Abstract
This work focused on the application of synchronous fluorescence (SF) spectroscopy, excitation-emission matrix (EEM) fluorescence spectroscopy and modified UV-VIS methods for characterization of oxidative status and antioxidant activity (AA) of refined rapeseed oils fortified with the novel antioxidant octyl sinapate (OSA) at two concentrations and butylated hydroxyanisole (BHA) stored in different types of packages under various storage conditions. Quality parameters such as amounts of the primary and secondary oxidation products in rapeseed oils increased after storage under various conditions, whereas the AA of oils decreased. However, OSA strongly inhibited the generation of primary oxidation products in oils exposed to light. The AA of rapeseed oil with 0.5% of OSA packed in transparent glass after exposure to light was 6 times higher than the AA of non-supplemented oil. Moreover, the intensities of bands attributed to tocopherols and phenolic compounds decreased during storage depending on the storage conditions, but characteristic peaks for generation of oxidation products appeared. Interestingly, the fluorescence spectra of oil fortified with 0.5% of OSA contained the information of a new fluorescent product. Moreover, the potential usefulness of EEM to study the effect of antioxidants on degradation of stored rapeseed oils was demonstrated. Fluorescence spectroscopy can be used to investigate the oxidation state of rapeseed oils packed in various containers during storage at different conditions. The addition of the lipophilic antioxidant to rapeseed oil effectively delayed the oxidation process and significantly increased its AA.
Highlights
Rapeseed oil is the most popular vegetable oil in Poland, while rapeseed is the second largest oilseed crop in the world, after soybean
Oxidation status of rapeseed oils without and with octyl sinapate (OSA) and butylated hydroxyanisole (BHA) after 6 months of storage was evaluated by characteristic parameters
Amounts of the primary (PV = 0.53 meq O2/kg) and secondary (p-AnV = 1.39) oxidation products, overall oxidation state (TOTOX = 2.45) and acidity (AV = 0.029 mg NaOH/g) of fresh rapeseed oil before antioxidant addition were the lowest and below the legal limits (PV < 5 meq O2/kg and p-anisidine value (p-AnV) < 8, TOTOX < 10 and acid value (AV) < 0.300 mg NaOH/g) permitted for refined oils according to International Organization for Standardization (2017, 2016, 1996)
Summary
Rapeseed oil is the most popular vegetable oil in Poland, while rapeseed is the second largest oilseed crop in the world, after soybean. Rapeseed oil is consider the healthiest culinary oil due to the presence of components such as unsaturated fatty acids with a balanced ratio of linoleic acid to linolenic acid (2:1), tocopherols, phenolic compounds (especially sinapic acid and its derivatives) and sterols (Szydłowska-Czerniak 2013). Unsaturated fatty acids undergo rapid oxidation and produce a complex mixture of the primary and secondary oxidation products that cause off-flavours and offodours. The rate of oil oxidation depends on. Methods (2020) 13:1973–1982 the synthesized compounds, namely phenolipids. It is well known that phenolipids can improve the AA and oxidative stability of vegetable oils, as well as extend their shelf life (Catel et al 2012; Szydłowska-Czerniak and Rabiej 2018)
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