Research and application on the characteristics of compound cold water soluble gel in petrifilm aerobic count plates

- The compound cold water soluble gel for colony count Petrifilm Plate was studied based on five standard aerobe strains.
- Cold water soluble gel characteristic parameters were optimized.
- Some additives were added, aiming to prepare a convenient and reliable microbial count Petrifilm Plate.

The performance of compound cold water soluble gel in petrifilm aerobic count plates was evaluated in terms of particle size, pH, transmittance, gel strength, water absorption, and water retention. Results demonstrated that when the ratio of sodium polyacrylate and guar gum is 2:8 in cold water soluble gel, the compound gel has 1.0% concentration, neutral pH, 446 g/cm2 gel strength, 79.6% transmittance, 103.6 g/g water adsorption, and 14.4% water retention, which have no significant difference with 1.0% agar. After surfactants, somatomedin, glucose, and bean dregs were added, the sample solution was absorbed completely and colony diameter on petrifilm plates reached 0.95 mm, which is appropriate for counting. The petrifilm plate method based on prepared cold water soluble gel can achieve the same limit of detection (10° cfu/mL) and sensitivity (100%) in counting of five strains compared with the National Standards of Aerobe Plate Count Method. The petrifilm plate method also showed high accuracy and linearly dependent coefficient (R2 = 0.9933). The accordance rate between the petrifilm plate method and the national standard agar plate count method reached as high as 90% in food detection. The compound cold water soluble gel can be used as a good petrifilm plate for aerobic bacterial count.