Metabolite profiling of dihydrochalcone compounds in apple germplasm collection

The major phenolic compounds found in apple (Malus x domestica) belong to the class of dihydrochalcones, represented by various phloretin derivatives (e.g. phloridzin, sieboldin, trilobatin). Phloridzin (phloretin 2’-O-glucoside) also occur beside others in strawberry fruits (Fragaria x ananassa), cranberries (Vaccinium macrocarpon) and sweet tea (Lithocarpus polystachus), but in significant lower amounts compared to apple. Beside their contribution to the bitter taste (flavor) of cider and the colour of apple juices due to oxidation products they were also associated with health effects of apple fruits, berries and their processed products (1). Phloridzin and other derivatives are found not only in the apple fruits (peel and seeds) but also in flowers, leaves, roots and bark of the entire tree whereas in strawberry it appears to be solely accumulated in fruits. Furthermore, significant variations between genotypes in both plant species and between orchards have been described (2). However, only little is known of the function of dihydrochalcones in plant physiology. It was shown that especially phloridzin may act in plant growth or development and can inhibit bacterial and fungal growth (2). Due to the supposed health benefits of these metabolites, knowledge on biochemical and molecular level of the involved proteins/genes is of major importance to support ongoing molecular breeding programmes (FEM-IASMA). Sensitive methods (e.g. UPLC/DAD & LC-MS) for detecting/identification of natural dihydrochalcone derivatives and their metabolites in plant tissues, animal or human matrices and processed fruit products will further enable an increased dietary intake of these compounds and understanding of their mode of biofunctionality. The Malus germplasm collection at FEM-IASMA includes around 300 accessions which will be screened for variation in dihydrochalcone profile and content in leaves. From a preliminary screen of the metabolic profile of around 70 accessions it became apparent that two classes can be distinguished: 1. Phloridzin group and 2. Sieboldin/Trilobatin group. Beside some intermediates all accessions of one group are clearly characterised by the major compound belonging to one or the other group. This knowledge will not only the basis for more detailed characterisation of the biosynthetic pathway but also for isolation of different dihydrochalcones and to prepare specific extracts rich in various combinations of dihydrochalcones for in vitro studies of their function and their bioavailability.