Tyrosine and Phenylalanine Catabolism by Lactobacillus Cheese Flavor Adjuncts

Abstract

Bacterial metabolism of Tyr and Phe has been associated with the formation of aromatic compounds that impart barny-utensil and floral off-flavors in cheese. In an effort to identify possible mechanisms for the origin of these compounds in Cheddar cheese, we investigated Tyr and Phe catabolism by Lactobacillus casei and Lactobacillus helveticus cheese flavor adjuncts under simulated Cheddar cheese-ripening (pH 5.2, 4% NaCl, 15 degrees C, no sugar) conditions. Enzyme assays of cell-free extracts indicated that L. casei strains catabolize Tyr and Phe by successive, constitutively expressed transamination and dehydrogenation reactions. Similar results were obtained with L. helveticus strains, except that the dehydrogenase enzymes were induced during incubation under cheese-ripening conditions. Micellar electrokinetic capillary chromatography of supernatants from L. casei and L. helveticus strains incubated under simulated cheese-ripening conditions confirmed that Tyr and Phe transamination and dehydrogenation pathways were active in both species and also showed these reactions were reversible. Major products of Tyr catabolism were phydroxy phenyl lactic acid and p-hydroxy phenyl acetic acid, while Phe degradation gave rise to phenyl lactic acid, phenyl acetic acid, and benzoic acid. However, some of these products were likely formed by nonenzymatic processes, since spontaneous chemical degradation of the Tyr intermediate p-hydroxy phenyl pyruvic acid produced p-hydroxy phenyl acetic acid, p-hydroxy phenyl propionic acid, and p-hydroxy benzaldehyde, while chemical degradation of the Phe intermediate phenyl pyruvic acid gave rise to phenyl acetic acid, benzoic acid, phenethanol, phenyl propionic acid, and benzaldehyde.

Overexpression of Lactobacillus casei d -Hydroxyisocaproic Acid Dehydrogenase in Cheddar Cheese

“…Specifically, the Phe catabolites phenylacetaldehyde and 2-phenethyl alcohol have been shown to impart floral, rose-like off-flavors, and the Tyr catabolite p-cresol imparts barny, medicinal, or utensil-like offflavors (15,22,32). Mechanisms for the production of these compounds in cheese have not been conclusively established, but AAA catabolism by lactococci and lactobacilli under simulated cheese-ripening conditions is initiated by aminotransferase (ATase) enzymes that convert AAAs into corresponding ␣-keto acids (17,20,21,39). Moreover, the aromatic ␣-keto acids produced by these reactions can be nonenzymatically converted to benzaldehyde, phenylacetaldehyde, 2-phenethyl alcohol, and other aroma compounds (17,19,20,21,38).…”

“…Mechanisms for the production of these compounds in cheese have not been conclusively established, but AAA catabolism by lactococci and lactobacilli under simulated cheese-ripening conditions is initiated by aminotransferase (ATase) enzymes that convert AAAs into corresponding ␣-keto acids (17,20,21,39). Moreover, the aromatic ␣-keto acids produced by these reactions can be nonenzymatically converted to benzaldehyde, phenylacetaldehyde, 2-phenethyl alcohol, and other aroma compounds (17,19,20,21,38). However, many lactic acid bacteria possess hydroxy acid dehydrogenases (HADH) such as D-hydroxyisocaproic acid dehydrogenase (D-Hic) that convert ␣-keto acids to ␣-hydroxy acids (7,23), and these enzymes are active in cells incubated under cheese-ripening conditions (20,21).…”

“…Moreover, the aromatic ␣-keto acids produced by these reactions can be nonenzymatically converted to benzaldehyde, phenylacetaldehyde, 2-phenethyl alcohol, and other aroma compounds (17,19,20,21,38). However, many lactic acid bacteria possess hydroxy acid dehydrogenases (HADH) such as D-hydroxyisocaproic acid dehydrogenase (D-Hic) that convert ␣-keto acids to ␣-hydroxy acids (7,23), and these enzymes are active in cells incubated under cheese-ripening conditions (20,21). Since ␣-hydroxy acids do not make a significant contribution to flavor development (38), this class of enzymes could be useful in controlling off-flavor development via their ability to divert the spontaneous degradation of AAA-derived ␣-keto acids to more-stable enzymatic products.…”

Identification of Antioxidants Produced byLactobacillus plantarum

“…[6][7][8] Certain strains of L. plantarum from sourdough have been reported to produce HPLA and PLA 8) and reported to be antifungal compounds. 8,9) An aromatic aminotransferase has been shown to be active with tyrosine, phenylalanine, tryptophan, methionine and leucine.…”

Dynamics of Aroma-Active Volatiles in Miso Prepared from Lizardfish Meat and Soy during Fermentation: A Comparative Analysis

“…Hypothetical pathways of those sulfur-containing compounds in miso products are presented in Fig.4 as suggested earlier by Landaud, Helinck, & Bonnarme [14] in several fermented products. Transamination is the first step in the degradation of amino acids such as methionine, leading to the formation of α-keto acids (α-KA), which finally leads to the formation of several sulfur-containing volatile compounds [15]. In the present study, 3-(methylthio)propanal (methional), the Strecker aldehyde of methionine, was detected in both miso samples.…”