1.3 Nutrition and Food Tests

Qualitative reagent

A substance used in chemical analysis to test for the presence of specific molecules

Qualitative

Relates to measuring the quality of something rather than its quantity

Benedict's reagent

When heated will turn from blue to a brick-red precipitate in the presence of reducing sugars

Results for Benedict's reagent

The solution will change from blue to green to yellow to brick-red depending on the level of reducing sugars present

Biuret reagent

Turns from blue to lilac/purple in the presence of proteins

Iodine test

Turns from yellow-brown or orange to blue-black in the presence of starch

Ethanol and water

When shaken will turn from colourless to a milky-white emulsion in the presence of lipids

Sudan III

When shaken will turn from brick-red to a red-stained oil layer in the presence of lipids

Carbohydrates

Provide energy for chemical reactions and can break down into sugars

Reducing sugars

A sugar such as glucose or fructose that can act as a reducing agent

Lipids

An energy store of fats and oils that can break down into glycerol and fatty acids

Precipitate

Deposits of solid in a solution

Mortar and pestle

Devices used for crushing and grinding up food substances

Water bath

A container of water heated to a given temperature for control purposes

Positive result

A result that shows the presence of a specific substance

Negative result

A result that does not show the presence of a specific substance

Energy content from food

Different foods have different energy contents, some act as quick sources of energy and others act as long-term stores of energy, such as fat

Balancing energy

The energy content of food eaten must be balanced with energy needs since excess energy will be stored as fat by the body, leading to obesity

Energy and food content requirements

Vary between individuals and depend on factors such as age, gender and activity levels

Calorimeter

An instrument used to measure changes in thermal energy

Burning food

Can be used to demonstrate the energy content of different food items

Mounted needle

A needle mounted in a wooden or metal handle that is used to impale a food source and hold it over a bunsen burner

Thermometer

An instrument used to measure temperature

Bunsen burner

Used safely to heat food products until they set alight, after which the food product is suspended below a boiling tube containing water and a thermometer

Boiling tube

Holds a set volume of water and a thermometer to act as a calorimeter

Clamp, boss and clamp stand

Keeps the boiling tube and water suspended at an appropriate height and angle

Electronic balance

A piece of equipment used to measure the mass of each food source

Dependent variable

The variable that is measured, in this case it is the energy content released from food or the change in temperature that results from burning food

Independent variable

The variable that is changed, in this case it is the type of food source that is burned

Control variables

Variables that are kept the same in an experiment such as the volume of water in the boiling tube, size or quantity of food sample used, distance of burning food source from boiling tube

Acclimatisation

It is important that the boiling tube with water is allowed to return to room temperature or a fresh water sample can be used between tests

Energy and temperature

The energy content of food can be determined by burning a food sample and immediately suspending it under a boiling tube of water with a thermometer in it, the temperature change suggests the energy content

Burning food process

Light a sample of food using a bunsen burner, move the burning food sample away from the bunsen burner and place it under a calorimeter, measure the temperature change that results from the burning food

Energy released from food equation

Energy released from food per gram = (mass of water x temperature increase x 4.2)/mass of food sample

Units for energy, mass, temperature

Energy is measured in Joules, mass for this experiment is measured in (kilo)grams, temperature is measured in degrees Celsius

One gram

The mass of one cm^3 of water

Specific heat capacity

The energy required to raise a unit mass of a substance by one degree Celsius, for water this value is 4.2 Joules per gram per degree Celsius

Metabolism

The sum of all the reactions in a cell or the body

Metabolism includes

The synthesis of new molecules, the breakdown of existing molecules and the process of respiration

Conversion of glucose to complex carbohydrates

Glucose can be converted into starch, glycogen and cellulose

Formation of lipid molecules

One molecule of glycerol joins with three fatty acids

Protein synthesis

Amino acids join together in specific arrangements to form proteins

Digestion

Requires energy from respiration to break down large insoluble molecules into smaller soluble molecules

Carbohydrates

Provide energy for chemical reactions and can break down into sugars

Simple sugars (carbohydrates)

The monomers of complex carbohydrates

Carbohydrate examples as simple sugars examples

Sugars, glucose and lactose that are sources of energy

Complex carbohydrate examples

Cellulose, starch and glycogen that are referred to as storage molecules

Proteins

The building blocks of cells and tissues that can break down into amino acids, structural and functional molecules in cells

Amino acids

The monomers that make up proteins

Lipids

An energy store of fats and oils that can break down into glycerol and fatty acids, also referred to as storage molecules

Glycerol and fatty acids

The monomers that make up lipids

Monomer

A simple compound whose molecules can join together to form polymers, such as glucose which can be used to make up a complex carbohydrate called glycogen

Polymer

A long molecule consisting of many similar or identical monomers linked together, such as glycogen which is made up of many glucose molecules