An ultrasonic-accelerated oxidation method for determining the oxidative stability of oily matrices

CLAUDIA E. DOMINI

Conferencia; 2nd international conference on ultrasonic-based applications: from analysis to synthesis; 2016

Purpose: The aim of this study was to develop an efficient alternative method to evaluate the oxidative stability of vegetable oils and biodiesel. The action of ultrasound energy to accelerate the oxidation of fatty acid alkyl esters (FAAS) was followed by UV?Vis spectrophotometric detection. Experimental description: The degradation was optimized using a central composite design. The optimal experimental conditions were 10 g of sample at 480 Watts of power and 20% duty cycles. The monitoring was conducted until a large change of the absorbance occurred, depending on the sample. At the end of the degradation process, the temperatures reached 170 ± 5 °C. During sonodegradation, aliquots of 25 µL of the sample were taken every 2 min. The absorbance measurements of solutions were taken at 270 nm.Results: Biodiesel and vegetables oil samples from different feedstock were studied in this work. During the experimental procedures, a rancid odour and a change in color were detected for biodiesel treated by ultrasound. In all cases, induction time (IT) was established as the inflection point of the absorbance versus time curve (Fig 1). The induction time values obtained by means of the proposed method were 7 to 96 min and the Rancimat reference procedure were between 10 and 532 min. The IT values of all biodiesel samples determined using the proposed method was in accordance with those measured through the Rancimat reference method by showing a R2 = 0.998 Fig. 1. Second derivative and absorbance (at 270 nm) versus degradation time curves of sunflower biodiesel.Conclusions: The oxidative stability of oily matrices is a very important quality parameter that is established through the determination of induction time directly related to the samples storage lifetime. In this work, an efficient system to accelerate the oxidation of FAAS through the action of ultrasounds was developed in order to study the oxidative stability.