Seleção e uso de isolados epifíticos de bactérias do ácido lático como inoculantes para silagem de grãos de milho reidratados

Abstract

Two experiments were carried out to select and evaluate the use of native microorganism from rehydrated corn grain silage (RCGS) as bacterial inoculants. For the first experiment, the aim with this study was to identify, characterized and select based on laboratory trials, LAB strains that can be used as bacterial inoculants for rehydrated corn grain silage (RCGS). The corn was grounded (1 mm) and rehydrated (320 H2O.ton-1

), reaching a humidity concentration of 33.9%. It was packed, in average, 5.096 ± 0.04 kg of rehydrated corn (density = 943.66 ± 8.67 kg.m-3

) and silages were storage by 1, 3, 5, 15, 30 and 60 days. The microorganism count was carried out using two different culture mediums: MP = standard MRS; MM = modified MRS. The isolates were evaluated in different tests: growth, the ability to reduce pH, organic compounds production, gas production, reduce deteriorate/pathogenic microorganism growth and starch degradation. The pH was lower than 4.00 for all the isolates evaluated and 78.5% of the isolates increased their count (5.000 to 9.674 log CFU.mL-1

). All the isolates were capable of to produce organic compounds and to reduce the deteriorate/pathogenic microorganism growth. A total of 140 viable isolates were obtained and 21 were selected to silage evaluation as bacterial inoculants. For the second experiment, the aim was to evaluate the effect of bacterial inoculants based on LAB isolates previously selected from rehydrated corn grain silage (RCGS) for these silages on fermentative profile, nutritive value and aerobic stability. The treatments were: RCGS without inoculant (control), RCGS inoculated with eight different bacterial isolates (S-52; S-82; S-106; S-110; S-116; S-180; S-190; S-221), and Lactobacillus hilgardii CNCM I-4785 (CCMA 0170) (S-LH), storage for 45 and 90 days. In average, 5.361 ± 0.08 kg of silage was packed, reaching a density of 992.85 ± 16.37 kg m-3 . The silage fermentative characteristics, nutritive value and aerobic stability were evaluated. The S-LH silage had higher DM losses (6.71%; P = 0,001). Inoculated silage with the 190 isolate and storage for 45 days had lower pH value in comparison to the other silages (3.71; P < 0.001). The NH3-N concentration increased with the storage time (2.30 vs 5.34%; P < 0.001). The S-190 silage had lower zein concentration (4.02%; P < 0.001). The yeast count was lower for S-116 silage (1.256 log CFU; P < 0.001), as well as the storage time (2.780 vs 1.409 log UFC; P < 0.001). The fermentation time increased the lactic (2.08 vs 2.43%; P = 0.010) and acetic (0.26 vs 0.35%; P < 0.001) acid concentrations and reduced the ethanol concentration (0.52 vs 0.42%; P = 0.033). The higher lactic and acetic acid concentrations were observed in S-116 and S-190 (2.79%; 2.90%; P < 0.001) and S-LH silages (0.52 vs 0.42%; P = 0.033), respectively. The S-LH silage storaged by 90 days had the higher aerobic stability (P = 0,019). The storage time increased (P < 0,001) the starch in situ digestibility.