FLOW-CYTOMETRY AND ACIDIFICATION POWER TEST AS RAPID TECHNIQUES FOR DETERMINATION OF THE ACTIVITY OF STARTER CULTURES OF LACTOBACILLUS-DELBRUECKII SSP BULGARICUS

The use of the rapid techniques, flow cytometry of 5-(and-6)-carboxyfl uorescein diacetate stained cells and acidification power (AP) test in predicting fermentation performance of cultures of Lactobacillus delb rueckii ssp. bulgaricus has been compared with traditional fermentatio n tests. Frozen freeze dried and frozen cultures stressed by exposure to 5 degrees C for 2 and 20 h were examined. The flow cytometric techn ique was able to differentiate between freeze dried and frozen culture s but it was not found sensitive enough to differentiate between the o ther cultures showing different fermentation performance. The AP test was found to be very sensitive and it discriminated between cultures w hich could not be distinguished by traditional fermentation test The r esults indicated that cell damage resulting from freeze drying, freezi ng and thawing reduced the ability of the cultures to utilize exogenou s carbohydrates but not their ability to spontaneously utilize endogen ous carbohydrates.