Food Chem 2 Reviewer PDF

# Unit 1: Enzymes ## 1.A. Enzyme Classification and Nomenclature ### Trivial Name - Gives no idea of source, function or reaction catalyzed by the enzyme. - Example: trypsin, thrombin, pepsin. ### Nomenclature and Classification - **Nomenclature:** system of naming organisms - **Classification:...

# Unit 1: Enzymes ## 1.A. Enzyme Classification and Nomenclature ### Trivial Name - Gives no idea of source, function or reaction catalyzed by the enzyme. - Example: trypsin, thrombin, pepsin. ### Nomenclature and Classification - **Nomenclature:** system of naming organisms - **Classification:** arranging them in groups according to their similarity or differences. ### Systematic Name - According to the International union of Biochemistry an enzyme name has two parts: - First part is the name of the substrates for the enzyme. - Second part is the type of reaction catalyzed by the enzyme. This part ends with the suffix "ase". - Example: Lactate dehydrogenase ### EC number - Enzymes are classified into six different groups according to the reaction being catalyzed. - The nomenclature was determined by the Enzyme Commission in 1961 (with the latest update having occurred in 1992), hence all enzymes are assigned an "EC" number. - The classification does not take into account amino acid sequence (ie, homology), protein structure, or chemical mechanism. - EC numbers are four digits, for example a.b.c.d, where "a" is the class, "b" is the subclass, "c" is the sub-subclass, and "d" is the sub-sub-subclass. - The "b" and "c" digits describe the reaction, while the "d" digit is used to distinguish between different enzymes of the same function based on the actual substrate in the reaction. - Example: for Alcohol: NAD+oxidoreductase EC number is 1.1.1.1 ## The Six Classes ### EC 1. Oxidoreductases - Catalyze the transfer of hydrogen or oxygen atoms or electrons from one substrate to another, also called oxidases, dehydrogenases, or reductases. - Note that since these are 'redox' reactions, an electron donor/acceptor is also required to complete the reaction. ### EC 2. Transferases - Catalyze group transfer reactions, excluding oxidoreductases (which transfer hydrogen or oxygen and are EC 1). - A-X+B → BX + A ### EC 3. Hydrolases - Catalyze hydrolytic reactions. - Includes lipases, esterases, nitrilases, peptidases/proteases. - A-X + H2O → Х-ОН + НА ### EC 4. Lyases - Catalyze non-hydrolytic (covered in EC 3) removal of functional groups from substrates, often creating a double bond in the product; or the reverse reaction, i.e, addition of function groups across a double bond - A-BA-B + X-YXY ### EC 5. Isomerases - Catalyzes isomerization reactions, including racemizations and cis-tran isomerizations. ### EC 6. Ligases - Catalyzes the synthesis of various (mostly C-X) bonds, coupled with the breakdown of energy-containing substrates, usually ATP # 1.B. Properties and Functions of Enzymes ## Properties 1. A high degree of specificity for their substrates. Each enzyme will catalyze only one particular reaction. 2. Enzymes are not used in the reaction they catalyze they can be used again and again. 3. When enzymes react they combine with substrates to form ES complexes. 4. Only a small amount of enzyme is needed to catalyze a lot of substrates. 5. Enzymes are fast-acting i.e. they have a high turnover number. They can convert many molecules of substrate per unit time. 6. Enzymes are affected by changes in temperature and pH. 7. Many enzymes work only if a chemical called cofactor is present. 8. Enzyme-catalyzed reactions are slowed down or stopped by inhibitors. ## Functions 1. Degradation reactions (catabolic) 2. Synthesis (anabolic) 3. Digestion 4. Protection # 1.C. Enzyme Kinetics and Reactions - Branch of biochemistry in which we study the rate of enzyme-catalyzed reactions. - Studying an enzyme's kinetics in this way can reveal the catalytic mechanism of that enzyme, its role in metabolism, how its activity is controlled, and how a drug or an agonist might inhibit enzyme. ## Rates of reaction and their dependence on Activation Energy ### Activation Energy (Ea) - The least amount of energy needed for a chemical reaction to take place. - Enzyme (as a catalyst) acts on substrates in such a way that they lower the activation energy by changing the route of the reaction. - The reduction of activation energy increases the amount of reactant molecules that achieve a sufficient level of energy so that they reach the activation energy and form the product. #### Example: - Carbonic anhydrase catalyzes the hydration of 105 CO2 molecules per second which is 107 x faster than spontaneous hydration. # 1.D. Factors Affecting Enzyme Activity - The activity of an enzyme is affected by its environmental conditions. Changing these alters the rate of reaction caused by the enzyme. - In nature, organisms adjust the conditions of their enzymes to produce an optimum rate of reaction, where necessary, or they may have enzymes which are adapted to function well in extreme conditions where they live. ## 1. Temperature - Increasing temperature increases the Kinetic Energy, increases random collisions between molecules per unit time. - Since enzymes catalyze reactions by randomly colliding with substrate molecules, increasing temperature increases the rate of reaction, forming more products. - However, increasing temperature also increases the vibrational energy which can strain on the bonds that hold the molecules together. - As temperature increases, more bonds, especially the weaker hydrogen and ionic bonds will break as a result of this strain. - Breaking bonds within the enzyme will cause the Active Site to change shape. Changes in the shape will complement lesser to the shape of the substrate thus, decreasing the likelihood of a reaction. - In summary, as the temperature increases, initially the rate of reaction will increase because of increased kinetic energy. However, the effect of bond breaking will become greater and greater, and the rate of reaction will begin to decrease. ## 2. pH - Acidity and Basicity - H+ and OH- ions are charged and therefore interfere with hydrogen and ionic bonds that hold together an enzyme since they will be attracted or repelled by the changes created by the bonds. - Different enzymes have different Optimum pH values. This is the pH at which the shape of their active site is the most complementary to the shape of their substrate. - Any changes in pH above or below the optimum will quickly cause a decrease in the rate of reaction. - Small changes in pH above or below the optimum do not cause a permanent change to the enzyme but, extreme changes can cause enzyme to denature and permanently lose their function. ## 3. Concentration - Changing the enzyme and substrate concentrations affects the rate of reaction of an enzyme-catalyzed reaction. - Changing the concentration of a substance only affects the rate of reaction if it is the limiting factor. - If it is the limiting factor, increasing concentration will increase the rate of reaction up to a point, after which any increase will not affect the rate of reaction. - As a reaction proceeds, the rate of reaction will decrease, since the substrate will get used up. - The highest rate of reaction, known as the Initial Reaction Rate is the maximum reaction rate for an enzyme in an experimental situation. - Increasing Substrate Concentration increases the rate of reaction. - However, after a certain concentration, any increase will have no effect on the rate of reaction, since substrate concentration will no longer be the limiting factor. ## 4. Inhibitors - Enzyme inhibitors are substances that alter the catalytic action of the enzyme and subsequently slow down, in some cases, stop catalysis. - There are 3 common types of enzyme inhibition: competitive, non-competitive, and substrate inhibition. # 1.E. Enzyme Immobilization - Process of confining the enzyme molecules to solid support over which a substrate is passed and converted to products. - Immobilized enzyme is one whose movement in space has been restricted either completely or to a small limited region. ## Why Immobilize Enzyme? - Production from degradation and deactivation - Re-use of enzyme for many reaction cycles, lowering the total production cost of enzyme mediated reactions. - Ability to stop the reaction rapidly by removing the enzyme from the reaction solution. - Enhanced stability - Easy separation of the enzyme from the product - Product is not contaminated with the enzyme ## Methods for Immobilization ### A. Physical 1. Adsorption-involves the physical binding of the enzyme on the surface of center matrix. It involves weak interaction like Vander Waal or H-bond. 2. Entrapment - the enzymes or cells are not directly attached to the support surface, but simply trapped inside the polymer matrix. Enzymes are held or entrapped within a suitable gels or fibers. 3. Encapsulation - involves enclosing the enzymes within semi-permeable polymer membranes ### B. Chemical 1. Covalent bonding - binding of enzymes and water-soluble carriers by covalent bonds. 2. Crosslinking-involves intermolecular cross-linking of enzyme molecules in the presence/absence of solid support. ## Limitations of Enzyme Immobilization - Cost of carriers and immobilization - Changes in properties (selectivity) - Mass transfer limitations - Problems with cofactor and regeneration - Problem with multienzyme system - Activity loss during immobilization # 1.F. Application of Enzymes in Food Processing ## 1. Dairy Production - rennet, lactase, protease, catalase ### Rennet - Extracted from the fourth stomach of young calves - Contains enzymes that cause milk to become cheese - It separates solid curd and liquid whey - Different animal rennet is used for different cheese ### Lactase - Present in the brush border of the small intestine - Artificially extracted from yeast - Required for the digestion of whole milk - Used in the production of lactose-free milk - Also used in the production of ice cream and sweetened and condensed milks ### Catalase - Produced from bovine livers or microbial sources - Breaks down hydrogen peroxide to water and molecular oxygen - Along with glucose oxidase it is used in treating food wrappers to prevent oxidation - Also used to remove traces of H2O2 in the process of cold sterilization ### Protease - Widely distributed in the biological world - Hydrolyses the specific peptide bond - Results in bitter flavor to the cheese and also in the desired texture ## 2. Brewing ### Protease - Works to provide the wort with amino acid nutrients that will be used by the yeast. - Breaks larger proteins which enhances the head retention of beer and reduces haze ### B-Glucanase - Represents a group of carbohydrate enzymes which breaks down glycosidic bonds within beta-glucan - Aids in filtration after mashing and brewing ### A-Amylase - Converts starch to dextrins in producing corn syrup - Solubilizes carbohydrates found in barley and other cereals used in brewing. - Decreases the time required for mashing. ### Amyloglucosidase - Optimum pH is 6.5 - Long incubation result in caramelization of the saccharides - resulting in product loss and increase in impurities ## 3. Baking ### Maltogenic amylase - Flour supplement - Anti-staling effect - Modifies starch while most of the starch starts to gelatinize - Resulting starch granules become more flexible during storage ### Glucose oxidase - Oxidizes glucose and produces gluconic acid and H2O2. - H2O2 is strong oxidizing agent that strengthens the disulfide and non-disulfide cross-links in gluten - Good working conditions help proper function of bakery system. ### Pentasanase - Improves dough machinability yielding a more flexible, easier-to-handle dough. - Dough is more stable and gives better oven spring during baking ## 4. Wine and fruit juice ### Pectinase - Prevents pectin from forming haze hence to get a clear solution - Breaks down pectin and releases methanol, which in high amounts is hazardous ### B-Glucanase - It accelerates all biological mechanisms linked to maturation on lees - Reduces maturation duration - Improves clarification and filtration, and improves the action of fining agents ## 5. Meat ### Protease ### Papain - Cleaves the bond that hold the amino acids together - As the enzymes break apart proteins, which disrupts or loosens muscle fibers and tenderizes it. - Found in papaya - 95% of meat tenderizers are available in grocery store are made from papain - It is extracted from the latex in papaya fruits # Unit 2 - BROWNING REACTIONS IN FOODS ## TYPES OF BROWNING REACTION 1. **Enzymatic Browning** - Enzymes are involved in bringing about color change in food. 2. **Non-Enzymatic Browning** - No enzymes are involved in the color change in food. ## 1. Enzymatic Browning - A chemical process which occurs in fruits and vegetables by the enzyme polyphenol oxidase. ## Enzyme-assisted biochemical processes that result in the formation of brown pigments. ### What actually happens in this reaction? Well, when certain fruits and vegetables are cut or bruised, the tissue exposed to the air quickly darkens. ### Why? - Because when the tissue is exposed to O2, phenolic enzymes (phenolases) bring about oxidation of the phenols in the food and brown or grey black pigments called melanins are formed. ### What are melanins? - Melanin is any of the group of brown or black pigments occurring in plants and animals. - Melanin provides color in the skin of humans ### Basic Mechanism - Phenolic substrate acted upon by the enzyme is converted to quinones, which in turn polymerize to form dark brown t-black, insoluble polymers called melanins - Involves a series of biochemical reactions ### Two kinds of PPO enzyme that exist in nature 1. Catechol oxidase - oxidizes o-diphenols to quinones and also hydroxylates monophenols to o-diphenols 2. Laccase - capable of oxidizing both o- and p- diphenols ### Polyphenols - Main component in enzymatic browning - Also called phenolic compounds - Substrate for the browning enzymes - Responsible for the color, taste and flavor ### Types of Polyphenols 1. Anthocyanins (colors in fruits) 2. Flavonoids (catechins, tanins in tea and wine) ### Where can we observe browning in foods? - Fruits (apples, bananas, pears) - Vegetables (potatoes, eggplant, etc.) - Seafoods (shrimps, crabs, lobster) ### Why is Browning Detrimental? - Discolored foods are unappealing and low in consumer acceptance - Directly affects the quality of food (quality indicator) - Limits the shelf life and decreases market value of the product - Contributes to post-harvest losses ## Main cause of enzymatic browning - Handling - Ripening - Storage - Processing of fruits and vegetables ## Browning during storage ### Fruits and Vegetables - During transport and warehouse storage, F&V subjected to mechanical injury (bruising) - Cells are broken, enzyme released, that leads to browning - It contributes to post-harvest losses ### Seafood - Also called melanosis - Common in crustaceans - Leads to discoloration of the shell and the muscle - Decreases the market value of otherwise highly priced products ## Post-harvest Losses - Major concern for developing countries - 50% F&V are wasted every year - Losses that occur between harvest and the moment of human consumption i.e. during handling, transport, storage etc. ## Minimizing Post-Harvest Losses ### Harvesting and Field Handling - Harvesting should be done at cooler parts of the day - Harvesting should be shifted to shade as early as possible ### Packing-House - Harvested crops should reach a packing house - Cleaning, grading, packing etc unit operations are carried out - This concept of packing house can reduce post-harvest losses considerably ### Cold Storage - Cold storage to be set up in F&V producing regions & in major consumption centers - Optimum temperature to be maintained (so as not to cause chill injury) - This also ensures supply round the year ## Benefits - Final product melanin - Has antimicrobial properties, which prevents any infection and inflammation - Antibacterial, antioxidant and anticancer properties - Increase color and flavor like in cocoa, tea, coffee, raisins and prunes ## Disadvantages - Nutritional qualities - Sensory qualities like bad odor, taste and flavor - Unappealing to consumer - Decrease shel life ## Prevention of Enzymatic Browning 1. **Blanching (70-100°C)** - Mild heat treatment for enzyme e=inactivation - Often used as a pre-treatment - Types: - steam blanching - microwave blanching 2. **Refrigeration - prevent spoilage of fruits and vegetables (below 7°C)** 3. **Freezing - stop browning reactions in fruit** 4. **Addition of Acidulants** - Change in pH - pH = 4.0 (+ citric acid and ascorbic acid) - enzyme activity is pH dependent 5. **Dehydration** - freeze drying - removing moisture by sublimation under vacuum (change from solid to gas) - lowering water activity - adding water binding chemicals like salts, sucrose, honey and syrups 6. **Irradiation** - process of killing bacteria and inhibiting enzyme activity using several types of X-rays and gamma rays - food is subjected to ionizing radiations (eg. X-rays, gamma rays) - enzymes are inactivated - low consumer acceptance 7. **High pressure treatment - food is subjected to elevated pressure (500-700 atm)** - High pressures can induce different changes in protein structures, and these changes can activate, inactivate, and modulate different enzymes, consequently affecting their enzymatic activity. 8. **Addition of Inhibitors** - Enzyme inhibitors are substances that alter the catalytic action of the enzyme and consequently slow down, or in some cases, stop catalysis. - reducing agents - sulphiting agents, ascorbic acid, etc. - chelating agents - phosphates, EDTA, organic acids - acidulants - citric acid, phosphoric acid 9. **Treatment with super critical carbon dioxide (SC-CO2)** - SC-CO2 is a fluid CO2 at high pressure - applied to destroy microorganisms - Applied also for enzyme inactivation especially for inactivation of PPO in shrimps, lobsters and potatoes. # 2. Nonenzymatic Browning ## Types of Nonenzymatic Browning 1. Maillard reaction 2. Caramelization 3. Ascorbic acid browning 4. Metal-Polyphenol browning ## Changes during nonenzymatic browning - This changes sometimes are desirable and sometimes undesirable - Produces flavor - Produces color - Produces antioxidant products - Produces toxic products - Loss and destroys nutrients (lysine) - Formation of undesirable products such as HMF (5-hydroxymethylfurfural) ## 1. Caramelization - This reaction leads to brown products when sugars are heated dry or in solution - The large quantities of industrial caramel color that are added to beverages (cola drinks), baked goods, and confections are made by heating high-conversion corn syrups in the presence of catalysts (acids, alkalis, salts) - The chemical transformations involved in caramelization are complex and poorly understood - They include dehydration, fragmentation, and polymerization - On the heating of pentoses, furfural is formed whch polymerizes to brown products. - Heating hexoses results in hydroxymethylfurfural, which polymerizes similarly. ## 2. Ascorbic acid browning - When ascorbic acid is heated in the presence of acid, furfural is formed - The latter, either by itself or after reacting with amino compounds, polymerizes to brown products - Citrus juices, especially their concentrates, develop browning, which has been attributed to ascorbic acid degradation ## 3. Metal-Polyphenol browning - Polyphenolic compounds form complexes with certain metals. The polyphenols of fruits and vegetables most commonly chelate iron. The resulting iron complexes are bluish black pigments. - This darkening is independent of the enzymatic browning that might develop as a result of cutting - The iron of the tissue must first be oxidized to the ferric state for the blackish complex to appear - Canned or pickled cauliflower may turn dark due to the interaction of polyphenols in the tissue with iron from external sources ## 4. Maillard reaction - Maillard reaction is caused by the condensation of an amino group and a reducing compound, resulting in complex changes in biological and food system - This reaction was described for the first time by Louis Maillard in 1912 ### Maillard Reaction Mechanism and Products - This reaction is a series of reactions occurring from the first encounter of carbonyl compound with an amine compound to the formation of brown pigments. - It is also known as the carbonyl-amine reaction, and its brown products are often called melanoidins, indicating their visual similarity to the melanins of enzymatic browning. - The most common carbonyl compounds of foods involved in the Maillard reaction are reducing sugars, and the most common amine compounds are amino acids. - Among sugars, pentoses are more reactive than hexoses, and hexoses are more reactive than reducing disaccharides - When free amino acids react with sugars, lysine appears to be the most active among them. - Maillard reaction occurs when virtually all foods are heated, and also occurs during storage - Maillard reaction form products that are desirable or undesirable - Desirable - Caramel aromas - Golden brown colors - Undesirable - Food darkness - Off-flavor development - Loss of nutrition component (lysine) - The Maillard reaction can seriously lower the nutritive value of the food - Toasting, for example, may reduce to one-half the protein efficiency ratio or bread ### How to measure browning - As the thermal treatment resulted in the increase in colored substances content, which is measured as an increase in absorbance at 420 and 560 nm by reactance colorimetry A420. ### Kinetic of nonenzymatic browning - First order and zero order kinetic models have been used to evaluate the development of non-enzymatic browning. - It is not always possible to apply kinetics as simple as first order or zero order to describe the color changes produced in fruit purees - Since these changes can be due not only to the Maillard reaction but also to the thermal destruction of pigments present in the samples. - First-order kinetics has been suggested for the destruction of natural fruit pigments - Based on data for the deterioration produced by thermal treatments. A two-staged mechanism si propose. - The first stage, color formation, is zero order and the second stage, pigment destruction - First-order kinetics has been suggested for the destruction of natural fruit pigments - Based on the data for the deterioration produced by thermal treatment, a two stage mechanism is proposed: - The first stage, color formation, is zero-order and the second stage, pigment destruction, is first-order - Consequently, an increase in temperature implies a greater increase in color - The kinetic constants for the color formation stage increased in value with increasing temperature ### Controlling Factors of the Maillard Reaction Products - Factors that influence the browning reaction are temperature, pH, moisture level (Aw), oxygen, metals, phosphates, sulfur dioxide, and other inhibitors. - Raising the temperature and/or pH accelerates the Maillard reaction. Intermediate water activity appears to maximize this reaction. - Water Activity (Aw) - Water is produced during Maillard reaction, thus the reaction occurs less readily in foods with a high Aw values while, at low Aw, the mobility of reactants is limited, despite their presence at increased concentrations. ### Prevention of Nonenzymatic Browning - As already indicated, nonenzymatic browning is desirable in certain instances and undesirable in others. - The availability of the reactants and the type of conditions (temperature, pH, moisture) will determine the extent of browning - A chemical preservative often used to inhibit nonenzymatic (and enzymatic) browning is sulfur dioxide. - An obviously way to prevent metal-polyphenol browning is to eliminate contact between susceptible tissues and reactive metals and use inoffensive equipment (stainless steel, glass-lined tanks, etc.) ## Conclusion - Nonenzymatic browning is desirable in some products like bread crust and meat and undesirable in other products like apple. - Types of nonenzymatic browning are caramelization, Maillard reaction, ascorbic acid browning, and metal-polyphenol browning. - The Maillard reaction is actually known as the carbonyl-amine reaction and its brown products are often called melanoidins. The most common carbonyl compounds of foods involved in the Maillard reaction are reducing sugars, and the most common amine compounds are amino acids. - Factors that influence the browning reaction are temperature, pH, moisture level(Aw), oxygen, metals, phosphates, sulfur dioxide, and other inhibitors. # Unit 3- Food Colorants ## Introduction - To understand colorants some terms are defined: - Color - refers to human perception of colored materials-red, green, blue, etc. - Colorant - any chemical, either natural or synthetic, that imparts color. - Pigments - are natural substances in cells and tissues of plants and animals that impart color. - Dyes - are any substances that lend color to materials. - Visible light - referred to as the energy range to which the eye is sensitive - Color is an important characteristic of food because first impression is made based on the color of the food - Color is closely associated with expectations (e.g. will it taste good or not?). - associates certain colors with certain flavors - Addition of color to food is a way to fulfill the expectations ## Why do food have colors? - Foods have color because of their ability to reflect or emit different quantities of energy at wavelengths able to stimulate the retina in the eye. ## Why do we see the specific color of food during day time? - The energy range to which the eye is sensitive is referred to as visible light. - Visible light, depending on an individual's sensitivity, encompasses wavelengths of approximately 380-770 nm. - This range makes up a very small portion of the electromagnetic spectrum In addition to obvious colors (hues), black, white, and intermediate grays are also regarded as colors. ## Colorants exempt from certification may also be used. These are natural pigments or substances synthesized, but identical to the natural pigment. A classification of colorants and an example within each class are given in Table 1. ### Table 1. ### Classification of Colorants | Colorant | Example | |---|---| | A Certified | | | 1. Dye | FD&C Red No. 40 | | 2. Lake | Lake of FD&C Red No. 40 | | B Exempt from certification | | | 1. Natural pigments | Anthocyanin, juice concentrate, annatto extract | | 2. Synthetic (nature identical) | B-Carotene | ## Why Food Colors? - To maintain or improve safety and freshness - To maintain or improve nutritional values - To improve taste, texture and appearance of the product - To influence the consumer to buy a product through visual perception - Colors and appearance are major, if not the most important, quality attributes of foods. - It is because of our ability to easily perceive these factors that they are the first to be evaluated by the consumer when purchasing foods. - One can provide consumers the most nutritious, safest, and most economical foods, but if they are not attractive, purchase will not occur. - The consumer also relates specific colors of foods to quality. - Specific colors of fruits are often associated with maturity-while redness of raw meat is associated with freshness, a green apple may be judged immature (although some are green when ripe), and brownish-red meat as not fresh. - Color also influences flavor perception. - The consumer expects red drinks to be strawberry, raspberry, or cherry flavored, yellow to be lemon, and green to be lime flavored. - The impact of color on sweetness perception has also been demonstrated. - It should also be noted that some substances such as b-carotene or riboflavin are not only colorants but nutrients as well. - It is clear therefore that color of foods has multiple effects on consumers, and it is wrong to regard color as being purely cosmetic. - Many food pigments are, unfortunately, unstable during processing and storage. - Prevention of undesirable changes is usually difficult or impossible. ## Natural Colors - any pigment which when added to food products enhances therapeutic and medicinal properties in it. These are obtained from: seeds, fruits, vegetables, algae, insects, and flowers. ### Types and uses of natural colours | Type | Color | Uses | |---|---|---| | Carmine | Bluish red | Soft drinks, sugar & flavor confectionary pickles, sousages | | Sandal wood | Orange-orange | Fish processing, alcoholic drinks sea food dressings, meat product | | Chlorophyll | red | Soups, fruit products, jams | | Beet powder | Olive green | Frozen ice creams flavored milk | | Turmeric | Bluish red | Yogurt, frozen products pickles | | Riboflavin | Bright yellow | Cereal products, sherbet, ice cream | | Safflower | yellow | Soft drinks alcoholic drinks | ### Types and uses of natural colours | Type | Color | Uses | |---|---|---| | Anthocyanin| Blue-reddish shades | Soft drinks, alcoholic drinks.pickles | | Annatto | Orange shades | Dairy & fat products and desserts | | Beta-carotene | Yellow-orange | Butter, fats oils soft drinks, fruit juices ice Creams | | Canthoxanthin | Orange red-red | Soups meat & fish dishes | | Paprika | Orange-red | Meat products, snack soups.salad | | Saffron | yellow | meat dishes soups | | Leutin | yellow | Ice creams dairy products, sugar, flour. Baked goods, rice dishes | ### Permitted Natural Colours - In India, Rule 26 of The Prevention of Food Adulteration Act, 1954 (PFA) and The Prevention of Food Adulteration Rules, 1955 & 1999 permitted following colours which are isolated from natural sources - Beet root concentrates - Annatto - Beta-carotene - Cochineal Extract - Grape extract - Paprika oleoresin - Turmeric Oleoresin - Luetin - Phycocyanin - Saffron ## LIMITATIONS OF USING NATURAL FOOD COLOUR - Some sources of natural colours have their own flavour which may affect the taste of the finished product. (Turmeric) - Actual colour may not retain as such when subjected to high temperatures. (Grape juice extract) - Can cause allergic reactions (Cochineal extract. Annatto) - Natural food colour are costlier than artificial colourings (Saffron) - At times raw ingredients remains scarce. (Marigold extract) - Require in large quantities when compared to Artificial dyes. (Cochineal extract) ## Factors affecting stability of Pigments 1. presence or absence of light, 2. oxygen, 3. heavy metals, 4. oxidizing or reducing agents, 5. Temperature, 6. water activity; and 7. pH. ## PIGMENTS IN ANIMAL AND PLANT TISSUE 1. HEME COMPOUNDS 2. Chlorophyll 3. Carotenoids 4. Flavonoids and other Phenols 5. betalains ### 1. HEME COMPOUNDS - Responsible for the red pigments in meat - Water-soluble - Heme associates with a protein forming a complex - Myoglobin in muscle tissue - Hemoglobin in red blood cells - The color of meat is mainly due to myoglobin ### Myoglobin/hemoglobin - **Structure of Heme Compounds** - Myoglobin is a globular protein consisting of a single polypeptide chain. - Its molecular mass is 16.8 kD - and it is comprised of 153 amino acids. - This protein portion of the molecule is known as globin. - The chromophore component responsible for light absorption and color is a porphyrin known as heme. - Within the porphyrin ring, a centrally located iron atom is complexed with four tetrapyrrole nitrogen atoms. - Thus, myoglobin is a complex of globin and heme. - The heme porphyrin is present within a hydrophobic pocket of the globin protein and bound to a histidine residue - The centrally located iron atom shown possesses six coordination sites, four of which are occupied by the nitrogen atoms within the tetrapyrrole ring. - The fifth coordination site is bound by the histidine residue of globin, leaving the sixth site available to complex with electronegative atoms donated by various ligands. - Hemoglobin consists of four myoglobins linked together as a tetramer. - Hemoglobin, a component of red blood cells, forms reversible complexes with oxygen in the lung. - This complex is distributed via the blood to various tissues throughout the animal where oxygen is absorbed. - It is the heme group that binds molecular oxygen. - Myoglobin within the cellular tissue acts in a similar fashion, accepting the oxygen carried by hemoglobin. - Myoglobin thus stores oxygen within the tissues, making it available for metabolism ### Chemistry and Color-Oxidation - Meat color is determined by the - chemistry of myoglobin, - its state of oxidation, - type of ligands bounds to heme, and - state of the globin protein. - The heme iron within the porphyrin ring may exist in two forms: either reduced ferrous (+2) or oxidized ferric (+3). - This state of oxidation for the iron atom within heme should be distinguished form oxygenation of myoglobin. - When molecular oxygen binds to myoglobin, oxymyoglobin (MbO₂) is formed and this is referred to as oxygenation. - When oxidation of myoglobin occurs, the iron atom is converted to the ferric (+3) state, forming metmyoglobin (MMb). Heme iron in the +2 (ferrous) state, which lacks a bound ligand in the sixth position, is called myoglobin. - Meat tissue that contains primarily myoglobin (also referred to as deoxymyoglobin) is purplish-red in color. - Binding of molecular oxygen at the sixth ligand yields oxymyoglobin (MbO2) and the color of the tissue changes to the customary bright red. - Both the purple myoglobin and the red oxymyoglobin can oxidize, changing the state of the iron from ferrous to ferric. - If this change in state occurs through autooxidation, these pigments acquire the undesirable brownish-red color of metmyoglobin (MMb). - In this state, metmyoglobin is not capable of binding oxygen and the sixth coordination position is occupied by water. - Color reactions in fresh meat are dynamic and determined by conditions in the muscle and the resulting ratios of myoglobin (Mb), metmyoglobin (MMb), and oxymyoglobin (MbO2). - Interconversion among these forms can occur readily ### Chemistry and Color-Discoloration - Two different reactions can cause green discoloration of myoglobin. - Hydrogen peroxide - react with either the ferrous or ferric site of heme, resulting in choleglobin (a green-colored pigment). - Presence of hydrogen sulfide and oxygen, can form green sulfomyoglobin. - It is thought that hydrogen peroxide and/or hydrogen sulfide arise from bacterial growth. A third mechanisms for green pigmentation occurs in cured meats and is mentioned later. ## 2. Chlorophyll - Fat-soluble pigments in all green plants - Fruits (particularly when it is unripe) - Vegetables (peas, broccoli, spinach) ## The least studied of the food pigments. ## Their complex structure is difficult to stabilize thus, it is the main drawback of their use in the industry. - Among the five different chlorophylls that exist, only (a) and (b) are used in the food industry as colorants. - a. Chlorophyll a - Bluish green - a. Chlorophyll b - Yellowish green ## 3. Carotenoids - A group of fat-soluble pigments red, orange, and yellow. - The most widespread natural pigments - Abundant in yellow/orange fruits and vegetables - All green leafy vegetables contain carotenoids but their color is masked with green chlorophylls - in animal tissue, eggyolk, salmon, shrimp ### A. B-carotene - The most abundant carotenoids in plants. (carrot, orange, pumpkin, sweet potato, squash) ### B. Lycopene - Red color (tomato, watermelon) - Processed tomato products are more available dietary sources of lycopene than fresh tomatoes ### C. Capsaicin - Red pepper ### D. Lutein (xanthopyll) - Yellow pigment (mango, papaya, cabbage, kale, kiwi) ### E, Bixin - Orange yellow very stable (annatto seed) ## 4. Flavonoids and other Phenols - Water-soluble plant pigments that have antioxidant and anti-inflammatory and impart a yellow color. - Common Flavonoids are - Catechin (in strawberry & green/black teas) - Kaempferol (brussels sprouts and apples) - quercetin (beans, onion skin, apples