A fritura é um meio de preparo de alimentos bastante utilizado em todo o mundo. Neste processo o óleo ou gordura é submetido a altas temperaturas na presença de ar e de água. Esta condição propicia a formação de um número considerável de substâncias oriundas de reações térmicas, oxidativas e hidrolíticas (CHANG; PETERSON; HO, 1978;MÁRQUEZ-RUÍZ, 1988; GASPAROLI, 1998;JORGE et al., 1996;MÁRQUEZ-RUIZ;TASIOULA-MARGARI;DOBARGANES, 1995;NAWAR, 1998;SCHWARTZ;RADY;CASTAÑEDA, 1994;VELASCO et al., 2004b). As reações hidrolíticas liberam substâncias como diacilgliceróis e ácidos graxos livres, e as reações térmicas e oxidativas formam um grande número de substâncias como triacilgliceróis dimerizados e polimerizados e monômeros de triacilgliceróis oxidados (VELASCO et al., 2004b).Estes grupos de substâncias constituem os compostos polares (AOAC, 2003). Neste sentido, legislações de muitos países preconizam para óleos e gorduras usados em frituras o valor máximo de 25%, m/m do óleo, em compostos polares (DANA; SAM SAGUY, 2001).A alteração tanto quantitativa quanto qualitativa destes óleos ou gorduras depende de um número elevado de variáveis entre elas, a que está relacionada com a adição de óleo novo AbstractDuring frying, fats and oils undergo degradation with the formation of polar compounds. Among these are polymeric triglycerides, as well as oxidized monomeric triglycerides. The last group has been related to several diseases and contains groups including epoxy, keto and hydroxy groups of importance from a quantitative point of view. In this study, monoepoxyacids, monoketoacids and monohydroxyacids were quantified in partially hydrogenated soybean oil, soybean oil and palm oil, after heating for 25 hours, at 180 °C, in frying experiments. The determination was carried out by gas chromatography after fat derivatization to fatty acid methyl esters at room temperature and concentration of the compounds of interest by solid phase extraction on silica cartridges. Quantitative analyses of polar fatty acids were also obtained by combination of adsorption and size exclusion chromatography. The major content corresponded to polymeric compounds. Amounts ranging from 3.30 to 8.24; from 1.51 to 4.32 and from 3.42 to 8.71 mg.g -1 were found for monoepoxyacids, monoketoacids and monohydroxyacids, respectively, for samples containing polar compounds between 20.8 and 44.1%. The results suggested that monounsaturated oils have a higher tendency to the formation of oxidized monomers while polyunsaturated oils have a higher tendency to the formation of polymers. Keywords: epoxy fatty acids; frying oils; hydroxy fatty acids; keto fatty acids; polar compounds; polymers. ResumoNa fritura, os óleos e gorduras sofrem degradação formando os compostos polares, como os triacilgliceróis polimerizados e os monômeros de triacilgliceróis oxidados, estes últimos têm sido relacionados a patologias e se constituem de grupos como os monoepoxiácidos, monocetoácidos e monohidroxiácidos. Foram determinados os teores destes três grupos de substâncias, atrav...
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