Styrene
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Styrene, present in wheat beer, is a vinyl aromatic phenol formed by decarboxylation of free cinnamic acid (a phenolic acid). Styrene is undesired in all foods due to its toxicological relevance and its classification as "possibly carcinogenic to humans" (group 2B) by the International Agency for Research on Cancer (IARC).[1] Styrene concentrations tend to positively correlate with concentrations of the key odorants 2-methoxy-4-vinylphenol (4-vinylguaiacol) and 4-vinylphenol in commercial wheat beers because they are produced via the same patahway from the respective phenolic acid precursors.
Cinnamic acid is decarboxylated either thermally or enzymatically during the brewing process, producing styrene. Styrene, in pure form, is a sweet-smelling volatile liquid, although it does not contribute significantly to beer flavor. The International Agency for Research on Cancer (IARC) has categorized styrene, with a temporary acceptable daily intake (ADI) of 0.4 µg/kg BW, as a probable human carcinogen (group 2B). The temporary ADI styrene is viewed as potentially harmful to human health due to the metabolized styrene-7.8-oxide causing DNA adducts. A carried out screening showed that the determined cinnamic acid concentration in full kettle wort of various wheat beers was between 75 and 375 µg/L and therefore below the average amount of ferulic acid and p-coumaric acid. In comparison, concentrations of up to 25 µg/L of styrene were found in wheat beer.[2]
Contained in the grain, cinnamic acid is released during the mashing process along with ferulic and p-coumaric acid. On the contrary, cinnamic acid is decarboxylated either thermally or enzymatically during the brewing process; however, it is metabolized to styrene, which does not contribute to the total flavor of wheat beer.[2]
The evaluation of styrene formation demonstrated that the enzymatic decarboxylation and cinnamic acid conversion starts immediately after pitching and it is very fast during the first hours of fermentation. The enzymatic conversion was also dependent on the concentration and on fermentation management and temperature (Schwarz et al., 2012a).[3]
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References[edit]
- ↑ Langos D, Granvogl M. Studies on the simultaneous formation of aroma-active and toxicologically relevant vinyl aromatics from free phenolic acids during wheat beer brewing. J Agric Food Chem. 2016;64(11):2325–2332.
- ↑ 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.
- ↑ Carvalho DO, Guido LF. A review on the fate of phenolic compounds during malting and brewing: technological strategies and beer styles. Food Chem. 2022;372:131093.