Uses of plant food residues as sources for phytochemical extracts

Examples of the actual use of wastes from fruit processing industries to produce extracts that are available in the market include orange, grape, apple and olive residues. The residues from orange-juice extraction industries (orange albedo and flavedo, and fruit segments) have already been exploited for many years for the extraction of flavanones (hesperidin and related compounds) and pectin. Grape wastes from the wine-making industries (grape pomace and seeds) are also used industrially for the extraction of anthocyanin pigments, procyanidins and polyphenol extracts (Gabrielska et al., 1997; Lu and Foo, 1999). From the olive-oil extraction industries the residues can also be used for extraction of hydroxytyrosol (Visioli et al., 1999), the main phenolic antioxidant in olive oil, an efficient process for this purpose, has been patented and exploited industrially (Fernandez-Bolanos et al., 2002). From the cider industries, the apple pomaces are already used for extraction of pectins although phytochemical extraction has not yet been implemented. Recently research has been developed to use the tomato-juice production residues for the extraction of lycopene, a bioactive terpenoid pigment from tomato, and this has been studied by different groups using specific extraction techniques (Baysal et al., 2000). The possible use of press-cake residues from berry-juice production (bilberry, blackcurrant and grapes) for the extraction of phytochemicals has already been explored (www.vtt.fi/virtual/maxfun).

The exploitation of residues from vegetable production and handling for extraction of phytochemicals is actually less developed (Tomas-Barberan et al., 2005). Vegetable packing houses produce large amounts of wastes and residues (leaves, stems, etc.). These residues are very perishable products and their management is not always easy, they are also responsible for environmental management problems in the industries. Minimising their environmental impact has been the subject of increasing concern in recent years. An interesting approach to give an added value to these materials is their use as sources of phytochemicals and natural antioxidant compounds, mainly phenolic compounds which in some cases have comparable activity to that of synthetic antioxidants (Azizah et al., 1999; Lu and Foo, 2000). A number of by-products have been previously studied as potential sources of antioxidants (onion, carrot, potato peel) (Mouré et al., 2001). However, as far as we know, there have been very few reports on the use of byproducts from vegetables such as artichoke, cauliflower or lettuce as a possible source of antioxidant phenolics. Natural antioxidants are in great demand nowadays due to both consumer preference and health concerns associated with the use of synthetic antioxidants such as butylated hydroxy toluene (BHT) and butylated hydroxyanisole (BHA) (Oyeneho and Hettiarachchy, 1993; Azizah et al., 1999).

Modern lifestyles have led to an increase in the demand for 'ready to eat' foods (canned, refrigerated, etc.) that generally contain smaller amounts of health-promoting compounds than the original fruits and vegetables (a large part of these metabolites have been removed during processing). Functional foods aim to promote healthy dietary habits by providing foodstuffs with health 'added-value'. These foods add new ingredients that increase the health-promoting properties of traditional products, or increase the bioavailability of active compounds (Roberfroid, 2000). In this context, addition of phytochemicals - enriched extracts derived from by-products -could be a feasible strategy to develop functional foods and at the same time would contribute the valorisation of these by-products (Schieber et al., 2001).

17.4.1 Potential uses of high-value co-products

The phytochemical extracts can be used either for their biological properties as ingredients for nutraceutical preparations or functional foods, or for their food-quality-related properties - which include antioxidant properties, colour properties (pigments) and flavour properties (Tomas-Barberan and Espin, 2001). The health-related uses of phytochemical extracts include their use as ingredients for nutraceutical preparations or functional foods.

17.4.2 Nutraceuticals

Examples of these would be pills or capsules containing olive waste extracts or grape seed extracts. In many ways they are pharmaceutical-like forms. Although they are produced from food products, and the active phyto-chemicals are constituents of foods normally consumed in the diet, they are concentrated and presented in pharmaceutical forms in which the active principles are present in higher amounts. The concentration and pres entation as pharmaceutical forms affect their bioavailability and bioactivity. They are generally prepared as vials, capsules, pills, elixirs, solutions, etc.

17.4.3 Functional foods

In this case the extracts constitute ingredients that are added to food. Two different strategies can be followed. One related to 'food enrichment' and another to 'novel formulations'. In the 'food enrichment' strategy the extracts are added to food of the same origin. Examples include: the addition to a salad lettuce of a sauce enriched with extracts from the waste external leaves that are much richer in phytochemicals; a grape or berry juice in which the extracts obtained from the press-cake wastes are incorporated into the juice to produce a 'whole-bran' juice; olive oils in which the phenolic antioxidants remaining in the residues are incorporated into the oil, etc. In the 'novel formulation' approach extracts are added to different foods for increasing the phytochemical content (e.g. orange juice with added bilberry press-cake extracts will provide the anthocyanins and other polyphenols from berries in addition to the natural constituents of orange; milk may have extracts of soy bean isoflavones added). In some of these cases the new food products obtained should be considered 'novel foods'.

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