Effect of quantity of food residues on resistance to desiccation, disinfectants, and UV-C irradiation of spoilage yeasts adhered to a stainless steel surface

- Drying decreased S. cerevisiae and D. hansenii count on stainless steel dishes.
- Small amounts of food residues increased the resistance of the cells to desiccation.
- For example, one μL of milk and orange juice, or 100 nL of egg-yolk protected the cells.
- The cells were also protected from disinfectants and UV-C by the milk and egg-yolk.
- Orange juice also protected the cells against UV-C irradiation.

Although Saccharomyces cerevisiae and Debaryomyces hansenii are important for food fermentation, they are considered as spoilage yeasts in various processed foods. In this study, we investigated the quantity-dependent effects of milk, egg yolk, and orange juice on the survival rates of food-spoilage yeasts when desiccated on a stainless steel surface. The protective effects on yeast cells before and after drying against disinfectants and UV-C irradiation were also investigated. Microbial suspensions (0.1 mL) were placed on a stainless steel dish (50 mmφ). After drying for 2 h at room temperature in the absence of food residue, viable cell counts of S. cerevisiae and D. hansenii decreased from 6 to <2 and 3-4 log CFU/dish, respectively. Even small quantities of milk (1 μL), egg yolk (0.1 μL), and orange juice (1 μL) per dish of yeast suspension protected the yeast cells from desiccation. Milk and egg yolk also protected the yeasts when treated with 0.02% w/v sodium hypochlorous acid and 0.2% w/v benzalkonium chloride. Yeast cells were protected from UV-C irradiation by milk, egg yolk, and orange juice. These results suggest that small sediments of food increase the resistance of surface adherent spoilage yeasts against desiccation, disinfectants, and UV-C irradiation.