Food Chemistry: Proteins PDF

CHT413A: FOOD CHEMISTRY Proteins Compiled by: Lowela C. Villarias  Proteins  Introduction: Important constituents of food include amino acids, peptides and proteins which supplies the necessary building blocks for biosynthesis of protein. They contribute to dev...

CHT413A: FOOD CHEMISTRY Proteins Compiled by: Lowela C. Villarias  Proteins  Introduction: Important constituents of food include amino acids, peptides and proteins which supplies the necessary building blocks for biosynthesis of protein. They contribute to development of flavors of food products during thermal processing, production and storage. Proteins also contribute to physical properties of food through their ability to form stabilize gels, foams, emulsions and fibrillar structures.  Amino Acids Peptides Proteins are simple organic compounds consisting of are highly complex compounds containing two or more amino acids polymers made up of 20 both amino (NH2-) and linked in a chain, the different amino acids carboxyl (-COOH) carboxyl group of each joined together by group, along with side acid being joined to the peptide bonds. chains specific for each amino group of the next The variation of side amino acid, joined by a bond of the type - chains that occur during together by peptide OC-NH amino acid linkage bonds to form the results in different primary structure of proteins to have proteins differences in chemical properties and widely different secondary and tertiary structures.  Amino Acids and their corresponding structure and name abbreviation Only half of the 20 amino acids are essential for human nutrition and the amount of these essential amino acids present determines the nutritional quality of proteins. Generally animal proteins are of higher quality than plant proteins. Egg protein is one of the best quality proteins widely used as a standard having biological value of 100 (protein efficiency ratio (PER) values uses egg white as standard. https://www.biochempages.com/memorize-structures-20-amino-acids-simple-way/ Nine amino acids are not synthesized by mammals and are therefore dietarily essential or indispensable nutrients. These are commonly called the essential amino acids. Histidine isoleucine Leucine lysine methionine phenylalanine Threonine Tryptophan valine  Protein Classification Simple Proteins yield only amino acid on hydrolysis  Classes of Simple Proteins 1. Albumins – usually with relatively low molecular weight proteins and are soluble in neutral, salt-free water. Examples: egg albumin, lactalbumin and 5. Scleroproteins – are fibrous proteins which have a serum albumin structural and binding purpose, insoluble in water and neutral 2. Globulins – soluble in neutral salt solutions and solvents and resistant to enzymatic hydrolysis. Examples: insoluble in water. Examples: serum globulins and collagen in muscle tissue, elastin a component of tendons, β-lactoglobulin in milk, myosin and actin in meat keratin component of hair and hoofs. and glycinin in soybeans 6. Histones – these are basic proteins defined by their high 3. Glutelins – insoluble in neutral solvents but are content of lysine and arginine, soluble in water and soluble in very dilute acid or base Example: precipitated by ammonia glutenin in wheat and oryzenin in rice 7. Protamines – strongly basic proteins of low molecular 4. Prolamins – soluble in 50 to 90 percent ethanol and weights (4000 to 8000) and are rich in arginine. Example: insoluble in water; contains large amount of proline clupien from herring and scrombrin form mackerel and glutamic acid found in cereals. Example: zein in corn, gliadin in wheat, hordein in barley  Protein Classification Conjugated Proteins contain an amino acid part combined with a non- protein material such as lipid, nucleic acid or carbohydrates  Classes of Major Conjugated Proteins 1. Phosphoproteins – an important group that contains many major food proteins, phosphate groups are linked to the hydroxyl group of serine and threonine. Example: casein in milk and phosphoproteins of egg yolk 2. Lipoproteins - combination of lipids with proteins and have excellent emulsifying capacity usually occurs in milk and egg yolks 3. Nucleoproteins – these are compounds found in cell nuclei composed of combinations of nucleic acids with proteins 4. Glycoproteins – these are combinations of carbohydrates with proteins, usually carbohydrates amount is small but some glycoproteins contain 8 to 20 percent carbohydrates. Example: ovomucin of egg white 5. Chromoproteins – proteins with colored prosthetic groups, compounds of this type includes hemoglobin, myoglobin, chlorophyll and flavoproteins  Protein Classification Derived Proteins these are compounds obtained by chemical or enzymatic methods. Depending on the extent of change that has taken place this can be classified into primary and secondary derivative which differ in breakdown products’ size and solubility. All are soluble in water and not coagulated by heat, but proteoses can be precipitated with ammonium sulfate solution. 1. Primary derivatives - are slightly modified and are insoluble in water  Example: rennet-coagulated casein 2. Secondary derivative – are extensively changed  Includes proteoses, peptones and peptides DENATURATION  is a process that changes the molecular structure without breaking any of the peptide bonds of a protein  can also be defined as major change in the native structure without alteration of the amino acid sequence  This process is special to proteins and affects different proteins to different degrees depending on the protein structure  Agents that brought about protein denaturation are heat, pH, salts and surface effects  involves loss of biological activity and significant changes in some physical or functional properties such as solubility and most of the time nonreversible  Protein denaturation application to food industry  Destruction of enzymes by heating – application to soy sauce manufacturing  Egg white proteins are readily denatured by heating and also by surface forces when egg white is whipped to foam  Denaturation of whey proteins during the production of skimmed milk powder  Meat proteins denaturate at 57 to 75°C thereby affecting texture, water holding capacity and shrinkage NON-ENZYMATIC BROWNING  Includes Maillard reaction and caramelization  could be desirable or undesirable depending on the product it  The browning rection can be defined as the sequence of events that starts with the reaction of the amino group of amino acids, peptides or proteins with the glycosidic hydroxyl group of sugars  the sequence is terminated with the formation of brown nitrogenous polymers or melanoidins (Ellis 1959)  lysine is the most reactive amino acid because of the free Ɛ-amino group, and many food proteins contains this limiting essential amino acid  Chemical Changes involving Protein in Food  Various chemical reactions involving protein occurs during processing and storage of foods  Changes that occur could either be desirable to some and undesirable to others Examples of desirable changes: Examples of undesirable changes: 1. Sulfur-containing amino acids may become more 1. Some chemical changes lead to formation of available and certain antinutritional factors such as compounds that are non-hydrolyzable by intestinal the trypsin inhibitors of soybeans may be enzymes deactivated. 2. Excessive heat in the absence of water can be 2. Mild heat treatments in the presence of water can detrimental to protein quality; for example, in fish significantly improve the protein's nutritional value proteins, tryptophan, arginine, methionine, and in some cases. lysine may be damaged. 3. Light-induced oxidation of proteins has been shown to lead to off-flavors and destruction of essential amino acids in milk. Patton (1954) demonstrated that sunlight attacks methionine and converts it into methional (3- methylmercaptopropionaldehyde) Functional Roles of Food Proteins in Food Systems END OF PRESENTATION Subject: CHT 413A Food Chemistry Compiled by: Lowela Villarias Carbohydrates The term carbohydrates goes back to times when it was thought that all compounds of this class were hydrates of carbon Types of macronutrients found in certain food and drinks Included in this group are sugars, starches and fibers Important source of energy Of great importance in balanced daily nutrition Also referred to as saccharides (derived from the term saccharose which means cane sugar)  Monosaccharides - simplest or smallest form of carbohydrates Disaccharides – formed by two Classification molecules of simple sugar of Oligosaccharides – contains 3 to 10 Carbohydrates single sugar residue Polysaccharides – large molecule made of many smaller monosaccharides Monosaccharides Simplest or smallest form of carbohydrates Cannot be broken down by hydrolysis into smaller or simpler units Commonly known as simple sugars general formula for (CH2O)n COMMON MONOSACCHARIDES Glucose Provides structure and energy to many organisms Glucose molecules can be broken down in glycosis, providing energy and precursors for cellular respiration. Most abundant monosaccharide If consumed in excess, it will be stored as glycogen Fructose Same formula with glucose but with different structure Entirely metabolized in the liver, with enzyme fructokinase Fructose is a ketose Galactose Produced in many organism especially mammals Galactose in milk from mothers give energy to their offspring Monosaccharide found in peas An aldose, hexose and is a reducing sugar  Disaccharides Also known as double sugar , formed by two monosaccharides Commonly have 12 carbon atoms with formula C12H22O11 Formed by dehydration reaction LV1 of two monosaccharides Slide 6 LV1 Lowela Villarias, 13/10/2021 COMMON DISACCHARIDES Sucrose Commonly known as table sugar in its refined form Important component in human diet as sweetener Maltose Also known as malt sugar Formed from two glucose molecules In plants maltose is formed when starch is broken down for food Lactose Or milk sugar Is made up of galactose and glucose Provides nutrients for the infants Lactose intolerance – inability of adults to digest dairy products Other less common disaccharide includes Trehalose, Lactulose, Cellobiose, and Chitobiose Oligosaccharides Polymers of monosaccharides whose number of units in a glycosidic chain is in range of 2 to 10 significant source of energy as well as structural elements classified according to the number of monosaccharides in an oligosaccharide chain. CLASSIFICATION OLIGOSACCHARIDES Classification Number of Monosaccharides trisaccharide 3 tetrasaccharide 4 pentasaccharide 5 hexasaccharide 6 heptasaccharide 7 octasaccharide 8 nonasaccharide 9 decasaccharide 10 Polysaccharides also called glycan is a large molecule made of many smaller monosaccharides. significant source of energy as well as structural elements Special enzymes bind these small monomers together creating large sugar polymers, or polysaccharides.  Glycogen Classification of Polysaccharides According to Composition Homopolysaccharide – composed of the same monosaccharides e.g. Starch and Glycogen Heteropolysaccharide – composed of varying monosaccharides e.g hyaluronic acid (D-gluconic acid and N-acetyl-D-glucosamine) Depending on which monosaccharides are connected, and which carbons in the monosaccharides connects, polysaccharides take on a variety of forms. Linear polysaccharide – straight chained polysaccharides e.g Cellulose Branched polysaccharide - while a chain that has arms and turns Cellulose e.g Glycogen FUNCTIONS OF POLYSACCHARIDES Energy Storage and Energy Production If the body already has enough energy to support its functions, the excess glucose is stored as glycogen (the majority of which is stored in the muscle and liver), similar to starch in plants. A molecule of glycogen may contain in excess of fifty thousand single glucose units and is highly branched, allowing for the rapid dissemination of glucose when it is needed to make cellular energy The primary role of carbohydrates is to supply energy to all cells in the body. Many cells in the body like red blood cells and the brain are only able to produce cellular energy from glucose. Cellular Communication Polysaccharides become glycoconjugates when they become covalently bonded to proteins or lipids and these glycolipids and glycoproteins can be used to send signals between and within cells. Cellular Support Cellulose is the primary support molecule in plants, while fungi and insects rely on chitin. COMMON POLYSACCHARIDES Cellulose and Chitin both structural polysaccharides with long linear chains that consist of many thousand glucose monomers combined in long fibers only difference between the two polysaccharides are that side-chains attached to the carbon rings of the monosaccharides cellulose can produce hard structures like wood, chitin can produce even harder structures, like shell, limestone and even marble when compressed. Glycogen and Starch most important storage polysaccharides on the planet, glycogen and starch are produced by animals and plants, respectively Glycogen is made up of only one molecule while starch is made up of two Glycogen has a branched structure while starch has both chain and branched components. Reactions Involving Saccharides Mutarotation – When a crystalline reducing sugar Non-enzymatic Browning – also called Millard is placed in water, an equilibrium is established reaction, it is the browning of foods on heating or between isomers, as is evidenced by a relatively on storage and is usually due to a chemical reaction slow change in specific rotation that eventually between reducing sugars, mainly D-glucose, and a reaches the final equilibrium value free amino acid or a free amino group of an amino acid that is part of a protein chain. Crystallization – one of the important characteristics of sugar is the formation of crystals. Caramelization – formation of caramel pigment, It is an important step in the purification of sugar can be considered a nonenzymatic browning in the during commercial production. In certain foods absence of nitrogenous compounds. As the process crystallization is undesirable, such as the occurs, volatile chemicals are released producing crystallization of lactose in sweetened milk or ice the characteristic caramel flavor. The reaction cream. involves the removal of water (as steam) and the break down of the sugar.  Caramelization Caramelization process 1. When heated sugar melts followed by foaming or boiling where steam is released Sucrose first decomposes to fructose and glucose during dehydration 2. Followed by condensation step when individual sugar loses water and reacts with each other hence the formation of hundreds of new aromatic compounds with range of complex flavors. Flavors of Caramel Diacetyl (2,3-butanedione) is an important flavour compound, produced during the first stages of caramelization. Diacetyl is mainly responsible for a buttery or butterscotch flavour. Esters and lactones which have a sweet rum like flavor. Furans which have a nutty flavor. Maltol has a toasty flavor.  Carbohydrates in Food Industry Three Main Types of Carbohydrates SUGARS - simple carbohydrates because they are in the most basic form - added to foods as sweeteners to candies, desserts, processed foods, and softdrinks - also include the kinds of sugar that are found naturally in fruits, vegetables, and milk STARCHES - complex carbohydrates - main ingredients in baked products such as bread, cereal, and pasta - also include certain vegetables, like potatoes, peas, and corn - have wide applications as stabilizers, texturizers, anti-caking agents etc. FIBERS - complex carbohydrates - Your body cannot break down most fibers, so eating foods with fiber can help you feel full and make you less likely to overeat, helps prevent constipation, lower cholesterol and blood sugar - is found in many foods that come from plants, including fruits, vegetables, nuts, seeds, beans, and whole grains Carbohydrates in Food Industry Starch Hydrolyzates (Corn Sweeteners) – variety of starches coming from corn, wheat, potato High Fructose Corn Syrup and cassava are hydrolyzed by DE 42-55 acids or enzymes or combination treatments. Maltodextrin DE 40°C the enzymatic activity because of protein denaturation https://www.evolvingsciences.com/Graphs%20and%20Factors%20.html SPECIFICITY  In an enzyme reaction the substrate combines with holoenzyme and is released in a modified form  The nature of each enzyme- substrate reaction requires that each enzyme reaction is highly specific  The shape, size, active site, and substrate are important  Types of specificity: - group - bond - stereo - absolute specificity - combination of the given above  Enzymes are classified by the Commission on Enzymes of the International Union of Biochemistry Classified according to groups of the type of reaction they catalyze Enzymes can be named in three ways 1. systematic name - α-1,4-glucan-4-glucanohydrolase 2. trivial name – α-amylase 3. Enzyme Commission number - EC3.2.1.1  Traditionally used industrial enzymes are prepared from plant and animal sources e.g. Rennet and Papain  developments have made it possible to synthesize microbial enzymes microbial enzymes are heat stable and have broader pH optimum