COMPARATIVE STUDIES OF OXIDATIVE STABILITY OF EDIBLE OILS BY CHEMICAL AND INSTRUMENTAL METHODS.

DOS SANTOS, CRISTINA; LEIVA, GRACIELA; SEGATIN, NATASA; SANTAGAPITA, PATRICIO R.; BUERA, M. PILAR; MAZZOBRE, M. FLORENCIA

Rosario

Congreso; XIV Congreso CYTAL (Congreso Argentino de Ciencia y Tecnología de Alimentos); 2013

Asociación Argentina de Tecnólogos Alimentarios (gral y filial Sta Fe)

Food health and safety may be affected by the presence of toxic substances produced during the oxidation or thermal degradation of lipids. Besides, the oxidation of polyunsaturated lipids often results in reduced sensory acceptability, due to the development of rancid odors and flavors associated with low molecular weight volatile compounds. Oxidative stability is thus one of the most important indicators of the quality of edible oils, and greatly influences its acceptability and market value. The oxidation of oils takes place through a chain of reactions, and a number of methods have been developed for evaluating the oxidative stability of oils at different stages of the reactions. The aim of this study was to evaluate the degree of vegetable oil oxidation and the relationship between different parameters, which can be determined by low field nuclear magnetic resonance (LF-NMR), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FT-IR). Three different commercial vegetable oils from Argentinean market were used for experiments: chia, rose hip seed and sunflower oils, each having different fatty acid composition. Rose hip oil contains more than 60% of linolenic acid, chia and sunflower contain more than 50% of linoleic acid. Oils were heated in an air force circulating oven at 175°C for 4 hours to favor their oxidation. Then all samples were cooled down to room temperature and stored under nitrogen at 5°C for further analysis. The first step of oil oxidation, i.e. formation of hydroperoxides, was evaluated with the peroxide value (PV) and the second step of oil oxidation, i.e. formation of aldehydes, was evaluated by the thiobarbituric acid reactive substances content (TBARs). The oxidation onset temperature (OOT), the crystallization and melting temperatures were obtained by DSC measurements. The relaxation times of 1H and crystallization kinetics were studied by LF-NMR and the changes of characteristic signals for hydroperoxide, double bonds and aldehyde group were determined by FT-IR. All determinations were performed in triplicate analysis. The OOT and the crystallization temperature obtained by DSC showed an excellent correlation with the PV and TBARs values independent of the edible oil source. The relaxation time of 1H determined by LF-NMR for both fresh and heated oils decreased as the TBARs values increased. Changes in aldehyde (1745 cm-1) and double bond (1655 cm-1) signals obtained by FT-IR were observed in the heated oils and compared with those of fresh oils. LF-NMR, DSC and FT-IR have the potential to be used as non-chemical techniques for determining oil quality parameters. These methods have the advantage of being simple, rapid, requiring no sample preparation or toxic chemical reagents.