No abstract

Previous studies have shown that canola oil (CA), compared with soybean oil (SO), shortens the life span of stroke-prone spontaneously hypertensive (SHRSP) rats, a widely used model for hemorrhagic stroke. SHRSP rats are highly sensitive to dietary cholesterol manipulations because a deficiency of membrane cholesterol makes their cell membranes weak and fragile. Phytosterols, abundant in CA but not in SO, can inhibit the absorption of cholesterol and also replace a part of cholesterol in cell membranes. This study was performed to determine whether the high concentration of phytosterols in CA might account for its life-shortening effect on SHRSP rats. Male, 35-d-old SHRSP rats (n = 28/group) were fed semipurified diets containing CA, SO, CA fortified with phytosterols (canola oil + phytosterols, CA + P), SO fortified with phytosterols (soybean oil + phytosterols, SO + P), corn oil (CO), olive oil (OO) or a fat blend that mimicked the fat composition of a representative Canadian diet (Canadian fat mimic, CFM; 10 g/100 g diet). These fats provided 97, 36, 207, 201, 114, 27 and 27 mg phytosterols/100 g diet, respectively. Ten rats from each group were killed after 30-32 d for blood and tissue analyses. The remaining rats (18/group) were used for determination of life span. The life span of SHRSP rats fed the high phytosterol oils (CA, CA + P, SO + P and CO) was significantly (P<0.05) shorter than that of CFM- and SO-fed rats. At 30-32 d, the groups fed the high phytosterol oils had greater levels of phytosterols and significantly (P<0.05) higher ratios of phytosterols/cholesterol in plasma, RBC, liver and kidney, and a significantly (P<0.05) lower RBC membrane deformabilty index than the groups fed oils low in phytosterols (SO, OO and CFM). The mean survival times were correlated with RBC deformability index (r(2) = 0.91, P = 0.0033) and cholesterol concentration (r(2) = 0.94, P = 0.0016), and inversely correlated with RBC phytosterol concentration (r(2) = 0.58, P = 0.0798) and phytosterols/cholesterol (r(2) = 0.65, P = 0.0579), except in the OO group. This study suggests that the high concentration of phytosterols in CA and the addition of phytosterols to other fats make the cell membrane more rigid, which might be a factor contributing to the shortened life span of SHRSP rats.

The fatty acid composition, total trans content (i.e., sum of all the fatty acids which may have one or more trans double bonds) and geometric and positional isomer distribution of unsaturated fatty acids of 198 human milk samples collected in 1992 from nine provinces of Canada were determined using a combination of capillary gas-liquid chromatography and silver nitrate thin-layer chromatography. The mean total trans fatty acid content was 7.19 +/- 3.03% of the total milk fatty acids and ranged from 0.10 to 17.15%. Twenty-five of the 198 samples contained more than 10% total trans fatty acids, and thirteen samples contained less than 4%. Total trans isomers of linoleic acid were 0.89% of the total milk fatty acids with 18:2 delta 9c,13t being the most prevalent isomer, followed by 18:2 delta 9c,12t and 18:2 delta 9t,12c. Using the total trans values in human milk determined in the present study, the intake of total trans fatty acids from various dietary sources by Canadian lactating women was estimated to be 10.6 +/- 3.7 g/person/d, and in some individuals, the intake could be as high as 20.3 g/d. The 18:1 trans isomer distribution differed from that of cow's milk fat but was remarkably similar to that in partially hydrogenated soybean and canola oils, suggesting that partially hydrogenated vegetable oils are the major source of these trans fatty acids.

No abstract

This study examined the stability of whole and ground flaxseed, either alone or as an ingredient in a muffin mix, by measuring oxygen consumption and changes in α‐linolenic acid under various conditions. When ground flaxseed was heated at 178°C in a sealed tube, headspace oxygen decreased from 21 to 2% within 30 min, while that of whole flaxseed decreased only slightly up to 90 min at 178°C. Under the same conditions, the oxygen consumption of lipids extracted from an equivalent amount of flaxseed was between the whole flaxseed and the ground flaxseed. After heating to 178°C for 1.5 h, α‐linolenic acid decreased from 55.1 to 51.3% in ground flaxseed, and to 51.7% in lipid extracts, but it remained unchanged in the whole flaxseed. Ground flaxseed with large (<20 mesh) or small (>35 mesh) particle size absorbed more oxygen than samples with medium particle size when heated at 122°C for 8 h. Long‐term storage of whole or ground flaxseed or lipid extracts showed that all three preparations were stable at room temperature for 280 d with 12 h light/dark cycles. A muffin mix, containing 28.5 wt% flaxseed flour, consumed oxygen more rapidly than a control muffin without flaxseed flour at a baking temperature of 178°C for 2 h, but the α‐linolenic acid remained unchanged in both muffin mixes. Polymers derived from triglyceride oxidation and newtrans isomers of α‐linolenic acid were not detected under the present experimental conditions. Under typical baking conditions, there is minimal loss of α‐linolenic acid from flaxseed, although the manner of incorporation of flaxseed in food products should be considered to minimize oxidation of α‐linolenic acids.