Cheese-dwelling yeast shows promise against ochratoxin A in ripened dairy products

A cheese-loving yeast may hold the key to safer aged cheeses. In a new laboratory study, researchers found that Debaryomyces hansenii, a yeast already common on the surface of ripened cheeses, significantly suppressed the growth of Aspergillus westerdijkiae—a mould notorious for producing ochratoxin A, a dangerous mycotoxin—on a cheese-like medium. The findings, published in Current Research in Food Science, suggest that this naturally occurring microorganism could serve as a protective culture to reduce mycotoxin contamination during cheese ripening.

Ochratoxin A (OTA) is one of the most concerning mycotoxins in the food supply. Classified by the International Agency for Research on Cancer as a group 2B agent—a possible human carcinogen—it carries nephrotoxic, immunotoxic, and teratogenic properties. While OTA contamination is well documented in cheese, no legal limits for the toxin in cheese currently exist, highlighting an urgent need for effective mitigation strategies. The European Food Safety Authority has identified cheese among the food categories contributing to chronic dietary OTA exposure in some consumer groups, making the search for solutions increasingly pressing.

Enter Debaryomyces hansenii. This yeast is one of the dominant species naturally found on the surfaces of many ripened cheeses, where it contributes positively to flavour development, proteolytic and lipolytic activities, and surface deacidification. It has been included in the European Qualified Presumption of Safety (QPS) framework since 2007, meaning regulators consider it safe for use in food. Previous research has shown that D. hansenii can limit ochratoxigenic fungi in fermented meats, but until now, no study had tested its effectiveness against A. westerdijkiae specifically on a cheese-like matrix.

The research team, led by scientists at the Institute of Sciences of Food Production (CNR-ISPA) in Bari, Italy, tested thirteen strains of A. westerdijkiae—twelve isolated from the surfaces of Italian cave cheeses and one from sorghum—against a single strain of D. hansenii (ITEM 19968), itself originally isolated from cheese. They used a Caciocavallo-based cheese agar medium designed to mimic the actual cheese environment from which the fungal strains were recovered.

The experimental design was straightforward but rigorous. The researchers inoculated the cheese agar with a suspension of D. hansenii at a concentration of 10⁶ cells per millilitre, then spotted fungal spores onto the surface in a symmetrical triangular pattern. Control plates received the fungal spores but no yeast. Plates were incubated for 20 days at 25°C in the dark, and mycelial growth was measured at 5, 10, 15, and 20 days post-inoculation. After the incubation period, the entire plate contents were collected and analysed for OTA using high-performance liquid chromatography with fluorometric detection.

The results revealed a striking temporal pattern. In the first five days, the interaction between the two microorganisms was heterogeneous: five of the thirteen fungal strains actually showed apparent growth stimulation in the presence of the yeast, with inhibition values ranging from −17% to +35%. However, by day 10, all thirteen strains exhibited reduced mycelial growth, with inhibition values ranging from 17% to 31%. These inhibition levels remained relatively stable through days 15 and 20, suggesting a sustained antagonistic effect once the yeast became established.

The most dramatic findings, however, concerned ochratoxin A production. At 20 days post-inoculation, OTA production was reduced by 63% to 100% across all toxin-producing strains. Seven strains—ITEM 9607, ITEM 18032, ITEM 19082, ITEM 19084, ITEM 19092, ITEM 19094, and ITEM 19095—showed complete inhibition, with OTA levels falling below the detection limit of 3 μg/kg. The control group’s baseline OTA production ranged from 5 to 1,603 μg/kg, meaning the yeast suppressed toxin output regardless of how intrinsically toxigenic each fungal strain was.

What makes these results particularly intriguing is that the reduction in OTA was proportionally greater than the reduction in fungal growth. This suggests that D. hansenii does not merely limit fungal proliferation but also directly interferes with the metabolic pathways involved in mycotoxin biosynthesis. Previous work by Gil-Serna and colleagues demonstrated that the yeast may downregulate genes involved in OTA production and adsorb the toxin onto its cell walls. The authors of the current study propose that nutrient competition, accumulation of yeast-derived metabolites, and modifications to the cheese environment’s physicochemical properties—such as lactate utilisation and surface pH increase—may all contribute to the observed antagonistic effects.

The temporal dynamics of the interaction are also noteworthy. The apparent stimulation of some fungal strains during the first five days likely reflects the yeast’s establishment phase, during which it adapts to the substrate and progressively alters local conditions without yet generating conditions restrictive enough to inhibit fungal growth. Once established, however, D. hansenii appears to create an environment hostile to both fungal expansion and toxin synthesis. This suggests that for practical applications in cheese ripening, the yeast would need to be active for at least ten days to exert meaningful biocontrol.

The researchers caution that their work was conducted under controlled laboratory conditions using a cheese-like medium, which may not fully replicate the complexity of real cheese ecosystems. The specific physiological and molecular mechanisms underlying the observed effects were not investigated and warrant further study using transcriptomic, metabolomic, and targeted biochemical approaches. Additionally, the sensory impact of the specific D. hansenii strain on cheese quality remains untested and must be evaluated under actual manufacturing conditions before practical application.

Nevertheless, the findings represent a significant step forward in the search for natural, sustainable solutions to mycotoxin contamination in dairy products. As consumer demand for clean-label foods grows and regulatory pressure on chemical preservatives intensifies, biocontrol approaches using microorganisms with a history of safe use in food fermentation are gaining traction. Debaryomyces hansenii, already a familiar inhabitant of cheese surfaces and a recognised contributor to cheese ripening, may soon play an even more important role—not just in shaping flavour and texture, but in actively protecting consumers from one of the food supply’s most persistent toxic threats.

Subject of Research: Biocontrol of ochratoxigenic Aspergillus westerdijkiae by Debaryomyces hansenii on cheese-like medium

Article Title: Debaryomyces hansenii as potential biocontrol agent against Aspergillus westerdijkiae and its ochratoxin A production on cheese-like medium

Article References: Carella, D., Cervellieri, S., Anelli, P., Gatto, A., De Girolamo, A., Lippolis, V., Moretti, A., & Susca, A. (2026). Debaryomyces hansenii as potential biocontrol agent against Aspergillus westerdijkiae and its ochratoxin A production on cheese-like medium. Current Research in Food Science, Article 101599. https://doi.org/10.1016/j.crfs.2026.101599

Image Credits: AI Generated

DOI: 10.1016/j.crfs.2026.101599

Keywords: Debaryomyces hansenii, Aspergillus westerdijkiae, ochratoxin A, mycotoxins, cheese ripening, biocontrol, food safety, yeast, dairy, biopreservation, Debaryomyces, hansenii