PRESERVATIVE EFFICACY TESTING BY A RAPID SCREENING METHOD FOR ESTIMATION OF D-VALUES

This report describes a rapid screening method for estimating D-values to determine whether products are adequately preserved. Estimated D-values (ED-values) are determined using aerobic plate counts of test organisms immediately after inoculation into test samples and at 24 hr for pathogenic microorganisms or at 7 days for non-pathogenic bacteria, yeasts, or molds. Products are judged to be adequately preserved if they meet the acceptance criteria of the linear regression method. There was excellent agreement between D-values and ED-values for 60 sets of data (correlation coefficient = 0.98). The mean D-values and ED-values for the 60 samples differed by 0.5 hr (6.6%) even though the D-values ranged from <0.1 hr to 39 hr. Where differences were observed, the ED-values generally were larger (i.e., more conservative) than D-values for the same samples. The rapid screening method offers about 50% savings in the labor and materials required for preservative efficacy testing by the original linear regression method.