Maize inoculation with aflatoxigenic and biocontrol fungi - toxin transfer from feed into milk and yoghurt

The consumption of milk can contribute to the consumers` exposure to aflatoxin as aflatoxin M1 (AFM1), a hydroxylated metabolite of aflatoxin B1 (AFB1), is transferred into the milk of AFB1 exposed dairy cows. As mitigation measures against AFB1 presence in cattle feed, fungal biocontrol strains are applied on plant materials to reduce toxigenic A. flavus growth. The present study investigates the impact of applying two biocontrol strains (Trichoderma afroharzianum and non-toxigenic Aspergillus flavus) compared with a toxigenic A. flavus strain on the mycotoxin transfer from maize into milk and milk products in a “farm to fork” approach. Firstly, in a feeding study three groups of high yielding dairy cows are exposed to different maize flours infested with biocontrol or AFB1-foming fungal strains for 14 days to monitor a potential toxin transfer from feed to milk. In the milk of cows exposed to AFB1, AFM1 was detected with a mean value of (95.6 ng/kg ± 13.7 ng/kg) while the mean transfer rates (3.8% ± 0.9%) were slightly higher than published in previous studies. Neither AFM1 nor cyclopiazonic acid could be detected in milk from the cows exposed to the two biocontrol strains. The data show, that the AFM1 limit of 50 ng/kg in milk can be exceeded when cattle feed is contaminated with AFB1 within the legal limit. Consequently, the use of cattle feed within the current European legal limits does not necessarily guarantee for obtaining milk compliant with European maximum levels. In the second part, AFM1 containing raw milk from the experimental cows was processed further into yoghurt to investigate the fate of the toxin under acidic fermentation conditions. No AFM1 degradation was found during authentic yoghurt making, albeit in a model experiment the hydration of AFM1 in presence of citric acid was shown. Further studies are necessary to investigate the exact conditions suitable for reducing the AFM1 content of contaminated milk during the processing of dairy products