Use of polar and nonpolar fractions as additional information sources for studying thermoxidized virgin olive oils by FTIR

Abstract

SUMMARY:Fourier transform infrared (FTIR) spectroscopy has been proposed to study the degradation of virgin olive oils (VOO) in samples undergoing thermoxidation. The polar and nonpolar fractions of oxidized oils have been analyzed by FTIR to provide further information on the minor spectral changes taking place during thermoxidation. This information assists in the interpretation of the spectra of the samples. For this purpose polar and nonpolar fractions of 47 VOO samples thermoxidized (190 °C) in a fryer were analyzed by FTIR. The time-course change of the band area assigned to single cis double bonds was explained by their correlation with the decrease in oleic acid (adjusted-R 2 =0.93). The bands assigned to the hydroxyl groups and the first overtone of ester groups was better studied in the spectra collected for the polar and nonpolar fractions, respectively. The bands assigned to peroxide, epoxy, tertiary alcohols and fatty acids were clearly observed in the spectra of the polar fraction while they are not noticeable in the spectra of the oils. KEYWORDS: FTIR spectroscopy; Polar and nonpolar fractions; Thermoxidation; Virgin olive oil RESUMEN: Uso de las fracciones polares y no polares como fuente de información adicional al estudio de aceites de oliva vírgenes por FTIR. La espectroscopía de infrarrojos por transformada de Fourier (FTIR) se ha propuesto para estudiar la degradación de los aceites de oliva vírgenes (AOV) sujetas a termoxidación. Las fracciones polares y no polares de aceites oxidados se analizaron mediante FTIR para obtener más información sobre los cambios espectrales menores que tienen lugar durante la termoxidación. Esa información ayuda en la interpretación de los espectros de las muestras puras. Con este objetivo, fracciones polares y no polares de 47 AOV termoxidados (190 °C) en una freidora se analizaron mediante FTIR. La banda asignada a dobles enlaces cis se explica por su correlación con la disminución de ácido oleico (R 2 -ajustado=0,93). Las bandas asignadas a los grupos hidroxilos y del primer sobretono de los grupos éster se estudió mejor en los espectros recogidos para la fracción polar y no polar, respectivamente. Grupos asignados a peróxidos, epoxi, alcoholes terciarios y los ácidos grasos se observan claramente en los espectros de la fracción polar.

Fourier transform infrared spectroscopy-chemometric approach as a non-destructive olive cultivar tool for discriminating Portuguese monovarietal olive oils

“…FTIR-chemometric tools allowed the quantification of several characteristics of olive oils (e.g., fatty acids, wax, diacylglycerol, squalene, iodine values, free acidity, peroxide value, color pigment contents, sensory intensities and rancid markers, phenol content and antioxidant activity, among others) [12][13][14][15][16][17][18][19], the identification of olive oil adulteration/mixing with different vegetable oils as well as to discriminate olive oils from other vegetable oils [14,[20][21][22][23][24][25][26], to discriminate the geographical origin of olive oils [12,27,28], to evaluate the thermo/auto oxidation of olive oils [29,30], and to differentiate/classify olive oils according to their commercial grade [31]. Besides these applications, olive oils were also successfully classified according to the olive cultivar/botanical variety, which constitute a major commercial interest due to the high value of monovarietal oils.…”

Profil Senyawa Polar Tiga Jenis Minyak Goreng Selama Penggorengan Tahu Dan Tempe

“…Hal ini sejalan dengan penurunan %T pada daerah 964-980 cm -1 menunjukkan terbentuknya trans ikatan rangkap. Tena et al (2014) menyatakan daerah infrared optimum pada minyak virgin olive untuk memprediksi adanya TPM dari minyak yang teroksidasi adalah 978-960 cm -1…”

“…. Tena et al (2014) menyatakan perubahan penyerapan pada 1780-1670 cm -1 khususnya pada puncak 1743 cm -1 dapat menunjukkan terjadinya hidrolisis trigliserida, namun tidak dapat memastikan gugus C=O sebagai pengurangan dari ester atau penambahan akibat adanya asam lemak bebas (sebagai asam karboksilat).…”

“…Puncak penyerapan tersebut menunjukkan adanya first over-tone gugus ester dari trigliserida. Pada bilangan gelombang lebih tinggi (spektrum menurun) menunjukkan adanya gugus hidroksil (stretching OH) yang dapat menunjukkan bahwa minyak goreng telah bertambah kepolarannya (Tena et al, 2014). Semakin banyak ditemukan gugus hidroksil maka semakin polar minyak tersebut.…”

Influence of natural and synthetic antioxidants on the degradation of Soybean oil at frying temperature

“…Frying leads to degradation of oil by accumulating polar compounds, which involves a set of physicochemical reactions such as thermo-oxidation, hydrolysis and polymerization (Orozco et al 2011;Tena et al 2014). Polar compounds include oxidized, dimerized and polymerized triacylglycerols along with diacylglycerols and free fatty acids.…”