FOOD CHEMISTRY FSTC 312/313, 3+1 Credits

1. FOOD CHEMISTRYFSTC 312/313, 3+1 Credits • Instructor: Dr. Steve Talcott • Office: 220F Centeq A • Phone: 862-4056 • E-mail: stalcott@tamu.edu

2. 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.

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

4. 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

5. Other Components • Growing/Harvesting • Packaging • Marketing/Retail • Food Service • Consumer Services

6. Components of Food Science • Food Chemistry • Food Microbiology • Food Processing • Regulations • Nutrition • Others

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

11. 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

12. Solutions and Emulsions

13. 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

14. 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 are “amphiphiles” Margarine butter milk ice cream mayo W/O emulsion O/W emulsion

15. Foods Are Made of Chemicals • Single elements • Chemically bonded elements (compounds)

16. Electrons Distributed via Energy Layers

17. 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

18. Functional Groups in Foods

19. Exams and Grading • 3 hourly exams • Material is not “cumulative”, but material will build upon itself. • Multiple choice, short answer, short essay format • 2 class assignments • Short term paper • Literature review • Topic of special interest • etc • Several announced or unannounced quizzes • Beginning or end of class • University excused absence policy will be followed

20. The “Basics” of Food Chemistry

21. Functional Groups in Foods

22. 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

23. 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”

24. 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.

25. 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

26. 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)

27. Aldehyde group - CHO There is actually a double bond between two atoms in this group: • C – H formaldehyde HCHO: H – C – H O 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.

28. We have already talked generally about covalent, ionic, and hydrogen bonds: 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

29. 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 “Acyl” linkage

30. 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.

31. 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 “I’m a fatty acid chain” a monoglyceride Glycerol

32. 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

33. 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

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

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

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

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

38. Organic Acids in Foods Application of functional groups

39. 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

40. Chemical Structures ofCommonOrganic Acids

41. 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

42. Titration Curve for Acetic Acid

43. 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

44. 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)

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

46. Acidity is important chemically • -Denaturation and precipitiation 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)

47. Functional Groups and Bonds • Acids • Amino • Alcohol • Aldehydes • Ester • Peptide • Glycosidic

48. Application: Organic Acids • 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)

49. Acidity is important chemically • Denaturation and precipitiation 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)

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