Temperature-independent pectin gel method for coliform determination in dairy products: collaborative study

Area of Science:

• Microbiology
• Food Science
• Analytical Chemistry

Background:

• Accurate coliform enumeration is crucial for dairy product safety and quality control.
• The standard violet red bile (VRB) agar method is widely used but may have limitations in sensitivity and precision.
• Development of alternative methods is essential for improving microbial testing efficiency.

Purpose of the Study:

• To compare the performance of a pectin-based VRB gel method against the standard VRB agar method for coliform enumeration in various dairy products.
• To evaluate the recovery, repeatability, and reproducibility of both methods across different food matrices and inoculum levels.

Main Methods:

• A collaborative study involving ten laboratories.
• Comparison of pectin-based VRB gel method with VRB agar-based standard method.
• Analysis of seven dairy food groups (cream, cheddar cheese, cottage cheese, homogenized milk, raw milk, sour cream, yogurt) using high, medium, low, and control inoculum levels.

Main Results:

• The pectin gel method yielded higher overall mean log counts in 18 of 21 cases, with 12 being statistically significant (P < 0.01).
• Repeatability variation (sr) favored the pectin gel method in 14 of 21 cases, with 7 highly significant differences (P < 0.01).
• Reproducibility variation (sR) also favored the pectin gel method in 14 of 21 results.

Conclusions:

• The pectin gel method demonstrates superior coliform recovery and precision compared to the VRB agar method for dairy products.
• The pectin gel method is a suitable and validated alternative for coliform enumeration in dairy products.
• The pectin gel method has been officially adopted for use.