4 °C - the National Sea Grant Library

Statistical Analysis
Irradiation D-Values (the irradiation required to eliminate 90% of the cell
population [D10]) in kGy were calculated [D10 = -l/slope] from the linear portion of
irradiation survival curves using standard linear regression analysis (LRA) using
Statistical Analysis System (SAS,1987). Mean differences were compared using
Tukey’s Pairwise Comparison (SAS, 1987).
The second method used to calculate irradiation D-Values was based on the
reduction of the initial cell population to zero. This method, to be termed total dose,
TD, used the beginning population in logs and the approximate amount of irradiation
required to have no culturable survivors:
Irradiation D-Value = dose in kGy/log population
This method was used to account-for survival curves that exhibited a shoulder, tail,
or two linear portions (Huhtanen et al., 1989) that might skew regression analysis.
All experiments were performed three separate times (three replicates) with double
plating of duplicate samples for each replicate.
RESULTS AND DISCUSSION
Irradiation of food products for the purpose of reducing spoilage bacteria or
reducing the risk of pathogenic microorganisms has traditionally been applied in a
single dose to achieve a targeted irradiation exposure. However, some foodbome
pathogenic bacteria, like Listeria monocytogenes, are resistant to federally approved
low doses (