Rosmariquinone interactions in autoxidation and light-sensitized oxidation of stripped soybean oil

Two studies were conducted, using a stripped soybean oil model system, to evaluate the antioxidant interaction(s) between rosmariquinone (RQ) and oil components, including chlorophyll (CHL), beta-carotene (CAR), and tocopherol(s) (TOCO), under both autoxidation and light-sensitized oxidation. In autoxidation, CHL alone had no effect on the level of oxidation, whereas CAR alone showed prooxidant (P < 0.05) activity. RQ and RQ + CHL or RQ + CAR were significantly (P < 0.05) better in controlling autoxidation. RQ appeared to be responsible for the activity in the test combinations. However, among the treatments containing TOCO, RQ, and RQ + TOCO, RQ + TOCO gave a level (P < 0.05) of inhibition that indicated a possible synergistic relationship. When tested in a light-sensitized oxidative system, CHL and CAR had no effect on oxidation relative to the control and, again, RQ alone or in combination with CHL or CAR was responsible for the greatest (P < 0.05) inhibition of oxidation. RQ + TOCO had better (P < 0.05) inhibitory activity than the individual compounds. In the second study, the interaction between RQ and TOCO was studied. TOCO, added at levels found in the nonstripped soybean oil, and RQ, added at two levels (100 and 200 ppm), were tested alone or in combination in both autoxidation and light-sensitized oxidation. In autoxidation, the combination of RQ at 200 ppm and TOCO was synergistic; however, in light-sensitized oxidation, this combination was not synergistic. Monitoring the loss of both RQ and TOCO suggested that during autoxidation RQ acted as a secondary antioxidant relative to TOCO.