experimental results are as follows:(1)The components in the tea cake were measured.The results showed that the tea cake contained 27.6%total sugar,4.1%ash,protein 16.2%,crude fiber 4.5%,and crude fat 13.0%.Mineral elements such as potassium,aluminum,calcium,magnesium and manganese were abundant.The basic amino acid such as lysine,arginine and acidic amino acid including glutamic acid,aspartic acid content was higher,and the unsaturated fatty acid In tea cake residue oil was up to 83.1%.(2)The extraction rates of tea saponin extracted by ultrasound-assisted alcohol extraction and subcritical-water extraction were compared.The results showed that the optimal conditions for ultrasonic extraction were 159 W ultrasonic power,22 min ultrasonic time,60%ethanol concentration and 1:20 solid-liquid ratio,and the extraction rate of tea saponin was 29.01%under the optimal conditions.The best process of subcritical extraction:time 19 ruin,temperature 100°C,ratio of material to liquid 1:25,under this process conditions,the tea saponin extraction rate was up to 31.04%.These results showed that subcritical-water extraction method was much more efficient than ultrasound-assisted alcohol extraction.Combined with the results of scanning electron microscopy,it was concluded that the subcritical water extraction method was an efficient,economical and environmentally friendly method for extracting tea saponin.(3)The purification effects of five macroporous resins of AB-8,X-5,D4020,D101 and NKA on tea saponin were compared.It was found that X-5 resin had the best purification effect.Further research results showed that the adsorption process of tea saponin on X-5 was consistent with the first-order kinetic model.By fitting the adsorption isothermal process,it was found that the Freundlich equation had a high fitting degree.The optimum conditions for the purification of tea saponin(Φ30 mm×300 mm,column volume is 60 mL)were as follows:loading 60 mL,loading concentration 15.45 mg/mL,loading flow rate 1 mL/min,elution with distilled water,40%ethanol,80%ethanol,elution flow rate 2 mL/min,three BVs eluted at each concentration.Under these conditions,the purity of tea saponin increased from 27.68%to 85.40%.and the recovery rate was 77.13%.(4)The free radical scavenging ability of tea saponin before and after purification were conpared,and it was found that DPPH and ABTS radical scavenging ability increased by 20%and 12%respectively,Fe ion reducing capacity increased by 249 uMFeSO4 equivalent and Cu ion complexing capacity increased by 73 uMTrolox.(5)The inhibitory effect of tea saponin on several common pathogenic bacteria was compared by using the minimum inhibitory concentration,and the inhibitory mechanism of tea saponin was revealed at the cell level according to such indicators as cell growth,protein leakage concentration,cell morphology,alkaline phosphatase and K+concentration.Tea saponin can prevent the normal growth of bacterial cells,and the effect on Salmonella and Bacillus sublilis is obvious.The minimum inhibitory concentration is 10 mg/mL.After treatmented with tea saponin,the appearance of Salmonella and Bacill2s subtilis bacteria was destroyed,sticking into a cluster,and collapsed,caves and lost the original shape,further research found that it had a destructive effect on the cell membrane and cell wall,which damaged to the cell membrane and the integrity of the cell wall changed the permeability of the cell membrane and cell wall,resulting in a decrease in barrier properties.Intracellular protein macromolecules,K+which maintains electrolyte balance,and gap enzyme alkaline phosphatase leak out of the cell,thus it interfered with the normal growth and reproduction of the cells.Through the metabolomics method,the antibacterial mechanism of tea saponin was further analyzed.The results showed that the addition of tea saponin had a great influence on the metabolites of Salmonella,and cluster analysis and principal component analysis showed that the metabolites of the treatment group(added MIC concentration tea saponin)and the control group were significantly different(P<0.05).It can be seen from the heat map and the principal component analysis chart that the treatment group and the control group can be well distinguished,divided into two clusters,and 19 metabolites were up-regulated,and the remaining metabolites were down-regulated.From the volcano map and box plot,the types and relative contents of some differential metabolites can be clearly seen,mainly some amino acids,guanidines and organic acids.The metabolic pathways involved in the alalysis can be seen that there are 32 metabolic pathways involved,mainly amino acid metabolism,tricarboxylic acid cycle,pentose phosphate pathway,glycerophospholipid metabolism,pyruvate metabolism,pyrimidine metabolism and so on,and metabolites that are up-or down-regulated will have an effect on these pathways.(6)The physical and chemical indicators and microbial indicators of chicken breast at different storage temperatures(-18℃,4℃,25℃)were studied.It was found that during storage,the TBA value,TVB-N value,pH value,whiteness,and total number of Salmonella colonies gradually increased,the water holding rate gradually decreased,and the quality gradually deteriorated.Moreover,the speed of deterioration of physical and chemical indicators of chicken breast meat added with tea saponin was lower than that of the control group at the same temperature,It was indicated that the presence of tea saponin can inhibit the growth and reproduction of Salmonella in chicken breast and effectively improve the chicken breast during storage.Further,the modified Gompertz model and the modified Logistic model were used to fit the first-order kinetic growth curve of Salmonella in chicken breast and the results showed that the coefficient of determination(R2)of the modified logistic model was higher than 0.99,indicating that the growth of Salmonella in chicken breasts accorded with the modified Logistic model.Based on the first-order kinetic model parameters,a secondary model was established,and the minimum amount of Salmonella spoilage was determined.The shelf-life model of the treatment group and the control group was finally determined,which were:SLEG=λ-(4.04-N0)/2.718×Umax×{ln(-ln[(6.17-N0)/(4.04-N0)]-1}SLCK=λ-(4.99-N0)/2.718×Umax×{ln(-ln[(6.17-N0)/(4.99-N0)]-1}... |
PDF Full Text Request