Invited review Functional components of grape pomace: their composition, biological properties and potential applications Jianmei Yu 1 * & Mohamed Ahmedna 2 1 Department of Family and Consumer Sciences, North Carolina A&T State University, 1601 East Market Street, Greensboro, NC 27411, USA 2 Centre for Excellence in Post-Harvest Technologies, North Carolina A&T State University, 500 Laureate Way, Suite 4222, North Carolina Research Campus, Kannapolis, NC 28081, USA (Received 20 April 2012; Accepted in revised form 25 July 2012) Summary The roles of functional foods on human health have been realised by more and more researchers, food producers and consumers. Functional food ingredients from both plant and animal sources such as die- tary fibre, soy protein isolate, whey protein isolate and omega 3 fatty acid have been widely used in func- tional food product development. Many fruit processing by-products such as grape, apple and orange peels are rich in bioactive phytochemicals, dietary fibre and unsaturated fatty acids, hence have potential to serve as functional food ingredients. In this review, we summarise recent advancement of research in grape pomace (GP), the residual of grapes after wine making. The polyphenol profile of GP and their bio- logical, antioxidant and antimicrobial activities, the stability of GP polyphenols in food system, the inter- action between GP polyphenol and other food ingredients, as well as the functionalities of grape seed oil and GP fibre are covered. Keywords Biological properties, dietary fibre, grape pomace, grape seed oil, grape seed protein, polyphenol composition, thermal stability. Introduction Grape pomace (GP) is a by-product of wine industry. GP consists mainly of peels (skins), seeds and stems and accounts for about 20–25% of the weight of the grape crushed for wine production. Grape seed is rich in extractable phenolic antioxidants such as phenolic acid, flavonoids, procyanidins and resveratrol, while grape skins contain abundant anthocyanins. The health benefits of GP polyphenols have been the great interest of researchers, food industry and nutraceutical industry. In addition to phenolic antioxidants, GPs also contain significant amount of lipid, proteins, non- digestible fibre and minerals. Grape seeds contain 13–19% oil, which is rich in essential fatty acids, about 11% protein, 60–70% of non-digestible carbohydrates, and non-phenolic antioxidants such as tocopherols and beta-carotene (Rao, 1994; Baydar & Akkurt, 2001; Bravi et al., 2007; Llobera & Can˜ellas, 2007). This review summarises the recent studies on major components of GP, their important properties and their possible applications that are. Phenolic compounds of GP and their properties Polyphenol composition of GP Phenolics are the secondary metabolites of plants. Chemically, phenolics can be defined as substances pos- sessing an aromatic ring bearing one or more hydroxyl groups, including their functional derivatives (Shahidi & Naczk, 2004). Polyphenols are compounds that have more than one phenolic hydroxyl group attached to one or more benzene rings (Vermerris & Nicholson, 2006). Most food phenolics have more than one hydroxyl group attached on the aromatic ring; therefore, in this review, phenolics and polyphenols are used interchange- ably. In food science research, natural phenolics are generally classified into classes and sub-classes based on the similarity of their chemical structures, that is, the types of building blocks that appear as repeated units. Four major classes of polyphenols found in foods are phenolic acids, flavonoids, lignans and stilbenes (Spencer et al., 2008). Major stilbenoids found in foods of plant origin are resveratrol and it glycosides. Resveratrol is a phytoalexin produced in the plant in response to pathogen attack. It has a low toxicity in humans and is a naturally occurring fungicide. *Correspondent: Fax: 336 334 7239; e-mail: jyu@ncat.edu International Journal of Food Science and Technology 2013, 48, 221–237 doi:10.1111/j.1365-2621.2012.03197.x © 2012 The Authors. International Journal of Food Science and Technology © 2012 Institute of Food Science and Technology 221