SELECTION AND PROPERTIES OF LACTOBACILLUS MUTANTS PRODUCING ALPHA-ACETOLACTATE

Many lactobacilli produce diacetyl, a desirable aroma in some fermente d dairy products. The objective of the present work was to obtain muta nts of lactobacilli that were deficient in a-acetolactate decarboxylas e and to determine whether they had improved aroma-producing activity. Nine mutants of Lactobacillus rhamnosus that were deficient in acetol actate decarboxylase were selected by screening for colonies that prod uced a-acetolactate from pyruvate on agar plates. When grown in milk, only one-third of the mutants exhibited the same acidification behavio r as the parent strain. In addition, even though alpha-acetolactate wa s produced by all of the mutants, none of them produced more diacetyl than did the parent strains. This result shows that the suppression of oc-acetolactate decarboxylase activity does not cause increased produ ction of diacetyl by all lactic acid bacteria. Such a strategy would b e interesting only for parent strains producing large quantities of ac etoin (e.g., citrate-utilizing Lactococcus lactis ssp. lactis)