Beef Supernatant-Fraction-Based Studies of Heterocyclic Amine-Mutagen Generation

Abstract

To characterize the reaction conditions that generate frameshift mutagens in cooked meats, we have concentrated on a supernatant fraction (S₂) prepared from (1:1) aqueous homogenates of lean round steak. Soluble compounds <500 MW 1n S₂ are the sources of the S-9 dependent Salmonella TA1538 mutagenic activity 1n these homogenates, Irrespective of how they are heated (100°C boiled, 200–300°C aqueous-pressure, or 200–300°C dry), as well as the outer surfaces (crust) of griddle-fried ground beef. Water is an important inhibitory reactant that influences not only the total TA1538 activity, but also the proportions of HPLC-polar, nitrite-resistant 2-amlno-3-methyl-imidazo-type mutagens, as opposed to HPLC-nonpolar, nitrite-sensitive mutagens. Dry-state heating beef S₂ favors the former. It yields eight of the heterocylic amine-mutagens that have been identified in the surfaces of 100g beef patties fried at 250–300°C, including 2-amlno-3-methylimldazo [4,5-f]quinoline (IQ), 2-amino-3-8-dimethylimidazo[4,5-f]qulnoxaline (NeIQx), and the predominant mutagen 2-amino-l-methyl-6-phenylimidazo [4,5-b]pyridinea (PhIP). Oven-baking the amounts of L-phenylalanine (Phe) and creatine (Cr) present in 100g (raw beef) equivalents of S₂ yields sufficient IQ and PhIP to accomodate the ppb quantities reported for high temperature fried beef patties. Dry-heating with heavy-isotope-labeled forms of Phe and Cr shows precisely how their C and N atoms are incorporated into PhIP. Our findings indicate that phIP and other 2-amino-3-methyl-imidazo-mutagens most likely arise in 250–300°C fried beef patties independent of Maillard reactions.