Lipid oxidation meat flavors

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. 

Meat flavor deterioration (MFD), formerly referred to as warmed-over flavor, is described as the loss of desirable meaty flavor with an increase in off-flavors (i-5). During this process, the increase in off-flavors is primarily contributed by hpid oxidation reactions. As lipids oxidize, they produce mixtures of aldehydes, ketones and alcohols that contribute to the off-flavors observed. Many of these compounds have been identified and the increase in their intensities during storage have been well documented (7, 4-6),... 

Over the years, scientists have used many types of antioxidants in a variety of foods to retard or inhibit lipid oxidation and, thus, increase shelf-life and preserve quality. These antioxidants include free radical scavengers, chelators, and oxygen absorbers. While there are numerous antioxidants available to food scientists, the objective of this report was to discuss several of these antioxidants as they relate to meat flavor quality research and to show how they were used to retard lipid oxidation and prevent meat flavor deterioration in ground beef patties. 

The flavor quality of food is a primary factor involved in a consumer s decision to purchase a food item. Therefore, food technologists require a thorough understanding of how flavor deteriorates if they are to prepare products that consumers will purchase repeatedly. This knowledge is particularly important in meat and meat products, since the deterioration of meat flavor is a serious and continual process (1-4) that involves both the loss of desirable flavor components 4,5) and the formation of off-flavor compounds (6-9) many of which are associated with lipid oxidation (10). 

EFFECT OF STORAGE ON THE GENERATION AND LOSS OF FLAVOR NOTES AND PRODUCTS OF LIPID OXIDATION IN COOKED MEATS ... 

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). 

Flavor notes and products of lipid oxidation in cooked meats, 85,86/ Flavor peptides convenient synthesis, 149-156 enzymatic synthesis, 151,154-156 protein recombination synthetic method, 149... 

The intensity of undesirable sensory notes has been positively correlated with the content of carbonyl compounds formed through lipid autoxidation reactions. In general, the carbonyl compounds present have the greatest impact on flavor owing to their low flavor thresholds in comparison with hydrocarbons, substituted furans, and alcohols. Aldehydes are major contributors to the loss of desirable flavor in meats because of their rate of formation during lipid oxidation and low flavor threshold. Thus, an alternative approach for monitoring the extent of lipid oxidation in fats and oils is to measure... 

Positive cooked-beef flavor components as perceived by descriptive sensory panelists are reduced during free radical catalyzed meat flavor deterioration (MFD) while negative flavor notes with descriptor definitions of cardboard and painty intensify, as reviewed recently by Love (13). Although the cardboard and painty off-flavors correlate well with lipid oxidation products and can be measured easily by gas chromatography (1, 14, 18). much less is known about the fate of the positive cooked-beef flavors in this MFD process (13). 

The chemical nature of flavor volatiles was representative of most classes of organic compounds. Hexanal was found to be the predominant volatile component In each case and Its content was directly proportional to the amount of TBA-reactlve species, while Inversely proportional to the flavor acceptability of meats. Nitrite curing depressed the production of lipid oxidation products and nltrlte-free curing composition duplicated the action of nitrite on meat, flavorwlse. 

Our own work has shown a great decrease In the concentration of the volatiles In the cured, as compared to uncured, meats (Figure 5) (Ifi). The concentration of aldehydes originally present in cooked pork was reduced to < 12 of their original quantities (Table III, unpublished results). However, we did not Identify any new flavor active compound which could have been responsible for the cured flavor. Lipid oxidation, as measured by TBA number, was almost eliminated In cooked pork by adding nitrite at a level of 150 ppm (13.) Furthermore in preliminary evaluations, our untrained panelists were unable to differentiate amongst the flavor of nitrite-cured meats prepared from beef, chicken, mutton and pork (unpublished results). 

The major precursors in meat flavors are die water-soluble components such as carbohydrates, nucleotides, thiamine, peptides, amino acids, and the lipids, and Maillard reaction and lipid oxidation are the main reactions that convert these precursors in aroma volatiles. The thermal decomposition of amino acids and peptides, and the caramelization of sugars normally require temperatures over 150C for aroma generation. Such temperatures are higher than those normally encountered in meat cooking. During cooking of meat, thermal oxidation of lipids results in the formation of many volatile compounds. The oxidative breakdown of acyl lipids involve a free radical mechanism and the formation of... 

Lipid-derived volatile compoimds dominate the flavor profile of pork cooked at temperatures below 100°C. The large numbers of heterocyclic compounds reported in the aroma volatiles of pork are associated with roasted meat rather than boiled meat where the temperature does not exceed 100 C (34,35). Of flie volatiles produced by lipid oxidation, aldehydes are the most significant flavor compounds (35,36). Octanal, nonanal, and 2-undecenal are oxidation products from oleic acid, and hexanal, 2-nonenal, and 2,4-decadienal are major volatile oxidation products of linoleic acid. 

Aldehydes are by far the most numerous compounds identified as dry-cured ham odorants, with different odors (green, rancid, toasted) and thresholds in air ranging from 0.09 to 480 ng/L (Table 1). Most of them were identified in the first works focused on dry-cured ham volatile compounds (7,2). Aldehydes are essential for meat flavor (70), but large quantities in meat and meat products have been related to lipid oxidation and deterioration (77). The effect of several quality factors has been researched and it was found that the rearing system of pigs (S) and ripening conditions (7) influence on the contribution to odor and the content of some aldehydes. 

The economical value and high popularity of meat lead to the production of meat-like flavors through process chemistry. Several heat-induced reactions lead to the formation of meat flavors. These reactions are the pyrolysis of peptides and amino acids, the degradation of sugars, the oxidation, dehydration, and decarboxylation of lipids, the degradation of thiamin and ribonucleotides, and interactions involving sugars, amino acids, fats, H2S, and NH3 [110],... 

The origin of meat flavor has been shown to arise from the combination of two primary sources. The first is the tissue fat, both extracellular and intracellular, which produces carbonyl and other lipid and lipid-oxidation products. The fat component of meat flavor is viewed as being responsible for the species specific flavor in meat (9). The second major component of meat flavor is the lean portion. The proteins, peptides, and amino acids of the lean, add not only to the muscle food s general meaty flavor, but also undergo Maillard reactions with sugars to produce Amadori and Heyns compounds having meat flavor characteristics. 

Sugars and carbonyl compounds interact with amino acids or proteins in a sequence of complex reactions known as the Maillard reaction or as non-enzymatic browning. The browning products from this reaction have a marked influence on lipid oxidation. They generally retard lipid oxidation in foods, and contribute to meat flavors. Lipid oxidation products can also react with proteins and amino acids, leading to the loss of essential amino acids with impact on the oxidative stability and the nutritional quality of foods. 

There is increasing evidence that degradation of proteins is associated with the development of the so-called warmed-over flavor . Selective methods to measure protein oxidation may be useful as a complementary approach in evaluating oxidative deterioration of meat products. The determination of protein carbonyls (as dinitrophenyl hydrazine derivatives) is now used for this purpose. More reliable methods are needed, however, to determine specific products of lipid oxidation and their interaction products acting as precursors of flavor compounds to establish the relative contribution of heme and nonheme iron to the development of rancidity in various meat products. 

---