Bruhl L.,Max Rubner InstituteInstitute of Quality and Safety of CerealsDetmoldGermany |
Weisshaar R.,Chemisches und Veterinaruntersuchungsamt CVUA StuttgartFellbachGermany |
Matthaus B.,Max Rubner InstituteInstitute of Quality and Safety of CerealsDetmoldGermany
European Journal of Lipid Science and Technology | Year: 2015
The occurrence of monoepoxy fatty acids in used frying oils and in other common foods has been determined. Monoepoxy fatty acids with trans-9,10- and cis-9,10-epoxystearate and trans-12,13-, trans-9,10-, cis-12,13- and cis- 9,10-epoxyoctadecenoate were found at average levels of 3.7g/kg in used frying fats and oils, but also at about 2g/kg in the fat fraction of chocolate. They were also detected in pumpkin seed, sweet almond, groundnut, sunflower, and olive oils at average levels of 3.4, 1.7, 1.4, 1.0, and 0.2g/kg, respectively. Their formation during heating at 175°C was observed for sunflower, rapeseed, soybean, and linseed oil and compared with the increase of polar compounds and polymerized triacylglycerols as other important quality indicators for frying oils. During heating for 16h, the level of monoepoxy fatty acids increased to about 30, 18, 8, and 4g/kg for olive, sunflower, linseed, and rapeseed oils, respectively. The influence of the heating temperature was surveyed for refined soybean oil at 160, 170, 180, and 200°C. Heating of two sets of five different refined and virgin rapeseed oils revealed a significant lower formation of monoepoxy fatty acids for refined oils at a median level of 4.6g/kg compared to7.7g/kg for virgin oils. Practical applications: Determination of fatty acid methyl esters is one of the most common analyses for the evaluation of oils and fats. The assessment of the monoepoxy fatty acids as part of these analyses can provide a first indication about used frying fats and oils, which reached the end of their applicability. The formation of monoepoxy fatty acids is affected by the fatty acid composition of the oil, the heating temperature, and the production of the oil. Therefore, frying oils may contain varying amounts of monoepoxy fatty acids at the maximum limit for polar compounds and polymerized triacylglycerols as used in the official food control. However, all used frying oils investigated by the official food control showing more than 7g/kg of monoepoxy fatty acids had to be rejected due to the limits exceeded for polar compounds and polymerized triacylglycerols. Therefore, this limit of 7g/kg monoepoxy fatty acids level is proposed as a level for screening the usability of used frying fats and oils. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.