Maillard reaction

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Revision as of 15:51, 18 December 2012 by RRM (talk | contribs) (Styrene)

The Maillard reaction is responsible for many colors and flavors in foods, in combination with other processes. The heat-induced reaction of amino groups of amino acids, peptides, and proteins with carbonyl groups of reducing sugars such as glucose results in the concurrent formation of so-called Maillard browning products, such as heterocyclic amines (HCAs), acrylamides, melanoidins (food-browning), Pent-4-en-1-amine, Styrene, Acetamide, Chloropropanols and Furan, which are all present in cooked foods.

Various reducing sugars vary in reactivity. Pentoses are more reactive than hexoses, which are more reactive than disaccharides.

  • Pentoses: Arabinose, xylose, lyxose, ribose, ribulose, xylulose (a pentosan is a polymere of pentoses)
  • Hexoses: Glucose, fructose, mannose, galactose, allose, altrose, gulose, idose, talose, sorbose, tagatose, psicose (a hexosan is a polymere of hexoses)
  • Disaccharides: Sucrose (glucose-fructose), lactose (galactose-glucose), maltose (glucose-glucose), etc.

Styrene

Styrene is considered the phenylalanine-glucose counterpart of acrylamide (instead of asparagine-glucose). In the presence of sugars, phenylalanine, similarly to asparagine and lysine, can undergo carbonyl-assisted decarboxylative deamination reaction to generate styrene[1]. Styrene is metabolized / activated in the human body to genotoxic styrene-7,8-oxide (SO).[2] SO is neurotoxic (synergistically with acrylamide).[3] Phenylalanine heated together with 1-hydroxyacetone or methylglyoxal yielded only 0.03 mol% styrene.[4]

Styrene is a polycyclic aromatic hydrocarbon (PAH), formed during incomplete combustion of organic compounds (as in cigarette smoke[5]) and a Maillard reaction product (and used in dyes). Similar to toluene and ethylbenzene, syrene is also released during food decaying processes[6] (as in spoiled salmon[7]). Styrene is not carcinogenic.[8] Environmentally, commercially manufactured polystyrene nanoparticles are taken up by algae and accumulate in fish, resulting in weight loss and altered cholesterol distribution[9], though may be eliminated within bile.[10] In rats, prenatal styrene exposure decreases postnatal serotonine and catecholamine levels in the brain.[11] Chronic exposure causes remodelling of the intestinal villi[12] and structural changes in apolipoproteins.[13] The testis may be the major target for styrene toxicity.[14] In rats, prenatal low level exposure to estrogenic styrene trimers obstructed genital organ development, and disrupted the endocrine systems of male rat offspring.[15]

Similar to bisphenol A and phthalates, plastic drink containers[16]] and plastic liners in cans and other packages[17] are a source of styrene exposure. Bottled drinking water may contain styrene (up to 29.5 mcg/L; increased to 69.53 mcg/L after 1 yr storage) leached from the polystyrene (PS) bottle.[18] Migration of styrene from disposable cups (styrofoam and PS, not paper cups) into drinks highly depends on fat content and temperature of drinks.[19] Butter[20], yoghurt[21], Olives and olive oil may also contain styrene[22], as the migration of styrene from packaging material very much depends on fat-contents of the liquid/food (and temperature).[23] Blue-cheese fungi (eg Gorgonzola, camembert[24]) also produce styrene, as well as the plastics used for packaging.[25] Due to gram-negative bacteria in dairy, all raw milk cheeses also contain styrene (and o-dichlorobenzene; a derivative of benzene).[26] Cinnamon constituents naturally contain the styrene structure (incl. cinnamic acid[27]), which may get released due to the activity of fungal species present on cinnamon.[28] Total daily styrene exposure is estimated at maximally 0.17 mcg/kg bw[29] and human lifetime risk for tumors is estimated to be very low.[30] In another study the daily styrene exposure is estimated to range from 18.2 to 55.2 mcg per person (roughly 0.2 to 0.8 mcg/kg bw) with the greatest proportion coming from inhaled styrene (exhaust fumes, cigarette smoke, indoor heating).[31]

Pent-4-en-1-amine

Is considered the lysine-glucose counterpart of acrylamide (instead of asparagine-glucose). In the presence of sugars, lysine, similarly to asparagine and phenylalanine, can undergo carbonyl-assisted decarboxylative deamination reaction to generate pent-4-en-1-amine. Alternatively, decarboxylation of lysine generates cadaverine (1,5-diaminopentane) followed by deamination to form pent-4-en-1-amine.[32]

Acetamide

Amides are derivates of ammonia or (carboxylated) amines. Acetamide is a carcinogenic derived from acetic acid, by dehydrating ammonium acetate[33], or by hydrolysis of acetonitrile[34]. Thermal degradation (>200°C) of chitin also yields acetamide.[35] Chitin is a good inducer for defense mechanisms in plants[36], and present in fungi, the exoskeletons of crustaceans such as crabs, lobsters and shrimps, in mollusks, and in the internal shells of squid and octopus. Acetamide is also a byproduct of thermochemical treatment of lignocellulosic biomass.[37]

Chloropropanols

3-monochloropropane-1,2-diol (3-MCPD) is a chloropropanol.

Furan

(Fur)furan (5-oxacyclopenta-1,3-diene or 1,4-epoxy-1,3-butadiene) is a toxic heterocyclic organic compound, readily converted to other compounds. Furan is present in coffee, canned and jarred food, and baby food.

  • 5-hydroxymethylfurfural
  • furosine