Our aim was to develop an Emmental juice-like medium (EJLM) for
the
growth of propionibacteria. Cheese juices were extracted by pressing three
different
Emmental cheeses before entering the warm room (i.e. before propionic fermentation)
and their composition was determined. They contained (g/kg) lactate
34·6–36·9,
protein 23·8–29·6, NaCl 15–23, Ca
5·9–7·3 and no residual sugar, and had a pH of 5·4.
In order to simulate this composition, EJLM was constituted from the microfiltrate
of a milk, enriched in native casein and fermented by a
Lactobacillus helveticus strain until lactose exhaustion.
PO43−, K+,
Mg2+, Ca2+ and Cl−
were added to reach a mineral
balance and an ionic strength close to those of juice. The main difference
was the
nitrogen content: that of juice was ∼3·5 times that of EJLM.
Four Propionibacterium freudenreichii strains grew with similar
growth
rates in EJLM and in juice at 24°C in anaerobiosis and reached
>3×109 cfu/ml. Using EJLM, Prop.
freudenreichii TL 173 grew at pH 5·4 or 6·0, at 24 or
30°C, in semi-anaerobiosis (static
culture) or anaerobiosis (CO2 atmosphere), showing a
synergic inhibition of growth at
low pH and temperature and in semi-anaerobiosis. EJLM provided a way to
study
propionibacteria in an environment similar to that in Emmental cheese.