Effect of processing on the oxidative stability of low erucic acid turnip rapeseed (Brassica rapa) oil

The effect of various processing conditions on the composition and the oxidative stability of mechanically pressed (90-95 degrees C) rapeseed oil was investigated. The five different rapeseed oils included crude (nondegummed), superdegummed, steam stripped (at 140 degrees C for 4 h, nondegummed), physically refined (degummed, bleached and deodorized at 240 degrees C), and cold pressed (40 degrees C) oils. Oils were autoxidized in the dark at 60 degrees C and under light at 25 degrees C. Oxidation was followed by measuring changes in the peroxide values (PV) and the consumption of locopherol and carotenoid was measured. In the dark the oils reached PVs of 10 meq/kg in the order: cold pressed > superdegummed > steam stripped congruent to crude > refined. However, under light conditions the order changed as follows: cold pressed > crude congruent to steam stripped > superdegummed > refined. Processing had no effect on fatty acid composition nor alpha-tocopherol content of the oils. Superdegumming and steam stripping decreased the carotenoid content of the oils while cold pressing and refining reduced also chlorophyll, gamma-tocopherol and phosphorus content of the oils.