Ferulic acid
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Ferulic acid, the main phenolic acid in barley and wheat malts, is ester-bound to arabinoxylans (in a constant arabinose : FA ratio). Feruloylated arabinoxylans are present in all parts of the grain, mainly in the aleurone layer (75%) and the endosperm. Only a minor part of ferulic acid (shown to be an effective antioxidant) is present in malts in free forms. Malting and mashing result in a limited release of free ferulic acid from arabinoxylans (by the enzyme deferuloylase).[1][2]
Ferulic acid is the main phenolic acid found in beers, representing between 48 and 58% of the total phenolic acids. It is present in barley, and approximately 10% in free form and the rest connected in the ester form with arabinoxylated polymers.[3]
Walters et al. showed that ferulic acid has greater antioxidant activity than catechin in the presence hydroxyl radical, in addition to being more effective in preventing of lipid oxidation. However, catechin showed greater sequestering activity of superoxide radicals.[3]
The ferulic acid (4.131) liberated is a potential anti-oxidant and if decarboxylated during boiling or by bacteria or pof+ yeast strains, gives rise to 4-vinyl guaiacol, a strongly flavored substance that is undesirable in most beers.[2]
The maximal release of FA occurs in the range of 45-50°C. Within the range of 25 to 60°C, a longer mashing-in time leads to a higher detachment of ferulic acid. Above 65°C, the mashing-in time has no more influence on the release. In this temperature range, most of the FA degrading enzymes are denatured. Consequently, the released amount of ferulic acid corresponds with the unbound water-soluble fraction in malt.[4]
The maximal release of free FA occurs at 40°C and pH of 5.8, and the level reaches a plateau after around 2 hours, although the mash reaches a maximal level only after temp is increased to 65°C or higher in order to extract the remaining water-soluble portion.[5] Even at optimal enzyme activity, no more than ~23% of the total wort FA is extracted. Within the optimal ranges of cinnamoyl esterase, stirring the mash significantly increases the extraction of ferulic acid because stirring increases the amount of arabinoxylan extraction.
The flavor threshold of 4VG in blond specialty beers is 370 ppb.[5]
Rye appears to have much higher levels of ferulic acid compared to barley and other grains.[4] Contrary to popular belief, wheat malt has a lower amount than barley malt.
Results of McMurrough et al. (88) suggested the release of ferulic acid through enzymatic hydrolysis of arabinoxylan during both malting and mashing. Levels of ferulic acid in barley have been reported to vary from 365 to 605 µg/g (130). Humberstone and Briggs (65,66) showed that the ferulic acid esterase activity level increased during the first 3 days of germination and remained high.[6]
ferulic acid (FA) is generally a flavor-inactive phenolic acid, having a flavor threshold in beer as high as 600 ppm.[5]
the content of each phenolic acid increases during kilning up to 80°C. Above 80°C, the content of hydroxycinnamic acids decreases. The phenolic acid content increases during kilning up to 80°C, which was partly attributed to the enhanced extractability of the drying tissue and partly to enzymatic release. During malting, phenolic acids are partly released due to the degradation of complex barley components.[7] However, cinnamoyl esterases, which are able to release hydroxycinnamic acids from cinnamoylated saccharides, have also been found in barley and barley malt.
- Graf, E. Antioxidant potential of ferulic acid. Free Radic. Biol. Med. 13:435-448, 1992.
- Kikuzaki, H., Hisamoto, M., Hirose, K., Akiyama, K., and Taniguchi, H. Antioxidant properties of ferulic acid and its related compounds. J. Agric. Food Chem. 50:2161-2168, 2002.
See also
References
- ↑ Szwajgier D. Dry and wet milling of malt. A preliminary study comparing fermentable sugar, total protein, total phenolics and the ferulic acid content in non-hopped worts. J Inst Brew. 2011;117(4):569–577.
- ↑ a b Briggs DE, Boulton CA, Brookes PA, Stevens R. Brewing Science and Practice. Woodhead Publishing Limited and CRC Press LLC; 2004.
- ↑ a b Siqueira PB, Bolini H, Macedo GA. O processo de fabricação da cerveja e seus efeitos na presença de polifenóis. (The beer manufacturing process and its effects on the presence of polyphenols.) Alimentos e nutrição. 2008;19(4):491–498.
- ↑ 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.
- ↑ a b c Vanbeneden N, Van Roey T, Willems F, Delvaux F, Delvaux FR. Release of phenolic flavour precursors during wort production: Influence of process parameters and grist composition on ferulic acid release during brewing. Food Chem. 2008;111(1):83–91. Cite error: Invalid
<ref>tag; name "vanvan" defined multiple times with different content - ↑ Egi A, Speers RA, Schwarz PB. Arabinoxylans and their behavior during malting and brewing. Tech Q Master Brew Assoc Am. 2004;41(3):248–267.
- ↑ Cite error: Invalid
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