The peptide hydrolase system of Lactobacillus reuteri

G.C. ROLLÁN; G.FONT DE VALDEZ

Los Angeles, California

Simposio; 100thGeneral Meeting of American Society for Microbiology; 2000

  The Peptide Hydrolase System of Lactobacillus reuteri   Lactic acid bacteria are also found in food ecosystems other than dairy products. These microorganisms have been isolated from or used as starters in sourdough breads. Lactobacilli are essential for acidification and proteolysis in order to develop a good texture and flavour as well as to improve the shelf-life of wheat sourdough breads. The aim of the present work was to investigate the peptide hydrolase system of Lactobacillus reuteri CRL 1098, isolated of artisanal sourdough, and to determine its cellular location. Aminopeptidase activity was evaluated by measuring the extent of hydrolysis of several amino-acid para-nitroanilide (p-NA) derivates. Dipeptidase and tripeptidase were determined by measuring (ninhydrin reaction) the amount of a-amino groups released after the hydrolysis of synthetic di and tripeptides. Results: Sourdough lactobacilli have a broad range of peptidases in a similar way to those found in dairy products isolates. Aminopeptidase was located mainly in the cytoplasmic fraction. The enzyme shows a broad substrate specificity. The aminopeptidases hydrolyzed Lys, Leu, Met, Ala, Phe pNA. Low activity was detected on Gly, Val and Glu p-NA. Pro p-NA was also hydrolyzed by L.reuteri, which indicates the presence of iminopeptidase activity. The microorganism shows active dipeptidylaminopeptidase activity also located in the cytoplasmic fraction. The highest di and tripeptidase activities were obtained with Leu-Leu and Leu-Leu-Leu as substrate, respectively. These activities were distributed in the cytoplasmic fraction and specially in the membrane/cell wall fraction. This study demonstrates that L. reuteri CRL 1098 has an active peptidase system which is partially associated to the cell wall and membrane fraction. The research was supported by grants of Fundación Antorchas.