Collaborative Study of the Impedance Method for Examining Raw Milk Samples.

Area of Science:

• Microbiology
• Food Science
• Analytical Chemistry

Background:

• Bacteriological contamination in raw milk poses a significant public health concern.
• Accurate and rapid methods for quantifying bacterial levels are crucial for milk safety and quality control.
• The impedance method presents a potential automated alternative to traditional culture-based techniques.

Purpose of the Study:

• To evaluate the reproducibility of the impedance method for predicting bacterial counts in raw milk.
• To compare the performance of the impedance method against the standard plate count (SPC) method.
• To assess inter-laboratory variability for both methods.

Main Methods:

• A collaborative study involving six laboratories.
• Analysis of frozen and unfrozen raw milk samples with bacterial counts ranging from 9 × 10⁴ to 4 × 10⁷ CFU/ml.
• Comparison of impedance method (Bactometer-predicted counts, BPC) with the standard plate count (SPC) method.

Main Results:

• The impedance method demonstrated lower inter-laboratory variability compared to SPC across all trials.
• Variance between split samples was smaller for the impedance method than for SPC.
• While SPC showed smaller variance between duplicate plates, the impedance method's overall inter-laboratory consistency was favorable.

Conclusions:

• The impedance method is a reproducible and rapid technique for determining bacteriological contamination in raw milk.
• It offers advantages in terms of reduced inter-laboratory variability compared to the standard plate count method.
• The impedance method is a viable automated tool for routine raw milk quality assessment.