Considered As A Dietary Constituent Biology Essay

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Fibers are generally complex carbohydrates that are mostly found in outer layer of plants. Although it is already in a part of human diet , it has been recently considered as a dietary constituent.( Nelson, 2001) It was firstly described as a plant cell wall in 1953 and later on in 1973 the definition was expanded with "indigestible polysaccharides and lignin" terms (Kamp, 2004) Recently , The American Association of Cereal Chemists (AACC) updated its definition as following; " Dietary fiber is the edible parts of plants or analogous carbohydrates that are resistant to digestion and absorption in the human small intestine with complete or partial fermentation in the large intestine. Dietary fiber includes polysaccharides, oligosaccharides, lignin, and associated plant substances. Dietary fibers promote beneficial physiological effects including laxation, and/or blood cholesterol attenuation, and/or blood glucose attenuation."

1.1.1 Sources & Production of Fiber Ingredients

Fibers are available in different kinds of plant sources that can be classified as fruits, cereals, plants generally. Since the water content of fruits is higher than cereals, they consist less dietary fiber. (Cho, Dreher, 2001) Therefore the commonly known above sources is cereal grains such as wheat bran, oat bran, rye flour.

Generally cereal grains consist four different parts in their structure; hull, bran layer, endosperm, and germ although the level and contents of these may be different. Hull is placed on the external part of the grain which is made up of insoluble fibers. The next layer after the hull is bran layer in which both soluble and insoluble fibers are found. On the contrary to the outer layers endosperm and germ part of the grain are composed of starch and lipids, respectively.

The process for production of fiber from cereal grains starts with dehulling of the grain to remove hull. Then dehulled grains are flaked, grinded and bran, germ and endosperm are obtained separately. These steps are part of milling process which especially determines various types of brans, germs. Further steps may be grinding, bleaching, roasting etc. After the separation fiber content of the parts are obtained however since complete separation is difficult, some of bran, endosperm and germ can be seen in each separated part.

The fiber content of bran differs due to different type of cereal grains as shown in the figure. (Nelson, 2001)

Bran Type

Total Dietary Fiber, %

Oat

16-32

Wheat

35-45

Barley

15-70

Rice

20-33

Corn

~55,80-90

Soybean

~65

Rye

~25-30

Simple extraction, drying, enzyme additions are other procedures than milling for isolating fiber from different sources. Even with waste products such as hulls, almond skins, waste of fruits etc. (Cho, Dreher, 2001)

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1.1.2 Physical Properties and Functions of Fibers

1.1.2.1 Water binding capacity:

Water binding capacity or holding capacity can be defined as capability of a food ingredient to capture water under some conditions. (Chen, Piva, 2006) The water binding capacity is high in fiber ingredients. It also assists retardation of staling, ice crystal formation, and decreases weeping. (Cho, Dreher, 2001) Water binding capacities of some fibers are shown in the table below ( Nelson, 2001)

Ingredient

Water Binding Capacity

(g water/g materialx100)

Apple pulp

230

Rice bran

100

Wheat bran

260

Oat bran

140

Corn bran

250

Soy bran

240

Sugar beet fiber

350

1.1.2.2 Viscosity/ Thickening agent

Viscosity is a resistance to flow of fluid which is rheological property. Due to the molecular weight and fiber length, the viscosity of a solution is affected directly; as molecular weight increases, viscosity increases. Thickening contribution of fibers depends on source ingredient of fiber. Plant derived fibers affect viscosity more than cereal based ones because of chemical properties.

1.1.2.3 Oil binding capacity

As water binding capacity fibers also have ability to bind oil because of its porosity structure rather than their affinity for oil. Since the main phenomenon is filling the porosities of fiber, if fiber contained product is interacted with water, water will place in porosities therefore the oil intake of fiber will decrease. This is important especially for bakery products. (Nelson, 2001)

1.1.2.4 Anticaking agent

Anticaking agent is a kind of additive to avoid cake formation by which product is improved for packaging and transport. Because of this property of fiber, flowability is improved in the product. (Cho, Dreher, 2001)

1.1.2.5 Antisticking agent

Adhereness of dough causes extrusion problems. Antisticking property of fiber decreases the stickiness of a product so that eliminate the problems during processing. (Cho, Dreher, 2001)

1.1.2.6 Mineral Binding

It can also be named as "cation-exchange capacity" because it is a capability of binding cations such as calcium, zinc due to the uronic acid group in the structure of fibers. Ph, ionic strength, type of fiber and cation nature influences this ability of fiber. For instance while pectin can bind to calcium ions, wheat bran has a low capacity to bind cations. (Nelson, 2001)

1.1.2.7 Solubility

Fibers differ from each other as insoluble and soluble. Solubility can not be defined as the solubility of a salt in water in fiber case. It actually means colloidal dispersion in a suspension. Branching, ioinizing groups, nonuniformity and interunit positional bonding determine the solubility property of a fiber. Briefly as branching increases solubility of a fiber increases as in the case of arabinogalactan. There is inverse relationship between ionizing group and solubility. Interchain bindings attenuate the solubility because of the positional bonding. Nonuniformity and solubility increases as direct proportion. (Nelson, 2001)

1.1.3 Factors Influencing Properties of Fiber

The properties of fiber have impact on functions of fiber this is why factors affecting properties are important when dealing with fibers. Properties of fibers depend on type of source and processing mainly.

Different structural arrangement has impact on properties of fibers. For instance because of presence of carboxyl group, pectin has a property of gelation. Similarly while pectin can bind calcium due to its uronic acids part, wheat bran has low ability to bind minerals. These examples demonstrate dependence of type of source on fiber properties.

To produce and isolate fiber from different sources, various methods are used which have impact on final product. These processes include milling, bleaching, grinding, enzyme treatments, stabilization, and extrusion, drying and roasting. During milling process if the separation of bran and endosperm is not done properly, starch may mix to bran part which increases water binding capacity and viscosity due to gelation property of starch. Bleaching is conducted to remove off-colors by oxidizing; grinding affects the solubility of fiber because of lowering the particular size while increasing the contact area with water. Stabilization is for reducing rancidity by heat treatment which may cause alteration in the properties of fiber. Because of the shear forces in the extrusion process, polymer chain of fiber may be cleaved. Drying and roasting both contain heat treatment which may cause changes on the fiber property. (Nelson, 2001)

1.1.4 Importance of Fibers, Health Benefits

The origin of the evolvement of human diet is still an argumentative topic. Early humans' diet was rich in plant based foods so that fiber although evidence of butchery depends on 2.6 million years ago. However after the animal husbandry, fiber dependent habituation changed and plant based food consumption level decreased. The descent of fiber consumption had continued until Dennis Burkitt and Hugh Trowell declared the benefits of fiber on human health, especially diabetes, cardiovascular diseases and cancer. (Kendall, Esfahani, 2010)

1.1.4.1 Coronary Heart Disease (CHD)

Throughout the world death because of cardiovascular is the most common situation that is 17.1 million occurs in a year according to World Health Organization (WHO) research. Causes of these diseases include tobacco use, stress, and inappropriate diet mainly. Therefore there is large number of studies on prevention of CHD by changing diet. One of the common concepts is link between fiber and CHD.

Fat consumption is related with CHD because of saturated fats and cholesterol mainly. Since fiber makes a person feel full, it helps to reduce fat intake. Beside that it damages the fat digestion so that excess amount of fat is removed from the body. In a study of Ellegard and Bosaeus it is proved that adding fiber to diet increases the excretion fat in 50% amount. (Kamp, Jones, 2004)

According to the survey conducted on 1999, women consuming fiber rich food have a 34% lower risk of CHD than those consumes in a low amount. In the other research it is proved that if 3g of fiber is consumed daily, it will decrease the risk of CHD mortality 27% (Kamp, Jones, 2004) Due to the facts mentioned above there is a positively relation between reduction of risk of CHD and fiber consumption.

1.1.4.2 Colon Cancer

According to WHO, colon cancer is the third most common (639000 death in 2004) cancer type after lung, and stomach in the USA. The risk factors of colon cancer are predominantly age, heredity, alcohol and tobacco use, and diet.

In order to understand the relation between colorectal cancer and fiber intake, several studies conducted especially animal studies which are rather low in cost. According to Kim and Mason (Nutrition chemoprevention of gastrointestinal cancers: a critical review), the mechanism of fiber on the reduction of colon cancer is summarized as that it reduces the transit time and prevents constipation. It decreases the ph of fecal and eliminates carcinogens by binding to them. After fermentation to short chain fatty acid, the ph of colonic system decreases also and inhibits the growth of carcinogens. (Cho, Dreher, 2001)

Wholegrain foods as a fiber source are significant target food for reduction of risk of colon cancer.

1.1.4.3 Diabetes

Diabetes is a chronic disease related to insulin functioning in the body. A patient can not produce enough insulin (Type 1) or can not use insulin efficiently (Type 2) so that blood sugar level is not hold under control. These conditions have consequences on glucose metabolism in the liver and muscles. (Cho, Dreher, 2001)

Fiber rich diet was recommended for diabetes in 1971 by American Diabetes Association (ADA). Before that wrong and inadequate information led to consumption of high level of fat in order not to eat carbohydrates. However according to the research high carbohydrate level food facilitate the toleration of insulin. Therefore in 1971 ADA declared and in 1979 reaffirmed that diabetes should consume same portion of carbohydrate like other people. (Cho, Dreher, 2001) After that industry tried to find a way to supply carbohydrates in a healthy way.

The glycemic index is a tool for determining of which food is appropriate for diabetes. Glycemic index (GI) is a property of a food which establishes the affect of carbohydrates on blood sugar level. Low GI demonstrates that carbohydrates are digested slowly so blood sugar level increases gradually. Therefore diabetic people should consume low GI foods in order to meet their carbohydrate need. Fibers are listed as lox GI food in Food and Drug Administration. Beside that at the article of Marangoni and Poli (2007) , fiber is added to bread and biscuit and GI values are compared with control group. According to article result the GI values reduce significantly when fiber is added.

1.1.5 Application of Fiber in Food Industry

There are several applications and studies on fortification of food products by fiber since it has various positive physiological affects on human health. However from technological point of view, ease of processing, bioavailability of functional food with fiber should be considered carefully in the dependence of properties of fibers such as solubility, viscosity etc. Since health benefits have been declared, food uses have been increasing in the industry recently. Fiber is placed already in bakery products, ready to eat meals, dairy products, beverage industry, and meat product.

1.1.5.1 Bakery Products

Fortification of bakery products is the most common application of fiber enrichment. Breads, cookies, cakes, muffins can be listed as food products that uses the affects of fiber on rheological properties. Firstly some of the fiber ingredients may increase the water holding capacity and it affects the consistency of dough. More water may be needed and it should be determined from the loaf volume, baking conditions, finished moisture by experiments. Secondly since hydrating of wheat gluten is retarded by fibers mixing time will be longer. Insufficient gluten hydration may cause crumbs on the final product. These crumbs can be prevented by strong gluten flours or adding methylcellulose as a gluten enhancing agent. The grittiness of the final product may be a problem with high fiber content and the prevention of this problem may be the reduction of fiber size. (Nelson, 2001)

1.1.5.2 Ready to eat meals

Ready to eat (RTE) meals such as cereals are fortified especially by oat and psyllium fiber. Texture of cereals may be affected negatively and surface cracking may occur on the other hand by fiber addition the shelf life of cereals becomes longer. (Marley, 2001)

1.1.5.3 Dairy products

Fiber use is not so common in dairy products but the applications are increasing day by day in dairy industry. It is preferred especially for reducing the fat and calorie content.

In cheese production fiber addition facilitate the precipitation of whey properties so that enhancing the body texture. (Nelson, 2001) Generally soluble fibers are used; however, for anticaking agent cellulose may be preferred as an insoluble fiber. In traditional cheese production it is difficult to use fibers because of high solid content and protein content dependence but it is rather easy to produce cheese spreads (Marley,2001) Because of the gelation and water binding capacity, viscosity of cheese alters and spreading becomes easier by fat replacement.

Fat reduction in milk and yoghurt is easier by water soluble fibers such as locust bean gum to increase creaminess and prevent syneresis. Insoluble fibers are rare in ice cream production but oats have been preferred in very small particle size in order to prevent gritty mouthfeel. (Nelson, 2001)

1.1.5.4 Beverage

As functional food popularity increases throughout the world, the usage of fiber in beverage production becomes common. Water soluble fibers are generally used as a thickening agent that increases the viscosity which means longer time in the mouth, more chance to have flavor of a beverage. Although water soluble are more common, insoluble fibers are also used in beverage industry with a shorter particle length. Other than influence on texture and flavor, water soluble fibers stabilize the system by reduction of droplet sizes.

Both water soluble fibers and insoluble fibers can be used in beverage industry nowadays but the important thing is choosing appropriate fiber for desired final product. For example if beverage requirement is high viscosity with low fiber content, gum arabic should not be used since it does not increase viscosity as much as guar gum.(Nelson,2001)

1.1.5.5 Meat Products

Fibers are preferred in meat products for different attitudes. The properties benefit from fibers in meat products are water binding capacity and texturization predominantly. Water binding capacity facilitates to maintain lubricity of a meat and leakage of water from dry product which is called purge. Beside that the shape of the product is maintained by this property and makes easy to slice the product. Texturization is a result of gel formation of water soluble fibers and helps holding of ingredients together. Choosing the suitable fiber is important for instance wheat bran is found be inappropriate for beef sloppy-joe formulas. (Nelson,2001)

1.2 Wheat and Wheat Bran

Wheat is an important agricultural commodity which is consumed in large amount all around the world among all grains. Wheat is processed for manufacturing flour and the flour is used for making bread, pasta, biscuit products as an ingredient.

Wheat kernel structure mainly consists 3 parts; endosperm, bran and germ. The inner part is the germ which is the embryo section of the kernel. It contains protein, B-vitamins and trace minerals. The section between bran and germ is called endosperm which is the 83% of weight of kernel. It contains starch abundantly and small amount of dietary fiber. The outer part is bran like all grain structure and it is the source of dietary fiber. (http://www.wheatflourbook.org/Main.aspx?p=23 the North American Export Grain Association (NAEGA) Wheat kernel's hull does not contain fiber as much as the other parts so independently to the type of wheat as soft, hard, red, white etc, wheat bran and germs are used for obtaining fiber.

To manufacture the wheat flour wheat milling process is conducted in which the starchy endosperm is separated from the bran and germ. ( C. Brett, Wheat:science and trade, 1987,VCH publisher) In wheat milling process, after the type of wheat selected and blended, the wheat is cleaned from foreign materials by sieves and air blasts. After cleaning wheat is conditioned by water addition for reaching optimum milling properties in which the bran part toughens while endosperm part softens. In milling process there are series of disintegrations followed by sieving. The flakes of bran are removed by the sieves( Desrosier, 1977)

Bran amount depends on further applications such as heating, grinding. Following applications are air classification and turbomilling in which wheat germ can be clarified and 10-12% total dietary fiber can be obtained.

Different kinds of wheat may influence the color, flavor of the final product. For instance, since hard red wheat bran has darker color than hard white wheat bran, it is preferred in bakery products, while white one is used in ready to eat products.

1.2.1 Antioxidants of Wheat and Wheat Bran

Antioxidant is a structure which inhibits the free radical formation as a result of oxidation reaction. In a food product it plays important role to extend the shelf life and improve the

1.3 Cracker

Crackers are thin and crispy bakery products generally made of unsweetened and unleavened dough. Cracker like food was firstly baked by Theodore Pearson of Newburyport in 1792 with flour and water solely. Although it was firstly named as Pearson's pilot bread, because of its shelf life it was used by sailors especially and called as "sea biscuit". Cracker name was developed in 1801 when Josiah Bent burnt all biscuits and heard a voice of crispiness.

Crackers contain rather fatter than other bakery products such as biscuits but less sugar. There are predominantly two types of crackers saltines and snacks which are differ from each other by leavening agent, yeast and chemicals respectively.

1.3.1 Cracker Ingredients and Their Affects on Rheology of Dough

Rheological properties of dough are an essential concept that should be understood well in bakery products. The reason is the final texture and quality of product depends on mainly rheology. Therefore fundamental mechanical properties should be explained clearly of dough. (F. Hamed, F. Jon "Dough Rheology and Baked Product Texture" 1989)

Cracker dough is subjected to rheological changes during processing. Rheological properties of cracker affect not only textural characteristics of final product, but also easiness during processing. Rheological properties of cracker especially are influenced because of ingredients therefore effects of them are discussed on the following topics.

1.3.1.1 Flour

Flour and its components are crucial for bakery products. It is selected due to its protein and moisture content basically because rheology of the dough is mostly affected by flour in bakery products. Hard flour is preferable for cracker. According to the study in 1977 a small reduction of moisture content of flour causes increase in firmness of dough. (Faridi, 1990). In addition to that because the water content of flour affects the amount of water as an ingredient, it should be noted during cracker production.

The protein content of flour, namely gluten is an important aspect for dough rheology although leavening and gluten development is not as major as other bakery products, cakes. It is suggested in 1991 that gluten has an impact on dough Rheology the reason may be interaction with starch. According to another research of Petrofsky and Hoseney in 1995, gluten starch interaction has a relationship with optimum water content and so that rheological properties.

Other than gluten and moisture content of flour, starch damage amount and ash content of flour are also responsible for rheological properties. Starch damage may occur during milling process and it causes the increment of absorption of water because of high water holding capacity of damaged starch. Since cracker should be in a low moisture amount, low starch damaged flour should be preferred.

The fiber is not commonly found at wheat endosperm. White flour contains mostly the endosperm part while whole wheat flours consists the outer layer. The bran amount of white flour 2.78% is comparable lower than whole wheat flour 12.57% (M.samuel "Bakery technology and Engineering 1992,USA)Amount of bran determines the amount of ash content in flour. It not only affects the color of the flour but also physically damage the gluten therefore has an impact on rheological properties. (Faridi, 1990)

1.3.1.2 Shortening

Fat is responsible for softening and water amount determination in the batch formula. The softening affect of fat alters the consistency of dough. Dough consistency can be defined as proper softness, stickiness, elasticity and extensibility of dough. Temperature, water amount has an influence on consistency. The more amount of water cause softer dough consistency. (Manley, 2001) Water amount is affected by fat because lubricating function in the dough is affirmed when the amount of fat is high. In addition to that the mixing order is critical. The addition of fat before water may cause prevention of gluten formation since flour surfaces will be layered by fat. (Faridi, 1990)

The texture of the dough depends on fat properties like fat crystals. Fat crystals vary due to production background of shortening namely heating process.

1.3.1.3 Water

Dough formation starts with the mixing of flour and water mainly. The ratio of water-flour depends on mainly flour properties. For instance as the moisture content of flour is lower, water absorption will be higher and vice a versa. Together with water content, bran content also influences the water amount as wholemeal flours can absorb more water than white flours.( Cauvain S. , Young L. "Baking Problems Solved" 2001, CRC press) Addition of water affects the rheological properties indirectly. The main function is to being catalyst in dough formation since high amount of it is removed during baking. (Manley, 2001)The consistency and water has an inverse relationship as increasing water, consistency will decrease. The amount of water should be enough for hydrating the flour otherwise gluten can not be fully developed. (Mirsaeedghazi, Emam-Djomeh, 2008)

Water functions also as a solvent for chemical agents in the formula. When chemicals are dissolved, they become available for reactions with other ingredients and increase the ph of dough especially with ammonium bicarbonate. High ph values causes weakening of gluten so that decrement in the consistency. (Manley, 2001)

1.3.1.4 Leavening Agents

In bakery products several reactions occurred during processing develops carbon dioxide in the dough which is the main leavening force. In cracker technology rather than yeast fermentation, chemical leaveners, such as sodium bicarbonate and ammonium bicarbonate, are preferred.

Being cheap, safe, relatively tasteless and odorless increases the usage of sodium bicarbonate to an extent amount. Beside that the pH of the sodium bicarbonate solution is comparatively lower which can be served as an advantage because of probability of undesirable colored brown spots formation at high pH regions. ((M.samuel "Bakery technology and Engineering 1992,USA) In addition to that during the processing over 120ÌŠC, sodium bicarbonate does not require leavening acid in order to form carbon dioxide and the following decomposition reaction is occurred due to high temperature; (W.P Edwards, The science of bakery products,2007,The royal society of chemistry)

2NaHCO3 + heat  Na2CO3 + CO2 + H2O

Among all of these advantageous, difficult to control its leavening action based on its rapid rate of solution and although it is a dry product, the deterioration occurs easily.

Ammonium bicarbonate is generally preferred in low moisture products such as cracker, biscuits as a supplementary leavening agent. Like sodium bicarbonate, the advantage of using ammonium bicarbonate is no need for leavening agents. Decomposition starts at 40ÌŠC as in the following; (W.P Edwards, The science of bakery products,2007,The royal society of chemistry)

NH4CO3  NH3 + CO2 + H2O

The carbon dioxide yielding is relatively high as can be seen in the reaction above, so that ammonium bicarbonate may cause large voids in the product when added as a dry ingredient. The problem can be resolved by adding ammonium bicarbonate to the ingredients after solving it in warm water in that case the uniformity is obtained. ((W.P Edwards, The science of bakery products, 2007, the royal society of chemistry)

It should be given attentions to moisture content and porous content of final product while using ammonium bicarbonate. If the moisture content is higher 5%, ammonia will be dissolved in water and if porous structure is not formed sufficiently, ammonia can not leave the product in which both results as an undesirable ammonia taste. ((M.samuel "Bakery technology and Engineering 1992,USA)

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