Production of a yeast extract rich in propionic acid

Yeast extract (YE) solutions (70 ou 100 g . L-1) enriched in lactate (10-20 g . L-1) or glucose (10-30 g . L-1) were fermented with cells of Propionib acterium freudenreichii ssp. shermanii Pr2000 immobilized in calcium algina te beads. The population of propionibacteria in the beads reached 7 x 10(9) CFU . g(-1), from an initial count of 3 x 10(8) CFU . mL(-1). However, hig her populations were reached (1,4 x 10(10) CFU . g(-1)) when concentrated b acterial suspensions were immobilized. Enumeration of propionibacteria in l actate agar did not give significantly different results as those obtained with the Petrifilm(TM) system. Fermentation of the YE-based medium containi ng 20 g . L-1 of lactate was completed in 24 h, with a 20% bead loading of the fermentor. There was a reduced assimilation rate of lactate in presence of glucose. In all cases, however, complete fermentation of lactate occurr ed within 24 h, while only 5 g . L-1 of glucose was assimilated. Alginate b eads containing the propionibacteria were used for three successive ferment ations, at the end of which propionic and acetic acids reached 22 and 12 g . L-1 respectively. The fermented yeast extracts were spray dried without s ignificant loss of the organic acids during the drying process.