VTT Technical Research Centre of Finland, Tietotie 2, P.O. Box 1000, FI-02044, VTT, Espoo, Finland.
Appl Microbiol Biotechnol. 2013 Aug;97(15):6919-30. doi: 10.1007/s00253-013-4955-1. Epub 2013 May 16.
Undesirable butter-tasting vicinal diketones are produced as by-products of valine and isoleucine biosynthesis during wort fermentation. One promising method of decreasing diacetyl production is through control of wort valine content since valine is involved in feedback inhibition of enzymes controlling the formation of diacetyl precursors. Here, the influence of valine supplementation, wort amino acid profile and free amino nitrogen content on diacetyl formation during wort fermentation with the lager yeast Saccharomyces pastorianus was investigated. Valine supplementation (100 to 300 mg L(-1)) resulted in decreased maximum diacetyl concentrations (up to 37 % lower) and diacetyl concentrations at the end of fermentation (up to 33 % lower) in all trials. Composition of the amino acid spectrum of the wort also had an impact on diacetyl and 2,3-pentanedione production during fermentation. No direct correlation between the wort amino acid concentrations and diacetyl production was found, but rather a negative correlation between the uptake rate of valine (and also other branched-chain amino acids) and diacetyl production. Fermentation performance and yeast growth were unaffected by supplementations. Amino acid addition had a minor effect on higher alcohol and ester composition, suggesting that high levels of supplementation could affect the flavour profile of the beer. Modifying amino acid profile of wort, especially with respect to valine and the other branched-chain amino acids, may be an effective way of decreasing the amount of diacetyl formed during fermentation.
在麦汁发酵过程中，缬氨酸和异亮氨酸生物合成会产生不良的黄油味顺式二酮作为副产物。一种有前途的降低双乙酰产量的方法是通过控制麦汁缬氨酸含量来实现，因为缬氨酸参与了控制双乙酰前体形成的酶的反馈抑制。在这里，研究了添加缬氨酸、麦汁氨基酸谱和游离氨基酸氮含量对巴氏酵母 Saccharomyces pastorianus 麦汁发酵过程中双乙酰形成的影响。在所有试验中，缬氨酸（100 至 300mg/L）的添加导致最大双乙酰浓度（降低高达 37%）和发酵结束时双乙酰浓度（降低高达 33%）降低。麦汁氨基酸谱的组成也对发酵过程中双乙酰和 2,3-戊二酮的产生有影响。未发现麦汁氨基酸浓度与双乙酰生产之间存在直接相关性，而是缬氨酸（和其他支链氨基酸）吸收速率与双乙酰生产之间存在负相关。发酵性能和酵母生长不受添加物的影响。氨基酸的添加对高级醇和酯的组成影响较小，这表明高浓度的添加可能会影响啤酒的风味特征。改变麦汁的氨基酸谱，特别是缬氨酸和其他支链氨基酸，可能是减少发酵过程中形成的双乙酰量的有效方法。
