The Maximum Recovery Diluent, produced by Liofilchem®, is a protective and isotonic diluent designed for maximizing the recovery of microorganisms during the preparation of initial suspensions and decimal dilutions of test samples. This diluent, also known as Peptone Salt Solution, complies with ISO 6887 standards and is essential for the microbiological examination of food.
Composition and Method Principle
The Maximum Recovery Diluent is composed of Enzymatic Digest of Casein and Sodium Chloride. The Enzymatic Digest of Casein provides amino acids, nitrogen, carbon, and minerals, essential for microbial growth. Sodium Chloride maintains the osmotic balance of the medium. The final pH of the solution is 7.0 ± 0.2 at 25°C. This composition ensures an optimal environment for maintaining the viability of various microorganisms, including those that are stressed or injured.
Preparation
To prepare the diluent, 9.5 g of the dehydrated medium is suspended in 1 liter of distilled or deionized water. The mixture is then brought to a boil, with frequent shaking, until completely dissolved. It is sterilized in an autoclave at 121°C for 15 minutes. This preparation process is crucial to ensure the diluent’s effectiveness in microbiological testing.
Test Procedure
The diluent is used according to specific procedures for the microbiological examination of food samples. For the ISO method, 10 g or 10 ml of the test sample is added to a sterile vessel or plastic bag, followed by the addition of 90 ml of Maximum Recovery Diluent. The mixture is homogenized using a blender or Stomacher. Subsequently, 1 ml of the macerate is transferred to 9 ml of sterile diluent and mixed well. The number of further decimal dilutions depends on the expected contamination level of the sample.
Interpreting Results
The isotonic properties of the diluent allow several organisms, even those stressed or injured, to recover and maintain their viability for 1-2 hours without multiplication. This property is critical for ensuring accurate microbial counts in food samples.
Appearance and Storage
The dehydrated medium appears as a free-flowing homogeneous beige powder, and the prepared medium is a clear, light amber solution. The powder, being very hygroscopic, should be stored at 10-30°C in a dry environment in its original container, tightly closed. Prepared tubes, bottles, and bags should be stored at 10-25°C, away from light.
Shelf Life and Quality Control
The shelf life of the dehydrated medium is 4 years, and 2 years for the medium in tubes, bottles, or bags. Quality control is ensured by inoculating the medium with specific microbial strains like Escherichia coli (WDCM 00012) and Staphylococcus aureus (WDCM 00034) and observing the growth on Tryptic Soy Agar.
Warnings and Precautions
While the product does not contain hazardous substances in concentrations exceeding current legislation limits, it is recommended to consult the safety data sheet for correct use. The product is intended for professional use and must be used by properly trained operators.
Disposal of Waste
The disposal of waste must be carried out according to national and local regulations in force.
In conclusion, Maximum Recovery Diluent is a critical component in the microbiological examination of food, offering a reliable and effective means of preparing samples for microbial analysis. Its specific formulation, ease of preparation, and quality control features make it an indispensable tool in food safety testing laboratories.
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