Amino Acid Uptake by Four Commercial Yeasts at Two Different Temperatures of Growth and Fermentation: Effects on Urea Excretion and Reabsorption

Abstract

Samples of various commercially processed juices were fermented under controlled conditions to determine variations in amino acid uptake (or excretion) during growth and fermentation. There was almost always rapid uptake of all the amino acids except alanine, proline, citrulline, ornithine, and arginine. Proline was not metabolized as long as the fermentation was anaerobic. Large increases in proline concentration result from the metabolism of arginine which occurs after the other major amino acids have been reduced to lower levels. The patterns of uptake are generally similar for the four yeasts studied. Some variation was seen with the <i>Torulaspora delbreukii</i> compared to the <i>Saccharomyces</i> yeasts. The urea excretion and uptake was dependent primarily on yeast strain and on amounts of arginine remaining in the juice during fermentation. Amounts of urea excreted tended to be increased at higher temperature. At very high amino acid levels, arginine was very slowly metabolized and this minimized urea excretion.