Impact of Selected Chemical Characteristics of Cold-Pressed Oils on their Oxidative Stability Determined Using the Rancimat and Pressure Differential Scanning Calorimetry Method

Food Analytical Methods, Nov 2017

In this study, 27 market and edible cold-pressed oils from 10 different oilseeds were analysed. Oxidative stability and the chemical composition of oils were evaluated. The oils were investigated for their primary quality, fatty acid composition, total phenolic content and antioxidant activity. Rancimat and pressure differential scanning calorimetry (PDSC) were used to assess oils oxidative stability. Principal component analysis (PCA) was conducted to determinate impact of selected chemical characteristics on tested oils’ oxidative stability in accelerated modes. PCA indicated that none of the chemical compounds correlated strongly with the oils’ oxidative stability determined by the Rancimat method. Correlation coefficients describing the impact of different chemical compounds on induction time determined using the Rancimat method were between r = −0.54 (C18:3) to r = 0.62 (chlorophyll pigments). Oxidative stability of oils determined using the Rancimat and pressure differential scanning calorimetry (PDSC) were characterised by low correlation (r = 0.66). According to the statistical analyses, oils were divided into four groups, which depend on the method of oxidative stability evaluation did not differ.

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Impact of Selected Chemical Characteristics of Cold-Pressed Oils on their Oxidative Stability Determined Using the Rancimat and Pressure Differential Scanning Calorimetry Method

Impact of Selected Chemical Characteristics of Cold-Pressed Oils on their Oxidative Stability Determined Using the Rancimat and Pressure Differential Scanning Calorimetry Method Edyta Symoniuk 0 1 Katarzyna Ratusz 0 1 Ewa Ostrowska-Ligęza 0 1 Krzysztof Krygier 0 1 0 Department of Food Chemistry, Faculty of Food Science, Warsaw University of Life Sciences , Warsaw , Poland 1 Department of Food Technology, Faculty of Food Science, Warsaw University of Life Sciences , Nowoursynowska St. 166, 02-787 Warsaw , Poland 2 Edyta Symoniuk In this study, 27 market and edible cold-pressed oils from 10 different oilseeds were analysed. Oxidative stability and the chemical composition of oils were evaluated. The oils were investigated for their primary quality, fatty acid composition, total phenolic content and antioxidant activity. Rancimat and pressure differential scanning calorimetry (PDSC) were used to assess oils oxidative stability. Principal component analysis (PCA) was conducted to determinate impact of selected chemical characteristics on tested oils' oxidative stability in accelerated modes. PCA indicated that none of the chemical compounds correlated strongly with the oils' oxidative stability determined by the Rancimat method. Correlation coefficients describing the impact of different chemical compounds on induction time determined using the Rancimat method were between r = −0.54 (C18:3) to r = 0.62 (chlorophyll pigments). Oxidative stability of oils determined using the Rancimat and pressure differential scanning calorimetry (PDSC) were characterised by low correlation (r = 0.66). According to the statistical analyses, oils were divided into four groups, which depend on the method of oxidative stability evaluation did not differ. Cold-pressed oils; Correlation coefficient; Oxidative stability; PCA; PDSC; Rancimat Introduction Oxidative stability is one of the most important parameters used to assess oil quality, determining its resistance to the oxidation process. Oxidation occurs in unsaturated fatty acids during oil storage or heat treatment and causes their quality deterioration. Particularly easily oxidised are oils having a high content of polyunsaturated fatty acids, especially linolenic acid. Oils obtained by cold pressed technology in addition to triacylglycerides also contained lipidaccompanying compounds. Therefore, its stability depends not only on the fatty acids composition but also on the content of antioxidants, primary and secondary oxidation products, metals and other contaminants which might accelerate or inhibit oxidation process (Choe and Min 2006; Górnaś et al. 2014; Szterk et al. 2010) . Edible oils’ oxidative stability might be determined using different methods. One of the most popular is the shelf-life test run under real state conditions. Shelf-life test involves placing oil samples on shelves and evaluating its basic quality features at regular time intervals (Farhoosh 2007) . Nevertheless, due to the long duration of the test (several months) and the need to apply chemical reagents currently, to determinate oil oxidative stability, accelerated methods are mainly used. The Rancimat test is a popularly used accelerated oxidative stability evaluation method, it allows for a faster determination of the stability time by submitting the oil sample to a high temperature and constant airflow. Oxidative stability in the Rancimat test is referred as the induction time or oxidative stability index (OSI). Induction time corresponds to a sudden growth in the water conductivity in measuring vessel. Water conductivity is dependent on volatile compounds formed from the decomposition of unstable peroxides produced during the first step of oxidation (Raczyk et al. 2016; Shahidi and Zhong 2005) . Oil oxidative stability can also be measured using thermal technics. The pressure differential scanning calorimetry (PDSC) is a useful way of measuring the oxidative stability of vegetable oils in an accelerated mode; results are obtained faster due to the use of high temperature and pressure. PDSC method uses the fact that oil oxidation is an exothermic process. A heat released during the oxidation of oil sample is compared with a reference sample. The difference in generated heat is recorded over time as a graph from which can be the determined onset time (τon) and the maximum of oxidation time (τmax). Both parameters are used to characterise oil oxidation process, but they correspond with different stages of oxidation (Ciemniewska-Żytkiewicz et al. 2014; Kowalski et al. 2004) . The products formed in the oxidation process have an adverse effect on the human body; therefore, proper assessment of the oxidative stability is a decisive step in the safety assessment of oil. Available methods used for evaluating oils’ oxidative stability are very diverse. The literature presents a number of differences between the Rancimat and differential scanning calorimetry methods (Šimon et al. 2000; Woo (...truncated)


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Edyta Symoniuk, Katarzyna Ratusz, Ewa Ostrowska-Ligęza, Krzysztof Krygier. Impact of Selected Chemical Characteristics of Cold-Pressed Oils on their Oxidative Stability Determined Using the Rancimat and Pressure Differential Scanning Calorimetry Method, Food Analytical Methods, 2017, pp. 1-10, DOI: 10.1007/s12161-017-1081-1