A parametric study on the effect of heating on the chemical composition of selected oils and fats
1998
Huyghebaert, G. (Centrum voor Landbouwkundig Onderzoek, Merelbeke (Belgium). Station voor Kleinveeteelt)
Four selected types of oils and fats (crude soybean oil, refined and partially hydrogenated soybean oil, refined lard and refined beef tallow) were subjected to repeated and discontinuous heating operations at deep frying temperature under either air or nitrogen supply. Free fatty acids, saponification value, iodine value, peroxide value, TBA-value, fatty acid profile (U/S-ratio), and (non)polar fraction were monitored at regular intervals. There was a general trend showing the modifications in composition to be proportional to the degree of unsaturation, the oxidative status of the gas medium, and the number of heating cycles. Nevertheless there were some more specific changes. The change in free fatty acids was rather limited. Saponification value was negatively correlated with I2 value and U/S-ratio. The course of the peroxide and TBA value with prolonged heating depended on the partial oxygen pressure. During heating, there was a continuous conversion of the nonpolar fraction into the polar and residue fraction, thereby being not related to the degree of unsaturation. The stability of the C18-unsaturates was inversely related to the number of double bonds. Additional research is needed to validate in-vivo the estimated MEn-values based on the present values of both iodine and nonpolar fraction.Regardless of the type of oil or fat, all analytical specifications for quality and reliability characteristics must be used with care.
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