Impact of Potentially Antioxidant Probiotic Strains on Fermentation Quality and Antioxidant Status in Alfalfa Silage

The study aimed to characterize the antioxidant properties of isolated lactic acid bacteria (LAB) and assess their impacts on fermentation quality and antioxidant status in alfalfa silage. Two LAB strains of <i>Lactiplantibacillus plantarum</i> XY15 and <i>Lactiplantibacillus plantarum</i> XY20 and a reference strain of <i>Pediococcus acidilactici</i> J17 were subjected to antioxidant property evaluation. This was followed by inoculation into alfalfa silage. The DPPH (2,2-diphenyl-1-picrylhydrazyl) and hydroxyl (OH) radical scavenging activities and the glutathione peroxidase (GSH-Px) activity of the cell-free supernatants of <i>L. plantarum</i> YX15 and <i>L. plantarum</i> YX20 were significantly (<i>p</i> < 0.05) higher than those of <i>P. acidilactici</i> J17. In all three strains, the superoxide dismutase (SOD) activity was higher in the cell-free supernatants than in the intracellular lysates. Among all three strains, <i>P. acidilactici</i> J17 showed the highest total antioxidant capacity (T-AOC) in the cell-free supernatant. Inoculating <i>L. plantarum</i> YX20 and <i>P. acidilactici</i> J17 increased lactic acid (LA) concentration and LAB counts, decreased dry matter (DM) loss, ammonia-N concentration, and pH, compared with control (CON) and <i>L. plantarum</i> XY15 inoculated alfalfa silages. After 1 d of ensiling, alfalfa silage inoculated with <i>L. plantarum</i> XY20 exhibited higher SOD activity than other silages. Inoculating <i>L. plantarum</i> XY20 and <i>P. acidilactici</i> J17 increased the DPPH free radical scavenging rates in alfalfa silage, compared with CON and <i>L. plantarum</i> XY15 inoculated 90 d-silages. Both <i>L. plantarum</i> YX15 and <i>L. plantarum</i> YX20 demonstrated a dual function of enhancing the lactic fermentation and improving the antioxidant status in alfalfa silage.