Screening,identification,and mechanism elucidation of zearalenone-reducing lactic acid bacteria from Chinese sourdough
[Background]Zearalenone(ZEN),a mycotoxin with estrogenic effects produced by Fusarium,is one of the pollutants that seriously jeopardize human health and agricultural safety worldwide.As a class of food-grade non-pathogenic microorganisms generally recognized as safe(GRAS),lactic acid bacteria have been proved to have good mycotoxin-reducing ability in recent years,demonstrating the application potential in safeguarding food safety.[Objective]To screen the lactic acid bacteria capable of reducing ZEN from seven Chinese sourdough samples collected from Shandong,Henan,and Gansu,and investigate the reducing mechanisms of ZEN by the bacteria.[Methods]The strains were isolated by the dilution-plate coating method.Ultra-high performance liquid chromatography was employed to screen the strains with ZEN-reducing activity,mass spectrometry(Q exactive)to identify the metabolites,and transmission electron microscopy(SEM)to observe the morphology of the strains.The adsorption effects were examined at different initial toxin concentrations and bacterial concentrations,and a kinetic model was fitted.Fourier transform infrared spectroscopy(FTIR)was employed to identify the functional groups involved in the adsorption of ZEN and elucidate the adsorption mechanism of ZEN.[Results]A total of 63 strains of Lactobacillus were isolated from the preliminary screening,and then three strains with ZEN-reducing activity were obtained.Strains 6-8 and 18-2 were identified as Levilactobacillus brevis,and strain 12-6 as Acetobacter tropicalis.The two strains of L.brevis had ZEN-degrading effects,with the degradation rates of 85.5%and 87.3%,respectively,within 48 h at ZEN concentration of 10 mg/L.The mass spectrometry results showed that the degradation product was α-ZEL.The other strain had a ZEN-adsorbing effect,with the adsorption rate reaching 62.9%within 20 min at a bacterial concentration of 4.26×1010 CFU/mL and a ZEN concentration of 10 mg/L.Moreover,the adsorption rate increased by 20%after strain inactivation.The adsorption process was fitted with both pseudo-first-order and pseudo-second-order models.Fourier transform infrared spectroscopy(FTIR)showed that the main adsorption sites of strain 12-6 were peptidoglycan and teichoic acid in the cell wall,involving hydroxyl,methenyl,carboxyl,and amide groups.[Conclusion]L.brevis 6-8 and 18-2 showed strong degradation capacity against ZEN,and A.tropicalis 12-6 had a strong adsorption capacity for ZEN.The adsorption kinetics conformed to pseudo-first-order and pseudo-second-order models,with the adsorption sites at teichoic acid and peptidoglycan in the cell wall.This study provides a theoretical basis for the application of lactic acid bacteria in the removal of harmful substances from food and feed.
zearalenonelactic acid bacteriaadsorptionfunctional groups
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