Non-enzymic browning reaction

E. J. Mulders, Volatile components from the non-enzymic browning reaction of the cys-teine/cystine-ribose system, Z. Lebensm. Unters. Forsch, 1973, 152, 193-201. 

K.-G. Lee and T. Shibamoto, Toxicology and antioxidant activities of non-enzymic browning reaction products Review, Food Rev. Int., 2002, 18, 151-175. 

K. Eichner, The influence of water content on non-enzymic browning reactions in dehydrated food and model systems and the inhibition of fat oxidation by browning intermediates, in Water Relations of Foods, R.B. Duckworth (ed), Academic Press, London, 1975, 417 134. 

In processed foods, non-enzymic browning reaction is the major source of its desirable flavors. Flavors of the products of this reaction depend upon the molecular structure of nitrogenous compounds (amines, amino acids, peptides, glycopeptides, proteins,... 

A contamination with several C1-C4 alkylated pyrazines, cyclopentapyrazines and pyridines was discovered in the second extracts. These compounds are described in detail as primary products of the Maillard reaction, the non-enzymic browning reaction between carbohydrates and amino acids (e.g. Mulders, 1973 Chen et al., 1998). Therefore, the occurence of these specific pyrazines and pyridines suggested either contemporary degradation processes of carbohydrates with amino acids or ammonia within the deposit landfill or the emission of waste derived Maillard products generated already before deposition. 

Initially, glucose was used as cryoprotectant however, colour problems were encountered due to the initiation of Maillard-type non-enzymic browning reactions. Sucrose was effective at the 8% level, but the resultant surimi was found to be too sweet. Currently, a combination of sucrose... 

The rate increasing influence of Cu(II) ions on the non-enzymic browning reaction between D-glucose and glycine (Maillard reaction) has been reinvestigated. At pH 3.00, melanoidin is formed which contains considerable amounts of Cu(II). In vitro experiments with model melanoidins and Cu(II) ions indicated that, in general, two protons are released for each ion bound. Melanoidins thus display the properties of acidic forms of anionic polymers. ... 

Kurata, T. Sakurai, Y. (1967). Degradation of L-ascorbic acid and mechanism of non-enzymic browning reaction. Part II. Agric. Biol Chem., 31,170-176. 

Since the non-enzymic browning of fruits and other foods is usually undesirable, much effort has been directed toward preventing the reactions which cause it. Such methods of inhibition can be classified under two headings firstly, imposition of unfavorable conditions and, secondly, addition of inhibitors. 

Saunders et al (13) reinvestigated the role of buffer salts in the non-enzymic browning, which term is also in use for the Maillard reaction. He used spectrophotometric measurement of the browning, the evolution of carbon dioxide (resulting from the Strecker degradation), and the change in the pH of the medium as the analytical techniques. The authors confirmed the findings of Schwimmer and Reynolds. 

Danehy, J.P. MailUard reactions non-enzymic browning in food systems with specific reference to the development of flavor. Adv. Food Res. 1986, 30, 77-138. 

FIGURE 11.9 Reaction of aldose with amino compound to give an aldosylamine (R, = (CH0H)4CH20H). (From Hurst, D.T., Recent developments in the study of non-enzymic browning and its inhibition by snl-phur dioxide, B.F.M.I.R.A. Scientific and Technical Surveys, No. 75, Leatherhead, England, U.K., 1972. With permission.)... 

The Maillard reaction (non-enzymic browning) is prevented by the addition of sulphur dioxide, either as the gas or as sulphite. Packaging that reduces the loss of SO2 due to oxidation or permeation (Davis et al., 1973) can decrease the need for this additive. 

Heterocyclic compounds are formed mainly in non-enzymatic browning reactions, especially in food surface layers during the thermal processing of foods by baking, frying and roasting. They also arise by pyrolysis of proteins, carbohydrates, lipids and other food components some heterocyclic compounds result from reactions catalysed by enzymes. 

Roos YH, JouppUa K, Zielasko B. Non-enzymic browning-induced water plasticization glass transition temperature depression and reaction kinetics determination using DSC. J Therm Anal 1996 47(5) 1437-1450. 

Non-cytochrome P450 enzymes may also be involved in oxidative reactions. One such enzyme is alcohol dehydrogenase whose substrates include vitamin A, ethanol, and ethylene glycol. Aldehyde dehydrogenase is another enzyme. Most reduction reactions also involve microsomal enzymes, with the exception of ketone reduction. Nitro compounds are reduced to amines and volatile anesthetics undergo dehalo-genation by microsomal enzymes. Hydrolysis reactions are involved in metabolism of compounds with amide bonds or ester linkages, as in the conversion of aspirin to salicylate (Brown, 2001). 

The Maillard reaction is best known as the phenomenon responsible for the browning of untreated foodstuffs, by non-enzymic oxidation. It involves the condensation of amino acids on sugars, both aldoses (glucose) and ketoses (fructose) (Figure 8.27). When aldoses are involved, the primary condensation products are aldimines (Rj = H) (or Schiff base), while ketoses produce ketimine (Ri H). Due to their enoliz-able character, these imines develop according to two tautomeric equilibriums into enaminol and... 

Fig. 8.27. Maillard reaction involved in the non-enzymic oxidative browning of plant tissues, (a) Formation of an imine by an amino acid reacting with an aldose (Ri = H) or ketose (Ri H). (b) Enolization of the imine to enaminol, then to an Amadori (Ri = H) or Heyns (Ri H) intermediate, (c) Breaking of the preceding intermediates, with the appearance of a reductone in redox equilibrium with an a-dicarbonylated compound, responsible for the non-enzymic oxidation phenomenon...

Phenolic compounds are also involved in the enzymatic and non-enzymatic browning of food products. The occurrence of browning reactions is often disadvantageous in the majority of fruit processing operations. Chlorogenic acid and catechin serve as the principal substrates for the phenolase complex that is responsible for the enzymic browning exhibited by many fruits and vegetables. 

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