Phytosterols in frying oils: evaluation of their absorption in pre-fried potatoes and determination of their destruction kinetics after repeated deep and pan frying

The levels of β-sitosterol and total phytosterols were monitored in pre-fried potatoes during eight successive pan- and deep-frying sessions in five different commercial frying oils (virgin olive oil, sunflower oil, palm oil, cottonseed oil and vegetable shortening oil). The amount of these constituents that were transferred from the frying oils to the potatoes at the end of each frying session was determined prior and after frying by GC/FID. Except for the potato enrichment with phytosterols, the kinetics of the destruction of β-sitosterol and total phytosterols, mainly due to thermal oxidation of the oils, were evaluated for each of the five different types of oil. The experiments showed that in most cases the destruction of both β-sitosterols and total phytosterols followed first order kinetics with quite good correlation coefficients (R>0.92) and the reaction constant k was found to be at the range of 0.004 - 0.028 min-1. Concerning the absorption of the two types of phytosterols in the fried potatoes during frying, they were found to be at the range (average) of 0.4-27% of their initial content in the oil at the beginning of each frying process (eight frying processes/session), depending on the type of oil and the constituent.