Flow cytometry and acidification power test as rapid techniques for determination of the activity of starter cultures of Lactobacillus delbrueckii ssp. bulgaricus

Abstract

The use of the rapid techniques, flow cytometry of 5- (and-6) -carboxyfluorescein diacetate stained cells and acidification power (AP) test in predicting fermentation performance of cultures of Lactobacillus delbrueckii ssp. bulgaricus has been compared with traditional fermentation tests. Frozen, freeze dried and frozen cultures stressed by exposure to 5° C for 2 and 20 h were examined. The flow cytometric technique was able to differentiate between freeze dried and frozen cultures but it was not found sensitive enough to differentiate between the other cultures showing different fermentation performance. The AP test was found to be very sensitive and it discriminated between cultures which could not be distinguished by traditional fermentation test. The results indicated that cell damage resulting from freeze drying, freezing and thawing reduced the ability of the cultures to utilize exogenous carbohydrates but not their ability to spontaneously utilize endogenous carbohydrates.