Ability of Thermophilic Lactic Acid Bacteria To Produce Aroma Compounds from Amino Acids

Abstract

Although a large number of key odorants of Swiss-type cheese result from amino acid catabolism, the amino acid catabolic pathways in the bacteria present in these cheeses are not well known. In this study, we compared the in vitro abilities of Lactobacillus delbrueckii subsp. lactis, Lactobacillus helveticus, and Streptococcus thermophilus to produce aroma compounds from three amino acids, leucine, phenylalanine, and methionine, under mid-pH conditions of cheese ripening (pH 5.5), and we investigated the catabolic pathways used by these bacteria. In the three lactic acid bacterial species, amino acid catabolism was initiated by a transamination step, which requires the presence of an ␣-keto acid such as ␣-ketoglutarate (␣-KG) as the amino group acceptor, and produced ␣-keto acids. Only S. thermophilus exhibited glutamate dehydrogenase activity, which produces ␣-KG from glutamate, and consequently only S. thermophilus was capable of catabolizing amino acids in the reaction medium without ␣-KG addition. In the presence of ␣-KG, lactobacilli produced much more varied aroma compounds such as acids, aldehydes, and alcohols than S. thermophilus, which mainly produced ␣-keto acids and a small amount of hydroxy acids and acids. L. helveticus mainly produced acids from phenylalanine and leucine, while L. delbrueckii subsp. lactis produced larger amounts of alcohols and/or aldehydes. Formation of aldehydes, alcohols, and acids from ␣-keto acids by L. delbrueckii subsp. lactis mainly results from the action of an ␣-keto acid decarboxylase, which produces aldehydes that are then oxidized or reduced to acids or alcohols. In contrast, the enzyme involved in the ␣-keto acid conversion to acids in L. helveticus and S. thermophilus is an ␣-keto acid dehydrogenase that produces acyl coenzymes A.Amino acid catabolism by the microflora is a major process for the formation of a large number of key aroma compounds in Swiss-type cheeses such as gruyere and emmental (7,14,17). However, the amino acid catabolic pathways in the different bacteria present in these cheeses are not well known. This knowledge could lead to the development of cultures with optimized aromatic properties.Amino acid catabolism by Lactococcus lactis and mesophilic lactobacilli has been extensively studied recently (2,8,11,19,26; S. Gummalla and J. R. Broadbent, Abstract, J. Dairy Sci. 79(Suppl.

Volatile components and sensory characteristics of Thai traditional fermented shrimp pastes during fermentation periods

“…Among this group, 3-methylbutanol was the most abundance detected in both Kapi types and reached maximal in and Kp-R4 (Table 3). In addition, some lactic acid bacteria have been reported to produce a large amount of 3-methylbutanol from phenylalanine, valine and leucine (Helinck et al 2004). Moreover, the amounts of alcohols were found to correlate with aldehyde levels in the fermented shrimp pastes in this study.…”

In Silico Reconstruction of the Metabolic Pathways of Lactobacillus plantarum : Comparing Predictions of Nutrient Requirements with Those from Growth Experiments

“…The auxotrophy for glutamate in LAB is well known and is caused by an incomplete TCA cycle and hence no supply of ␣-ketoglutarate. The role of glutamate dehydrogenase is probably related to transamination reactions involved in amino acid degradation and not in glutamate biosynthesis (15,52). Actually, all reactions in LacplantCyc that could eventually produce glutamate use either ␣-ketoglutarate or glutamine (which was not present in the medium as a substrate).…”

Propionibacterium freudenreichii strains quantitatively affect production of volatile compounds in Swiss cheese

“…They also have a major contribution to cheese proteolysis, and the activity of their enzymes results in the release of free amino acids, which are the precursors of many flavour compounds. Moreover, lactic acid bacteria are also capable of forming various volatile compounds, and in particular, significant amounts of carbonyl compounds [17,19,35,48,51]. PAB have been known for a long time to contribute to the development of Swiss cheese flavour and cheese opening, achieved through the fermentation of lactic acid into propionic acid, acetic acid and CO 2 [6,18,40].…”

“…Thermophilic lactobacilli are known to play a main role in the release of peptides and free amino acids in Swiss cheese, through the activity of their numerous aminopeptidases [11], and this activity is enhanced by cell lysis [50]. They are also capable of converting amino acids into various BC volatile compounds in vitro, and in particular catalyse transamination reaction, which is the first step of amino acid catabolism in cheese [17,22,51]. Therefore, the stimulatory effect that LH77 exerted on the synthesis of BC volatile compounds by PAB may have been due to its contribution to the release of BC precursors of volatile compounds, which may be amino acids or keto acids resulting from transamination.…”