Objective  Roles of antioxidase and phospholipid fatty acid (PLFA) play in the response of Lactobacillus plantarum R23 to sulfur dioxide stress were studied.

  Methods  L. plantarum R23 was exposed to a gradient of sulfur dioxide to observe the ultrastructural changes on the bacterium under scanning electron microscopy, determine the antioxidase activity and MDA content by ELISA and coomassie brilliant blue method, and analyze the PLFA composition using MIDI.

  Results  The increasing sulfur dioxide stress induced in L. plantarum R23 a high antioxidase activity, especially CAT. Under 80 mg·L⁻¹ of sulfur dioxide exposure, 1.64-fold rise on SOD activity, 2.14-fold on CAT, and 1.62-fold on GPX were found in the bacteria that afforded a relatively low increasing rate on MDA and maintained a largely intact morphology. However, the imposition of 120 mg·L⁻¹ sulfur dioxide lowered the antioxidase activity and intensified the lipid peroxidation with appearance of wrinkles on the cellular surface. The PLFAs underwent varying degrees of increases on saturated, straight-chain, long-chain, and cyclopropane fatty acids under the stress. The straight-chain fatty acids accounted for 52% of all with a ratio to the branched-chain fatty acids significantly raised from 7.15 to 9.72.

  Conclusion  When L. plantarum R23 encountered sulfur dioxide stress, by increasing the antioxidase activity and/or altering the PLFA composition (especially the saturated, straight-chain, long-chain, and cyclopropane fatty acids) it lowered the cell membrane permeability to deter the invasion of toxic substances or removed the excessive free radicals to prevent and mitigate possible damage.