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Abstract
In the last few years, an increasing attention has been diminishing the environmental impact of industrial wastes. In particular, many food industries have an adverse environmental impact because of the presence in their wastes of residual phenols from the plant raw material used. In industrial wastewaters, these compounds considerably increase biochemical and chemical oxygen demands, with detrimental effects on the flora and fauna of discharge zones, while in solid residues for obtaining fertilizers, relatively high levels of phenolic compounds are a problem because of their inhibition of germination properties. However, polyphenols have many favourable effects on human health, such as the inhibition of the oxidization of low-density proteins (Frankel et al., 1993; Frankel et al., 1995; Meyer et al., 1997),thereby decreasing the risk of heart diseases (Frankel et al., 1993). They also have anti-carcinogenic properties. (Bailey and Williams, 1994).
Grapes (Vitis vinifera) are one of the world׳s largest fruit crops, with an annual production of approximately 76 million metric tons (FAO, 2004) the composition and properties of grapes have been widely investigated. It has been found that grapes contain high amounts of phenolic compounds (Bonilla et al., 1999; Guendez et al., 2005 b). Grape- and juice-derived by-products are largely available and show high phenolic content. This hinders their direct utilization in agriculture, but could be favorable for processes intending the selective separation and recovery of natural compounds with antioxidant activity. Waste solids from wine-making are heterogeneous, and the various materials present in them have different compositions (Macheix et al., 1990). The major phenolic compounds in Vitis Vinifera grape seeds are epicatechin (accounting for 60% of the monomers) followed by catechin and gallic acid (Saito et al., 1998; Yamaguchi et al., 1999), whereas the most abundant phenolics in grape peels are epicatechin, epigallocatechin, gallic acid, and catechin (Hurtado et al., 1997; Pastrana-Bonilla et al., 2003). The presence of phenolic acids such as caftaric acid, coutaric acid, catechin, epicatechin, astilbin, and engeletin as well as myricetin, kaempferol, and quercetin glucosides in stalks has been reported (Souquet et al., 2000).
Grapes (Vitis vinifera) have gained increased research focus due to the presence of phytochemicals in the grapes and grape by-products, commonly referred to as grape pomace. Grape pomace consists of skin, seeds and the pulp remaining from the production of juice and wine. The grape skins and seeds have been shown to have high levels of polyphenols, particularly the proanthocyanidins (Torres and Bobet, 2001). The seed and skin by-products are good sources of antioxidant compounds suitable for use as dietary supplements (Yilmaz and Toledo, 2004). In addition to the antioxidant activity of grape, the grape by-products may possess biological properties such as anti-inflammatory, anti-carcinogenic and anti-microbial properties.
Grapes by-products are valuable raw materials for extraction of polyphenols (Yilmaz and Toledo, 2006). Grape seed extracts contain a number of polyphenols including phenolic acids, procyanidins and proanthocyanidins; many of which are powerful free radical scavengers (Feng et al., 2005). The recognition of health benefits (i.e. anti-atherogenic, anti-carcinogenic, anti-ischemic, etc.) associated with the polyphenols in grape by-products has facilitated the use of grape seed extracts as a dietary supplement (Kim et al., 2006). Thus, extraction of phytochemicals from permeable solid plant material, using liquid food-grade solvents, constitutes an important step in the preparation of phytochemical rich products (Cacace and Mazza, 2002). Additionally, due to the growing interest in phenolic compounds in grapes and grape by-products , there is a need to isolate, identify and quantify the phytochemicals in fruits and vegetables and evaluate their potential health benefits (Liyana-Pathirana and Shahidi, 2005; Sellappan et al., 2002).
Lipid peroxidation is one of the main reasons for deterioration of food products during processing and storage. It is of great economic importance to the food processing industry because the reaction leads to the development of rancid flavors and odors which can render edible oil and fat containing foods unacceptable or reduce their shelf life. Oxidative rancidity also reduces nutritional quality of food through the loss of essential fatty acids and fat soluble vitamins. Certain oxidative products are potentially toxic (Nawar, 1985). Antioxidants are compounds that in small quantities delay the onset or greatly retard the oxidation of food that contain fat. Many types of compounds have been used as food antioxidants, both natural and artificial. Synthetic antioxidants such as butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), propyl gallate (PG) and tert-butylhydroquinone (TBHQ) are widely used as food additives to increase the shelf life, especially of lipids and lipid-containing products by retarding the process of lipid peroxidation. However, BHT and BHA are known to have not only toxic and carcinogenic effects on humans (Ito et al., 1986; Wichi, 1988), but also abnormal effects on enzyme systems (Inatani et al., 1983). Therefore, the interest in natural antioxidants, especially of plant origin, has greatly increased in recent years (Jayaprakasha and Jaganmohan Rao, 2000). Natural antioxidants can protect the human body free radicals that may cause some chronic diseases including cancer, cardiovascular diseases and cataract (Kinsella et al., 1993; Lai et al.; 2001). Grape seed polyphenols are natural compounds having antioxidant properties (Negro et al.; 2003; Jayperasha et al., 2001).
Substitution of synthetic antioxidants by natural ones has gained interest over the past few years in the food industry due to health and safety concerns. In this context, plant-derived materials have been tested as sources for active antioxidants. Residual biomass (from agricultural or industrial activities) is a favorable raw material for chemical processing due to its low cost and the possibility of avoiding environmental problems caused by its disposal (Duh et al., 1997; - Moure et al., 2001). On the other hand, the external fibrous and lignified parts of plants (such as peels, hulls, or seeds) appearing in wastes present higher contents of phenolics potentially useful as antioxidants than the corresponding inner parts
There is considerable interest in the development and evaluation of natural antioxidants and radical scavengers from plant materials that are rich in flavanoids and other polyphenolic compounds (Burns et al., 2001). Grape seeds have become an ideal candidate as a cost-effective product with natural and high value-added polyphenolic phytochemicals (Guendez et al., 2005 a). Therefore, there is a need for more research focusing on extracting and characterizing the phenolic compounds from grape skin and seeds (Ju and Howard, 2003). Because of the potential health benefits of phenolic compounds, there is also an interest in developing analytical methodologies to detect and measure phenolic compounds from plant sources (Kiendrebeogo et al., 2006).
Phytochemicals have been shown to have roles in the reduction of platelet aggregation, modulation of cholesterol synthesis and absorption, and reduction of blood pressure (Liu, 2003). Other positive effects of increased consumption of phytochemicals includes elevated high-density lipoprotein (HDL), a reduction in the atherogenic lipoproteins (LDL), a reduction in stress, and a reduction in platelet activity (Kinsella et al., 1993). According to Yilmaz and Toledo (2004), muscadine grape seed proanthocyanidins reduced atherosclerotic activity of low density lipoprotein (LDL) by inhibiting oxidation. In another study performed by van Velden et al. (2002), it was concluded that lipid profiles responded significantly as being more anti-atherogenic to red wine compared to white wine with a decrease in total cholesterol, increase in HDL cholesterol, and decrease in LDL cholesterol, with minimal effect on triglyceride levels (van Velden et al., 2002).
Microbial activity is a primary mode of deterioration of many foods and is often responsible for the loss of quality and safety. Concern over pathogenic and spoilage microorganisms in foods is increasing due to the increase in outbreaks of food borne disease (Tauxe, 1997). Currently there is a growing interest to use natural antibacterial compounds, like plant extracts of herbs and spices for the preservation of foods, as these possess a characteristic flavour and sometimes show antioxidant activity as well as antimicrobial activity.
Extracts of grape seeds have been shown to have strong antimicrobial activity. Ahn et al. (2004) reported the inhibitory action of Activin, a commercial grape seed extract, against gram-negative bacteria, Escherichia coli, and Salmonella Typhimurium, and against gram-positive bacteria including Listeria monocytogenes. Palma and Taylor, (1999) reported the antimicrobial action of a grape seed extract against a range of human and plant pathogenic microorganisms. Jayaprakasha et al., (2003) reported the antimicrobial action of Vitis vinifera grape seed extract against Bacillus cereus, Bacillus coagulans, Bacillus subtilis, Staphylococcus aureus (all gram-positive bacteria), but not including Listeria monocytogenes, and the gram-negative bacteria Escherichia coli and Pseudomonas aeruginosa and found that gram-positive bacteria were more susceptible to the grape seed extract than gram-negative bacteria. A number of purified phenolic compounds present in grapes and wine, many of which have been described in the preceding sections, have been shown to possess antimicrobial activity (Pratt et al., 1960; Powers, et al, 1960; Hamdy et al., 1961; Somaatmadja et al., 1963)
The objectives of this study were:
1- Studying the chemical composition of grape wastes including (seeds, skin, and stem) from different cultivars.
2- Studying the chemical composition of phenolic compounds in the wastes including (seeds, skins, and stems) as sources of polyphenolic antioxidants.
3- Studying the antioxidant activity of extracts from the grape seeds, skins and stems.
4- Studying the antimicrobial activity of grape seed extracts.
5- Separation and identification of the major phenolic compounds in grape byproduct using GC-MS