Glutamate dehydrogenase activity in Lactobacillus isolated from artisanal fermented sausages

CECILIA A. FONTANA; GRACIELA M. VIGNOLO; PIER S. COCCONCELLI

Bologna, Italia

Congreso; . Foodmicro 2006. Food safety and food biotechnology: diversity and global impact; 2006

International Commitee on Food Microbiology and Hygiene

Microbial metabolism during sausages ripening is essential for flavour development. Relatively little is known about the ability of meat lactobacilli to metabolize released amino acid which are used as source of energy after sugar depletion. Amino acid breakdown by LAB is initiated by transamination and the resultant á -keto acids are further transformed by enzymes or chemical reactions. The ability of LAB to produce aroma compounds from amino acids is closely related to their glutamate dehydrogenase (GDH) activity. LAB strains exhibiting GDH activity are capable to produce á-ketoglutarate (á-KG) from glutamate (Glu) and therefore they are able to degrade amino acids in a reaction medium containing Glu. In this study the presence of GDH activity in Lactobacillus strains isolated from artisanal fermented sausages was investigated. GDH activity in L. sakei (2/8) and L. plantarum (2/2) strains was detected. It was established that this enzymatic activity was strongly strain specific, GDH(+) strains displaying different levels of activity. Primers design and PCR reactions to amplify the gdh gene in L. sakei strains were performed and the population of gdh+ Lactobacillus was investigated by quantitative Real Time-PCR (RT-PCR) among total Lactobacillus developed during sausage ripening process (14 days). Two quantitative reaction were performed, total Lactobacillus and gdh+ Lactobacillus number being estimated by comparing the Ct values obtained with the respective standard curve. Lactobacillus total number estimation by RT-PCR using genus specific primers increased from 103 CFU/g to 106 CFU/g within 5 days, these values remaining stable up to 14 days. On the other hand, CFU/g of gdh+ Lactobacillus estimated after gdh gene amplification by RT-PCR showed the same CFU/g increase when comparing with total Lactobacillus population estimation, this indicating a selection of gdh+ Lactobacillus during ripening. The identification and selection of Lactobacillus strains with high GDH activity to be used as starter culture would ensure or intensify aroma formation during sausage fermentation.