From Grape to Wine: Targeted Profiling of Selected 34 Bioactive Phenolics in Negoska Variety, an Unexplored Indigenous Greek Grape Cultivar

Wine is a widely consumed beverage and important source of bioactive polyphenols, molecules with well-established health beneficial properties. The winemaking process produces byproducts, such as pomace, seeds and stems, which also comprise a valuable resource for sustainable valorization because of their phenolic content. The study herein concerns the exploitation of Negoska, a rare indigenous red grape variety of northern Greece cultivated in the Protected Designation of Origin (PDO) terroir of Goumenissa. In this context, we investigated various vinification fractions of Negoska, such as grapes, must, wine, pomace, seeds and stems in respect to their content in selected phenols, metabolites’ content and antioxidant properties. The respective results indicated the presence of 34 non-anthocyanin phenolics, which were quantified by LC–MS/MS analysis. Principal Component Analysis (PCA) revealed a clear differentiation in the distribution between the grape fractions and the processed products. In particular, the phenolic compound pattern of Negoska wine was characterized by a high concentration of gallic (69.8 mg/L), caffeic (40.8 mg/L) and p-coumaric (31.1 mg/L) acids, while procyanidin B2 (24.0 mg/L) was among the most abundant compounds detected in wine. In must, procyanidin B2 was the predominant phenolic compound (9.7 mg/L). On the other hand, pomace, stems and seeds were identified as particularly rich reservoirs of various bioactive phenolics, with the molecule of procyanidin B2 representing one of the most abundant compounds in these matrices, reaching concentrations of 83.1–1015.1 mg/Kg DM. The investigated phenolic content fluctuated greatly among the samples investigated with procyanidin B2 and diosmin being the most abundant compounds in dried grapes, luteolin-4′-O-glucoside and diosmin in pomace, procyanidin B2, gallic acid and catechin in seeds, and procyanidin B2, epigallocatechin and luteolin-4′-O-glucoside were the prevailing molecules in stems. These findings constitute the first targeted characterization of selected phenolic compounds and their metabolites’ profiles in Negoska grapes and the respective winemaking fractions, highlighting the potential of this indigenous cultivar and its byproducts to serve as source of valuable bioactive compounds for valorization by the food and cosmetic industries.