Evaluation of the Oxidative Stability of Cold‐Pressed Rapeseed Oil by Rancimat and Pressure Differential Scanning Calorimetry Measurements

Abstract

Cold‐pressed market rapeseed oils are evaluated for oxidative stability using two accelerated methods: Rancimat and pressure differential scanning calorimetry. In the study, oils are also determined by their acid, peroxide and p‐anisidine values, fatty acid composition, antioxidants capacity, and phenolic compounds content. Obtained results of oxidative stability are correlated to determine the possibility of using interchangeably tested methods. To examine the impact of individual quality factors on oil oxidative stability, the principal components analysis is applied. Analyzed oils are characterized by good quality, having a typical fatty acid composition, and oxidative stability. Rapeseed oils induction time are determined by Rancimat measurement at 100 °C and pressure differential scanning calorimetry test at a temperature of 120 °C. The induction times obtained using these two methods are strongly correlated (r = 0.96). A high value of correlation coefficient might be caused by too little differentiation; thus the possibility of using these methods interchangeably may be applied only to results range between 12.96 and 14.03 h for a Rancimat method and 60.28–67.05 min for PDSC measurements. Principal components analysis shows that the greatest influence on rapeseed oil induction time in Rancimat, and PDSC methods have peroxide values (r = −0.73 and r = −0.80, respectively), Totox indicators (r = −0.67 and r = −0.75, respectively), and total polyphenols content (r = 0.67 and r = 0.78, respectively). There is no correlation between the monounsaturated fatty acid content and the antioxidant capacity. Moreover, the induction time is poorly correlated with saturated, polyunsaturated fatty acids, and pigments content. Practical Applications: The results show that Rancimat and pressure differential scanning calorimetry (PDSC) methods might be used interchangeably (r = 0.96) for assessing the oxidation stability of cold‐pressed rapeseed oil, for a given set of data. PDSC can be recommended as an appropriate objective method for evaluating the oxidative stability of cold‐pressed rapeseed oils. Results of the principal component analysis (PCA) proved that its primary oxidation state has a high influence on cold‐pressed rapeseed oil oxidative stability. Differences in rapeseed oil oxidation stability do not depend on its fatty acid composition. Market cold‐pressed rapeseed oils are evaluated for their chemical composition and oxidative stability using Rancimat and PDSC measurements. Based on the obtained results the correlation between oxidative stability determined by these two methods and the influence of the individual quality factors on oil oxidative stability is determined by applying the principal component analysis.

Low concentration short time ozonation of rapeseed seeds reduces the stability of the oil and content of some antioxidant components

“…Symoniuk et al . () concludes that there is no high correlation between the tocopherol content and oxidative stability in the Rancimat apparatus. In addition, many less strong or weak linear statistically significant relationships have been demonstrated.…”

“…Low R 2 indicate a poor fit of the model of the effect of ozonation time on the induction time. The autoxidation process is influenced by the content of fatty acids and the location and type of bonds present therein, as well as the qualitative and quantitative composition of the antioxidant groups contained in the oil (Symoniuk et al ., ). In the studied oils, oxidative stability primarily depended on the cultivar, but statistical analysis showed that ozonation also caused changes in this parameter.…”

“…The literature lacks reports on the ozone effects on the oxidative stability of vegetable oils. The obtained results of the induction times tested by the Rancimat test for rapeseed oil are characteristic for this raw material and comparable with those obtained by other authors (Wroniak et al ., ; Symoniuk et al ., ).…”

“…In the Redondo-Cuevas et al (2018) studies phenolic compounds and saturated fatty acids were the main factors that correlated positively with oxidative stability, whereas unsaturated, polyunsaturated fatty acids and tocopherols correlated negatively. Symoniuk et al (2019) concludes that there is no high correlation between the tocopherol content and oxidative stability in the Rancimat apparatus. In addition, many less strong or weak linear statistically significant relationships have been demonstrated.…”

“…Results related to antioxidant activity compared by different methods: DPPH, FRAP, ORAC, TEAC are strongly correlated (Szydłowska-Czerniak et al, 2010). The antioxidant activity of the oil is associated with the presence of carotenoid pigments, tocopherols and phenolic compounds (Symoniuk et al, 2019). The activity of methanol extracts against the DPPH radical was 61.5% and 51.8% for the 1 and 2 cultivar, while the oils -85.0% and 77.8% respectively.…”