Stabilization of canola oil by naturally-occurring antioxidants

Wanasundara, Udaya Nayanakantha (1993) Stabilization of canola oil by naturally-occurring antioxidants. Masters thesis, Memorial University of Newfoundland.

[English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (10MB)

Abstract

The antioxidant activity of ethanolic extract of canola meal at 100, 200, 500 and 1000 ppm and commercially-available flavonoids at 200 ppm level on refined bleached canola oil was examined and compared with commonly used synthetic antioxidants such as BHA/BHT/CA (butylated hydroxyanisole/butylated hydroxytoluene/citric acid) at 250 ppm and TBHQ (tert-butylhydroxyquinone) at 200 ppm levels. Accelerated oxidation under Schaal oven test conditions at 65°C was investigated over a 17 day period. Progression of oxidation was monitored by employing weight gain, peroxide value, conjugated diene value, TOTOX value and 2-thiobarbituric acid reactive substances (TBARS) tests. Canola extracts at 500 and 1000 ppm levels were better than BHA/BHT/CA, but less effective than TBHQ. Among the flavonoids tested, myricetin, quercetin, rutin and (-)epicatechin were more effective than BHA/BHT/CA in retarding the formation of primary and secondary oxidation products. Myricetin was the most effective flavonoid tested. -- In order to identify the most active antioxidative compound in the ethanolic extract of canola meal, the extract was passed through a Sephadex LH-20 column and fractionated into seven major fractions according to UV absorbance, phenolic and sugar contents. Fraction IV showed the best antioxidative activity as evaluated in a (β-carotene-linoleate model system. Further separation of fraction IV by thin layer chromatographic techniques indicated that the compound responsible for strong antioxidative activity of fraction IV was phenolic in nature. Spectroscopic studies indicated that this compound was 1-O-β-D-glucopyranosyl sinapate (1-O-β-D- glucopyranosyl 3,5-dimethoxy-4-hydroxy cinnamate). -- A novel nuclear magnetic resonance (NMR) spectroscopic method was also used to monitor oxidation of canola and soybean oils. The ratios of aliphatic to olefinic and aliphatic to diallylmethylene protons in both oils indicated a steady increase in their numerical values with increasing the length of storage period. A highly significant correlation was found between these ratios and TOTOX values of both oils, thus suggesting that NMR methodology can be used as an effective means to simultaneously estimate both primary and secondary oxidation changes in both canola and soybean oils.

Actions (login required)

View Item