Class notes
Food Composition
- Course
- HNU 146
- Institution
- St. Francis Xavier University (STFX )
These notes will give you an in-depth, step-by-step way as to how food is composed
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Topic: Food CompositionChap: 3 & 25
Key educational goals/outcomes for today:
▪ Describe the main functional groups in foods.
▪ Explain the key chemical reactions in carbohydrates, proteins and fats.
Questions to guide the reading/to think about ahead of time for students
1. What are the main chemical bonds and functional groups in food?
2. How are carbohydrates, lipids and proteins classified?
3. What key chemical reactions occur in carbohydrates, lipids and proteins
food components?
4. What are the main functions of interfering agents in candy making?
Intro: Proximate Composition (100%)
- Water
- Carbs
- Proteins
- Lipids
- Vits Vits & Mins are usually combined to make= ASH
- Mins
What elements are important for food?
Carbon, Hydrogen, Nitrogen, Oxygen
Covalent Bonds: sharing electrons
Ionic Bonds: formed by the transfer of electrons,
it’s the atoms that transfer the electrons you have the
cation (+) and the anion (-)
,Concept 1: Functional Groups
C=O → this carbon double bond to oxygen is called a Carbonyl Carbon
The ESTER group: acid + alcohol = ester
- Isoamyl acetate → banana
Pectin: methyl, viscosity, gelation
The PHOSPHATE group: sodium phosphate = salt
- Emulsifying salt for processed cheese acts as a preservative
The SULFHYDRLY group: (SH)
- Gluten formation in doughs
Concept 2: Food Compositing: Water
Water: the smallest nutrient, yet most important
- Can be bound or free
o Fruits/Veggies= 70-95% Aw
o Whole milk= Over 80% Aw
o Most meats= just under 70% Aw
- Structure of water: one oxygen flanked by 2 hydrogens, therefore, making
H2O
- The function of water in food:
o Transfer medium for heat
o Universal solvent
o Agent in chemical rxns
o Factor in perishability & preservation of foods
Concept 3: The Chemistry of Carbohydrates
- CHOs= Sugars, starches & fibers found in foods
- Basic chemical formula= Cn(H2O)n, the n stands for s number ranging from
2→ thousand
- Plants are primary sources (except milk = lactose). CHOs are made by the
process of photosynthesis
- Most COHs are stored in seeds, roots, stems, and fruits
, Concept 4: Composition of Polysaccharides
Polysaccharides:
- The most common polysaccharides in food are starch, glycogen, & fiber
- Contain many monosaccharides linked together
- Divided into two major groups
o Digestible (starch & glycogen)
o Indigestible (fiber).
Composition of CHO – Polysaccharides:
- Starch
- Digestible polysaccharides from plant sources
- Glucose derived from photosynthesis is stored as starch
- The body can break starch down into individual glucose units for absorption
o In food, heat, enzymes, & acid are used to break down starches into
smaller, sweeter segments (called dextrin).
- Composition of CHO – Glycogen
o Glycogen (a.k.a. animal starch)
o Digestible polysaccharides from animal sources
o Starch stored by animal bodies in long chains of glycogen in the liver
& muscles
o Glycogen in meat is converted to lactic acid during slaughtering, so is
not present after.
- Composition of CHO – Polysaccharides
o Fibre (a.k.a. roughage or bulk)
o Indigestible polysaccharide
o Sugar units in fibres are held together by bonds that can’t be broken
down &, hence, don’t provide energy
o Found only in plants
- Common fibres
o Cellulose, hemicellulose, & pectic substances.
- Polysaccharides:
- Dietary Fiber:
o After exposure to digestive enzymes, the undigested portion of
carbohydrates remains in a food sample.
- Gum Fiber from Vegetable Gums:
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