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FOOD CHEMISTRY FSTC 605 Instructor: Dr. Steve Talcott Office: 220F Centeq A Phone: 862-4056 E-mail: [email protected] Course website: http://nfscfaculty.tamu.edu/talcott Recommended Text Food Chemistry, 3rd Edition Owen Fennema ed. Classes My Meet: Mon, Wed, and Fri office is open at all times www.ift.org IFT Definition of Food Science Food science is the discipline in which biology, chemistry, physical sciences and engineering are used to study: The nature of foods The causes of their deterioration The principles underlying food processing. Food Science: An Interdisciplinary Field of Study Microbiology Biology Chemistry Food Science Physics Engineering Nutrition Food Chemistry Basis of food science Water Carbohydrates Proteins Lipids Micronutrients Phytochemicals Others Food Chemistry Examples Lipids in Peanuts Opened jar peanut butter: chemical reaction in the oil phase Oxidation of the unsaturated fatty acids in the peanut oil results in production of a rancid odor. Peanut butter represents a special food system called an emulsion H C H oxygen H C H C H C H Hydrocarbon chain Solutions and Emulsions Solutions are homogeneous mixtures in which solute particles are small enough to dissolve within solvent Solute examples: salt, sugar, vitamin C, other small solid particles Solute liquid examples: water, ethanol; gas examples: CO2 Droplets of dispersed phase within the continuous phase Examples of colloids MILK Dispersions (colloidal dispersions) are mixtures in which solutes do not dissolve (too large) milk protein (casein) egg white protein (albumen) gelatin protein pectin polysaccharide Ca and Mg (minerals) What is an emulsion? Mixture of two immiscible liquids oil Surface tension acts to keep the liquids from mixing H2O Result: oil “sits” on top of the water phase Stable food emulsions = addition of emulsifiers lecithin, sucrose esters, MAG, DAG, etc O/W emulsion milk ice cream mayo W/O emulsion Margarine butter Common Chemical Bonds in Foods Covalent Ionic Sharing 1 or more pairs of electrons Very strong bonds, not easily broken in foods C-C or C=C bonds Filling of orbitals through the transfer of electrons Cations (+) and Anions (-); Na+ + Cl- => NaCl Hydrogen Compounds containing O or N with bound hydrogen Very weak bonds; C-H or N-H Functional Groups in Foods The “Basics” of Food Chemistry SOME FOOD MOLECULES important in food chemistry H–O–H Na H CO3 CH3 – COOH C6H12O6 NH2 – CH2 - COOH O=C=O NaCl CH3 – (CH2)n - COOH SOME FOOD MOLECULES important in food chemistry WATER sodium bicarbonate The amino acid “glycine” acetic acid glucose carbon dioxide sodium chloride general structure of a fatty acid A Few Food Functional Groups: ACID GROUP: “carboxylic acid” COOH acids donate (lose) protons COOH COO(-) + H(+) This means acids form ions (charged species) anion has (-) charge cation has (+) charge Vinegar contains acetic acid CH3COOH Tartaric acid found in grapes is a di-carboxylic acid – what does this mean? Citric acid is tri-carboxylic acid. AMINO GROUP: NH2 Derived from ammonia (NH3) Amines are “basic” – means they gain protons methyl amine: CH3 – NH2 trimethylamine is found in fish, and is responsible for “fishy odor” CH3 – CH – COOH NH2 Alanine, an amino acid Alcohol group - OH “hydroxyl group” Methyl alcohol = methanol: CH3- OH Ethanol C2H5OH is produced during the fermentation of sugars; it is water-soluble and is called “grain alcohol” because it is obtained from corn, wheat, rice, barley, and fruits. Yeasts use sugars for food – they ferment simple carbohydrates and produce ethanol and CO2: STARCH hydrolysis C6H12O6 2 C2H5OH + 2 CO2 Glucose Ethanol Carbon Dioxide Other food molecules that contain OH groups: cholesterol (a lipid), tocopherol (a vitamin), retinol (a vitamin), & calciferol (a vitamin) Aldehyde group - CHO There is actually a double bond between two atoms in this group: formaldehyde HCHO: H–C–H O Aldehydes can be formed from lipid oxidation, and generally have very low sensory thresholds. For example, fresh pumpkin has the smell of acetaldehyde; fresh cut grass the small of hexenal. Covalent: Sharing of electrons, strong bonds, C-C or C=C bonds Ionic: Transfer of electrons, NaCl Hydrogen: Weak bonds with O or N with bound hydrogen There are 3 other important bonds in foods: (1) An ester bond (linkage) in lipids (2) A peptide bond (linkage) in proteins (3) A glycosidic bond (linkage) in sugars An ester bond (linkage) in lipids: In food fats, fatty acids are attached to glycerol molecules, through what is called an ester linkage O Glycerol C O Ester linkage fatty acid Glycerol is a small molecule, containing only 3 carbons But, to each carbon atom of glycerol, one fatty acid can attach, via an ester bond. A mono-, di-, or tri-esterified fatty acid to a glycerol is: A MONOACYLGLYCEROL. A fat molecule that has ONE fatty acid attached (“esterified”) to glycerol. A DIACYLGLYCEROL. A fat molecule that has TWO fatty acids esterified to glycerol. A TRIACYLGLYCEROL. A fat molecule that has THREE fatty acids esterified to glycerol. H H H–C–OH H–C–OH H–C–OH O H – C – O – C - (CH2)n – CH3 H–C–OH Fatty acid chain H–C–OH H H a monoglyceride Glycerol What do peptide bonds (linkages) in proteins look like? In food proteins, or “polypeptides”, individual amino acids are attached to each other through what is called a peptide linkage Amino acid Peptide linkage Amino acid. . . repeat AMINO ACIDS contain both the amino (NH2) and the acid (COOH) group in their structure. In the formation of a peptide bond, one of the amino acids loses one H atom, and the other loses O and H. H O H O NH2 C – C - O – H ------------- NH2 C – C - O – H R is any Side chain “R” Acid group of the amino acid “R” Amino group The formation of peptide bond N-C-C-N A glycosidic linkage in sugars connects sugar units into larger structures Glycosidic linkage glucose O glucose MALTOSE, a disaccharide composed of 2 glucose units Structures of sugar disaccharides Alpha 1,4 glycosidic bond Beta 1,4 glycosidic bond Alpha 1,4 glycosidic bond Polymeric Linkages CH 2 OH O O OH CH 2 OH O O OH OH OH Amylose Cellulose Alpha 1,4 Linkage Digestible Beta 1,4 Linkage Indigestible Organic Acids in Foods Application of functional groups Acids in Foods Organic acids Citric (lemons), Malic (apples), Tartaric (grapes), Lactic (yogurt), Acetic (vinegar) Food acids come in many forms, however: Proteins are made of amino acids Fats are made from fatty acids Fruits and vegetables contain phenolic acids Organic acids are characterized by carboxylic acid group (R-COOH); not present in “mineral acids” such as HCl and H3PO4 Chemical Structures of Common Organic Acids Acids in Foods Add flavor, tartness Aid in food preservation by lowering pH Acids donate protons (H+) when dissociated Strong acids have a lot of dissociated ions Weak acids have a small dissociation constant Acids dissociate based on pH As the pH increases, acid will dissociate pKa is the pH equilibrium between assoc/dissoc Titration Curve for Acetic Acid Acids in Foods Weak acids are commonly added to foods Citric acid is the most common When we eat a food containing citric acid, the higher pH of our mouth (pH 7) will dissociate the acid, and giving a characteristics sour flavor pH and Titratable Acidity pH measures the amount of dissociated ions TA measures total acidity (assoc and dissoc) The type of food process is largely based on pH They also have other roles in food Control pH Preserve food (pH 4.6 is a critical value) Provide leavening (chemical leavening) Aid in gel formation (i.e. pectin gels) Help prevent non-enzymatic browning Help prevent enzymatic browning Synergists for antioxidants (for some, low pH is good) Chelate metal ions (i.e. citric acid) Enhance flavor (balance sweetness) Acids in Foods In product development you can use one acid or a combinations of acids -flavor -functionality - synergy - naturally occurring blends - food additives Acidity is important chemically -Denaturation and precipitation of proteins -Modify carbohydrates and hydrolysis of complex sugars -Hydrolysis of Generally fatty acids from TAG’s under alkaline conditions Inversion of sugars (sucrose to glu + fru) Chemical Reactions in Foods (1) Enzymatic (2) Non-enzymatic Generically applied to: Carbohydrates Lipids Proteins CARBOHYDRATE chemical reactions: Enzymatic browning Non-enzymatic browning Hydrolysis Fermentation Oxidation/reduction Starch gelatinization PROTEIN chemical reactions: Buffering Non-enzymatic browning Hydrolysis Condensation Oxidation Denaturation Coagulation LIPID chemical reactions Oxidation Hydrolysis Hydrogenation Chemical Bonds to Chemical Rxns Chemical Reactions in Foods Enzymatic Enzymes are proteins that occur in every living system Enzymes can have beneficial and detrimental effects Bacterial fermentations in cheese, pickles, yogurt Adverse color, texture, flavor, and odor High degree of specificity (Enzyme – Substrate) Non-enzymatic Those reactions that do not require enzymes Addition, redox, condensation, hydrolysis The Active Site of the ES Complex Enzyme Reactions Enzymatic reactions can occur from enzymes naturally present in a food Or as part of food processing, enzymes are added to foods to enable a desired effect Enzymes speed up chemical reactions (good or bad) and must be controlled by monitoring time and temperature. Typically we think of enzymes as “breaking apart” lipids, proteins, or carbs; but there are several enzyme categories sucrase sucrose “invertase” glucose + fructose Enzyme Class Characterizations 1. Oxidoreductase Oxidation/reduction reactions 2. Transferase Transfer of one molecule to another (i.e. functional groups) 3. Hydrolase Catalyze bond breaking using water (ie. protease, lipase) 4. Lyase Catalyze the formation of double bonds, often in dehydration reactions, during bond breaking 5. Isomerase Catalyze intramolecular rearrangement of molecules 6. Ligase Catalyze covalent attachment of two substrate molecules Common Enzyme Reactions (some reactions can also occur without enzymes) HYDROLYSIS Food molecules split into smaller products, due to the action of enzymes, or other catalysts (heat, acid) in the presence of water OXIDATION / REDUCTION: Reactions that cause changes in a food’s chemical structures through the addition or removal of an electron (hydrogen). Oxidation is the removal of an electron Reduction is the addition of an electron Oxidation vs Oxidized The removal of an electron is oxidation (redox reactions). When a food system is oxidized, oxygen is added to an active binding site For example, the result of lipid oxidation is that the lipid may become oxidized. In the food industry, we common speak of “oxidizing agents” versus “reducing agents”. Both are used in foods. Reducing agents are compounds that can donate an electron in the event of an oxidation reaction. L-ascorbic acid is an excellent reducing agent as are most antioxidants Oxidizing agents induce the removal of electrons Benzoyl peroxide is commonly added to “bleached” wheat flour Lets put Enzymes and Chemical Reactions into Perspective Enzymes Living organisms must be able to carry out chemical reactions which are thermodynamically very unfavorable Break and/or form covalent bonds Alter large structures Effect three dimensional structure changes Regulate gene expression They A common biological reaction can take place without enzyme catalysis do so through enzyme catalysis …but will take 750,000,000 years With an enzyme….it takes ~22 milliseconds Even improvement of a factor of 1,000 would be good Only 750,000 years Living system would be impossible Effect of Enzymes A bag of sugar can be stored for years with very little conversion to CO2 and H2O This conversion is basic to life, for energy When consumed, it is converted to chemical energy very fast Both enzymatic and non-enzymatic reactions Enzymes are highly specialized class of proteins: Specialized to perform specific chemical reactions Specialized to work in specific environments Enzymes • Food quality can be changed due to the activity of enzymes during storage or processing • Enzymes can also be used as analytical indicators to follow those changes • Enzyme-catalyzed reactions can either enhance or deteriorate food quality • Changes in color, texture, sensory properties Enzyme Applications in the Food Industry Carbohydrases: making corn syrup from starch Proteases: Meat tenderizers Lipases: Flavor production in chocolate and cheese Pectinases Glucose oxidase Flavor enzymes Lipoxygenase Polyphenol oxidase Rennin (chymosin) Water Content of Foods Tomatoes, lettuce -- 95% Apple juice, milk -- 87% Potato -- 78% H Meats -- 65-70% O H Bread -- 35% Honey -- 20% Rice, wheat flour -- 12% Shortening -- 0% H O H Water Works Water must be “available” in foods for the action of both chemical and enzymatic reactions. The “available” water represents the degree to which water in a food is free for: Chemical reactions Enzymatic reactions Microbial growth Quality characteristics Related to a simple loss of moisture Related to gel breakdown Food texture (gain or loss) Water Works Very important (#1 ingredient in many foods) Structure Polar nature, hydrogen bonding Can occur in many forms (S,L,V) Acts as a dispersing medium or solvent Solubility Hydration Emulsions Gels Colloids Water Works The amount of “free” water, available for these reactions and changes is represented by Water Activity. As the percentage of water in a food is “bound” changing from its “free” state, the water activity decreases Water Activity is represented by the abbreviation: Aw Aw = P/ Po P = Vapor pressure of a food Po = Vapor pressure of pure water (1.0) Vapor pressure can be represented as equilibrium RH Is based on a scale of 0.0 to 1.0 Any food substance added to water will lower water activity….so, all foods have a water activity less than 1.0 Water Free vs. bound Water activity (Aw) Measured by vapor pressure of food This value is directly correlated to the growth of microorganisms and the chemical reactions 3 Forms of Water Free water (capillary water or Type III) Water that can be easily removed from a food Water that is responsible for the humidity of a food Water from which water activity is measured Bound water (adsorbed or Type II) Water that is tied up by the presense of soluble solids Salts, vitamins, carbohydrates, proteins, emsulifiers, etc. Water of hydration (Structured or Type I) Water held in hydrated chemicals . Na2SO4 10H2O Water Sorption Isotherm Type I Hydration 0 0.1 0.2 Type II Absorbed 0.3 0.4 0.5 0.6 Water Activity Type III Free 0.7 0.8 0.9 1 Water Sorption Isotherm Type I Hydration 0 0.1 0.2 Type II Absorbed 0.3 0.4 0.5 0.6 Water Activity Type III Free 0.7 0.8 0.9 1 Moisture sorption isotherm (MSI) How to Use the Isotherm Moisture sorption isotherms Shows the relationship between water activity and moisture at a given temperature (the two are NOT equivalent) Represent moisture content at equilibrium for each water activity Allow for predictions in changes of moisture content and its potential effect on water activity If the temperature is altered, then the relationships can not be compared equivalently Each reaction is governed by its own temperature-dependence Acid hydrolysis reactions are faster at high temperatures Enzyme-catalyzed reactions cease to function at high temperatures Influences on Water Activity Foods will naturally equilibrate to a point of equilibrium with its environment Therefore, foods can adsorb or desorb water from the environment Desorption is when a “wet” food is placed in a dry environment Analogous to dehydration; but not the same Desorption implies that the food is attempting to move into equilibrium (ie. in a package) Dehydration is the permanent loss of water from a food In both cases, the Aw decreases Desorption is generally a slow process, with moisture gradually decreasing until it is in equilibrium with its environment. Adsorption is when a “dry” food is placed in a wet environment As foods gain moisture, the Aw increases The term “hygroscopic” is used to describe foods or chemicals that absorb moisture A real problem in the food industry (lumping, clumping, increases rxn rates) Water Activity in Practice Bacterial growth and rapid deterioration High water activity in meat, milk, eggs, fruits/veggies 1.0-0.9 Yeast and mold spoilage Intermediate water activity foods such as bread and cheese 0.75-0.9 Analogous to a pH < 4.6, an Aw < 0.6 has the same preservation effect Aw in Low Moisture Foods Water activity and its relationship with moisture content help to predict and control the shelf life of foods. Generally speaking, the growth of most bacteria is inhibited at water activities lower than 0.9 and yeast and mold growth prevented between 0.80 and 0.88. Aw also controls physiochemical reactions. Water activity plays an important role in the dehydration process. Knowledge of absorption and desorption behavior is useful for designing drying processes for foods. How to “Control” water The ratio of free to bound water has to be altered You can either remove water (dehydration or concentration) Or you can convert the free water to bound water Can change the physical nature of the food Alter is color, texture, and/or flavor Addition of sugars, salts, or other water-soluble agents You can freeze the food This immobilizes the water (and lowers the Aw) However, not all foods can be or should be frozen Frozen foods will eventually thaw, and the problem persists Water Water contains intramolecular polar covalent bonds Effects Boiling point Freezing point Vapor pressure Easy formation of H bonds with food molecules Properties of Water The triple point is the temperature and pressure at which three phases (liquid, ice, and vapor) coexist at equilibrium, and will transform phases small changes in temperature or pressure. The dashed line is the vapor pressure of supercooled liquid water. Chemical and functional properties of water Solvation, dispersion, hydration Water activity and moisture Water as a component of emulsions Water and heat transfer Water as an ingredient Freezing Foods Controlling Water Freezing Greatly influenced the way we eat Freezing curves Water Freezes “Pure” Frozen Foods Must be super-cooled to below 0°C Crystal nucleation begins Temperature rises to 0°C as ice forms Refrigerated and Frozen Foods The Market Meals and entrees Meat, poultry, fish Dairy, beverage Fruits and veggies Bakery products Snacks, appetizers, and side dishes Annual Sales ($Billion) $83.7 69.8 21.9 11.6 16.1 15.8 Freezing Foods Temperature 40 35 Freezing Point 20 30 25 60 70 20 15 90 Super-cooling 95 Latent heat of Crystallization 10 5 0 2 4 6 8 98 99 99.9 10 12 14 16 18 20 22 24 26 28 30 Freezing Time Freezing Freezing Food Require lower temp. to continue freezing Last portion of water is very hard to freeze Unfrozen water is a problem ***As long as unfrozen water is present in a food, the temperature will remain near 0°C due to the latent heat of crystallization. Freezing Quality changes during freezing Concentration effect = small amount of unfrozen water Excess solutes may precipitate Proteins may denature pH may decrease Gases may concentrate (i.e. oxygen) Freezing Quality changes during freezing Damage from ice crystals Puncture Large cell membranes crystals cause more problems Fast freezing much more desirable Less concentration effect Smaller ice crystals Freezing Final storage temperature -18°C is standard Safe microbiologically Limits enzyme activity Non-enzymatic changes are slow Can maintain fairly easily Good overall shelf-life Freezing Intermittent thawing Partial thawing, then refreezing Complete thawing does not have to occur Get concentration effect Get larger ice crystals as water re-freezes Freezing Factors determining freezing rate: Food composition Fat and air have low thermal conductivity, slow down freezing This is a “buffering” effect. Freezing Ways to speed up freezing Thinner foods freeze faster Greater air velocity More intimate contact with coolant Use refrigerant with greater heat capacity High Pressure Effects Freezing is regarded as one of the best methods for long term food preservation. The benefits of this technique are primarily from low temperatures rather than ice formation. Freezing Foods Freezing can be damaging to food systems due to To reduce the chemical and mechanical damage to food systems during freezing, technologies have been developed to freeze foods faster or under high pressures. Benefits include: Formation of ice crystals (especially large ice crystals) Concentration of soluble solids Concentration of gasses (ie. oxygen) Intermittent thawing (poor temperature control) Higher density ice (less “space” between crystals from air or solids) Increased rate of freezing Smaller ice crystal formation Uniform crystal formation With high-pressure freezing the increasing pressure decreases the temperature needed to freeze water, thus the ice nucleation rate increases. HP freezing generally involves cooling an unfrozen sample to -21C under high pressures (300MPa) causing ice formation to occur. Another method involves pressure shift freezing where the food is cooled under high pressures without causing freezing. Once the pressure is released, the sample freezes instantly. The Phase diagram shows us the process which takes place as water is added to a lipid system. It can be seen that the lipid phase transition temperature falls with increasing water content. So,below that particular temperature the chains are crystalline and when the temperature is above it they are melted in a fluid condition. Note: The phosphatidyl cholines bind a significant amount of water. This is said to be 'bound' or 'unfreezable' water. Water content in a food system influences the rate of chemical reactions by shifting reaction equilibria via LeChatelier's principle or by the more subtle effect of changing the pH. Essentially, as water is removed those solutes involved in degradation reactions are concentrated. These solutes are responsible for the pH of the system. Back in 1923, two researchers, Corran and Lewis, showed that the activity of the hydronium ions (-OH) increased with increasing sucrose concentration. Basically the sucrose bound the water resulting in a decrease in pH, or an increase in the acidity of a given solution. Recent research has demonstrated that reaction rate of amino acid degradation reactions are pH dependent. Dehydration and Concentration of Foods Controlling Water Dehydration and Concentration Factors affecting drying rates Surface area Temperature Air velocity Humidity Pressure (vacuum) Solute concentration Amount of free and bound water Moisture Content Drying Curve of a Food 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0 Water that is easily removed Water that is difficult to remove 0 1 2 3 4 5 6 7 Time (Hrs) 8 9 10 11 12 Dehydration and Concentration Quality changes Browning Enzymes - sulfite will prevent Carmelization - lower temps. will limit Maillard reaction - reaction of sugars and amino acids - lower temps will limit Acrylamide…??? Flavor changes Carbohydrates in Foods A general overview CARBOHYDRATES Classifications for the main categories of food carbohydrates are based on their degree of polymerization. Types of Carbohydrates CARBOHYDRATES Carbohydrates are carbon compounds that contain many hydroxyl groups. The simplest carbohydrates also contain either an aldehyde (these are termed polyhydroxyaldehydes) or a ketone (polyhydroxyketones). All carbohydrates can be classified as either monosaccharides, disaccharides, oligosaccharides or polysaccharides. An oligosaccharide is anywhere from about two to ten monosaccharide units, linked by glycosidic bonds. Polysaccharides are much larger, containing hundreds of monosaccharide units. The presence of the hydroxyl groups (–OH) allows carbohydrates to interact with the aqueous environment and to participate in hydrogen bonding, both within and between chains. CARBOHYDRATES SUGARS contain 2 important and very reactive Functional groups: -OH (hydroxyl group) Important for solubility and sweetness -C=O (carbonyl group) Important for reducing ability and Maillard browning GLUCOSE is an ALDOSE sugar with one C atom external to the 6-membered ring FRUCTOSE is a KETOSE hexose with two carbon atoms external to the 6-membered ring Monosaccharides The monosaccharides commonly found in foods are classified according to the number of carbons they contain in their backbone structures. The major food monosaccharides contain six carbon atoms. Carbohydrate Classifications Hexose = six-carbon sugars Glucose, Galactose, Fructose Fischer Projection of a-D-Glucose Haworth Projection of a-D-Glucose Chair form of a-D-Glucose Disaccharides Bonds between sugar units are termed glycosidic bonds, and the resultant molecules are glycosides. The linkage of two monosaccharides to form disaccharides involves a glycosidic bond. The important food disaccharides are sucrose, lactose, and maltose. Sucrose: prevalent in sugar cane and sugar beets, is composed of glucose and fructose through an α-(1,2) glycosidic bond. Lactose: is found exclusively in the milk of mammals and consists of galactose and glucose in a β-(1,4) glycosidic bond. Maltose: Is the major degradation product of starch, and is composed of 2 glucose monomers in an α-(1,4) glycosidic bond. Polysaccharides Most of the carbohydrates found in nature occur in the form of high molecular weight polymers called polysaccharides. The monomeric building blocks used to generate polysaccharides can be varied; in all cases, however, the predominant monosaccharide found in polysaccharides is D-glucose. When polysaccharides are composed of a single monosaccharide building block, they are termed homopolysaccharides. Starch Starch is the major form of stored carbohydrate in plant cells. Its structure is identical to glycogen, except for a much lower degree of branching (about every 20-30 residues). Unbranched starch is called amylose Branched starch is called amylopectin. FUNCTIONAL PROPERTIES OF CARBOHYDRATES Reducing sugars Browning reactions (caramelization and Maillard) Sweetness and flavors Crystallization Humectancy Inversion Oxidation and reduction Texturizing Viscosity Gelling (gums, pectins, other hydrocolloids) Gelatinization (Starch) Invert sugar Invert sugar is a liquid carbohydrate sweetener in which all or a portion of the sucrose present has been inverted: The sucrose molecule is split and converts to an equimolar mixture of glucose and fructose. Invert sugars have properties from sucrose; they help baked goods retain moisture, and prolong shelf-life. Candy manufacturers use invert sugar to control graining. Invert sugar is different from high fructose sweeteners SUCROSE + invertase enzyme glucose + fructose Sucrose Where does sucrose come from? Invert sugar Invert sugar is a liquid carbohydrate sweetener in which all or a portion of the sucrose present has been inverted: The sucrose molecule is split and converts to an equimolar mixture of glucose and fructose. Invert sugars have properties from sucrose; they help baked goods retain moisture, and prolong shelf-life. Candy manufacturers use invert sugar to control graining. Invert sugar is different from high fructose sweeteners SUCROSE + invertase enzyme glucose + fructose Corn syrups Corn syrups are manufactured by treating corn starch with acids or enzymes. Corn syrups, used extensively by the food industry and in the home kitchen, contain primarily glucose (dextrose) but other sugars as well. High-fructose corn syrup (HFCS) is made by treating dextrose-rich corn syrup with enzymes (isomerase). The resulting HFCS is a liquid mixture of dextrose and fructose used by food manufacturers in soft drinks, canned fruits, jams and other foods. HFCS contains 42, 55, 90 or 99 percent fructose. PROCESSING OF CORN STARCH HFCS Corn starch is treated with α-amylase, of bacterial origin, to produce shorter chains of sugars (dextrins) as starch fragments. Next, an enzyme called glucoamylase, obtained from the fungus Aspergillus niger, breaks the fragments down even further to yield the simple sugar glucose. A third enzyme, glucose isomerase, is expensive, and converts glucose to various amounts of fructose. HFCS-55 has the exact same sweetness intensity as sucrose (cola) HFCS-42 is less sweet, used with fruit-based beverages and for baking Glucose isomerase is so expensive that it is commonly immobilized on a solid-based “resin” bead and the glucose syrup passed over it. Can be used many times over before it slowly looses its activity. HFCS HFCS is selected for different purposes. Selection is based on specific desired properties: Retain moisture and/or prevent drying out Control crystallization Produce a higher osmotic pressure (more molecules in solution) than for sucrose Control microbiological growth Provide a ready yeast-fermentable substrate Blend easily with sweeteners, acids, and flavorings Provide a controllable substrate for browning and Maillard reaction. Impart a degree of sweetness essentially = to invert liquid sugars High sweetness Low viscosity Reduced tendency toward crystallization Costs less than liquid sucrose or corn syrup blends Retain moisture and/or prevent drying out of food product HFCS HFCS has the exact same sweetness and taste as an equal amount of sucrose from cane or beet sugar. Despite being a more complicated process than the manufacture of sugar, HFCS is actually less costly. It is also very easy to transport, being pumped into tanker trucks. Two of the enzymes used, α-amylase and glucose-isomerase, are genetically modified to make them more thermostable. This involves exchanging specific amino acids in the primary sequence so that the enzyme is resistant to unfolding or denaturing. This allows the industry to use the enzymes at higher temperatures without loss of activity. Starch Starches- #1 Hydrocolloid Hydrocolloids are substances that will form a gel or add viscosity on addition of water. Most are polysaccharides and all interact with water. The most common is starch Starch is a mixture of amylose and amylopectin. The size distribution of these hydrocolloids is the most important factor in the texture and physical features of foods STARCH Polymers of glucose AMYLOSE linear chain of glucose Glucose polymer linked α-1,4 AMYLOPECTIN branched polymer of glucose Amylose Amylopectin AMYLOSE Linear polymer of glucose α 1 - 4 linkages Digestable by humans (4 kcal/g) 250-350 glucose units on average Corn, wheat, and potato starch ~10-30% amylose AMYLOPECTIN Branched chain polymer of glucose α 1 - 4 and α 1 - 6 glycosidic linkages Fully digestable by humans 1,000 glucose units is common Branch points every ~15-25 units Starch Amylopectin (black) Amylose (blue) Modified Starches Gelatinization is the easiest modification Heated in water then dried. Acid and/heat will form “dextrins” α-Amylase β-Amylase hydrolyzes α (1-4) linkage random attack to make shorter chains Also attacks α (1 - 4) linkages Starts at the non-reducing end of the starch chain Gives short dextrins and maltose Both enzymes have trouble with α (1 - 6) linkages DEXTRINS are considered to be hydrolysis products of incompletely broken down starch fractions Polysaccharide Breakdown Products What’s the difference between…? Maltose Maltitol Maltodextrins Dextrins Dextrans Maltose = glucose disaccharide Maltitol = example of a “polyol” Maltodextrins = enzyme converted starch fragments Dextrins = starch fragments (α-1-4) linkages produced by hydrolysis of amylose Dextrans = polysaccharides made by bacteria and yeast metabolism, fragments with mostly α (1 - 6) linkages Maltodextrins and enzyme-converted starch: STARCH fermentation SUGARS ETHANOL MODIFIED STARCHES GELATINIZED STARCH alpha amylase Maltodextrins Corn Syrups Sugars The smaller the size of the products in these reactions, the higher the dextrose equivalence (DE), and the sweeter they are Starch DE = 0 Glucose (dextrose) DE = 100 Maltodextrin (MD) DE is <20 Corn syrup solids (CS) DE is >20 Low DE syrup alpha amylase MD beta amylase High DE Syrup Hydrocolloids Binding water with carbohydrates “Gums” “Vegetable gum” polysaccharides are substances derived from plants, including seaweed and various shrubs or trees, have the ability to hold water, and often act as thickeners, stabilizers, or gelling agents in various food products. Plant gums - exudates, seeds Marine hydrocolloids - extracts from seaweeds Microbiological polysaccharides - exocellular polysaccharides Modified, natural polysaccharides FUNCTIONS IN FOOD Gelatin Viscosity Suspension Emulsification and stability Whipping Freeze thaw protection Fiber (dietary fiber) Gut health Binds cholesterol STRUCTURAL CONSIDERATIONS Electrical charge, pH sensitive Interactions with oppositely charged molecules Salts Low Chain pH effects length Longer Linear chains are more viscous vs Branched chains Inter-entangled, enter-woven molecules Gums GUAR (Guran Gum) Most used, behind starch, low cost Guar bean from India and Pakistan Cold water soluble, highly branched galactomannan Stable over large pH range, heat stable Thickening agent, not a gel Often added with xanthan gum (synergistic) XANTHAN Extracellular polysaccharide from Xanthomonas campestris Very popular, inexpensive from fermentations Forms very thick gels at very low concentrations Gums LOCUST BEAN Branched galactomannan polymer (like guar), but needs hot water to solubilize Bean from Italy and Spain Jams, jellies, ice cream, mayonnaise SEAWEED EXTRACTS Carrageenans (from Kappa red seaweed) (gel) Iota (gel) Lambda (thickener only) Milk, baking, cheese, ice cream Agar Alginates “Structural” Polysaccharides Cellulose Polymer of glucose linked ß-1,4 Hemicellulose Similar to cellulose Consist of glucose and other monosaccharides Arabinose, xylose, other 5-carbon sugars Pectin Polymer of galacturonic acid MODIFIED CELLULOSES Chemically modified cellulose Do not occur naturally in plants Similar to starch, but β-(1,4) glycosidic bonds Carboxymethyl cellulose (CMC) most common Acid treatment to add a methyl group Increases water solubility, thickening agent Sensitive to salts and low pH Fruit fillings, custards, processed cheeses, high fiber filler PECTINS Linear polymers of galacturonic acid Susceptible to degrading enzymes Gels form with degree of methylation of its carboxylic acid groups Many sources, all natural, apple and citrus pomace Polygalacturonase (depolymerize) Pectin esterases (remove methyl groups) Longer polymers, higher viscosity Lower methylation, lower viscosity Increase electrolytes (ie. metal cations), higher viscosity pH an soluble solids impact viscosity PECTIC SUBSTANCES: cell cementing compound; fruits and vegetables; pectin will form gel with appropriate concentration, amount of sugar and pH. Basic unit comprised of galacturonic acid. Composition: polymer of galacturonic acids; may be partially esterified. Pectic Acid Pectin Molecule Pectins Pectins are important because they form gels Mechanism of gel formation differs by the degree of esterification (DE) of the pectin molecules DE refers to that percentage of pectin units with a methyl group attached Free COOH groups can crosslink with divalent cations Sugar and acid under certain conditions can contribute to gel structure and formation LM pectin “low methoxyl pectin” has DE < 50% ; gelatin is controlled by adding cations (like Ca++ and controlling the pH) HM pectin “high methoxyl pectin” has DE >50% and forms a gel under acidic conditions by hydrophobic interactions and Hbonding with dissolved solids (i.e. sugar) Hydrophobic attractions between neighboring pectin polymer chains promote gelation BETA-GLUCANS Extracts from the bran of barley and oats Long glucose chains with mixed ß-linkages Very large (~250,000 glucose units) Water soluble, but have a low viscosity Can be used as a fat replacer Responsible for the health claims (cholesterol) for whole oat products Formulated to reduce the glycemic index of a food Others CHITIN Polymer of N-Acetyl-D-glucosamine Found in the exoskeleton of insects and shellfish Many uses in industry, food and non-food. INULIN Chains of fructose that end in a glucose molecule Generally a sweet taste Isolated from Jerusalem artichokes and chicory Act as a dietary fiber Potentially a pre-biotic compound COMPONENTS OF DIETARY FIBER COMPONENT SOURCE Cellulose All food plants Hemicellulose All food plants, especially cereal bran Pectin Mainly fruit Lignin Mainly cereals and 'woody' vegetables Gums and some food thickeners Food additives in processed foods HYDROCOLLOIDS A key attribute of gums is to produce viscous dispersions in water Viscosity depends on: Gum type Temperature Concentration of gum Degree of polymerization of gum Linear or branched polymers Presence of other substances in the system Solubility (dispersability in water) varies among gums Agar is insoluble in cold water; dissolves in boiling water Methylcellulose is insoluble in hot water, but soluble in cold ! Our First Browning Reaction Caramelization BROWNING REACTIONS in CARBOHYDRATES There are 2 different kinds of browning reactions with carbohydrates: Caramelization Maillard (or non-enzymatic) browning CARAMELIZATION occurs when sucrose is heated >150-170°C (high heat!) via controlled thermal processing Dehydration of the sugar, removal of a water molecule The structure of caramelized sugar is poorly understood but can exist in both (+) and (-) species Commonly used as a colorant (+) charged caramel = promotes brown color in brewing and baking industries (-) charged caramel in beverage/ soft drink industry (cola and root beer) CARAMELIZATION What is referred to as “caramel pigment” consists of a complex mixture of polymers and fragments of indefinite chemical composition Caramelans (24, 36, or 125 carbon lengths) Since caramel is a charged molecule, to be compatible with phosphoric acid in colas the negative form is used Caramel flavor is also due to these and other fragments, condensation, and dehydration products. diacetyl, formic acid, hydroxy dimethylfuranone Artificial and Alternative Sweeteners The perception of sweetness is proposed to be due to a chemical interaction that takes place on the tongue Between a tastant molecule and tongue receptor protein THE AH/B THEORY OF SWEETNESS A sweet tastant molecule (i.e. glucose) is called the AH+/B“glycophore”. It binds to the receptor B-/AH+ site through mechanisms that include H-bonding. AH+ / B- γ B Glycophore Hydrophobic interaction AH AH B γ Tongue receptor protein molecule For sweetness to be perceived, a molecule needs to have certain requirements. It must be soluble in the chemical environment of the receptor site on the tongue. It must also have a certain molecular shape that will allow it to bond to the receptor protein. Lastly, the sugar must have the proper electronic distribution. This electronic distribution is often referred to as the AH, B system. The present theory of sweetness is AH-B-X (or gamma). There are three basic components to a sweetener, and the three sites are often represented as a triangle. Identifying the AH+ and Bregions of two sweet tastant molecules: glucose and saccharin. Gamma (γ) sites are relatively hydrophobic functional groups such as benzene rings, multiple CH2 groups, and CH3 WHAT IS SUCRALOSE AND HOW IS IT MADE? Sucralose, an intense sweetener made from sugar, is approximately 600 times sweeter than sugar. In a patented multi stage process three of the hydroxyl groups in the sucrose molecule are selectively substituted with 3 atoms of chlorine. This intensifies the sugar like taste while creating a safe, stable low kcal sweetener with zero calories. Although its chemical structure is very close to that of sucrose (table sugar), sucralose is not recognized by the body as a carbohydrate and has no effect on insulin secretion or overall carbohydrate metabolism in healthy human beings. Developers found that selective halogenations changed the perceived sweetness of a sucrose molecule, with chlorine and bromine being the most effective. Chlorine, as a lighter halogen, retains higher water solubility, so chlorine was picked as the ideal halogen for substitution. Sucrose portion Fructose portion Compared to sucrose, sucralose has three key molecular differences that make it similar in structure, yet different in metabolism and function. These three differences are chlorine. Three chlorine atoms, in the form of chloride ions, replace three hydroxyl groups in native sucralose. It was determined that the tightly bound chlorine created a stable molecular structure, approximately 600 times sweeter than sugar. In sucralose, the two chlorine atoms present in the fructose portion of the molecule comprise the hydrophobic X-site, which extends over the entire outer region of the fructose portion of the sucralose molecule. The hydrophobic and hydrophilic regions are situated on opposite ends of the molecule, similar to sucrose, apparently unaffected by the third chlorine on the C4 of the pyranose ring. The similar structure of sucralose to native sucrose is responsible for its remarkably similar taste to sugar. hydrophobic Area (AH+): This area has hydrogens available to hydrogen bond to chlorine attached to the glucose bottom portion of the molecule. hydrophilic Area (B -): This area has a partially negative oxygen available to hydrogen bond to the partially positive hydrogen of an alcohol group. hydrophilic The drastically increased sweetness of sucralose is due to the structure of molecule. In sucralose, the two chlorine atoms present in the fructose portion of the molecule lead to more hydrophobic properties on the opposite side of the molecule (upper left), which extends over the entire outer region of the fructose portion of the sucralose molecule. In 2005 Coca-Cola released a new formulation of Diet Coke sweetened with sucralose, called “Diet Coke with Splenda”. Wheat Bran Removed Whole Wheat Corn Milled, Polished Rice Cereals Cereals Starch, protein, fiber Water Lysine Structure Husk (inedible) Bran (fiber) Endosperm (starch, protein, oil) Germ (oil) Wheat Kernel Endosperm Starch Protein Oil Endosperm Bran Bran Fiber Germ Germ Oil Protein Cereal Grain Composition of Cereals Grain Water Carbo. Protein Fat Fiber Corn 11 72 10 4 2 Wheat 11 69 13 2 3 Oats 13 58 10 5 10 Sorghum 11 70 12 4 2 Barley 14 63 12 2 6 Rye 11 71 12 2 2 Rice 11 65 8 2 9 Buckwheat 10 64 11 2 11 Wheat 2 types of wheat HARD = higher protein (gluten), makes elastic dough, used for bread-making Higher “quality” High water absorption SOFT = lower protein (gluten), make weak doughs/batters, used for cakes, pastries, biscuits, cakes, crackers, etc. Lower “quality” due to lower protein content and useful applications Wheat Wheat Milling To produce flour Cleaned with air (dust, bugs, chaff) Soaked to 17% moisture - optimum for milling Remove husk Crack seeds - frees germ from endosperm Wheat Wheat Milling Rollers- two metal wheels turning in opposite direction of each other Endosperm is brittle and breaks Germ and bran form flat flakes and are removed by screens or sieves Endosperm = flour Less Whole color and less nutrients as milling continues wheat flour = do not remove all of the bran and/or germ Wheat Mill Grinding Rolls Wheat Milling Sifters Wheat Wheat Enrichment Add B-vitamins and some minerals to most white flours (since missing the bran) Uses of flour Cakes, breads, etc. Pasta, noodles, etc. Course flour, not leavened Rice Processing Rice Rice Milling Most rice is "whole grain" Remove husk, bran, germ by rubbing with abrasive disks or rubber belts Polish endosperm to glassy finish Brown rice = very little milling Rice Rice Enrichment Add some vitamins, minerals Coat rice with nutrients (folic acid) Parboiling or steeping (converted rice) Boil rice before milling (~10 hrs, 70°C) Nutrients, vitamins and minerals, will migrate into endosperm (no fortification) Rice Rice Other rice products Quick cooking (instant) = precooked, dried Rice flour Sake (15-20% alcohol) Advantages/Disadvantages of Milling Rice Brown Rice Minimal milling Higher in lipid (shortens shelf-life) Higher in minerals (not removed in milling) White (Milled) Rice Extreme milling Vitamins and minerals removed (Thiamin) Fortification to prevent Beriberi disease Anatomy of Corn Corn Corn Some fresh/frozen/canned corn, but most is milled Dry milling (grits, meal, flour) Adjust moisture to 21%- optimum for "dry" milling Loosen hull (pericarp) and germ by rollers Dry to 15% moisture Remove husk with air blast; germ and bran by sieving Continue grinding endosperm to grits, meal or flour Process very similar to wheat milling at this point. Grits = large particle size Meal = medium particle size Flout = small particle size Grain Processing Wet milling (corn starch, corn syrups) Soak corn Grind with water into a wet "paste" Slurry is allowed to settle and the germ and hulls float to top (high in oil) Remainder is endosperm (starch/protein) Centrifuged or filtered to remove/collect the starch Grain Processing Wet milling (cont'd.) Dried starch = corn starch Can produce corn syrups from starch Use enzymes (amylase) to break starch into glucose (corn syrup) Use another enzyme (isomerase) to convert glucose into fructose (HFCS) Can also produce ethanol from corn syrup Products from Corn Grain Usage Other grains- mostly for animal feed Barley = used in beer Rye = can not use alone (poor protein quality) Oats = oatmeal, flakes Breakfast cereals Made from many different grains Baking Ingredients Flour Starch Protein = gluten; forms elastic dough that will expand during rising Baking Ingredients… Leavening agent Rising due to carbon dioxide or air Yeast = alcoholic fermentation produces carbon dioxide Baking powder = chemical reaction that releases carbon dioxide Baking …Ingredients Leavening Air leavening = sponge cake Partial leavening = pie crusts, crackers Eggs Add flavorings Add color Helps holds air when whipped Baking …Ingredients Shortening Tenderizes Hold air Sugar Tenderizes Sweetness Fermentable sugar Helps retain moisture Baking Oven baking Gas production and rising continues Denaturation and coagulation of proteins Drying and crust formation Flavor development Color development = Carmelization and Maillard reaction Baking High altitudes Excessive gas production (less pressure) Weakens and collapses dough Not as bad for bread Can alter formula Less baking powder Make tougher dough Add less tenderizers Legumes and Oilseeds Soybeans, peanuts, etc. Higher in oil (20-50%) and protein (20%) Methionine and/or cysteine are limiting amino acids Protein complementation with cereals Legumes and Oilseeds Soybeans = used for both oil and protein Peanuts = whole nut, oil, peanut butter
