Isolation and identification of polar lipophilic aldehydes in oxidized vegetable oils.

摘要

alpha-,beta-Unsaturated hydroxyaldehydes, including 4-hydroxy-2- trans-nonenal (HNE) and 4-hydroxy-2-trans-hexenal (HHE) are known to be toxic products of the peroxidation of the unsaturated fatty acids linoleic acid and linolenic acid, respectively. Soybean oil, which contains both of these fatty acids (∼53% linoleic acid and ∼7% linolenic acid) is widely available and is often used for frying food. HNE was identified by HPLC and GC-MS as the major polar lipophilic secondary lipid peroxidation product generated during the thermal oxidation of soybean oil at frying temperature (185°C) in the presence of air. In addition to HNE, HHE and two other hydroxyaldehydes, 4-hydroxy-2-trans-octenal (HOE) and 4-hydroxy-2- trans-decenal (HDE) were also found in heated soybean oil. The formation of these and other polar lipophilic peroxidation products was observed to increase when the oil was continuously heated at frying temperature, up to a maximum concentration, after which time the amount of the oxidation products decreased, possibly as the aldehydes underwent further oxidation, degradation, or polymerization. When soybean oil was heated in intermittent heating periods for a short time each day with a resting period at room temperature in between heating sessions, the formation of HNE and the other hydroxyaldehydes was the same as when heat was continuously applied. The absorption of HNE into food fried in thermally oxidized oil was also investigated. It was found that HNE was absorbed into the fried food along with the frying oil and that the oil in the food had the same HNE content as the frying oil. These experiments indicate that heat treatment, such as frying, of linoleic acid and linolenic acid containing vegetable oil results in the formation of several toxic lipid peroxidation products. The detrimental biological effects associated with lipid peroxidation may be due in part of consumption of these hydroxyaldehydes in fried foods.