The suffix for nonreducing sugars is -ide. The relevance of sucrose to food technology, nutrition, and world trade is monumental. It occurs in mushrooms and insects and is metabolized by humans. The nonreducing and moderate sweetness properties of trehalose make possible some innovative food applications. The structures and names for an extensive list of known disaccharides are given in Unit 9 of the Appendix.
BLBSc01 10 October 17, Structure and Optical Activity Enantiomers were previously defined as nonsuperimposable stereoisomeric molecules that are mirror images. The two molecules can be visualized as mirror images by placing them head-tohead or, alternatively, placing one below the other. They have the property of being able to rotate plane-polarized light in equal amounts but in opposite directions.
Optical activity is the ability to rotate plane-polarized light. The specific rotations of several Dand L-sugars are shown in Table 1. Note that some D-sugars e. Thus, being a D- or L-sugar does not predict whether a sugar is dextrorotary or levorotary.
The designation D and L should not be confused with d and l, which denotes having optical activity that is dextrorotary or levorotary. The trivial names dextrose and levulose for glucose and fructose, respectively, have their origin from D-glucose being dextrorotary and D-fructose being levorotary.
The appendix contains instructions for demonstrating the existence of polarized light and the ability for sugar solutions to rotate it using plastic polarizing material, a light source such as a flashlight, and sugar solutions. Anecdotal information D- and L-glucose have identical physical and chemical properties i. L-Sugars are not used by humans, however, and are noncaloric. In , Bioospherics Inc. Their petition to the FDA for its use, however, was denied. Specific rotation is a physical property of sugars that is useful in identifying sugars and measuring their concentration.
Measurements are taken with a polarimeter that has a source of plane-polarized light, and a prism that enables measurement of the degree that a sugar solution in a cell through which the light is being transmitted will be rotated. The equation for calculating specific rotation is shown below. Not only do different sugars e.
Observing whether a crystalline sugar will mutarotate is another method for determining whether it is reducing or nonreducing. The Appendix includes a laboratory exercise on polarimetry of sugars. Whether a sugar is D or L will not predict whether it is dextrorotary or levorotary. Being d or l is a fairly reliable predictor of sugar conformation, however. D-Pyranose sugars that favor the C-1 conformation are dextrorotary, whereas those favoring the 1-C conformation are levorotary.
Conventionally, the structures are drawn with C-1 oriented to the right of the ring oxygen for glucose and C-2 to the right of the ring oxygen of fructose. The molecules, of course, will not always be oriented in this direction, and drawing them with a different spatial orientation, as per the structures of glucose in trehalose Figure 1. Drawing L-sugars can be particularly troublesome. One approach is to make the molecular model and then draw the conformational structure. Shallenberger and others developed a systematic procedure for determining the conformation, chiral family, and anomeric form for sugar pyranoid ring structures.
The step-wise procedure requires that one locate the anomeric carbon atom and the reference carbon atom. One determines whether the structure is drawn with the ring oxygen above or below the plane of the ring and whether the structure is oriented clockwise or counterclockwise.
The Appendix contains an exercise for determining the above features for selected sugars. Structure and Nomenclature of Sugar Derivatives with Relevance to Food Chemistry Glycols Alditols Glycols alditols are sugar alcohols, the carbonyl group being reduced to an alcohol.
The rules for systematic nomenclature are to replace the -ose suffix with —itol; that is, the alditol derivative of D-glucose is D-glucitol. The trivial name for D-glucitol is sorbitol, which is widely distributed in nature. Commercially, sorbitol is manufactured by catalytic reduction of glucose Figure 1. The body will passively absorb sorbitol, and it is converted to glucose in the liver, thus it is glucogenic the body can convert it to glucose and caloric. Some diabetics can accommodate sorbitol because of its slow absorption rate; it is found as an ingredient in diabetic confections and jams.
Sorbitol that is not absorbed in the small intestine will go to the colon, where it can cause diarrhea because of its hygroscopic affinity for water quality. Sorbitol is used to retard sugar crystallization in confections, and to provide viscosity and body in some beverage formulations. Xylitol has some unique properties and is approved for use in some special dietary foods. Food applications are in chewing gums and some candies. It has a negative heat of solution, its endothermic enthalpy of dissolution being approximately ten times that of sucrose.
Thus, it will provide a cooling effect when dissolved in the mouth. Xylitol has symmetry and is not optically active. Therefore, it is neither D nor L with respect to its configuration. Additional alditols that are achiral without handedness and optically inactive are glycerol, erythritol, ribitol, allitol, and galactitol. Glyconic, Glycuronic, and Glycaric Acids Mild oxidation of an aldose sugar will produce a glyconic acid that can cyclize intramolecularly to form lactones. Aldonic acids are named by replacing the suffix -ose with -onic acid.
This slow release of acid finds application in certain leavening systems. Salts of gluconic acid are water-soluble; calcium gluconate provides a means of increasing water solubility to effectively deliver calcium in dietary calcium supplements. Ferrous gluconate is an approved color additive in the United States; its major application is for black olives. The gluconate function renders water solubility to the salt, which permits iron to be distributed throughout the fruit where it can complex with phenolics to produce a black color.
BLBSc01 16 October 17, Oxidation of the primary alcohol group of an aldose sugar to a carboxylic acid produces a glycuronic acid. Glycuronic acids are named by replacing the suffix -ose of an aldose sugar with -uronic acid. The structure of D-galacturonic acid, a major constituent of pectin, is shown below.
Galactaric acid also known as mucic acid serves as an example. Galactaric acid has symmetry and is not optically active. Additional aric acids will have this property, as discussed previously for alditol derivatives. Rhamnose has an important structural role in the polysaccharide pectin and is frequently found as a phenolic glycoside in plants. They are named as a substituted deoxy sugar, placing in alphabetical order the substituting group and the prefix deoxy e. Better use of the wastes from crab, lobster, and shrimp processing is a continuing research topic for seafood processors.
Chitin is also present in insect exoskeleton and in molds. Its detection has been proposed as an index for mold contamination in foods Cousin Glycosyl amines are sugar derivatives that have the anomeric hydroxyl group replaced with an amino function. Not only are amino sugars and glycosyl amine named differently, they are also very different with respect to chemical reactivity.
They are named by first listing the substituting group followed by the sugar with the suffix -ose replaced with -ide. They are named by designating the number of the substituted carbon, followed by -O- and the substituting group, and then the sugar. If the sugar is a reducing sugar, the -ose suffix is retained. Trimethylsilyl ethers are sugar derivatives that permit sugar analysis by gas-liquid chromatography see Chapter 6.
Note that the trimethylsilyl function on the anomeric carbon is a glycoside, and so named. Sugar hydroxyls can combine with organic and inorganic acids to form sugar esters. Sugar acetates and succinates occur in nature, and sugar phosphates are important metabolic intermediates. Sucrose polyester trade name OlestraTM is an approved food additive in which sucrose is fully esterified with fatty acids.
It is a lipophilic, nondigestible and nonabsorbable fat-like molecule. Hence, it is noncaloric and approved for limited use in foods as a fat substitute. BLBSc01 October 17, 20 Polarimetry, saccharimetry and the sugars. Perusal of this book should generate admiration for monumental work in sugar chemistry by the U. National Bureau of Standards. Chitin as a measure of mold contamination of agricultural commodities and foods.
J Food Protect The chemistry of tetrose sugars. The degradation of dXylose by the method of Wohl. The rotation of d-threose. J Am Chem Soc Configuration of the pyranoses in relation to their properties and nomenclature. Bur Stand J Res Alternative sweeteners, 2nd ed. Pigman W, Isbell HS. Mutarotation of sugars in solution. Advances in carbohydrate chemistry. Calculation and specification of the multiple chirality displayed by sugar pyranoid ring structures.
J Chem Educ 58 8: Handbook of chemistry and physics, 51st edition. The Chemical Rubber Co. This is not surprising considering the roles that dietary sugars may play in diabetes, obesity, lactose intolerance, dental caries, and athletic performance. Caretakers find they need to adjust their cooking and food purchase habits when family members are diagnosed with diabetes and lactose intolerance. Food technologists find they need to adjust product formulations to provide healthier products in light of new nutritional knowledge and to cater to consumer demands and niche markets.
There is no shortage of information and misinformation about dietary sugars from Food Carbohydrate Chemistry, First Edition. It is prudent that food professionals have a working general knowledge of sugar composition of foods and where to access accurate compositional data. Using high-performance liquid chromatography HPLC they measured the concentrations of the following individual sugars: The category of high-sugar foods includes sugar itself, candies, dried fruits, jams, and preserves.
The high sugar content of dried fruit, jams, and preserves is brought about by water removal and also by sugar addition in the case of jams and preserves. They are historical examples of food preservation by reducing the water activity so these products will not support microbial growth. Sugar-sweetened cereals that appeal to children are in the high category, which has concerned many parents and health professionals. Most breakfast cereals are in the medium category; however, people will always have the option of adding table sugar ad libitum.
Other foods in the medium category include most fruits, fruit juices, ice creams, and soft drinks. Vegetables, nuts, milk, many snack foods, wine, and beer have low sugar content. Arabs in the eighth century introduced it to the Mediterranean countries. It was among the early crops brought to the Caribbean Islands and the southern United States by the Spanish. A combination of climate, slave labor, and industrial technology set the stage for sugar to become a major trade commodity and common food staple.
In the refining process, shredded sugarcane is mixed with water and pressed Pancoast and Junk The pH of the cane juice is adjusted to 7 with lime to prevent sucrose hydrolysis. BLBSc02 26 October 8, The syrup is further concentrated and seeded with crystalline sucrose. Sugar crystals are separated from molasses by centrifugation. Raw sugar is further refined through a series of washing, concentration, salt removal, and filtration steps. The purified syrup is concentrated to supersaturation and repeatedly recrystallized under vacuum.
Sugar beets Beta vulgaris L. In beet sugar refining, the beets are sliced into thin strips and subjected to counter-current extraction with hot water. The pH of the raw juice is adjusted with lime, and the subsequent concentration, purification, and crystallization steps are similar to that for sugar cane. Types of Sugar Products Available Granulated sugar—Pure sugar is available in various crystal or granular sizes e. Brown sugar—Historically, brown sugar was less-refined sugar crystals that contained entrapped molasses. Today, most commercial brown sugar is produced by adding various amounts of molasses to white sugar to give varying shades of color from light yellow to dark brown.
They contain varyious amounts of amorphous sugar, ash, and water. Liquid sugar—Aqueous solutions of refined sucrose are available for some industrial applications. Invert sugar—Sucrose will readily undergo enzymic or acid hydrolysis to produce glucose and fructose. Honey Honey has been a popular sweetener since biblical times. The floral nectar source contributes heavily to its flavor. Dried free-flowing honey granules and products are available commercially that have been manufactured by spray drying and combinations of microwave vacuum and freeze-drying.
Starch-Derived Sweeteners Starch is the major energy reserve for many plants, and contemporary agriculture has succeeded in efficiently making cornstarch available as an inexpensive food item. The creativity of chemists and engineers has exploited this material to produce a wide variety of food ingredients with different chemical, physical, and functional properties. Corn Syrup Water-insoluble starch granules can be solubilized with mechanical stirring and heat.
Now in Food Carbohydrate Chemistry, author Wrolstad emphasizes the application of alike will benefit from this latest addition to the IFT Press book series. Division and Fruit & Vegetable Division of the Institute of Food Technologists. Editorial Reviews. From the Back Cover. Not since “Sugar Chemistry” by Shallenberger and Food Carbohydrate Chemistry (Institute of Food Technologists Series) - Kindle edition by Ronald E. Wrolstad. Download it once and read it on your.
Traditionally, the solubilized starch was treated with dilute hydrochloric acid under pressure to produce glucose, maltose, and other glucose oligosaccharides. Today, a milder treatment using amylase enzymes is used for hydrolysis. Dextrose equivalency DE is a measure of the percentage of reducing sugars in a starch product. Thus, glucose has a DE of and glucose syrups will have a minimum DE of High-Fructose Corn Syrup HFCS Conversion of glucose to fructose with the enzyme D-xylose isomerase was first developed in , with technological improvements in the s.
The sweetness properties of HFCS are substantially greater than the glucose syrups and very similar to other invert syrups. BLBSc02 28 October 8, Highly concentrated solutions of fructose can be made, which are crystallized with difficulty. Maltodextrins Maltodextrins are another product of corn syrup manufacture, being glucose oligosaccharides consisting of 3—20 glucose units.
Another way of stating their size is that they have a degree of polymerization DP of Conversely, they have a DE of 33 to 5. Thus, maltodextrins are a family of products having a wide range of functional properties and food applications. Their sweetness will vary inversely with their DP. Inulin Syrup Inulin is a polysaccharide found typically in the rhizomes and roots of plants, such as onions, Jerusalem artichokes, chicory, etc. It consists primarily of fructose, with inulin from some sources containing some glucose units.
Hydrolyzed inulin syrup from Jerusalem artichoke has a fructose: Sugar Composition of Fruits and Fruit Juices Different fruits vary considerably with respect to sugar content. Grapes are relatively high in total sugar content, making the fruit very susceptible to fermentation, which was discovered centuries ago. Cranberries and lemons are both low in sugar and high in acid. Sugar needs to be added to their juices to render them palatable. Refractometry is a convenient means of measuring sugar content of fruits and fruit juices. A solution of 10 g of sugar in 90 g of water will be a Sugar content of a given fruit commodity can vary considerably with variety, maturity, growing region, and farming practices, such as irrigation.
Fru, fructose; Glu, glucose; Suc, sucrose; Sorb, sorbitol; tr, trace. In , the weather was unseasonably cold, and the apples were slow to ripen. Joe Briggs repeatedly contacted Made In Nature, advising the company that the apples were ready for harvest. Briggs stated that depletion of starch by the starch iodine test was a more reliable indication of maturity, and the fruit was past the optimum harvest date. Eventually, the apples were allowed to rot. Litigation took place, and the defense of Made In Nature for nonpayment of the fruit was that the apples were below the single-strength standard of The different fruits exhibit distinctive patterns that are characteristic of the fruits.
Glucose and fructose are the major sugars in all these fruits, and many fruits blackberries, blueberries, cherries, oranges, raspberries have an invert pattern of nearly equal amounts of glucose and fructose. This is readily seen by the glucose: Apples and pears accumulate more fructose than glucose, and cranberry is unusual in that it accumulates more glucose than fructose. Sucrose tends to be present in small quantities or is nonexistent.
Sucrose values for fruit juices tend to be highly variable because of acid or enzymic hydrolysis that can occur during processing and storage. Some fruits, such as apples, pears, cherries, peaches, and plums, accumulate significant amounts of sorbitol. Sorbitol can serve as a marker compound for these juices, when they are undeclared and illegally used to extend more expensive nonsorbitolcontaining fruit juices Wrolstad et al. Trace amounts of sorbitol in juices from nonsorbitol-containing fruits, such as strawberries and raspberries, may indicate contamination from other fruit juices.
Another possibility, however, could be that the source was commercial juice-processing enzymes, which sometimes are in solutions that contain sorbitol as a protective osmotic agent Durst et al. Sorbitol is nonfermentative; hence, fruit wines from sorbitol-containing fruits, such as pears, will have BLBSc02 October 8, This may be useful to some diabetics, as sorbitol is more slowly absorbed.
The proportions and ratios of these sugars are less variable than the absolute content of individual sugars Wrolstad and Shallenberger Anecdote The Beech-Nut adulterated apple juice for babies scandal that surfaced in is a landmark case in food law Wrolstad ; Wrolstad and Durst In fact, the concentrate was formulated from invert beet sugar syrup, corn syrup, synthetic malic acid, caramel coloring, and imitation apple juice flavoring. Additional chemical evidence for the juice not being authentic was an invert sugar pattern and the absence of sorbitol. The sugar profile for authentic apple juice was firmly established in the literature at that time, and Beech-Nut should have been aware that the concentrate was not authentic.
Effect of fruit maturation on sugar and organic acid composition in two blueberries Vaccinium BLBSc02 32 October 8, Determination of authenticity and percent juice of cranberry products. Adulteration of fruit juice beverages. Inulin syrup from dried Jerusalem artichoke. Code of Federal Regulations. Percentage juice declaration for foods purporting to be beverages that contain fruit or vegetable juice. Accessed October 18, Nagy S, Wade RL, editors.
Methods to detect adulteration of fruit juice beverages, volume I. J Assoc Off Anal Chem Sugar and nonvolatile acid composition of blackberries. Cloning, expression, and characterization of sorbitol transporters from developing sour cherry fruit and leaf sink tissues. Lodge N, Perera CO. NZ Kiwifruit July Composition of apple juice. Handbook of sugars, 2nd ed. Compositional profiles of fruit juice concentrates and sweeteners.
Sugar patterns of exotic fruits on a German fruit market. United States standards for grades of extracted honey. USDA national nutrient database for standard reference, release Accessed September 10, Ethical issues concerning food adulteration. Establishing criteria for determining the authenticity of fruit juice concentrates.
Teranishi R, Barrera-Benitez H, editors. Quality of selected fruits and vegetables of North America. ACS Symposium Series American Chemical Society, pp. BLBSc02 October 8, Authentication of food and wine. Free sugars and sorbitol in fruits: Although there are a few exceptions, most of these reactions occur under the relatively mild conditions that prevail during processing and storage. This chapter will not address reactions of chemical synthesis and sugar structure proof. Stick is recommended for its excellent treatment of sugar synthesis and basic sugar reactions.
Mutarotation Mutarotation can be defined as the change in optical rotation that is observed when a reducing sugar is dissolved in water, due to the formation of different tautomeric forms. These forms have different chemical and physical properties e.
The amounts of the tautomers will be governed by conformational free energy. Complex mutarotation denotes that more than 3 tautomers are present in significant amounts, making calculation of quantities from optical rotation measurements difficult, if not impossible. This temperature effect can have some very important ramifications for foods that are consumed hot, ice-cold, or at room temperature.
Larger amounts of the openchain form exist at higher temperatures. Many sugar reactions, such as reaction of reducing sugars with amino compounds in the Maillard reaction Chapter 4 , will occur at a more rapid rate proportional to the amount of sugar in the open-chain from. In general, pentose sugars have higher 38 October 8, Shallenberger and Birch Ring opening can be catalyzed by both acid and base Figure 3. Under acidic conditions, a proton will attack the ring oxygen with subsequent ring opening. In alkaline conditions, the hydroxide ion will initiate ring opening through removal of the proton of the anomeric hydroxyl group.
The mechanism was substantiated by conducting experiments in H2 O Mutarotation will occur under neutral conditions because water can function as either an acid or a base. The Appendix includes a laboratory experiment that demonstrates mutarotation and the optical properties of sugar solutions using a polarimeter.
Wrolstad has authored over professional publications, including papers in refereed journals and 17 books or book chapters. In April , the Swedish National Food Authority reported the presence of elevated levels of acrylamide in certain types of food that had been processed at high temperatures Taeymans et al. Observing whether a crystalline sugar will mutarotate is another method for determining whether it is reducing or nonreducing. Developed in partnership with Wiley-Blackwell, IFT Press books serve as leading-edge handbooks for industrial application and reference and as essential texts for academic programs. Names and Structures of Oligosaccharides Index The following material is strongly influenced by the excellent chapter by Eskin , which is highly recommended. Shallenberger and others developed a systematic procedure for determining the conformation, chiral family, and anomeric form for sugar pyranoid ring structures.
Oxidation of Sugars Aldose sugars can be readily oxidized to aldonic acids e. There are a number of qualitative and quantitative tests used to detect and measure reducing sugars that are based on sugar oxidation. Not all ketoses will give a positive test, however. The described protocol is qualitative.
It can be modified to be quantitative and is frequently used in the wine industry to determine the amount of reducing sugars Zoecklein et al. There are other similar methods for determining reducing sugars that are based on sugar oxidation and metal ion reduction, for example, Somogyi-Nelson, Munson-Walker, etc. BLBSc03 40 October 8, Enzyme test kits are available that permit measurement of D-glucose content in the presence of other sugars in foods and biological systems see Chapter 6. Another food application is the use of a combination of glucose oxidase and catalase in glucose-containing foods for removal of either glucose or oxygen Parkin It is used to deplete egg white of glucose before spray drying to minimize the Maillard reaction see Chapter 4.
It is also effective for removal of oxygen in citrus fruit juices and within sealed package systems. Reversion sugars are oligosaccharides that are formed from acid-catalyzed condensation of glucose. The hydroxyl functions on carbons 2, 3, 4, and 6 will serve as a proton acceptor, but the anomeric hydroxyl is ineffective in this regard. Glycosans anhydro sugars , which are intramolecular glycosides and therefore nonreducing, can be formed from aldose sugars subjected to acid and heat.
When glucose and idose are subjected to identical reaction conditions, levoglucosan will be produced in only 0. In order for the reaction to occur, the sugar must be in the 1-C conformation, which is the preferred conformation for idose and almost nonexistent for glucose. The important role of conformation for this reaction is clearly demonstrated with molecular models.
It is classified as soluble fiber and is used to increase the nondietary fiber content of foods through partial replacement of sugar, starch, and fat in a wide range of food products. The polymer is manufactured by pyrolysis of glucose, sorbitol, and citric acid with the proportions of 89 parts glucose, 10 parts sorbitol, and 1 part citric acid.
The carbohydrase enzymes in the intestinal mucosa will not hydrolyze many of these linkages. Hence, much of the material is not digested, absorbed, or used. The formation of trimethylsilyl derivatives of sugars permits analysis of anomeric and ring forms of sugars by gas-liquid chromatography. In the derivation reaction shown in Reaction 3. Hydrolysis of the glycosidic linkage in reducing and nonreducing sugars is catalyzed by protonation of the exocyclic OR group. A carbonium ion is formed that abstracts a hydroxyl group from water to form free sugars Wong Hydrolysis rates of glycosidic linkages occur in the following decreasing order: Aldose sugars will undergo acid-catalyzed dehydration to form deoxy sugars and furfurals.
Initial proton attack at C-3 results in hydroxyl removal at C-3, and subsequent proton removal at C-2 gives the enol form; ketol-enol rearrangement produces 3-dexoyglucosone. Further dehydration occurs down the chain with subsequent ring closure to produce hydroxymethylfurfural from aldose sugars and furfural from pentoses.
Another laboratory application is for visualization of sugars in different chromatographic systems. For example, a thin-layer chromatogram of separated sugars can be sprayed with an acidic solution and heated to produce furfurals that are subsequently reacted with amines to give a colored complex Lewis and Smith Alkaline-Catalyzed Sugar Reactions Mutarotation can be alkaline catalyzed whereby hydroxide ion initiates proton removal from the anomeric hydroxyl, followed by ring opening Figure 3.
In the case of nonreducing sugars, there is no anomeric hydroxyl group. Therefore, under alkaline conditions, hydrolysis will not take place.
BLBSc03 44 October 8, Reducing sugars will undergo enolization to form different isomers Figure 3. The reaction is favored in alkali but can also occur under acidic conditions.
The enediol is readily oxidized by metal ions, and, in addition, acid hydrolysis of labile nonreducing sugars, such as sucrose, is prevented. The reaction is catalyzed by sodium aluminate. Lactulose is not hydrolyzed by lactase, not absorbed, and noncaloric. It is used as a laxative but is not approved for food use. BLBSc03 October 8, Summary Key reactions in carbohydrate chemistry are influenced by conditions of acidity and alkalinity.
Similarly, many carbohydrate reactions can be categorized as being reactions of reducing and nonreducing sugars. The properties of reducing and nonreducing sugars can be summarized as shown in Table 3. Transformation of compound 2 to compound 3 is conformational change C-1 to 1-C. Conversion of compound 3 to compound 4 is formation of the Table 3. Conversion of compound 5 to 6 is enolization, with subsequent isomerization to fructose compounds 10 and 11 and mannose compounds 8 and 9. Acid catalyzed enolization compound 7 leads to formation of hydroxymethylfurfural compound 12 and formation of polymers and saccharinic acids.
Vocabulary Mutarotation—The change in optical rotation that is observed when a reducing sugar is dissolved in water due to the formation of different tautomeric forms. Reversion sugars—Oligosaccharides formed from acid-catalyzed condensation of glucose Glycosans—Anhydro sugars, which are intramolecular glycosides and therefore nonreducing References BeMiller JN. Food analysis, 4th ed. Mechanism in carbohydrate chemistry. Lewis BA, Smith F.
CRC Press, pp — Mechanism and theory in food chemistry. Wine analysis and production. Neither is a single chemical reaction; rather, they consist of a series of complex reactions that follow different routes under changing conditions. A French chemist, Louis Maillard, was the first to describe the formation of brown pigments from heating a solution containing glucose and lysine Maillard Inspection of the annual indexes for the Journal of Agricultural and Food Chemistry and the Journal of Food Science will predictably have numerous articles on nonenzymatic browning from the time the journals were first published.
Science Citation Index lists articles on the topic of Maillard browning in the time period from to the present SCI Nonenzymatic browning reactions are responsible for the desirable colors of many baked goods and beverages. In beer production, for example, it is critical that the color intensity be controlled so that consumer expectations for the appearance of lager, ale, and stout are met Shellhammer and Bamforth The formation of brown pigments during processing and storage are often a quality defect that needs to be minimized.
Flavors are also generated through nonenzymatic browning that may be desirable, for example, the flavors of roasted coffee and the South American dessert dulce de leche. The reaction has nutritional significance in that it can reduce protein quality from the degradation of lysine and other essential amino acids. Formation of mutagens and harmful compounds, such as acrylamide, are reasons for continued active research on the topic. Food technologists will monitor reaction products during processing and storage and establish purchase and quality specifications on the basis of the extent of their formation.
This chapter will not be a comprehensive review of the topic. For such information, the following references are suggested: Waller and Feather ; Ames ; Martins et al. Recent reviews and symposia reflect the shift in research interest to antioxidant properties Manzocco et al. An effort will be made to present the key reactions and mechanisms involved in nonenzymatic browning, in order to have an understanding that will permit one to minimize undesirable effects and optimize and control desirable characteristics of the Maillard reaction.
BLBSc04 October 14, 4: It presents generalized structures of the types of compounds that appear as reducing sugars, and amino acids react sequentially to produce melanoidin pigments and flavor volatiles.
Two routes are presented, one representing acidic reaction conditions and the other, a more alkaline environment. Sugar-Amino Condensation The initial reaction in Maillard browning is the condensation of a sugar and an amino compound to form a glycosyl amine, with loss of water Reaction 4. The reaction involves nucleophilic attack of the amino group on the anomeric carbon. Condensation will be favored under concentrated conditions. A high pH with a greater proportion of the amino function in the free amine form will also favor the reaction.
Eskin , with permission. The acyclic Schiff base intermediate is shown in Reaction 4. Those sugars that exist in solution with a comparatively higher proportion in the acyclic form refer to Table 3. The suggested mechanism involves ring opening, loss of water with formation of a Schiff base, formation of an enol through protonation of the amine, proton loss at carbon-2, enol-keto transformation, and ring closure. BLBSc04 October 14, 54 4: Formation of an amino-substituted ketose from an aldosyl-amine. A ketosyl amine will undergo a similar rearrangement to form an amino-substituted aldose.
Dehydration, Enolization, and Rearrangement Reactions Under acidic conditions, the Amadori compound undergoes protonassisted loss of a hydroxyl group at carbon-3, water elimination, enolization, loss of the amino acid through hydrolysis, and enol-keto transformation to form a 3-deoxyosulose Figure 4. Regeneration of the amino acid accounts for why only a small concentration of amino acids need be present for Maillard browning to occur. Under more alkaline conditions, the Amadori compound undergoes base-assisted loss of a proton at carbon-3, loss of water, and loss of the amino compound through hydrolysis to generate the amino acid and 1-methyldicarbonyls Figure 4.
The Hodge scheme Figure 4. Compounds having two enolic hydroxyls in conjugation with a carbonyl are known as reductones. Ascorbic acid is a reductone. Formation of an amino-substituted aldose from a ketosyl-amine. Generation of reductones through Maillard browning can account for some of the apparent increases in antioxidant properties of some foods during processing and storage as measured by oxygen radical absorbance capacity ORAC and ferric reducing antioxidant power FRAP Nursten The nitrogen-containing fragment can rearrange and break down to generate ammonia that is transferred to other components of the system.
Two fragments can condense to form various pyrazines, which are potent flavor compounds found in coffee, roasted nuts, and other foods. In addition to its flavor significance, the Strecker degradation Figure 4. Condensation and Polymerization The compounds formed in the Maillard browning scheme presented so far are colorless. Students and professionals alike will benefit from this latestaddition to the IFT Press book series. In FoodCarbohydrate Chemistry , upper undergraduate and graduatestudents will find a clear explanation of how basic principles ofcarbohydrate chemistry can account for and predict functionalproperties such as sweetness, browning potential, and solubilityproperties.
Professionals working in product development andtechnical sales will value Food Carbohydrate Chemistry as aneeded resource to help them understand the functionality ofcarbohydrate ingredients. And persons in research and qualityassurance will rely upon Food Carbohydrate Chemistry forunderstanding the principles of carbohydrate analytical methods andthe physical and chemical properties of sugars andpolysaccharides.
Now in Food Carbohydrate Chemistry, author Wrolstademphasizes the application of carbohydrate chemistry tounderstanding Now in Food Carbohydrate Chemistry , author Wrolstademphasizes the application of carbohydrate chemistry tounderstanding the chemistry, physical and functional properties offood carbohydrates. Structure and nomenclature of sugars and sugarderivatives are covered, focusing on those derivatives that existnaturally in foods or are used as food additives.
And persons in research and quality assurance will rely upon Food Carbohydrate Chemistry for understanding the principles of carbohydrate analytical methods and the physical and chemical properties of sugars and polysaccharides. Food Carbohydrate Chemistry Ronald E. Added to Your Shopping Cart. Description Not since "Sugar Chemistry" by Shallenberger and Birch has a text clearly presented and applied basic carbohydrate chemistry to the quality attributes and functional properties of foods.
Now in Food Carbohydrate Chemistry , author Wrolstad emphasizes the application of carbohydrate chemistry to understanding the chemistry, physical and functional properties of food carbohydrates. Structure and nomenclature of sugars and sugar derivatives are covered, focusing on those derivatives that exist naturally in foods or are used as food additives. Chemical reactions emphasize those that have an impact on food quality and occur under processing and storage conditions.