Chemistry of a Stable Vitamin C Glycoside in Apples (Malus spp.) and Other Fruit Crops

The primary aim of the research described in this thesis was to investigate an ascorbyl glycoside tentatively identified in crab apples (Malus sylvestris) by a non-targeted metabolomics study (unpublished thesis, J. Cho, 2016). The interest in this metabolite arose from the possibility that it may be involved in the translocation of ascorbate from leaf to fruit in apples. This hypothesis was based on its similarities to tutin-glycosides and sucrose-glycosides which are utilised for long distance translocation in Coriaria and Cucurbita spp. respectively. The chemotaxonomy of the Coriaria genus was also investigated as part of this research (Appendix 2). Isolation of the target ascorbyl glycoside from crab apples was achieved via acetylation of the crude extract and subsequent purification. This compound was definitively characterised by comparison to a synthetic standard and found to be 2-O-β-D-glucopyranosyl-L-ascorbic acid (AA2βGlc). This derivative was found to have greater stability than ascorbate and was comparable to AA2αGlc, which is commonly used in cosmetic products as stabilised pro-vitamin C. This was only the third reported occurrence of an ascorbyl glycoside in plants, and the second report of this specific metabolite. Quantitative HILIC LC-MS was used to analyse leaf and fruit tissue of five apple genotypes at three separate collection dates representing the start, middle and end of fruit development. Crab apples were found to have an extremely high concentration of AA2βGlc in their fruit (>500 mg/100 g FW), but only trace quantities (