Lipid oxidation oxidative changes

Zienkowicz, L., Kofakowska, A. and Domiszewski, Z., 2001, Lipid oxidation changes in fried Baltic herring and sprat during storage at 5°C, presented at 24th World Congr. ISF Lipids, Fats, and Oils Reality and Public Perception, Berlin, September 16-20, 54. 

Meat products have to be stabilised in some cases, as meat lipids contain no natural antioxidants or only traces of tocopherols. Most muscle foods contain, however, an efficient multi-component antioxidant defence system based on enzymes, but the balance changes adversely on storage. The denaturation of muscle proteins is the main cause of the inbalance as iron may be released from its complexes, catalysing the lipid oxidation. Salting contributes to the negative effects of storage, as it enhances oxidation. Using encapsulated salt eliminates the deleterious effect of sodium chloride. 

It is not only lipids but also essential oils which are sensitive to oxidative changes on storage. Sometimes stabilised by synthetic or natural antioxidants, they usually contain substances showing moderate antioxidant activity, but these may be lost by evaporation or oxidised by air oxygen unless more powerful phenolic antioxidants are added. 

An old hypothesis is based on the observations of Dahlen et al. (D3), who demonstrated that above a certain concentration in plasma, Lp(a) could bind to glycosaminoglycans in the arterial wall (B12). Colocalization of Lp(a) and fibrin on the arterial wall can lead to oxidative changes in the lipid moiety of Lp(a) and induce the formation of oxidatively modified cholesterol esters, which in turn can influence the interaction of Lp(a) and its receptors on macrophages. This process is promoted by the presence of calcium ions. Cushing (C14), Loscalzo (L22), and Rath (R3) reported a colocalization of undegraded Lp(a) and apo-Bl00 in the extracellular space of the arterial wall. In contrast to LDL, Lp(a) is a substrate for tissue transglutaminase and Factor XUIa and can be altered to products that readily interact with cell surface structures (B21). 

M. 1. Trenell, K. G. Hollingsworth, E. L. him and R. Taylor, Increased daily walking improves lipid oxidation without changes in mitochondrial function in type 2 diabetes. Diabetes Care, 2008, 31,1644-1649. 

The changes in the protein composition and flavor of "cooked" and "cooked- -stored" beef seemed to be related to degradation by free radical species induced during lipid oxidation 1-10, 16, 22, 23), Based on the information presented in the aforementioned publication, it seemed reasonable to suggest that the appearance of "bitter" and "sour" tastes and the disappearance of "meaty" and "beefy" flavors were a result of the activity of the free radicals derived from lipid oxidation on flavor proteins (2, 24-28),... 

The formation of free radicals after lipid oxidation is known to play a key role in the deterioration of meat flavor 8, 23), Since proteins constitute a major portion of the muscle s composition, the relationship between chemically active radical species and decomposition of food flavor proteins and peptides needs to be studied in detail. Data has been presented showing the correlation of proteins with flavor (Figures 5 and 6). Data is now presented showing how soluble meat proteins change in an environment where free radicals are induced by a free-radical oxidation generating system or FROG (Figure 10). 

Dried whole milk is prepared by conventional spray or roller drying, with some modifications of the preheat treatment of the milk. The product is usually stored under nitrogen to delay lipid oxidation and off-flavor development. In spite of the processing changes, flavor defects and short storage life have limited the markets for dried whole milk most of it is used in the confectionery and baking industries. Federal and FAO standards require a minimum of 20% but less than 40% milk fat and a maximum of 5% moisture. 

Gawel, J. and Pijanowski, E. 1970. Observations on the oxidative changes of skim milk lipids. Nahrung 14, 469-474. (German). 

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. 

Two other types of oxidative changes occur during heating of lipids which result in undesirable flavor of meat. These are referred to as "warmed-over flavor" (WOF) and "grassy" flavor. 

---