The study, published in Food Chemistry, found that the addition of antioxidants led to suppression in trans isomerisation. The researchers said that such inhibitory effects were associated with the kinds of what and concentrations.
“Our results suggested that the appropriate addition of antioxidants to edible oils during processing and cooking would facilitate the control of heat-induced trans isomerization of unsaturated lipids,” said Wakako Tsuzuki, from the National Food Research Institute in Japan, who authored the study.
He added that the antioxidants investigated in the research may also serve as anti-isomerizing agents during the heat-induced isomerisation of unsaturated lipids.
Trans fats are found naturally in small amounts in foods such as meat and dairy, but the vast majority are formed during the partial hydrogenation of vegetable oil that converts the oil into semi-solids for a variety of food applications.
Trans fats are attractive for the food industry due to their extended shelf life and flavour stability, and have displaced natural solid fats and liquid oils in many areas of food processing.
But scientific reports that trans fatty acids raise serum levels of LDL-cholesterol, reduce levels of HDL-cholesterol, can promote inflammation can cause endothelial dysfunction, and influence other risk factors for cardiovascular diseases, has led to a well-publicized bans in places like New York City.
Denmark introduced legislation in 2004 that required locally and imported foods to contain less than two per cent industrially made TFAs, a move that effectively abolished the use of partially hydrogenated vegetable oils in the country.
In the food industry this has been mirrored by an increase the in pressure on food manufacturers to reduce or remove trans fatty acids from their products and reformulate.
Trans fatty acids are produced during the purification processes of crude oils, such as thermal refining, bleaching, and deodorization.
“Although the amount of trans fatty acids contained in fresh purified edible oils is low, their amount are changed slightly, when purified edible oils are used for cooking and frying … Hence, studies focusing on the production of trans fatty acids in heated oils have increased markedly,” wrote the author.
Tsuzuki said that in partially hydrogenated oils, the double bonds in the unsaturated fatty acids are reduced, and some of them are converted from the natural cis to trans configuration.
“These changes in the molecular structures of the double bonds in lipids are responsible for imparting thermal stabilities to partially hydrogenated oils, unlike in unhydrogenated oils that are prone to thermal deterioration,” he explained.
Tsuzuki investigated the relationship between heat-induced cis/trans isomerization and thermal oxidative degradation of double bonds in unsaturated lipids, by testing the effects of several edible antioxidants on these two molecular structural changes of double bonds in triolein (cis-9, 18:1) and trilinolein (cis-9, cis-12, 18:2), heated to 180°C.
“The synchronous suppression in trans isomerization and cis deterioration of double bonds in these triacylglycerols were found by addition of antioxidants, whose inhibitory effects were associated with their kinds and concentrations,” said Tsuzuki.
He suggested that “the appropriate addition of antioxidants to edible oils during processing and cooking would facilitate the control of not only thermal oxidative degradation but also heat-induced trans isomerization […] in unsaturated lipid.”
Source: Food Chemistry
Published online ahead of print, doi: 10.1016/j.foodchem.2011.04.036
“Effects of antioxidants on heat-induced trans fatty acid formation in triolein and trilinolein”
Authors: W. Tsuzuki