Selection and Properties of Lactobacillus Mutants Producing α-Acetolactate

Abstract

Many lactobacilli produce diacetyl, a desirable aroma in some fermented dairy products. The objective of the present work was to obtain mutants of lactobacilli that were deficient in α-acetolactate decarboxylase and to determine whether they had improved aroma-producing activity. Nine mutants of Lactobacillus rhamnosus that were deficient in α-acetolactate decarboxylase were selected by screening for colonies that produced α-acetolactate from pyruvate on agar plates. When grown in milk, only one-third of the mutants exhibited the same acidification behavior as the parent strain. In addition, even though α-acetolactate was produced by all of the mutants, none of them produced more diacetyl than did the parent strains. This result shows that the suppression of α-acetolactate decarboxylase activity does not cause increased production of diacetyl by all lactic acid bacteria. Such a strategy would be interesting only for parent strains producing large quantities of acetoin (e.g., citrate-utilizing Lactococcus lactis ssp. lactis).