1. total plate count (TPC) aerobic plate count (APC) total mesophilic plate count
Total bacterial number is an important indication for food quality
Basic principle for TPC
Sampling size, 25 or 50 g
Solid sample
Add 9 times volume of buffer (25 g mL wt:vol; 25 mL mL vol:vol)
Homogenize
Homogenizer or stomacher

2. Materials and methods Food samples
store at room temperature
Depend on the food samples to decide the dilution range
Dilution range is from -1 to -4

3. Detection limit No dilution -1 dilution
1 CFU/ml; 10 CFU/g
-1 dilution
10 CFU/ml; 100 CFU/g
However, we need 25 to 250 CFU in one plate
Thus, reliable detection limit is:
25 CFU/ml; 250 CFU/g
250 CFU/ml; CFU/g

4. Dilutions (every group has their own) 25 g + 225 mL phosphate buffer
培養基
TSA
Dilutions (every group has their own)
25 g mL phosphate buffer
Homogenize for 2 min
Decimal serial dilution (1:9)

5. procedures Homogenize sample Decimally serial dilution
For milk, no homogenization
Decimally serial dilution
Place one mL of the undiluted homogenate into a Petri-dish (0 dilution)
Add agar to mix the sample: 混稀 pour plate
Place 0.1 mL of the undiluted homogenate onto a Petri-dish (-1 dilution) 塗抹: spread plate
Place 0.1 mL of -1 dilution the homogenate onto a Petri-dish (-2 dilution)

7. Incubate the plates at 37C for 24 (spread) to 48 (pour) hours
Count the colony ( colony/plate)
Calculate bacterial number in food sample
Solid food: average CFU number x dilution x 10
E.g. 56 x 103x 10 = = 5.6 x 105 CFU/g = 5.75 log10 CFU/g
Milk: average CFU number x dilution
E.g. 56 x 103 = = 5.6 x 104 CFU/g = 4.75 log10 CFU/mL