Enhancing propionic acid formation and biogas yield from grass silage via co-fermentation of Pediococcus acidilactici and Lentilactobacillus buchneri

This study investigated the effect of co-fermentation by Pediococcus acidilactici KKP 2065p and Lentilactobacillus buchneri KKP 2047p on propionic acid production and biogas yield from grass silage. The research was conducted in three stages. First, the growth dynamics and acid production of mono- and co-cultures were assessed in modified MRS media supplemented with glucose and 1,2-propanediol (1,2-PDO) under laboratory conditions. Len. buchneri monoculture produced the highest concentration of propionic acid (3.06 g/L), while co-culture with P. acidilactici yielded 2.88 g/L. In co-cultures of P. acidilactici KKP 2065p and Len. buchneri KKP 2047p, no synergistic increase in propionic acid or 1-propanol production was observed compared to monocultures. In MRS medium with 1,2-PDO, Len. buchneri primarily contributed to acetic acid synthesis, while P. acidilactici was responsible for propionic acid and propanol formation. Notably, a high concentration of 1-propanol was associated with a possible metabolic shift or intermediate accumulation. Second, silages were prepared from grass and inoculated with the selected LAB strains. Silage fermentation was evaluated through analysis which revealed increased lactic acid content (7.30 vs. 2.83 g/kg DM in control) and a dominant presence of Lactobacillus (91.8 %) in inoculated silages, alongside a marked reduction in Weissella and Enterococcus spp. The synergism of the selected two strains significantly affected the increase in acetic acid content, which occurred more relevant in anaerobic digestion and biomethane yield in the third step when the biogas potential of the silages was assessed. Inoculated silages showed a 14-21 % increase in methane yield (up to 376 mL/g VS), with methane content reaching 46-55 % (compared to 36-45 % in the control). These results demonstrate that the combined use of P. acidilactici and L. buchneri can enhance both the volatile organic acids content in ensiled plant material and renewable energy output.