Influence of bleaching by ultrasound on fatty acids and minor compounds of olive oil. Qualitative and quantitative analysis of volatile compounds (by SPME coupled to GC/MS)

Abstract

The effects of bleaching using high power ultrasound (20 kHz) on the quality of olive oil were considered in this study, in order to verify the modifications that can occur in fatty acid composition and minor compounds. During the treatment of olive oil under ultrasonic waves, a rancid odour has been detected. Treated olive oils show no significant changes in their chemical composition but the presence of some volatile compounds, due to ultrasonic treatment. Some off-flavour compounds (hexanal, hept-2-enal and 2(E),4(E)-decadienal) resulting from the sonodegradation of olive oil have been identified. A wide variety of analytical techniques (GLC, HPLC and GC/MS) were used to follow the quality of bleached olive oils with ultrasonic waves by the determination of the amounts of certain minor compounds such as sterols and tocopherols. Steradienes, resulting from the dehydration of sterols, were detected with small quantities especially in severe conditions of sonication. Solid phase micro-extraction (SPME) coupled to gas chromatography was known to be a sensitive technique to follow changes in the oxidative state of vegetable oils by measuring the amount of volatile materials produced during the refining process.

Optimisation of soya bean oil bleaching by ultrasonic processing and investigate the physico‐chemical properties of bleached soya bean oil

“…Reduction in α‐tocopherols under ultrasonic process was observed by Jahouach‐Rabai et al . (). Different forms of tocopherols have vitamin E activity (α > β > γ > δ‐tocopherol) and antioxidant activity (δ > γ > β > α‐tocopherol).…”

“…According to Jahouach‐Rabai et al . (), the collapse of bubbles and cavitation occurs when the oil is treated by ultrasound for a period of time longer than 20 min and also, oil changes are only seen in the most severe conditions. In this study, the changes in pigment and oil colour were observed at range 20–30 min.…”

Ultrasonic inactivation of microorganisms: A compromise between lethal capacity and sensory quality of milk

“…In the case of the burnt off-flavour, octanoic acid could be directly involved in its perception, given that it is characterised by an unpleasant rancid smell and taste (Budavari, O'Neal, Smith, Heckelman, & Kinneary, 1996). The formation of decanoic acid methyl ester could be the result of lipid oxidation, which has been reported to occur during sonication and which results in the degradation of lipoperoxides, leading to the formation of deterioration products such as aldehydes, ketones, esters and short organic acids (Chemat, Grondin, Shum Cheong Sing, & Smadja, 2004;Jahouach-Rabai et al, 2008). Moreover, the production of δ-dodecalactone is most likely due to the thermal degradation of δ-hydroxyacids esterified into triglycerides as reported by Dimick, Walker, and Patton (1969), due to the localised high temperatures reached during sonication (Piyasena et al, 2003).…”

Improved Nile red staining of Scenedesmus sp. by combining ultrasonic treatment and three-dimensional excitation emission matrix fluorescence spectroscopy

“…When it was more than 5.0 min, the fluorescence intensity decreased markedly to 609.8 a.u. Given that oxidation is the main cause of lipid degradation [46], sonication energy beyond the level needed for algal cell disruption might induce lipid oxidation [29]. These results suggested that long ultrasonic treatment could lead to the degradation of lipids and unfavorably affect the Nile red fluorescence intensity.…”