Lipid oxidation indication

A review by Bailey and Swain ( ) cited several references which indicated nitrite was responsible for cured meat flavor. These same authors presented chromatograms of volatiles from cured and uncured hams and while the chromatograms were similar, some quantitative differences led to the conclusion that the major difference due to nitrite was its reactivity to retard lipid oxidation. Greene and Price ( ) suggested, however, that sodium chloride was the major factor responsible for cured meat flavor rather than sodium nitrite or an absence of lipid oxidation. It has been concluded from other recent work (2) that nitrite was necessary to produce a typical ham aroma and flavor as well as to retard the development of off-odors and flavors during storage of cooked cured meat. 

UV-irradiated cells. Using cell-free cytosolic keratinocyte extracts, Simon and colleagues26 confirmed the role of membrane oxidation in NF-kB activation. Particularly important aspects of the experimental design employed by Simon and colleagues was the use of keratinocytes versus cells derived from a cervical cancer patient, and the use of biologically relevant UVB (290 to 320 nm) radiation versus UVC (200 to 290 nm) radiation, which is filtered out by the atmospheric ozone layer and does not reach the earth s surface. Overall, these data indicate that the activation of cytokine transcription, a step essential for the induction of immune suppression, can occur independently of UV-induced DNA damage and suggest that membrane lipid oxidation can serve as a UV photoreceptor. 

A simple method for assessing lipid oxidation is measuring the headspace concentration of hexanal by capillary GLC. Also, the total volatiles appearing in the chromatogram up to hexanal can be taken as oxidation index. The method was applied to determine the amounts of lipid peroxides present in rat liver cells. Enhancement of the hexanal concentration can be achieved on adding ascorbic acid (22), that reduces Fe(ni) present in the matrix to Fe(II), which catalyzes decomposition of hydroperoxides to aldehydes. Significant correlations are found between hexanal concentrations and various oxidation indices, such as TBARS (Section IV.D.2)" . ... 

Standards and Controls. In all experiments, the 85 g standard patties were made from freshly ground top round steaks (excess fat trimmed) and immediately frozen in covered glass petri plates until the day of the assay. The fat content was routinely from 4-5%, determined by the method of Koniecko (57). The standards generally had relatively low values for hexanal, total volatiles (TV) and TEARS, and low intensity values for painty (PTY), cardboardy (CED), sour (SUR) and bitter (ETR). These results indicated the absence of lipid oxidation and no formation of off-flavors. As expected, the desirable flavor notes, cooked beef/brothy (CEE), beefy/meaty (EM), brothy (ERO), browned/caramel (ERC) and sweet (SWT) had high intensity values. 

When the antioxidants were used in the cooked/stored samples, data indicated that they were very effective in inhibiting lipid oxidation and MFD. The chemical and off-flavor indicators were reduced and the on-flavor notes were increased. Thus, phenolic-type primary antioxidants that function as free radical scavengers are very effective tools for preventing lipid oxidation and MFD in ground beef. It should also be noted that the intensity of the desirable flavor notes remained at very high levels, which meant that the patties retained their beefy tastes. Therefore, for an antioxidant to be highly effective, it should not only prevent lipid oxidation, but it should also retain the desirable flavor properties of the food commodity. 

Secondary antioxidants, i.e., sequestrants or chelators, are important compounds in the prevention of lipid oxidation. The effect of chelators tested varied with the different compounds. Of those chelators tested, ethylenediaminetetraacetic acid (EDTA, tetrasodium salt) and sodium phytate were the most effective inhibitors of lipid oxidation (so indicated by low hexanal and TEARS values) and MFD (as seen by high CBB and low PIT and CBD intensity values), see Table 5. Sodium phytate was previously shown to chelate iron and thus, was proposed as a food antioxidant(7J). Sodium citrate at a concentration of 500... 

Effect of Water Activity. A preliminary study was done to determine the a at which encapsulated orange peel oil was the most stable to oxidation. Figure 1 summarizes the results of this study. The formation of the limonene oxidation product, limonene oxide, was the slowest for the powder adjusted over Mg(NO3)2 (a 0.536). While the levels of oxidation product do not follow in exact order of a, it is evident that better storage stability correlates with a higher a of the powder. This relationship was not anticipated. Literature on lipid oxidation (2, 2) indicates that there is an optimum a for product... 

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. 

Lipoxygenases, of which the enzyme from soy beans has been studied the most, also catalyze oxidation of polyunsaturated fatty acids in lipids as indicated in Eq. 21-17. Formation of the hydroperoxide product is accompanied by a shift of the double bond and conversion from cis to trans configuration. Soybean lipoxygenase is a member of a family of related lipoxygenases that are found in all eukaryotes. All... 

Measuring the content of primary oxidation products is limited due to the transitory nature of peroxides. Yet, their presence may indicate a potential for later formation of sensorially objectionable compounds. The peroxide content increases only when the rate of peroxide formation exceeds that of its destruction. In cases where peroxide breakdown is as fast as or faster than peroxide formation, monitoring lipid peroxides is not a good indicator of oxidation. This can occur in frying oils and sometimes in meat products, particularly in cooked meats where iron is very active and peroxide breakdown is quite rapid. Because the acceptability of an oil or lipid-containing food product depends on the degree to which oxidation has progressed, the simultaneous detection of primary and secondary lipid oxidation products helps to better characterize lipid quality. It is... 

The time to reach a certain PV may be used as an index of oxidative stability for food lipids. The effects of antioxidants and food processing on fats are often monitored in this way. Thus, a longer time period to reach a certain PV is generally indicative of a better antioxidant activity for the additive under examination. However, a low PV represents either early or advanced oxidation the breakdown of peroxides to secondary oxidation products will result in a decrease in PVs during the storage period. For determination in foodstuff, a major disadvantage to the classical iodometric PV assay is that a 5-g test portion is required it is sometimes difficult to obtain sufficient quantities of lipid from foods low in fat. Despite its drawbacks, PV determination is one of the most common tests employed to monitor lipid oxidation. 

This group evaluated the impact of changes in fatty acid composition on headspace aldehyde content of fresh pork and demonstrated the utility of these saturated aldehydes as an indicator of lipid oxidation. 

A constant observation when the MRP were separated by various methods was that antioxidative effect was found in many different fractions. Both the dialysates and the retentates from dialysis were antioxidative to some extent. All the electrophoresis fractions exhibited some antioxidative effect. Attempts to separate the MRP by column chromatography on Sephadex G-50 have resulted in several fractions with some antioxidative effect, and so on. This indicates that several antioxidative products are formed by the Maillard reaction, possibly differing in molecular size and chemical structure, but perhaps with one single antioxidative functional group in common, such as a free radical function. However, it can not be excluded that the MRP contain a few entirely different antioxidants with different modes of action. Various mechanisms have also been suggested. Eichner (6) claimed MRP to inactivate the hydroperoxides formed by the lipid oxidation. There are also reports on the complex binding of metals by MRP (18, 19). 

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. 

However, while some reports (Schwartz and Parks, 1974) indicate a correlation between the oxidation of ascorbic acid and the development of an oxidized lipid flavor, Smith and Dunkley (1962c) concluded that the oxidation of ascorbic acid alone cannot be used as an index of lipid oxidation. They reported that although ascorbic acid oxidation curves for homogenized and pasteurized milk were similar, the homogenized samples had a significantly lower tendency to develop oxidized flavor. 

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