Automated Impedance Measurements for Rapid Screening of Milk Microbial Content

Area of Science:

• Microbiology
• Food Science
• Analytical Chemistry

Background:

• Microbial metabolism and growth cause chemical changes that alter the electrical impedance of media.
• The time required for a detectable impedance change (detection time - DT) correlates with initial microbial load.

Purpose of the Study:

• To evaluate electrical impedance monitoring as a rapid method for microbial enumeration in milk.
• To compare detection times (DT) with Standard Plate Counts (SPC) for various milk types.

Main Methods:

• Electrical impedance measurements were used to determine detection times (DT) for milk samples.
• DTs were compared against Standard Plate Counts (SPC) for homogenized, low-fat, skim, and raw milk.
• A preliminary study assessed impedance monitoring at 21°C for psychrotroph estimation in pasteurized milk.

Main Results:

• For pasteurized milk, a DT of ≤7 hours correctly classified 323/380 samples (85%) as having ≥10,000 organisms/ml.
• For raw milk, a DT of 10 hours differentiated samples with > or < 10,000 organisms/ml.
• Impedance monitoring at 21°C achieved 88% accuracy in classifying pasteurized milk for >1,000 organisms/ml within 22 hours, and 91% accuracy for >10,000 organisms/ml within 13.7 hours.

Conclusions:

• Electrical impedance monitoring is a viable, rapid alternative to Standard Plate Counts for microbial analysis in milk.
• Impedance measurements show promise for predicting milk's keeping quality, outperforming traditional counts.
• This method offers efficient screening for microbial contamination in raw and pasteurized milk products.