The capacity of silage inoculant bacteria to bind aflatoxin B1 in vitro and in artificially contaminated corn silage

Abstract

The objectives were to examine the aflatoxin B (AFB)-binding capacity of silage bacteria and factors affecting the responses. Experiments 1 and 2 examined the effects of bacterial strain and population on the AFB-binding capacity of 10 bacteria. When applied at 10 cfu/mL to an in vitro medium, only Lactobacillus plantarum PT5B bound the AFB and the binding capacity was low (4%). When applied at 10 cfu/mL, all 10 bacteria bound AFB, but L. plantarum R2014 (Lp) and EQ12, Lactobacillus buchneri R1102 (Lb), and Pediococcus acidilactici R2142 and EQ01 (Pa) had the greatest capacity (23.9 to 33%). Experiment 3 examined the AFB-binding capacity of viable and nonviable (HCl-treated) forms of Lp, Lb, and Pa at different pH. Nonviable Lb and Lp, but not Pa, increased AFB binding. Binding of AFB was greatest at pH 2.5 and least at pH 8. As the nonviable Lb and Lp that bound AFB in experiment 3 would not be effective silage inoculants, experiment 4 examined effects of benign versus severe treatments (85 vs. 100°C; pH 2.5 vs. <1) on the viability of Lp, Lb, and Pa. The population of bacteria was reduced from 9 to 4 log cfu/mL by treatment with HCl at pH 2.5 and to 2 log cfu/mL by 85 or 100°C, whereas acidification at pH <1 eliminated the bacteria. Experiment 5 determined the effect of the ensiling duration and benign treatment methods [37 (viable cells) or 85°C (heated cells) or acidification with HCl at pH 2.5 (acid-treated cells)] on binding of AFB and silage quality during the fermentation of corn forage. Corn forage was ensiled after treatment with only deionized water (control), AFB (30 µg/kg of fresh forage), or a mixture of AFB and 10 cfu/g of each of the treated bacteria. Adding AFB alone to corn forage reduced the pH decline during the first 3 d of ensiling and increased or tended to increase butyric acid concentration and final pH after ensiling for 21 d. Bacterial inoculation inhibited these negative effects. The fermentation profile of silage treated with Lb and Pa did not differ from those of the control silage. In all silages treated with the toxin, the AFB concentration decreased linearly (from 30 to ≤0.35 µg/kg) within 3 d of ensiling. Certain silage bacteria can bind AFB but the efficacy depends on several factors.

Lactic Acid Bacteria as Antifungal and Anti‐Mycotoxigenic Agents: A Comprehensive Review

“…Contrary to this, Luz, Ferrer, Mañes, and Meca (2018) reported a decrease in the OTA binding capacity of Lactobacillus johnsonii, Lactobacillus bulgaricus and Lactobacillus salivarius from 16% in MRS with pH 3.5 to 4, 1.6 and 4.4%, respectively, in the same medium at pH 6.5 (Table 3). Ma et al (2017) also reported the highest binding of AFB1 to L. plantarum and Lactobacillus buchneri at pH 2.5, and the least binding was observed at the pH value of 8.5 in phosphate buffer.…”

“…Ma et al. () also reported the highest binding of AFB1 to L. plantarum and Lactobacillus buchneri at pH 2.5, and the least binding was observed at the pH value of 8.5 in phosphate buffer.…”

“…For instance, Zhao et al (2015) and El-Nezami et al (1998) reported a significant correlation between the initial bacterial count and mycotoxin binding. Ma et al (2017) reported the removal of only 0% to 4% AFB1 from silage initially inoculated with 10 6 CFU/mL, as compared to 18% to 33% AFB1 being removed from the silage initially inoculated with 2 × 10 9 CFU/mL. environment and digestive enzymes.…”

“…Ma et al. () reported the removal of only 0% to 4% AFB1 from silage initially inoculated with 10 6 CFU/mL, as compared to 18% to 33% AFB1 being removed from the silage initially inoculated with 2 × 10 9 CFU/mL.…”

“…LAB strains are widely used in silage as microbial inoculants, where they are known to enhance the aerobic stability of silage. Ma et al (2017) for the first time used LAB in corn silage to check the efficacy of bacteria to reduce AFB1. LAB species reduced the initial AFB1 concentration in the silage from 30 to 2 µg/kg within 2 hr, probably due to the immediate binding.…”