Correlations between trans isomers of α‐linolenic acid and polar components in linseed oil during heating

Abstract

During heating of oils, trans fatty acids can be formed via various chemical reactions, which are not treated as free fatty acids but as part of triglycerides. The factors that influence the formation of trans isomers of a-linolenic acid (TALAs) and the correlation between TALAs and total polar components were studied by heating linseed oil. Both heating temperature and time affected TALA formation. Increasing temperature from 170°C to 200°C for 2 h produced more TALAs than conducting 14 h heating at 170°C. Pumping air promoted oxidation of a-linolenic acid, reducing the content of TALAs, especially c9, c12, t15-C18:3. TALA contents were positively correlated with total polar components, triglyceride oligomer, triglyceride dimer and diglyceride (DG) (r = 0.456-0.813), but negatively correlated with free fatty acids (r = À0.650-0.469). No correlation was found between TALAs and oxidised triglyceride monomer. Compared with di-TALAs, mono-TALAs had stronger correlation with DG.

Characterization of the evolution of free radicals and TALAs in linseed oil during heat treatment

“…Based on these results, it appears that the isomerization of the double bonds located at positions 9 and 15 could happen with a higher probability compared to the isomerization of the double bonds situated at position 12. This was due to the proximity of positions 12 and 15 to the structural chain's extremities [ 6 , 10 ].…”

“…The interconversion of fatty acid types, along with concurrent processes of isomerization, polymerization, and oxidation, further complicates the composition of these oil systems. Consequently, these complexities hinder the research emphasis on the properties and advantages of trans fatty acids (TFAs) [ 6 ]. TFAs have always been the focus of food safety issues; excessive intake of TFAs will lead to an increase in the incidence of cardiovascular disease.…”

“…The ability of free radicals to promote isomerization is well documented [ 6 ], with thermal processing inducing the isomerization of UFAs to yield more stable TFAs [ [23] , [24] , [25] , [26] ].This method allows for the evaluation of early-stage lipid oxidation related to various diets [ 27 , 28 ]. Li et al [ 29 ] proposed that when α-linolenic acid is heated at high temperatures, it can produce single-TALAs, double-TALAs, and tri-TALAs.…”