Influence of addition of ammonium and different amino acid concentrations on nitrogen metabolism in spontaneous must fermentation

The effect of the addition of different amino acid concentrations in must on yeast nitrogen metabolism during alcoholic fermentation was studied. To do this, fermentations of Mazuelo must, poor in nitrogen compounds, were carried out. Ammonium and different concentrations of amino acids (0, 45, 120, 250 and 450 mg/l) were added to the must. Addition of 45, 120 and 250 mg/l of proteic amino acids to the must increased the rate of fermentation. Proline was mainly consumed in fermentations with smaller amounts of amino nitrogen and, at the same time, this amino acid showed the highest residual concentration in the final wines. The consumption of other proteic amino acids was directly proportional to their concentration in the musts, with the exception of leucine and isoleucine that were synthesized. However, a difference in the percentages of the amino acids consumed by the yeasts was observed. The percentages of aspartic acid, alanine and arginine consumed were higher in the fermentations supplemented with amino acids than in the fermentation where only ammonium was added. The percentages of tyrosine and phenylalanine consumed gradually increased with increase of their initial concentration.