Effect of Initial Oxygen Concentration on Diacetyl and Acetoin Production by Lactococcus lactis subsp. lactis biovar diacetylactis

Abstract

The production of aroma compounds (acetoin and diacetyl) in fresh unripened cheese by Lactococcus lactis subsp. lactis biovar diacetylactis CNRZ 483 was studied at 30°C at different initial oxygen concentrations (0, 21, 50, and 100% of the medium saturation by oxygen). Regardless of the initial 02 concentration, maximal production of these compounds was reached only after all the citrate was consumed. Diacetyl and acetoin production was 0.01 and 2.4 mM, respectively, at 0% oxygen. Maximum acetoin concentration reached 5.4 mM at 100% oxygen. Diacetyl production was increased by factors of 2, 6, and 18 at initial oxygen concentrations of 21, 50, and 100,o respectively. The diacetylacetoin concentration ratio increased linearly with initial oxygen concentration: it was eight times higher at 100% (3.3%) than at O%o oxygen (0.4%). The effect of oxygen on diacetyl and acetoin production was also shown with other lactococci. At 01% oxygen, specific activity of a-acetolactate synthetase (0.15 U/mg) and NADH oxidase (0.04 U/mg) was 3.6 and 5.4 times lower, respectively, than at 100o oxygen. The increasing cv-acetolactate synthetase activity in the presence of oxygen would explain the higher production of diacetyl and acetoin. The NADH oxidase activity would replace the role of the lactate dehydrogenase, diacetyl reductase, and acetoin reductase in the reoxidation of NADH, allowing accumulation of these two aroma compounds.

Effect of oxidoreduction potential on aroma biosynthesis by lactic acid bacteria in nonfat yogurt

“…Boumerdassi et al (1996) confirmed that oxygen increases NADH oxidase activity (Condon, 1987), which causes NADH reoxidation to the detriment of activities of lactate de- Table 2. Evolution of average amounts of the aroma compounds quantified in the headspace of the yogurts made under the different oxidoreduction potential (Eh) conditions during 28 d of storage 1 hydrogenase, butanediol dehydrogenase, and acetoin dehydrogenase (Bassit et al, 1993). Then, excess pyruvate is eliminated partially through acetolactate production, which increases production of diacetyl (Boumerdassi et al, 1996).…”

Imbalance of leucine flux in Lactococcus lactis and its use for the isolation of diacetyl-overproducing strains

“…AL and diacetyl plus acetoin were assayed as described previously (17,29,30). Diacetyl alone was measured after distillation (1). Lactose, citrate, lactate, acetate, formate, ethanol, pyruvate, and butanediol production was determined by high-performance liquid chromatography with an HPX-78P anion-exchange column (Bio-Rad, Inc.) with 0.01 NH 2 SO 4 as the elution fluid.…”

“…Diacetyl is a flavor compound essential in many dairy products such as butter, cream, and some cheeses. Its production was shown to depend on the strains used as starter cultures (9) and the conditions of fermentation such as pH, oxygen, and temperature (1,4,12). Although changing the conditions of fermentation can lead to a very significant increase in diacetyl concentration, it is sometimes impossible to apply optimal conditions in actual factory processes.…”

Efficient production of acetoin by fermentation using the newly isolated mutant strain Lactococcus lactis subsp. lactis CML B4

“…Under aerobiosis, however, the situation is somewhat different because an additional enzyme, NOX, is also involved. Water-forming NOX, encoded by the noxE gene, catalyzes the oxidation of NADH to NAD + at the expense of oxygen, which is reduced to H2O [14,20]. Therefore, in the presence of oxygen, NOX competes with LDH for NADH, resulting in a decrease in the NADH/NAD + ratio and, consequently, in a lower LDH activity.…”