The Chemistry of Nitrosamine Formation: Relevance to Malting and Brewing

Abstract

This paper reviews the chemistry of nitrosamine formation with special reference to malting and brew ing. Whilstthe main emphasisison the formation of nitrosodimethylamine(NDM A), the chemistry is also related to the formation of other nitrosamihes and certain other nitrocompounds. It seems likely that in malting and brewing the only important source of the nitroso group is the mixture of oxides of nitrogen (NO,) in the hot air in contact with malt during kilning. Under normal commercial conditions there appears to be little if any formation of nitrosamines at other stages of malting or brewing.It is suggested that much of the nitrosation is due to NO, which exists temporarily in the form of nitro gen trioxide (N2O3) and nitrogen tetroxide (N2O4) as it dissolves in water in the moist malt or in malt lipids. The dissolved NO, subsequently reaches equilibrium with nitrite and nitrate ions formed from it. The origin of the dimethylamine portion of the NDMA is still not clear. The most likely sources are free DMA, gramine and hordenine, all of which are produced in germinating barley. On balance it seems that hordenine is the most important source of NDMA in the malt at the end of kilning. The reasons for the low yield of nitrosamines from the precursors and NO, present during kilning are discussed and related to the formation of other nitroso-and nitro-compounds. The occurrence of competing reactions which reduce nitrosamine formation is also described.

N-nitrosamines in 21^th Century

“…Podle atomu, na který je tato skupina vázána, lze dále rozlišovat C-, N-, S-a O-nitroso sloučeniny. Tyto látky mohou vznikat přímým působením nitrosačních činidel na příslušné prekurzory nebo prostřednictvím transnitrosač-ních reakcí, kdy je nitroso skupina přesunuta z jedné molekuly na jinou (Wainright, 1986a). Nejvýznamnějšími nitrososloučeninami v potravinářství jsou N-nitrososloučeniny, konkrétně N-nitrosaminy.…”

“…They can be further divided into C-, N-, Sand O-nitroso compounds. These substances are formed by direct reaction of nitrosating agents with appropriate precursors or by transnitrosation reactions, in which the nitroso groups are transferred from one molecule to another (Wainright, 1986a). N-nitroso compounds, especially N-nitrosamines, are the most important nitroso compounds in food industry.…”

“…Dalším významným prekurzorem N-nitrosaminů je kreatin, který se rozkládá na aminokyselinu sarkosin. Ten může být následně nitrosován (Wainright, 1986a) a jak již bylo výše uvedeno, může být termálně dekarboxylován na NDMA.…”

“…Another precursor is creatine, which is decomposed to the amino acid sarcosine. Sarcosine can then be nitrosated (Wainright, 1986a) and thermally decarboxylated into NDMA.…”

Possible Reactions of Dietary Phenolic Compounds with Salivary Nitrite and Thiocyanate in the Stomach

“…In the stomach, nitrite is protonated producing nitrous acid (pKa = 3.3), an oxidizing and nitrosating agent, to react with food components. It is well known that nitrous acid can transform amines into carcinogenic compounds nitrosoamines [10], and it has been reported that phenolic compounds can reduce nitrous acid to a functional compound nitric oxide ( • NO) [11,12]. The functions of • NO produced in the gastric lumen include the increase in gastric mucosal blood flow, the increase in gastric mucus thickness, and the relaxation of gastric smooth muscle [13][14][15][16].…”