Читать книгу Analytical Food Microbiology - Ahmed E. Yousef - Страница 63

When all plates produce no colonies, the count is estimated to be smaller than the minimum detection limit of the procedure followed. The minimum detection limit is the count that would result from the presence of one colony on the plate receiving the lowest dilution of the sample. Apply equation 3.4 to estimate the count using the lowest dilution plated and substitute the numerator of the equation with < 1. For example, if no colonies appeared on any of the plates receiving the dilutions shown in the previous example (Table 3.1), then

(3.4)

It is not necessary in this case to report the count as “est.” because the presence of the less than (<) sign indicates the uncertainty of the count.