Identification of the main esterase involved in lipolysis by Propionibacterium freudenreichii

ABEIJÓN MUKDSI, M.C.; FALENTIN, H.; MAILLARD, M.B.; MEDINA, R.B.; PARAYRE, S.; LORTAL, S.; THIERRY, A.

New Orleans, Louisiana

Encuentro; American Dairy Science Association (ADSA)-American Society of Animal Science (ASAS) Joint Annual Meeting; 2011

American Dairy Science Association (ADSA)-American Society of Animal Science (ASAS)

Free fatty acids are important flavor compounds in cheese, where they bring pungent, rancid, cheese, and fruity notes. They mainly result from the lipolytic activity of cheese microorganisms. Propionibacterium freudenreichii, a specie used as a ripening culture in Swiss cheese, is the main agent of Swiss cheese lipolysis, with 96% of the free fatty acids released during the ripening resulting from P. freudenreichii activity [Dherbécourt et al. 2010 J. Agric. Food Chem. 58:11732-11739]. Our aim was to identify the most probable lipolytic esterase(s) involved in cheese lipolysis by P. freudenreichii. Since cheese lipolysis mainly occurs during P. freudenreichii growth, we focused our study on surface-exposed or secreted esterases. Out of the twelve putative esterases previously predicted from the genome sequence of P. freudenreichii CIRM-BIA1 [Dherbécourt et al. 2008 Microb. Cell Fact. 7], the lipolytic esterase PF#279 was shown to be secreted, and the putative esterase PF#774 was predicted to be anchored in the plasma membrane [Dherbécourt et al. 2010 Appl. Environ. Microbiol. 76:1181-1188]. To evaluate the respective role of these two proteins in lipolysis, P. freudenreichii CIRM-BIA1 was knocked out and then complemented for the genes encoding these two proteins, separately. Each of these genes was also over expressed in P. freudenreichii CIRM-BIA1. All these genetically modified strains were assessed for their lipolytic activity during their growth in a medium containing an emulsion of milk fat. Results showed that the mutants inactivated for PF#279 showed a very low residual lipolytic activity, whereas inactivating or over-expressing PF#774 had no impact on lipolysis level. This study shows that only one lipolytic esterase, PF#279, is involved in milk fat hydrolysis in P. freudenreichii CIRM-BIA1 and is a key component in Swiss cheese lipolysis.