ANTIOXIDANT

1. ANTIOXIDANT

2. Antioxidants The chemical compounds which can delay the start or slow the rate of lipid oxidation reaction in food systems.

3. Mechanism of Antioxidant 14 13 12 11 10 9 C H ( C H ) C H C H C H C H C H C H C H R 3 2 3 2 2 2 Initiation Metal Energy Reactive oxygen species Lipoxygenase Substrate effect -  H 13 12 11 10 9 C H ( C H ) C H R C H C H C H C H C H 3 2 4 2  E0= 600mv Oxygen consumption, Conjugated diene Electron spin resonance + 3O2 K=109/sec

4. 13 12 11 10 9 C H ( C H ) C H C H C H C H C H C H R 3 2 4 2 O Propagation (K= 10o M-1sec-1) +  H from RH (triglyceride) R. O  E0=1000mv (K= 107 M-1sec-1) . O H O C ( C H ) +  H from 3 3 C ( C H ) 3 3 O C H 3 O C H 3 E0 = 300-500mv

5. 13 12 11 10 9 C H ( C H ) C H C H C H C H C H C H R 3 2 4 2 O Peroxide value O Most reactive oxygen species -  OH Transition Metal H E0=2300 mv 13 12 11 10 9 C H ( C H ) C H C H C H C H C H C H R 3 2 2 4 O  E0=1600 mv Termination Sensory evaluation Volatile compounds C H ( C H ) C HO 3 2 4 C H C H ( C H ) 3 3 2 3

6. Are you ready to fight the attack of prooxidants? O-2, 1O2, .OH, H2O2, Cu, Fe. R•, RO•, ROO • Antioxidant Prooxidant Jail R•, RO•, ROO•, 1O2, O-2, -OH, H2O2, Cu, Fe

7. Preventive Antioxidants • Superoxide dismutase • Catalase • Glutathione peroxidase • Singlet oxygen quencher • Transition metal chelators (EDTA) Preventive antioxidants minimize the formation of initiating radicals

8. Superoxide dismutase Catalase Superoxide dismutase 2O2·-H2O2O2 +H2O 2H+ Glutathione Oxidase GSSG + 2H2O 2GSH Glutathione Reductase NADP+ NADPH + H+ NADP+ Reductase

9. Gluthione H H H O N C N C C CH2COOH O CH2 CH2 SH CH2 NH2 HC COOH

10. Singlet Oxygen Quenching Mechanism of Carotenes 1O2 + 1-CAROTENE 3O2 + 3-CAROTENE 3-CAROTENE 1-CAROTENE RADIATIONLESS

11. Prooxidant Activities of Transition Metals Formations of alkyl free radical by direct reaction with fats and oils. + 3+ 2+ Fe + RH Fe + R + H · Hydroperoxide decomposition to form peroxy or alkoxy radical. + 3+ 2+ Fe + ROOH Fe + ROO + H · 2+ 3+ - Fe + ROOH Fe + RO + OH · Activation of molecular oxygen for singlet oxygen formation. - 2+ 3+ 1 Fe + O Fe + O O 2 2 2

12. Radical Scavenging Antioxidant • Vitamin C • Tocopherol • Quercetin • Anthocyanin Radical scavenging antioxidants break free radical chain reaction by donating hydrogen to free radicals

13. Standard One-Electron Reduction Potential Compounds E (mV) HO· H+ / H2O 2310 RO· H+ / ROH 1600 HOO. H+ / ROOH1300 ROO· H+ / ROOH 1000 R· H+ / RH 600 Catechol· H+ / Catechol 530 - Tocopheroxyl· H+ / - Tocopherol 500 Ascorbate· H+ / Ascorbate282

14. Resonance Stabilization of Antioxidant Radicals O H C ( C H ) 3 3 E0=1000mv (K= 107 M-1sec-1) E0 = 300-500mv + RH , ROH , ROOH R , RO , ROO • • • O C H 3 . O O . C ( C H ) C ( C H ) 3 3 3 3 O C H O C H 3 3 O O . C ( C H ) C ( C H ) 3 3 3 . O C H O C H 3 3

15. Minimization of Lipid Oxidation • If a compound inhibits the formation of free alkyl radicals in the initiation step, or if the chemical compound interrupts the propagation of the free radical chain, the compound can delay the start or slow the chemical reaction rate of lipid oxidation. • The initiation of free radical formation can be delayed by the use of metal chelating agents, singlet oxygen inhibitors, and peroxide stabilizers. • The propagation of free radical chain reaction can be minimized by the donation of hydrogen from the antioxidants and the metal chelating agents.

16. Characteristics of Antioxidants • The major antioxidants currently used in foods are monohydroxy or polyhydroxy phenol compounds with various ring substitutions. These compounds have low activation energy to donate hydrogen. The resulting antioxidant free radical does not initiate another free radical due to the stabilization of delocalization of radical electron. • The resulting antioxidant free radical is not subject to rapid oxidation due to its stability. • The antioxidant free radicals can also react with lipid • free radicals to form stable complex compounds

17. O H O H C ( C H ) 3 3 ( C H ) C C ( C H ) 3 3 3 3 O C H 3 C H 3 Antioxidants Butylated Hydroxy Anisole Butylated Hydroxy Toluene

18. O H O H C ( C H ) O H O H 3 3 O H C O O C H 3 7 C H O O H O H C H O O H O H O H O H C H C H 3 3 C H C H C H C H C H C H 3 3 3 3 Antioxidants Propyl Gallate TBHQ Gossypol

19. Mechanism of Antioxidants • Hydrogen donation to free radicals by antioxidants. • Formation of a complex between the lipid radical and the antioxidant radical (free radical acceptor).

20. Reaction of antioxidants with radicals R + AH RH + A · · RO + AH ROH + A · · ROO + AH ROOH + A · · R + A RA · · RO + A ROA · · ROO + A ROOA · · Antioxidant + O Oxidized Antioxidant 2

21. O H C ( C H ) 3 3 O C H 3 O O . C ( C H ) C ( C H ) 3 3 3 3 O C H O C H 3 3 O C ( C H ) 3 3 O C H 3 Stable Resonance Formation of BHA R , RO , or ROO · · · . RH, ROH + or ROOH O . C ( C H ) 3 3 . O C H 3

22. C H H a - tocopherol 3 2 O H H 2 C H C H C H 3 3 3 O O 2 ( C H ) C H ( C H ) C H ( C H ) C H ( C H ) 2 3 2 3 2 3 3 2 C H 3 C H 3 O C H C ( C H C H 2 2 2 C H O 3 C H 3 Tocopherol and Oxygen Reaction C H C H C H 3 3 3 ) C H ( C H ) C H ( C H ) 3 2 3 3 2 O H a tocoquinone -

23. Mechanisms of Metals in Accelerating Lipid Oxidation Formations of alkyl free radical by direct reaction with fats and oils. + 3+ 2+ Fe + RH Fe + R + H · Hydroperoxide decomposition to form peroxy or alkoxy radical. + 3+ 2+ Fe + ROOH Fe + ROO + H · 2+ 3+ - Fe + ROOH Fe + RO + OH · Activation of molecular oxygen for singlet oxygen formation. - 2+ 3+ 1 Fe + O Fe + O O 2 2 2

24. Kinds of Metal Chelators • Metal chelators deactivate trace metals that are free or salts of fatty acids by the formation of complex ion or coordination compounds. • 1. Phosphoric acid • 2. Citric acid • 3. Ascorbic acid • 4. Ethylene-Diamine-Tetra-Acetate (EDTA)

25. Metal Ions – EDTA Complex Formation O C O C H O 2 C C H 2 N O C H 2 M C H 2 O N C H C C H 2 2 O O C O

26. Synergism in Lipid Oxidation • Synergism occurs when mixtures of antioxidants produce a more pronounced activity than the sum of the activities of the individual antioxidants when used separately. • To have maximum efficiency, primary antioxidants are often used in combination with (1) other phenolic antioxidants, or with (2) various metal chelating agents.

27. Factors Affecting the Efficiency of Antioxidant • 1. Activation energy of antioxidants to donate hydrogen should be low • 2. Oxidation potential should be high • 3. Reduction potential should be low • 4. Stability to pH and processing. • 5. Solubility in oil should be .

28. Antioxidant Safety • Food Additive, Meat Inspection, and Poultry Inspection Acts. • Total concentration of authorized antioxidants added singly or in combination, must not exceed 200 parts per million by weight • on the basis of fat content of the food.

29. Possible Future Antioxidants • 1. Polymeric antioxidant. • 2. Antioxidant attached to the packaging materials. • 3. Development of new, non-absorbable polymeric • antioxidants for use in foods.

30. Long-Term Safety of Monomeric Antioxidants • Pathological effect. • Carcinogenic potential • Interactions with enzymes • Effects of reproduction • The exact nature of the metabolism rate in man.

31. Isolation and Identification of Oxidation Product of 2,6-Di-(Tert-Butyl)-4-Methylphenol H O C H C H O H 2 2 3,3' ,5,5'-Tetra-Bis-( Tert-Butyl)-4,4'-Dihydoxyl-1,2-Diphenylethane C H C H O O 3,3' ,5,5'-Tetra-Bis-( Tert-Butyl)- Stillbenequinone

32. Ideal Antioxidants • No harmful physiological effects • Not contribute an objectionable flavor, odor, or color to the fat • Effective in low concentration • Fat-soluble • Carry-through effect  No destruction during processing • Readily-available • Economical • Not absorbable by the body

33. Biochemical Control of Lipid Oxidation

34. Biochemical Control of Lipid Oxidation in Mayonnaise Composition of Mayonnaise Composition (%) Soybean oil 77.0 Whole egg 7.0 Water 7.0 Vinegar 3.0 Egg yolk 2.0 Glucose 1.0 Fructose 1.0 Salt 0.9 Natural Flavor 0.1 100%

35. Glucose oxidase/catalase Reaction Mechanism. Glucose oxidase/catalase reaction: Glucose Oxidase 2 Glucose + 2O + 2H O 2 Gluconic acid + 2H O 2 2 2 2 Catalase 2H O 2H O + O 2 2 2 2 The net chemical reaction is: Glucose Oxidase 2 Glucose + O2 2 Gluconic acid Catalase

37. Kinds of Antioxidants • Natural antioxidants: • 1.Tocopherols (delta>gamma>beta>alpha) • 2.Nordihydroguaretic Acid (NDGA) • 3.Sesamol • 4.Gossypol • Synthetic antioxidants: • 1.Butylated Hydroxy Anisole (BHA) • 2.Butylated Hydroxy Toluene (BHT) • 3.Propyl Gallate (PG) • 4.Tertiary Butyl Hydroquinone (TBHQ)

38. Choices of Antioxidants • Different antioxidants show substantially different antioxidant effectiveness in different fats and oils and food systems due to different molecular structures. • We should consider the following: • Safety • Antioxidant effectiveness • Off-odor • Off-color • Convenience of antioxidant incorporation to foods • Carry-through effect • Stability to pH and food processing • Availability • Cost • Non-adsorbable, if possible

39. Antioxidants for Different Food Systems • A small surface-to-volume ratio – PG and TBHQ • A large surface-to-volume ratio – BHA and BHT

40. Application of Antioxidants to Foods • Direct addition of antioxidants to oil or melted fat. • Addition of antioxidants to the food after they are diluted in oil. • Spraying antioxidant solution in oil on the food or dipping food into antioxidant solution.