Abstract: The characteristics of phenolic accumulation in seeds of two muscadine grape cultivars, ‘Noble’ and ‘Carlos’ at different stages of berry development were studied by using ultra performance liquid chromatography tandem triple quadrupole time-of-flight mass spectrometry (UPLC-Triple-TOF-MS/MS) in comparison with two Vitis vinifera cvs, ‘Cabernet Sauvignon’ and ‘Riesling’. A total of 106 phenolic compounds were identified and quantified in grape seeds collected from four developmental stages investigated, including 48 ellagic acids and precursors, 24 flavonols, 20 hydroxy benzoic acids, 9 flavan-3-ols, 3 stilbenes and 2 hydroxy cinnamic acids. Among them, ellagic acids, precursors (mostly precursors) and flavan-3-ols (mainly gallates and monomers) were the predominant phenolics detected in seeds of muscadine and Vitis vinifera grapes, respectively; however, there were great differences in their contents between years and among cultivars. The precursors in ‘Noble’ seeds accumulated abundantly at the young berry stage, but was decreased gradually until veraison, and increased again at the end of veraison, while for ‘Carlos’, these compounds were dominant before veraison, and then slightly decreased. The flavan-3-ols in ‘Riesling’ seeds were increased progressively with berry development in the year 2013, reaching the highest level at veraison, and declined thereafter, while their content remained constant during the growth season in 2014. For ‘Cabernet Sauvignon’, the highest content was found in young and fully ripe berries in 2013 and 2014, respectively.

Key words: muscadine, Vitis vinifera, seeds, berry development and ripening, phenolic accumulation