Use of DSC for the determination of oxidation temperature of unrefined vegetable oils obtained by cold extraction
Articulos de Divulgación
Iñiguez-Moreno, M., Barros-Castillo, J.C., Calderón-Santoyo, M., Cuevas-Glory, L.F., Ragazzo-Sánchez, J.A.
In the last years, the consumption of vegetable oils has increased in comparison with those obtained from animal sources, due to their high nutritional value. These oils can be extracted from seeds, fruits, and nuts by solvent extraction and physical methods. Unrefined vegetable oils are of particular interest because during their obtention chemical compounds are not used. This study aimed the evaluation of the physicochemical properties [peroxide value (PV), free acidity (AF), and total phenols content (TPC)], and oxidation stability by Differential Scanning Calorimetry (DSC) of cold extracted oils from avocado pulp, almond, peanut, and pumpkin seeds. Because of this, oil from avocado pulp, almond, and peanut was obtained by centrifugation; whereas, pumpkin oils were obtained by mechanical pressing. PV and AF values ranged from 3.56 to 9.06 meq O2/kg oil and 0.55 to 0.81% expressed as oleic acid, respectively. These values were within the established international standards. The higher TPC determined was in peanut oil (2177.56 ± 2.92 mg GAE/kg oil), due to its great important considering the biological activities associated with them. Oxidation temperatures estimated by DSC were 162.84 and 185.15 ºC for avocado pulp and pumpkin seed (Cucurbita moschata) oils, respectively. In addition, pumpkin seed oils showed a higher oxidation induction time (> 15 min at 160 ºC). These results confirm that DSC is a technique that facilitates the analyses of the oxidation stability of oils, requiring small samples and short-time analyses. The high oxidative stability of pumpkin, peanut, and almond oils suggested that can have promised for applications in processing foods with heat (including the frying process). Centrifugation and mechanical pressing methods are great alternatives for the obtention of vegetable oils that complies with international standards. Additionally, using mechanical or physical methods to extract oil reduces the need for chemicals that are bad for both human health and the environment.
Keywords: differential scanning calorimetry, oxidative stability, peroxide index, total phenols content, vegetable oils.