Osmophilic or osmotolerant yeasts are able to grow in products containing high concentrations of organic solutes, particularly sugars. These organisms do not require a high water activity value and tolerate drier environments than non-osmotolerant organisms. Osmophilic yeast can cause spoilage of honey, corn syrup, jam, molasses,flavored syrups and toppings, and concentrated fruit juices. Many of the yeasts causing this spoilage belong to the genus Zygosaccharomyces. It is of great importance in the food industry to test for these organisms. Although no osmophilic organisms are highly pathogenic, they may cause food poisoning and opportunistic infections, especially in people with weakened immune systems.
Although there are many techniques used to test and enumerate Osmophilic yeast, a standard method has not been attained. Different types of growth media have been suggested, but like the techniques, not one type of agar has been adopted as the standard. Using the plate count method, samples are blended with sterile phosphate buffer containing high concentration of glucose. Petri dishes are then inoculated with the appropriate dilution of the product, and agar medium that would promote growth of the Osmophilic yeast is added, depending on the type of product. Plates are incubated for 5-7 days. Membrane filtration technique can also be utilized to test the Osmophilic yeast. Typically, a 25-gram sample is added to the flask and mixed well with sterile distilled water. After filtration, provided that the product can be filtered, the walls of the flask and funnel are rinsed with the distilled water, and the filter placed on a desired growth medium and incubated for 5-7 days. Both the plate count and membrane filtration techniques pose threats to damaged organisms from general processing procedures, temperature of agar, and temperature, pressure and duration of incubation. Colonies may also be very small and difficult to count.
The BioLumix Osmophilic Yeast Vial
The BioLumix system provides Osmophilic Yeast results 3 days faster than the aforementioned methodologies. The Osmophilic Yeast vial has a CO2 sensor that is monitored by the yellow LED light in the BioLumix Instrument. This particular vial contains much more sugar than a typical Yeast and Mold vial, to allow only Osmophilic yeast to grow. The vial also contains Chloramphenicol to prevent the growth of bacteria.
The procedure to test for Osmophilic yeast is very simple; just add 10 grams of product to 90mL Tryptic Soy Broth or buffer, and add the appropriate amount to ready-to-use Osmophilic vials. For some product the sample can be added directly into the vial. From this 1:10 dilution, other dilutions can be made if necessary. From the appropriate dilution, 0.1 to 1.0 mL is added to the BioLumix vial. compared to the plate method. Figure 1 shows curves generated by the Zygosaccharomyces rouxii ATCC 34890 (blue) and 28253 (green). organisms while preventing product interference. It offers a reduced work load, faster time-to-results, and fewer costs associated with testing. The BioLumix system can make the microbiological testing simpler, faster and automated. The test runs for 48 hours, cutting the time-to-results by three days as The BioLumix system allows for selectivity of organisms while preventing product interference. It offers a reduced work load, faster time-to-results, and fewer costs associated with testing. The BioLumix system can make the microbiological testing simpler, faster and automated.
Downes, Frances P., and Keith Ito. Microbiological Examination of Foods. 4th ed. Washington, DC: American Public Health Association, 2001.