In vitro models to evaluate the capacity of different sequestering agents to adsorb aflatoxins

Eight potential aflatoxin-sequestering agents (SAs) were tested for their ability to adsorb aflatoxin B-1 (AfB(1)) and aflatoxin G(1) (AfG(1)) in vitro. They belong to main SA classes: silicate minerals (calcium, magnesium and sodium bentonites, kaolinite, zeolite and clinoptinolite), activated carbon and yeast cell wall-derived. The AfB(1) and AfG(1) used in present work were extracted from a contaminated corn meal (82.21 mg/kg of AfB(1) and 97.20 mg/kg of AfG(1)). Three single-concentration adsorption tests, consisting of a simply-water (W), a gastro-intestinal simulating monogastric model (MM) and a ruminant model (RM) were used. The methods differed for dilution media, incubation steps and pH condition in which they were conducted. In particular, one step (2h at 39 degrees C) at pH 7 for W; two steps (4h at 39 degrees C) at pH 2 and 7 for MM; and a pre-incubation in rumen fluid (pH 7 for 2h at 39 degrees C) + two steps (4h at 39 degrees C) at pH 2 and 7 for RM, characterized each method. The AfB(1):SA ratio (g/g) and dilution factor (ng of incubated AfB(1):mL of volume) were chosen (1:500,000 and 4.1, respectively) to reflect field conditions. The AfB(1) and AfG(1) recovered in controls were 92.3% and 104.9% in W and 89.5% and 101.5% in MM; while in RM were 65.2% and 81.9%; respectively. This supported the idea of intrinsic rumen fluid factors could be involved in sequestering of aflatoxins. In the present study, three SAs (activated carbon, Mg bentonite and Na bentonite) were very efficient to sequester the available AfB(1), with a sequestering activity of over 99.0% with each method. The Ca bentonite and clinoptinolite were able to bind available AfB(1) in MM and RM methods, while they appeared inefficient (available AfB(1) sequestered less than 80%) when W was used. The adsorption ability of zeolite was confirmed only with the W method. Ineffective or limited sequestering activity were obtained with kaolinite and yeast cell wall-derived products with each method. The AfB(1) and AfG(1) sequestering efficiencies observed in the present work resulted very similar showing strong and positive correlation (P<0.001) within methods (r=0.79, r=0.96 and r=0.99, respectively for W, MM and RM methods). The two simulated gastrointestinal methods (MM and RM, respectively) gave similar results and could be considered useful for in vitro pre-screening of potential sequestering agents. However, the major practical and analytical implications related to rumen fluid method suggested that MM method should be used.