Ability of lactic acid bacteria to produce N-heterocycles causing mousy off-flavour in wine

Abstract

Thirty-four strains of the genera and species representative of the wine lactic acid bacteria (LAB) were screened in an ethanolic grape juice medium for the production of mousy off-flavour as determined by an alkaline test strip sensory method. Most Lactobacillus spp., Oenococcus oeni and Leuconostoc mesenteroides produced mousy off-flavour, whereas Pediococcus spp. were generally incapable of detectable off-flavour formation. To verify these results, selected LAB were tested for the ability to produce the three sensorially potent N-heterocycles, 2-ethyltetrahydropyridine (ETPY), 2-acetyltetrahydropyridine (ACTPY) and 2-acetyl-1-pyrroline (ACPY), which are associated with the mousy off-flavour in wine. N-heterocycle formation was determined by incubating a high density of bacterial cells in a chemically defined N-heterocycle assay medium, and quantifying the 'mousy' compounds by gas chromatography-mass spectrometry. Most strains produced each of the three N-heterocycles, with the general order for this capability being Lactobacillus (heterofermentative) > Oenococcus > Pediococcus. Strains of Lactobacillus hilgardii and Lactobacillus brevis were characterised as producing the highest concentration of ACTPY (328-580 µg/L, sensory threshold in water = 1.6 µg/L ), whereas ACPY and ETPY were produced at a moderate concentration (< 50 and < 10 µg/L, respectively). In addition to the formation of ACPY and ACTPY, three of five strains of the commercially important wine malolactic bacterium, O. oeni, produced the highest concentration of ETPY (87-162 µg/L). Strains of the homofermentative LAB, Pediococcus sp. and Lactobacillus plantarum L11a, however, produced only a relatively low concentration of each mousy N-heterocycle (≤ 37 µg/L), suggesting that the ability of LAB to produce mousy N-heterocycles is linked to the pathway of sugar catabolism. The importance of selecting LAB for induction of malolactic fermentation which have limited ability to produce mousy N-heterocycles is emphasised.Abbreviations LAB lactic acid bacteria; L. Lactobacillus; O. Oenococcus; P. Pediococcus; MLF malolactic fermentation; ETPY 2-ethyltetrahydropyridine; ACTPY 2-acetyltetrahydropyridine; ACPY 2-acetyl-1-pyrroline;GC-MS gas chromatography-mass spectrometry; GJ medium grape juice medium; MRSA medium de Man, Rogosa and Sharpe medium supplemented with 20% v/v preservative-free apple juice;MRS-CT medium de Man, Rogosa and Sharpe medium modified by the inclusion of casamino acids and trypticase peptone; m/z mass to charge ratio

Malolactic Fermentation: The ABC’s of MLF

“…Three main compounds are involved: 2-acetyl-1-pyrroline (ACPY), 2-ethyltetrahydropyridine (ETPY) and 2-acetyltetrahydropyridine (ACTPY) (Lonvaud-Funel, 1999;Costello et al, 2001). The formation of these compounds is mostly associated with heterofermentative LAB, such as O. oeni, some Lactobacillus species and Leuc.…”

Inactivation of an aminoaldehyde dehydrogenase is responsible for fragrance in rice

“…In rice the nitrogen in the pyrroline ring of proline becomes the nitrogen in the pyrroline ring of 2AP while the carboxyl group of proline is removed and replaced with an acetyl group from another source (Yoshihashi et al 2002b). Costello et al (2001) found that in L. hilgardii the acetyl group of 2AP can be derived from fructose when either ethanol or acetaldehyde are supplied in excess. They further suggested D 1 pyrroline, a product of proline catabolism via putrescine oxidation, is the immediate precursor of the pyrroline ring of 2AP and the acetyl group was most likely formed from reaction with acetyl-CoA or acetaldehyde in either a chemical or enzymatic reaction.…”

“…As well as being the major chemical component of fragrance in rice (Buttery et al 1983a), 2AP is a significant aroma chemical in a number of organisms and foodstuffs including Pandanus (Buttery et al 1983b;Laohakunjit and Noomhorm 2004;Thimmaraju et al 2005), popcorn (Schieberle 1995), corn tortillas (Buttery and Ling 1995), baguettes (Zehentbauer and Grosch 1998), ham (Carrapiso et al 2002), cheese (Zehentbauer and Reineccius 2002), mung bean (Brahmachary and Ghosh 2002), green tea (Kumazawa and Masuda 2002), bread flowers (Vallaris glabra Ktze) (Wongpornchai et al 2003) some yeasts (Snowdon et al 2006) and select bacteria (Romanczyk et al 1995;Costello et al 2001;Rungsardthong and Noomhoom 2005;Snowdon et al 2006;Adams and De Kimpe 2007) including the wine spoilage bacteria Lactobaccillus hilgardii (Costello et al 2001;Snowdon et al 2006).…”

“…Studies into the biological formation of 2AP have shown it can be derived from either proline or ornithine in rice (Yoshihashi et al 2002b), Pandanus (Thimmaraju et al 2005) and L. hilgardii (Costello et al 2001). In rice the nitrogen in the pyrroline ring of proline becomes the nitrogen in the pyrroline ring of 2AP while the carboxyl group of proline is removed and replaced with an acetyl group from another source (Yoshihashi et al 2002b).…”

Studies on Two Exoenzymes Which Lyse Wine-Spoiling Bacteria

“…In particular, strains of Lactobacillus brevis have been frequently isolated from must and wine [3]- [5]. They are spoiling microorganisms due to their ability to produce biogenic amines [5]- [7], ethyl carbamate [6], volatile phenols [8] and mousy off-flavors [9].…”