Mold and yeast detecting board

1. Principle & application scope

Molds and yeasts widely exist in air, water and soil. Most of them are harmless, but some are harmful for human health, such as aspergillus flavus, which can secrete a strong carcinogen. Molds can also stimulate human stomach and intestine, cause food poisoning and injure liver. Mold and yeast detecting board which contains nutrient culture medium, bibulous gel and enzyme-chromogenic reagent can greatly save the time of medium preparation, disinfection and cleaning. It is easy to use and very convenient for detection of molds and yeasts in all kind of food and drinking water. It is suitable for institutes of food hygiene inspection and food factories. 

Executive standard: National Food Safety Standard, Food Microbiological Examination, Enumeration of molds and yeasts (GB 4789.15)

2. Using method

2.1 Sample preparation: Prepare the 1:10 solution by placing 25g or 25mL sample into 225mL sterile water and shaking evenly. Then prepare 1:100 solution by suck 1mL solution (1:10) into 9mL sterile water. According to the pollution level of sample, prepare solutions of other dilution ratios if necessary. 

2.2 Inoculation: Select 2-3 appropriate dilution ratios to do the test for ordinary food, while for some liquid samples which has little bacteria, directly suck raw liquid to do the test. Place the detecting board on a flat experiment table; uncover the upper film. Suck 1mL solution with sterile pipette, and then drop it into the detecting board. Cover the film gently and shake the detecting board horizontally to let the solution be adsorbed by filter paper. Stand for 10s until the solution is adsorbed completely. Inoculate two detecting boards for each sample solution and do a blank control.

2.3 Culture: Superimpose the detecting board; place them upside down in the incubator in the temperature of 29℃±1℃ for 48-72 hours.

3. Result 

Mold and yeast will show blue spots after growing on the detecting board, mold colony is radial and relatively larger than yeast, while yeast colony is small and smooth. Select the detecting boards of which the colony quantity is between 10CFU and 150CFU to do the counting.

4. Counting method & report

4.1 Select the detecting boards of which the colony quantity is between 10CFU and 150CFU to do the counting. Calculate the average value and then multiply it by the corresponding dilution multiple. (see Example 1)

4.2 If the colony average values of all the dilution ratio detecting boards are more than 150CFU, select the maximum dilution multiple detecting boards to do the counting, then multiply the corresponding dilution multiple as report data, other detecting boards can be recorded as TNTC (too numerous to count). (see Example 2)

4.3 If the colony average values of all the dilution ratio detecting boards are less than 10CFU, calculate the average value of the minimum dilution multiple detecting boards and multiply the dilution multiple as report data. (see Example 3)

4.4 If there is not any mold and yeast growing on all the detecting boards, report it in terms of less than one multiply the minimum dilution multiple.(see Example 4)

5. Additional explanatory notes

5.1 Mold and yeast widely spread in the air in the form of spore. It is demanded that mold and yeast cannot be detected for most samples; therefore, it is essential to operate carefully when using mold and yeast detecting board. All the sampling tools, dilute water, sucker and other utensils should be thoroughly disinfected. In order to avoid air flows during the inoculation, inoculate as quickly as possible. It’s better to make two blank controls with sterilized saline to avoid the false positive results.

Dispose used detecting boards according to the biology safety waste treatment rule, because there are live bacteria on them.