CHEM 479 Seminar Food Lipids antioxidant preservatives types and mechanisms

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CHEM 479 (Seminar) Food (Lipids) antioxidant
preservativestypes and mechanisms

• Yasser Khalid Al-Duailej 223142

Prepared By
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Overview

• Food Preservatives
• what and why
• Antioxidant Preservatives
• Types
• Mechanisms
• Conclusion

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Different Types and Mechanisms of Food
Antioxidant Preservatives

• Objective
• To discuss and describe types and mechanisms of
  food antioxidant preservatives and to emphasize
  their importance

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What are (Lipids)?

• The term LIPIDS are usually used as a synonym of
  FATS. But fats are in fact a subgroup of lipids.

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Food PreservativesWhat and Why

• Food preservatives are compounds that keep food
  fresh by preventing/delaying growth of microbes
  in food and inhibiting its decay
• Chemical food preservatives can't replace more
  strict preservation methods, such as commercial
  sterilization1, which destroys most enzymatic and
  bacterial activity. But chemicals can be used
  effectively to slow spoiling and keep
  microorganisms at bay
• 1 Sterilization (or sterilisation) refers to any
  process that effectively kills or eliminates
  transmissible agents (such as fungi, bacteria,
  etc.) from a surface, equipment, foods,
  medications, or biological culture medium.

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Antioxidants

• Antioxidants are compounds that prevent or slow
  an oxidation reaction
• In biology, antioxidants either prevent reactive
  oxygen species (radicals) from being formed, or
  remove them before they damage vital components
  of the cell (such as DNA, proteins, lipids)

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Antioxidants

• Oxidants can damage cells by
• starting chemical chain reactions such as lipid
  peroxidation
• or by oxidizing DNA or proteins
• Damage to DNA can cause mutations and possibly
  cancer, if not reversed by DNA repair mechanisms,
• Damage to proteins causes enzyme inhibition,
  denaturation (major change) and protein
  degradation

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Antioxidantslipids oxidation Effects

• Flavor Quality Loss
• Rancid flavor
• Changes of color and texture
• Consumer Acceptance
• Economic loss
• Food Quality Loss
• Essential Fatty Acids
• Vitamins
• Health Risks
• Growth Retardation
• Heart Diseases

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AntioxidantsTypes of Antioxidants

• Hydrogen donating compounds
• Singlet oxygen quenchers
• Metal Chelators
• Enzymes
• Oxygen scavengers

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Antioxidantslipids oxidation Initiation of
Oxygen Oxidation

• Initiation of autoxidation occurs when hydrogen
  atom at ?-methylene group in double bonds is
  removed to form an alkyl radical (R?)

Linoleic acid
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Antioxidantslipids oxidation Propagation
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Antioxidantslipids oxidation Termination
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Antioxidantslipids oxidation Control of Lipid
Oxidation

• Application of antioxidants
• Elimination of oxygen by nitrogen flushing or
  vacuum packaging
• Elimination of photosensitizers1
• Denaturation of lipoxygenase2
• Low temperature and dark storage
• 1 Photosensitizer is a compund that readily
  undergoes photoexcitation and then transfers its
  energy to other molecules, thus making the
  reaction mixture more sensitive to light
• 2 lipoxygenase are a family of iron-containing
  enzymes that catalyze the dioxygenation of
  polyunsaturated fatty acids in lipids

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Antioxidantslipids oxidation Function of
Antioxidant on Lipid Oxidation

• Inhibits or slows the formation of free alkyl
  radicals in the initiation step
• Interrupts the propagation of free radical chain
• Delays the start or slows the chemical reaction
  rate of lipid oxidation

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AntioxidantsResonance of Antioxidant Radicals
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AntioxidantsEffectiveness of Antioxidants

• The stability of antioxidant radical.
• The resonance delocalization
• Further oxidation of antioxidant radicals

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AntioxidantsSynthetic Antioxidants
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AntioxidantsNatural Antioxidants Benefits and
Limits

• Benefits
• Health implication
• Limits
• Characteristic flavor
• Safety test required

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AntioxidantsNatural Antioxidants Tocopherols
Trivial Name Chemical Name R1 R2 R3 ?-Tocophero
l 5,7,8-Trimethyltocol CH3 CH3 CH3 ?-Tocopherol
5,8-Dimethyltocol CH3 H CH3 ?-Tocopherol 7,8-Di
methyltocol H CH3 CH3 ?-Tocopherol 8-Methyltocol
H H CH3
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AntioxidantsNatural Antioxidants Ascorbic Acid

• Hydrogen donation to lipid radicals
• Reduction of singlet oxygen
• Removal of molecular oxygen

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AntioxidantsNatural Antioxidants Ascorbic Acid
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Conclusion

• Antioxidant preservatives are important because
  they
• Inhibit or slow the formation of free alkyl
  radicals in the initiation step
• Interrupt the propagation of free radical chain
• Delay the start or slow the chemical reaction
  rate of lipid oxidation
• Good packaging and storing is also necessary to
  prevent food spoiling

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Questions and Discussion

• Thank you for listening
• Any questions?