CHEN 333 Lecture 1 PDF

Chapter 1 Introduction to Food Science and Technology 1 Food Science: An Interdisciplinary Field of Study Microbiology Biology Chemistry Food Science Physics Nutrition Engineering...

Chapter 1 Introduction to Food Science and Technology 1 Food Science: An Interdisciplinary Field of Study Microbiology Biology Chemistry Food Science Physics Nutrition Engineering 2 Dimensions of Food Science and Technology Food Processing and Manufacture Food Preservation and Packaging Food Wholesomeness and Safety Food Quality Evaluation Food Distribution Consumer Food Preparation and Use 3 IFT Definition of Food Science Food science is the discipline in which biology, physical sciences and engineering are used to study the nature of foods, the causes of their deterioration and the principles underlying food processing. 4 Cans Extend the Shelf Life of Foods Photo Courtesy of USDA Photography Center 5 Products Developed by Food Scientists 6  Food Scientists Do Not Work In Isolation Production and Sales and Research and Manufacturing Marketing Development Food Scientists Advertising Regulatory Issues Environmental and Issues Merchandising 7  Phytochemical Plant derived chemical that is biologically active and thought to function in the body to prevent certain disease processes; Photo Courtesy of USDA Photo Gallery considered nonnutritive. 8 Scientist Working in Food Microbiology Lab Photo courtesy of the USDA Photography Center 9 Food Safety Experts Examine Poultry Photo Courtesy of USDA Photography Center 10  Chapter 2 FOOD CHEMISTRY 11 The Carbohydrates 12 What we will cover today… The chemistry of carbohydrates Simple carbohydrates Complex carbohydrates Digestion and absorption of carbohydrates Glucose in the body 13 What we will cover today… Health effects and recommended intakes of sugars Health effects and recommended intakes of starch and fiber Alternatives to sugar 14 The Chemistry of Carbohydrates 15 16 Definition Carbo = carbon (C) Hydrate = with water (H2O) Carbohydrates: Compounds composed of carbon, oxygen and hydrogen arranged as monosaccharides (1 structural unit), oligosaccharides (2-10 structural unit), or polysaccharides(>10). Most, but not all, carbohydrates have a general empirical formula (CH2O)n. Most carbohydrates end with the suffix -ose 17 Carbohydrates Carbohydrates make up three quarters of the dry weight of all land plants and seaweeds, thus serving as the primary nutritive energy sources from foods like grains, fruits, and vegetables. 18 Functions of Carbohydrates Provide energy source: A fuel source when catabolized during cellular respiration. Energy is stored in the chemical bonds within the molecule and released during cellular respiration. Usually simple sugars. Provide energy storage: Plants store energy in a complex carbohydrate form called starch (amylose). Animals store energy in a complex carbohydrate in their muscle tissue and liver in the called glycogen. Structural Building Material: Plants build their cell walls of a complex carbohydrate material called cellulose. Animals such as arthropods build their exoskeletons of a complex carbohydrate called chitin. Chitin is also found in the cell walls of Fungi. 19 Carbohydrates (CH2O)n Simple carbohydrates ◦ Monosaccharides ◦ Mono = one ◦ Saccharide = sugar ◦ Disaccharides ◦ Di = two Complex carbohydrates ◦ Glycogen ◦ Starches ◦ Fibers 20  Monosaccharides (Simple sugars) They may exist in a linear molecule or in ring forms. They are classified according to the number of carbon atoms in their molecule. 5 carbons are called pentoses ex. Ribose 6 carbons are called hexoses ex. Glucose Many forms exists as isomers. Isomers are molecules which have the same empirical formula (recipe) but have different structures (shapes) due to arrangement of the atoms in the molecule. This also gives them different properties. Glucose and fructose both have the empirical formula C6H12O6, but they have different structural formulas or shapes. MONOSACCHARIDES ARE THE BUILDING BLOCKS FOR ALL OTHER CARBOHYDRATES! 21 Monosaccharide Structure 22  Nomenclature and structure The term aldose indicates the presence of an aldehyde group while ketose indicates that a ketone group is contained. The common food-related monosaccharaides glucose , mannose , and galactose are aldoses since they contain an aldehyde group while fructose is a ketose having a ketone group. 23  Monosaccharides The monosaccharides are classified as aldoses or ketoses depending on whether they contain an aldehyde or ketone group. Each carbon atom carries a hydroxyl group, with the exception of the atom that forms the carbonyl group ,which is also known as the reducing group. By convention, the carbon atoms in the monosaccharide molecule are numbered such that the reducing group carries the lowest possible number; therefore , in aldoses the reducing group is always numbered 1 and in ketoses the numbering is started from the end of the carbon chain closest to the reducing group. 24 Monosaccharides 25  Monosaccharides The α and β conventions refer to the configuration of the hydroxyl group attached to the carbonyl carbon , where α indicates the hydroxyl group is below the plane of the ring structure and β indicates it is above the ring plane, respectively drawn as ‘down’ and ‘ up’. The carbonyl carbon is designated the anomeric carbon atom corresponding to C-1 in glucose and C-2 in fructose. Interconversion between α and β forms occurs by a process know as mutarotation. The switch between anomers takes place via the open chain form. As an example,100% β-D glucose , or 100% α -D glucose , dissolved in water will equilibrate a few hours at 36% α -D glucose , 64% β -D glucose, and far less than 1% open chain. Such changes can be detected by measuring changes in absorption of optically polarized light. 26  Monosaccharide Isomers H H H—C—OH H—C—OH O H C O C C H H H C C OH OH H OH H C C OH C C OH H OH H OH α- GLUCOSE FRUCTOSE H—C—OH H What is the empirical formula 27 for these molecules? Monosaccharides ◦ C6H12O6 ◦Glucose ◦Essential energy source - somewhat sweet ◦Fructose ◦Found in fruit - very sweet ◦Galactose ◦Rarely occurs as a single sugar - not sweet 28 Glucose 29 Fructose & Galactose 30 Condensation 31 Hydrolysis 32 Sucrose ≠ Maltose 33 Sucrose ≠ Maltose Sucrose Maltose 34 Disaccharides Maltose ◦ Glucose + glucose ◦ Produced during the germination of seeds and fermentation Sucrose ◦ Glucose + fructose ◦ Refined from sugarcane and sugar beets Lactose ◦ Glucose + galactose ◦ Found in milk and milk sugar 35 Humectancy The ability of a substance to bind water is termed humectancy. Sometimes it is desirable to control water water’s ability to enter and exit foods. For example, to avoid stickiness in baked icings one needs to limit the entry of water. Maltose and lactose have low humectancies ; therefore , they allow for sweetness as well as the desired texture. Glucose and fructose contain the same number of hydroxyl units ; however, fructose binds more water than glucose. 36 Lactose Lactose is found in mammalian milk. To aid the digestion of lactose, the intestinal villi of infant mammals secrete an enzyme called lactase. In most mammals the production of lactase gradually reduces with maturity into adulthood, leading to the inability to digest lactose and so-called lactose intolerance. However, in cultures where cattle, goats and sheep are milked for food there has evolved a gene for lifelong lactase production. 37  Polysaccharide Structure and Formation Polysaccharides are chains of monosaccharides (>10) that have been joined by many dehydration synthesis reactions. The function of the polysaccharide depends on what type of isomer of glucose the polysaccharide is made. This determines how the glucose molecules bond together (linkage) and whether they can be used for energy storage or structural molecules. 38 Alpha and Beta Glucose and Their 1,4 Linkages Alpha and beta glucose are structural isomers. They differ only in the location of the hydrogen and hydroxyl group location on carbon 1. Alpha linkage can be broken by enzymes present in plants and animals. In other words, it can be metabolized. (energy storage) Beta linkage can not be broken by enzymes present in plants and animal, therefore it can not be metabolized. (structural) 39  Storage Polysaccharides Starch and glycogen both have alpha 1,4 linkage and form helical chains that are often highly branched. The diagram to the left show starch or amylose granules in a plastid of a plant cell. The diagram to the left shows glycogen granules in a liver section of an animal. Glycogen is usually more highly branched than amylose. 40 Structural Polysaccharides Cellulose is the plant structural carbohydrate and has beta 1,4 linkage. Cellulose is the primary component of the plants primary or outermost cell wall. 41 Starch Amylose is a linear polymer of α(1→4) linkages with 4-5% of glucose units also being involved in α(1→6) linked branches. Amylose molecules contain in the region of 103 glucose units. Amylopectin is a much larger molecule than amylose, containing approximately 106 glucose units per molecule , and forms a complex structure. 42 Starch Starch granules undergo a process called gelatinization if heated above their gelatinization temperature (55-70ºC depending on the starch source) in the presence of water. Prolonged storage of starch gel leads to the onset of a process termed retrogradation, during which amylose molecules associate together to form crystalline aggregates and starch gels undergo shrinkage. 43  Complex Carbohydrates Polysaccharides (poly = many) ◦ Glycogen ◦ Stored in muscle and liver ◦ Starches ◦ Plants way of storing glucose ◦ Found in grains, tubers (roots), and legumes ◦ Fibers ◦ Provide structure in plants ◦ Can’t be broken down by human enzymes 44 Glycogen Glycogen is similar in structure to amylopectin , but has much higher molecular weight and a higher degree of branching. Branching aids the rapid release of glucose since the enzymes that release glucose attack on the non-reducing ends, cleaving one glucose molecule at time. The metabolism of glycogen continues post-mortem, which means that by the time meat reaches the consumer it has lost all of its glycogen. 45 46 Bonds make the difference 47  Complex Carbohydrates Fibers ◦ Cellulose ◦ Occurs in plant walls ◦ Found in fruits, vegetables and legumes ◦ Used in food processing ◦ Hemicelluloses ◦ Found in cereal grains ◦ Pectins ◦ Found in fruits and vegetables ◦ Used to control texture and consistency in foods 48  Complex Carbohydrates Fibers ◦ Gums and mucilages ◦ Used as thickeners and stabilizers ◦ Lignin ◦ Provides strength to foods ◦ Found in carrots and strawberries ◦ Resistant starches ◦ Found in legumes, raw potatoes and unripe bananas ◦ Escape digestion 49 Fiber Characteristics ◦Soluble fibers (absorb water) ◦Viscous-form a gel like consistency ◦Fermentable in the colon ◦Found in fruits and legumes 50  Complex Carbohydrates Fibers ◦Insoluble fibers (don’t dissolve in water) ◦Nonviscous ◦Found in grains and vegetables Phytic acid ◦Associated with fiber ◦Can bind to minerals 51  Have You Had Your Fiber Today? Because cellulose has beta 1,4 linkage all animals lack the enzymes necessary to digest this material. In our case it simply passes through our gut and out of the body. We call it fiber or roughage. Animals such as termites and cows rely on simple, symbiotic, unicellular organisms such as protozoa or bacteria to carryout the job of digestion for them! In return the tiny organisms live in an ideal environment with a bountiful food supply. 52 Structural Polysaccharides Chitin is the “plastic- like” material that composes the exoskeletons of arthropods (insects, arachnids, and crustaceans). Most fungi (mushrooms) have chitin present A structural within their cell walls. monomer of chitin. 53 Reaction of Carbohydrates 1) Caramelization When a concentrated solution of sugars is heated to temperatures above 100ºC, various thermal decomposition reaction can occur leading to formation of flavor compounds and brown-coloured products. This process, which particularly occurs during the melting of sugars is called caramelization. Caramelization is a non-enzymic browning reaction. 54 Reaction of Carbohydrates 2) Maillard browning The maillard reaction is the chemical reaction between an amino acid and a reducing sugar. It leads to the formation of flavor compounds and melanoidin pigments ( non-enzymic browning). It requires heat ( usually > 100ºC) Promoted by low moisture content Accelerated in an alkaline environment. 55 Toxic sugar derivatives The maillard reaction , while desirable in many respects, does have certain implications for : The loss of essential amino acids(cysteine and methionine) The formation of mutagenic compounds The formation of compounds that are implicated in diabetes. 56 Toxic sugar derivatives The most concerning aspect is the potential for toxic sugar derivatives with mutagenic properties primarily the group of compounds called heterocyclic amines. These are particularly associated with cooked meat, especially that which has been grilled at high temperature for long cooking times. In recent times the formation of acrylamide has been an issue of concern in potato based snack foods. 57 Digestion of Carbohydrate s 58 Digestion Mouth ◦Salivary amylase ◦Begins to hydrolyze starch Stomach ◦Fibers delay gastric emptying and provides a sense of fullness (satiety) 59 Digestion Small intestine ◦Maltase, sucrase, lactase Pancreas ◦Pancreatic amylase 60 Fibers Large Intestine ◦ Fibers help to attract water and soften stools ◦ Are fermented by intestinal bacteria and provide short chain fatty acids that fuel immune cells 61 Digestion Available carbohydrates vs. unavailable carbohydrates Sugars and starches are available because we can break them down and obtain their nutrients Fibers are unavailable because we cannot break down their bonds 62 63 Digestion Large intestine ◦Fermentation of viscous fibers ◦Water, gas, short-chain fatty acid production 64 65 Absorption 66 Lactose Intolerance Symptoms ◦Bloating, abdominal discomfort, and diarrhea Causes ◦Lactase deficiency 67 Lactose Intolerance Prevalence ◦ Highest in Southeast Asians ◦ Lowest in Northern Europeans 68 Carbohydrate Metabolism Storing glucose as glycogen Using glucose for energy 69 Carbohydrate Metabolism Making glucose from protein ◦Gluconeogenesis ◦Protein-sparing action of carbohydrates ◦Protein not broken down for energy when sufficient amount of carbohydrate available in body 70  Carbohydrate Metabolism Making ketone bodies from fat fragments as an alternate fuel source during starvation ◦Ketosis: the accumulation of ketone bodies in blood ◦Upsets acid-base balance in blood ◦50-100 g of carbohydrates needed to spare protein and prevent ketosis 71 Carbohydrate Metabolism Converting glucose to fat ◦ When needs are met, excessive carbohydrates converted to fat ◦ Energetically expensive-much easier for body to convert fat to fat 72  Constancy of Blood Glucose Regulating hormones ◦ Insulin: released in response to glucose in blood by pancreas- transports glucose into cells ◦ Glucagon: when blood glucose is low, glucagon signals the liver and muscle to breakdown glycogen ◦ Epinephrine: helps in quickly releasing glucose from storage in times of stress-”fight or flight response” 73 74 Constancy of Blood Glucose Diabetes ◦Type 1 diabetes ◦Failure of insulin production ◦Type 2 diabetes ◦Obesity 75 Constancy of Blood Glucose Hypoglycemia ◦Low blood sugar ◦Rare in healthy people 76 Constancy of Blood Glucose Glycemic response ◦Glycemic index ◦Note that this is based on single food items and is altered when foods are combined 77 Sugars Added sugars ◦Sucrose, invert sugar, corn syrups, high fructose corn syrup, etc. 78  Sugars Health effects of sugars ◦Nutrient deficiencies 79 80  Sugars Health effects of sugars ◦Dental caries ◦Dental plaque 81  Accusations Against Sugars Sugar causes obesity Sugar causes heart disease 82 Starch and Fiber Health effects ◦Heart disease ◦Diabetes ◦GI health 83 Starch and Fiber Health effects ◦Cancer ◦Weight management ◦Harmful effects of excessive fiber intake 84 Viscous Fibers Soluble and more fermentable Gums and mucilages Pectins Psyllium Some hemicelluloses 85 Viscous Fibers Sources ◦Whole-grains, fruits, legumes, seeds and husks, vegetables ◦Extracted and used as food additives 86 Viscous Fibers Lower blood cholesterol Slow glucose absorption Slow transit of food through upper GI tract 87 Viscous Fibers Holds moisture in stools, softening them Yield small fat molecules that the colon can use for energy 88 Viscous Fibers Lower risk of heart disease Lower risk of diabetes 89 Viscous Fibers 90 Nonviscous Fibers Insoluble and less fermentable Cellulose Lignins Psyllium Resistant starch Many hemicelluloses 91 Nonviscous Fibers Sources ◦Brown rice, fruits, legumes, seeds, vegetables, wheat bran, whole grains ◦Extracted and used as food additives 92 Nonviscous Fibers Increase fecal weight Speed fecal passage through colon Provide bulk and feelings of fullness 93 Nonviscous Fibers Alleviate constipation May help with weight management 94 Nonviscous Fibers 95 96 Guideline s to Groceries More whole Grains 97 98 Alternatives to Sugar Artificial sweeteners vs. sugar replacers (nutritive sweeteners) 99 100 101 102