Effect of Kluyveromyces marxianus on the growth and survival of bifidobacteria in milk.

Four strains of bifidobacteria (B. bifidum 93, B. infantis ATCC 17930, B. longum ATCC 15707, and B. longum JR) cultivated in MRS broth modified by the addition of cysteine-hydrochloride (0.05%) were serially subcultured in unsupplemented cow milk alone or in combination with Kluyveromyces marxianus var. marxianus 269 under aerobic conditions. In monoculture, bifidobacteria did not multiply after the second subculture. In contrast, in coculture with yeast bifidobacteria reached counts about 8 log CFU/g even during 15 subcultures. In addition, K. marxianus var. marxianus 269 significantly prolonged the survival of bifidobacteria in milk at 4 degrees C. The most susceptible strains (B. longum JR and B. infantis ATCC 17,930) completely lost their viability within 5 and 12 d of storage, respectively, while in coculture with yeasts all bifidobacteria cultures tested survived for at least 40 d. The results could be useful in producing kefir-like fermented milks containing bifidobacteria.