Proanthocyanidin Composition and Antioxidant Potential of the Stem Winemaking Byproducts from 10 Different Grape Varieties (Vitis vinifera L.) María Reyes Gonza ́ lez-Centeno, † Michael Jourdes, § Antoni Femenia, † Susana Simal,* ,† Carmen Rosselló , † and Pierre-Louis Teissedre § † Department of Chemistry, University of the Balearic Islands, Crta Valldemossa, Km 7.5, 07122 Palma de Mallorca, Spain § Unite ́ de Recherche Œnologie, EA 4577, USC 1366-INRA, Institut de Sciences de la Vigne et du Vin, Universite ́ Bordeaux Segalen, 210 Chemin de Leysotte, 33882 Villenave d’Ornon Cedex, France ABSTRACT: Stem byproducts from 10 different grape (Vitis vinifera L.) varieties were evaluated in terms of their total phenolic and total proanthocyanidin contents, flavan-3-ol and proanthocyanidin profiles, and antioxidant capacity measured by ABTS, CUPRAC, FRAP, and ORAC assays, with a view to the recovery of their natural bioactive compounds. Stems from Callet, Syrah, Premsal Blanc, Parellada, and Manto Negro varieties yielded the highest total phenolic and total proanthocyanidin contents and showed the greatest antioxidant capacities, whereas Chardonnay and Merlot stems presented the lowest values. Varieties differed significantly (p < 0.05) with regard to both the phenolic composition and antioxidant capacity of their stems. However, no significant differences (p > 0.05) were observed when stems from red and white varieties were considered separately. For the 10 grape varieties investigated, this is the first study presenting a detailed description of their stem flavan-3-ol composition determined by HPLC-UV-fluo. All of the analyses confirmed the stem byproducts as a potential polyphenol-rich source, especially promising in the case of the Callet variety. KEYWORDS: grape stems, winery byproducts, proanthocyanidins, antioxidant capacity, total phenolic content, mean degree of polymerization ■ INTRODUCTION It is well-known that moderate wine consumption plays an important role in protection against certain human diseases and dysfunctions, mainly due to the beneficial effects of its natural bioactive compounds, which have potential health-promoting and disease-protective qualities. 1 Most of these components, or at least their precursors, come directly from the vineyard and remain in significant concentrations in the two main wine- making byproducts, stems and grape pomaces. Stems may preserve their original phenolic profile almost intact, because they are usually directly discarded. 2 Thus, they are recognized as rich sources of interesting plant secondary metabolites. 3 The main reason is the high value of these biocompounds and their promising applications in the cosmetic, pharmaceutical, and food industries, as an alternative to synthetic substances commonly used in these fields, which are increasingly being rejected by consumers concerned about their healthiness. 4 According to the ninth General Assembly of the Interna- tional Organization of Vine and Wine (Porto, 2011), with a global production of 65 million tons in 2009, grapes are the main fruit crop in the world, around 80% being used for wine production. Considering these data and the fact that the winemaking process generates large amounts of solid waste, which might account for >30% (w/w) of the grapes used, 5 the residues derived from the wine industry exceeded 15 million tons in 2009. As this constitutes an important environmental problem, there is a continuous and growing pressure to develop new exploitation strategies for these underutilized resources, to reassimilate them into the food cycle, taking advantage of their interesting potential. To date, the most common revaluation of these inexpensive and easily available agricultural byproducts is the production of antioxidant and/or dietary fiber concentrates in the form of value-added ingredients for food supplementa- tion 6,7 or their utilization to make fertilizers. 8 For this second purpose, extraction of polyphenols is required before further treatment, due to their phytotoxicity and antimicrobial effects during the composting process. Thus, the main potential uses and applications of wine waste involve the recovery and reuse of their phenolic constituents, which would represent a significant step forward in maintaining environmental balance and supporting a sustainable agricultural production. There is a great diversity of grape varieties, each one characterized by different contents and profiles of phenolic compounds, the antioxidant capacity and health-promoting properties of which could significantly differ from one to another. In this regard, different studies have been carried out in recent years to evaluate the quantity and/or quality of the phenolic constituents in the winery residues. Most of these studies focused on grape pomace byproduct, above all from the Cabernet Sauvignon grape variety, whereas information about stem byproducts is rather scarce, 5 despite they also contain an important amount of polyphenols. In fact, there is no detailed description of stems’ flavan-3-ol composition previously Received: July 14, 2012 Revised: October 24, 2012 Accepted: October 27, 2012 Published: October 27, 2012 Article pubs.acs.org/JAFC © 2012 American Chemical Society 11850 dx.doi.org/10.1021/jf303047k | J. Agric. Food Chem. 2012, 60, 11850-11858