Use of the Direct Epifluorescent Filter Technique for predicting the keeping quality of pasteurized milk within 24 hours

Abstract

The keeping quality (KQ) of pasteurized milk stored at 5.degree. and 11.degree. C was predicted within 24 h by pre-incubating samples and counting bacteria by the Direct Epifluorescent Filter Technique (DEFT). For samples from 5.degree. C storage, 0.03% (wt/vol) benzalkonium chloride and 0.002% (wt/vol) crystal violet (final concentration) were added to inhibit the growth of gram-positive bacteria during pre-incubation. The samples from milk stored at 11.degree. C were pre-incubated without the addition of inhibitors. After pre-incubation there was a satisfactory relationship between the DEFT count and the KQ of milks at 5.degree. and 11.degree. C. The DEFT count following pre-incubation correctly classified > 80% of pasteurized milks on the basis of KQ.