Lipid oxidation interactions

SEVERINI c and lerici c r (1995) Interaction between Maillard reaction and lipid oxidation in model systems during high temperature treatment , Ital J Food Sci, 1 (2) 189-96. 

Interaction of lipid oxidation products and amino compounds. Amino acids and primary amines may be involved in other reactions which could lead to the formation of compounds having the potential to undergo N-nitrosation. Malonaldehyde, produced as a result of oxidation of lipids, particularly polyunsaturated fatty acids, has been shown to react with amino acids to produce... 

Food flavor is governed by many factors, including lipid oxidation and protein degradation. Enzyme-catalyzed oxidation ( ) and autoxidation (2) can substantially alter the flavor q ality of foods. In "addition, protein degradation, whether caused by enzymes, heat, or interactions with other compounds, can also affect flavor characteristics of certain foods (3, 4, ... 

The importance of direct gas chromatography and combined direct GC/MS to the food industry is demonstrated by the analysis of volatile flavor components and contaminants in experimental samples of rice, food blends, and raw and roasted peanuts. By examining these samples, we are able to investigate flavor systems that are probably associated with lipid oxidation, thermal degradation of protein, or protein interactions with other compounds. 

The often conflicting reports in the literature indicate that more research is needed to clarify the role of interacting enzyme systems that control the generation and survival of active forms of oxygen and their involvement in the initiation and propagation of lipid oxidation in milk. 

Oxidation results from the interactions between atmospheric oxygen and the double bonds of unsaturated fatty acids. Several parameters can catalyze lipid oxidation, while others can prevent or slow down the reactions. Metals, light, moisture and heat can all enhance oxidation, while antioxidant compounds (e.g., BHT and vitamin E) can be utilized to retard oxidation. Oxidation of double bonds leads to intermediate peroxides that eventually break down into a variety of stable compounds. 

The major cause of deterioration of food products is lipid oxidation, from which low-molecular-weight, off-flavor compounds are formed. This deterioration is often caused by the oxidation of the unsaturated lipids present in foods. Off-flavor compounds are created when the hydroperoxides, formed during the initial oxidation, are degraded into secondary reaction compounds. Free radicals are also formed which can participate in reactions with secondary products and with proteins. Interactions with the latter can result in carbonyl amino... 

The finding that water-soluble flavonoids could exert their beneficial properties at the hydrophobic portion of the membrane was also observed in in vivo studies and in cells in culture. For example, erythrocytes obtained from animals fed a flavanol- and procyanidin-rich meal showed reduced susceptibility to free-radical-mediated hemolysis [Zhu et al., 2002]. Consistently, we demonstrated that procyanidin hexamers, which interact with membranes but would not be internalized, protected Caco-2 cells from AMVN- and bile-induced oxidation [Erlejman et al., 2006]. When liposomes were preincubated with a series of flavonoids with diverse hydrophobicity, not only hydrophobic flavonoids prevented AMVN-mediated lipid oxidation but also the more hydrophilic ones [Erlejman et al., 2004]. Similarly to what was previously found in liposomes, the protective effects of flavonoids against AMVN-supported oxidation was strongly associated with their capacity to prevent membrane disruption by detergents, supporting the hypothesis of a physical protection of membranes by preventing oxidants to reach fatty acids. 

These findings are of interest with respect to the mechanism of the antioxidative action of the MRP. The stable free radicals of the MRP might interact with the free radicals formed in the lipid oxidation and thus lead to an inhibition of the lipid oxidation chain mechanism. 

N-Heterocyclics. The reaction of primary amines with the carbonyl products derived from lipid oxidation is a major pathway in lipid-protein interactions. Formation of Schiff s base intermediates followed by cyclization and rearrangement can yield imines, pyridines and pyrroles (5,15,30,31). For example, 2-pentylpyridine may result from the reaction of ammonia with 2,4-decadienal, one of the principle aldehydes from the autoxidation of linoleate (5). 

Lipid-Protein-Carbohydrate Interactions. Evidence for such complex interaction was recently reported by Huang et al (36) who observed that the addition of corn lipids to zein and corn carbohydrates enhanced the formation of alkylpyrazines, indicating that lipid-derived free radicals may accelerate the rate of Maillard reactions. Two of the alkylpyrazines, identified in such mixtures after heating for 30 minutes at 180°C, have 5-carbon alkyl substitution at the pyrazine ring and could only be explained by interaction of lipid or lipid decomposition products. These authors suggested that condensation of amino ketones, formed by protein-carbohydrate interaction, may yield 3,6-dihydropyrazine which would in turn react with pentanal, a lipid oxidation product, to form 2,5-dimethyl-3-pentylpyrazine. 

To gain insight into the effect of physical state and/or molecular organization on lipid oxidation, a variety of model systems have been used. These include dispersions, liposomes or vesicles (37,38), monolayers adsorbed on silica (39,40,41), and red blood cell ghosts (42). In most of these studies, oxidation was conducted at relatively low temperatures, i.e., 20 - 40°C. Very little information is available on the effects of physical state on high temperature oxidative reactions or interactions of lipids. 

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. 

Lipid oxidation products react with proteins and other amino compounds to form brown substances, similar to melanoidins. The formation of such brown substances was reviewed already at the first Maillard Symposium.150 The pigments formed are partly soluble in chloroform-methanol and partly insoluble, whereas true melanoidins are largely water-soluble. As most brown pigments of fish muscle are soluble in benzene-methanol and only to a lesser extent in water, the implication is that here oxidised lipid-protein interactions are more important than Maillard browning due to ribose-amino acid interactions. 

Thiazoles with long alkyl chains in the 2-position provide evidence of the interaction of lipid oxidation products with Maillard intermediates. The presence of such thiazoles has been reported for fried chicken, roast beef, and fried potatoes (see Mottram152). Thiophens with long alkyl chains in the 2-position have also been encountered. They were obtained when phospholipid was added to a cysteine-ribose system.153 Lipid degradation to the 2,4-dienal, followed by reaction with H2S, was thought to be responsible.154... 

A plausible interpretation of the interaction between residual moisture and microorganism stability can be drawn from the works of Labuza et al. [18]. Figure 7 shows the progression of the lipid oxidation rate as a function of water activity (a ). This parameter reflects the availability of water for chemical reactions within the product. Its value varies from 0 for an anhydrous product to 1 for pure... 

Antioxidents Lipid oxidation is influenced by many factors the medium, oxygen concentration, temperature, light, degree of unsaturation, and metal ions among others. In the presence of oxygen, oxidation cannot be entirely prevented nor can it be reversed, but it can be inhibited, delaying the buildup of oxidized products to unacceptable levels. Antioxidants can interact with several steps of free-radical or photooxidation. Their performance is medium and concentration dependent and requires care as they can also act as prooxidants under some conditions (51). 

Figure 2. Possible interactions of primary and secondary antioxidants with lipid oxidation pathway in foods.

Compounds such as superoxide anion and peroxides do not directly interact with lipids to initiate oxidation they interact with metals or oxygen to form reactive species. Superoxide anion is produced by the addition of an electron to the molecular oxygen. It participates in oxidative reactions because it can maintain transition metals in their active reduced state, can promote the release of metals that are bound to proteins, and can form the conjugated acid, perhydroxyl radical depending on pH, which is a catalyst of lipid oxidation (39). The enzyme superoxide dismu-tase that is found in tissues catalyzes the conversion of superoxide anion to hydrogen peroxide. 

In native state, proteins exist as either fibrous or globular form. Protein should be denatured and unfolded to produce an extended chain structure to form film. Extended protein chains can interact through hydrogen, ionic, and hydrophobic bonds to form a three-dimensional stmcture (24). Protein films are excellent gas barriers but poor moisture barriers because of their hydrophilic nature. Mechanical properties and gas permeability depend on the relative humidity (1). Al-ameri (25) smdied the antioxidant and mechanical properties of soy, whey and wheat protein, and carrageenan and carboxymethyl cellulose films with incorporated tertiary-butylhy-droquinone (TBHQ), butylated hydroxytoluene (BHT), fenugreek, and rosemary extracts. Armitage et al. (26) studied egg albumin film as a carrier of natural antioxidants to reduce lipid oxidation in cooked and uncooked poultry. 

The basic reactions contributing to thermal flavour generation are the Maillard reaction, Strecker degradation, lipid oxidation and thiamin degradation. Interaction of products formed by these different mechanisms additionally leads to further flavour components. 

In some cases reduction of ferric iron can be accomplished by enzymically utilizing electrons from NADH and, to a lesser extent, NADPH through an enzymic system associated with both the sarcoplasmic reticulum and mitochondria. Ferrous iron can activate molecular oxygen by producing superoxide. Superoxide may then undergo dismutation spontaneously or by the action of SOD and produce the hydrogen peroxide that can interact with another atom of ferrous iron to produce the hydroxyl radical. The hydroxyl radical can initiate lipid oxidation. It is generally accepted that ferrous iron is the reactive form of iron in oxidation reaction. Since it is likely that most iron ordinarily exists in the cell as ferric iron, the ability to reduce ferric to ferrous iron is critical. 

---