The improved RIDA®COUNT Yeast & Mold Rapid (R1008) test from R-Biopharm is now available with effect of November 2010! The ready-to-use test cards, coated with dry nutrient medium (modified yeast-glucose-chloramphenicol medium), are designed for the detection of yeasts and molds within just 48 hours.
The metabolic enzymes of the yeasts and molds convert the chromogenic substance contained in the medium during their growth, and the colonies that emerge take on a Bordeaux-red color.
The medium of the hitherto available version of the product made use of chromogenic substances that were reduced by the enzymes of the respiratory chain of the yeasts and molds to form blue dyes, resulting in a blue coloration of the emerging colonies.
Since many untreated food products contain enzymes that are similar to those contained in the molds (cereals, vegetables, fruit, meat, etc.), in frequent instances the investigation of these matrices yielded a blue background coloration on the test cards of the RIDA®COUNT Yeast & Mold Rapid. Depending on the intensity of the background color, in many cases this made it difficult - or even impossible - to detect yeasts and molds in low sample dilutions.
This problem has now been largely solved thanks to the improved chromogenic system of detection of the new RIDA®COUNT Yeast & Mold Rapid test (R1008). The Bordeaux-red-colored colonies are now distinctly set off against a pink-colored background, even in foods with a high content of metabolic enzymes (e.g. liver, meat, fish, etc.).
The illustration shows the difference between the old (left) and new (right) versions of the product.
Untreated barley grains (ground, diluted 1:10 with 0.9 % NaCl solution) applied in 1-ml portions to the RIDA®COUNT Yeast & Mold Rapid test card in the former format (left) and to the test card with the new, improved detection system (right).
Both test cards were incubated at 25°C for 48 hours after application of the samples. The activity of the enzymes contained in the barley grains converts the chromogenic agent that was an ingredient of the former version of the product, and the test card turns blue in color.
Colonies of yeasts and molds cannot be distinguished from the background. The color of the test card in the new product version is not influenced by the food enzymes, and colonies of yeasts and molds can be easily recognized.