Interactions oxidized lipids

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... 

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. 

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... 

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. 

Low molecular weight antioxidants react with ROS in cell compartments which for some reasons are lack of antioxidant enzymes. Thus, suppression of bifurcate chain reactions of lipid peroxidation in hydrophobic core of cell membrane is mostly effectively performed by vitamin E (a-tocopherol). Interaction of lipid molecules with hydroxyl radical in the absence of vitamin E results in bifurcation of oxidative processes and formation of peroxyl and alcoxyl radicals. They are quickly accumulated in the restricted volume of the membrane and reaction began to be uncontrolled. a-Tocopherol interacts with peroxyl radicals with high affinity, reduces them and is then oxidized itself into relatively nonactive phenoxyl radical [8]. The latter can be accumulated within the bilayer until it will be returned to initial state by reduction by ascorbate [9]. Pair Vitamin E - Vitamin C is a good example of a mutual interaction between hydrophobic and hydrophilic low molecular weight antioxidants. Recently, tight relations were demonstrated for several natural antioxidants which interaction balances the red/ox state of the cell [3.5.10-12]. Figure 4 demonstrates such interaction between some of them. 

It is now well established that proteins can induce phase transitions in lipid membranes, resulting in new structures not found in pure lipid-water systems (c/. section 5.1). However, this property is not peculiar to proteins the same effect can be induced by virtually any amphiphilic molecule. Depending on the structure and nature of proteins, their interactions with lipid bilayers can be manifested in very different ways. We may further assume that the role of proteins in the biogenesis of cubic membranes is analogous to that in condensed systems, and lipids are necessary for the formation of a cubic membrane. This assumption is supported by studies of membrane oxidation, which induce a structure-less proteinaceous mass [113]. However, the existence of a lipid bilayer by itself does not guarantee the formation of a cubic membrane, as proteins may also play an essential role in setting the membrane curvature. In this context, note that the presence of chiral components e.g. proteins) may induce saddle-shaped structures characteristic of cubic membranes. (This feature of chiral packings has been discussed briefly in section 4.14)... 

The Maillard reaction and the oxidation of lipids are two of the most important reactions for the formation of aromas in cooked foods. Interactions between lipid oxidation and the Maillard reaction have received less attention, despite the fact that lipids, sugars, and amino acids exist in close proximity in most foods. Lipids, upon exposure to heat and oxygen, are known to decompose into secondary products, including alcohols, aldehydes, ketones, carboxylic acids, and hydrocarbons. Aldehydes and ketones produce heterocyclic flavor compounds reacting with amines and... 

Firestone et al. investigated the relationship between the molecular architecture of a series ofpoly(ethyleneoxide)-b-poly(propylene oxide) (PEO—PPO) di- and triblock copolymers and the nature of their interactions with lipid bilayers [213], The number of repeat units in the hydrophobic PPO block has been found to be a critical determinant for the polymer-lipid bilayer association. Further studies showed that temperature, polymer architecture and concentration also control the mode of interaction of PEO—PPO—PEO copolymers with lipid bilayers. Increasing either the number of repeat units in the PEO block or the polymer concentration promotes a greater degree of structural ordering [197],... 

It has already been emphasized that apoptotic cells can be both, the source of oxidized phospholipids as well as the initiators of apoptosis. Oxidation of (poly)-unsaturated phospholipids leads to a large variety of oxidation products (see Chapter 1 and (Fruhwirth et al., 2007)). These compounds may have very different chemical structures. It can be anticipated that they exert very different physical effects in membranes and undergo specific interactions with their target proteins and lipids. As a consequence, the great variety of oxidized phospholipids should be reflected by a corresponding diversity of biological effects. In many studies investigating cell survival and/or cell death, the effects of oxidized lipid... 

NO can interact with other free radicals most notably, NO reacts with the superoxide anion (O 2) to produce the potent oxidant peroxynitrite (ONOO") (Radi et al., 1991). Although it is a simple molecule, ONOO is chemically complex. It can display hydroxyl radical-like and nitrogen dioxide (NO2) radical-like activity, can oxidize lipids, and can directly nitrate proteins. ONOO" has been shown to nitrate a tyrosine residue on superoxide dismutase (SOD) (Beckman et al., 1992). 

The reactivity of fish lipids and proteins depends on variety of both the level of oxidation and reaction conditions. PULA interact more easily and form stronger bonds with proteins and starches than other FA. DHA is preferentially bound. Fresh lipids are more reactive than oxidized lipids. The interactions of fish lipids with amylose are different than those with amylopectin. The effect of heating and freezing on lipid-protein, lipid-amylose, and lipid-amylopectin interactions is also different (Bienkiewicz and Kolakowska, 2001a,b). The interactions of lipids with other food components create new products attributes and also affect the properties of fats, particularly their extractability and availability in the human organism. 

Functional Groups of Oxidized Lipids and Proteins Likely to React in Lipid-Protein Interactions... 

On the contrary, the nutritional value of oxidized lipid-protein interaction products is substantially lower than that of the original lipoproteins. The main reason is the lower digestibility most covalent bonds formed in the interactions are not attacked by proteases under the conditions of digestion. The 6-amino group of bound lysine is particularly sensitive to interactions with carbonylic oxidation products (Janitz et al., 1990), and the resulting imine bonds substantially reduce the lysine availability. Lysine losses correlate with the increase in fluorescence. Other amino acids, such as tyrosine, tryptophan, and methionine, are also partially converted into unavailable products. Interaction products may be allergenic even when allergenic proteins have reacted (Doke et al., 1989). 

On the contrary, the interaction products of oxidized lipids with food proteins are not easily moistened and emulsified, and result in deterioration of the texture after food ingestion. The functional properties of beef proteins are deteriorated by... 

The more unsaturated FA, the easier and stronger they bond with starch, both with amylose and amylopectin, provided they are not oxidized. The most efficient and most stable interactions are those produced by polyenoic FA from BHA-protected lipids. Docosahexaenoic acid was preferentially bonded. Oxidized lipids do not interact readily. 

Doke, S., Nakamura, R., and Torii, S. 1989. Allergenicity of food proteins interacted with oxidized lipids in soybean-sensitive individuals, Agric. Biol. Chem., 53, 1231-1235. 

The main reactions that lead to the formation of flavor can be listed as Maillard reactions, the Strecker degradation of amino acids, lipid oxidation and microbial and enzymatic reactions, and interactions between lipids, proteins, and carbohydrates. 

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