manual of methods for determining micronutrients in fortified foods

C. Calculations
15. Calculate the average of the % transmittance for each tube with the same volume of solution.
16. Calculate the weight of cells per tube (mg cells in dry weight).
17. Plot a chart with the content of cells (mg cells in dry weight, X axis) vrs. % transmittance in each
solution, y axis. Calculate the equation and calculate the correlation coefficient.
18. Correlation coefficient should be higher than 0.99 to confirm that there is a relation between the
instrument response and the concentration of bacteria in suspension.
Repeat appropriate verification step at least twice more for the spectrophotometer to be used in the assay.
Draw composite curve, best representing 3 or more individual curves, relating % T to mg dried cell
weight under conditions for the assay.Once appropriate curve is established, all subsequent relationships
between % T and cell weight are determined directly from this curve. Respective assay limits expressed
as mg dried cells weight/tube are so determined.
XII.
Cleaning glassware procedure
1. Autoclave the glassware which was in contact with the bacteria for 30 minutes at 121°C.
2. Rinse the glassware three times with tap water.
3. Soak the glassware in Sodium Lauryl Sulfate (5% v/v) for 24 hours.
4. Clean the test tubes with a brush.
5. Rinse the glassware eight times with tap water.
6. Rinse two times with distilled water.
7. Dry the glassware in the oven at 250 °C.
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