Fatty Acid Profile of Canadian Dairy Products with Special Attention to the trans-Octadecenoic Acid and Conjugated Linoleic Acid Isomers

Current scientific evidence indicates that consumption of industrial trans fatty acids (TFA) produced via partial hydrogenation of vegetable oils increases the risk of coronary heart disease. However, some studies have suggested that ruminant TFA, especially vaccenic acid (VA or 11t-18:1) and rumenic acid (RA or 9c,11t-18:2), which is a conjugated linoleic acid (CLA) isomer, may have potential beneficial health effects for humans. To date, no concerted effort has been made to provide detailed isomer composition of ruminant TFA and CLA of Canadian dairy products, information that is required to properly assess their nutritional impacts. To this end, we analyzed the fatty acid profile of popular brands of commercial cheese (n = 17), butter (n = 12), milk (n =8), and cream (n = 4) sold in retail stores in Ottawa, Canada, in 20062007 by silver nitrate thin-layer chromatography and gas liquid chromatography. The average total TFA content of cheese, butter, milk, and cream samples were 5.6, 5.8, 5.8, and 5.5 of total fatty acids, respectively. VA was the major trans-octadecenoic acid (18:1) isomer in all the Canadian dairy samples with average levels of (as total trans-18:1) 33.9 in cheese, 35.6 in butter, 31.0 milk, and 30.1 in cream. The different dairy products contained very similar levels of CLA, which ranged from 0.5 to 0.9 of total fat. RA was the major CLA isomer of all the dairy products, accounting for 82.483.2 of total CLA. There were no significant differences (P > 0.05) in the fatty acid profile between the 4 different dairy groups, which suggests lack of processing effects on the fatty acid profile of dairy fat.

An oxidized metabolite of linoleic acid stimulates corticosterone production by rat adrenal cells

Oxidized derivatives of linoleic acid have the potential to alter steroidogenesis. One such derivative is 12,13-epoxy-9- keto-10-( trans)-octadecenoic acid (EKODE). To evaluate the effect of EKODE on corticosterone production, dispersed rat zona fasciculata/reticularis (subcapsular) cells were incubated for 2 h with EKODE alone or together with rat ACTH (0, 0.2, or 2.0 ng/ml). In the absence of ACTH, EKODE (26 μM) increased corticosterone production from 5.3 ± 2.3 to 14.7 ± 5.0 ng · 106 cells · h−1. The stimulatory effect of ACTH was increased threefold in the presence of EKODE (26.0 μM). Cholesterol transport/ P-450scc activity was assessed by measuring basal and cAMP-stimulated pregnenolone production in the presence of cyanoketone (1.1 μM). EKODE (13.1 and 26.0 μM) significantly increased basal and cAMP-stimulated (0.1 mM) pregnenolone production. In contrast, EKODE decreased the effect of 1.0 mM cAMP. EKODE had no effect on early or late-pathway activity in isolated mitochondria. We conclude that EKODE stimulates corticosterone biosynthesis and amplifies the effect of ACTH. Increased levels of fatty acid metabolites may be involved in the increased glucocorticoid production observed in obese humans.