Maillard reaction

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 and a Maillard reaction product (and used in dyes). Similar to toluene and ethylbenzene, syrene is also released during food decaying processes[5] (as in spoiled salmon[6]). Environmentally, commercially manufactured polystyrene nanoparticles are taken up by algae and accumulate in fish, resulting in weight loss and altered cholesterol distribution[7], though may be eliminated within bile.[8] Chronic exposure causes remodelling of the intestinal villi[9] and structural changes in apolipoproteins.[10] The testis may be the major target for styrene toxicity.[11] In rats, prenatal low level exposure to estrogenic styrene trimers obstructed genital organ development, and disrupted the endocrine systems of male rat offspring.[12]

Similar to bisphenol A and phthalates, plastic drink containers[13]] and plastic liners in cans and other packages[14] 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.[15] Migration of styrene from disposable cups (styrofoam and PS, not paper cups) into drinks highly depends on fat content and temperature of drinks.[16] Butter[17], yoghurt[18], Olives and olive oil may also contain styrene.[19] Blue-cheese fungi (eg Gorgonzola, camembert[20]) also produce styrene, as well as the plastics used for packaging.[21] Due to gram-negative bacteria in dairy, all raw milk cheeses also contain styrene (and o-dichlorobenzene; a derivative of benzene).[22] Cinnamon constituents naturally contain the styrene structure (incl. cinnamic acid[23]), which may get released due to the activity of fungal species present on cinnamon.[24] Total daily styrene exposure is estimated at maximally 0.17 mcg/kg bw[25] and human lifetime risk for tumors is estimated to be very low.[26]

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.[27]

Acetamide

Amides are derivates of ammonia or (carboxylated) amines. Acetamide is a carcinogenic derived from acetic acid, by dehydrating ammonium acetate[28], or by hydrolysis of acetonitrile[29]. Thermal degradation (>200°C) of chitin also yields acetamide.[30] Chitin is a good inducer for defense mechanisms in plants[31], 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.[32]

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