Lymphatic absorption of α-linolenic acid in rats fed flaxseed oil-based emulsion

The bioavailability of a-linolenic acid (ALA) from flaxseed oil in an emulsified form v. a non-emulsified form was investigated by using two complementary approaches: the first one dealt with the characterisation of the flaxseed oil emulsion in in vitro gastrointestinal-like conditions; the second one compared the intestinal absorption of ALA in rats fed the two forms of the oil. The in vitro study on emulsified flaxseed oil showed that decreasing the pH from 7.3 to 1.5 at the physiological temperature (37 degrees C) induced instantaneous oil globule coalescence. Some phase separation was observed under acidic conditions that vanished after further neutralisation. The lecithin used to stabilise the emulsions inhibited TAG hydrolysis by pancreatic lipase. In contrast, lipid solubilisation by bile salts (after lipase and phospholipase hydrolysis) was favoured by preliminary oil emulsification. The in vivo absorption of ALA in thoracic lymph duct-cannulated rats fed flaxseed oil, emulsified or non-emulsified, was quantified. Oil emulsification significantly favoured the rate and extent of ALA recovery as measured by the maximum ALA concentration in the lymph (Cmax > 14 mg/ml at 3 h in the emulsion group v. 9 mg/ml at 5 h in the oil group; P<0.05). Likewise, the area under the curve of the kinetics was significantly higher in the emulsion group (48 mg/h/ml for rats fed emulsion v. 26 mg/h/ml for rats fed oil; P<0.05). On the whole, ALA bioavailability was improved with flaxseed oil ingested in an emulsified state. Data obtained from the in vitro studies helped to partly interpret the physiological results. (Author's abstract)
The bioavailability of a lipid nutrient present in food depends on a number of varialbes incldung the physical state of the TAG.  The aim of the present study was to measure the intestinal absorption of alpha-linolenic acid (ALA) in rats after the administration of flaxseed oil in both emulsified and non-emulsified states. This research demonstrated that TAG were more efficiently absorbed when provided as an emulsion rather than as a bulk phase. As a result, fatty acid and ALA enrichment in chylomicrons was greater (Cmax) and faster (Tmax) in rats fed emulsified oil than in rats fed bulk oil. The results suggest that TAG of the emulsified oil may be hydrolysed faster by pancreatic lipase, resulting in an increased absorption of hydrolysed products. In contrast, in the case of flaxseed oil in the bulk phase, the interface must be created by the mechanical mixing in the stomach and intestine. ALA enrichment in chylomicrons was observed irrespective of the dietary form of flaxseed oil. However, the percentage of ALA esterified at the sn-2 position of chylomicron TAG was slightly lower (18 and 23% for oil and emulsion, respectively) compared with that in dietary flaxseed oil (28 %). The present results showed that the extent of fatty acid absorption, and especially of ALA, was significantly higher in the rat group ingesting emulsified oil compared with the group given oil in the non-emulsified state. This type or investigation is key in the development of supplemental flax oil which is not only efficacious but bioavailable. (Editor's comments)