Isolation and purification of acid‐labile carotenoid 5,6‐epoxides on modified silica gels

Abstract

The acid-labile carotenoid 5,6-epoxides occur in all green plants and in most fruits, but their isolation or purification is complicated and expensive because they decompose on normal silica gels. Alkaline stationary phases in open column chromatography (OCC) have low capacities, which makes them unsuitable for preparative scale. To find a simple high-capacity stationary phase for OCC that does not induce transformations of acid-labile compounds. Commercially available silica gel was treated with aqueous sodium bicarbonate solution to neutralise its slightly acidic character, and was then washed and dried. The effect of the treated gel (named silica-9) on violaxanthin was studied. The modified gel was also applied to the OCC of different complex natural extracts (maple leaves and fruits of yellow paprika). Carotenoids were examined by HPLC-PAD both before and after chromatography on the modified gel. Violaxanthin decomposed rapidly on normal silica gels but not on the modified gel. Chromatography of plant extracts showed that the modified gel had a similar capacity to the untreated gel but did not effect epoxy-carotenoids, which could be separated or enriched readily on a large scale. The modified gel does not induce any transformation or decomposition of epoxy-carotenoids but still exhibits a high capacity, suggesting that it can be used in preparative organic chemistry as an additional and convenient tool in the OCC for the separation of other acid-labile compounds.