Lipid oxidation and production of off-odor in irradiated meat

Emulsion-type raw and cooked pork sausage with different fat content or fatty acids was prepared to determine the effect of irradiation on lipid and cholesterol oxidation, color changes, and volatile production during storage. Lipid oxidation increased with the increase of fat content or irradiation dose in both raw and cooked pork products. Irradiated batters had higher cholesterol oxide content than non-irradiated, and the major cholesterol oxides formed in raw irradiated pork batters were 7alpha- and 7beta-hydroxycholesterol. Hunter a- and b-values of both raw and cooked pork products in aerobic packaging decreased with irradiation regardless of fat content. In vacuum packaging, however, irradiated cooked pork sausage had higher Hunter a-values than nonirradiated. Irradiation significantly increased the amount of 1-heptene, 1-nonene, and total volatile compounds in raw and cooked pork sausage. The amounts of 1-heptene and 1-nonene were not associated with TBARS values of pork sausage but were closely related to irradiation dose. In both irradiated and nonirradiated pork sausage, aerobic packaging produced more volatile compounds during storage than did vacuum packaging. The production of aldehydes, ketones, and alcohols in aerobic-packaged pork sausage were not influenced by irradiation at O-day storage. However, irradiation accelerated lipid oxidation and increased the amounts of aldehydes, ketones, and alcohols during storage. The TBARS of aerobic- or vacuum-packed sausage prepared with lard were higher (p \u3c 0.05) than the sausage prepared with flaxseed oil likely a result of the high tocopherol content in flaxseed oil;To investigate the distinction between volatile compounds related to oxidized flavor and irradiation odor, and to understand the mechanisms of off-odor production in irradiated meat on a chemical basis, oil emulsions containing amino acids or proteins were analyzed. The increase of aldehydes (e.g. hexanal, heptanal, octanal, and nonanal, p \u3c 0.05) in the oil emulsion after irradiation indicated that irradiation accelerated lipid oxidation of the oil emulsion model system containing amino acids, glutathione, bovine serum albumin, gelatin, or myofibrillar proteins. Irradiation also produced new volatile compounds from amino acids (e.g., leucine, valine, isoleucine, phenylalanine, methionine, and cysteine) via radiolytic degradation. These radiolytic compounds along with lipid oxidation by-products may be the major sources of off-odor from irradiated meat