Antioxidant Properties of Lactic Acid Bacteria

Lactic acid bacteria (LAB) are widely used in fermentation processes for the preparation of various foodstuffs, including dairy, meat and vegetable products. In the course of industrial biotechnological processes, lactobacilli are often exposed to oxidative stress, which occurs due to accumulation of reactive oxygen species (ROS) inside the cells. ROS are formed as a result of incomplete reduction of molecular oxygen to superoxide radical (O₂^{ - }), hydrogen peroxide (H2O2), or hydroxyl radical (OH•) and cause serious damage to all cellular macromolecules. Since LAB do not possess a complete electron transport chain, it was previously believed that they are incapable of existence under oxic conditions. Nevertheless, a number of LAB strains were found to possess the principal antioxidant defense enzymes with high specific activity. These include two types of catalases and NADH peroxidase. Heme-containing catalase is synthesized in many species of lactobacilli if heme or hematin is present in the culture medium. Both monofunctional catalase and bifunctional catalase-peroxidase were found in the cells of many LAB. Catalases of the second type (Mn-containing), which do not require the presence of heme, are also present in the cells of some lactobacilli species. Many LAB strains are characterized by high intracellular levels of Mn (II). Probiotic LAB cultures with pronounced antioxidant activity are in high demand, since they are potentially able to protect the host organism from the toxic effects of ROS and contribute to the prevention of cardiovascular, inflammatory, and oncologic diseases. In this review, antioxidant defense systems in LAB cells are described based on a thorough analysis of the current scientific data. In particular, the review describes the effect of oxidative stress on the metabolism of lactobacilli, their main antioxidant enzymes (NADH oxidase, NADH peroxidase, catalase, superoxide dismutase, and thioredoxin reductase), as well as the key regulatory proteins and the genes responsible for oxygen uptake as one of the mechanisms for decreasing the ROS concentration.