Situation
While the Delvotest® range of products is validated primarily for use with raw milk, there are instances where testing other dairy matrices—such as milk powders, creams, and whey—may be necessary. These products differ from raw milk in various physical and chemical properties, which can affect the performance of microbial inhibition tests like Delvotest® T with the Delvotest® Accelerator Smart.
Complication
Testing other dairy matrices presents several challenges:
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Absence of Defined Maximum Residue Limits (MRLs)
Unlike raw milk, processed milk products lack established MRLs due to variability in processing methods and product concentrations. This makes it difficult to standardize testing thresholds for antibiotic residues in these products.
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Variability in Physical Properties
Other dairy matrices may have different concentrations, solids content, or pH levels compared to raw milk. For example, milk powders are more concentrated, and alkaline whey has a higher pH. These differences can influence the performance of microbial inhibition tests that rely on pH indicators, potentially leading to inaccurate results.
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Impact on Test Performance
The differing properties of these products can affect incubation times and test sensitivity. Applying standard protocols designed for raw milk without adjustments may compromise the accuracy and reliability of the results.
Resolution
To address these challenges and ensure accurate testing, follow these steps:
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Follow IDF guidelines for sample preparation
Document FIL-IDF B-471 Detection of Inhibitors and Antimicrobial Residues in Milk and Dairy Products by Screening Methods—Guidance on Preparation of the Test Portion provides detailed instructions on how to prepare different dairy matrices for testing, ensuring compatibility with microbial inhibition tests. It can be accessed via the following links:
https://www.fil-idf.org/wp-content/uploads/woocommerce_uploads/2014/03/B471-2014Inhibitors-and-antimicrobial-residues-in-milk-and-milk-products.CAT_-rts6zg.pdf
https://shop.fil-idf.org/collections/publications/products/detection-of-inhibitors-and-antimicrobial-residues-in-milk-and-dairy-products-by-screening-methods-guidance-on-preparation-of-the-test-portion
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Validate test performance for each dairy matrix
Before testing any unknown samples, it is essential to validate your Delvotest® T plates using the specific dairy matrix you intend to analyse. Begin by preparing known negative samples of the dairy matrix to determine the appropriate incubation time, accounting for any matrix-specific factors that may influence the test's timing. Next, prepare positive control samples by spiking the dairy matrix with known concentrations of antibiotics relevant to that product. This step confirms the test's sensitivity and ensures it can reliably detect antibiotic residues in the specific matrix. By thoroughly validating with both negative and positive controls, you establish baseline performance metrics tailored to the dairy product you're testing, ensuring accurate and reliable results.
By meticulously preparing samples according to established guidelines and validating the test performance for each specific dairy matrix, you are responsible for ensuring that the test is suitable for the products being analysed and complies with any regulatory or quality standards applicable to your laboratory operations. This approach allows you to extend the use of Delvotest® T with your Delvotest® Accelerator Smart system beyond raw milk, maintaining the integrity of your testing processes and ensuring accurate microbial inhibition testing across a variety of dairy products.
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