Degradation of α‐linolenic acid during heating

Abstract

Degummed bleached rapeseed oil was heated at 210, 220, and 230°C for up to 86 h under reduced pressure with nitrogen stripping. No significant change of total linoleic acid content was found, but a decrease of the total linolenic acid content was observed under extreme conditions. The degradation rate of linolenic acid is described as a function of heating time and operating temperature. Linolenic acid degradation can be predicted for any set of conditions by the established model. No significant degradation of linolenic acid can occur under standard deodorization conditions. Vegetable oils are refined by means of alkali-or physical refining. In both industrial processes, the last step consists of heating the oil for 1 to 4 h at a high temperature (180-260°C), under low pressure (1-10 mbar), with steam or nitrogen injection. The effects of processing on minor components of oils, such as sterols, steryl esters, tocopherols, polymeric triglycerides and trans fatty acids, have been thoroughly investigated (1), but little information is available on degradation of polyunsaturated fatty acids during deodorization.Studies about refined oils that are subjected to long-term heat treatment mainly cover the user's point of view, e.g., heating in the presence of air and deep-frying of different foods. These papers focus on the measurement of free fatty acids, conjugated dimers and trimers, polymeric triglycerides, and trans fatty acid isomers (2-5). Also data related to fatty acid degradation can be found (6-9).In previous laboratory experiments at Lesieur Research and Development Center (Coudekerque-Branche, France), in addition to the isomerization of the polyunsaturated fatty acids, a decrease in the linolenic acid content was observed during long-term heating under vacuum, depending on time and temperature.To complete the study, special heating trials with extremely long residence time were carried out on a pilot scale for investigation of the degradation kinetics. EXPERIMENTAL PROCEDURESExperiments. The experiments were carried out in the pilot plant refinery of Cereol Group Research and Development Centre in Budapest (Hungary). Degummed and bleached oil was supplied by the Cereol physical refinery of Martfu (Hungary); the fatty acid composition of this treated oil was as follows: 16:0, 4.8%; 16:1, 0.2%; 18:0, 1.8%; 18:1, 60.1%; 18:2, 21.3%; 18:3, 8.3%; 20:0, 0.6%; 20:1, 1.3%; 22:0, 0.4%; 22:1, 0.4%; and unidentified, 0.8%. Heating of the oil was performed at 1.5 mbar pressure at 210, 220, and 230°C for 86, 48, and 24 h, respectively, in a pilot-scale batch deodorizer. In all three experiments, 100 L of oil were heated, under reduced pressure (<2 mbars) and nitrogen stripping, up to the operating temperature (±1°C). Continuous heating lasted from 24 to 86 h, depending on the temperature. Samples were taken for the analysis of the fatty acid composition every 2 h through a cooled sampling system.Determination of total fatty acid composition. Fatty acid methyl esters (FAME) were prepared according to the official method ...

Physical refining of sunflower oil

“…In the frame of an EU-funded FAIR project, Cereol and Lesieur R&D Laboratory have carried out a laboratory and pilot test and as a result a kinetic model has been established and validated at pilot scale level [12][13][14].…”

Physical refining of edible oils

“…The cis, trans isomerization did not take place at all at low temperatures of only 190°C [130]. In model experiments degummed and bleached rapeseed oil was heated at 210, 220, and 230°C for up to 86 hours (not applied in the industrial production) under reduced pressure and with nitrogen stripping [134,135]. Small amounts of cyclic acids with 5-6 member cycles were detected in heated dienoic and trienoic acid-rich oils [132].…”

Role of the central R&D laboratories of an international group in the field of Food-Feed Safety

“…Each process is evaluated for its effectiveness at removing contaminants (pesticide residues, heavy metals) and unwanted compounds (prooxidative metals, degradation products) and the risk of formation unwanted compound (trans fatty acids dimer, trimer, polymer). (For more details of our results see [1][2][3][4]6]. )…”