Characterization of the Fat-soluble Vitamin and Carotenoid Profile of Green and Golden Kiwi by HPLC-DAD Tandem MS Hyphenation

Fat-soluble vitamins are essential micronutrients involved in important biological functions and classified into four groups: vitamin A, vitamin D, vitamin E, and vitamin K. Each group is characterized by an heterogeneity of forms about whose natural distribution little is known. In fact, the conventional analytical methods are often addressed to determine one single form, i.e. the most stable and/or widespread one. The reasons of this choice are basically economic, but also due to a series of analytical difficulties: 1) subtle chemical differences between vitamers belonging to the same vitamin group; 2) unavailability of standards; 3) low and different endogenous levels in complex food matrices; 4) occurrence of bound forms. The main purpose of this work was to characterize the fat-soluble vitamin and carotenoid fraction of kiwifruits belonging to the genuses Actinidia deliciosa (green kiwi whose Italy is the world leader producer) and Actinidia chinensis (golden kiwi, launched on the worldwide market under the trade name Zespri Gold in 2000). A novel analytical approach, based on LC-DAD-APCI-MS/MS hyphenation, was developed in order to perform both the quantitative analysis of ten target micronutrients (lutein, zeaxanthin, β-carotene, β-cryptoxanthin, α-tocopherol, δ-tocopherol, γ-tocopherol, ergocalciferol, phylloquinone, menaquinone-4) and the screening analysis of other pigments whose standards are commercially unavailable. MSPD was used as a mild technique for the extraction/clean-up procedure, with recoveries of all compounds exceeding 60%. Non aqueous reversed phase (NARP) chromatography on a C30 column was used for the analytes separation. The combined DAD-MS chromatographic detection proved itself as a potent tool for obtaining a comprehensive profile of fat-soluble vitamers and carotenoids occurring in the analyzed fruits. The unexpected presence of menaquinone-4 (K2 vitamer) and the detection of geometric isomers, which were not artefacts of the applied extraction procedure, were only some of the achieved results.