U-HPLC-MS/MS analysis to quantify the antioxidant content of tomatoes subjected to different cultivation conditions

Tomato (Solanum lycopersicum L.) is one of the most popular and extensively consumed vegetable crops worldwide and is consequently fulfilling a key role in the human diet. Tomato constitutes an excellent source of health-promoting compounds including several antioxidants such as the carotenoids lycopene and β-carotene and the vitamins ascorbate and α-tocopherol. Within this research the effect of salinity level on antioxidant content of tomato fruits was verified. To evaluate the effect of applied salinity treatments, chemical-analytical procedures for the quantification of the fat-soluble antioxidants lycopene, β-carotene and α-tocopherol were optimized. The optimized extraction procedure was based on liquid-liquid partition and made use of ethanol and hexane. Although in previous papers mainly classical HPLC was used for chromatographic separation, in this study U-HPLC (equipped with a Hypersil GOLD column, 100 x 2.1 mm, 1.9 μm) was preferred. With this technique a significant reduction in analysis time from in general 45 minutes to only 6 minutes was achieved without any loss of chromatographic resolution. In comparison with the frequently used UV-VIS detectors, the usage of a triple quadrupole tandem mass spectrometer allowed a more certain identification of target analytes, due to the higher selectivity. Optimized procedures were applied on tomato fruits, exposed to one of four salinity treatments (2.5, 4.0, 5.0 and 8.0 dS/m). When calculated over all treatments, average concentration levels for lycopene, β-carotene and α-tocopherol were 50.02, 1.23 and 2.67 mg/kg respectively. Although the 4.0 dS/m treatment seemed to be the most favourable for antioxidant content, significant differences between treatments were not detectable. Nevertheless the chemical-analytical procedures were successfully optimized and applied, the time consuming and labour intensive features of the extraction procedure were identified as major drawbacks. Therefore a new extraction procedure, based on the recent developed in-tube solid-phase micro extraction, will be optimized. This technique makes use of an extraction column and requires only small amounts of sample and is less solvent consuming.