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Abstract
INTRODUCTION
Historically, flaxseed has been prized for its oil, called linseed oil, which is used in industrial applications. Most of the protein is concentrated in flaxseed meal, a by-product of the flaxseed- crushing industry (Bhatty, 1993). Flaxseed is one of the richest plant sources of the n-3 fatty acid, α-linolenic acid (ALA), and the richest source of secoisolariciresinol diglycoside (SDG). SDG, a lignan precursor, is converted by the bacterial flora of the human colon to two major mammalian lignans, enterodiol and enterolactone (Thompson, et al, 1997), found in the biological fluids of humans and animals (Setchell, et al., 1980). Lignans are thought to exert protective effects by interfering with endogenous sex hormone metabolism (Adlercreutz, et al, 1981). Reproduction, being dependent upon sex hormone balance, could be affected by changes in that balance.
The name of flax, Linum usitatissimum of the family Linaceae recognizes its usefulness for a variety of purposes, not only as a food source. Flax is a versatile, blue-flowered crop the seeds for food and feed uses are harvested and then Sieved through fine mesh screens, resulting in a clean, uniform batch of whole seeds (considered99.9% pure).The seed itself is flat and oval with a pointed tip. It is a little larger than a sesame seed and measures about 2.5 x 5.0 x 1.5 mm (Freeman, 1995).
Flaxseed contains a seed mat (hull) with a thin endosperm, an embryo axis and two cotyledons comprising 36%. 4% and 55% of the total seed weight (Bhatty and Cherdkiatgumchai, 1990) The seeds have a crisp and chewy texture and a pleasant, nutty taste (Carter,. 1996).
Environmental endocrine active compounds, including phytoestrogens, can have pronounced effects on reproduction and fertility (e.g., genistein). Japanese women who consume high levels of phytoestrogens tend to have longer menstrual cycles than American women. Perturbations of the estrous cycle indicate that lignans affect estrogen action. Alteration in the regularity and length of the menstrual cycle of humans has been related to breast cancer risk.
On a dry weight basis, flaxseed contains about 230 g/kg total dietary fiber rich in pentosans with the hull fraction containing 2–7% soluble polysaccharides. The quantity of hull in oil-free, moisture-free flaxseed meal is estimated at 38%, twice the level of hulls in canola or soybean meals. Furthermore, flaxseed fiber can be incorporated at levels not exceeding 20 g/kg monogastric diet (dry weight basis) due to its high gel forming capacity and bulkiness. Because much of the fiber is in the hull, efforts are directed towards removing the maximum amount of hull from the seed or meal and simultaneously obtaining a pure hull fraction with physiological properties.
Flaxseed contains both soluble and non-soluble fibre, which accounts for about 28% of the weight of full-fat flax seeds. The proportion of soluble to insoluble fibre in flaxseed varies between 20:80 and 40:60. The major insoluble fibre fraction in flaxseed consists of cellulose and lignin, and the major soluble fibre fractions are the mucilage gums. Mucilage gums are a type of polysaccharide that becomes viscous when mixed with water or other fluids. These fibre fractions in flax can be classified as either dietary fibre or functional fibre. The classification depends on whether they are found intact in flax or are extracted from flax, purified and added to foods and other products. Thus, whole flax seeds and ground flax are sources of dietary fibre; while mucilage gums extracted from flax seeds and added to laxatives and cough syrups are functional fibres.
The fibre fractions in flax can be classified as either dietary fibre or functional fibre. The classification depends on whether they are found intact in flax or are extracted from flax, purified and added to foods and other products. Thus, whole flax seeds and of dietary fibre, while mucilage gums extracted from flax seeds and added to laxatives and cough syrups are a functional fiber.
Natural polymers including polysaccharides, mainly produced by micro- organisms or extracted from plants, have found many applications in various industries (Stephen, and Churms1995). Plant polysaccharides may correspond to storage polymers or to molecules involved in the cell-wall structure. A third group includes exudates or mucilage coming from plant organs as stems or seeds. Mucilage and plant polysaccharide exudates represent an easy and cheap access to an important stock of polysaccharides, and some of them, like Arabic gum, are incorporated in food products.
Mucilage gums are a type of polysaccharide that becomes viscous when mixed with water or other fluids. Flaxseed mucilage consist of a mixture of two fractions: an acidic polymer containing high galacturonic content and a neutral polymer with low galecturonic content (Hunt and Jones, 1962; Cui, et al., 1994, Vaisey- Genser, and Morris 2003)
Rheological properties of flaxseed mucilage are influenced by several factors especially extraction conditions and cultivar (Cui et al., 1996, Yong Wang, et al.2008, Warrand et al, 2005).The range of viscosity from an almost viscous fluid (cv. Liflora) to that of a nearly elastic gel (cv. Szegedi 62) are due to variations in polysaccharide content, branching and molecular. As well, the type of polysaccharide, that is, the relative amounts of neutral to acidic fraction affects the viscoelastic properties of each gum cultivar solution (Cui et al, 1996, Warrand ,et al ,2005). Extraction conditions such as pH, temperature and water-seed ratio also have a substantial influence on flaxseed gum yield, composition and rheological properties (Cui, et al., 1994; Fedeniuk and Biliaderis, 1994).
For many years, flaxseed mucilage has found specific applications in the cosmetic field (Warrand, et al., 2003). Recently, the positive image related to the health benefits of the dietary consumption of flaxseed has increased its utilization in food products. Therefore it is necessary to understand the behaviour of this polysaccharide in food applications. These mucilages can be extracted from a low-value by-product and could find commercial applications as value-added dietary fiber ingredients. One potential use of flaxseed is as an ingredient in milk-based beverage emulsions to improve their nutritional value (Khalloufi ,et al., 2008).