Detection of post-pasteurization contamination of cream by impedimetric methods

Impedimetric methods for evaluating post-pasteurization contamination and shelf-life of cream were assessed. Over 94% of the samples tested were in agreement, using selected cut-offs of 20 h for detection time measured at 21 degrees C with creams containing inhibitors for the growth of Gram positive bacteria on standard plate count agar as growth media, and 3.2 X 10(7) cfu/g for plate counts obtained on cream which had been pre-incubated in the presence of inhibitors for the growth of Gram positive organisms, and on cream stored at 6 degrees C for 7 d. Agreement between the impedimetric method and plate count was not as good if either Brain Heart Infusion or Milk Agar was used in place of Plate Count Agar in the former technique. A poor correlation was obtained between plate count methods for enumerating post-pasteurization contamination and keeping quality with impedimetric measurements on cream alone. It was possible, with a reasonable degree of certainty, to determine if cream had suffered post-pasteurization contamination within 20 h of production.