Investigation on Bacterial Growth and pH in Milk after the Expiration Date
Table 1
Sensory test of three milk samples left open for 24 hours.
Milk type
Whole milk
2% milk
Fat-free milk
Days after exp.
pH
Color
Smell
Taste
Appearance
pH
Color
Smell
Taste
Appearance
pH
Color
Smell
Taste
Appearance
0
7
White
Homogeneous
7
White
Homogeneous
7
White
Homogeneous
1
7
White
Homogeneous
7
White
Homogeneous
7
White
Homogeneous
2
7
White
Homogeneous
7
White
Homogeneous
7
White
Homogeneous
3
7
White
Homogeneous
7
White
Homogeneous
7
White
Homogeneous
4
7
White
Homogeneous
7
White
Homogeneous
7
White
Homogeneous
5
6.5
White
Homogeneous
7
White
Homogeneous
7
White
Homogeneous
6
6.5
White
Small clot+
7
White
Homogeneous
7
White
Homogeneous
7
6.5
White
sour+
Small clot++
7
White
Homogeneous
7
White
Homogeneous
8
6.5
White
sour+
sour+
Large clot+, liquid+
7
White
Small clot+, liquid+
6.5
White
Homogeneous
9
6.5
White
sour++
sour+
Large clot++, liquid+
6.5
White
sour+
Small clot+, liquid+
6.5
White
Homogeneous
10
6
Light yellow
sour+++
sour++
Large clot+++, liquid+
6.5
White
sour++
sour+
Small clot++, liquid++
6.5
White
Homogeneous
Note. All samples were kept in a refrigerator (4°C) until opening. The sensory evaluation was tested for each sample which was opened on the days (0–10) after expiration and left at room temperature for 24 hours after opening. Of note, there were no sensory or appearance changes in any of the samples immediately after opening.
