Screening and selection of lactic acid bacteria suitable for enhancing the quality of maize silage

The effects of lactic acid bacteria as a microbial additive on the fermentation properties of silage are mainly due to the production of beneficial metabolites that can inhibit the growth of pathogenic and destructive microorganisms. Therefore, the ability of a strain to use numerous substrates in forage plants and produced different metabolites can be useful in competition with other microorganisms. This ability can be used as a principle for selecting inoculants. Nevertheless, research has shown that published articles on inoculant selection to limit the growth of these destructive and pathogenic microorganisms are still scarce. Some researchers have reported the effects of microbial inoculants on silage fermentation. However, despite numerous articles on the effects of inoculants on silage fermentation, there is little descriptions for the systematic selection of strains. The aim of this study was to isolate, identify and select strains of lactic acid bacteria with the ability to improve fermentation properties and prevent the growth of pathogenic and destructive microorganisms and evaluate the effect of inoculation of these strains on nutritional value and aerobic stability of maize silages.

This study was performed to select the lactic acid bacterial (LAB) strains isolated from different sources and evaluate their effect on the quality of maize silage. Lactic acid bacteria strains were inoculated to evaluate metabolite production and pH reduction in aqueous extract obtained from maize forage. One hundred and twenty-one strains were isolated from various sources in the laboratory. All isolated strains were gram-positive, catalase-negative and mainly lactic acid-producing, which were considered lactic acid bacteria. 16S ribosomal DNA sequence analysis of 22 representative strains was used to confirm the presence of dominant groups. The sequences of different isolates of lactic acid bacteria had a high degree of similarity to the GeneBank type strains, which showed between 99 and 100% similarity. Four strains of lactic acid bacteria that showed the best results were evaluated in experimental silos. This experiment was performed in a completely randomized design with five treatments (four strains of lactic acid bacteria and one control without inoculum) and nine replications. Inoculants were used in 106 colony forming unit/g of fresh forage to chopped maize forage, which were then ensiled for 105 days. After opening the silos, silages were sampled for analysis of chemical compositions and fermentation products.

Inoculation of lactic acid bacterial strains affected the chemical composition, fermentation properties and microbial population. Inoculation of lactic acid bacterial strains significantly affected the chemical composition and concentration of lactic and acetic acids, ethanol and 1,2-propandiol of silage. Among all treatments, silages inoculated with Lactobacillus fermentum had higher acetate concentration (p < 0.0001), but lactate concentration (p < 0.008) and yeast counts (p < 0.0001) were lower than other silages. Also, inoculation of silage with L. fermentum (strain 16) resulted in silage with higher lactic acid bacterial population and improved aerobic stability after air exposure (p < 0.0001). Silages inoculated with L. fermentum and fallowed by with L. salivarius contained the lowest number of yeasts (p < 0.0001) and filamentous fungi during fermentation. Between silages, silage inoculated with L. fermentum showed higher aerobic stability (p < 0.0001).

The pre-selection method based on the production of metabolites was efficient in selecting new inoculation strains along good correlation with experiments in laboratory silos. Inoculation of lactic acid bacterial strains in maize silage resulted in differences in nutritional value or population of pathogenic and destructive microorganisms. Strains 16 and 7, identified as Lactobacillus fermentum and Lactobacillus salivarius, were considered promising sources for use as inoculants in maize silages because they provide silages with better fermentation properties and improve aerobic stability after exposure to air.