Reverse transcription quantitative PCR revealed persistency of thermophilic lactic acid bacteria metabolic activity until the end of the ripening of Emmental cheese

• Published in: Food microbiology Vol. 29; no. 1; pp. 132 - 140
• Main Authors: Falentin, Hélène, Henaff, Nadine, Le Bivic, Pierre, Deutsch, Stéphanie-Marie, Parayre, Sandrine, Richoux, Romain, Sohier, Daniele, Thierry, Anne, Lortal, Sylvie, Postollec, Florence
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.02.2012; Elsevier
• Subjects: Acidification; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Biological and medical sciences; Cheese - microbiology; Food industries; Food microbiology; Fundamental and applied biological sciences. Psychology; Gene expression; Hot Temperature; Lactic Acid - metabolism; Lactic acid bacteria; Lactobacillus - genetics; Lactobacillus - growth & development; Lactobacillus - metabolism; Lactobacillus helveticus; Life Sciences; Microbiology and Parasitology; Milk and cheese industries. Ice creams; Reverse Transcriptase Polymerase Chain Reaction; Ripening; RT-qPCR; Starter; Streptococcus thermophilus - genetics; Streptococcus thermophilus - growth & development; Streptococcus thermophilus - metabolism; Swiss cheese; Ripening; Lactic acid bacteria; Gene expression; Starter; RT-qPCR; Swiss cheese; Polymerase chain reaction; Dairy product; Reverse transcription; Cheese; Molecular biology; Metabolism; BACTERIE LACTIQUE; STREPTOCOCCUS THERMOPHILUS; FROMAGE; AFFINAGE; EMMENTAL; PCR
• ISSN: 0740-0020; 1095-9998
• DOI: 10.1016/j.fm.2011.09.009

For Emmental manufacture two kinds of adjunct culture are added: (i) thermophilic lactic acid bacteria (starters) such as Lactobacillus helveticus (LH), and Streptococcus thermophilus (ST) growing the first day of the manufacture and (ii) ripening culture. ST and LH have a key role in curd acidification and proteolysis at the beginning of the manufacture but are considered to be lyzed for a great part of them at the ripening step. The aim of this work was to assess the metabolic activity of these bacteria throughout manufacture and ripening. During Emmental cheesemaking, LH and ST were subjected to i) population quantification by numerations and by quantitative PCR (qPCR) ii) reverse transcription (RT) Temporal Temperature Gel Electrophoresis (TTGE) iii) transcript quantification by RT-qPCR targeting 16S rRNA, tuf and groL mRNAs to evaluate bacterial metabolic activity. During ripening, ST and LH numerations showed a 2.5 log 10 loss of culturability whereas qPCR on pelleted cells revealed only one log 10 of decrease for both of these species. 10 9 ST and 10 8 LH cells/g of cheese still remained. They contained a stable number of 16S transcript and at least 10 6 copies of mRNAs per 10 9 cells until the end of ripening. These results prove the unexpected persistency of thermophilic lactic acid bacteria starters (ST and LH) metabolic activity until the end of ripening and open new perspectives in term of their involvement in the quality of cheeses during ripening. ► Emmental cheeses were manufactured and ripened for 2 months. ► Thermophilic starter bacteria (ST, LH) were counted throughout manufacture by Q PCR. ► Lysis during manufacture appeared 1.5 log 10 less than suspected with plate count. ► More than 7 log 10 thermophilic bacteria/g are peletable throughout the ripening. ► rRNA, mRNA quantifications showed metabolic activity of ST and LH during ripening.