1029
Sodium azide and Potassium dichromate not suitable preservative of raw milk for detection b-lactamase by cylinder plate method
Upon selecting the appropriate sample of raw milk, keeping the stability of physicochemical property of β-lactamase relevant compounds is essential for its successful detection and identification in systematic analysis. However, there is no particular standard pre-treatment procedure for detection of β-lactamase in raw milk. This study examined the storage time of refrigeration (4 h, 8 h, 24 h, 48 h) and freeze (1 d, 7 d, 30 d), the temperature (25 °C, 40 °C, 60 °C) and times (1 time, 3 time, 5 time) of thawing for freeze sample and the kinds of preservative (sodium azide, potassium dichromate, sodium thiocyanate, bronopol, methanol) using cylinder plate method. Milk sample, collected from individual cow and negative for β-lactamase testing by cylinder plate method, was divided into 10 aliquot of the milk sample, two aliquot of the milk sample adding nothing were the control group, eight aliquot of the milk sample adding 4 U/mL β-lactamase were the experiment group. Refrigeration time within 48 h and freeze time within 30 d had no influence on the detection result of β-lactamase, thawing temperature below 60 °C and thawing times below 5 times for freeze sample were also no influence. β-lactamase could not be detected when adding sodium azide and potassium dichromate in raw milk, whereas sodium thiocyanate, bronopol and methanol had no effect, suggesting sodium azide and potassium dichromate were not suitable preservative of raw milk for detection β-lactamase by cylinder plate method.
Keywords: pre-treatment, β-lactamase, raw milk