In Depth Proteome Analysis of Ripening Muscadine Grape Berry cv. Carlos Reveals Proteins Associated with Flavor and Aroma Compounds

Ripening in nonclimacteric fruits such as grape involves complex chemical changes that have a profound influence on the accumulation of flavor and aroma compounds distinct to a particular grape genotype. In this study, proteome characterization of wine type bronze muscadine grape (Vitis rotundifolia cv. Carlos), primarily grown in the Southeastern United States was performed during berry ripening. Stage-specific protein expression was obtained among different stages of berries. Differential analysis showed the expression of 522 proteins that regulate diverse biological processes and metabolic pathways. Of these, 30 proteins are associated with the production of key phenolic compounds, whereas 25 are associated with the production of muscadine aroma compounds. These proteins are involved in the phenylpropanoid pathway, terpene synthesis, fatty acid derived volatiles and esters that affect muscadine berry flavor and aroma characteristics. Further, gene expression analysis during ripening validated the expression pattern of 12 proteins. Catechin, epicatechin, and four stilbenes were quantified to correlate observed proteome changes. This study not only revealed biochemical changes during muscadine berry ripening but also offers indicators for marker-assisted breeding to enhance organoleptic properties of muscadine grape to improve its flavor and aroma properties.