Effect of citrate on production of diacetyl and acetoin by Lactococcus lactis ssp lactis CNRZ 483 cultivated in the presence of oxygen

The effect was studied of trisodium citrate addition on the growth and formation of diacetyl and acetoin by Lactococcus lactis ssp. lactis CNRZ 483 in a whey-based medium under an oxygen pressure of 2 atm. Growth increased, as shown by the final absorbance of the culture, which was 1.2 in the absence of citrate and 2.8 in the presence of 26 mM citrate. In the absence of citrate, maximal concentrations of diacetyl and acetoin were 0.09 and 0.29 mM, respectively. When citrate was added at 6.2, 11.5, and 26 mM, the maximal diacetyl concentrations were 0.45, 0.53, and 0.85 mM, and those of acetoin were 3.6, 4.5, and 8.5 mM, respectively. However, under these conditions, the yield of citrate bioconversion to diacetyl and acetoin decreased as the initial concentration of citrate increased. Yields were 121, 83, and 70% in the presence of 6.2, 11.5, and 26 mM citrate, respectively.