PALMITIC ACID IS THE MAJOR FATTY-ACID RESPONSIBLE FOR SIGNIFICANT ANTI-N-METHYL-N'-NITRO-N-NITROSOGUANIDINE (MNNG) ACTIVITY IN YOGURT

We describe here the isolation and identification of palmitic acid as being responsible for significant anti-N-methyl-N'-nitro-N-nitrosoguan idine (MNNG) activity in yogurt. The Ames test (Salmonella typhimurium TA100) was used to direct fractionation of activity. Yogurt was freez e-dried and extracted with acetone to yield a crude extract. The crude extract was purified by normal phase silica gel, Sephadex LH-20, and reversed phase medium pressure liquid chromatographies. The major comp ound in the active medium pressure liquid chromatographic fractions wa s determined to be palmitic acid on the basis of gas chromatography-ma ss spectrometry (GC/MS), MS/MS, by co-elution with authentic palmitic acid on GC and high pressure liquid chromatography (HPLC) systems, and by nuclear magnetic resonance (NMR) analysis. Other saturated straigh t chain and methyl branched fatty acids were detected by GC/MS and wer e later shown to possess anti-MNNG activity. Of the straight chain fat ty acids, palmitic acid had the highest anti-MNNG activity. All omega - 1 methyl branched fatty acids tested were more active than their str aight chain counterparts. A trace amount of isopalmitic acid (14-methy l pentadecanoic acid), a minor milk lipid, was detected in one of the active fractions, and was later shown to be five times more active tha n palmitic acid. Isopalmitic acid also inhibited mutagenesis induced b y 4-nitroquinoline-N-oxide (4NQO), and 7,12-dimethyl benz[a]anthracene (DMBA), and was found to inhibit the metabolic activation of DMBA.