Different extracts obtained from wastes are already in the market or are potential candidates to be in the market soon. From the olive-oil industry wastes, extracts enriched in the antioxidant hydroxytyrosol are already prepared and marketed, as antioxidants for food preservation or as ingredients for functional foods or nutraceuticals (Fernandez-Bolanos et al., 2002). Pomegranate tannins from fruit husks (a mixture of punicalagins and other ellagitannins) can be easily prepared and introduced to the market due to the nutraceutical properties of these metabolites (Gil et al., 2000). Anthocyanin-rich extracts are prepared from grape residues produced in the wine industries. Alternatively, extracts from press-cake residues from the berry-juice industries are also being marketed and these extracts provide, in addition to pigments, an excellent source of flavonols and other phenolics (www.vtt.fi/virtual/maxfun). Procyanidin extracts from grape seeds are already available in the market, but procyanidins from other residues will also be good alternatives with different profiles of polymeric forms that will give different biological properties and bioavailability. Lycopene extracts from tomato are also available in the market. Different qualities can be found related to the lycopene content. Extracts from artichoke residues or artichoke blanching waters are rich in hydroxycinnamates; these extracts are already being produced and marketed. During the extraction and concentration of the extracts some caffeoyl-quinic derivatives are partially transformed to isomers that are only present as traces in the natural plant material (Gil-Izquierdo et al., 2001). The extracts prepared from the brines of caper preparation have a high content of quercetin glycosides and in addition some quercetin aglycone (Inocencio et al., 2000).
Extracts containing large amounts of citrus flavanones are obtained from the wastes of the citrus-juice industries (Braddock, 1995). Different fla-vanone profiles can be obtained depending on the citrus species. Sweet oranges produce extracts in which hesperidin is the main constituent, while neohesperidin is the most characteristic of sour oranges, naringin of grapefruits and eriocitrin of lemons. Many applications for these extracts have been reported, both for their biological activity and for their potential uses as food antioxidants.
From onion residues, flavonol (quercetin) extracts can be produced although these are not yet on the market (Erlund, 2004). Grapes are also a source for stilbenoids (resveratrol and piecatannol). Their content in grapes is very small but can be concentrated in the extracts. Several strategies can be used to increase the resveratrol content of grapes before extract production (Cantos et al., 2001). Glucosinolate extracts could also be prepared from Brassicaceae wastes; these are not yet available in the market. A combination of glucosinolates with flavonols and hydroxycinnamates could be a reasonable approach for extract preparation from broccoli wastes (Tomás-Barberán et al., 2005).
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