Amino acids
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Amino acids are the basic building blocks of proteins, and they all contain nitrogen.
Structurally, amino acids consist of an amino group, a carboxyl group, and a side chain all bound to a central carbon. Amino acids differ from each other with respect to their side chains.[1]
Amino acids and ammonium (NH4+) salts are the most important sources of nitrogen for yeast nutrition.[2] The amino acid contribution to fermentation is expressed as free amino nitrogen (FAN), which is the concentration (mg/L) of nitrogen contributed by all amino acids, regardless of type (even the ones not utilized). See Yeast.
The amino acid composition of wort or must influences the quality of the beer or wine produced. In particular, the utilization of branched-chain amino acids such as valine, leucine, and isoleucine is likely to influence the production of the corresponding higher alcohols isobutanol, isoamyl alcohol, and amyl alcohol and possibly also the corresponding esters. In addition, valine may play a role in the levels of diacetyl due to its influence on the production of the diacetyl precursor α-acetolactate. Diacetyl is formed when intracellular α-acetolactate is released by yeast into the wort and undergoes spontaneous oxidative decarboxylation. Diacetyl, which adds a buttery note to beers, may be acceptable in certain ales but is generally considered to be undesirable in lager beers and is therefore of particular importance in the brewing industry, where extended maturation times are required for its removal. The diacetyl concentration of wort peaks during midfermentation and is subsequently lowered through the action of yeast reductases in the latter part of fermentation and during the maturation stage following fermentation. When the valine concentration in wort is less than adequate, the yeast responds by synthesizing this amino acid, with α-acetolactate and hence diacetyl being natural by-products of this reaction. A relatively high valine concentration in the wort would be expected to reduce the anabolic production of valine, thereby reducing the concentration of diacetyl in the beer. Other amino acids may influence the diacetyl or vicinal diketone (VDK) concentrations in beer in a more indirect manner, e.g., by influencing fermentation time. Faster fermentations occurring as a result of lysine supplementation have resulted in higher VDK concentrations, as the VDK has less time to be reduced after peak concentrations have been reached. Likewise, methionine supplementation, which increased fermentation time, also resulted in green beers with lower levels of diacetyl. This effect on diacetyl concentration has been observed in worts with high and low total FAN levels, presumably due to the relative increase or decrease in valine in these worts. Amino acids may also affect beer flavor by influencing the production of hydrogen sulfide. Addition of the sulfur-containing amino acid cysteine (but not methionine) to fermentation wort was found to increase the production of hydrogen sulfide by up to sevenfold, relative to control worts with no supplementation. The influence of amino acids on beer quality is not restricted to flavor, however. Furukubo et al found a negative correlation between the concentrations of basic amino acids and the ability of foams to adhere to glass and suggested that brewing conditions that influence the level of these amino acids also affect this property.[3]
Amino acids are released enzymatically by carboxypeptidase, dipeptidase, and aminopeptidase. Within the fermentation they are metabolized by yeast enzymes and function here, inter alia, as precursors of aroma-active esters and higher alcohols. Especially the amino acids such as phenylalanine, methionine, and leucine influence the fruity and malty wheat beer aroma. Present amino acids in wort are products of yeast Ehrlich metabolism, namely the higher alcohols phenyl ethanol, isobutanol, propanol, methionol, and isoamyl alcohol and the esters ethyl acetate, isoamyl acetate, phenyl acetate, ethyl acetate, and 2-methylbutyl acetate.[4]
| Amino acid | Higher alcohol | Ester |
|---|---|---|
| Leucine | Isoamyl alcohol | Isoamyl acetate |
| Isoleucine | Amyl alcohol | Amyl acetate |
| Phenylalanine | 2-Phenyl ethanol | 2-Phenyl acetate |
| Methionine | Methional | 3-(Methylthio)propylacetate |
From our amino acid composition data, it is more likely that true hordeins are high in proline and true glutelins are high in glutamines[5]
Although the molecular mechanisms of Lys and His for improving fermentability were still unclear, they were obviously the key amino acids during both normal and high gravity fermentation.[6]
In addition to the numerous phenolic compounds, aromatic amino acids also have antioxidant properties. According to Spreng and Hofmann (2018) [54], the content of phenylalanine, tyrosine and tryptophan correlates significantly with the ORAC values; tyrosine content with the FRAP values in the different barley malts.[7]
For Pro to be absorbed by yeasts, a mitochondrial oxidase, which is inactive under anaerobic conditions, is required. Making it the less absorbable AA, explaining why it is normally present in higher amounts in beers when compared to other AA[8]
Amino acids can directly influce beer flavor, such as by promoting bitterness.[8]
Under oxidative conditions proline is oxidized to glutamic acid and becomes available to the yeast.[9]
Different amino acids have different effects on fermentation performance. Proline, for example, is not typically metabolized by yeast during a brewery fermentation, but may have a role in protecting yeast against the high ethanol or osmotic stresses[10] Supplementing the "wrong" amino acids can actually impair fermentation performance. Complex nitrogen sources (casamino acids, peptides) may generally be regarded as being more beneficial for fermentation performance than simple nitrogen sources such as ammonium sulphate.
See Esslinger chapter 2 for a table of amino acids in various cereal grains.
- Tomáš Vrzal, Karolína Drábková, Karel Štěrba, Jana Olšovská, Pilot sensomic study revealing the potential of amino acids to highly influence sensory properties of a lager beer, Journal of Food Composition and Analysis, 10.1016/j.jfca.2021.104028, 102, (104028), (2021).
See also[edit]
References[edit]
- ↑ Evans E. Mashing. American Society of Brewing Chemists and Master Brewers Association of the Americas; 2021.
- ↑ Pahl R, Meyer B, Biurrun R. Wort and Wort Quality Parameters. In: Bamforth CW, ed. Brewing Materials and Processes: A Practical Approach to Beer Excellence. Academic Press; 2016.
- ↑ Malting, Brewing, and Distilling J.S. Swanston, ... B.R. Gibson, in Barley (Second Edition), 2014
- ↑ a b Schwarz KJ, Boitz LI, Methner FJ. Release of phenolic acids and amino acids during mashing dependent on temperature, pH, time, and raw materials. J Am Soc Brew Chem. 2012;70(4):290–295.
- ↑ Osman AM, Coverdale SM, Onley-Watson K, Bell D, Healy P. The gel filtration chromatographic-profiles of proteins and peptides of wort and beer: effects of processing—malting, mashing, kettle boiling, fermentation and filtering. J Inst Brew. 2003;109(1):41–50.
- ↑ Lei H, Zheng L, Wang C, Zhao H, Zhao M. Effects of worts treated with proteases on the assimilation of free amino acids and fermentation performance of lager yeast. Int J Food Microbiol. 2013;161(2):76–83.
- ↑ Shopska V, Denkova-Kostova R, Dzhivoderova-Zarcheva M, Teneva D, Denev P, Kostov G. Comparative study on phenolic content and antioxidant activity of different malt types. Antioxidants. 2021;10(7):1124.
- ↑ a b Baigts-Allende DK, Perez-Alva A, Ramirez-Rodrigues MA, Palacios A, Ramirez-Rodrigues MM. A comparative study of polyphenolic and amino acid profiles of commercial fruit beers. J Food Compos Anal. 2021;100:103921.
- ↑ Gump BH, Zoecklein BW, Fugelsang KC. Prediction of prefermentation nutritional status of grape juice: The formol method. Food microbiology protocols. 2001:283-96.
- ↑ Gibson BR. 125th anniversary review: improvement of higher gravity brewery fermentation via wort enrichment and supplementation. J Inst Brew. 2011;117(3):268–284.