FOOD CHEMISTRY FSTC 605

1. FOOD CHEMISTRYFSTC 605 • Instructor: Dr. Steve Talcott • Office: 220F Centeq A • Phone: 862-4056 • E-mail: stalcott@tamu.edu • Course website: http://nfscfaculty.tamu.edu/talcott

2. Recommended TextFood Chemistry, 3rd EditionOwen Fennema ed. • Classes Meet: Mon, Wed, and Fri • My office is open at all times

3. www.ift.org IFT Definition of Food Science Food science is the discipline in which biology, chemistry, physical sciences and engineering are used to study: The nature of foods The causes of their deterioration The principles underlying food processing.

4. Food Science: An Interdisciplinary Field of Study Microbiology Biology Chemistry Food Science Physics Nutrition Engineering

5. Food Chemistry • Basis of food science • Water • Carbohydrates • Proteins • Lipids • Micronutrients • Phytochemicals • Others

6. Food Chemistry Examples

10. Lipids in Peanuts • Opened jar peanut butter: chemical reaction in the oil phase • Oxidation of the unsaturated fatty acids in the peanut oil results in production of a rancid odor. • Peanut butter represents a special food system called an emulsion H H H H C C C C H H Hydrocarbon chain oxygen

11. Solutions and Emulsions

12. Solutions are homogeneous mixtures in which solute particles are small enough to dissolve within solvent Solute examples: salt, sugar, vitamin C, other small solid particles Solute liquid examples: water, ethanol; gas examples: CO2 Droplets of dispersed phase within the continuous phase Dispersions (colloidal dispersions) are mixtures in which solutes do not dissolve (too large) Examples of colloids milk protein (casein) egg white protein (albumen) gelatin protein pectin polysaccharide Ca and Mg (minerals) MILK

13. What is an emulsion? Mixture of two immiscible liquids Surface tension acts to keep the liquids from mixing oil H2O Result: oil “sits” on top of the water phase Stable food emulsions = addition of emulsifiers lecithin, sucrose esters, MAG, DAG, etc Margarine butter milk ice cream mayo W/O emulsion O/W emulsion

14. Common Chemical Bonds in Foods • Covalent • Sharing 1 or more pairs of electrons • Very strong bonds, not easily broken in foods • C-C or C=C bonds • Ionic • Filling of orbitals through the transfer of electrons • Cations (+) and Anions (-); Na+ + Cl- => NaCl • Hydrogen • Compounds containing O or N with bound hydrogen • Very weak bonds; C-H or N-H

15. Functional Groups in Foods

16. The “Basics” of Food Chemistry

17. SOME FOOD MOLECULES important in food chemistry O = C = O CH3 – COOH H – O – H C6H12O6 Na H CO3 NaCl NH2 – CH2 - COOH CH3 – (CH2)n - COOH

18. SOME FOOD MOLECULES important in food chemistry WATER acetic acid carbon dioxide glucose sodium bicarbonate sodium chloride general structure of a fatty acid The amino acid “glycine”

19. A Few Food Functional Groups: ACID GROUP: “carboxylic acid” COOH acids donate (lose) protons COOH  COO(-) + H(+) This means acids form ions (charged species) anion has (-) charge cation has (+) charge Vinegar contains acetic acid CH3COOH Tartaric acid found in grapes is a di-carboxylic acid – what does this mean? Citric acid is tri-carboxylic acid.

20. AMINO GROUP: NH2 Derived from ammonia (NH3) Amines are “basic” – means they gain protons methyl amine: CH3 – NH2 trimethylamine is found in fish, and is responsible for “fishy odor” CH3 – CH – COOH Alanine, an amino acid NH2

21. Alcohol group- OH “hydroxyl group” Methyl alcohol = methanol: CH3- OH Ethanol C2H5OH is produced during the fermentation of sugars; it is water-soluble and is called “grain alcohol” because it is obtained from corn, wheat, rice, barley, and fruits. Yeasts use sugars for food – they ferment simple carbohydrates and produce ethanol and CO2: STARCHhydrolysis C6H12O6  2 C2H5OH + 2 CO2 Glucose Ethanol Carbon Dioxide Other food molecules that contain OH groups: cholesterol (a lipid), tocopherol (a vitamin), retinol (a vitamin), & calciferol (a vitamin)

22. Aldehyde group - CHO • There is actually a double bond between two atoms • in this group: • formaldehyde HCHO: H – C – H • O • Aldehydes can be formed from lipid oxidation, and • generally have very low sensory thresholds. • For example, fresh pumpkin has the smell of • acetaldehyde; fresh cut grass the small of hexenal.

23. Covalent: Sharing of electrons, strong bonds, C-C or C=C bonds Ionic: Transfer of electrons, NaCl Hydrogen: Weak bonds with O or N with bound hydrogen • There are 3 other important bonds in foods: • An ester bond (linkage) in lipids • A peptide bond (linkage) in proteins • (3) A glycosidic bond (linkage) in sugars

24. An ester bond (linkage) in lipids: In food fats, fatty acids are attached to glycerol molecules, through what is called an ester linkage O Glycerol C O fatty acid Ester linkage

25. Glycerol is a small molecule, containing only 3 carbons But, to each carbon atom of glycerol, one fatty acid can attach, via an ester bond. A mono-, di-, or tri-esterified fatty acid to a glycerol is: A MONOACYLGLYCEROL. A fat molecule that has ONE fatty acid attached (“esterified”) to glycerol. A DIACYLGLYCEROL. A fat molecule that has TWO fatty acids esterified to glycerol. A TRIACYLGLYCEROL. A fat molecule that has THREE fatty acids esterified to glycerol.

26. Ester H H – C – O H H – C – O H H – C – O H H H O H – C – O – C - (CH2)n – CH3 H – C – O H H – C – O H H Fatty acid chain a monoglyceride Glycerol

27. What do peptide bonds (linkages) in proteins look like? In food proteins, or “polypeptides”, individual amino acids are attached to each other through what is called a peptidelinkage Amino acid Amino acid. . . repeat Peptide linkage

28. AMINO ACIDS contain both the amino (NH2) and the acid (COOH) group in their structure. In the formation of a peptide bond, one of the amino acids loses one H atom, and the other loses O and H. O O H H NH2 C – C - O – H ------------- NH2 C – C - O – H “R” “R” R is any Side chain Amino group Acid group of the amino acid

29. The formation of peptide bond N-C-C-N

30. A glycosidic linkage in sugars connects sugar units into larger structures Glycosidic linkage glucose glucose O MALTOSE, a disaccharide composed of 2 glucose units

31. Structures of sugar disaccharides Alpha 1,4 glycosidic bond Beta 1,4 glycosidic bond Alpha 1,4 glycosidic bond

32. Polymeric Linkages Alpha 1,4 Linkage Digestible Beta 1,4 Linkage Indigestible

33. Organic Acids in Foods Application of functional groups

34. Acids in Foods Organic acids • Citric (lemons), Malic (apples), Tartaric (grapes), Lactic (yogurt), Acetic (vinegar) • Food acids come in many forms, however: • Proteins are made of amino acids • Fats are made from fatty acids • Fruits and vegetables contain phenolic acids • Organic acids are characterized by carboxylic acid group (R-COOH); not present in “mineral acids” such as HCl and H3PO4

35. Chemical Structures ofCommonOrganic Acids

36. Acids in Foods • Add flavor, tartness • Aid in food preservation by lowering pH • Acids donate protons (H+) when dissociated • Strong acids have a lot of dissociated ions • Weak acids have a small dissociation constant • Acids dissociate based on pH • As the pH increases, acid will dissociate • pKa is the pH equilibrium between assoc/dissoc

37. Titration Curve for Acetic Acid

38. Acids in Foods • Weak acids are commonly added to foods • Citric acid is the most common • When we eat a food containing citric acid, the higher pH of our mouth (pH 7) will dissociate the acid, and giving a characteristics sour flavor pH and Titratable Acidity • pH measures the amount of dissociated ions • TA measures total acidity (assoc and dissoc) • The type of food process is largely based on pH

39. They also have other roles in food • Control pH • Preserve food (pH 4.6 is a critical value) • Provide leavening (chemical leavening) • Aid in gel formation (i.e. pectin gels) • Help prevent non-enzymatic browning • Help prevent enzymatic browning • Synergists for antioxidants (for some, low pH is good) • Chelate metal ions (i.e. citric acid) • Enhance flavor (balance sweetness)

40. Acids in Foods • In product development you can use one acid or a combinations of acids • -flavor • -functionality • - synergy • - naturally occurring blends • - food additives

41. Acidity is important chemically • -Denaturation and precipitation of proteins • -Modify carbohydrates and hydrolysis of complex sugars • -Hydrolysis of fatty acids from TAG’s • Generally under alkaline conditions • Inversion of sugars (sucrose to glu + fru)

42. Chemical Reactions in Foods (1) Enzymatic (2) Non-enzymatic Generically applied to: Carbohydrates Lipids Proteins

43. CARBOHYDRATE chemical reactions: • Enzymatic browning • Non-enzymatic browning • Hydrolysis • Fermentation • Oxidation/reduction • Starch gelatinization

44. PROTEIN chemical reactions: • Buffering • Non-enzymatic browning • Hydrolysis • Condensation • Oxidation • Denaturation • Coagulation

45. LIPID chemical reactions • Oxidation • Hydrolysis • Hydrogenation

46. Chemical Bonds to Chemical Rxns

47. Chemical Reactions in Foods • Enzymatic • Enzymes are proteins that occur in every living system • Enzymes can have beneficial and detrimental effects • Bacterial fermentations in cheese, pickles, yogurt • Adverse color, texture, flavor, and odor • High degree of specificity (Enzyme – Substrate) • Non-enzymatic • Those reactions that do not require enzymes • Addition, redox, condensation, hydrolysis

48. The Active Site of the ES Complex

49. Enzyme Reactions • Enzymatic reactions can occur from enzymes naturally present in a food • Or as part of food processing, enzymes are added to foods to enable a desired effect • Enzymes speed up chemical reactions (good or bad) and must be controlled by monitoring time and temperature. • Typically we think of enzymes as “breaking apart” lipids, proteins, or carbs; but there are several enzyme categories sucrase sucrose glucose + fructose “invertase”

50. Enzyme Class Characterizations • Oxidoreductase Oxidation/reduction reactions • Transferase Transfer of one molecule to another (i.e. functional groups) • Hydrolase Catalyze bond breaking using water (ie. protease, lipase) • Lyase Catalyze the formation of double bonds, often in dehydration reactions, during bond breaking • Isomerase Catalyze intramolecular rearrangement of molecules • Ligase Catalyze covalent attachment of two substrate molecules