Chap 5: Food Chemistry Flashcards
Food Chemistry
encompasses the composition and properties of food components and the chemical changes they undergo during handling, processing, and storage
Chemical Bonds
- Holds atoms and molecules together
- Requires energy
- Only electrons involved
Types of Bonds
- Covalent
- Ionic
- Hydrogen
Covalent Bonds
- Sharing one or more pairs of electrons
(Fats, proteins, and carbohydrates incorporate covalently bonded atoms to form backbones of food molecules)
Ionic Bonds
- Transfer of electrons
Hydrogen (Bond)
- Type of covalent bond
- Unequal sharing of electron
- Compounds containing oxygen, nitrogen bonded to hydrogen
Composition vs Decomposition
Composition - two or more substances combined to form a product A + B = AB
Sugars/Amino Acids —-> Polysaccharides/Proteins
Decomposition - One substance breaking down to form two or more products AB = A+B
Polysaccharides —-> Sugar
Enzymes
- Biological Catalysts
- Speeds up reactions
- Lowers activation energy
Desirable
Fermentation
Pickles, Tea, Yogurt
Oxidation
addition of oxygen or removal of hydrogen
Reduction
losing oxygen or gaining of hydrogen
Browning of fruits and vegetables (catalyst)
Polyphenol Oxidase
Browning of fruits and vegetables (melanin)
Oxidizes Polyphenols
Properties of Water
- Acts at a dilutant and carrier of hydrophilic substances
- Fat replacer
- Dispersing/solvent action
- Medium for heat transfer
- Plasticizer
Dipolar
Hydrogens share electron pair with oxygen
Boiling and Freezing Point
BP: 100 C & 212 F
FP: 0 C & 32 F
Solubility
Forming hydrogen bonds with water
Hydration
Process by which water molecules surround and interact with solutes by acting as a solvent
Amphiphatic
Containing both hydrophilic and hydrophobic ends
Water disperses amphipathic substances by
Forming Micelles
Types of Water
Free, Adsorbed, and Bound
Free Water
Lightly entrapped
Easily pressed out
Easily boils and freezes
Flow properties
Adsorbed Water
Structural
Bound Water (bread, crackers)
Tightly chemical bound
Doesn’t exhibit typical properties of water
Doesn’t act as a solvent
Polar (Ex)
Salts
Minerals
Carbohydrates
Vitamins
Amphipathic (Ex)
Phospholipids
Sterols
Proteins
Vitamins
Water Activity
Amount of water available for chemical, enzymatic, or microbial reactions
Aw=P/Po
Range = (None) 0.0 - 1.0 (Pure Water)
Higher Moisture Foods
Water Activity Range - greater than 0.84 (microorganisms grow)
Moisture Content Range - greater than 40%
Intermediate Moisture Foods
Water Activity Range - (Chemical reactions take place, oxidation) 0.6 - 0.84
Moisture Content Range - 15%-40%
Intermediate Moisture Foods
Water Activity Range - (Chemical reactions take place, oxidation) 0.6 - 0.84
Moisture Content Range - 15%-40%
Low Moisture Foods
Water Activity Range - less than 0.6
Moisture Content Range - less than 15%
Tartaric Acid
Leavening (bread)
Phosphoric Acid
Cola beverage (preservation in cola, decreases pH)
Amino Acid cysteine
reduced sulfhydryl groups
SH groups are oxidized during processing
hardening of dough
Fumaric acid added to
establish reducing conditions
pH
potential of hydrogen ion concentration
pH =
-log{H+}
High acid foods
pH 4.6 and below
Ex. Orange Juice and Canned Tomatoes
Low acid foods
pH 4.6 and above
Ex. Fermented foods
