The Citrate Metabolism in Homo- and Heterofermentative LAB: A Selective Means of Becoming Dominant over Other Microorganisms in Complex Ecosystems

Abstract

The\rcitrate metabolism has been extensively studied in lactic acid bacteria (LAB)\rfor its aroma compound production. Among the 4-carbon (C4) by-products\robtained from citrate fermentation, diacetyl is one of the better known\rproducts for its contribution to the buttery aroma of dairy products. A lot of\rdocuments deal with ways to improve diacetyl concentration in food matrices.\rApart from these organoleptic advantages, in a microbial ecosystem, the citrate\rmetabolism gives selective advantages to citrate positive microorganisms.\rCitrate metabolism allows the LAB to use another carbon source for their growth,\rwithstand acidic conditions and generate a “proton motive force” (PMF).\rMoreover, the citrate/glucid co-metabolism leads to the fast release of organic\rcompounds known for having bacteriostatic effects. Under specific conditions,\rthe C4 pathway liberates diacetyl which is bacteriostatic. In this\rreview we first describe the citrate metabolism and the enzymes involved in the\rtwo homo- and heterofermentative LABLc\rdiacetylactisandLeuconostocspp.\rMoreover, the way to shift the metabolic pathway toward the production of\raromatic compounds is discussed for both of these fermentative types of\rbacteria. Finally, the selective advantages of citrate metabolism for LAB in\rcomplex microbial ecosystems are delineated.