By-Products from Plant Foods are Sources of Dietary Fibre and Antioxidants

World Health Organization (WHO) and worldwide health authorities such as United States Department of Agriculture (USDA) promote a high consumption and variety of fruit and vegetables. In addition, the source of fibre in a healthy dietary pattern such as Mediterranean Diet has been described as an important qualitative difference on health. Fruit and vegetable related dietary fibre transports a significant amount of polyphenols and carotenoids linked to the fibre matrix through the human gut. Despite these effects and recommendations, the intake of plant foods remains low and, consequently, both dietary fibre and antioxidant compounds are usually deficient in most diets around the world.


Introduction
Fruit and vegetables have been recognized as important sources for a wide array of non digestible components and phytochemicals that individually, or in combination, may act synergistically to contribute to the nutritional and health benefits of these food commodities.
World Health Organization (WHO) and worldwide health authorities such as United States Department of Agriculture (USDA) promote a high consumption and variety of fruit and vegetables. In addition, the source of fibre in a healthy dietary pattern such as Mediterranean Diet has been described as an important qualitative difference on health. Fruit and vegetable related dietary fibre transports a significant amount of polyphenols and carotenoids linked to the fibre matrix through the human gut. Despite these effects and recommendations, the intake of plant foods remains low and, consequently, both dietary fibre and antioxidant compounds are usually deficient in most diets around the world.
On the other hand, the food industry processing plant foods produces large amounts of waste and residues (leaves, stems, wastewaters, etc.) that are good sources of dietary fibre and phytochemicals. Several of them contain more dietary fibre than their respective edible portion.
A variety of plant food byproducts are rich in fibre and polyphenolic compounds meeting the criteria of antioxidant dietary fibre. A broad spectrum of these will be summarized in the present work. In this chapter information on nutritional and phytochemical composition will be also included. Special attention nutritional claims criteria with reference to European Regulation has been given to quality ingredients for functional foods and/or dietary supplements. The application of byproducts in the food industry results in added value to both, the industry and the consumer. The industry benefits from economic incomes and the consumer from the excellent nutritional value of these materials with potential health claims.
Mediterranean Diet offers a nutritional model enriched by diverse cultures which over centuries has essentially maintained the same food structure and the same proportions: olive oil, fresh fruits and vegetables, grains and derivatives, fish and to a lesser extent, nuts, dairy products and meat. There is also a moderate consumption of wine, coffee and tea during meals while respecting religious rules and beliefs. Mediterranean Diet is not just a diet (mixture of food), it means a lifestyle because it also implies the way to prepare food and how foods are consumed around the same table. To eat in the Mediterranean Dietary Pattern is a moment of social meeting that complies with several functions: social, cultural and nutritional. The recognition of dietary qualities, and the positive impact on the health of the people who follow this dietary pattern, indicates the model of healthy diet we must try to encourage (UNESCO, 2010).
The definition of the Mediterranean Diet is mainly based on consumption of foods. However, despite the robust inverse association between Mediterranean Diet and mortality found in observational and epidemiological studies, it is not clear which food constituents of this dietary pattern contribute most to its health effects.
With regards to the intake of nutrients and / or food constituents, it appears that both dietary patterns are similar in terms of energy, energy profile and dietary fibre. As far as micronutrients are concerned, clear significant differences in the intake of vitamins and minerals in Northern and Southern European countries have not been reported . However, the intake of monounsaturated fatty acids is higher in the Mediterranean area in opposition to the intake of saturated fatty acids whose values are higher in countries of Northern and Central Europe where there is a higher prevalence of chronic diseases. These facts are related to food consumption patterns that show a remarkable difference. In countries with Mediterranean diet, consumption of fruit and vegetables is significantly higher, being very important not only the quantity of these foods but also the variety of them. Moreover, there are also differences in relation to fat consumption. Mediterranean recorded high availability of olive oil and unprocessed red meat, while Central and Northern European preferably consumed fat from meat products (Naska et al., 2006). These data are in agreement with the fatty acid profile of food consumed in both dietary patterns.
On the other hand, plant foods in Mediterranean Diet, of which there is a considerable amount and variety, seems to have a significant impact on the nutritional assessment of the Mediterranean Diet, as mentioned later, defines some health indicators of this dietary pattern. Plant foods, especially fruit and vegetables contribute a large proportion of the overall dietary intake of dietary fibre and bioactive compounds and a small proportion of the overall dietary intake of energy. Therefore, the role of bioactive compounds or phytochemicals as a key factor in the health effects of the Mediterranean dietary pattern is an attractive hypothesis. The composition and the physicochemical structure of dietary fibre and phytochemicals in fruit and vegetables have specific characteristics which lend these food groups significant nutrition and health related properties. Indeed, the potential health benefits of fruit and vegetables are mainly attributed to the effects of dietary fibre and antioxidants.
It is argued that an increasing intake of 400 to 800 g/person/day of fruits and vegetables is a public health strategy of considerable importance for individuals and communities worldwide. For this reason the World Health Organization (WHO) recommends a daily intake of more than 400 g per person daily, and health authorities worldwide promote high consumption of fruit and vegetables. Currently, the Food Standards Agency recommends the consumption of five portions of fruit and vegetables daily. There is no guidance on the specific type of fruit and vegetables to consume other than a suggestion of a variety; this is because to date, there is a lack of convincing evidence for their identification. It is therefore of priority to indentify fruit and vegetables which would significantly contribute to a reduction in cardiovascular diseases and other chronic non-communicable diseases. This way we could make public health recommendations and provide scientific information to the food industry about the selection of ingredients for functional foods.
Although inconclusive, evidence has alluded to synergistic effects of combinations of polyphenols, which may be more protective against cardiovascular diseases than isolated polyphenols, and that a combination of fruits, in the context of a balanced diet and healthy lifestyle, would help to protect against these pathologies (Chong et al., 2010) Many of the putative chemoprotective phytochemicals in fruits and vegetables are coloured. Therefore, a good strategy may be guidelines based on selecting one daily serving of fruits and vegetables from each of seven colour classes, so that a variety of phytochemicals is consumed. In this context, a complementary definition of the Mediterranean Diet was recently proposed, based on the following dietary indicators: 1) monounsaturated/saturated lipid ratio; 2) intake of dietary fibre defined as food indigestible fraction; 3) intake of antioxidant capacity of the whole diet; 4) intake of phytosterols. These indicators were selected based on the scientific evidence to support the beneficial health effects and because they are differential features in Mediterranean Diet (Saura-Calixto & Goñi, 2009).
There is general consensus among scientists as to the significant role of the monounsaturated to saturated fat ratio in disease aetiology. This ratio is predictive of total mortality and is a common feature in Mediterranean countries, where is much higher than in other parts of the world including northern Europe and North America (Naska et al, 2006).
As it is indicated above, dietary fibre intake is quantitatively similar in Mediterranean and non-Mediterranean European countries (around 20 g per capita). However, there are qualitative differences arising from the fact that a large proportion of the dietary fibre intake in Mediterranean countries comes from fresh fruit and vegetables, while in Northern European countries it comes more from cereals. Consequently, the composition and properties of the dietary fibre in the Mediterranean Diet has specific characteristics related to the type of food, nutrient and phytochemicals contents and healthy properties.
There is a lack of comprehensive data on the antioxidant capacity of whole diets. This parameter is derived from the accumulative and synergistic antioxidant power of a wide variety of sources. Total dietary antioxidant capacity is probably higher in Mediterranean Diet than in other dietary patterns because of the amount and variety of plant foods rich in antioxidant phytochemicals.
Finally, the intake of phytosterols has been established as a factor in the lower cardiovascular disease death rates in Mediterranean countries and it is a specific essential dietary indicator.
The intake of bioactive compounds in recognized healthy diets such as the Mediterranean Diet may serve as a benchmark until scientific knowledge in this field is sufficiently www.intechopen.com advanced to establish daily allowances. Traditional Mediterranean foods are rich in dietary fibre and bioactive compounds and the Mediterranean Diet is a specific type of healthy diet.

Fruit and vegetables are source of dietary fibre and antioxidant phytochemicals
Plant foods, particularly fruit and vegetables, have been consistently identified in epidemiological research as the key components of dietary patterns that reduce risk for the development of chronic and degenerative diseases, including atherosclerotic cardiovascular diseases, insulin resistance and type II diabetes and many cancers (Hu et al., 2000;Kant et al., 2004;Mokdad et al., 2000). One of the predominant mechanisms of their protective action is due to their antioxidant activity and the capacity to scavenge free radicals. There has been increasing interest in the nutritional properties of fruit and vegetables as sources of dietary fibre and other health-promoting phytochemical compounds (Knekt et al., 2002;Kris-Etherton et al., 2004;Mennen et al., 2004;Most, 2004).
Fruit and vegetables are generally high in water, low in fat and, in addition to vitamins and minerals, contain significant amounts of dietary fibre and phytochemicals -mainly polyphenols and carotenoids -with significant biological properties, including antioxidant activity.
The composition and the physicochemical structure of dietary fibre and phytochemicals in fruit and vegetables are specific characteristics which lend significant nutrition-and healthrelated properties to this food group. Indeed, the potential health benefits of fruit and vegetables are mainly attributed to the effects of dietary fibre and antioxidants.

Phytochemicals
Phytochemicals or phytonutrients are bioactive substances that can be found in foods derived from plants and are not essentials for life. The human body is not able to produce them. Phenolic compounds are widely distributed throughout the plant kingdom and range from simple molecules such as phenolic acids to complex polymerised compounds (i.e. polyphenols) (Rice- Evans et al., 1996). Recently, some of their characteristics, mainly their antioxidant capacity, have given rise to research related to their protective properties on health and the mechanisms of action involved. The health benefits of antioxidant of natural origin are associated with their role in the prevention of several disorders called oxidative stress pathologies (Herrera et al., 2009). These are related to the damaging effect of oxygen free radicals, or more generally reactive oxygen species, products of normal metabolism that become harmful when they cannot be neutralized by the cellular antioxidant defense systems. In this condition of oxidative stress an uncontrolled oxidizing process may occur that damages biological molecules, disturbs cellular functions, and can potentially lead to the development of one or more diseases (Valko et al., 2007).
Dietary phytochemicals are defined as bioactive, non-nutrient plant compounds that are associated with reduced risk of chronic diseases (Liu, 2004). Prospective cohort studies consistently suggest that when consumed in whole foods, these phytochemicals may contribute to important protection against chronic diseases, such as cardiovascular diseases and certain cancer (Okarter & Liu, 2010). The additive and synergistic effects of these bioactive phytochemicals found in plant foods may be responsible for the health benefits associated with the diet; additionally, the phytochemicals present in the different groups of plant foods in the diet complement each other when they are consumed together (Adom et al., 2005;Liu, 2004;Okarter & Liu, 2010).
Plant foods phenolic compounds may provide benefits to human subjects via several mechanisms (Nijveldt et al., 2001). The best described and most well known mechanism is through their antioxidant properties and modulation of biological oxidative stress to prevent damage to cellular lipids, protein and DNA. Directly, they may scavenge superoxide and other reactive oxygen species such as hydroxyl and peroxy radicals. Overall, phenolic compounds have multiple paths for benefiting human health, most notably, through their actions as antioxidants and modifying cellular events. Their specific actions are likely to be dependent on the composition and time course of metabolites appearing in plasma (Crozier et al., 2009;Hollman et al., 1997;Manach et al., 2005). The intake of these antioxidants can lead to sustained reduction of the kind of oxidative damage to lipids, proteins and DNA that is associated with the development of chronic diseases (Evans & Halliwell 2001).
Notwithstanding the need for more research, the collected data suggest that the consumption of phenolic-rich fruits increases the antioxidant capacity of blood, and when they are consumed with high fat and carbohydrate "pro-oxidant" foods, they may counterbalance their negative effects. Given the content and availability of fat and carbohydrate in the Western diet, regular consumption of phenolic-rich foods, appears to be a prudent strategy to maintain oxidative balance and health (Burton-Freeman, 2010). Vitamins (C and E), polyphenolic compounds and carotenoids are the main groups of antioxidants present in fruit and vegetables. Vitamins are single molecules, but polyphenols and carotenoids are made up of hundreds of compounds with a wide range of structures and molecular masses.
Dietary fibre and antioxidants are generally addressed separately as groups of food constituents in both chemical and nutritional studies. However, it is a little known fact that a substantial proportion of the antioxidant polyphenols and carotenoids contained in fruit and vegetables are linked to dietary fibre , and some of the postulated benefits of the fibre intake can be attributed to these associated compounds.
Most biological properties of polyphenols depend on their bioavailability; the latter is largely influenced by chemical and physical properties and plant-derived conjugation. While a small proportion of some dietary polyphenols can be absorbed through the small intestine, the majority are either not absorbed, or are excreted and become fermentable substrates for bacterial microflora in the colon along with the non digestible food fraction . Polyphenols bound to dietary fibre can account for a substantial part of total polyphenols in foods. These polyphenols are not bioavailable in the human upper intestine and reach the colon, where they become fermentable substrates for bacterial microflora, along with the other dietary fibre components. The fermentation of polyphenols in the colon improves antioxidant status and yields different metabolites with potential systemic effects.
The majority of studies on determining the bioavailability of phenolic compounds are conducted by the analysis of blood phenolic metabolites a short time after ingestion. However, it should be noted that among the many polyphenols present in food, most of www.intechopen.com them do not reach the bloodstream in the early hours of food digestion. Nevertheless, they do the transit until the large intestine where they can be metabolized through other pathways involving the enzymatic activities of the colonic microbiota. Therefore, it is expected that the protective effects of polyphenols are broader than those listed, as will be indicated later.

Dietary fibre
Dietary fibre is a major constituent of plant foods and its importance in nutrition and health is widely recognized. Numerous clinical and epidemiological studies have addressed the role of dietary fibre in intestinal health, prevention of cardiovascular disease, cancer, obesity, and diabetes (Buttriss & Stokes, 2008). The recommended daily intake of dietary fibre is 25-35 g/person (Buttriss & Stokes, 2008 Just as there are significant differences in the consumption of fruit and vegetables among European countries we also note differences in dietary fibre intake. The source of fibre in a healthy dietary pattern is an important qualitative difference. Table 1 summarizes the daily intake of dietary fibre among European countries (Bingham et al., 2003).
The intake of dietary fibre is low and quantitatively similar in Mediterranean and non-Mediterranean European countries. These data were consistent with other published works (Elmadfa et al., 2005). Dietary fibre intake in Mediterranean countries comes from fresh fruit and vegetables, while in Northern European countries it comes more from cereals. Accordingly, the incidence of chronic diseases is higher in northern European countries.
Currently there is not a harmonized definition of dietary fibre at the European Community level. The term dietary fibre was originally defined as the portion of food which is derived from cellular walls of plants which are digested very poorly by human beings (Trowell, 1976). The recognition that other food components could have effects similar to those originating from plant cell walls led to a redefinition of dietary fibre to include all undigestible food components. The indigestible fraction of food has been defined as the part of plant foods that is not digested nor absorbed in the small intestine, reaching the colon where it is a substrate for the fermentative microbiota. As such, it comprises not only dietary fibre (traditional concept), but also other compounds of proven resistance to the action of digestive enzymes such as a fraction of dietary starch (resistant starch), protein, certain polyphenols, and other associated compounds (Saura-Calixto et al., 2000. This definition, basically physiological in nature, has been accepted by the majority of scientists working in the field. In this line, a method to quantify the food indigestible fraction in plant foods was presented. In this method, the digestible portion of the food is removed by using digestive enzymes and mimicking the digestive process in the small intestine. Then, a majority of indigestible components are isolated (Saura-Calixto et al., 2000). The value of dietary fibre includes resistant starch in this analytical method. However, resistant oligosaccharides and inulin are not included, and therefore need to be measured separately and subsequently added to the total food indigestible fraction estimate. The concept of indigestible fraction as dietary fibre is more reliable when applied to epidemiological and nutritional studies (Saura-Calixto & Goñi, 2004).
On the other hand, a number of physiological effects in human beings, e.g. decreased intestinal transit time, increased stools bulk, reduction of blood total and/or LDL cholesterol levels, and reducing post-prandial blood glucose and/or insulin levels, are often associated to the intake of dietary fibre. However, these effects vary depending on fibre component. Therefore, each fibre may have specific effects, which suggests not including physiological properties in the definition.

Dietary fibre as a carrier of bioactive compounds
Fruit and vegetables possess a higher soluble/insoluble fibre ratio than cereals, what is considered as an indicator of nutritional quality. A part of the postulated benefits of the Mediterranean dietary pattern might then be attributable to the intake of food undigestible components (Saura-Calixto et al., 2000). It is important to note at this point that the use of food dietary fibre data in nutrition may be subject to some limitations arising from the concept of dietary fibre itself and from the methodology used to determine dietary fibre in foods.
Dietary fibre does not constitute a defined chemical group but a combination of chemically heterogeneous substances. Moreover, dietary fibre, especially from fruits and vegetables, is a carrier of bioactive compounds. Dietary fibre of fruit and vegetables transports a significant amount of polyphenols and carotenoids linked to the fibre matrix through the human gut (Saura-Calixto et al., 2006. Therefore, associated phytochemicals can make a significant contribution to the health benefits attributed to the dietary fibre of fruit and vegetables. Thus, phytochemicals may be considered dietary fibre constituents in view of the similarity of their properties in terms of resistance to digestive enzymes and colonic fermentability (Saura-Calixto et al., 2006. Physiological and physicochemical effects of dietary fibres depend on the relative amount of individual non-digestible components. Therefore, when a dietary fibre contains associated compounds with antioxidant activity, this property is conferred to the total dietary fibre complex and may be considered as antioxidant dietary fibre (Saura-Calixto et al., 1998).
In the Spanish diet, considered as Mediterranean pattern diet, fruit and vegetables provide a daily intake of 700-1000 mg of polyphenols/person/diet, a major fraction of this (600 mg/person/day) associated with dietary fibre . These issues constitute an important qualitative difference in relation to other dietary patterns.

By-Products from plant foods as sources of dietary fibre and antioxidants
Fruit and vegetables have been recognized as important sources for a wide array of non digestible components and phytochemicals that individually, or in combination, may act synergistically to contribute to the nutritional and health benefits of these food commodities.
Despite the consumption recommendations, the intake of fruit and vegetables remains low and, consequently, both dietary fibre and antioxidant compounds are usually deficient in most diets around the world.
Nowadays dietary fibre and bioactive compounds are widely used as functional ingredients in processed foods. The market in this field is competitive and the development of new types of quality ingredients is a challenge for the food industry. In this regard, it is interesting to consider not only the nutritional quality of the ingredient, but also its distribution, cost and other additional benefits, since the use of these ingredients would give added value to the production of these materials. There is a trend to find new sources of functional ingredients such as plant food byproducts that have traditionally been undervalued (Rodríguez et al., 2006). The term "byproduct" suggests that plant food wastes might be usable and have their own market (Sánchez-Zapata et al., 2009). The plant food processing industry produces large amounts of wastes and residues, estimated to be around 800 000 tons per year of fresh fruit and vegetable matter globally, without considering the wastage during processing ( Dietary fibre does not constitute a defined chemical group but a combination of chemically heterogeneous substances. The health significance of foods fibres has led to the development of a large and potential market for fibre-rich products and ingredients (Rodríguez et al., 2006). In general, agricultural and industries residues are important sources of dietary fibre. Table 2 shows the percentage of byproducts generated from fruit and vegetables processing industries. These byproducts are made up mainly of skins, seeds, stems, leaves, wastewaters and unusable pulp which are normally discarded (Ajila et al., 2007). The amount of byproducts might represent more than 40% of total plant food in cases such as artichoke, asparagus, cactus pear fruit, mango, orange, papaya, pineapple, red chicory and tiger nuts. Dietary fibre of fruit and vegetables transports a significant amount of polyphenols and carotenoids linked to the fibre matrix through the human gut (Saura-Calixto et al., 2006. Therefore, associated phytochemicals can make a significant contribution to the health benefits attributed to the dietary fibre of fruit and vegetables. Moreover, phytochemicals may be considered dietary fibre constituents in view of the similarity of their properties in terms of resistance to digestive enzymes and colonic fermentability (Saura-Calixto et al., 2006.
An interesting approach to providing an added value to byproducts is their use as sources of dietary fibre and also as natural antioxidant compounds. Particularly, plant food residues are a good source of phytochemicals such as polyphenols.
The phenolic content of a wide variety of plant food byproducts are displayed in Tables 4  and 5. It can be noted that peel byproducts from grape, mango, pomegranate, apple, bambangan, cactus pear and cladodes as well as seeds of avocado, longan and mango, are remarkably the highest in polyphenol concentration. Likewise, general byproducts from asparagus, artichoke, blueberry, cranberry, buckwheat and grape seed are rich in polyphenols including proanthocyanidins. Grape antioxidant dietary fibre is the most concentrated source of polyphenols with a concentration of 19740 mg/100 g dry weight (Pérez-Jiménez et al., 2008).  Table 4. Phenolic content (mg/100 g fresh weight) measured in solvent extracts of plant byproducts. *mg/g of extract.
A wide array of phenolic compounds has been described in plant food by-products. Almond hull extracts contain hydroxybenzoic and cinnamic acid derivatives, with minor presence of flavan-3-ols, including the presence of epicatechin and glycosylated flavonols (Rubilar et al., 2007). Five phenolic acids (gallic acid, caffeic acid, p-coumaric acid, ferulic acid, and sinapic acid) were identified in hazelnut byproducts (both free and esterified forms) (Shahidi et al., 2007).
Caffeic acid derivatives are the main phenolic compounds in artichoke heads, with a wide range of caffeoylquinic acid derivatives with chlorogenic acid (5-Ocaffeoylquinic acid) as the most important of these derivatives. Other phenolics such as the flavonoids apigenin and luteolin (both glucosides and rutinosides) as well as different cyanidin caffeoylglucoside derivatives have been identified (Llorach et al., 2002). The analysis of cauliflower byproduct extracts revealed the presence of both flavonoids and hydroxycinamic acids (caffeic acid and sinapic acid). Different combinations of flavonols such as kaempferol and quercetin with sinapic acid and glucose were the main phenolic compounds present (Llorach et al., 2003).
Analyses of lettuce byproducts revealed the occurence of both hydroxycinnamic acids and flavonoids. The flavonoid profile of lettuce byproducts was composed of flavones (luteolin derivatives) and flavonols (quercetin derivatives), whereas the chicory byproducts were composed only of kaempferol derivatives (Llorach et al., 2004).  Table 5. Phenolic content (mg/100 g dry weight) in different plant foods byproducts. *mg proanthocyanidins/100 g dry weight.
The prominent phenolic compounds identified in peels of raw and ripe mango fruits were protocatechuic acid, gentisic acid and gallic acid. Gallic acid, syringic acid, mangiferin, ellagic acid, gentisyl-protocatechuic acid, quercetin were the phenolic compounds identified in both raw and ripe peels, while raw peel showed the presence of glycosylated iriflophenone and maclurin derivatives also (Ajila et al., 2010b). The main flavonoids found in citrus species are hesperidin, narirutin, naringin and eriocitrin. Peel and other solid residues of lemon waste mainly contained hesperidin and eriocitrin, while the latter was predominant in liquid residues (Schieber et al., 2001). Otherwise, the polyphenol profile of solvent extracts of various byproducts (barks, kernels, peels, and old and young leaves) from Brazilian mango crops showed the occurrence of xanthone C-glycosides, gallotannins, and benzophenones (Barreto et al., 2008).
In the composition of extracts of white and red grape pomace several of these compounds were also detected but basically consisted of glycosylated flavonols (quercetin, kaempferol) (Rubilar et al., 2007). Phenolic compounds present in grape pomace antioxidant dietary fibre have been widely described (Tourino et al., 2008), comprising: hydroxybenzoic and phenolic acids and their derivatives, monomeric flavonoids (catechins and flavonols aglycones) and flavonoids such as oligomeric proanthocyanidins, flavonols, flavones, and flavanones; anthocyanin, anthocyanidins delphinidin, cyaniding, petudin, peonidin, petunidin, pelargonidin and malvidin) and their mono and acetyl glucoside derivatives were also identified as well as polimeric proanthocyanidins (types A and B).
One recognized characteristic of a healthy diet includes components that counteract oxidative stress, which is involved in the etiopathogeny and progression of chronic diseases, contributing to the process of aging (Herrera et al., 2009). Dietary fruit and vegetables provide a significant amount of compounds (vitamins, carotenoids and polyphenols) that act as physiological antioxidants. Polyphenols are the major dietary antioxidants.
Since part of the total content of antioxidant phytochemicals is linked to dietary fibre as noted above, an appreciable proportion of the total antioxidant capacity in fruit and vegetables is associated with dietary fibre. We address mainly polyphenols associated with dietary fibre in fruit and vegetables because of the important biological properties derived from them and the significant phenolic content in these foods. Table 6 summarizes the antioxidant or radical scavenging activity of plant food byproducts. Those from bambangan, cactus pear, cladodes, hazelnut and, especially grape antioxidant dietary fibre, possess a potent antioxidant capacity.

Application of plant food byproducts as functional ingredients
The definition of a functional food by the International Life of Science Institute (ILSI 1999) is "a food product can be functional if it has satisfactorily been proven that it produces a beneficial effect on one or more physiological functions, besides its conventional nutritional effects, being this relevant for improving human health and/or reducing the risk of suffering certain diseases" (Roberfroid, 2000). Dietary fibre holds all the characteristics required to be considered as an important ingredient in the formulation of functional foods due to its proven beneficial effects (Rodríguez et al., 2006).
The Regulation on Nutrition and Health Claims (European Comission 2007, EU Regulation (EC) No 1924) allows claims to be made with respect to the fibre content of food (Table  7) as source of fibre if its levels exceed 3 g per 100 g or high in fibre for 6 g per 100 g (Buttriss & Stokes, 2008). The claims for dietary fibre are as follows ( Byproducts obtained when processing cereal, algae, fruit and vegetables can be added as functional ingredients, providing advantageous dietary fibre and bioactive compounds. These byproducts serve as non-caloric bulking agents, enhance water and oil retention, and improve emulsion and oxidative stability. The literature reports addition of fibre to food products such as baked goods, beverages, confectionary, dairy, meat and pasta (Elleuch et al., 2011).
Addition of byproducts in bakery products are muffin butter supplemented with peach dietary fibre (Grigelmo-Miguel et al., 1999), and cake dough enhanced with prickly pear cladode fibre (Ayadi et al., 2009) at levels up to 5%. Incorporation of cauliflower by-products into ready-to-eat snacks enhanced nutritional and textural characteristics, increasing dietary fibre levels in the finished product by over 100% (Stojceska et al., 2008).
Fibres can also be introduced into meat products. Addition of 1.5% of orange fibre or 3% of carrot fibre to dry fermented sausages does not affect its organoleptic characteristics (Eim et al., 2008;Garcia et al., 2002). Citrus fibre with associated antioxidant bioactive compounds when added to meat products inhibits lipid oxidation and decrease residual nitrite levels (Fernández-Ginés et al., 2003). Pork burgers elaborated with tiger nut fibre had higher nutritional value in terms of fibre content and better cooking characteristics such as higher cooking yield, fat and moisture retention (Sánchez-Zapata et al., 2010). Grape pomace antioxidant dietary fibre when added to minced fish (Sánchez-Alonso et al., 2007) and chicken hamburgers (Sáyago-Ayerdi et al., 2009) improves oxidative stability and thus prolong shelf life. By-product fibre addition to burgers is a promising and convenient application considering dietary fibre of burgers can be significantly increased without changes in sensory acceptance.
The addition of unripe banana flour to spaghetti increased the dietary fibre and the content of phenolic compounds. Consequently, spaghetti had a slow and low rate for enzymatic hydrolysis and an increased antioxidant capacity (Ovando-Martínez et al., 2009). Mango peel powder was incorporated into macaroni (7.5%) to increase dietary fibre from 8.6 to 17.8%, polyphenols from 0.46 to 1.80 mg/g and carotenoid content from 5 to 84 µg/g of macaroni, resulting in an enhanced nutritional quality without affecting its cooking, textural and sensory properties (Ajila et al., 2010a).

Conclusion
Several fruit and vegetable byproducts from food processing industries meet the criteria of antioxidant dietary fibre definition. They are certain to be an excellent source of dietary fibre and natural antioxidants if used as high-quality ingredients in functional foods or dietary supplements. Furthermore, compliance with the nutritional claims criteria recognized in the European Regulation would be met. The applications of plant food byproducts will definitely bring about added value to both, the industry and the consumer. The industry benefits from econimic incomes and the consumer from the excellent nutritional value of these materials with potential health claims.

Acknowledgment
The present work was performed under the financial support of the Spanish Ministry of Science and Innovation, National Program of I+D, AGL-2008-01633. D. Hervert-Hernández acknowledges predoctoral fellowships from the Mexican institutions CONACyT and SEP.

References
Adom