Screening Of Dominant Lactic Acid Bacteria And Fermentation Qualitty Control Of Corn Silage Processing

A total number of 35 representative strains of lactic acid bacteria(LAB) were isolated and screened at 3‐5 days afterpredominant ensiling fermentation of corn, which were harvested in Henan, Shannxi, Shanxi, Hebei and other 8 provinces in China.The fermentation characteristic and bacterial inhibitory were studied based on identification and characterization of those 35 representative LAB strains and Lactobacillus buchneri by using 16 S r RNA analysis. We examined the roles of those isolates on the corn silage fermentation, fermentation products and rumen fermentation in vitro.We also reported the impact of urea on the population of LAB and fermentation products duringcorn fermentation.1.Isolation and screening of representative LAB strains fromcorn silage fermentationEffect of corn silage fermentation is known to depend on profile structure and physical number of representative LAB population during the predominant fermentation. Understanding ofspecies profile, physicalpopulation and characteristics of representative LAB strains will be important to predict silage quality, develop new additives of LAB silage and control silage fermentation. Whole corn and green corn stalks were collected from 12 sites in China and used for experimental fermentation. We isolated 35 strains of representative LAB strains and carried out the identification and characterization by using 16 Srna.Representative strains were identified as Lactobacillus plantarum(54.2%), Lactobacillus brevis(28.6%), Lactobacillus sp.(14.3%), and Lactobacillus spicheri(2.9%). Lactobacillus plantarum, Lactobacillus brevis, and Lactobacillus sp.were suggested as predominant strains of corn silage fermentation in this study.2. Acid‐producing and bacterial inhibitory of representative LAB strains isolated from silageWe compared acid producing activities of 35 representative LAB strains by culturing them in MRS and Corn Juice Medium. The mechanisms of bacterial inhibitory of the selected 9 LAB strains were also explored by using Oxford Cup Vitality method. The results suggested:(1) acid‐producing activities varied a lot among strains independent of using MRS or Corn Juice Medium; and(2) Three strains out of the 9 strains for bacterial inhibitory test showed the ability to inhibit growth of E.coli, while, the other 6 strains being tested demonstrated antibacterial activities to Staphylococcus aureus.3.Effect of LAB inoculants of different sources on corn silage fermentationIn order to explore effect of LAB strains on corn silage fermentation, representative LAB strains were inoculated into whole corn. The following physiological and chemical indicators were measured on the 4 and 90 days after ensiling, including p H, the total organic acidslactic acid, acetic acid, and ratiobetween concentrations of lactic acid and acetic acid. The representative LAB strains were shown to change p H, and the concentration and composition of organic acid, thus influencing silage fermentation quality. Strain of LAB 531 was found to decrease p H of silage both on the 4 or 90 days after ensiling(p<0.05). Strains of LAB 531 and Lactobacillus buchneri could increase the excretion of lactic acid on the 4 days after ensiling(p<0.05). The excretion of acetic acid was increased by strains of Lactobacillus buchneri and LAB 332 on the 90 days after ensiling(p<0.05).Lactobacillus buchneri were reponsbile for the increase of organic acid on the 90 days after ensiling(p<0.05).4. Comparison of fermentation mechanism of Lactobacillus plantarum and Lactobacillus buchneri and their roles in corn silage fermentationIn order to compare their fermentation mechanismand evaluation their effects on the fermentation process and aerobic stability of corn silage fermentation, we inoculated Lactobacillus plantarum and Lactobacillus Buchneri into MRS and whole corn silage. We measured p H, total organic acids, lactic acid, acetic acid, and ratio between concentrations of lactic acid and acetic acid during fermentation. The results indicated that Lactobacillus plantarum and Lactobacillus buchneri differed a lot in acid producing activities in MRS: the inoculation of Lactobacillus plantarum accelerated the dropping of p H during fermentation, but decreased the aerobic stability of corn silage. And inoculation of Lactobacillus buchneriin whole corn silage were observed to be able to slow down p H dropping, decrease the ration between lactic acid and acetic acid, inhibit fungal growth and increase aerobic stability. It was suggested that combined inoculation of Lactobacillus plantarum and Lactobacillus buchneri could increase total organic acid and increase aerobic stability of silage feed.5. Effects of adding urea on the microbial changes in the fermentation of whole cornIn order to evaluate impact of ureaon change of microbes changes during the fermentation of whole‐plant corn silage fermentation, we added urea at levels of 0.1%, 0.4%, 0.6%, and 0.8% and the complex of urea(0.35%) and ammonium sulfate(0.1%). On days after ensiling(1,3, 7, 21, 56, and 91), we measured the changes of p H and microbial population changes of LAB, yeast, mold, total organic acids,lactic acid, acetic acid during the fermentation process. The value ofp H, dry matter content, crude protein, concentrations of ammonia nitrogen were determined on days of 56 and 91 after ensiling. The results indicated that the addition of urea has decrease the speed of p H dropping and the deterioration of LAB population in the middle and late stages of fermentation. Urea also inhibited fungal growth.The above effects of slowing and inhibitory were increased with increased addition of urea. The addition of complex was found to exhibit those above two effects faster than adding urea alone. With the increasing of added urea, the ratio between lactic acid and acetic acid were increased. Total organic acid were found to increase in the fermentation with addition of the complex. The concentration of ammonia nitrogen of the five experiment groups were significantly higher the control. We also observed the decreasing trend of dry matter, increasing of crude protein, and the increase followed by decrease of the aerobic stability. The results suggested that the addition of complex might significantly increase the ammonia nitrogen and aerobic stability of corn silage.6. Effect of representative LAB strains on in vitrorumen fermentationWe inoculated into rumen fluid at level of 109cfu/Lof two LAB strains of Lactobacillus plantarum and Lactobacillus brevis from natural fermentation of corn and 1 heterofermentative strain of Lactobacillus buchneri. The control was glucose inoculation at level of 10g/l. Both Lactobacillus plantarum and Lactobacillus brevis were shown to be capable to grow in vitro rumen fermentation. When glucose was added, Lactobacillus brevis and Lactobacillus buchneri were observed to increase excretion of lactic acid at the start of fermentation. Lactobacillus buchneri were found to increase the acetic acid content of the rumen fermentation fluid.