In Vitro Evaluation Of The Probiotic Properties Of Lactobacillus Paracasei NCU622

Lactobacillus paracasei exists widely in traditional fermented dairy products and human gastrointestinal tract, is able to regulate the balance of intestinal flora,enhance the immunity, prevent disease and so on. In this study, Lactobacillus paracasei NCU622 was examined for resistance to human gastrointestinal environments. The adhesion strain was tested with the in vitro cell model( Caco-2cells). The antimicrobial activity was examined using the Oxford cup method. The antioxidant activity of L. paracasei NCU622 was examined by the four terms of DPPH and hydroxyl radical scavenging activity, reducing powder, inhibition of the lipid peroxidation. The main research results are as follows:(1) Characteristics of growth and metabolism. The lag phase was short, but the stationary phase was long when L. Paracasei was cultured in the MRS broth.Moreover, lactic acid except acetic acid was produced during the fermentation.(2) Tolerance to human gastrointestinal environments. The viable counts of L.paracasei NCU622 did not change significantly after 3h and 4h cultivation respectively in artificial gastric juice and artificial intestinal juice. L. paracasei NCU622 retained high survival rates after 4 h exposure to MRS broth supplemented with 0.3 and 0.5 g/100 mL oxgall. The viable counts of L. paracasei NCU622 after24 h incubation in MRS broth supplemented with 5 g/100 mL NaCl were not different significantly from that of the control. In conclusion, L. paracasei NCU622 showed good resistance to the human gastrointestinal environments.(3) Adhesion properties. L. paracasei NCU622 expressed a strong adhesion property to Caco-2 cells((21.19±0.94) CFU/Caco-2 cell). And its adhesion was affected by the bacterial concentration, incubation time and growth stage.(4) Antimicrobial activity. The culture and cell-free culture supernatant of L.paracasei NCU622 showed good inhibition against both Gram-positive and Gram-negative bacteria. One of the main inhibitory mechanisms may be the production of lactic acid and the lowering of pH of the medium. The antimicrobialsubstances were heat stable and had no proteinaceous nature. Furthermore, the inhibition was not due to the production of hydrogen peroxide.(5) Antioxidant activity. All the cell-free culture supernatant, intracellular cell-free extracts and metabolites presented scavenging activities towards DPPH and hydroxyl radicals, reducing powder, inhibition of the lipid peroxidation.The results indicated that L. paracasei NCU622 showed good tolerance to gastrointestinal environments, had strong adhesion property, had good inhibition against both Gram-positive and Gram-negative bacteria, presented antioxidant activity. In conclusion, L. paracasei NCU622 possesses favorable strain-specific properties for its utilization as probiotic and deserves further research.