Swiss-type cheeses such as Emmental are characterized by the successive
development of thermophilic lactic acid bacteria (TLAB) and propionibacteria.
The
aim of this study was to determine whether the choice of TLAB strain influenced
propionibacteria. TLAB and propionibacteria were cultured sequentially
under the
conditions prevailing in cheese. Firstly, 11 Emmental juice-like media
were prepared
by fermenting casein-enriched milk with pure or mixed cultures of TLAB
(Lactobacillus helveticus, Lb. delbrueckii subsp.
lactis and Streptococcus thermophilus),
differing in their proteolytic activities. TLAB cells were then removed
by
microfiltration. Finally, five strains of Propionibacterium freudenreichii
were grown
on these media at 24°C under anaerobiosis and their growth characteristics
and
lactate consumption determined. The media mainly differed in their contents
of
peptides (1·9–5·3 g/kg) and free amino acids
(1·0–5·6 g/kg) and the proportions of
lactate isomers (42–92% of the L(+) isomer).
Propionibacteria were significantly
(P<0·05) influenced by TLAB strains
(differences in doubling times of up to 20% and
differences in lactate consumption after 600 h culture of up to 52%). The
influence
of TLAB was similar for all the propionibacteria tested, depended on the
TLAB
strains and could not be generalized to the TLAB species. Propionibacteria
were
stimulated by high peptide levels, low levels of free amino acids and NaCl,
a low
proportion of L(+)-lactate and other undetermined factors. However,
variations due
to TLAB were less than those between propionibacteria strains.
Method for differentiated enumeration of mixed cultures of thermophilic lactic acid bacteria and bifidobacteria by using only one culture medium