| Cheese is a kind of nutritious and high-value dairy products,which has huge market potential and research value.The microbial resources in the special cheese not only give the cheese unique flavor,but also establish the foundation for industrial production and application of cheese starter in the future.The rich protein in cheese releases many biological active peptide components under the action of various enzymes.These peptides endue cheese some certain functions,such as antioxidant activity.At present,domestic research mainly focuses on flavor improvement,nutrition and process research.But a little research has been done on functionality.In this paper,seven representative strains of lactic acid bacteria isolated from cheese samples taken from Xinjiang,Yunnan,Tibet and other places were selected for evaluation of acid production,viscosity production,autolytic properties,and aminopeptidase activity.According to the fermented performance of different strains,these strains were combined,so that optimized combinations among strains have better production performance in various aspects,and then they are applied to fresh cheese production,and the texture and dynamic rheological characteristics are analyzed in order to select suitable starter for the fresh cheese production.Finally,the antioxidant peptide components of the advantageous cheese were analyzed and the antioxidant activity of the cheese after digestion of the gastrointestinal tract in vitro were explored.Seven strains lactic acid bacteria were activated and passaged using MRS and M17 media,and studied in the acid production performance,viscosity production of the strains in fermented milk,the autolytic properties and aminopeptidase activity.Then these strains were applied to fresh cheese production,and the texture and rheological properties were evaluated.The results of a single lactic acid bacteria strain are as follows: Lactococcus lactis E11 has the strongest acid production performance ?p H(2.23±0.02),and Lactococcus lactis C44 has the highest viscosity production with a value of 0.351 Pa·s and aminopeptidase activity of C44 was up to 15.9 U/m L.When a single strain was applied to fresh cheese,the results showed that the fresh cheese with Lactococcus lactis E11 and C44 strains were close to the control group in texture and rheology,so the single strain of Lactococcus lactis E11 and C44 can be considered for fresh cheese.Generally,a single lactic acid bacteria strain cannot meet the rich flavor requirements of cheese.So seven strains were combined into six strain combinations to achieve mutually complementary performance.And the characteristics of the fermented milk of the combined strains were conducted,according to the research,the acid production rate of Combination-1 was the fastest,and the viscosity was up to 0.481 Pa·s.Among combinations,Combination-2 has the best water holding capacity with a value of 47±0.36%,followed by Combination-1 with a value of 42±1.88%.These combinations were applied to fresh cheese.It was found that the cheeses of Combinations-1,2 and 3 were at a higher value in color,sensory,and yield,which were better than or close to the control group.Compared with the control group,the hardness,spreadability and viscoelasticity have been greatly improved.Therefore,Combination-1 can be used as a starter for fresh cheese production,and Combinations-2 and 3 are considered for use.The antioxidant activity of cheese was evaluated in vitro through ABTS,DPPH free radical scavenging experiments,and reducing power experiments.It was found that the antioxidant activity of the water-soluble extract of a single strain of G12 cheese was the highest in TEAC values in ABTS and DPPH free radical scavenging experiments,the values respectively were 2276.39±0.37 ?mol/L Trolox,112.74±0.11 ?mol/L Trolox.Compared with the single strain,the cheeses with combined strains has improved ABTS free radical scavenging activity,and the range of reducing power has increased from 0.1 to 0.2 of the single strain to 0.2 to 0.3 of these combinations.Among combinations,the performance of Combination-3 presents optimal values in all antioxidant experiments,the values respectively were 2494.44±0.43 ?mol/L Trolox,58.72±0.26 ?mol/L Trolox,and the absorbance value is 0.23.The peptides with antioxidant activity in the water-soluble extract of Combination-1,2,and 3 cheese were analyzed by Nanoliter liquid-quadrupole ultra-high resolution electrostatic orbit trap mass spectrometry.The analysis found that the antioxidant peptides of Combination-3 cheese had VLPVPQK,PYVRYL accounting for 28.3% and 24% of the total peptides,including the peptides RYLGY and RY with proven high antioxidant capacity.Finally,in vitro gastrointestinal digestion experiments of cheeses showed that the average TEAC value of ABTS free radical scavenging experiments was 2500?2600 ?mol/L Trolox.In the DPPH free radical scavenging experiment,the TEAC value was significantly improved compared to the sample before digestion,the TEAC value of the sample after digestion of Combination-3 was 52 times that before digestion;the absorbance value of the reducing power reached more than 0.3.And the antioxidant capacity of the fresh cheese after digestion was greatly improved.The discovery of new lactic acid bacteria for fresh cheese provides more opportunities for the choice of cheese starter in the future.The research of excellent fresh cheese and the exploration for antioxidant of cheese have laid the foundation for the development of functional cheese. |
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