ABSTRACT
I. Introduction.......................................................................................................................... 322 II. Basic Chemistry of Lipid Oxidation.................................................................................... 322
A. Initiation ....................................................................................................................... 323 B. Propagation .................................................................................................................. 324 C. Termination.................................................................................................................. 325
III. Muscle Composition and Lipid Oxidation .......................................................................... 325 A. Muscle Structure and Function.................................................................................... 325 B. Biochemical Changes in Muscle Postmortem ............................................................. 325 C. Variability between and within Muscles ..................................................................... 326 D. Lipid Substrate ............................................................................................................. 327
1. Fatty Acid Unsaturation........................................................................................ 327 2. Lipid Composition of Muscle............................................................................... 328 3. Susceptibility of Lipid Classes to Oxidize ........................................................... 329 4. Susceptibility to Oxidation of Membrane Lipids ................................................. 330 5. Hydrolysis of Lipids and Associated Effects on Lipid Oxidation ....................... 330
E. Catalysts ....................................................................................................................... 331 1. Transition Metal Ions............................................................................................ 331 2. Singlet Oxygen Generation Systems .................................................................... 333 3. Enzymic Initiation Systems .................................................................................. 334
F. Antioxidants ................................................................................................................. 334 1. Tocopherol ............................................................................................................ 334 2. Ascorbic Acid ....................................................................................................... 336 3. Carotenoids ........................................................................................................... 337 4. Glutathione............................................................................................................ 337 5. Carnosine .............................................................................................................. 338 6. Flavonoids and Phenolic Acids ............................................................................ 338 7. Antioxidant Enzymes............................................................................................ 339
G. Mathematical Modeling ............................................................................................... 339 IV. Effect of Processing Treatments on Oxidation.................................................................... 340
A. Bleeding ....................................................................................................................... 340 B. Rinses ........................................................................................................................... 341 C. Washing ....................................................................................................................... 342 D. Skinning ....................................................................................................................... 342 E. Mincing ........................................................................................................................ 342 F. Salting .......................................................................................................................... 343
343 1. Nitrite-Based Curing Agents ................................................................................ 343 2. Nitrite-Free Curing Agents................................................................................... 343
H. Smoking ...................................................................................................................... 344 I. Heating=Cooking......................................................................................................... 344 J. Deep-Fat Frying .......................................................................................................... 345 K. High Pressure .............................................................................................................. 345 L. Drying.......................................................................................................................... 345 M. Irradiation .................................................................................................................... 345 N. Glazing ........................................................................................................................ 346 O. Freezing ....................................................................................................................... 346 P. Packaging .................................................................................................................... 347
V. Summary ............................................................................................................................... 347 References ..................................................................................................................................... 347
Following storage at refrigerated or frozen temperatures lipid oxidation is one of the major causes of quality deterioration in muscle foods. Often seen in later stages of storage, quality losses are manifested through a variety of mechanisms, which are summarized in Table 12.1 [1-17]. Although lipid oxidation usually causes a decrease in consumer acceptance, in some cases lipid oxidation leads to enhancement of product quality. An example is the enzymatic production of fresh-fish aromas. This chapter reviews the fundamental mechanisms of lipid oxidation as they apply to muscle foods. Included in this chapter is a discussion of the impact of tissue structure and compositional factors on pathways, kinetics, and extent of oxidation. Also included is a section describing the effect of various food processing applications on lipid oxidation reactions. Throughout this chapter, the reader will be made aware of the multiple interactions among muscle constituents during the process of lipid oxidation. Therefore, this chapter (Section III.G) details how mathematical models may be used to account for these interactions and indicates how shelf-life predictions and conditions for optimal stability may be derived.
