OCCURRENCE OF ARTIFICIAL TRANS-POLYUNSATURATED FATTY-ACIDS IN REFINED (DEODORIZED) WALNUT OILS

The fatty acid composition of commercial refined or cold-pressed walnut oils was determined with a special attention to geometrical isomers of linoleic (cis-9,cis-12 18:2) and linolenic (cis-9,cis-12,cis-15 18:3) acids. In contrast to cold-pressed samples, relined walnut oils contain such artificial isomers. Linolenic acid geometrical isomers (LAGIs) represent from 0.6 to 1.4% of total fatty acids in these oils. These values correspond to degrees of isomerization of linolenic acid ranging from 5 to 10%. Total trans-polyunsaturated fatty acids account for 0.8 to 1.8% of total fatty acids. The nature and relative distribution of individual LAGIs in refined walnut oils are similar to those found in commercial refined soybean and rapeseed oils. The cis9,cis-12,trans-15 ; cis-9,trans-12,cis-15 ; trans-9,cis-12,cis-15 and trans-9,cis-12,trans-15 18:3 isomers account for 49.2-52.9%, 6.3-7.8%, 38.1-41.9% and 2.2-3.1%, respectively, of total LAGIs. Heating a cold-pressed walnut oil under vacuum at 230-degrees-C leads to the formation of the same four isomers in about the same proportions, except for the minor trans-9,cis-12,trans-15 18:3 isomer which is present in trace amounts only (<2% of total LAGIs). It is deduced that deodorization of the refined walnut oils was conducted at temperatures equal to or higher than 230-degrees-C during more than 3 h.