ABSTRACT
I. Introduction .......................................................................................................................... 511 II. General Changes in Oils and Fats Due to Heating and Frying ............................................ 513 III. Chemical Changes in Fatty Acids Due to Heating and Frying ............................................ 516 A. Total Changes in the Oils and Fats: Polar Compounds .................................................. 516 B. Total Changes in Fatty Acids ......................................................................................... 519 a. Polar Fatty Acids ...................................................................................................... 519 b. Fatty Acid Composition ........................................................................................... 520 C. Modi) ed Fatty Acids ...................................................................................................... 521 a. Modi) ed Fatty Acid Monomers ............................................................................... 521 D. Fatty Acid Polymers ....................................................................................................... 527 a. Nonpolar Dimers ...................................................................................................... 527 b. Polar Dimers ............................................................................................................. 528 c. Higher Oligomers ..................................................................................................... 528 IV. Fat and Oil Transfer during Frying ...................................................................................... 529 A. Food Fatty Acid Changes ............................................................................................... 531 B. Fat Interchange during Deep Frying of Fatty Foods ...................................................... 532 a. Fresh Fatty Foods ..................................................................................................... 532 b. Frozen Prefried Foods .............................................................................................. 533 C. Food Matrix-Cooking Oil/Fat Interaction ..................................................................... 534 V. Final Remarks ...................................................................................................................... 535 Acknowledgments ....................................................................................................................... 535 References ................................................................................................................................... 535
Edible fats and oils usually contain more than 95% triglycerides. The main characteristics of the acyl groups forming triglycerides are chain length (number of C-atoms) and the number and position of unsaturations in the molecules. Before absorption, triglycerides must be hydrolyzed into free fatty acids and monoglycerides. These triglyceride-derived compounds are placed into intestinal micelles and absorbed. Later triglycerides are reesteri) ed within the enterocyte and incorporated to chylomicrons (Sánchez-Muniz and Sánchez-Montero, 1999). Chylomicrons and other lipoproteins participate in the very complex lipoprotein metabolism carrying cholesterol, fatty acids, and other fat-soluble compounds to/between the different body tissues (Elmadfa and Wagner, 1999). The amount and quality of dietary fats and oils may inC uence the cell, tissue, and body physiology (Elmadfa and Wagner, 1999; Mahungu et al., 1999). Diet supplies some fatty acids that are essential or play very important metabolic regulations. A basic function of the mother dietary fatty acids,
oleic (C18:1, n-9), linoleic (18:2, n-6), and linolenic (c18:3, n-3), apart from being metabolic energy substrates, is to be unsaturated and elongated to long-chain fatty acids of 20 and 22 C-atoms. These long-chain fatty acids, once incorporated to membrane phospholipids or cellular membrane regions enriched in es) ngomielins (Jump, 2004), can modulate the cell gene expression and generation of several bioactive molecules, through different and complex metabolic ways. Moreover, the balanced quantitative and qualitative intake of fatty acids can reduce the cholesterolemia, the lipid and lipoprotein oxidizability, and the thrombogenesis, and also modify the lipogenesis-lipolysis equilibrium, and so forth (Mensink and Katan, 1992; Massaro et al., 2002, 2006; Mata et al., 2002). Thus, adequate intake of dietary fat is essential for health. At present, it has been accepted by most of the Nutrition Organizations that total fat must contribute up to 30% and saturated fatty acids only less than 10% of the total energy intake (Kris-Etherton, 1999; Ros, 2001).
