Experimental Food Science Exam #2

Structure of polysaccharides

"Dextrins" Technically, oligosaccharides ARE polysaccharides, but generally the term polysaccharides indicates much larger molecules. Some of the most important polysaccharides in food are composed only of glucose units linked together by alpha or beta-glucosidic linkages. The simplest of these substances are dextrins. These molecules range widely in size but are distinctly shorter in chain length than starch, the related substance. Dextrin molecules are composed entirely of glucose, and these units are linked together by 1,4 alpha glucosidic linkages, as shown previously for maltose. Unlike mono- and disaccharides, which are characterized as sweet in taste and quite soluble, dextrins exhibit rather different properties. -Dextrins have slight solubility, a barely sweet taste, and limited thickening ability. They are formed when flour is being browned using dry heat. Dextrans are another type of polysaccharide and are found in bacteria and yeasts. Again, composed of glucose but with a 1,6 alpha glucosidic linkage. Branching occurs in dextrans, with the point of branching being unique to a particular species or strain. A portion of a dextran molecule follows. Note that dextrins and dextrans differ in their linkages, having 1,4 alpha and 1,6 alpha glucosidic linkages, respectively.

Structure and functional properties of amylose and amylopectin.

Amylose:

Oligosaccharides

Carbohydrate formed by the union of three to ten monosaccharides joined by the elimination of water.

Simple sugars

Monosaccharides and disaccharides (these are what simple sugars are referred to). Notice: Chemists categorize carbohydrates according to the number of basic units linked together: monosaccharide, disaccharide, oligosaccharide, and polysaccharide.

Polysaccharide

Polysaccharides are grouped together as complex carbohydrates. Carbohydrate formed by the union of many saccharide units, with the elimination of a molecule of water at each point of linkage.

Structure of hexose

Saccharide with six carbon atoms, the most common size unit. ALSO: Glucose (also called dextrose because of its ability to bend polarized light to the right), fructose (sometimes referred to as levulose or left-binding), and galactose are especially important to hexoses. (A dextrose = a synonym for glucose; so named because polarized light bends to the right in a glucose solution.) Others found in foods include mannose, gulose, and sorbose. Hexoses with only 1 carbon atom external to a 6-membered ring are classified as aldoses (glucose, galactose, mannose, and gulose are examples of aldoses). When a hexose has two carbon atoms external to a 5-membered ring, the sugar is a ketose (fructose and sorbose are ketoses).

What are reducing sugars?

Sugar having a free carbonyl that can combine with an amine, leading to non-enzymatic browning via the Maillard reaction.

Glucose and galactose are...........

aldoses and have the 6th carbon external to the ring.

Information that is not on my card that I need to remember.

composed entirely of glucose units linked together and of a shorter chain than starch. 1,4--glucosidic linkage like maltose, just more glucose units slight solubility, barely sweet taste, limited thickening ability (flour browned under dry heat) Dextrans are complex polysaccharides found in bacteria and yeast. 1,6--glucosidic linkage Branching at certain points (species/strain specific) (should know this...it isn't on the study guide but she will probably ask questions on it) Chemical properties of sugar:Hydrolysis - occurs during the normal preparation of candies, its extent is influenced by the rate of cooking and the ingredient used. - disaccharides undergo hydrolysis when heated - acidic medium and presence of water favor the condition - inversion, forming invert sugar (a mixture of equal parts of fructose and glucose from hydrolysis) from sucrose. Degradation by Heating - opening the ring structure as the prelude to the breakdown of sugars, result in organic acids and aldehydes. - occurs in both acidic and alkaline medium Caramelization - involves heating sugars to intense temperatures (338ºF, 170 ºC for sucrose) to melt which ultimately leads to a charred or burned product - can be halted by boiling water addition to cool extremely hot sugar mixture rapidly; cool water addition is not recommended due to safety measures (extreme splattering and potential skin burning) Maillard reaction: colored pigments (melanoidins) formed through enolization (reversible reaction between an alkene and a ketone, p. 146) and dehydration Syneresis -loss of liquid from a gel, either due to aging of the gel or cutting. -water separates from a starch gel when the surface is cut and the trapped liquid is released from the area that have been exposed by the cut. Retrogradation -Gradual increase of crystalline aggregates in starch gels during storage, result of amylose molecules rearranging in an orderly fashion; detected on the tongue as a somewhat gritty texture. -Undesirable and reduces the quality of the food in which it occurs. -Heating eliminates the crystalline aggregates of amylose in the food because the heat energy is sufficient to break the hydrogen bonds holding the amylose molecules together and allow them to move in the gel again. (ex: stale bread tightly covered & reheated). *(amylopectin also participates in retrogradation, albeit at a slower rate than does amylose- outer branches of amylopectin molecules are also capable of forming some H bonds with other molecules in a starch gel) endosperm= largest apart of a cereal grain and the area where the starch is deposited.

Oligosaccharides are

formed during the transition of complex carbohydrates trisaccharides in legumes (stachyose, raffinose), NOT digestible in humans, NOT cariogenic

Fructose and ketose are..........

the 1st and 6th carbon atoms external to the ring.

Characteristics of crystalline/amorphous candies

*Food Applications* Crystalline candies (fudge, penuche, fondant): candies that are easy to bite and have large organized crystalline areas and some liquid. Made by boiling sugar and water to concentrate the sugar syrup sufficiently to form a firm, crystalline structure when cooled. Other ingredients can be found in candy recipes (corn syrup, cream of tartar, flavoring). Most crystalline candies have sugar concentration of 80% or higher (achieved when the boiling temp. is 112C). INVERSION by boiling and the addition of acid produces equal amounts of glucose and fructose (invert sugar) is significant in influencing textural characteristics of the finished product (ex: softer, smoother texture). Corn syrup and fat can interfere with aggregation of sugar crystals and promote smooth texture (ex: cream and chocolate for fudge making). Butter added at then end of the boiling to 1) promote fine texture by interfering with crystallization 2) enhance flavor.

Types of sweeteners and alternative sweeteners

-Sucrose: the most common sugar available in crystalline form, granulated sugar is the type used for most applications. -Confectioners sugar: pulverized sucrose blended with cornstarch (3%) to prevent caking of the sugar. -Brown sugars: more acidic and higher in moisture than granulated sugar, the impurities in brown sugar contribute to flavors. -Corn syrup: Sweet syrup of glucose and short polymers produced by hydrolysis of cornstarch. represents a mixture of carbohydrate (glucose to oligosaccharide); high-fructose corn syrup is made by using enzymes to convert some of the glucose in corn syrup into fructose. -High-fructose corn syrup: has a high dextrose equivalent of 65 D.E. (DE measure of the amount of free dextrose (glucose) ) which indicates greater sweetness, fermentability, browning reaction potential, and hygroscopicity than those of regular corn syrup. -Molasses: brown syrup remaining after sugarcane juice has been boiled and some of its sugar removed during the refining of sugar. -Honey: is high in fructose which promotes rapid browning in baked products. -Polyhydric alcohols: -Saccharin -Aspartame -Acesulfame-K -Sucralose

Carbohydrates

1. Simple sugars (mono and disaccharide) sweet taste, ease of solubility, ability to contribute to mouthful in candies and syrups, browning at very high temperatures, contribution to volume in baked products. 2. Oligosaccharide (3~10 carbohydrates) 3. Polysaccharide (complex carbohydrate) thickening ability, texture modifying, thickening agents, etc.

Physical properties of sugar

1. Sweetness: when dissolved all sugars are sweet to the tongue, but some are sweeter than others. The relative ability to sweeten a food product is of interest because sugars contribute 4 kilocalories per gram. Theoretically, a sugar that is very sweet can be used in smaller quantities than a sugar that is less sweet, resulting in a reduction in calories without sacrificing sweetness. The temperature of the solution containing the sugar influences the relative sweetness values for sugars. Ex: fructose is about 1.4 times sweeter than sucrose at 5 degrees C (41 degrees F), comparable in sweetness when the solution is at 40 degrees C (104 degrees F) , but only 0.8 times as sweet at 60 degrees C (140 degrees F). However, maltose sweetness ratings are essentially independent of temperature. Clearly, most of the non-sugar sweeteners provide far more sweetening than a comparable weight of any of the sugars can contribute. 2. Hygroscopicity: Definition: ability to attract and hold water, which is a characteristic of sugars to varying degrees. -Hygroscopicity can be useful in maintaining the freshness of some baked products, but it can be a source of potential problems in texture when the relative humidity is high. An elevation in temperature also increases the absorption of moisture from the atmosphere. 3. Solubility: the amount of sugar that will go into solution in water varies with the type of sugar and also with the temperature of the water. As the temperature of water rises, the amount of sugar able to dissolve in a given amount of water also increases. Solubility is important because of its relationship to food texture. Candies containing fructose are softer than those containing other sugars because of the greater solubility of fructose. The very low solubility of lactose (the sugar in milk) is a particular textural problem in the manufacture of ice cream. The low temp required in ice cream storage promotes the formation of lactose crystals (detected by the tongue as a somewhat gritty texture), due to the low solubility of this particular sugar. 4. Chemical reactions a. Hydrolysis: Disaccharides undergo hydrolysis when heated. An acidic medium favors the degradative reaction, as does the presence of water. However, even if seemingly dry sugars are heated alone, the uptake of a molecule of water and the resultant splitting into the 2 component monosaccharides occur. The reaction for the hydrolysis of sucrose, the disaccharide particularly susceptible to hydrolysis. Hydrolysis occurs during the normal preparation of candies. Its extent is influenced by the rate of cooking and the ingredients used. b. Degradation: Definition: Opening of the ring structure as the prelude to the breakdown of sugars.... The first step in the actual heat degradation of sugars in cookery us the opening of the ring structure to form an aldehyde or ketone, depending on whether the original sugar was a pyranose or furanose ring. In the presence of acid, dehydration of the molecule occurs as 3 molecules of water are eliminated. Organic acids and aldehydes are the result. These reactions can occur in an acidic medium, but they take place even more readily in an alkaline medium. c. Caramelization: When sugars are heated to such intense temperatures that they melt (170 degrees C or 338 degrees F for sucrose), a series of chemical reactions begins, which can lead to a charred or burned product. However, some caramelization of sugar creates a pleasing color and flavor changes. The overall process of caramelization involves multiple steps. Beginning with inversion of sucrose (conversion to invert sugar). After the ring structures in the components of the invert sugar are broken, some condensation of the compounds occurs, which creates some polymers ranging in size from trisaccharides to oligosaccharides (as many as 10 subunits polymerized). Sever chemical changes at the very high temps involved also lead to dehydration reactions and the formation of organic acids and some cyclic compounds, as well as many other substances. Caramelizing can be halted abruptly by adding boiling water to cool the extremely hot sugar mixture rapidly. Surprisingly, boiling water is much cooler than the caramelizing sugar. Of course, the addition of cool water will halt the caramelization process. However, this practice is not recommended because of the extreme splattering and potential for burning one's skin that result when the 2 liquids come into contact and equalize their extreme differences in energy. Evidence of the creation of acids during caramelization can be seen by stirring some baking soda into the caramelizing sugar, as is done in preparing peanut brittle. The carbon dioxide that forms when the soda neutralizes the acids creates a porous product as the gas expands in the hot, viscous candy solution.

The Maillard reaction (definition and overall reaction, no chemical reaction details)

Definition: Non-enzymatic browning that occurs when a sugar protein and a sugar are heated or stored together for sometime. Overall reaction: the maillard reaction is a series of reactions involving the condensation of a reducing sugar and an amine. Glucose, fructose, and galactose are reducing monosaccharides; lactose and maltose are reducing disaccharides. Lactose undergoes non-enzymatic browning most readily of the reducing sugars, followed in descending order by ribose, fructose, and glucose. These reducing sugars can combine with amines in milk and other protein-containing foods to cause non-enzymatic browning. Sucrose, however, is not a reducing sugar and does not participate in the Maillard reaction. It must undergo inversion to glucose and fructose before it can enter into this type of non-enzymatic browning. The color changes during the steps of the maillard reaction occur rather slowly and with less energy input than is required for caramelization. The progression is from an essentially colorless substance to a golden color, on to a somewhat reddish brown and then a dark brown. This range of colors can be followed as caramels are boiled to their final temp or during the baking of a plain or white cake as the crust color develops. Similarly, the reactions can be traced by watching the the color development in sweetened condensed milk when it is heated in a water bath. A pH of 6 or higher accelerates the Maillard reaction. The Maillard reaction proceeds rather quickly at elevated temperatures, but it also can occur at room temperature during extended periods of storage. In fact, one of the early problems in developing packaged cake mixes was prevention of the Maillard reaction, which sometimes occurred during prolonged marketing operations. (non-enzymatic browning= browning resulting from chemical changes that may be facilitated by heat)

Polysaccharides

Dextrins- composed entirely of glucose units linked together and of a shorter chain than starch, 1,4-glucosidic linkage like maltose, just more glucose units, slight solubility, barely sweet taste, limited thickening ability (flour browned under dry heat).

Structure of disaccharides

Disaccharides are structurally related to monosaccharides. Disaccharides form when 2 monosaccharides join together by a glycolytic linkage, eliminating a molecule of water. The 3 disaccharides common in foods (sucrose, maltose, and lactose) all contain glucose. Sucrose is formed from glucose and fructose.

What is Inversion?

Inversion= formation of invert sugar by either boiling a sugar solution (especially with acid added) or adding an enzyme (invertase) to the cool candy.

Functional properties of sugars

The sweet taste of sugar is utilized in many food products ranging from minute to the major ingredient, as in candies. When sugar-containing products are heated to very high temperatures, as occurs in candy making, the degradation products that begin to form contribute additional flavor components. Sugars contribute color to products that are heated either to a high temp or for an extended period of time. Part of the color noted on the surface of cakes is due to some chemical breakdown of the sugar, and part is the result of the Maillard reaction (non-enzymatic browning) that also is responsible for much of the color that develops while caramels are boiling. Caramelization is the key process responsible for coloring brittles and toffee, which are heated to a much higher temp than are caramels. Depending on their concentration in a product, sugars can have considerable impact on the texture of various food products. Sugar syrups become increasingly viscous as the sugar content is increased by boiling water away. Cakes become increasingly tender as sugar content is increased until a critical maximum is reached. Volume also is increased with some increase in sugar if the sugar level does not become so high that the structure ruptures, and the cake falls. The effects of sugar content on the mouthfeel of candy are discussed in the next section. Sugar stabilizes egg white meringues and also causes the foam to have smaller cells and a finer texture as a result of the need for increased beating. In starch-thickened puddings, sugar serves as a tenderizing ingredient. Custards and other protein-containing products with increased sugar levels need to be heated to somewhat higher temps to coagulate the protein than is necessary when less sugar is used. Food applications: Crystalline candies (candies with organized crystalline areas and some liquid... aka mother liquor). These candies are easy to bite and have large areas of organized sugar crystals. Crystalline candies are made by boiling sugar to concentrate the sugar syrup sufficiently to form a firm crystalline structure when cooled. To sum it up: 1. contributes to sweet taste in food products. 2. flavor development after intensive heating. 3. contribute color to products heated at high temps or for an extended period of time. 4. caramelization is the key process responsible for coloring brittle and toffee. 5. impact on texture (ex: increase tenderness, viscosity) and volume of food products 6. effects of sugar content on the mouthfeel 7. serve as stabilizing and tenderizing agent.