Flavour Formation by Lactobacillus casei via citrate metabolism and glutamate dehydrogenase activity

PABLO MORTERA; FEDERICO ZULJAN; JUKE LOLKEMA; CHRISTIAN MAGNI; SERGIO ALARCON

Congreso; IUFOST, 16th World Crongress of Food Science and Technology; 2012

Lactobacillus casei is the most frequently non starter lactic acid bacteria (LAB) growing during the cheese ripening. Also, some strains of Lb. casei are consider probiotic and used by food industry. In some cases, citrate can remain in the cheese matrix to be metabolized by Lb. casei. This compound serves as energy source when is cometabolized with sugars in some LABs. Since citrate degradation in the most of LAB produced flavor compounds its metabolism is an important issue in Lb. casei fermentations. Also, the amino acids catabolism contributes to the flavor production, being the glutamate a key compound in the amino acid recycling and hidroxy-acids transformations. The aims of this work was study the flavour generations throught the citrate and amino acid metabolism showing that citrate is not an energy source and the presence of galactose or glucose repress the citrate utilization in Lb. casei  ATCC 334 grown in modified MRS medium. Also we determined the citrate consumption rate in 50 mM potassium phosphate at pH 5.8 and the citrate-Ca2+ transport specificity instead citrate-Mg2+. Finally, it was determined that the citrate metabolism in Lb. casei produces pyruvate, acetate and acetoin as end products. In addition, we showed by informatics approach a difference between the gene encoding in two Lb. casei (ATCC 334 and BL 23), both with industrial interest. Thus we evaluated the GDH activities in these strains and their influence in formation of volatile compounds.