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The influence of the UV irradiation on degradation of virgin rapeseed oils



This paper presents research which is a continuation of the investigations described earlier. The aim of these studies was to determine the influence of UV irradiation on flavor and the oxidative stability of different rapeseed oils varieties. For the purpose of this study, oil samples underwent accelerated deterioration for 4.5 h under a UV light test. In the obtained sample, characteristic values (peroxide (PV, 1.23–1.62 meq O2/kg), anisidine (AnV, 0.53–1.20) and TOTOX (3.02–4.14)), concentration of conjugated dienes (equation image at 232 nm 1.21–2.08) and trienes (equation image at 268 nm 0.11–0.34), carotenoids and chlorophylls, oxidative stability (DSC-test), volatiles were determined and a sensory evaluation was carried out. Changes in the PV and AnV values in the function of irradiation time have fluctuating character (e.g., for PV from 0.45 meq O2/kg before UV treatment to 1.61 meq O2/kg after 4.5 h of the UV irradiation and for AnV from 0 to 1.20), therefore they cannot be used as quality indicators. There was no correlation between these values and the level of generated sensory descriptors and the sum of volatiles as well as the initial oils stability (DSC-test). During UV irradiation, the decrease in carotene and chlorophyll content had a linear pattern. The absolute losses of carotenoids were from 1 ppm (samples 5 and 6) to 3.8 ppm (sample 2) and for chlorophylls from 0.02 ppm (sample 5) to 0.25 ppm (sample 4). There was a high correlation (R2 = 0.87) observed between the maximum intensity of the varnish descriptor and IP-DSC of the virgin oils for all samples.