Maillard Reaction Products in Different Types of Brewing Malt

Abstract

Individual Maillard reaction products (MRPs), namely, free and protein-bound glycated amino acids as well as dicarbonyl compounds, were quantitated in various types of brewing malt using chromatographic means. Among the protein-bound glycated amino acids, which were analyzed following enzymatic hydrolysis, N-ε-fructosyllysine was the dominating compound in light (EBC < 10) and dark (10 < EBC < 500) malts, accounting for up to 15.9% of lysine derivatization, followed by N-ε-maltulosyllysine (light malts, up to 4.9% lysine derivatization) or pyrraline (dark malts, up to 10.4% lysine derivatization). Roasting of malt led to the degradation of most of the protein-bound glycated amino acids. The same trends were visible for free glycated amino acids. A novel MRP-derived Strecker aldehyde, namely, 5-(2′-formyl-5′-hydroxymethylpyrrol-1′-yl)-pentanal (pyrralinal), was detected in dark malt. The most abundant 1,2-dicarbonyl compound in malt samples was 3-deoxyglucosone (up to 9 mmol/kg), followed by 3-deoxymaltosone (up to 2 mmol/kg). Only few MRPs such as 5-hydroxymethylfurfural, furfural, the dicarbonyl compounds glyoxal, methylglyoxal, and diacetyl as well as protein-bound rhamnolysine and MG-H1 correlated with the malt color. A comparison of MRPs present in malt with corresponding amounts in beer points to neoformation of MRPs such as MG-H1 and 3-deoxygalactosone during the brewing process.

The post-translational modification landscape of commercial beers

“…Roasted malts are roasted at high temperatures after kilning to imbue them with dark colours and rich flavours 1 . This roasting process should cause most glycated amino acids that were formed during kilning to be degraded, resulting in very little glycation on either free amino acids or proteins 20 . However, these dark beers should still contain substantial amounts of pale malt, and it is therefore unclear why this is not reflected in the presence of glycation in their glycoproteomes.…”

The post-translational modification landscape of commercial beers

“…Roasted malts are roasted at high temperatures after kilning to imbue them with dark colours and rich flavours (1). This roasting process should cause most glycated amino acids that were formed during kilning to be degraded, resulting in very little glycation on either free amino acids or proteins (20). However, these dark beers should still contain substantial amounts of pale malt, and it is therefore unclear why this is not reflected in the presence of glycation in their glycoproteomes.…”

“…The reaction forms a reactive Schiff’s base which undergoes Amadori rearrangement, producing intermediates with highly reactive carbonyl groups, α-dicarbonyls, like glyoxal, methylglyoxal, and 3-deoxylglucosone (19–21). These α-dicarbonyl compounds can react with amino acids and proteins forming stable advanced glycation end products (AGEs) (20, 21). AGEs are important in contributing to malt and beer flavour and colour (19).…”

“…This involves the reaction of an aldehyde group of a reducing sugar such as glucose with an amine group in a protein, such as the N-terminus or internal Lys or Arg (19). The reaction forms a reactive Schiff's base which undergoes Amadori rearrangement, producing intermediates with highly reactive carbonyl groups, α-dicarbonyls, like glyoxal, methylglyoxal, and 3deoxylglucosone (19)(20)(21). These α-dicarbonyl compounds can react with amino acids and proteins forming stable advanced glycation end products (AGEs) (20,21).…”

“…AGEs are important in contributing to malt and beer flavour and colour (19). Kilning during the malting process leads to the production of AGEs (20, 21), which may also continue during the mash and boil (10, 22, 23).…”