Effect of heating oils and fats in containers of different materials on their trans fatty acid content

Abstract

The nature of the container material and temperature employed for deep-frying can have an influence on the development of trans fatty acids (TFAs) in the fat used. The present study was undertaken to determine the effect of heating vegetable oils and partially hydrogenated vegetable fats with different initial TFA content in stainless steel, Hindalium (an aluminium alloy), cast iron and glass containers. Ground nut oil (oil 1), refined, bleached and deodorised (RBD) palmolein (oil 2) and two partially hydrogenated vegetable oils with low (fat 1) and high (fat 2) TFA content were uniformly heated at 175-185 °C over a period of 12 h. An increase in TFA content to 20 g kg⁻¹ was observed in oil 2 in the cast iron container, while a decrease in TFA content of 20-30 g kg⁻¹ was observed in fat 2 in all containers. The heating process of fats and oils also led to an increase in Butyro refractometer reading and colour values. This study showed that the TFA 18:1t content of oil 1, oil 2 and fat 1 increased with repeated or prolonged heating. The cast iron container showed the highest increase in TFA 18:1t for RBD palmolein (oil 2). The amount of linoleic acid trans isomers formed in the heating process was negligible. Fat 2 with high initial TFA content showed a decrease in TFA 18:1 and 18:2 on heating in all containers. Oils heated in glass and stainless steel containers showed less TFA 18:1t formation.