Quantitation of short-chain glycerol-bound compounds in thermoxidized and used frying oils. A monitoring study during thermoxidation of olive and sunflower oils.
Major short-chain glycerol-bound compounds were investigated in olive oil (OO) and conventional sunflower oil (SO) during thermoxidation at 180 degrees C for 5, 10, and 15 h. These compounds included methyl heptanoate (C7:0), methyl octanoate (C8:0), methyl 8-oxo-octanoate (8-oxo-C8:0), methyl 9-oxononanoate (9-oxo-C9:0), dimethyl octanodiate (C8:0 diester), and dimethyl nonanodiate (C9:0 diester), which were analyzed by GC after derivatization of triacylglycerols to fatty acid methyl esters. An acceptable linear correlation (r = 0.967) was found between the total content of these compounds and the total content of polar compounds, suggesting that quantitation of the major short-chain glycerol-bound compounds provides a good indication of the total alteration level of oils heated at frying temperature. Samples with levels of polar compounds around 25% on oil showed total contents within 2-3 mg/g of oil. To determine the content of these compounds in used frying oils, 10 samples from restaurants and fried-food outlets in Spain were analyzed. Results showed total levels between 2.13 and 7.56 mg/g of oil in samples with contents of polar compounds ranging from 18.8 to 55.5% on oil. Samples with levels of polar compounds of approximately 25% showed total contents of the short-chain compounds similar to those found in the thermoxidized oils, that is, within 2-3 mg/g of oil.
Velasco
Joaquín
J
Instituto de la Grasa (CSIC), Avenida Padre García Tejero 4, 41012 Sevilla, Spain. jvelasco@cica.es
Marmesat
Susana
S
Berdeaux
Olivier
O
Márquez-Ruiz
Gloria
G
Dobarganes
Carmen
C
D002849:Chromatography, Gas; D005227:Fatty Acids / Q000032:analysis / Q000378:metabolism; D005990:Glycerol / Q000378:metabolism*; D006358:Hot Temperature; D006861:Hydrogen Peroxide / Q000032:analysis; D000069463:Olive Oil; D010084:Oxidation-Reduction; D010938:Plant Oils / Q000737:chemistry*; D000074242:Sunflower Oil; D014280:Triglycerides / Q000737:chemistry
D005227:Fatty Acids; D000069463:Olive Oil; D010938:Plant Oils; D000074242:Sunflower Oil; D014280:Triglycerides; D006861:Hydrogen Peroxide; D005990:Glycerol