Melanoidins
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Melanoidins, which consist of tan and brown compounds, are formed via Maillard reactions during kilning, mashing and wort boiling and have been detected in beer.8 Melanoidins play an important role in the formation of color, aroma and flavor, foam stability and can influence the oxidation–reduction processes of beer due to their strong antioxidant properties and other biological effects.[1]
Melanoidins formed as a result of heat treatment of the malt made from reductive sugars and amino acids or proteins contribute to the forming of the antioxidative activity of worts and the final beers [16–18]. Colored macromolecules formed in the final stage of the Maillard reaction are subjected to a number of studies consequential to their interesting biological properties and unknown chemical structure [19]. Melanoidins positively affect antioxidative abilities of food products, as well as storage stability. The mechanism of their antioxidative activity relies on the ability to break chain reactions of radicals, chelation of metals, H 2 O 2 reduction and scavenging of free radicals [16,17]. Melanoidins, apart from their antioxidative properties, also demonstrate antiviral and antimutagenic activity, and the ability to reduce cholesterol levels and stimulate growth of intestinal bacteria. However, some of the compounds, formed during early stages of the Maillard reaction process, are considered carcinogenic and mutagenic. Therefore, it is difficult to explicitly decide which of the activities are dominant [20,21]. One of the compounds formed during the heating of the malt is 5-hydroxymethylfurfural (HMF), which is also formed during thermal treatment of food, e.g., malt, dried fruit, fruit juices, coffee, bread or vinegar. Toxic effects of HMF consumption have been proved after receiving a dose of 75 mg/kg of body weight [22].[2] Compared to other food products, the HMF content in beer is relatively low.
During roasting, the main chemical reactions are the Maillard reactions. These are a series of changes initiated by the reaction between reducing sugars and amino groups, leading to the formation of compounds responsible for the color and flavor of heat-treated products. The non-enzymatic browning reactions can be divided into several stages. In the first of them, the early phase reaction products are created. They are mainly products of the Amadori rearrangement. The second step involves the formation of intermediates such as: HMF, Strecker aldehydes and pyrazines. The last, third stage is the formation of the melanoidins, which are reaction end products [39]. Melanoidins are a group of compounds with a very diverse structure. They differ in chemical properties depending on the origin. Melanoidins give beer its color and provide it with antioxidant activity [40].[2]
An increase of melanoidins fosters the Strecker degradation of amino acids and the oxidation of alcohols.[3]
Melanoidins are macromolecular, nitrogenous and brown colored products of Maillard reactions, which are formed during the malting and brewing process.[4]
- Carvalho, D.O.; Correia, E.; Lopes, L.; Guido, L.F. Further insights into the role of melanoidins on the antioxidant potential of barley malt. Food Chem. 2014, 160, 127–133.
References
- ↑ Zhao H, Li H, Sun G, Yang B, Zhao M. Assessment of endogenous antioxidative compounds and antioxidant activities of lager beers. J Sci Food Agric. 2013;93(4):910-917.
- ↑ a b Gąsior J, Kawa-Rygielska J, Kucharska AZ. Carbohydrates profile, polyphenols content and antioxidative properties of beer worts produced with different dark malts varieties or roasted barley grains. Molecules. 2020;25(17):3882.
- ↑ Narziss L. Technological factors of flavour stability. J Inst Brew. 1986;92:346–353.
- ↑ Martinez-Gomez A, Caballero I, Blanco CA. Phenols and melanoidins as natural antioxidants in beer. Structure, reactivity and antioxidant activity. Biomolecules. 2020;10(3):400.