Van Der Sluis Catrinus, Rahardjo Yovita S P, Smit Bart A, Kroon Pieter J, Hartmans Sybe, Ter Schure Eelko G, Tramper Johannes, Wijffels Renéh
Wageningen University, Department of Agrotechnology and Food Sciences, Food and Bioprocess Engineering Group, P.O. Box 8129, 6700 EV Wageningen, The Netherlands.
J Biosci Bioeng. 2002;93(2):117-24. doi: 10.1016/s1389-1723(02)80002-0.
Alpha-keto acids are key intermediates in the formation of higher alcohols, important flavor components in soy sauce, and produced by the salt-tolerant yeast Zygosaccharomyces rouxii. Unlike most of the higher alcohols, the alpha-keto acids are usually not extracellularly accumulated by Z. rouxii when it is cultivated with ammonium as the sole nitrogen source. To facilitate extracellular accumulation of the alpha-keto acids from aspartate-derived amino acid metabolism, the amino acids valine, leucine, threonine and methionine were exogenously supplied during batch and A-star cultivations of (routants of) Z. rouxii. It was shown that all alpha-keto acids from the aspartate-derived amino acid metabolism, except alpha-ketobutyrate, could be extracellularly accumulated. In addition, it appeared from the concomitant extracellular accumulation of alpha-keto acids and higher alcohols that in Z. rouxii, valine, leucine and methionine were converted via Ehrlich pathways similar to those in Saccharomyces cerevisiae. Unlike these amino acids, threonine was converted via both the Ehrlich and amino acid biosynthetic pathways in Z. rouxii.
α-酮酸是高级醇形成过程中的关键中间体，高级醇是酱油中的重要风味成分，由耐盐酵母鲁氏接合酵母产生。与大多数高级醇不同，当鲁氏接合酵母以铵作为唯一氮源进行培养时，α-酮酸通常不会在细胞外积累。为了促进天冬氨酸衍生氨基酸代谢产生的α-酮酸在细胞外积累，在鲁氏接合酵母的分批培养和A-star培养过程中，外源添加了缬氨酸、亮氨酸、苏氨酸和蛋氨酸。结果表明，除α-酮丁酸外，天冬氨酸衍生氨基酸代谢产生的所有α-酮酸都可以在细胞外积累。此外，从α-酮酸和高级醇同时在细胞外积累的情况来看，在鲁氏接合酵母中，缬氨酸、亮氨酸和蛋氨酸是通过与酿酒酵母中类似的埃利希途径转化的。与这些氨基酸不同，苏氨酸在鲁氏接合酵母中是通过埃利希途径和氨基酸生物合成途径进行转化的。
