Synthesis of two modified carotenoids and their behavior during light exposure

Two modified carotenoids, β‐6‐hydroxy‐2, 5, 7, 8‐tetramethyl‐chromane carboxylic acid β‐apo‐8'‐carotenoate (Caro‐Trolox) and 3, 5‐di‐tert‐butyl‐4‐hydroxy benzoic acid β‐apo‐8'‐carotenoate (Caro‐BHT) were synthesized by esterification of β‐apo‐8'‐carotenol with Trolox and with 3, 5‐di‐tert‐butyl‐4‐hydroxy benzoic acid, respectively. Their activity under light exposure was examined comparatively to that of Trolox, α‐tocopherol, β‐carotene, β‐apo‐8'‐carotenoic acid (CA} and ethyl β‐apo‐8'‐carotenoate. The substrate used was purified sunflower oil. In the absence of a photosensitizer (240 W/m² , 25 °C) Caro‐Trolox (200 mg/kg) behaved as an antioxidant and was quite stable (1/5 of the initial amount remained after 2‐wk storage). Caro‐BHT (200 mg/kg) showed no antioxidant activity and was quite unstable (it was destroyed within 7 d). In the presence of 5 mg/kg chlorophyll α (12000 lx, 25 °C) similar observations were made. The activity of Caro‐Trolox was concentration‐dependent. At a 100‐mg/kg level of addition its activity was similar to that of the mixture of α‐t_copherol (100 mg/kg) and β‐carotene (10 mg/kg). Its performance at the 10‐mg/kg level was slightly better than that of the other carotenoids. The antioxidant behavior of the modified carotenoids was attributed to the presence of the phenolic moiety as supported by the results of the 1, 1‐diphenyl‐2‐picrylhydrazyl test (e.g. EC₅₀ after 15 min: 26.2, Caro‐Trolox; 35.8, Caro‐BHT; 122, CA; 22.3, Trolox).