GIÁO TRÌNH ANH VĂN CHUYÊN NGHÀNH CÔNG NGHỆ THỰC PHẨM

HoChiMinh University of Industry - Institute of Biotechnology & Food Technology UNIT 1: WHAT IS FOOD SCIENCE? Food Science and Technology is a convenient name used to describe the application of scientific principles to create and maintain a wholesome food supply Food Science has given us frozen foods, canned foods, microwave meals, milk which does not need refrigeration, easily prepared traditional foods and, above all, variety in our diets The Food Scientist learns and applies a wide range of scientific knowledge to maintain a high quality, abundant food supply Food Science allows us to make the best use of our resources in a sustainable manner and minimize waste To be a Food Scientist and help handle the world's food supply to maximum advantage, you need some familiarity in a number of disciplines including the application of microbiology, chemistry, aspects of biochemistry and some specialized statistics The investigation of how biological materials behave in harvesting, processing, distribution, storage and preparation is complex and full awareness of all important aspects of the problem requires broad-based training With the special training in the applied science known as Food Science, a wide range of employment opportunities exist for the trained professional Examples include the Product Development Specialist, Sensory Scientist, Quality Control and Quality Assurance Specialist, Technical Sales Specialist, Research and Development Scientist, Marketing, Consumer Behavior and Management to name a few Food Science can lead to many exciting and productive careers A number of interesting and unique options in the Food Science and Technology program include: Food Processing Product Development Food Chemistry Food Microbiology Food Quality Management Biochemistry Marketing and Consumer Behavior Human Resource Management and Industrial Relations Asian Studies Business Management Why does there seem to be so much chemistry in Food Science? What if I haven't done well in this subject before? Food Science requires about the same amount of basic science as other science programs The difference is that in Food Science every student gets an exposure to a wide range of scientific disciplines and has a chance to succeed in more areas The chemistry you study in the program is not pure chemistry but applied chemistry e.g in studying the formation of alcohol during a wine fermentation or the flavor components of coffee Food Science classes then allow the student to apply those basic ideas learned in general science classes QUESTIONS What you know about Food Science and Technology? As a Food Scientist, what specialized subjects you need apply? After the training course in Food Science, what jobs can you get? List some options in the Food Science and Technology program Is it right if chemistry that you study in the program is pure chemistry? oooOooo -Specialized English in Food Science and technology -1- HoChiMinh University of Industry - Institute of Biotechnology & Food Technology UNIT 3: CARBOHYDRATES Carbohydrates make up a group of chemical compounds found in plant and animal cells They have the empirical formula CnH2nOn, or (CH2O)n An empirical formula tells the atomic composition of the compound, but nothing about structure, size, or what chemical bonds are present Since this formula is essentially a combination of carbon and water, these materials are called ―hydrates of carbon‖, or carbohydrates for short Carbohydrates are the primary products of plant photosynthesis The simplified light-driven reaction of photosynthesis results in the formation of a carbohydrate: nH2O+ nCO2 -(CH2O)n- + nO2 This type of carbohydrate is found in the structures of plants and is used in the reverse reaction of photosynthesis (respiration) or is consumed as fuel by plants and animals Carbohydrates are widely available and inexpensive, and are used as an energy source for our bodies and for cell structures Food carbohydrates include the simple carbohydrates (sugars) and complex carbohydrates (starches and fiber) Before a big race, distance runners and cyclists eat foods containing complex carbohydrates (pasta, pizza, rice and bread) to give them sustained energy Carbohydrates are divided into monosaccharides, disaccharides, and polysaccharides Monosaccharides Monosaccharides are single-molecule sugars (the prefix ―mono‖ means one) that form the basic units of carbohydrates They usually consist of three to seven carbon atoms with attached hydroxyl (OH) groups in specific stereochemical configurations The carbons of carbohydrates are traditionally numbered starting with the carbon of the carbonyl end of the chain (the carbonyl group is the carbon double-bonded to oxygen).The number of carbons in the molecule generally categorizes monosaccharides For example, three-carbon carbohydrate molecules are called trioses, five-carbon molecules are called pentoses, and six-carbon molecules are called hexoses One of the most important monosaccharides is glucose (dextrose) This molecule is the primary source of chemical energy for living systems Plants and animals alike use this molecule for energy to carry out cellular processes Mammals produce peptide hormones (insulin and glucagon) that regulate blood glucose levels, and a disease of high blood glucose is called diabetes Other hexoses include fructose (found in fruit juices) and galactose Different structures are possible for the same monosaccharide Although glucose and fructose are identical in chemical composition (C6H12O6), they are very different in structure Such materials are called isomers Isomers in general have very different physical properties based on their structure Disaccharides Disaccharides are two monosaccharide sugar molecules that are chemically joined by a glycosidic linkage (- O -) to form a ―double sugar‖ (the prefix ―di‖ means two) When two monosaccharide molecules react to form a glycosidic bond (linkage), a water molecule is generated in the process through a chemical reaction known as condensation Therefore, condensation is a reaction where water is removed and a polymer is formed The most well known disaccharide found in nature is sucrose, which is also called cane sugar, beet sugar, or table sugar Sucrose is a disaccharide of glucose and fructose Lactose or milk sugar is a disaccharide of glucose and galactose and is found in milk Maltose is a disaccharide composed of two glucose units Disaccharides can easily be hydrolyzed (the reverse of condensation) to become monosaccharides, especially in the presence of enzymes (such as the digestive enzymes in our intestines) or alkaline catalysts Invert sugar is created from the hydrolysis of sucrose into glucose and fructose Bees use enzymes to create invert sugar to make honey Taffy and other invert sugar type candies are made from sucrose using heat and alkaline baking soda Specialized English in Food Science and technology -2- HoChiMinh University of Industry - Institute of Biotechnology & Food Technology Disaccharides are classified as oligosaccharides (the prefix ―oligo‖ means few or little) This group includes carbohydrates with to 20 saccharide units joined together Carbohydrates containing more than 20 units are classified as polysaccharides Polysaccharides Polysaccharides (the prefix ―poly‖ means many) are formed when many single sugars are joined together chemically Carbohydrates were one of the original molecules that led to the discovery of what we call polymers Polysaccharides include starch, glycogen (storage starch in animals), cellulose (found in the cell walls of plants), and DNA Starch is the predominant storage molecule in plants and provides the majority of the food calories consumed by people worldwide Most starch granules are composed of a mixture of two polymers: a linear polysaccharide called amylose and a branched-chain polysaccharide called amylopectin Amylopectin chains branch approximately every 20-25 saccharide units Amylopectin is the more common form of starch found in plants Animals store energy in the muscles and liver as glycogen This molecule is more highly branched than amylopectin For longer-term storage, animals convert the food calories from carbohydrates to fat In the human and animals, fats are stored in specific parts of the body called adipose tissue Cellulose is the main structural component of plant cell walls and is the most abundant carbohydrate on earth Cellulose serves as a source of dietary fiber since, as explained below, humans not have the intestinal enzymes necessary to digest it Starch and cellulose are both homopolymers (―homo‖ means same) of glucose The glucose molecules in the polymer are linked through glycosidic covalent bonds There are two different stereochemical configurations of glycosidic bonds—an alpha linkage and a beta linkage The only difference between the alpha and beta linkages is the orientation of the linked carbon atoms Therefore, glucose polymers can exist in two different structures, with either alpha or beta linkages between the glucose residues Starch contains alpha linkages and cellulose contains beta linkages Because of this difference, cornstarch has very different physical properties compared to those for cotton and wood Salivary amylase only recognizes and catalyzes the breakdown of alpha glycosidic bonds and not beta bonds This is why most mammals can digest starch but not cellulose (grasses, plant stems, and leaves) Food Uses of Carbohydrates Carbohydrates are widely used in the food industry because of their physical and chemical properties The sweet taste of sucrose, glucose, and fructose is used to improve the palatability of many foods Lactose is used in the manufacture of cheese food, is a milk solids replacer in the manufacture of frozen desserts, and is used as a binder in the making of pills/tablets Another useful aspect of some carbohydrates is their chemical reducing capability Sugars with a free hemiacetal group can readily donate an electron to another molecule Glucose, fructose, maltose, and lactose are all reducing sugars Sucrose or table sugar is not a reducing sugar because its component monosaccharides are bonded to each other through their hemiacetal group Reducing sugars react with the amino acid lysine in a reaction called the Maillard reaction This common browning reaction produced by heating the food (baking, roasting, or frying) is necessary for the production of the aromas, colors, and flavors in caramels, chocolate, coffee, and tea This non-enzymatic browning reaction differs from the enzymatic browning that occurs with fresh-cut fruit and vegetables, such as apples and potatoes Carbohydrates can protect frozen foods from undesirable textural and structural changes by retarding ice crystal formation Polysaccharides can bind water and are used to thicken liquids and to form gels in sauces, gravies, soups, gelatin desserts, and candies like jelly beans and orange slices They are also used to stabilize dispersions, suspensions, and emulsions in foods like ice cream, infant formulas, dairy desserts, creamy salad dressings, jellies and jams, and candy Starches are used as binders, adhesives, moisture retainers, texturizers, and thickeners in foods Specialized English in Food Science and technology -3- HoChiMinh University of Industry - Institute of Biotechnology & Food Technology QUESTIONS: What are monosaccharides? What is the most important monosaccharides? What is its role? Explain the term isomers What are disaccharides? Give some examples of disaccharides How is invert sugar created? What are polysaccharides? Give some examples of polysaccharides What are starch granules composed of? Can human digest starch or cellulose? Why? What are the important roles of carbohydrates in food processing? oooOooo UNIT 4: PROTEINS Proteins are the most complex and important group of molecules because they possess diverse functionality to support life Every cell that makes up plants and animals requires proteins for structure and function Enzymes, specialized proteins, catalyze chemical reactions that are necessary for metabolism and cell reproduction Our muscles are made from a variety of proteins, and these proteins allow our muscles to contract, facilitating movement Other types of proteins in our body are the peptide hormones; insulin and glucagon are two common examples Proteins are complex polymers composed of amino acids Amino acids contain carbon, hydrogen, nitrogen, and sometimes sulfur and serve as the monomers for making peptides and proteins Amino acids have a basic structure that includes an amino group (NH2) and a carboxyl group (COOH) attached to a carbon atom This carbon atom also has a side chain (an ―R‖ group) This side chain can be as simple as an -H or a -CH3, or even a benzene group There are twenty amino acids found in the body Eight of these amino acids are essential for adults and children, and nine are essential for infants Essential means that we cannot synthesize them in adequate quantities for growth and repair of our bodies, and therefore, must be included in the diet Amino acids are linked together by a peptide bond in which the carboxyl carbon of one amino acid forms a covalent bond with the amino nitrogen of the other amino acid Short chains of amino acids are called peptides Longer chains of amino acids are called polypeptides Although the term polypeptides should include proteins, chains with less than 100 amino acid residues are considered to be polypeptides, while those with 100 or more amino acid residues are considered to be proteins Many of the major hormones in the body are peptides These hormones can influence enzyme action, metabolism, and physiology Certain antibiotics and a few anti-tumor agents are also peptides The artificial sweetener aspartame is a dipeptide composed of aspartic acid and phenylalanine with a methyl group attached at the carboxyl terminal group (L-aspartyl-L-phenylalanine methyl ester) The sequence of amino acid residues in a polypeptide chain is critical for biological function A single structural change resulted in a dramatic alteration in physiological function The ability of an enzyme to catalyze a particular reaction depends on its specific shape It’s a lot like a key and lock; if the key is broken or in a different shape, it won’t open the lock The receptor sites on cell surfaces must be in a specific shape for polypeptide hormones to interact with the cell With twenty different amino acids and each polypeptide consisting of hundreds of amino acids, it is no wonder that proteins play such a variety of roles in the human body Chemistry of Proteins Specialized English in Food Science and technology -4- HoChiMinh University of Industry - Institute of Biotechnology & Food Technology The protein backbone is formed from the peptide bonds created from the amino and carboxyl groups of each monomer that repeat the pattern -N-C-C- or C-C-N- The number and sequence of amino acids in a polypeptide chain is referred to as the primary structure of a protein The free amino group and carboxyl group on opposite ends of a polypeptide chain allow proteins to act as pH buffers (resist changes in pH) inside the cell The amino group (NH2) accepts a proton and becomes (NH3+ ), and the carboxyl group (COOH) donates a proton and becomes dissociated (COO-) As noted previously, each amino acid residue in the polymer may have a different side chain or chemical group attached to it, such as hydroxyl (OH), amino (NH2), aromatic ring (conjugate rings such as the phenol ring in phenylalanine), sulfhydryl (SH), carboxyl (COOH), or various alkyl (CHn) This variety of side chain groups on the polymer backbone gives proteins remarkable chemical and physical properties For example, carboxylate groups can function as carboxylic acids (COO-), or amino groups can behave as bases (NH3+) This allows protein polymers to be multifunctional molecules, with both acidic and basic behavior at the same time! Additionally, the presence of hydroxyls, carboxylates, sulfhydryls, and amino groups allows hydrogen bonding, and the alkyl groups provide hydrophobic interactions, both within the protein polymer itself and between separate protein molecules In the case of macromolecules, such as proteins, the polymeric structure of the macromolecule allows it to simultaneously carry many different charges (on different amino acid residues) However, unlike the small single molecules, the amino acid residues are constrained by linear peptide linkages and thus cannot move freely to randomly associate with other charged molecules Assuming that charged residues will seek to bond with the nearest convenient counter ion, it is most likely that oppositely charged amino acid residues located at different points within a single protein chain will bond These structural differences result in the folding of proteins into a three-dimensional structure, which is, in part, responsible for their functional properties as biocatalysts, structural materials, muscles, and chemical receptors Proteins can be shaped as long flat sheets or in globular spheres This leads to the names fibrous or globular for protein shapes Most enzymes are globular proteins In standard acid base chemistry, we know that molecules carry electrostatic charges based on the type of atoms that make up a molecule and the environment of the molecule Given that opposite charges attract, cationic and anionic atoms can combine to form covalent bonds, in which electrons are shared between atomic orbitals, or form ionic bonds, in which only electrostatic attractions exist In solution with smaller molecules, such as HCl (an acid) or NaOH (a base), protein molecules can freely move around and associate with each other on a more-or-less random basis Protein polymers extend the simple acid base charged chemical species concepts to explain how biological systems have greater levels of complexity and can utilize simple, monomeric chemical structures (like amino acids) to create exquisitely complex biological structures like antibodies, muscle, and skin Protein polymers have physical structure, even when dissolved in liquids The charged and hydrophobic residues within a protein tend to associate, causing the protein to fold up When you unfold the protein molecule (called denaturation), its charged residues can reassociate with other charged molecules (precipitation or coagulation) Protein precipitation is widely used to recover recombinant protein products, enzymes, or in the production of many common foods Cheeses and soybean tofu are examples of coagulated protein food products Food Uses of Proteins Proteins also serve important roles in the processing of food products They are used for their thickening, gelling, emulsifying, and water-binding properties in meats (sausages), bakery products, cheese, desserts, and salad dressings Proteins are used for their cohesive and adhesive properties in sausage making, pasta, and baked goods Egg proteins are used for their foaming properties in desserts, cakes, and whipped toppings Milk, egg, and cereal proteins are used as fat and flavor binders in low-fat bakery products Proteins are used for texture and palatability in bakery products (breads, cakes, crackers, and pizza crust) and sausages Specialized English in Food Science and technology -5- HoChiMinh University of Industry - Institute of Biotechnology & Food Technology Milk protein consists of 80% casein and 20% whey proteins There are four major types of casein molecules: alpha-s1, alpha-s2, beta, and kappa Milk, in its natural state, is negatively charged The negative charge permits the dispersion of casein in the milk When an acid is added to milk, the H+ concentration neutralizes the negatively charged casein micelles When milk is acidified to pH 4.7, the isoelectric point (the point at which all charges are neutral) of casein, an isoelectric precipitate known as acid casein is formed Cottage cheese and cream cheese manufacture involves an acid precipitation of casein with lactic acid or lactic acid producing microorganisms Acid casein is used in the chemical industry and as a glazing additive in paper manufacturing Casein also can be coagulated with the enzyme rennin, which is found in rennet (an extract from the stomach of calves) Rennin works best at body temperature (37°C) If the milk is too cold, the reaction is very slow, and if the milk is too hot, the heat will denature the rennin, rendering it inactive The mechanism for the coagulation of the casein by the rennin is different from the acid precipitation of casein The rennin coagulum consists of casein, whey protein, fat, lactose, and the minerals of the milk, and has a fluffier and spongier texture than the acid precipitate Rennet is used in the manufacture of cheese and cheese products, and rennet casein is used in the plastics industry Casein is solubilized with sodium hydroxide and calcium hydroxide to produce sodium caseinate and calcium caseinate, respectively Caseinates are added to food products to increase their protein content and are key ingredients in non-dairy coffee creamers Approximately 90% of soybean proteins are classified as globulins, based on their solubility in salts More specifically, the proteins are conglycinin (a glycoprotein) and glycinin Tofu is manufactured by coagulating the proteins in soymilk with magnesium sulfate As bonding occurs between the positively charged magnesium ions and negatively charged anionic groups of the protein molecules, the proteins coagulate QUESTIONS What are proteins? Why are proteins important group of molecules? Describe a basic structure of amino acid What does essential amino acid mean? How are amino acids linked together in protein molecule? Distinguish the terms ―peptides‖ and ―polypeptides‖ What are the important roles of protein in the processing of food products? What is rennin? For what reason we utilized rennin in cheese processing? oooOooo UNIT 6: ENZYMES Living systems contain large protein molecules called enzymes Those large globular proteins range in molecular weight from about 10,000 to several million Each of the thousands of known enzymes has a characteristic three- dimensional shape with a specific surface configuration as a result of its primary, secondary, and tertiary structures The unique configuration of each enzyme enables it to ―find‖ the correct substrate from among the large number of diverse molecules in the cell Although some enzymes consist entirely of proteins, most consist of both a protein portion called an apoenzyme and a nonprotein component called a cofactor Together, the apoenzyme and cofactor form a holoenzyme, or whole enzyme If the cofactor is removed, the apoenzyme will not function The cofactor can be a metal ion or a complex organic molecule called a coenzyme Coenzymes may assist the enzyme by accepting atoms removed from the substrate or by donating atoms required by the substrate Some coenzymes act as electron carries, removing electrons from the substrate and donating them to other molecules in subsequent reactions Many coenzymes are derived from vitamins Specialized English in Food Science and technology -6- HoChiMinh University of Industry - Institute of Biotechnology & Food Technology The name of enzymes usually end in –ase All enzymes can be grouped into six classes, according to the type of chemical reaction they catalyze Enzymes within each of the major classes are named according to the more specific types of reactions they assist They are: Oxidoreductase: oxidation-reduction in which oxygen and hydrogen are gained or lost Transferase: Transfer of functional groups, such as an amino group, acetyl group, or phosphate group Hydrolase: hydrolysis (addition of water) Lyase: removal of groups of atoms without hydrolysis Isomerase: Rearrangement of atoms within a molecule Ligase: joining of two molecules (using energy usually derived from break down of ATP) Mechanism of Enzymatic Action Enzymes can speed up chemical reaction in several ways Whatever the method, the result is that the enzyme lowers the activation energy for the reaction without increasing the temperature or pressure inside the cell Although scientists not completely understand how enzymes lower the activation energy of chemical reaction, the general sequence of events in enzyme reaction is as follows: The surface of the substrate contacts a specific region of the surface of the enzyme molecule, called the active site A temporary intermediate compound forms, called an enzyme-substrate complex The substrate molecule is transformed by the rearrangement of existing atoms, the breakdown of the substrate molecule, or combination with another substrate molecule The transformed substrate molecules – the products of the reaction – are released from the enzyme molecule because they no longer fit in the active site of the enzyme The unchanged enzyme is now free to react with other substrate molecules Enzymes are extremely efficient Under optimum conditions, they can catalyze reaction at rates 108 to 1010 times (up to 10 billion times) higher than those of comparable reactions without enzymes In living cells, enzymes serve as biological catalysts As catalysts, enzymes are specific Each acts on a substrate (or substrates, when there are two or more reactants), and each catalyzes only one reaction For example, a specific enzyme may be able to hydrolyze a peptide bond only between two specific amino acids Other enzymes can hydrolyze starch but not cellulose; even though both starch and cellulose are polysaccharides composed of glucose subunits, the orientation of the subunits in the two polysaccharides differ Enzymes have this specificity because the three dimensional shape of the active site fits the substrate somewhat as a lock fits with its key However, the active site and substrate are flexible, and they change shape somewhat as they meet to fit together more tightly The substrate is usually much smaller than the enzyme, and relatively few of the enzyme’s amino acids make up the active site A certain compound can be a substrate for a number of different enzymes that catalyze different reactions, so the fate of a compound depends on the enzymes that acts upon it Glucose 6-phosphate, a molecule that is important in cell metabolism, can be acted upon by at least four different enzymes, and each reaction will yield a different product Factors influence enzyme activity Several factors influence the activity of enzyme The more important are temperature, pH, substrate concentration, and presence or absence of inhibitors The rate of most chemical reactions increases as the temperature increases Molecules move more slowly at lower temperatures than at higher temperatures and so may not have enough energy to cause a chemical reaction For enzymatic reactions, however, elevation beyond a certain temperature drastically reduces the rate of reaction This decrease is due to the enzyme’s denaturation, the loss of its characteristic three-dimensional structure (tertiary configuration) Denaturation of a protein involves Specialized English in Food Science and technology -7- HoChiMinh University of Industry - Institute of Biotechnology & Food Technology breakage of hydrogen bonds and other noncovalent bonds As might be expected, denaturation of an enzyme changes the arrangement of the amino acids in the active site, altering its shape and causing the enzyme to lose its catalytic ability In some cases, denaturation is partially or fully reversible However, if denaturation continues until the enzyme has lost its solubility and coagulates (as with cooked albumin) the enzyme cannot regain its original properties Enzymes can be denatured by concentrated acids, bases, heavy-metal ions (such as lead, arsenic, or mercury), alcohol, and ultraviolet radiation Most enzymes have an optimum pH at with their activity is characteristically maximal Above or bellow this pH value, enzyme activity, and therefore the reaction rate, declines When the H + concentration (pH) in the medium is changed, many of the enzyme’s amino acids are effected and the protein’s three-dimensional structure is altered Extreme changes in pH can cause denaturation There is a maximum rate at which a certain amount of enzyme can catalyze a specific reaction Only when the concentration of substrate(s) is extremely high can this maximum rate be attained Under condition of high substrate concentration, the enzyme is said to be saturation; that is, its active site is always occupied by substrate or product molecules In this condition, a further increase in substrate concentration will not effect the reaction rate because all active sites are already in use If a substrate’s concentration exceeds a cell’s saturation level for a particular enzyme, the rate of reaction can be increased only if the cell produces additional enzyme molecules However, under normal cellular conditions, enzymes are not saturated with substrate(s) At any given time, many of the enzyme molecules are inactive for lack of substrate; thus, the rate of reaction is likely to be influenced by the substrate concentration Enzyme inhibitors are classified according to their mechanism of action as either competitive or noncompetive inhibitors Competitive inhibitors fill the active site of an enzyme and compete with the normal substrate for the active site A competitive inhibitor is able to this because its shape and chemical structure are similar to those of normal substrate However, unlike the substrate, it does not undergo any reaction to form products Some competitive inhibitors bind irreversibly to amino acids in the active site, preventing any further interactions with the substrate Others bind reversibly, alternately occupying and leaving the active site, these slow the enzyme’s interaction with the substrate Reversible competitive inhibition can be overcome by increasing the substrate concentration As active site becomes available, more substrate molecules than competitive inhibitor molecules are available to attach to the active sites of enzymes Noncompetitive inhibitors not compete with the substrate for the enzyme’s active site; instead, they interact with another part of the enzyme In this process, called allosteric (―other space‖) inhibition, the inhibitor binds to a site on the enzyme other than the substrate’s binding site This binding causes the active site to change its shape, making it nonfunctional As a result, the enzyme’s activity is reduced This effect cab be reversible or irreversible, depending on whether or not the active site can return to its original shape In some cases, allosteric interaction can activate an enzyme rather than inhibit it Another type of noncompetitive inhibition can operate on enzymes that require metal ions for their activity Certain chemical can bind or tie up the metal ion activators and thus prevent an enzymatic reaction Cyanide can bind the iron in iron-containing enzymes, and fluoride can bind calcium or magnesium Substances such as cyanide and fluoride are sometimes called enzyme poisons because they permanently inactivate enzymes QUESTIONS: What enzymes generally consist of? What can the cofactor be? How coenzymes work? What is the important role of enzyme? Describe the general sequence of events in enzyme reaction Why enzymes have their own specificity? Specialized English in Food Science and technology -8- HoChiMinh University of Industry - Institute of Biotechnology & Food Technology Can a certain compound be a substrate for a number of different enzymes that catalyze different reactions? What are the important factors that influence the activity of enzyme? What does denaturation of a protein involve? 10 What does denaturation of an enzyme cause? 11 By what factors can arrangement enzymes be denatured? 12 When the enzyme is said to be saturation? 13 How are enzyme inhibitors classified? 14 Are substrate’s shape and chemical structure similar to those of competitive or noncompetive inhibitors? 15 What competitive inhibitors do? 16 What is the difference between competitive inhibitors and noncompetitive inhibitors? oooOooo UNIT 8: STERILIZATION VERSUS PASTEURIZATION Thermal processing covers the broad area of food preservation technology in which heat treatments are used to inactivate microorganisms to accomplish either commercial sterilization or pasteurization Sterilization processes are used with canning to preserve the safety and wholesomeness of ready-to-eat foods over long terms of extended storage at normal room temperature (nonrefrigerated) without additives or preservatives, and pasteurization processes are used to extend the refrigerated storage life of fresh foods Although both processes make use of heat treatments for the purpose of inactivating microorganisms, they differ widely with respect to the classification or type of microorganisms targeted, and thus the range of temperatures that must be used and the type of equipment systems capable of achieving such temperatures SECTION I: PASTEURIZATION Pasteurization is a relatively mild heat treatment given to foods with the purpose of destroying selected vegetative microbial species (especially the pathogens) and inactivating the enzymes Because the process does not eliminate all the vegetative microbial population and almost none of the spore formers, pasteurized foods must be contained and stored under conditions of refrigeration with chemical additives or modified atmosphere packaging, which minimize microbial growth Depending on the type of product, the shelf life of pasteurized foods could range from several days (milk) to several months (fruit juices) Because only mild heat treatment is involved, the sensory characteristics and nutritive value of the food are minimally affected The severity of the heat treatment and the length of storage depend on the nature of the product, pH conditions, the resistance of the target microorganism or enzyme, the sensitivity of the product, and the method of heating Most pasteurization operations involving liquids (milk, milk products, beer, fruit juices, liquid egg, etc) are carried out in continuous heat exchangers The product temperature is quickly raised to the pasteurization levels in the first heat exchanger, held for the required length of time in the holding tube, and quickly cooled in a second heat exchanger For viscous fluids, a swept surface heat exchanger is often used to promote faster heat transfer and to prevent surface fouling problems In-package pasteurization is similar to conventional thermal processing of foods except that it is carried out at lower temperatures The thermal processing of high acid foods (natural or acidified) is also sometimes termed pasteurization to indicate that relatively milder heat treatment is involved (generally carried out at boiling water temperatures) SECTION II: STERILIZATION Specialized English in Food Science and technology -9- HoChiMinh University of Industry - Institute of Biotechnology & Food Technology Sterilization implies the destruction of all viable microorganisms and is not the appropriate word to be used for thermal processing of foods, because these foods are far from being sterile in the medical sense of the word The success of thermal processing does not lie in destroying all viable microorganisms but in the fact that together with the nature of the food (pH), environment (vacuum), hermetic packaging, and storage temperature, the given heat process prevents the growth of microorganisms of spoilage and public health concern In essence, it presents a thermal process in which foods are exposed to a highenough temperature for a sufficiently long time to render them commercially sterile The process takes into account the heat resistance of the spore formers in addition to their growth sensitivity to oxygen, pH, and temperature The presence of vacuum in cans prevents the growth of most aerobic microorganisms, and if the storage temperature is kept below 250C, the heat-resistant thermopiles pose little or no problem From the public health perspective, the most important microorganism in low-acid (pH > 4.5) foods is Clostridium botulinum, a heat-resistant, spore-forming, anaerobic pathogen that, if it survives processing, can potentially grow and produce the deadly botulism toxin in foods Because C botulinum and most spore formers not grow at pH < 4.5 (acid and medium-acid foods), the thermal processing criterion for these foods is the destruction of heat-resistant yeasts and molds, vegetative microorganisms, or enzymes Because spore formers generally have high heat resistance, the low-acid foods that support their growth are processed at elevated temperatures (115-1250C), whereas acid foods need only to be brought to 80900C for adequate inactivation of enzymes or destruction of vegetative cells, yeasts, and molds QUESTIONS What is the difference between sterilization and pasteurization? The main purpose of sterilization and pasteurization Are spore –former microorganisms destroyed in pasteurization? Can pasteurized foods be preserved in normal storage condition? Does the pasteurization process affect greatly the sensory characteristics and nutritive value of the food? Are enzymes inactivated in the pasteurization process? Give example of food products which is treated by pasteurization Describe the stages in the pasteurization process What is the equipment for holding the pasteurization temperature called? 10 What does the term ―pasteurization‖ mean for heat treatment of high acid foods? 11 Are all viable microorganisms destroyed by sterilization or pasteurization? 12 What microorganism is considered as the most important in terms of public health concern, especially in low acid foods ? Why? 13 What are the ph values for low-acid and acid foods? 14 What target microorganisms are destroyed by heat processing for acid foods? 15 Why is temperature requirement of thermal processing for acid foods lower than for low acid foods? oooOooo UNIT 9: MAKING PEANUT BUTTER The first step in making peanut butter is growing the peanuts, of course! From the harvest the nuts go to shelling operations These plants, located near the growing fields, remove the shells, clean the nuts, and pack them into huge bags for shipment to the peanut butter plant Each bag holds more than 2,000 pounds of peanuts! At the plant, the bags are unloaded into bucket conveyors that move the nuts from each processing step to the next one The first step is to insure that all impurities, such as stems and sticks from the peanut Specialized English in Food Science and technology - 10 - HoChiMinh University of Industry - Institute of Biotechnology & Food Technology Specialized English in Food Science and technology - 35 - HoChiMinh University of Industry - Institute of Biotechnology & Food Technology Specialized English in Food Science and technology - 36 - HoChiMinh University of Industry - Institute of Biotechnology & Food Technology Specialized English in Food Science and technology - 37 - HoChiMinh University of Industry - Institute of Biotechnology & Food Technology PASSIVE VOICE Specialized English in Food Science and technology - 38 - HoChiMinh University of Industry - Institute of Biotechnology & Food Technology Specialized English in Food Science and technology - 39 - HoChiMinh University of Industry - Institute of Biotechnology & Food Technology Specialized English in Food Science and technology - 40 - HoChiMinh University of Industry - Institute of Biotechnology & Food Technology Specialized English in Food Science and technology - 41 - HoChiMinh University of Industry - Institute of Biotechnology & Food Technology Specialized English in Food Science and technology - 42 - HoChiMinh University of Industry - Institute of Biotechnology & Food Technology Specialized English in Food Science and technology - 43 - HoChiMinh University of Industry - Institute of Biotechnology & Food Technology Specialized English in Food Science and technology - 44 - HoChiMinh University of Industry - Institute of Biotechnology & Food Technology Specialized English in Food Science and technology - 45 - HoChiMinh University of Industry - Institute of Biotechnology & Food Technology PREPOSITION Prepositions of time Preposition of time on in at Explanations Example   days weekend (American English)   Many shops don't open on Sundays What did you on the weekend?    months / seasons / year morning / evening / afternoon period of time  I visited Italy in July, in spring, in 1994 In the evenings, I like to relax This is the first cigarette I've had in three years    night weekend (British English) used to show an exact or a particular time:    It gets cold at night What did you at the weekend? There's a meeting at 2.30 this afternoon / at lunch time  from a particular time in the past until a later time, or until now  England have not won the World Cup in football since 1966  used to show an amount of time  I'm just going to bed for an hour or so  back in the past; back in time from the present:  The dinosaurs died out 65 million years ago  at or during a time earlier than  She's always up before dawn  used when saying the time, to mean before the stated hour  It's twenty to six  telling the time  five past ten  until a particular time, marking end of a period of time  It's only two weeks to Christmas  used to show the time when something starts  The museum is open from 9.30 to 6.00 Tuesday to Sunday  up to (the time that)  We waited till / until half past six for you since   for ago before to past to from till / until Specialized English in Food Science and technology - 46 - HoChiMinh University of Industry - Institute of Biotechnology & Food Technology not later than; at or before  She had promised to be back by five o'clock  by Preposition of place Preposition of place Explanation  Example inside     in   I watch TV in the living-room I live in New York Look at the picture in the book She looks at herself in the mirror She is in the car Look at the girl in the picture This is the best team in the world used to show an exact position or particular place table events place where you are to something typical (watch a film, study, work)          attached next to or along the side of (river) used to show that something is in a position above something else and touching it left, right a floor in a house used for showing some methods of traveling television, radio  not far away in distance  The girl who is by / next to / beside the house  in or into the space which separates two places, people or objects  The town lies halfway between Rome and Florence  at the back (of)  I my coat behind the door  further forward than someone or something else  She started talking to the man in front of her  lower than (or covered by) something  the cat is under the chair  at       on by, next to, beside, near    between behind in front of under Specialized English in Food Science and technology - 47 -     I met her at the entrance, at the bus stop She sat at the table at a concert, at the party at the movies, at university, at work Look at the picture on the wall Cambridge is on the River Cam The book is on the desk A smile on his face The shop is on the left My apartment is on the first floor I love traveling on trains /on the bus / on a plane My favorite program on TV, on the radio HoChiMinh University of Industry - Institute of Biotechnology & Food Technology else  lower than something else  the plane is just below the the cloud  above or higher than something else, sometimes so that one thing covers the other more than across from one side to the other overcoming an obstacle    She held the umbrella over both of us Most of the carpets are over $100 I walked over the bridge She jumped over the gate  higher than something else, but not directly over it  a path above the lake  from one side to the other of something with clear limits / getting to the other side  She walked across the field/road He sailed across the Atlantic  from one end or side of something to the other  They walked slowly through the woods   in the direction of bed   We went to Prague last year I go to bed at ten  towards the inside or middle of something and about to be contained, surrounded or enclosed by it  Shall we go into the garden?  in the direction of, or closer to someone or something  She stood up and walked towards him  used to show movement into or on a particular place  I slipped as I stepped onto the platform  used to show the place where someone or something starts:  What time does the flight fromAmsterdam arrive? below over    above across   through to  into towards onto from Other kinds of prepositions Preposition from Explanation  Example used to show the origin of something or someone Specialized English in Food Science and technology - 48 -  "Where are you from?" "I'm from Italy." HoChiMinh University of Industry - Institute of Biotechnology & Food Technology Preposition Explanation used to show the material of which something is made used to show a change in the state of someone or something   The desk is made from pine Things went from bad to worse used to show possession, belonging or origin used after words or phrases expressing amount, number or particular unit   a friend of mine a kilo of apples  used to show the person or thing that does something:  I'm reading some short stories (written) by Chekhov    used for showing some methods of travelling entering a public transport vehicle  It'd be quicker to get there on foot / on horse get on the train  entering a car / Taxi  She got in the car and drove fast  leaving a public transport vehicle  She got off the bus  leaving a car / Taxi  She got out of the train  used to show measurements or amounts travelling (other than walking or horse-riding)  Their wages were increased by 12% She went by car, by bus, by train  age  In theory, women can still have children at the age of 50  on the subject of; connected with  What's that book about?    of  by on in off out of by Example   at about Specialized English in Food Science and technology - 49 -