Cooperation between wild lactococcal strains for cheese aroma formation

Several wild lactococcal strains were tested for their ability to produce aroma compounds during growth in milk. Strains were incubated alone and in combination with Lactococcus lactis IFPL730, which is characterized by showing α-keto acid decarboxylase activity. Volatile compounds from incubated milks were analyzed by means of solid-phase microextraction (SPME) and evaluated by gas chromatography-mass spectrometry (GC-MS). Incubated milks were also sniffed for sensory analysis to describe aroma attributes. The combination of L. lactis IFPL326 that showed the highest branched chain aminotransferase activity with IFPL730 contributed to the highest formation of leucine-derived volatile compounds, such as 3-methylbutanal, 3-methyl-1-butanol and 2-hydroxy-4-methyl pentanoic acid methyl ester. In addition, the milk incubated with this combination of strains was awarded, by the test panellists, the highest scores for >ripened cheese> attribute and aroma intensity. The results indicate that combination of L. lactis strains harbouring complementary catabolic routes can contribute to improved cheese aroma formation, the combined cultures with L. lactis IFPL730 resulting in higher volatile compound formation than isolate strains. © 2005 Elsevier Ltd. All rights reserved.This work was performed under the auspices of the Consejo Superior de Investigaciones Científicas and was supported by Research Project AGL2002-03277.Peer Reviewe

Conversion of methionine to methional by Lactococcus lactis

Lactic acid bacteria were screened for methional production from 4-methylthio-2-ketobutanoate. Only Lactococcus lactis IFPL730 produced high amounts of methional. It was demonstrated that production of this compound was an exclusively enzymatic reaction. The present work describes for the first time that L. lactis can convert enzymatically methionine to methional in a process mediated by aminotransferase and α-ketoacid decarboxylase activities. The activity seems to be strain dependent. © 2001 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.This work was supported by European Commission FAIR Programme Contract FAIR-CT97-3173 and Research Projects ALI97-0737 and FEDER-CICYT 2FD97-1025.Peer Reviewe

Lactobacillus casei and Lactobacillus plantarum initiate catabolism of methionine by transamination

Aims: To study the ability of Lactobacillus casei and Lact. plantarum strains to convert methonine to cheese flavour compounds. Methods and Results: Strains were assayed for methionine aminotransferase and lyase activities, and amino acid decarboxylase activity. About 25% of the strains assayed showed methionine aminotransferase activity. The presence of glucose in the reaction mixture increased conversion of methionine to 4-methylthio-2-ketobutanoate (KMBA) and 4-methyl-thio-2-hydroxybutanoate (HMBA) in all strains. The methionine aminotransferase activity in Lact. plantarum and Lact. casei showed variable specificity for the amino group acceptors glyoxylate, ketoglutarate, oxaloacetate and pyruvate. None of the strains showed methionine lyase or glutamate and methionine decarboxylase activities. Conclusions: The presence of amino acid converting enzymes in lactobacilli is strain specific. Significance and Impact of the Study: The findings of this work suggest that lactobacilli can be used as adjuncts for flavour formation in cheese manufacture.This work was supported by the European Commission FAIR Programme Contract FAIR-CT97-3173 and Spanish CICYT through Research Projects ALI-97-0737 and FEDER-CICYT 2FD97±1025. G.T. wishes to express his appreciation to COLCIENCIA (Colombia) for his fellowship.Peer Reviewe

Diversity of amino acid converting enzymes in wild lactic acid bacteria

A total of 156 lactic acid bacteria isolates belonging to the genera Lactococcus, Lactobacillus and Leuconostoc were analysed for the amino acid converting enzymes aminotransferases, glutamate dehydrogenase, and α-ketoisovalerate decarboxylase. All isolates showed aminotransferase activity towards phenylalanine (substrate for the aromatic aminotransferase AraT) and isoleucine (substrate for the branched-chain aminotransferase BcaT). Although there was a high variability inter- and intra-species, the lactococcal strains showed the highest values for both aminotransferase activities. Moreover, α-ketoisovalerate decarboxylase (Kivd) activity was only found in lactococcal isolates, although at low relative numbers (16%). On the other hand, glutamate dehydrogenase (Gdh) activity values were highest in facultative heterofermentative lactobacilli (FHL) and the activity was found at high relative numbers (50%) in leuconostocs. Results showed a high variability in amino acid convertase activities within the wild LAB isolates assayed, therefore the utilisation in the dairy industry of new strains with high flavour-forming abilities could be a powerful tool to enhance cheese aroma development. © 2005 Elsevier Inc. All rights reserved.This work was performed under the auspices of the Consejo Superior de Investigaciones Científicas and was supported by Research Project AGL2002-03277Peer Reviewe

Formation of methional by Lactococcus lactis IFPL730 under cheese model conditions

The present work describes the capacity of Lactococcus lactis to produce methional and other sulphur compounds derived from methionine (Met) in a cheese model system. Cheese slurries were prepared from pasteurized ewes' skimmed milk, chemically acidified with glucono-δ-lactone and homogenized aseptically adding Met, α-ketoglutarate, pyridoxal 5′-phosphate, thiamine pyrophosphate and NaCl. Slurries were incubated at 12°C for 14 days with cellular suspensions of L. lactis IFPL359, L. lactis IFPL730 and L. lactis NCDO763 in different combinations. Slurries added with resting cells and the intracellular fraction from L. lactis IFPL730 showed the highest production of methional at the outset of incubation, which decreased during incubation along with a concomitant increase in 3-methylthiopropanol. The sensorial analysis of slurries indicated a characteristic methional aroma (cooked potato-like) in samples containing 4-methylthio-2-ketobutyrate and the intracellular fraction from L. lactis IFPL730. As incubation proceeded, the intensity of methional aroma decreased but samples were judged by the panel tasters as developing a cheese-like flavour. © Springer-Verlag 2001.This work was supported by European Commission FAIR Programme Contract FAIR-CT97–3173 and Research Projects ALI97–0737 and FEDER-CICYT 2FD97–1025. G. Taborda wishes to express his appreciation to COLCIENCIAS (Colombia) for his financial fellowshipPeer Reviewe