Evaluation of the oxidative stability of cold‐pressed rapeseed oil by Rancimat and Pressure Differential Scanning Calorimetry measurement

Abstract

Cold‐pressed market rapeseed oils were evaluated for oxidative stability using two accelerated methods: Rancimat and Pressure Differential Scanning Calorimetry. In the study, oils were also determined to their acid, peroxide and p‐anisidine value, fatty acid composition, antioxidants capacity and phenolic compounds content. Obtained results of oxidative stability have been 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 was applied. Analysed oils were characterised by good quality, had a typical fatty acid composition and oxidative stability. Rapeseed oils induction time were 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 were 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 12.96–14.03 h for a Rancimat method and 60.28–67.05 min for PDSC measurements. Principal Components Analysis analysis showed that the greatest influence on rapeseed oil induction time .in Rancimat and PDSC methods have peroxide value (r= ‐0.73 and r= ‐0.80, respectively), Totox indicator (r= ‐0.67 and r= ‐0.75, respectively) and total polyphenols content (r= 0.67 and r= 0.78, respectively). There was no correlation between the monounsaturated fatty acid content and the antioxidant capacity. Moreover, the induction time was 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 had a high influence on cold‐pressed rapeseed oil oxidative stability. Differences in rapeseed oil oxidation stability do not depend on its fatty acid composition.

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