AbstractRecent studies have shown that a 20 % trans,trans conjugated linoleic acid (CLA)‐rich soy oil significantly reduces heart disease and diabetes risk factors in obese rats. Furthermore, trans,trans‐CLA has been reported to have superior anti‐carcinogenic activity than other CLA isomers. Therefore, a more concentrated source of trans,trans‐CLA oil would be highly desirable. The objectives of this study were to (1) determine the yield of trans,trans‐CLA isomers resulting from photo‐irradiation of Tonalin® (BASF Global, Florham Park, NJ, USA) and identify trans,trans‐CLA positional isomers; and (2) derive a mathematical model of kinetics of trans,trans‐CLA TAG formation from Tonalin®. Fifty‐five percent trans,trans‐CLA rich oil was obtained in about 140 min when Tonalin® was photo‐isomerized with 0.35 % iodine, which is almost three times more than is possible with photo‐isomerized soy oil. Photo‐isomerization of Tonalin® requires about 2 h, compared to 12 h for photo‐isomerization of soy oil. This reaction is a first‐order reversible reaction with the forward rate constant (kf) = 13.17 × 10−3min−1 and backward rate constant (kb) = 5.334 × 10−3min−1. The major isomers identified were trans‐9,trans‐11‐ and trans‐10,trans‐12‐CLA.