Food Studies (Notes)

Factors that affect food choices
Culture- have particular foods associated with that form part of countries cultural identity e.g china-rice
Nutritional- people make nutritional conscious when making food choices
Families -children's food choices are influenced by what the parents eat
Eating patterns - influenced by school/ work
Money available - families with less money will pay less for food meaning that sometimes they might unhealthy
Food availability- seasons affect food choice

Nutrients
Compounds in food that the body requires for proper growth, maintenance, and functioning

Macronutrients
A chemical substance that an organism must obtain in relatively large amounts

Micronutrients
vitamins and minerals that are essential to the body in small amounts

elemental composition
Nutrients are formed from molecules that are made of elements e.g protein = carbon, oxygen, nitrogen

chemical formula
How a nutrient is formed by stating the number of elements in each molecule e.g glucose = c6h12o6

Classification
The arrangement of nutrients into groups e.g carbohydrates =monosaccharides, disaccharide, polysaccharide

Sources
Food or origin that provides nutrients to the body e.g calcium from milk

Properties
Characteristics that are unique to specific nutrients e.g lipids are insoluble in water

biological functions
The function or job a nutrient carries out in the body e.g lipids provide insulation

RDA
recommended daily allowance

deficiency disease
A sickness caused by a lack of an essential nutrient

Digestion
Breakdown of food substances into simpler forms that can be absorbed and used

Absorption
The process by which nutrient molecules pass through the wall of the digestive system into the blood

utilisation
How the body uses the digested nutrients.

Elemental composition of protein
carbon, hydrogen, oxygen, nitrogen

What do some proteins contain?
Sulfur, iron and phosphorus

Chemical structure of amino acid
H
|
|
NH2 ————-C—————COOH
|
|
R

example of amino acids
H.
|
|
NH2 ————-C—————COOH.
|
|
H.

Glycine

essential amino acids
Amino acids that are needed, but cannot be made by the body; they must be eatin in foods

Name the essential amino acids
histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine

non-essential amino acids
amino acids that the body can synthesize on its own; does not need to get from dietary sources

Name the non-essential amino acids
alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, tyrosine

When are peptide bonds formed?
Peptide bonds form when water is removed to hold amino acids together

Stages of formation of peptide links
The COOH group of one amino acid reacts with the NH2 group of another
The COOH group loses an OH group. The NH2 group loses a hydrogen atom and the hydrogen atom and the OH group join together to form water molecule that is lost
The result is a CO-NH bond. This new molecule is called a dipeptide

What is it called when more than 20 amino acids join together?
Polypeptide

What is it called when more than 50 amino acids are joined together?
Protein

What is a primary protein structure?
sequence of a chain of amino acids

What is a secondary protein structure?
Involves the folding of the primary structure of proteins into definite shapes
Two types- disulfide bonds, hydrogen bond

disulfide bonds
Occur when two sulfur's and two amino acids join together from either a single polypeptide chain or two polypeptide chains

Hydrogen bonds
Occurs when a hydrogen from the N-H group of one amino acid and an oxygen (o) from the c=o group of another amino acid join together from either a single polypeptide chain or two different polypeptide chains or two different polypeptide chains

tertiary structure of protein
protein structure is formed when the twists and folds of the secondary structure fold again to from a larger 3D structure
Two types= fiborous and globular

fibourous proteins
Insoluble In water and not easily denatured e.g gluten
(Straight, zig zag, and spiral )

globular proteins
proteins that are water soluble and easily denatured
E.g ovalbumin

Classification of proteins
Simple proteins
Animal < fibrous- elastin and collegen - meat connective tissue
Globular - ovalbumin and lactalbumin- egg white and milk
Plant < glutennis - glutenin, oryzenin - wheat and rice
Polamines- gliadin, Zein - wheat and maize
Conjugated proteins
Lipoproteins - lecithin- eggs

Phosphoproteins - caseinogen - milk

High biological value protein
food protein that is able to provide all essential amino acids in proportions that meet human need. Also called complete protein.
E.g eggs , milk, meat, fish

Low Biological Value Protein
Where a food is missing one or more of the essential amino acids. They are usually plant foods.
E.g rice, maize , wheat

properties of proteins
Denaturation, elasticity (gluten in wheat is elastic ) Maillard reaction ( roast potatoes ), solubility ( most proteins are insoluble in water)
Gel formation ( when collagen is heated it is converted to gelatin)( cheesecake) foam formation ( meringues )

Effects of dry and moist heat on protein
Coagulates
Colourchange
Over cooking = indigestable

elemental composition of lipids
carbon, hydrogen, oxygen

Glycerol
a three-carbon alcohol with a hydroxyl group attached to each carbon

fatty acid molecule
Formula R-COOH

Classification of fatty acids
saturated, monounsaturated, polyunsaturated

saturated fatty acid
A fatty acid in which all carbons in the hydrocarbon tail are connected by single bonds, thus maximizing the number of hydrogen atoms that can attach to the carbon skeleton.

examples of saturated fats
Butyric acid in butter
Stearin acid in meat

Consistency of saturated fats
Solid at room temp
High melting point

monounsaturated fatty acid
A fatty acid whose molecular structure includes only one double carbon bond.

Examples of mono-unsaturated fatty acids?
Oleic acid in olive oil

Consistency of monounsaturated fatty acids
Soft or liquid at room temp
Low melting point

polyunsaturated fatty acid
two or more double bonds

examples of poly unsaturated fatty acids
Alpha linolenic acid in seed oil
Lenoleic acid In nuts
Arachidonic acid in oily fish

essential fatty acids
fats needed by the body that must be consumed in the diet because the human body cannot manufacture them

Sources of EFAs
Nuts, seeds, olive oil, oily fish

Functions of EFAs
Aid cell membrane formation
Reduce risk of coronary heart disease by raising high-density lipoproteins which helps remove cholesterol from blood and lowering low-density lipoproteins which deposits cholesterol in the blood

omega-3 fatty acids
polyunsaturated fatty acids commonly found in fish oils that are beneficial to cardiovascular health

Sources of omega-3 fatty acids
flaxseed oil, walnuts, some fish

Functions of Omega 3 fatty acids
Reduces risk of coronary heart disease, heart attacks and strokes by raising HDL and lowering LDL
Decreases viscosity of blood, preventing clots
Aids foetal brain development during pregnancy

cis fatty acids
hydrogen atoms are located on the same side of the double-bond

Sources of cis fatty acids
Naturally occurring in foods such as olive oil and oily. Fish

Health effects of cis fatty acids
Generally good for health as they raise HDL while lowering LDL

trans fatty acids
hydrogen atoms are nearly always on opposite sides of the two carbon atoms that are double bonded

sources of trans fatty acids
hydrogenated oils
margarine
vegetable cooking oils

Health effects of trans fatty acids
Generally bad for health as they lower HDL while raising LDL

Classification of lipids
Animal - mainly saturated - meat, meat fats, butter, cream, cheese
Plant - mainly unsaturated - vegetable oils, nuts and nut oil
Marine- manly polyunsaturated- oily fish

Properties of lipids
Solubility- insoluble in water
Absorbtion of flavors- absorb flavors easily
Heating lipids - melting point 30-40, smoke point 200/250, flash point 310
Emulsions- water in oil emulsions e.g butter, marg. Oil in water emulsions e.g milk, mayonnaise, temporary emulsions e.g formed when the two immiscible liquids e.g vinegar and oil in mayo, permanent emulsions formed when an emulsifier such as lecithin in egg yolk
Emulsifiers = molecules that have a hydrophilic head and hydrophobic tail e.g lecithin
Hydrogenation - hydrogen gas, in the presence of a nickel catalyst, is forced through the doublebonds
Rancidity- two types oxidative rancidity and hydrolytic rancidity
Plasticity- describes how soft a fat is at given temperature e.g marg

Oxydative rancidity
Occurs when oxygen in the air combines with the carbon in a double bond of the unsaturated fatty acid - unpleasant odour and taste

hydrolytic rancidity
triglycerides breakdown by enzymes and fatty acids are released

Biological functions of lipids
Supply body with heat and energy
Form a protective layer
Supply the body with the fat soluble vitamins (a,k,d,e)
Essential fatty acids
Excess lipid intake is stored as adipose tissue under skin

RDA lipids
70g= adults men =no more than 30g of saturated fats women = no more than 20g of saturated fats

Energy value of lipids
1g of lipids = 9 kcal

Associated dietary disorders of lipids
Obesity, coronary heart disease and strokes

digestion of lipids
Starts in the mouth, moves to stomach, completed in the small intestine; In intestine fat interacts with bile to become emulsified so that pancreatic enzymes can break the triglycerides into two fatty acids and a monoglyceride;

Structure of egg
Shell 10% - hard protective layer composed of calcium carbonate - inedible and porous
White 60%- viscous, colorless liquid that surrounds the yolk composed of ovalbumin, globulin
Yolk 30%- a viscous dark - yellow center held in place by a string like structure called chalazae. Composed of Vitellin and livetin p, saturated fats, cholesterol, lecithin, minerals, vitamins and water

Average nutritional composition of eggs
Proteins 13%(whole eggs) 11%(white) 16%(yolk)
Fat 12%(whole egg) 0.2%(white) 32%(yolk)

Nutritional value of eggs
Protein - HBV proteins= ovalbumin and globulin in white and livetin in the yolk
Fat - white is fat free, yolk contains cholesterol, fat present in the yolk is dispersed
Carbs - lack of carbs
Vitamins - a good source of b-group, yolk are a good source of vitamins a,d,e and k, lack vitamin C
Minerals- a good source of calcium,phosphorus, zinc, and sulfur, non-haem iron is present in the yolk
Water- high water content, with the majority found in the white

Dietetic value of eggs
Excellent source of HBV, low in kilocalories, versatile, inexpensive, cook quickly, high in sat fats and cholesterol, lack of carbs and vit C

Buying eggs
Buy eggs from a retailer with a strict food hygiene, check best before date, buy eggs with bord bia quality mark, avoid purchasing eggs with cracked shells, ensure they feel heavy for their size

Box labeling regulations
Must have name and address of Packer or seller, number of eggs, class/quality e.g class A, best before date, production method, weight, storage instructions

Egg labeling regulations
A number to distinguish production method, two letters denoting the country of origin, a code containing a letter and a number to identify and a number to identify the country and producer, best before date

Storage of eggs
In a fridge, away from strong smelling foods, ensure eggs are stored pointing up, minimize the amount of time eggs are in storage

Effects of cooking on eggs
Egg whites change colour, white coagulates at 60C and yolks coagulates at 68C, bacteria are destroyed, some b group vitamins are lost, eggs can curdle if cooked at very high heats, eggs become tough and difficult to digest if overcooked- yolk becomes crumbly and white becomes rubbery, reaction between iron and sulfur in an egg causes green ring to form

Properties of an egg
Aeration- when eggs are whisked the protein chains unfold and create air bubbles which are then I trapped in the chains creating a foam
Coagulation- when eggs are heated, protein chains unfold, straighten and bond together around small pockets of water, causing coagulation e.g fried eggs
Emulsification- lecithin is a natural emulsifier present in egg yolk. It has the ability to join two immiscible liquids e.g oil and water

Grading of eggs
Participation in routine salmonella testing of the hens, accurate records are kept an the origin, sex, vet treatments, breed
All feed given to hens is heat treated, implementation of a thorough sanitation and pest-control programme