**2. Antioxidant effect**

Probiotic originated from longevity research by the well-known Eli Metchnikoff. As we all known, various published evidence suggested reduction of oxidative stress led to longevitypromoting consistent with Harman's Free Radical Theory of Aging [15]. These two observations inspired the investigation of antioxidant ability of probiotics.

Oxidative stress induced by obesity tend to produce surplus reactive oxygen species (ROS) which may cause further damage by free radical chain reaction mechanism [16]. ROS have some deleterious effects on polyunsaturated lipids in cell membrane leading to damage of cell structure and malondialdehyde (MDA), which was also toxic to DNA and protein and formed as a marker of lipid peroxidation at the same time [17] [18]. As for the oxidative stress, human body has its own antioxidant defense system including superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px) , glutathione (GSH) and so on [19]. Many *Lactobacillus* strains with antioxidative effects were not only reducing MDA level, but also enhance the antioxidants production (Table1).



**Table 1.** Antioxidative effects of probiotics
