Etiket Arşivleri: Food Chemistry

Food Chemistry Example Exam ( CLM206 )

CLM206  FOOD CHEMISTRY

1) Table sugar is which type of sugar?

  1. a) Fructose b) Galactose c) Glucose     (d) Sucrose

2) Please fill in the gaps in sentences below.

  • Attraction among water molecules is more than polar-polar in nature. The O atoms are small and very electronegative. As a result, the positive H atoms (protons) are very attractive to the negative O atoms of neighboring molecules. This O- – -H – O strong attraction is called a ………………………… (hydrogen bond).

  • …………………. reactions, ……………… changes, and ……………… growth may occur readily in foods with high water contents. (Chemical reactions, enzymatic changes, and microbial growth)

  • Proteins are polymers of ………….. which are made up of carbon, hydrogen, oxygen and nitrogen and some may also have sulfur. (amino acids)

  • When many amino acids bond together to create long chains, the structure is called a protein. It is also called a …………… because it contains many peptide bonds. (polypeptide)

  • ……………….. are the major class of dietary lipids including fats & oils which made up of 3 units known as fatty acids and 1 unit called glycerol. (Triglycerides)

  • The body can synthesize all of the fatty acids it needs from carbohydrates, fat or protein except for two: …………………………….….. and ……………………..………(Linoleic acid and Linolenic acid).

3) Why do cut apples, pears, bananas and potatoes turn brown?

Answer: Apples and other produce (e.g., pears, bananas, peaches, potatoes) contain an enzyme (called polyphenol oxidase or tyrosinase) that reacts with oxygen and iron-containing phenols that are also found in the apple. The oxidation reaction basically forms a sort of rust on the surface of the fruit. You see the browning when the fruit is cut or bruised because these actions damage the cells in the fruit, allowing oxygen in the air to react with the enzyme and other chemicals.

The reaction can be slowed or prevented by inactivating the enzyme with heat (cooking), reducing the pH on the surface of the fruit (by adding lemon juice or another acid), reducing the amount of available oxygen (by putting cut fruit under water or vacuum packing it), or by adding certain preservative chemicals (like sulfur dioxide). On the other hand, using cutlery that has some corrosion (as is seen with lower quality steel knives) can increase the rate and amount of the browning by making more iron salts available for the reaction.

4) How many types of browning reactions are there? Briefly define/explain them.

5)Which statement is true (T) or false (F)?

T: Denatured proteins have a greater tendency to aggregate.

F: Chemical reactions, enzymatic changes, and microbial growth may occur readily in foods with low water contents.

T: Rates of deteriorative changes and microbial growth at normal food storage conditions often depend on water content and water activity.

T: Amino acids contain carbon, hydrogen, nitrogen and sometimes sulfur and serve as the monomers to make peptides and proteins.

T: Unsaturated fatty acid is a fatty acid with one or more points of unsaturation. They are found in foods from both plants & animal sources.

T: Fat-soluble vitamins are more likely to be toxic to your health if taken in excess, because they are stored in the body, where as water-soluble are excreted.

F: More unsaturated a fat is the more solid it is at room temperature.

F: Starch is most common storage polysaccharide in plants and composed of 10–30% amylopectin and 70-90% a-amylose depending on the source.

F: Lactose (maltose) produced by the partial hydrolysis of starch (either salivary amylase or pancreatic amylase).

T: The functions of fat in food: provide calories (9 per gram), provide satiety, carry fat-soluble vitamins & essential fatty acids, contribute aroma & flavor.

T: Water is eaten, absorbed, transported, and utilized by cells.

F: Polysaccharides are large molecules that may consist of hundreds, or even thousands of amino acids.

T: Most carbohydrates are found naturally in bound form rather than as simple sugars.

T: Carbohydrates have an empirical formula CnH2nOn or (CH2O)n. Since this formula is essentially a combination of carbon and water.

T: Lipids include fats, oils, waxes, and cholesterol. In the body, fat serves as a source of energy, a thermal insulator, and a cushion around organs; and it is an important component of the cell. Since fats have 2.25 times the energy content of carbohydrates and proteins, most people try to limit their intake of dietary fat to avoid becoming overweight.

T: There are 20 amino acids found in the body. Eight of these are essential for adults and children, and nine are essential for infants. Essential means that we cannot synthesize them in large enough quantities for growth and repair of our bodies, and therefore, they must be included in our diet.

6) How many types of browning reactions are there? Briefly define/explain them.

Answer:

a.Enzymatic (polyphenoloxidase).

b.Caramelization.

c.Lipid Browning.

d.Vitamin C Browning.

e.THE MAILLARD REACTION

Briefly define/explain them.

7) What are the factors affecting the Maillard reaction?

Answer:

  1. Rapidly accelerated by temperature

  2. Significant acceleration at intermediate water activities

  3. Sugar type

Pentose>hexose>disaccharide>>polysaccharide

  1. Protein concentration (free amines)

  2. Inhibited by acid / amines are protonated and used up, pH drops

  3. Sulfur dioxide

8) Fill in the blank.

………………..is a phenomenon that involves transformation of a well-defined, folded structure of a protein, formed under physiological conditions, to an unfolded state under non-physiological conditions. (Denaturation)

……………….represents the ratio of the water vapor pressure of the food to the water vapor pressure of pure water under the same conditions (The water activity)

…………………..is a common phospholipids and often used as an emulsifier in foods such as margarine, chocolate & salad dressings. (Lecithin)

…..…………..are heteropolysaccharides found in the pulp of fruits (citrus, apples) and used as gelling agents (to make jellies) (Pectins)

…..……participate in biological transport, cell-cell recognition, activation of growth factors, modulation of the immune system. (Carbohydrates)

……..……maintains biological activities of proteins, nucleotides, and carbohydrates, and participates in hydrolyses, condensations, and chemical reactions that are vital for life. (Water)

…………commercially obtained from sugar cane or sugar beet. (Sucrose)

9) Describe the correlation between water activity and growth of microorganism in foods.

10) Explain the interaction mechanism of water with non-polar substances of foods.

11) Discuss the browning reactions of food. Explain the merits and demerits of these reactions.

12) Describe the general characteristics of auto-oxidation of lipids.

13) Differentiate between hydrolytic rancidity and oxidative rancidity.

14) Comment on safety of heated and oxidized fat.

15) What do you understand by denaturation of proteins. Explain its implications and name the physical and chemical agents causing denaturation of proteins.

16) Define aw. Explain the effect of temperature on aw. Discuss correlation between aw and stability of foods.

17) Explain the importance of hydrolysis reaction of carbohydrate in food industry.

18) Describe the structure function relationship of polysaccharides and their implications infoods.

19) Describe the emulsifying and foaming properties of food proteins.

20) What are the factors affecting the rate of autooxidation reaction?

Laboratory‎ > Determination of Moisture Content ( Kenan ÖZ )

FE 272 FOOD CHEMISTRY LAB Experiment 1

DETERMİNATİON OF MOISTURE CONTENT

Name of Experiment            : DETERMINATION OF MOISTURE CONTENT

Number of Experiment       : 1

Submitted by                        : Kenan ÖZ

QUESTIONS

  • Define the moisture content.

The determination of moisture is one of the most important and widely used analytical measurements in the processing and testing of food products.

The moisture content is frequently an index of stability and quality, and is also a measure of yield and quantity of food solids. It is closely concerned with the economics and legal aspects of food processing.

The moisture content of foods varies considerably: for fresh fruits, from 65% in ripe avocados to 95% in rhubarb; for fresh vegetables, from 66% in green beans to 96% in cucumbers; for fresh meat and fish, from 50 – 75%. The moisture content of processed foods varies even more from about 7 – 12% for dried vegetables to 27 -35% for jams and jellies.

  • What is the relationship between water activity and moisture content?

Water activity is an important means of predicting and controlling the shelf life of food products. Shelf life is the time during which a product will remain safe, maintain desired sensory, chemical, physical and microbiological properties, and comply with nutritional labeling.

 The relationship between moisture content and water activity is complex. An increase in aw is almost always accompanied by an increase in the moisture content, but in a nonlinear fashion. This relationship between water activity and moisture content at a given temperature is called the moisture sorption isotherm. These curves are determined experimentally. Moisture sorption isotherms are sigmoidal in shape for most foods, although foods that contain large amounts of sugar or small soluble molecules have a J-type isotherm curve shape. A moisture sorption isotherm prepared by adsorption (starting from the dry state) will not necessarily be the same as an isotherm prepared by desorption (starting from the wet state). This phenomenon of different aw vs. moisture values by the two methods is called moisture sorption hysteresis and is exhibited by many foods. Many disciplines use water content calculations to regulate product quality, however, water content measurement can be inaccurate, time-consuming and require a precision balance.

  • Write the importance of monolayer value for the foodstuffs.

The importance of monolayer value for the foodstuffs is physically bound as monolayer the surface of the food constituents.

  • What are the advantages and disadvantages of each methods (drying, distillation, chemical and instrumental methods)?

  1. Drying Methods:

Advantages: Different temperature of drying may result in a different amount of free water loss, so it is important to compare results obtained using the same condition.

Disadvantages: Weight lost, volatile oils may be lost.

  1. Distillation Methods:

Advantages: It has advantages of needing little attention and do not separate with the water and so are not measured.

GID 221E Food Chemistry I Midterm Examination 2 ( 2003 )

1.  Explain how fatty acids are given systematic names and what are the differences       in omega (ω) fatty acids? Give one example. (7 points)    Systematic names of fatty acids are given by considering the carbon numbers (1   point)  and  by  a  suffix  -noic  acid  (1  point).  If  there  is  a  double  bond  in  the   structure then “enoic acid” suffix (1 point) is given. If double bond is more than   one ; 2- dienoic, 3- trienoic suffixes (1 point) are used.   When counting starts from CH3 (methyl end) of the chain (2 point), then suffix ω is   used.   ω-9  Oleic acid, ω-6  Linoleic acid , ω-3  Linolenic acid (1 point for one example)    2.  Which property of lipids allows us to determine the presence of double bonds?  (5       points)    Halogen addition reactions: We can determine the number of double bonds in an   oil/fat by their iodine number (5 points).

Basic Food Chemistry ( Dr. M.A. IDOWU and Mrs. G.O. FETUGA )

COURSE CODE: FST 309 COURSE TITLE: BASIC FOOD CHEMISTRY COURSE UNIT: 3 UNITS COURSE LECTURERS: DR. M.A. IDOWU AND MRS. G.O. FETUGA LECTURE I – INTRODUCTION 1.0 HISTORICAL BACKGROUND – Accidental discoveries of processes and attempt to control man’s environment. – Passage of Food and Drug Act by the United States (U.S) congress (1906) catalysed by the study of food chemistry. – First official document of AOAC (Official methods of Analysis of the Association of Official Agricultural Chemists) in 1955. – Food Chemistry today. 1.1 DEFINITION OF FOOD CHEMISTRY – The study of composition of foods and of the reactions which lead to changes in their constitution and characteristics. 1.2 BENEFITS DERIVABLE FROM THE STUDY OF FOOD CHEMISTRY – Basic knowledge of the constituents of food. – Determination of appropriate processing and preservation method. – Aids understanding of microbiological reactions in food. – Information on chemical reactions involving food. – Useful information in New Food Product Development – Useful information to Engineers in design and fabrication of appropriate food processing equipment. – Help in choice of packaging material, equipment and technique. – Useful in storage stability and shelf life studies of food and food products. LECTURE 2 2.0 WATER IN FOODS – Water as basic constituent of ALL foods. 2.1 FORMS OF WATER IN FOOD – Free water/moisture

– Hydrates of water – Imbibes water – Adsorbed water 2.2 PROPERTIES OF WATER – Structure and Bonds in water H2O, covalent and H-bonds. – Some physical properties of water and ice. * Density * Vapour pressure * Refractive index * Viscosity * Specific heat * Heat of vapourization * Thermal conductivity * Dielectric constant * Coefficient of thermal expansion * Melting point * Boiling point. 2.3 WATER ACTIVITY – The concept of water activity relates the moisture (water) in a food to the RH of the air surrounding the food and is defined as ratio of the partial pressure of water in a food to the vapour pressure of water at the same temperature. a = p/p wherre P = vapour pressure of water in food w o P = vapour pressure of pure water at the same temperature o a = Water Activity. w OR aw can be defined as the ratio of the vapour pressure of water in a food to the saturated vapour pressure of water at the same temperature. i.e. P/P where P (pa) = Vapour pressure of water in food o Po = Vapour pressure of pure water at the same temperature. a = water activity w – for pure water a = 1.0 w – High m.c. amount of moisture > that of solids, aw ≤ 1.0 – Adsorption process

Dry product subjected to increasing moisture levels in the surrounding/Environment. – Desorption process Moist product gradually equilibrating with lower moisture levels of the surrounding/environment. – Hysteresis loop · Difference between abdorption and desorption isotherms. · It occurs because adsorption and desorption isotherms are more identical. 2.4 WATER ACTIVITY AND FOOD SPOILAGE – Moisture content and aw are important factors which affect ratio of spoilage of food in terms of chemical, biochemical and microbiological reaction. – for M.c 5- 15% – moist, dried foods (powdered) – Great storage stability – M.C. 20-40% – Intermediate moisture foods – less stable than dried foods. 2.4.1 Biochemical/Chemical Reactions Attached By a w – Most Enzymes are inactivated when a < 0.85 e.g. Amylases, peroxidases etc w – Lipases are still active at a 0.3 or less. w – Maillard reactions occur at a 0.6 – 0.7. w 2.4.2 Microbiological reactions – Bacterial growth – Impossible at a < 0.90 w – Molds and yeasts – Inhibited between a 0.88 – 0.80 w – Osmophilic yeasts can grow at aw of 0.65 LECTURE 3 3.0 PROTEINS – Complex organic substances present in all living matter (plants, animals and microorganisms). – ALL proteins, apart from consisting of C, H and O also contains N and sometimes may contain S as well as P.

3.1 AMINO ACID – Structural units of all proteins are amino acids. General formula RCN (NH ) 2 COOH. – There are 200 such amino acids. * Aliphatic monomerino monocarboxylic amino acids Gycine, Alanine, Valine, Lecicine, Isoleucine, Serine, Threonine and Proline. * Sulphure containing amino acids. Cycteine cystine & methionine. * Mono a,omp Dicarboxylic amino acids. Aspartic acid and colutamic acid. * Basic Amino acids. Lysine, Arginine and Histialine * Aromatic amino acids. Phenyl alanine, agrosine and Tryptophan * Derivatives of other amino acids 4 – Hydroproline and 5-Hydrolysine. 3.1.1 Properties of Amino acids – Optical Activity – Zwitterion formation (Electrostatically neutral form). – Isoelectic point –pH at which the amino acid consist of mainly Zwitterion e.g. for Glyes pHi = 5.97 3.2 CLASSIFICATION OF PROTEINS – can be based on solubility, coagulation or prosthesic groups. – Simple proteins proteins that will yield only amino acids on hydrolysis e.g. Asbamins, globalins, colutelins, protamines etc. – Complex proteins Proteins that contains non-protein entities attached to the polypeptide chain e.g. phospoproteins, Glycoproteins, Lipoproteins, Chromoproteins, Nucleoproteins etc. 3.2.1 Properties of Proteins – Amphoterism – Solubility – Colour Reactions e.g. Biuret reaction

Food Chemistry, Nutrition and Traditional Foods

Module 8: Food Chemistry, Nutrition, and Traditional Foods
Molecules of Food: Carbohydrates

6-C rings, 5-C rings
Mono-saccharides (sugar, fructose) Dissacharides (lactose, sucrose) Polysaccharides (starch, fibre, glycogen)
Carbohydrates are assimilated in the body as “mono-saccharides” following digestion
Glucose: Body’s Primary Fuels
Molecules of Food: Lipids and Fats
Fats: Large biological molecules, diverse compositions, insoluble in water (i.e. non-polar in nature)
Types:
Fatty acids (assimilable form)
Triglycerides (in blood)
Phospholipids (cell membranes)
Sterols (e.g. cholesterol)
Roles:
Source of energy (during sustained activity)
Structure of cell membrane
Free Fatty Acids (one chain)
Saturated
Unsaturated (e.g. Omega-3, Omega-6)
Fatty Acids
Long-chain fatty acids (12+ carbons) are abundant in meats and fish
Short-chain fatty acids (12 carbons or less) are abundant in dairy products
Cold-water fish are rich in essential omega fatty acids
Unsaturated fatty acids, when cooked, change conformation to a “trans” shape (which tend to accumulate in blood vessels)
Unsaturated fats are more prone to react with oxygen, causing rancidity (common in stored fish)
Triglycerides
Phospholipids
Phospholipids are “modified” triglycerides where one fatty acid chain is replaced by a phosphate group
Soluble in water
Important in cell membrane
Phospholipids
Sterols
Multiple rings of carbon
Best-known sterols: cholesterol (the building block for all other sterols)
Bile acids, some hormones, Vitamin C
Sterols
Absorption of Lipids
Fat breakdown occurs in intestines
Smaller units: fatty acids, glycerol, and sterols
Cholesterol and triglycerides are non-polar, hence need “lipoproteins” to carry them in the bloodstream
Molecules of Food: Proteins
Chains of Amino Acids
Diverse roles: enzymes, hormones, regulators, molecular transports, antibodies, building tissue like muscles, and energy
Made up of C, H, O, N, other ions
Amino Acids
Four components around a central carbon (C)
One hydrogen
An amino group (-NH2)
An acid (-COOH)
A functional group
Amino Acids
Molecules of Food: Vitamins
Essential organic compounds to ensure proper metabolism
Little caloric value
Water-soluble vitamins (enter directly into bloodstream)
Fat-soluble vitamins (must be transported by carrier proteins)
Several diseases are associated with vitamin deficiencies
Caloric Contents of Food Molecules
Subsistence Food Provisioning
Nutrition for indigenous people in the Arctic is changing rapidly; from 100% to <50% “country food”.
Presence of larger communities, presence of “Co-op” or “Bay” stores, and an increasing cash economy contribute to changes in feeding habits.
Lastly, hunting activities are costly when modern technologies are used à the “pay off” of traditional food provisioning is decreasing.
Concepts
Subsistence activities: The hunting, fishing, and gathering of local foods for consumption, sharing, and trade or barter.
e.g. caribou, whales, seals, marine birds, waterfowls, eggs, fruits (largely a carnivore diet)
Note: Commercial trapping or fishing is generally not viewed as traditional food gathering; although they could be traditional activities.
Example of Subsistence Food Economy
Inupiat households in Barrow, Alaska
Production vs. Sharing
Food provisioning is crucial, but sharing is an intricate part of subsistence
Sharing touches upon all members of a community, and represents a way of establishing and maintaining ties to family and within the community at large (e.g. support of elders, non-hunting members)
Sharing is viewed as part of the “culture” of indigenous society
Quality Food: Arctic Char
Quality Food: Beluga
Quality Food: Caribou
Quality Food: Muskox
Quality Food: Polar Bear
Quality Food: Ring Seal
What is special about a subsistence diet in the North?

The Chemistry of Food Lecture 2 ( Dr AN Boa )

1º and 2º Structure The Chemistry of Food • Peptide bonds join amino acids →the primary structure is Lecture 2 the specific amino acid sequence of a protein • Ordered structures can be stabilized by H-bonds so forming secondary structures such as – Helices Chemistry in Context 5.4 Å O R = N N -C-C H 06525/06529/06509 H – β-sheets (antiparallel peptide strands) O O N = = C H C – disulfide bonds (R-S-S-R) N-C-C-N H H O = formed by oxidation of neighbouring O O C = = N Dr AN Boa C-C-N-C C H Cys residues (R=CH2SH) H 1 3 Proteins 3º Structure • Proteins are polymers of amino acids • Globular proteins Hydrophobic amino – Hydrophobic residues acids avoid contact peptide (amide) bond buried in interior Charged groups with water • Large fraction of avoid interior + hydrophobic units – Hydrophilic, charged + groups on outside + • Amino acids are chiral molecules (except glycine, where R = H) – Most compact structure Roughly spherical shape • Our DNA encodes for L amino acids only • Amino acids can be divided into groups depending on the side • Fibrous proteins chain functionality. – Broadly there are hydrophilic and hydrophobic side chains, – More hydrophilic, less – these can be subdivided into acidic, basic, polar, aromatic and aliphatic2 compact

Essential amino acids Muscle • ends blend in with tendon Bundle of muscle cells • Amino acids are needed as building blocks – for our body’s own proteins – for purines and pyrimidines (nucleic acids) Muscle cell (or fiber) – for porphyrins (e.g. haemoglobin) • surrounded by sarcolemma • surrounded by thin connective – for other important substances tissue layer • The liver can biosynthesise some amino acids but others must come from diet – the so-called essential amino Muscle fibril acids: Ile, Leu, Lys, Met, Phe, Thr, Trp, Val, His • Proteins are degraded by stomach and intestinal Sarcomere (myofilaments) enzymes (proteases) into individual components. 5 Actin and myosin 7 Myofibrillar Proteins Making Bread: forming dough • Actin • Doughs are viscoelastic (they flow and recoil) – small spheres arranged like string of beads • Structure largely from proteins called glutens – consist of gliadins and glutenins – two strings twisted together ⇒thin filaments – 30% of amino acid residues are hydrophobic • Myosin – shaped like golf clubs • Kneading bread subjects it to shear forces – cluster ⇒thick filaments – promote interactions between glutenin molecules – H- bonding, hydrophobic interactions, S-S bonds – creates elastic protein networks (films) which trap gas – viscosity enhanced by gliadins and starch molecules

Lipids Triglycerides • A structurally diverse range of compounds • Food fats/oils are primarily triacylglycerols (esters of fatty acids • Non-polar and hydrophobic with glycerol) • also commonly known as triglycerides – 3 fatty acid chains on a glycerol backbone – Fats (solid at room temperature) – Oils (liquid at room temperature) • Fatty Acids • Triglycerides • Steroids • Waxes • Phospholipids • Terpenes 9 11 Attributes of Food Lipids Fatty acids • Three major functions in foods • Many R groups are alkyl groups (no C=C) – Energy and health – these are called saturated fatty acids – Influence food flavours • free fatty acids contribute flavours • Other R groups are alkenyl groups (with C=C) – Texture – 1 to 6 double bonds • solid vs liquid – cis-double bonds, methylene interrupted • mixed with water (emulsions) • one double bond are called monounsaturates • Attributes determined by types and positions of fatty • two or more double bonds are called acids on glycerol backbone polyunsaturates

Naming fatty acids Lorenzo’s oil • Fatty acid chains are named using a specific numbering • True story and topic of 1992 film system. • Lorenzo’s oil is possible treatment for rare disease adrenoleukodystrophy (ALD) methylene interrupt – involves accumulated saturated, very long chain fatty acids (VLCFA) in blood stream • patient cannot break down these VLCFAs cis • especially C26:0 • synthesized from shorter dietary fatty acids – Lorenzo’s oil is 50:50 mixture of oleic acid (C18:1) and erucic acid (C22:1) • shifts metabolism to form long chain unsaturated fatty acids can be named as 18:2∆9,12 or as 18:2ω6,9 • Lorenzo’s oil may not affect later disease progression 13 15 Important Food Fatty Acids COLOURS Abbreviation Systematic Name Common Name Symbol The molecular basis of colour 4:0 Butanoic Butyric B 6:0 Hexanoic Caproic H Colour Wavelength (nm) Complementary Colour Light absorbed Colour observed 8:0 Octanoic Caprylic Oc 10:0 Decanoic Capric D Violet 400 12:0 Dodecanoic Lauric La Yellow 14:0 Tetradecanoic Myristic M Blue 450 16:0 Hexadecanoic Palmitic P Orange Green 500 18:0 Octadecanoic Stearic St 70 °C Red 18:1 9-Octadecenoic Oleic O 10.5 °C Yellow 550 18:2 9,12-Octadecadienoic Linoleic L -5 °C Violet 18:3 9,12,15-Octadecatrienoic Linolenic Ln Orange 600 20:0 Eicosanoic Arachadic A Blue Red 650 20:4 5,8,11,14-Eicosatetraenoic Arachadonic An Green 22:1 13-Docosenoic Erucic E 700

Colour: green Colour: reds, mauves, blues • Leafy green vegetables and • The colours in berries and apple skins contain similar fruits are due to the chlorophylls a and b anthocyanins • Used in photosynthesis • Contain anthocyanidin aglycone often based • Cooking (heating) results in: on the flavylium cation – loss of phytol side chain • Six natural variants (OH, H, OMe) of the aglycone forming chlorophyllide – Loss of magnesium to form – Can have various sugars attached via glycosidic link at position 3 brown pheophytins (over (sometimes at 5, rarely elsewhere) cooked cabbage) – Sugars often esterified at C6 with cinnamic acid derivatives (caffeic = p-OH + chlorophyll a, R = H m-OH; coumaric = p-OH; ferulic = p-OH + m-OMe) chlorophyll b, R = CHO 17 19 Colour: yellow and orange Colour: browns • Yellows and oranges are due to the carotenoid group of terpenes, • On cutting apples and potatoes brown rapidly due to the e.g. lycopene and β-carotene action of phenoloxidase on chlorogenic acid Lycopene caffeic acid CHLOROGENIC ACID • Oxidation of polyphenols form reactive quinones which β-carotene then polymerise forming brown pigments called melanins – Causes desirable browning in tea, cider, dried fruit etc. • Terpenes made from repeating isoprene units derived from – Tannins form as red wine matures – polymerisation of anthocyanins mevalonic acid. Having 8 isoprene units, the carotenoids are tetra- terpenoids (monoterpenes have 2 units).

Enzymatic browning PO = phenoloxidase PO PO polymerisation • Prevention of browning – Eliminating oxygen (storing in an inert atmosphere or vacuum) – Lowering enzyme enzyme activity • The optimum pH for phenoloxidase is 7, and so citric or malic acid can be added to retard browning • Briefly heat to deactivate enzyme (blanching) • Add reducing agents (ascorbic acid, sulfites) 21 The colour of your steak N N • Myoglobin – protein containing iron Fe2+ – purplish-red N – Fe2+ N Globin O2 N N • Oxymyoglobin Fe2+ – supermarket red – Fe2+ O 2 H2O N N N N Globin • Metmyoglobin – brownish-red Fe3+ – Fe3+ H O 2 N N Globin