Changes in nitrogen compounds in must and wine during fermentation and biological aging by flor yeasts.
Urea, ammonium, and free amino acid contents were quantified in a must from Vitis vinifera cv. Pedro Ximenez grapes and in fermented wine and after a short aging of this wine by Saccharomyces cerevisiae race capensis yeast under variable oxygen availability conditions. The previous compounds were also determined in a wine in which the nitrogen source was depleted by the same race of flor yeast (old wine) and also following the addition of ammonium ion, L-glutamic acid, and L-proline. Under specific conditions such as low oxygen level and the absence of some nutrients, the yeasts release some amino acids including L-threonine, L-tryptophan, L-cysteine, and L-methionine to the medium. These amino acids must originate primarily in a de novo synthesis from ethanol that regenerates NAD(P)+. On the basis of these results, the yeasts may be able to use amino acids not only as nitrogen sources but also as redox agents to balance the oxidation-reduction potential under conditions of restricted oxygen, when electron transport along the respiratory chain may be hindered or limited.
Mauricio
J C
JC
Departamento de Microbiología, Universidad de Córdoba, Campus Universitario de Rabanales, Edificio C-6, 14014 Córdoba, Spain. mi1orruj@uco.es
Valero
E
E
Millán
C
C
Ortega
J M
JM
D000375:Aging; D005285:Fermentation; D017672:Nitrogen Compounds / Q000032:analysis*; D010084:Oxidation-Reduction; D010100:Oxygen; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D014920:Wine / Q000382:microbiology*
D017672:Nitrogen Compounds; D010100:Oxygen