Production of freeze-dried Lactobacillus inoculants and evaluation of the effect of inoculation rate on ensiling of forage maize

Abstract

Favorable lactic acid bacteria (LAB) inoculants are used to enhance forage ensiling. The study aimed to produce freeze-dried inoculants from Lactobacillus plantarum, L. rhamnosus and L. oris which were isolated from silage of maize, sorghum and guinea grass, respectively and asses the influence of the inoculation rate on ensiling of forage maize. The Lactobacillus isolates were inoculated separately into MRS broth and incubated at 37ᵒ C for 18 hours (MRS mother culture). The mother cultures were inoculated into skim milk broth (10 %) and incubated at 37ᵒ C for 72 hours. Their growth kinetics were studied. All LAB species exceeded 109 CFU/mL by 24 h and reduced the pH value to 3.92 – 4.11 by 72 h. Therefore, skim milk (10 %) broth was chosen as lyophilization media for making freeze-dried LAB inoculants. Pelleted MRS mother cultures (10 mL) were dissolved in 10 % skim milk broth (30 mL) and the suspensions (0.5 mL) were freeze-dried in vials (LAB inoculant). The effect of inoculation rate on forage maize ensiling was assessed at 3 inoculation rates (0, 104 and 106 CFU/g fresh forage). The experiment was conducted as a complete randomized design which included 2 factors (LAB species, inoculation rate). Chopped (10-15 mm) fodder maize was treated with respective LAB inoculant and inoculation rate. They were ensiled in I L Weck glass jars. Each treatment combination had 3 replicates. Laboratory silos were opened at 14 days post-ensiling and dry matter, pH value, lactic acid content and ammonia nitrogen contents were measured. The species of LAB inoculant and inoculation rate had significant (P<0.05) effect on the pH value of maize silage. An increasing trend of lactic acid content was evident with increasing inoculation rate of L. plantarum. The pH value was low (P<0.05) when forage maize was inoculated with L. rhamnosus and L. oris at 106 CFU/g rate (3.43 and 3.41), respectively. The study confirmed the potential of production of freeze-dried LAB inoculants from L. plantarum, L. rhamnosus and L. oris that isolated from maize, sorghum and guinea grass, respectively. Ensiling forage maize with freeze-dried L. rhamnosus L. oris inoculants at 106 CFU/g fresh matter ensures rapid drop of pH value during ensiling forage maize.