Food, heterocyclic compounds

The importance of the penicillins as a class of heterocyclic compounds derives primarily from their effectiveness in the treatment of bacterial infections in mammals (especially humans). It has been estimated that, in 1980, the worldwide production of antibiotics was 25 000 tons and, of this, approximately 17 000 tons were penicillins (81MI51103). The Food and Drug Administration has estimated that, in 1979 in the U.S.A., 30.1 x 10 prescriptions of penicillin V and 44.3 x 10 prescriptions of ampicillin/amoxicillin were dispensed. This level of usage indicates that, compared to other methods of dealing with bacterial infection, the cost-benefit properties of penicillin therapy are particularly favorable. Stated differently, penicillin treatment leads to the elimination of the pathogen in a relatively high percentage of cases of bacterial infection at a relatively low cost to the patient in terms of toxic reactions and financial resources. 

Kirk-Othmer. 1966. Kirk-Othmer encyclopedia of chemical technology. 2nd ed. Vol. 10. Food additives to heterocyclic compounds. New York, NY ... 

This approach utilizes various computer programs which, when provided with an appropriate input (starting materials, reaction conditions), can generate structures of chemical compounds which can be potentially formed from their respective precursors. The information can be of help to food chemists in their search for various new, hitherto unidentified heterocyclic compounds in food flavors (55,56). 

As mentioned before, the sensory properties of the various heterocyclic compounds discussed in this contribution are one of the important factors determining food quality. The data on sensory characteristics of the various numerous compounds formed through the reaction of aldehydes with ammonia or ammonium sulfide, in the presence or in the absence of acetoin, are scattered in the literature (57) and thus are not easy to find. At the same time, information on sensory characteristics of compounds of this type is of primary importance to food chemists. Sultan (29) has compiled much of this information which is presented here in Table IV where also the appropriate references to the original literature are given. 

Many heterocyclic compounds have found a use in the area of veterinary medicine where the growth in the world requirement for animal food products and increasing economic pressures make it essential for the farmer to produce animals as efficiently and as cheaply as possible. 

Oxidation of the lipid structure in foods containing oils and fats produces carbonyl compounds which are responsible for the flavor and odor associated with rancidity (B-81MI11508) the use of a suitable antioxidant can delay this process. Several heterocyclic compounds are among the antioxidants suitable for use in food ascorbic acid (69) and certain of its derivatives and erythorbic acid. The quinoline derivative (70) is mainly used as an antioxidant in animal feed, but it can also be used to preserve the color of paprika, chili powder and ground chili. 

Mottram, D.S. 1985. The effect of cooking conditions on the formation of volatile heterocyclic compounds in pork. J. Sci. Food Agric. 36 377-382. 

Heterocyclic compounds as meat volatiles have been reviewed recently by Ohloff and Flament (23) and by Shibamoto (24) More comprehensive coverage of these constituents as food flavorants is currently being published (Vernin, 25). 

Vernin, G. "Heterocyclic Compounds and Their Precursors in Food Aroma," 1982 Ellis Harwood Ltd. ... 

Scheme I. Formation of heterocyclic compounds in food products. (Reprinted with permission from ret 4. Copyright 1982 Ellis Horwood Limited.)...

Heterocyclic compounds are primarily formed through non-enzymatic browning reactions. Recent studies of deep-fat fried food flavors led to the identification of pyrazines, pyridines, thiazole, oxazoles and cyclic polysulfides which had long-chain alkyl substitutions on the heterocyclic ring. The involvement of lipid or lipid decomposition products in the formation of these compounds could account for the long-chain alkyl substitutions. Model systems were used to study the participation of lipids in the formation of pyrazines, pyridines, thiophenes and cyclic polysulfides. 

More than 10,000 compounds have been identified as volatiles of foods. Of these, heterocyclic compounds are an important class, be cause of their exceptional sensory properties (1). Heterocyclic compounds contain one or more heteroatoms (0, S and/or N) in rings or fused ring systems. 

The majority of heterocyclic compounds are formed through thermal interactions of reducing sugars and amino acids, known as Maillard reactions. Other thermal reactions such as hydrolytic and pyrolytic degradation of food components (e.g. sugars, amino acids and vitamins) and the oxidation of lipids also contribute to the formation of heterocyclic compounds responsible for the complex flavor of many foodstuffs. 

Interest in the influence of lipids on pyrazine formation has recently been generated by the identification of long-chain alkyl-substituted heterocyclic compounds in foods and in model systems. Pyrazines in this category include 2-heptylpyrazine isolated from french fried potato flavor (7), and 2-methyl-3(or 6)-pentylpyrazine and 2,5-dimethyl-3-pentylpyrazine, isolated from extruded zein/corn amylopectin/corn oil systems (8, 9). Only the involvement of lipids or lipid-decomposition products in the formation of these compounds could account for the long-chain alkyl substitution on the pyrazine ring. 

The thermal interaction between 2,4-decadienal and cysteine was selected as a model for lipid-protein interaction. 2,4-Decadienal is the major degradation product of linoleic acid and cysteine is a sulfur-containing amino acid in foods. Some heterocyclic compounds identified in the reaction mixture of 2,4-decadienal and cysteine are listed in Table I. 

Heterocyclic compounds, especially those which contain nitrogen and sulfur atoms, possess potent sensory qualities at low concentrations. They are formed in foods by thermal decomposition and interaction of food components. The identification of many long-chain alkyl-substituted heterocyclic compounds suggests that their formation mechanisms directly involve lipids or lipid decomposition products. 

The Maillard reaction has received much attention since the 1950 s as the source of flavor chemicals in cooked foods. Numerous compounds produced by this reaction have been reported in the last two decades. The major flavor chemicals are nitrogen- and sulfur-containing heterocyclic compounds. For example, nitrogen-containing pyrazines contribute a characteristic roasted or toasted flavor to cooked foods. Sulfur-containing thiophenes and thiazoles give a characteristic cooked meat flavor. A striking property of these compounds is their extremely low odor thresholds. 

In heated foods the main reactions by which flavors are formed are the Maillard reaction and the thermal degradation of lipids. These reactions follow complex pathways and produce reactive intermediates, both volatile and non-volatile. It has been demonstrated that lipids, in particular structural phospholipids, are essential for the characteristic flavor development in cooked meat and that the interaction of lipids with products of the Maillard reaction is an important route to flavor. When model systems containing amino acids and ribose were heated in aqueous buffer, the addition of phospholipids had a significant effect on the aroma and on the volatile products. In addition a number of heterocyclic compounds derived from lipid - Maillard interactions were found. The extent of the interaction depends on the lipid structure, with phospholipids reacting much more readily than triglycerides. 

Lipids play an important part in the development of aroma in cooked foods, such as meat, by providing a source of reactive intermediates which participate in the Maillard reaction. Phospholipids appear to be more important than triglycerides. The addition of phospholipid to aqueous amino acid + ribose mixtures leads to reductions in the concentrations of heterocyclic compounds formed in the Maillard reaction. This effect could be due to lipid oxidation products reacting with simple Maillard intermediates, such as hydrogen sulfide and ammonia, to give compounds not normally found in the Maillard reaction. The precise nature of the odoriferous products obtained from lipid - Maillard interactions is dictated by the lipid structure and may depend on the fatty acid composition and the nature of any polar group attached to the lipid. 

Of the different types of lipids in foods, the phospholipids, being more unsaturated, are particularly important in relation to aroma formation in meat.151 The aroma of cooked meat was not affected by the prior extraction of triglycerides with hexane, but the use of a more polar solvent (chloroform-methanol), which extracts all lipids, including phospholipids, resulted, after cooking, in the replacement of the meaty aroma by a roast or biscuit-like one. This was reflected in the volatiles, the dominant aliphatic aldehydes and alcohols being replaced by alkylpyrazines. This implies that the participation of the lipids in the Maillard reactions inhibited the formation of heterocyclic compounds. 

F. B. Whitfield, D. S. Mottram, S. Brock, D. J. Puckey, and L. J. Salter, Effect of phospholipid on the formation of volatile heterocyclic compounds in heated aqueous solutions of amino acids and ribose, J. Sci. Food Agric., 1988, 42, 261-272. 

G. Vemin and Vernin, Genevieve. Heterocyclic aroma compounds in foods occurrence and organoleptic properties, in Chemistry of Heterocyclic Compounds in Flavours and Aromas, G. Vernin and C. Parkanyi (eds), Ellis Horwood, Chichester, 1982, 92-97. 

M. Sakaguchi and T. Shibamoto, Formation of heterocyclic compounds from the reaction of cysteamine and D-glucose, acetaldehyde, or glyoxal, J. Agric. Food Chem., 1978, 26, 1179-1183. 

G. Vernin, Recent progress in food flavors the role of heterocyclic compounds, Ind. Alim. Agric., 1980, 97, 433 149. 

K. Yanagimoto, K. G. Lee, H. Ochi, and T. Shibamoto, Antioxidant activity of heterocyclic compounds found in coffee volatiles produced by Maillard reaction,./. Agric. Food Chem., 2002, 50, 5480-5484. 

Sulfur Heterocyclics. Sulfur containing compounds (thiols, thiophenes, thiazoles,. .. etc.) play a major role in the flavor of raw and processed foods. These compounds have characteristic flavor notes and the flavor thresholds are mostly low. Several reviews (ill, 112, 113) demonstrate the important role of sulfur compounds in food flavors. Organoleptic properties of these compounds may be pleasant, strong nut-like odor of U-methyl-5-vinylthiazole which is present in cocoa (llU) objectionable pyridine-like odor of thiazole (115) quinoline-like odor of benzothia-zole (ll6) strong tomato leaf-like odor of isobutylthiazole (117) and bread crust flavor of acetyl-2-thiazoline (ll8). A mixture of oxazoles, thiazoles, thiazolines, imidazoles, trithiolanes and... 

Alessandra Napolitano graduated in chemistry in 1984 at the University of Naples Federico II under the guidance of Prof. G. Prota. In 2001 she was made associate professor of organic chemistry. Her main research interests lie in the field of heterocyclic compounds, with special reference to hydroxyindoles and benzothiazines, oxidative chemistry of phenolic natural products, food chemistry, lipid peroxidation, and analytical chemistry. Currently, she is involved in several research projects dealing with the chemistry of natural pigments, including pheomelanins, and the chemical basis of diseases. 

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