IB Food Chemistry

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Distinguish between a food and a nutrient.
Food - Any substance, processed, semi-processed, or raw that is intended for human consumption and is not a drug.

Nutrient - Any substance obtained from food and used by the body to provide energy. Proteins, lipids, carbohydrates, vitamins, minerals, and water are considered nutrients.
Describe the chemical composition of lipids (fats and oils), carbohydrates and proteins.
Lipids - Triesters
Carbohydrates - Monosacchorides (CH20)
Proteins - 2 - Amino Acids
Describe the difference in structure between saturated and unsaturated (mono- and poly-unsaturated) fatty acids.
Fats contain a mixture of saturated, mono-unsaturated and poly-unsaturated lipids. Fats are classified by the predominant type present.
Predict the degree of crystallization (solidification) and melting point of lipids from their structure and explain how this helps the real world.
Unsaturated fats (Mono, Poly) are liquid at room temperature (Crystallization)
Saturated fats are solid at room temperature (Crystallization)
The melting point of lipids increases with an increase in molecular mass or an increase in the degree of saturation.

Cis Lipids (Hydrogen atoms on the same side of double bonded Carbon) have a lower melting point then trans lipids (Hydrogen atoms on opposite sides of double bonded carbons)
Lipids are chosen for cooking on the basis of melting temperature.
Deduce the stability of fats and oils from their structure.
Saturated fats are more stable than unsaturated fats. The carbon to carbon double bonds in unsaturated fats react with oxygen, hydrogen, light and enzymes/heat/water.
Describe the process of hydrogenation of unsaturated fats.
The addition of hydrogen to the carbon to carbon double bond of a fatty acid in the presence of heat, pressure and a finely divided metal catalyst (Zn, Cu, Ni) increases the amount of saturation, which can be partial or full.
Discuss the advantages and disadvantages of hydrogenating fats and oils.
Advantages:
• changes a liquid oil to a semi-solid or solid, to make the melting point of an unsaturated fat more like that of a saturated fat
• decreases the rate of oxidation (stability increases with increasing saturation)
• increases hardness
• controls the feel and plasticity (stiffness).
Disadvantages:
• mono- and poly-unsaturated fats are healthier for the heart than saturated fats
• in partial hydrogenation, trans fatty acids can form
• trans fatty acids are hard to metabolize, accumulate in fatty tissue, are difficult to excrete from the body, increase levels of LDL (bad) cholesterol and are a low-quality energy source.
Explain the meaning of the term shelf life.
A food reaches its shelf life when it no longer maintains the expected quality desired by the consumer because of changes in flavor, smell, texture and appearance or because of spoilage.
Discuss the factors that affect the shelf life and quality of food.
Chemical factors that cause a decrease in the shelf life include:
• water content—loss of nutrients, browning and rancidity; dry foods become vulnerable to spoilage if they take on moisture
• chemical change, for example, pH—off flavors,
color changes, browning and loss of nutrients
• light—rancidity, vitamin loss and fading of natural colors
• temperature—changes the rate of other forms of spoilage
• contact with air.
Describe the rancidity of fats.
Rancidity is the perception of flavours in lipids, those that our senses perceive as off because they have a disagreeable smell, taste, texture or appearance.
Compare the processes of hydrolytic and oxidative rancidity in lipids.
Hydrolytic rancidity: The breaking down of a lipid into its component fatty acids and glycerol. It takes place more rapidly in the presence of enzymes (lipase), heat and moisture. In deep frying, water present in food and high temperatures increase the rate of hydrolysis. Examples of off-flavored fatty
acids include:
• butanoic, hexanoic and octanoic acid in rancid milk
• palmitic, stearic and oleic acids give chocolate an oily or fatty flavor
• lauric acid gives palm and coconut oil in cocoa butter substitutes a soapy flavor
• butanoic acid in butter.
Oxidative rancidity: The fatty acid chains are
oxidized, typically by the addition of oxygen
across the carbon to carbon double bond of the
unsaturated fatty acid. Oily fish (such as herring and
mackerel) contain a high proportion of unsaturated
fatty acids and are prone to oxidative rancidity. The
process can be catalysed by light (photo-oxidation)
and enzymes. Details of the free-radical chain
mechanism will not be assessed.
Describe ways to minimize the rate of rancidity and prolong the shelf life of food.
Processing—examples include:
• limiting lipase hydrolysis by storing dairy products at low temperatures (refrigeration)
• reducing light levels during storage or storing in
coloured glass
• keeping moisture levels low during processing
(adding salt or sugar, smoking).
Packaging—examples include:
• using an inert gas, which minimizes contact with
oxygen, by covering food
• using low-gas-permeability packaging film or
hermetic sealing
• minimizing the amount of air in the headspace
above oil and canning.
Adding additives—examples include:
• sodium sulfite, sodium hydrogensulfite and
citric acid to delay the onset of non-enzymic
browning
• sodium and potassium nitrite and nitrate for
curing meats, fixing colour and inhibiting microorganisms
• sodium benzoate and benzoic acid as
antimicrobial agents in fruit juices, carbonated
beverages, pickles and sauerkraut
• sorbic acid, propanoic acid, calcium propanoate
and sodium propanoate for delaying mould and
bacterial growth in breads and cheeses
• ethanoic acid and benzoic acid for delaying
mould and bacterial growth in pickled meats
and fish products, and also adding to flavor
Describe the traditional methods used by different cultures to extend the shelf life of foods.
Examples include fermentation, preserving, pickling, salting, drying and smoking.
Define the term antioxidant.
A substance that delays the onset or slows the rate of oxidation. It is used to extend the shelf life of food.
List examples of common naturally occurring antioxidants and their sources.
Naturally occurring antioxidants include:
• vitamin C (ascorbic acid) in citrus fruits, green peppers, broccoli, green leafy vegetables, strawberries, raw cabbage and potatoes
• vitamin E in wheat germ, nuts, seeds, whole grains, green leafy vegetables, vegetable oils like canola and soya bean (the antioxidants present in vitamin E are called tocopherols)
• β-carotene in carrots, squash, broccoli, sweet potatoes, tomatoes, kale, cantaloupe melon, peaches and apricots
• selenium in fish, shellfish, red meat, eggs, grains, chicken and garlic.
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