Carbohydrate Presentation Part 2 PDF

Carbohydrates: Part 2 Under certain circumstances reducing sugars can produce brown colours that in some cases are desirable, and undesirable in others Examples : Desirable: Undesirable:  Carbohydrates: Part 2 Under certain circumstances reducing sugars...

Carbohydrates: Part 2 Under certain circumstances reducing sugars can produce brown colours that in some cases are desirable, and undesirable in others Examples : Desirable: Undesirable:  Carbohydrates: Part 2 Under certain circumstances reducing sugars can produce brown colours that in some cases are desirable, and undesirable in others Examples : Desirable: Browning of baked goods in the oven Undesirable:  Carbohydrates: Part 2 Under certain circumstances reducing sugars can produce brown colours that in some cases are desirable, and undesirable in others Examples : Desirable: Browning of baked goods in the oven Undesirable: Browning of stored sugar, overcooking browning This browning reaction is due to the reaction of glucose with the amino groups on protein molecules. This is called a Maillard Reaction. The Maillard reaction is a non-enzymatic browning process. It is termed non- enzymatic in order to distinguish it from browning reactions that are catalyzed through enzymatic activity. (ie: browning of cut apples) The Maillard reaction alters proteins, especially those with the amino acid Lysine. Lysine is an essential amino acid and its loss through this process is of concern to those concerned with ensuring nutritional content of food products. For example, bread can lose up to 40% of its Lysine through this reaction. Total Maillard effects are a function of : 1. Time 2. Temperature: Increase temperature and you speed up the reaction. 3. pH : increase pH and you increase the rate of Maillard Reaction decrease pH and you slow the rate of the Maillard Reaction Fructose also undergoes this reaction with protein but at a much slower rate than glucose. The browning colour change and the generation of flavouring compounds makes the Maillard Reaction an important consideration in the production of pasteurized milk, toffee, caramel and fudge. Caramelization : Caramelization takes place when a carbohydrate, especially sucrose, is heated in the absence of nitrogen. A non-enzymatic polymerization occurs that generates the characteristic brown colour and flavours associated with caramelization. This brown colour is formed through the linking of unsaturated carbohydrate rings. (no C=0 bonds).  Polysaccharides Polysaccharides are polymers of monosaccharides. They are compounds made up of sugars units linked in linear or branched arrangements. Polysaccharides are composed of more than 20 sugar units, most have from 200- 3000 but larger ones such as cellulose have 7000-15,000 sugar units. Starch amylopectin contains more than 60,000 sugar units. It is estimated that 90% of the carbohydrate mass in nature occurs as a polysaccharide. Polysaccharides are sometimes referred to as “glycans” If the sugar units in a glycan are the same, then it is referred to as a homoglycan. Example: cellulose and starch amylose the sugar units are linear in arrangement.. Glucose Glucose Glucose Glucose Glucose In starch amylopectin the sugar units are the same but the structure has branches: Glucose Glucose Glucose Glucose Glucose Glucose Glucose Glucose Glucose Polysaccharides made up of two or more different monosaccharides are called : heteroglycans. These often have a common spine with the branches made of a different monosaccharide. sugar 2 sugar 2 sugar 2 sugar 2 sugar 1 sugar 1 sugar 1 sugar 1 sugar 1 sugar 1 sugar 2 sugar 2 sugar 2 sugar 2 sugar 2 Examples of heteroglycans are Guar Gum, Algins, Locust Bean Gum Polysaccharide Solubility Due to the presence of the hydroxyl units and the C=O units, polysaccharides are charged molecules. As a result they have a strong affinity for water and hydrogen bonds are easily established. Polysaccharides hydrate readily when water is available. If water is available, polysaccharides will take up the water, swell and may undergo partial or total hydrolysis. What is interesting in this process of hydration is that the water attracted to the polysaccharide will not freeze. Why could this characteristic of a polysaccharide be beneficial ? Polysaccharide Solubility Due to the presence of the hydroxyl units and the C=O units, polysaccharides are charged molecules. As a result they have a strong affinity for water and hydrogen bonds are easily established. Polysaccharides hydrate readily when water is available. If water is available, polysaccharides will take up the water, swell and may undergo partial or total hydrolysis. What is interesting in this process of hydration is that the water attracted to the polysaccharide will not freeze. Why could this characteristic of a polysaccharide be beneficial ? This property prevents the phase separation of solutes dissolved in water in frozen foods. This makes the use of polysaccharides very important in protecting quality attributes of frozen foods. (Stored at -18°C) Cellulose has a very linear arrangement of its component glucose units. It is the Hydrogen Bonding that occurs between the homoglycan linear chains that gives cotton and wood fibre its strength, insolubility and resistance to breakdown. Enzymes are unable, or have a very difficult time attacking the cellulose fibre structures due to the variable orientation of the cellulose chains.  Large Molecule Electrostatic Attractions Hydrogen Bonding Occurs at these Beta Glucose points Cellulose has a very linear arrangement of its component glucose units. It is the Hydrogen Bonding that occurs between the homoglycan linear chains that gives cotton and wood fibre its strength, insolubility and resistance to breakdown. Enzymes are unable, or have a very difficult time attacking the cellulose fibre structures due to the variable orientation of the cellulose chains. However, such linear chain arrangements are rare, usually polysaccharides exist in helical shapes and readily hydrate and dissolve in water. Branched heteroglycans cannot form regular links (Hydrogen Bonds) between chains, therefore they too are generally very soluble in water. Generally speaking, the better the chains of a polysaccharide fit together, the less soluble they are. Water soluble polysaccharides used in the food industry are known as “gums”. Polysaccharide Viscosity and Stability Polysaccharides are used as thickeners or gelling agents in food formulation. They modify the flow properties and textures of the products they are put in to. They are normally used at concentrations of 0.25-0.5 % (w/w or w/v) in order to accomplish their gelling effects. The viscosity of a polymer solution is a function of the size and shape of its component molecules. In a food matrix where water is present the linear polysaccharide molecules move around and “sweep” a large space. This creates conditions where collisions will occur, this creates friction which consumes molecular energy (usually with heat loss occurring). This loss of energy reduces molecular motion and increases the viscosity of the food matrix. Using this model, linear polysaccharides produce solutions of higher viscosity than non-linear polysaccharides of similar molecular weight. Therefore viscosity depends on the : 1. Size of the polysaccharide molecule. 2. The shape of polysaccharide molecule. 3. The structural “rigidity” of the polysaccharide molecule. Gels A gel is a three dimensional network of connected molecules that entraps a large volume of continuous fluid. (like a sponge) In many food products the gel is a network of polysaccharide or protein. Gels have some characteristics of both solids and liquids: Solid Characteristic: Gels have some characteristics of both solids and liquids: Solid Characteristic: Shape retention due to the network bonding that occurs. Liquid Characteristic: Gels have some characteristics of both solids and liquids: Solid Characteristic: Shape retention due to the network bonding that occurs. Liquid Characteristic: the liquid portion softens the solid, thus providing product elasticity. Gels usually contain 1% (w/w or w/v) polymer and 99% (w/w or w/v) water. Examples of gels: dessert gels, jellies, jams Polysaccharide Hydrolysis Polysaccharides can be broken down during heating at lower pH levels ( pH 4.0 or less). Polysaccharides are also susceptible to microbial attack and enzyme degradation. Some of the negative effects of this hydrolysis and attack are : 1. Phase separation 3. Off Odours 2. Off flavours 4. Potential food poisoning due to bacterial growth and/or toxin formation. A processor must remember that gums and gelling agents are rarely supplied in a sterile state, so processing conditions must be such that food safety is preserved. This often involves good communication with suppliers to deal with potential quality and food safety concerns AND a knowledgeable processor staff to know what to look for !.  Starch Starch is a major plant food reserve compound. It is estimated that it provides 70-80% of the global human caloric intake. Its use exceeds that of all the other polysaccharides. Starch Structure In nature, starch is unique as it appears as distinct particles called granules. Starch granules are insoluble and hydrate only when heated. As a result they are easy to transfer and mix. Starch granules are composed of a mix of two polymers, these being: 1. Amylose: a linear polysaccharide. 2. Amylopectin: a highly branched polysaccharide Rice granules are the smallest of the starch granules found in nature, tuber starch granules are the largest. Starch Granule Gelatinization As mentioned undamaged starch granules are insoluble in cold water. When heated starch granules undergo a process of gelatinization. Typical Starch Hydration Viscosity/Temperature Curve Starch Granule Gelatinization As mentioned undamaged starch granules are insoluble in cold water. When heated starch granules undergo a process of gelatinization. Gelatinization is the disruption of the molecular order within the starch granules. Due to water absorption swelling of the starch granules begins. Total gelatinization occurs over a temperature range that is unique to each type of starch granule species (i.e.: potato, rice, corn etc.) The initial temperature of gelatinization depends upon : 1. Starch/Water Ratio 2. Granule Type/Species 3. Degree of Heterogeneity among the granule population As water is absorbed into the starch granule, the granule begins to swell. You will also see the migration of some of the amylose molecules away from the starch granule into the surrounding solution. This may cause a problem for the processor as phase separations and sugar phases may appear in the finished product. Hence starch selection and temperature of processing is very important. As the starch granules swell they have difficulty in moving past each other. Hence the viscosity of the food matrix increases and the food takes on a pudding like texture.. Excessive heating will cause the fracture of the starch granules, leading to a reduction in viscosity and if taken to the extreme complete hydrolysis of the starch into simple sugars may take place. Hydrated starch granules are very fragile and fracture easily if subjected to a shear force. Hence mixing of heated starch solutions is a very delicate operation. The fracture of starch granules can therefore lead to: 1. Reduced Viscosity 2. Water loss and Phase Separation 3. Loss of Product Structure. Microscopic View of Starch Granule Hydration (400X)  As the starch granules swell they have difficulty in moving past each other. Hence the viscosity of the food matrix increases and the food takes on a pudding like texture.. Excessive heating will cause the fracture of the starch granules, leading to a reduction in viscosity and if taken to the extreme complete hydrolysis of the starch into simple sugars may take place. Hydrated starch granules are very fragile and fracture easily if subjected to a shear force. Hence mixing of heated starch solutions is a very delicate operation. The fracture of starch granules can therefore lead to: 1. Reduced Viscosity 2. Water loss and Phase Separation 3. Loss of Product Structure. Retrogradation and Staling As hot starch cools the starch becomes less soluble. In some dilute solutions the starch may actually precipitate out. This process of cooling and solubility reduction is called retrogradation. This can lead to many product quality defects. Some potential problems are: 1. Bread staling: see an increase in crumb firmness as starch elasticity is lost. Many polar lipids are added to the dough mixture to retard this process (ex: sodium sterol(2)lactate, glycerol monopalmitate) 2. Precipitation formation in soups and sauces Starch molecules are broken down (depolymerised) in the presence of hot acids (HCl). This process, or the use of enzymes will breakdown starch into glucose and maltose. Enzymatic attack is the primary way in which glucose syrup is manufactured. Glucose syrup is often referred to as Corn Syrup, to reflect the starch source. As an alternative to glucose, the glucose isomerase enzyme is used to convert the glucose to fructose. In this way fructose can easily be made in order to use it as a glucose substitute. Uses of Unmodified Starch Unmodified starches are used to Uses of Unmodified Starch Unmodified starches are used to : 1. Provide Texture 2. Starches can provide body and bulk (ex: baked goods) where gelatinization is important to produce desired product properties. Some of these properties include: a) Low amounts of gelatinization result in slower digestion of the product by humans. b) In low moisture dough you end up with firm and flakey crust, high moisture dough's create more elastic products. Most commercially used starches are “modified food starches”. Modification generates a starch with greater consistency in handling and performance along with a truer flavour profile than do natural starches. Processors prefer to use starches with better, more consistent behavioural properties than natural starches. Processors must be able to produce a consistent product despite the seasonal and regional differences in their starch supply. Modifications are made to improve the characteristics of the pastes and gels the starches are used to make. Some of these desirable characteristics are : Processors prefer to use starches with better, more consistent behavioural properties than natural starches. Processors must be able to produce a consistent product despite the seasonal and regional differences in their starch supply. Modifications are made to improve the characteristics of the pastes and gels the starches are used to make. Some of these desirable characteristics are : 1. Heat tolerance 2. Shear resistance 3. Introduction of specific functionalities Processors prefer to use starches with better, more consistent behavioural properties than natural starches. Processors must be able to produce a consistent product despite the seasonal and regional differences in their starch supply. Modifications are made to improve the characteristics of the pastes and gels the starches are used to make. Some of these desirable characteristics are : 1. Heat tolerance 2. Shear resistance 3. Introduction of specific functionalities Modifications can be made through chemical transformations. Most of the chemical starch modification procedures target the hydroxyl group of the starch molecule components. In the U.S.A. starch can be modified by only 4, closely regulated processes. The chemical changes are used to: a) Increase cross linkages between starch molecules: this will increase gelatinization temperatures, increase shear resistance and increase the viscosity of the matrix the starch is used in. (example: canning industry starches for stews) b) Increase starch molecule stabilization: this lowers the gelatinization temperature and increases the freeze thaw stability of a product when compared to the use of a non-modified starch Modified food starches are specifically made for specific applications/products. Properties that can be controlled are : a) Adhesion g) Flavour Release b) Clarity of solution or paste h) Hydration Rate c) Colour i) Moisture holding capacity d) Emulsion stability j) Heat and cold stability e) Film forming ability k) Shear stability f) Viscosity l) Resistance to Acids Cold Water Starches These are often referred to as instant starches. Basically they are pre-cooked gelatinized starches that have been carefully cooled. Many starch granules are broken so the release of the amylose and amylopectin will be fast and not dependent upon heating to be able to interact with water. As a result they are soluble in cold water therefore they can be used in products that do not need cooking. Their properties include: viscosity increase in the product matrix and have a high shear tolerance that facilitates mixing. They are widely used in dry mixes (ex: pudding) Cellulose: Cellulose is made up of flat linear arrangements of polymerized glucose. These strands of glucose are linked together through Hydrogen bonding. Due to the large amount of Hydrogen bonding that occurs between strands cellulose is essentially insoluble in water. As it cannot be digested by humans dieticians value cellulose as a source of crude fibre. Purified cellulose is added to food to provide bulk (ex. Bread). Chemical purity is not a priority as it is a natural component of fruits and vegetables. Cellulose addition has minimal flavour, colour and microbial contamination of the foods it is added to.. Guar and Locust Bean Gum Both Guar and Locust Bean gums are used as thickening agents. Guar gum generates the greatest viscosity of any natural commercial gum. Guaran, the major polysaccharide of Guar Gum is found in the endosperm of seeds. The polysaccharides found in Locust Bean Gum have fewer branched units and work well in combination with other gums. (Guar gum does not). As a result Locust Bean Gum is widely used in the dairy and frozen food and dessert industries. Guar gum is widely used in the production of ice cream. Xanthan Gum Xanthan Gum is produced by the bacterium Xanthomonas campestris. It is commonly found on plant leaves and produces through fermentation a polysaccharide called Xanthan, commonly called Xanthan Gum. Xanthan has a similar polysaccharide chain structure as cellulose and serves to increase the viscosity of the products it is added to. Of interest is the fact that it has a synergistic effect when working with Guar Gum. Xanthan Gum is useful as it is soluble in both hot and cold water and does not undergo any viscosity change between 0 – 100 °C. Why is this beneficial ? Xanthan Gum Xanthan Gum is produced by the bacterium Xanthomonas campestris. It is commonly found on plant leaves and produces through fermentation a polysaccharide called Xanthan, commonly called Xanthan Gum. Xanthan has a similar polysaccharide chain structure as cellulose and serves to increase the viscosity of the products it is added to. Of interest is the fact that it has a synergistic effect when working with Guar Gum. Xanthan Gum is useful as it is soluble in both hot and cold water and does not undergo any viscosity change between 0 – 100 °C. Why is this beneficial ? This makes Xanthan Gum an ideal thickener for pourable products that are hot or refridgerated ! Xanthan Gum Xanthan Gum is produced by the bacterium Xanthomonas campestris. It is commonly found on plant leaves and produces through fermentation a polysaccharide called Xanthan, commonly called Xanthan Gum. Xanthan has a similar polysaccharide chain structure as cellulose and serves to increase the viscosity of the products it is added to. Of interest is the fact that it has a synergistic effect when working with Guar Gum. Xanthan Gum is useful as it is soluble in both hot and cold water and does not undergo any viscosity change between 0 – 100 °C. Why is this beneficial ? This makes Xanthan Gum an ideal thickener for pourable products ! Carrageenan Carrageenan is a glycan extracted from red seaweeds. It serves to increase the viscosity of a food matrix but suffers from the fact that it will dissolve in hot acids. This is a concern for the food processor. Carrageenan is used to form gels in milk and water. It binds well with proteins and holds them in suspension. This is of particular interest to the chocolate milk industry as carrageenan holds cocoa particles in suspension. Carrageenan is also used to assist brine absorption in cold ham and poultry roll production. Sometimes the brine absorption can be increased between 20-80 %. Carrageenan can sometimes be rather chewy, thus its inclusion into a product needs to be evaluated carefully. Agar: Like carrageenan this has a seaweed origin and is used as a moisture holder in canned meat products and bakery mixes. Pectin: Pectin is present in the cell wall , and between the cell walls of plants. Commercially it is obtained from citrus fruit peel and apple pomice. It is acid resistant and is therefore very useful in the formation of spreadable gels. Carrageenan is also used to assist brine absorption in cold ham and poultry roll production. Sometimes the brine absorption can be increased between 20-80 %. Carrageenan can sometimes be rather chewy, thus its inclusion into a product needs to be evaluated carefully. Agar: Like carrageenan this has a seaweed origin and is used as a moisture holder in canned meat products and bakery mixes. Pectin: Pectin is present in the cell wall , and between the cell walls of plants. Commercially it is obtained from citrus fruit peel and apple pomice. It is acid resistant and is therefore very useful in the formation of spreadable gels.  Dietary Fibre and Carbohydrate Digestibility Carbohydrates are used to provide energy and bulk in the food we eat. The cellulose in the plant cell wall is indigestible to humans and is a major source of dietary fibre. Gums also serve in this capacity. Some of the carbohydrates and polysaccharides humans consume are broken-down into component parts in the large intestine. Here simple sugars may be absorbed, thus all of the carbohydrates in a food product may have a caloric value. It is estimated that up to 7% of human caloric intake occurs in this way. Dietary fibre is considered to be important as it ensures the proper functioning of the intestinal tract. It serves to increase fecal bulk, and serves to increase intestinal throughput and regularity. It is estimated that humans require 25-50 g of dietary fibre per day. Dietary fibre is alleged to reduce cholesterol levels and thus reduce the risk of heart disease. It is also argued that due to its intestinal scraping action colon cancer risk is reduced.