Overexpression of Lactobacillus caseid-Hydroxyisocaproic Acid Dehydrogenase in Cheddar Cheese

ABSTRACT Metabolism of aromatic amino acids by lactic acid bacteria is an important source of off-flavor compounds in Cheddar cheese. Previous work has shown that α-keto acids produced from Trp, Tyr, and Phe by aminotransferase enzymes are chemically labile and may degrade spontaneously into a variety of off-flavor compounds. However, dairy lactobacilli can convert unstable α-keto acids to more-stable α-hydroxy acids via the action of α-keto acid dehydrogenases such as d-hydroxyisocaproic acid dehydrogenase. To further characterize the role of this enzyme in cheese flavor, the Lactobacillus casei d-hydroxyisocaproic acid dehydrogenase gene was cloned into the high-copy-number vector pTRKH2 and transformed into L. casei ATCC 334. Enzyme assays confirmed that α-keto acid dehydrogenase activity was significantly higher in pTRKH2:dhic transformants than in wild-type cells. Reduced-fat Cheddar cheeses were made with Lactococcus lactis starter only, starter plus L. casei ATCC 334, and starter plus L. casei ATCC 334 transformed with pTRKH2:dhic. After 3 months of aging, the cheese chemistry and flavor attributes were evaluated instrumentally by gas chromatography-mass spectrometry and by descriptive sensory analysis. The culture system used significantly affected the concentrations of various ketones, aldehydes, alcohols, and esters and one sulfur compound in cheese. Results further indicated that enhanced expression of d-hydroxyisocaproic acid dehydrogenase suppressed spontaneous degradation of α-keto acids, but sensory work indicated that this effect retarded cheese flavor development.

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Heterologous Production of Methionine-γ-Lyase from Brevibacterium linens in Lactococcus lactis and Formation of Volatile Sulfur Compounds

Applied and Environmental Microbiology ◽

10.1128/aem.02417-08 ◽

2009 ◽

Vol 75 (8) ◽

pp. 2326-2332 ◽

Cited By ~ 16

Author(s):

Sean B. Hanniffy ◽

Mark Philo ◽

Carmen Peláez ◽

Michael J. Gasson ◽

Teresa Requena ◽

...

Keyword(s):

Lactococcus Lactis ◽

Sulfur Compounds ◽

Mass Spectrometry Analysis ◽

Gas Chromatography Mass Spectrometry ◽

Volatile Sulfur Compounds ◽

Brevibacterium Linens ◽

Cell Extracts ◽

Cheese Flavor ◽

Flavor Development ◽

Volatile Sulfur

ABSTRACT The conversion of methionine to volatile sulfur compounds (VSCs) is of great importance in flavor formation during cheese ripening and is the focus of biotechnological approaches toward flavor improvement. A synthetic mgl gene encoding methionine-γ-lyase (MGL) from Brevibacterium linens BL2 was cloned into a Lactococcus lactis expression plasmid under the control of the nisin-inducible promoter PnisA. When expressed in L. lactis and purified as a recombinant protein, MGL was shown to degrade l-methionine as well as other sulfur-containing compounds such as l-cysteine, l-cystathionine, and l-cystine. Overproduction of MGL in recombinant L. lactis also resulted in an increase in the degradation of these compounds compared to the wild-type strain. Importantly, gas chromatography-mass spectrometry analysis identified considerably higher formation of methanethiol (and its oxidized derivatives dimethyl disulfide and dimethyl trisulfide) in reactions containing either purified protein, whole cells, or cell extracts from the heterologous L. lactis strain. This is the first report of production of MGL from B. linens in L. lactis. Given their significance in cheese flavor development, the use of lactic acid bacteria with enhanced VSC-producing abilities could be an efficient way to enhance cheese flavor development.

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Inhibition of glycine oxidation by pyruvate, α-ketoglutarate, and branched-chain α-keto acids in rat liver mitochondria: Presence of interaction between the glycine cleavage system and α-keto acid dehydrogenase complexes

Archives of Biochemistry and Biophysics ◽

10.1016/0003-9861(86)90002-0 ◽

1986 ◽

Vol 249 (2) ◽

pp. 263-272 ◽

Cited By ~ 15

Author(s):

Hideo Kochi ◽

Hiroshi Seino ◽

Kazuo Ono

Keyword(s):

Rat Liver ◽

Liver Mitochondria ◽

Rat Liver Mitochondria ◽

Keto Acid ◽

Glycine Cleavage System ◽

Acid Dehydrogenase ◽

Keto Acids ◽

Glycine Cleavage ◽

Branched Chain

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Effect of Dietary Branched-chain α-Keto Acids on Hepatic Branched-chain α-Keto Acid Dehydrogenase in the Rat

Journal of Nutrition ◽

10.1093/jn/107.8.1528 ◽

1977 ◽

Vol 107 (8) ◽

pp. 1528-1536 ◽

Cited By ~ 16

Author(s):

Balwant S. Khatra ◽

Rajender K. Chawla ◽

Allan D. Wadsworth ◽

Daniel Rudman

Keyword(s):

Keto Acid ◽

Acid Dehydrogenase ◽

Keto Acids ◽

Branched Chain

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FLAVOR DEVELOPMENT AND MICROBIOLOGY OF SWISS CHEESE-A REVIEW

Journal of Milk and Food Technology ◽

10.4315/0022-2747-36.12.593 ◽

1973 ◽

Vol 36 (12) ◽

pp. 593-609 ◽

Cited By ~ 76

Author(s):

T. Langsrud ◽

G. W. Reinbold

Keyword(s):

Fatty Acids ◽

Carbonyl Compounds ◽

Lactate Production ◽

Flavor Compounds ◽

Swiss Cheese ◽

The Third ◽

Keto Acids ◽

Flavor Development ◽

Eye Formation ◽

Acetic Acids

This paper, the third of four, discusses the ripening and flavor production processes of Swiss cheese. First, general ripening changes are reviewed; then, a discussion of eye formation and body and texture changes follows. The important flavor compounds found in Swiss cheese are examined in detail beginning with consideration of the analytical methods used to isolate and measure fatty acids. The different volatile and nonvolatile fatty acids and their importance in Swiss cheese are considered, as well as production of propionic and acetic acids from lactate, production of keto acids, and lipolysis. Then, analyses for and significance of carbonyl compounds, alcohols, esters, lactones, hydrocarbons, and diacetyl are presented. Possibilities for production of these compounds by microorganisms are given. Subsequent sections deal with nitrogeneous compounds, degradation of caseins to peptides and amino acids and their importance to flavor, and end with a review of sulfur compounds present.

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