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Applied Microbiology and Biotechnology, Vol.74, No.2, 511-516, 2007
Modification of the data-processing method for the turbidimetric bioassay of nisin
The data processing method of the turbidimetric bioassay of nisin was modified to facilitate its industrial application. The influence of the initial indicator concentration was minimized by a redefined specific dose of the bacteriocin as the quotient between the titer of the added bacteriocin and the initial population density of the indicator in the suspension. It was found that d(c)=0.125 mu g ml(-1) was the critical dose of nisin that can cause a complete inhibition of the indicator, Pediococcus acidilactici UL5, with an initial OD of 0.135. To eliminate the interference of the cell debris, an equation, epsilon(I) = ODi(1 -di)/OD0 = epsilon(A)(1 - di/dc), exploiting d(c), was formulated to obtain the intrinsic survival proportion. The use of the specific dose of the bacteriocin and the intrinsic survival proportion as parameters of the dose/response curve greatly enhanced its repeatability and feasibility. A dual-dosage approach was developed to further simplify the conventional standard dose/response curve method.