Short-term in vivo digestibility of triglyceride polymers, dimers, and monomers of thermoxidized palm olein used in deep-frying

Palm olein used to fry potatoes 40 and 90 times was tested in a short-term in vivo digestibility experiment. Total alteration, expressed as polar cont ent, reached 26.4 g/100 g of olein, and the amount of triglyceride polymers , triglyceride dimers, and oxidized triglycerides increased severalfold, as a result of repeated frying use of the olein. True digestibility of used a nd unused whole palm olein and that of the nonoxidized triglycerides and di fferent polar compounds was tested after 1 g of palm olein/100 g of body we ight was administered to young adult Wistar rats by means of an esophageal probe. Luminal fat was obtained 4 h later, and its polar and nonpolar fract ions were separated and quantified using column chromatography. Thermoxidiz ed and hydrolytic compounds were quantified by high-performance size exclus ion chromatography and compared to the compounds administered. The true dig estibility coefficient of palm olein used in frying 90 times was 30% lower than that of unused palm olein. True digestibility of triglyceride polymers and dimers of unused palm olein was quite high (>50%). After 90 uses, dige stibility of dimers was significantly lower (p < 0.01), being similar to 30 %. Nonoxidized triglyceride hydrolysis was negatively affected by the prese nce of large amounts of thermoxidized compounds. The amount of monoglycerid es and free fatty acids found in the luminal fat also decreased as a conseq uence of the arrest of pancreatic lipase activity by thermoxidized compound s formed through repeated frying.