Physiological, Morphological and Antioxidant Responses of Pediococcus pentosaceus R1 and Lactobacillus fermentum R6 Isolated from Harbin Dry Sausages to Oxidative Stress

Abstract

As functional starter cultures and potential probiotics, the ability of lactic acid bacteria to resist oxidative stress is essential to maintain viability and functional properties. This study investigates the effects of H₂O₂ at different concentrations (0, 1, 2, and 3 mM) on the physiological, morphological, and antioxidant properties of Pediococcus pentosaceus R1 and Lactobacillus fermentum R6 isolated from Harbin dry sausages. The increase in H₂O₂ concentration induced a significant increase in reactive oxygen species and a decrease in intracellular ATP levels (p < 0.05). Based on scanning electron microscopy, transmission electron microscopy, and electric conductivity analysis, H₂O₂ stress caused cell deformation, the destruction of cell membrane integrity, partial loss of the cytoplasm, and an increase in the cell conductivity of both strains. H₂O₂ stress with 1 mM or 2 mM concentrations could effectively improve the scavenging rates of free radicals, the activities of superoxide dismutase and glutathione peroxide, and the total antioxidant capacity of both strains (p < 0.05). In conclusion, an appropriate oxidative stress contributed to the activation of the antioxidant defense system of both strains, conferred strains a better effect in inhibiting the oxidation of fermented foods, and improved the health of the host.

Keywords: Lactobacillus fermentum; Pediococcus pentosaceus; antioxidant activity; cell morphology; oxidative stress; probiotics.

Figure 1

Changes in colony counts (A), intracellular reactive oxygen species (ROS) levels (B), and intracellular ATP concentrations (C) of Pediococcus pentosaceus R1 and Lactobacillus fermentum R6 incubated in MRS broth with different H₂O₂ concentrations for 1 h. Different uppercase letters (A–D) denote statistical differences (p < 0.05) within the same strain under different H₂O₂ concentrations; different lowercase letters (a and b) denote statistical differences (p < 0.05) for both strains within the same H₂O₂ concentration.

Figure 2

Scanning electron micrographs of Pediococcus pentosaceus R1 and Lactobacillus fermentum R6 incubated in MRS broth with different H₂O₂ concentrations for 1 h.

Figure 3

Transmission electron micrographs of Pediococcus pentosaceus R1 and Lactobacillus fermentum R6 incubated in MRS broth with different H₂O₂ concentrations for 1 h.

Figure 4

Analysis of electric conductivity of Pediococcus pentosaceus R1 (A) and Lactobacillus fermentum R6 (B) treated with different H₂O₂ concentrations for 1 h.

Figure 5

Changes in 2′,2′-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging rates (%) (A), hydroxyl radical (•OH) scavenging rates (%) (B), superoxide anion radical (O₂^•−) scavenging rates (%) (C), and reducing powers (D) of Pediococcus pentosaceus R1 and Lactobacillus fermentum R6 after incubation in MRS broth with different H₂O₂ concentrations for 1 h. Different uppercase letters (A–C) denote statistical differences (p < 0.05) of the same components in the same strain (intact cell or intracellular cell-free extract) under different H₂O₂ concentrations; different lowercase letters (a–d) denote statistical differences (p < 0.05) for both strains within the same H₂O₂ concentration.

Figure 6

Superoxide dismutase (SOD) activity (A), glutathione peroxide (GSH-Px) activity (B), and total antioxidant capacity (T-AOC) (U/mg protein) (C) of Pediococcus pentosaceus R1 and Lactobacillus fermentum R6 after incubation in MRS broth with different H₂O₂ concentrations for 1 h. Different uppercase letters (A–D) denote statistical differences (p < 0.05) within the same strain under different H₂O₂ concentrations; different lowercase letters (a and b) denote statistical differences (p < 0.05) for both strains within the same H₂O₂ concentration.