Effect of using mycotoxin-detoxifying agents in dairy cattle feed on natural whey starter biodiversity.

Food and feed contamination with mycotoxins is worldwide of increasing importance. These metabolites, produced by toxigenic fungi, reach humans and animals by different routes, including contaminated crops (cereals and vegetables) and from animal feedstuffs to animal food products. For example, aflatoxin B1, when ingested by a lactating cow through contaminated feed, is bio-transformed into the toxic and carcinogenic metabolite aflatoxin M1 (AFM1), which is excreted into milk. Given that AFM1 represents a potential risk for public health, several countries have regulated its maximum residue level in milk and cheese. In cheese, AFM1 concentration is related to different factors, including cheese type and technology factors.

Cheese production is from fermentation processes by starter cultures used to generate lactic acid enabling gel syneresis, whey expulsion, and curd formation. Natural whey cultures (NWC) are undefined cheese starters obtained by the traditional back-slopping procedure. They play a key role in cheese specificity, uniqueness, and development of sensory characteristics. The relationships among the lactic acid bacteria (LAB) species in whey cultures and their diversity can be affected by many biotic and abiotic factors, such as bacteriophages, environmental conditions, and changes in whey and cheese-making parameters. Since de-toxifying agents are used to combat mycotoxin contamination in feeds, and they alter the microbial composition, the hypothesis in this study was that these agents could alter the faecal microbiota and, consequently, the biodiversity in raw milk and whey. Therefore, the effect of two mycotoxin-detoxifying agents [sodium smectite and lignocellulose-based material (B1); leonardite and betaine (B2)] on the microbiota of NWC used in production of a Grana-like cheese was investigated. 

Microbiological and flow cytometry analyses showed that the content and viability of lactic acid bacteria (LAB) and the total whey microbiota were not affected by the detoxifying agents, and Streptococcus thermophilus, Lactobacillus helveticus, and Limosilactobacillus fermentum were the dominant taxa. Random amplified polymorphic DNA-PCR fingerprinting and metagenomic analysis highlighted differences in the bacterial community of the NWC and in the relative abundance of Bacteroidetes that increased when B1 and B2 were included in the diet. Two of six St. thermophilus biotypes were detected only in control samples; conversely, none of the Lb. helveticus biotypes found in control samples were isolated from B1 and B2. In vitro tests showed that the two binders did not significantly affect the development of St. thermophilus, but they stimulated the growth of Lb. helveticus strains recovered only from B1 and B2 NWC.

Conclusions: The two mycotoxin-detoxifying agents did not affect the LAB counts or acidifying activity of the NWC but did affect the LAB biotypes present in NWC. There was an increase in the relative abundance of Bacteroidetes when B1 or B2 was included in the cow diet, showing their effect on the gut microbiota. Detoxifying agents that are blended into feed are known to pass through the digestive tract of animals and then discharged with faeces. Because different studies have revealed that cow faeces greatly affect milk microbiota composition, the hypothesis is that these agents shift the faecal microbiota and, consequently, the microbial composition of the raw milk and whey starter. Thus, it is possible that changes in the whey microbiota can have negative consequences for the quality and sensory characteristics of the cheese.