A simple screening methodfor isovaleric acidproduction by Propionibacterium freudenreichii in Swiss cheese
Résumé
Isovaleric acid (3-methylbutyric acid) and 2-methylbutyric acid are cheese flavour compounds and are produced in Swiss cheese mainly by propionibacteria (PAB), with large variations in amounts depending on the strain. To evaluate the possibility of screening this property in vitro, the production of both acids (referred to as methylbutyric acids) was compared for eight Propionibacterium freudenreichii strains both in mini-Swiss cheeses and in liquid cultures (salted-yeast extract-peptone-lactate medium, pH 5.4, incubated at 24°C then at 6°C). Similar time courses of methylbutyric acid production were observed in cheeses and in liquid cultures. PAB produced methylbutyric acids during propionic fermentation at 24°C (8–37 mg kg−1, and 5–13 mg L−1, respectively, in cheeses and cultures), and during further storage at 6°C for 2 months (11–77 mg kg−1 and 5–17 mg L−1). PAB strains significantly (P<0.05) influenced the amounts produced, and they were similarly classified in cheeses and in liquid cultures. This simple screening method has potential for selection of high- or low-producing strains for cheese manufacture.