Column and high-performance size exclusion chromatography applications to the in vivo digestibility study of a thermoxidized and polymerized olive oil

This study aimed (i) to design an in vivo model to study fat digestibility, and (ii) to apply this design to test the in vivo digestibility of a highl y thermoxidized olive oil. True digestibility of unheated olive oil was tes ted 2, 4, 6, and 7 h after administering 1 g of olive oil/100 g body weight to young adult Wistar rats by means of esophageal probes. Remaining gastro intestinal lumen fat showed an inversely linear relationship (r = -0.9932; P < 0.001) with the length of the experiment. A 4-h test was considered ade quate because after this period, half of the oil administer still remains i n the lumen, making it possible to accurately measure the different nondige sted, nonabsorbed thermoxidized compounds. In a second experiment, fresh ol ive oil (3.6 mg polar content/100 mg oil) was heated at 180 degrees C for 5 0 h in the presence of air; the polar content in this oil rose to 46.0 mg/1 00 mg oil. After 4 h, the true digestibility coefficient of 50-h heated oli ve oil did not significantly change, although it tended to decrease (24%) w ith respect to the unheated oil. Silica gel column chromatography and high- performance size exclusion chromatography were used to quantify nonthermoxi dized and thermoxidized products present in the oils and in the gastrointes tinal lumen after these test periods. True digestibility of the different t hermoxidized compounds from the heated oil was 30-40%, whereas that of ther moxidized compounds from the fresh oil was much higher (similar to 80%). No noxidized triacylglycerol hydrolysis was negatively affected by the presenc e of large amounts of thermoxidized compounds. The present proposed model s eems to be a useful toot for the study of thermoxidized oils. Data also sha w that thermoxidized compounds from abused olive oil are poorly but activel y hydrolyzed and absorbed in vivo.