A methodological approach to screen diverse cheese-related bacteria for their ability to produce aroma compounds
Résumé
Microorganisms play an important role in the development of cheese flavour, producing a variety of
aroma compounds for which lactose/citric acid, proteins and fat are precursors. There is a demand
from cheese producers to diversify the flavour of semi-hard cheeses. A large screening is required to
identify strains of interest among the diversity of cheese-related bacterial species and strains. This step
cannot be bypassed and is time-consuming. Our aim was to develop a methodological approach to
facilitate and expedite the screening of various cheese-related bacteria for their ability to produce
aroma compounds. Our strategy was to combine: (i) the use of a curd-based broth medium incubated
under conditions mimicking cheese manufacturing and ripening, ii) a powerful method of extraction of
volatiles, headspace trap, coupled to gas chromatography-mass spectrometry, and iii) a metabolomicsbased
method of data processing using the XCMS package of R software and multivariate analysis.
This approach was applied to eleven species: lactic acid bacteria (Leuconostoc lactis, Lactobacillus
sakei, Lb. paracasei, Lb. fermentum, and Lb. helveticus), surface bacteria (Brachybacterium articum,
Brachybacterium tyrofermentans, Brevibacterium aurantiacum, Microbacterium gubbeenense),
Propionibacterium freudenreichii and Hafnia alvei. All the strains grew, with maximal populations
ranging from 7.4 to 9.2 log CFU/g. In total, 53 volatile compounds were identified, of which 50 varied
significantly in abundance between bacteria. Principal component analysis of volatile profiles
differentiated species on their ability to produce ethyl esters (associated with Brachybacterium), sulfur
compounds and branched-chain alcohols (H. alvei), branched-chain acids (H. alvei, P. freudenreichii
and Lb. paracasei), diacetyl and related carbonyl compounds (M. gubbeenense and Lb. paracasei),
among others. The present approach was then successfully applied to screen collections of lactic and
propionic acid bacteria. The metabolomics-based method of data processing can be widely applied in
the field of food flavour chemistry.