Sweeteners - Composition, Types, and Functions

Transcription

1 Any reproduction of this material without the express written consent of the American Institute of Baking is prohibited. Sweeteners - Composition, Types, and Functions Definitions In traditional terminology, the word sugar has meant table sugar, or sucrose. A wide variety of chemical compounds have been found to be sweet tasting, and therefore fall into the category of sweetener. The current U.S. definition of sugar, for food labeling purposes, includes all monosaccharides and disaccharides. As such, sugars are nutritive carbohydrate sweeteners and are used by the baking industry to add sweetness, flavor, fermentable solids, and contribute other physical and chemical properties to the finished product. The basic building blocks of all sugars are monosaccharides (one molecule sugars), such as those listed in Table 1. Sucrose, lactose, and maltose are disaccharides (two molecule sugars), which are formed by combining two monosaccharides (bottom of Table 1). Glucose or dextrose, fructose, sucrose, and maltose are the sugars of most interest to bakers. The structure of common sugars are shown in Figures 1 and 2. Sucrose Sucrose is by far the best known of the sugars. Sucrose is not directly fermentable by baker s yeast. It has to be first hydrolyzed by dilute acids or by the enzyme invertase, which will break it down to an equal mixture of fructose and glucose. This mixture is called invert sugar. Although the U.S. government standard for commercial granulated sugar is 99.% pure, commercial sugar containing 99.8% sucrose is common. This sugar is graded by crystal color, hardness, particle Table 1 Sugar Composition -Carbon or Hexose Monosaccharides Glucose (also called Dextrose) Fructose (also called Levulose) Galactose Disaccharides Composed of Source Sucrose Glucose + Fructose Cane or Beet Maltose Glucose + Glucose Cereal Starches Lactose Glucose + Galactose Milk size, and sharpness. Sucrose that is free from invert sugar is hard. Sucrose is obtained from sugarcane, sugar beets, certain sorghum plants, and from the sap of the American maple tree. If present at equal levels, there is no difference in sweetening power of sucrose isolated from different sources. The characteristic aroma and flavor imparted by some sugars is caused by small amounts of certain esters contaminating the sugar. There are marked differences between the chemical and physical characteristics of these sugars when they are in the raw or partly refined state. These variations result from the percentages of invert sugars, mineral matter, and nitrogenous organic matter that are contaminants. Methods of production, extraction, and purification have become more sophisticated over the hundreds of years that sucrose has been produced, although the process still resembles what was originated in the Middle East and India. Clean sugar cane or sugar beets are cut into pieces and mixed with hot water to remove the sugar. This juice is then con- N\archive\communic\cheri\jobfiles\BST-residentcourse-Science\section7\science-sec7.pm Page 1

2 Figure 1 Chemical Structure of Common Monosaccharides Glucose Fructose Galactose Glucose Fructose Galactose Page 2

3 Figure 2 Chemical Structure of Common Disaccharides 1 Sucrose Glucose Unit Fructose Unit Maltose Glucose Unit Glucose Unit 3 2 Lactose Galactose Unit Glucose Unit Page 3

4 Table 2 Typical Bakers Special Sucrose Specifications % Moisture Supplier # Supplier # Supplier # % Sucrose % Invert % Ash Screen Analysis % Over US Less than 2 % Over US % Thru US 140 & Thru US Maxiumum 20 Less than Table 3 Typical Powdered Sugar Specifications % Moisture X X 0. 12X 0. % Sucrose % Starch Screen Analysis % Over US 70 < 0. <0. <0.01 % Over US 100 % Thru US <0.1 > & Thru US Table 4 Typical Molasses Composition Imported First Third Final % Solids % Sucrose % Invert % Total Sugars % Ash ph Color From AIB Technical Bulletin June 199, Joseph Hickenbottom. densed, filtered, refined, and allowed to crystallize several times until it is sufficiently purified. Dry sucrose products are classified according to granulation. The coarsest available sugars are the sanding or coarse granulated, with the regular or medium granulation being typical table sugar. Bakers special is very uniform in crystal size, smaller than typical table sugar (Table 2). Powdered sugars are pulverized crystalline sucrose, ranging in categories from 2X to 12X (Table 3). The higher the number assigned, the smaller the particle size (more grinding applied). Because of the Page 4

5 large surface area created by grinding powdered sugars, they are very hygroscopic. Therefore, dried starch or tricalcium phosphate is often added as a flow agent, to prevent water pickup and caking of the sugar. Fondant sugar is the smallest particle size of sucrose available to the baker. Paste fondant is prepared by heating a concentrated sucrose solution to boiling, then cooling gradually with controlled mixing such that the sucrose crystallizes as very fine particles suspended in a saturated sucrose solution. Dry fondant is manufactured by blending a finely ground sucrose with invert sugar or maltodextrin. Molasses is the concentrated juice (liquor) extracted from sugar cane, containing naturally occurring substances in addition to sucrose. Sugar beet molasses has a very astringent off-flavor and aroma, and is not generally used in food applications. Because of the many variables involved in producing molasses, it can fluctuate widely in flavor and composition. Sun-ripened sugar cane grown in the Caribbean area is pressed and clarified (but not otherwise processed) into what is called imported molasses. It is subjected to controlled curing and maturing; resulting in a premium grade molasses in terms of its light color, mellow flavor, mild aroma, high sweetness, and clarity. Imported unsulphured molasses is also called cane juice molasses. U.S. sugar cane is processed into several grades of Table Typical Brown Sugar Specifications Light % Moisture % Sucrose % Invert % Total sugars 91-9 Dark Table Typical Invert Sugar Composition Medium Total % Moisture % Sucrose 30-3 <3 % Invert % Ash ph mill molasses, varying in the number of crystallizations through which the liquor has gone (Table 4). The lower the molasses grade (higher number), the smaller the amount of total sugars remaining. Therefore, the highest grade (first molasses) has the most total sugars present, is lightest in color, and has the least flavor. Molasses is often used more as a flavoring and coloring agent (and humectant) than as a sweetening agent. Brown sugars contain a small percentage of invert sugar and moisture in addition to sucrose. Historically they were sugars that had received less refinement. Today brown sugars are made by addition of molasses to refined sugar. This allows a better control of composition and particularly color (Table ). Brown sugar is used both as a sweetener and as a flavoring agent. The darker the brown sugar the stronger the flavor it carries. The storage conditions for brown sugar must be controlled to avoid formation of hard lumps in the product. Optimum conditions are - 70% relative humidity. If brown sugar is exposed to low relative humidity the surface molasses tends to dehydrate, crystallize, and eventually form hard lumps. Bagged brown sugar also should not be stored in large stacks, to prevent compression of the bottom layers, another cause of lumps. Mixed Sugars Invert sugar is made by treating sucrose with acid and/or enzymes to hydrolyze (split) the sucrose into fructose and glucose. Many types of invert syrup are available, with medium and total inverts being the most common (Table ). Invert syrups are used for their humectancy, although they are generally being replaced by high fructose corn syrups. Honey, often called nature s invert syrup, is by far the oldest sweetener used by man. However, the glucose:fructose ratio is not 1:1 and even varies between sources (Table 7). As the fructose content increases, crystallinity problems decrease. In addition, honey contains proteins, enzymes, organic acids, mineral substances, pollen, oils and other substances. It may additionally include sucrose, maltose, and several oligosaccharides. Nectar from flowers of many types is condensed and modified in the bee s gastrointestinal tract and stored in their hives, from which it is collected. Honey is sold by grade, based on the floral source of nectar, which impacts the flavor and color. Honey is used in specialty products where specific flavor and aroma characteristics are Page

6 Table 7 Typical Honey Composition % Moisture 18.3 % Fructose * 41 % Glucose * 34 % Sucrose 2.42 * Fructose:Glucose ratio varies Table 8 Dextrose Equivalents Properties Solid Syrup High viscosity Low viscosity Not sweet Sweet Nonfermentable Fermentable Low osmotic pressure Highly osmotic Functional Uses Bodying agent Browning agent Cohesive agent Flavor enhancer Foam stabilizer Freezing point depression Prevent ice crystal growth Flavor transfer medium Prevent sugar crystallization Hygroscopic desired. For that reason, bakers honey is usually stronger flavored and darker than table honey. Malt extracts or malt syrups are viscous concentrates of the water extract of malted cereals, generally barley. The predominant sugar is maltose, although some glucose and larger oligosaccharides will be present. Malt syrups are either diastatic (enzyme active) or nondiastatic (enzyme inactive). The primary enzymes of interest in malt syrups are the amylases, particularly α-amylase, although many other enzymes such as protease are also present. Nondiastatic malt has been heated to inactivate the enzymes, and is used for flavor. Diastatic malt adds flavor and supplements any α-amylase deficiency in the flour. Corn Syrups (Glucose Syrups) Corn syrups are derived from cornstarch, a readily available source of glucose polymers (long strings of glucose or dextrose sugars). Glucose syrups can be produced from any starch source. The discovery that starch could be converted into a sweet liquid by heating in dilute acid was made in a Russian laboratory in the early 1800 s. The first US plant for manufacturing cornstarch was opened in 18, producing up to 42 DE corn syrup, although modern enzymatic hydrolysis methods have made 9 DE corn syrups possible. Various amylase enzymes can convert gelatinized starch into maltodextrins, maltose, and dextrose. Purified enzymes do not have side reactions and by choosing the correct enzyme or enzymes specific sugars can be produced. Dextrins (small fragments of starch) and maltose are produced using a mixture of primarily α- and β-amylase. A mixture of pullulanase (a debranching enzyme) and β-amylase will produce an almost pure maltose syrup. The enzyme amyloglucosidase (glucoamylase) will produce a syrup containing essentially all glucose (>9%). Dextrose Equivalent (DE), a measure of the percentage of glucosidic bonds in starch that have been hydrolyzed, refers to the level of reducing sugars present in the glucose or corn syrup. DE tells us how many of the bonds are broken but does not tell anything about which sugars are produced. Commercial corn or glucose syrups contain dextrose (or glucose), maltose, and varying quantities of Table 9 Typical Corn or Glucose Syrup Composition % Solids ph 3 DE %Glucose 1 % Maltose 12 % Trisaccharides 11 %Higher saccharides 2 42 DE 2 DE 9 DE Dry Basis Composition higher saccharides with varying degrees of polymerization. The higher the level of mono- and disaccharides the sweeter the syrup and the higher the DE (Table 8). Dextrose has a DE of 100 and starch has a DE of 0. Page

7 Table 10 Typical High Fructose (Corn) Syrup Specifications 42% % 90% % Solids Dry Basis Composition % Glucose % Fructose % Higher Saccharides 4 3 Table 11 Recommended Syrup Storage Temperatures Storage Temperature F C 42 DE DE DE % HFCS % HFCS % HFCS Medium Invert Combining enzyme technology with acid hydrolysis, manufacturers are able to produce a wide variety of DE corn syrups or glucose syrups (Table 9). The lower DE corn syrups (3-2 DE) are used primarily for added texture and body, such as in chewy cookies and creme fillings. Higher DE syrups (2-9 DE) are added for sweetness and fermentability. None of the common corn syrups are as sweet as sucrose. When 9 DE corn syrup is exposed to the enzyme glucose isomerase, under controlled conditions, some of the glucose is converted to fructose, resulting in a sweeter syrup (Table 10). Storage conditions of all corn or glucose syrups must be carefully regulated to minimize crystallization and browning (Table 11, Figures 3 and 4). As with honey, the higher the glucose content, the more readily crystallization will occur. Commercial dextrose was initially solidified high DE corn syrup, sold as corn sugar. Dextrose has the unique ability to produce a cooling sensation as it dissolves on the tongue, because of its negative heat of solution. Bakers dextrose is actually crystalline dextrose monohydrate (Table 12). Products vary only in particle size. Finer granulation is preferred for use in icings and creme fillings, the major applications for dextrose. Figure 3 Effect of Temperature on Color of 42% High Fructose Corn Syrup Color, CIRF x O F(43 O C) 100 O F (38 O C) 90 O F(32 O C) 80 O F (27 O C) Storage (Weeks) From: AIB Technical Bulletin, June Page 7

8 Figure 4 Effect of Temperature on Corn Syrup Viscosity Viscosity (Poises) E C B % Moisture A 8. % Glucose % Ash ppm Iron DE >99. O F O C A - 42% High Fructose Corn Syrup B - % High Fructose Corn Syrup C - 2 % DE Corn Syrup E - 42 % DE Corn Syrup From: AIB Technical Bulletin, June Table 12 Typical Dextrose Composition Lactose The only readily available sugar not from plant material is lactose, which is from milk. Dried whey, which is more than 70% lactose, is the source of most purified lactose. Milk, milk powder, and whey are the common forms of lactose used in bakeries. Lactose is a reducing sugar with very little sweetness, and is not fermentable. Thus, it is used as a browning agent when additional sweetness is not desirable. Sweetness A comparison of the sweetness level of many common sweeteners is given in Table 13. Sucrose is always given a rating of 100. However, sweetness is a perception, and varies between people and between matrices (food system - what else is with the sweetener). The values given are therefore relative and not set in concrete. Table 13 Sweetness Ratings Sweetener Sucrose Dextrose (glucose) Fructose Maltose Lactose Galactose Invert sugar (medium) Invert sugar (total) Molasses 42 DE corn syrup 2 DE corn syrup 9 DE corn syrup 42% HFCS % HFCS 90% HFCS (1) Based on sucrose as 100 (2) Syrup sweetness on a dry solids basis Rating (1)(2) Page 8

9 Alternative Sweeteners Consumers are often looking for food products with decreased levels of fat, sugar, and calories, and bakery products are no exception. Legal status changes regularly, and varies between countries. Therefore, always check before including any of these sweeteners in your baked product. Several options exist to replace the sugar in food products, including high-intensity or non-nutritive sweeteners (top of Table 14). All sugar substitutes that are rated sweeter than sucrose will be used in much lower quantity than sucrose, so that even if the caloric value is not 0, the total caloric contribution will be less than if sucrose were used. Bulking agents are often used to replace some of the nonsweetening functions of sugar. Another option for bakers is to use bulking sweeteners. Most of this category is made of sugar alcohols, also called polyols or polyalcohols (bottom of Table 14). Polyols are derived from sugars by hydrogenation of the sugar molecule, reducing the carbonyl group to an alcohol or hydroxyl group. Because they have some caloric value, bulking sweeteners are considered nutritive sweeteners. Sugar substitutes vary in heat stability, offflavors, and other characteristics, so careful research must be done before changing ingredients. Product High Intensity Saccharin Cyclamate Alitame Aspartame Sucralose Acesulfame K Thaumatin Bulking Xylitol Maltitol Sorbitol Mannitol Lactitol Hydrogenated starch hydrolysates Table 14 Alternative Sweeteners Sweetness (1) Calories (2) 30,000 3, ,000 1,000-22,000 0,000 20, , , (1) Sweetness compared to sucrose = 100 (2) Calories/gram (sucrose = 4) Page 9

10 Page 10